Current Issues in Environmental Regulation and Public Health:

PERCHLORATE Carter Franz Francesco Ramos

Table of Contents

I. Executive Summary ............................................................................................. ii

II. Physical and Chemical Properties ....................................................................... 1

III. Common Commercial Applications .................................................................... 4

IV. Commercial and Natural Production ................................................................... 6

V. Environnemental Occurrence .............................................................................. 13

VI. Health Effects ................................................................................................... 16

VII. Regulation ......................................................................................................... 20

VIII. Treatment Options ........................................................................................... 22

References ................................................................................................................ 29   

Tables Table 1: Physical and chemical properties of perchlorate ............................................................................ 3 Table 2: Annual estimated use and production of perchlorate compounds .................................................. 4 Table 3: Estimated annual perchlorate releases from commercial and natural applications ......................... 6 Table 4: Selected perchlorate sources, releases and detections .................................................................... 8 Table 5: Selected DOD sites with perchlorate detections ............................................................................. 9 Table 6: Measured perchlorate concentration in common foods ................................................................ 15 Table 7: Relative source contributions remaining for water based on TDS for various sub-groups .......... 15 Table 8: State drinking water regulations ................................................................................................... 20 Table 9: Relative source contributions of perchlorate in drinking water for vulnerable subpopulations ... 21 Table 10: Applicability of common treatment technologies ....................................................................... 23 Table 11: National cost of federal regulation .............................................................................................. 28 Figures Figure 1: Molecular geometry of perchlorate ............................................................................................... 2 Figure 2: Energy for a chemical reaction ...................................................................................................... 3 Figure 3: Locations of known users and manufacturers of perchlorate ........................................................ 8 Figure 4: Fate and Transport of perchlorate in groundwater aquifer and estimated residence time ........... 10 Figure 5: Schematic of perchlorate plume at Stringfellow Superfund Site ................................................. 11 Figure 6: Pathway of Tronox plume in the south west United States ......................................................... 12 Figure 7: Suspected or known perchlorate releases and detections ............................................................ 14 Figure 8: Percent of total U.S. perchlorate detections found in each state ................................................. 14 Figure 9: Perchlorate mode of action and adverse affect when ingested .................................................... 17 Figure 10: The thyroid and its role in hormone secretion ........................................................................... 18 Figure 11: Progression of perchlorate regulation at the federal level in the United States ......................... 20 Figure 12: Quantification and calculations for toxicological effects of perchlorate ................................... 21 Figure 13: Schematic representation of the ion exchange between perchlorate and chloride .................... 23 Figure 14: Ion exchange treatment for perchlorate removal ....................................................................... 24 Figure 15: Schematic representation of a membrane filtration system for the treatment of perchlorate .... 25 Figure 16: Enzymatic pathway of the dissimilatory perchlorate reducing bacteria (DPRB) ..................... 26 Figure 17: Phytoremediation of perchlorate. This process is an emerging technology for perchlorate remediation ................................................................................................................................................. 27

I. Executive Summary

On October 8, 2009 the U.S. Environmental Protection Agency (EPA) accepted the last public comment (out of 22,000) regarding a federal drinking water regulation for perchlorate, a ‘candidate contaminant’ of the EPA’s since 1998. Perchlorate, a common constituent of solid rocket fuel, has been linked to adverse health effects related to the hormonal homeostasis of the thyroid gland in mice. Known to be released in large amounts nearby ground and surface water supplies at U.S. Department of Defense, NASA research, and manufacturing sites, perchlorate was chosen for evaluation to determine whether or not it causes adverse health effects in humans at environmentally present concentrations. If so, a regulatory standard will have to be set which would require municipal entities to treat water supplies to meet that standard.

This report outlines the chemical and physical properties that make perchlorate popular among defense contractors and other users, and those properties that make it problematic for environmental remediation efforts and finally those that possibly cause adverse health effects in vulnerable populations. Perchlorate rose in popularity beginning with the Second World War because of its oxidizing potential. Subsequently, it was used in munitions, rocket launchers, fireworks and other related uses. Commercially viable only as a solid salt, 90% of perchlorate demand is for ammonium perchlorate, and these salts are highly soluble in water and unable to adsorb to soil, making them extremely mobile in aqueous medium.

The time period since perchlorate was established as a candidate for regulation, new research has yielded the following conclusion regarding the health effects of perchlorate: The vulnerable population group is the fetuses of iodine deficient pregnant women exposed to concentrations of perchlorate in water of over 15µg/L (ppb). This comes after a body of animal studies on mice was summarily discounted as non-analogous to healthy adults and adolescents because of differences in the pituitary gland. In 2005 a Center for Disease Control study concluded that higher urinary perchlorate concentrations were a positive predictor of unbalanced hormonal behavior regulated by the thyroid gland in iodide deficient women. However, they noted that the hormonal behavior was within healthy range, and that there was no precedent in the research indicating those urinary levels of perchlorate would cause any adverse health effects.

Various technologies are available to treat perchlorate, and depending on whether or not a regulatory standard is set, 3.4% or 1.4% of the nation’s public water supply would require adoption of these unconventional treatment technologies. The cost implications of setting a Federal drinking water limit for perchlorate are that compliance would cost 2.1 billion USD with a maximum contaminant level (MCL) of 4 ppb and 100 million USD with an MCL of 24 ppb. Regulating perchlorate would cost the nation less than previous drinking water standards, and the costs would fall on a small number of municipalities and private entities.

We conclude that perchlorate is an environmental contaminant which can cause negative health affects at high doses, especially to the fetuses of iodine deficient pregnant women. While the cost of implementing a federal drinking water standard is low compared to previous limits, the cost would fall upon a few individuals. Clearly, there are many stakeholders and we hope the political process serves both sides of the debate fairly. If a regulation is put in place, we would recommend the ion exchange method as the most reliable and capable of removing perchlorate from public drinking water systems.

INTRODUCTION

erchlorate is a highly soluble anion used in solid rocket fuel and found naturally in the environment. Previous disposal methods at U.S. Department of Defense and other user sites consisted of dumping perchlorate salts or liquid waste into the Earth untreated. In the late 1990’s

perchlorate was detected in high concentrations in public water supplies of the American south west and subsequently throughout the entire United States. Public health officials were concerned that ingestion of perchlorate may cause hypothyroidism, a condition characterized by an underactive thyroid and a slowing metabolism. The EPA added perchlorate to its candidate contaminant list in 1998, and the report that follows is a summary of research concerning the health effects, regulatory framework, and environmental remediation efforts associated with perchlorate up to 2009. As with any new regulatory standard, there is debate in the public sphere as to whether or not a national drinking water limit for perchlorate would improve the health of the population. The first section will elaborate on the chemical and physical properties governing the behavior of perchlorate. These properties are the basis for understanding perchlorates nature as a commercial commodity, a persistent ground water contaminant, and a potential human health concern.

P“As with any new regulatory standard, there is debate in the public sphere as to whether or not a national drinking water limit for perchlorate would improve the health of the population.”

II. Physical and Chemical Properties of Perchlorate Molecular Geometry. Figure 1 shows the sp3 tetrahedral arrangement of the perchlorate anion, which consists of one chloride bonded to four oxygen atoms. Because of this geometry perchlorate has a large ionic volume and low charge density. Therefore, it is a poor complexing agent with cations in aqueous solutions. This low association with cations makes perchlorate highly soluble and mobile in aqueous environments, and prevents bioaccumulation and soil sorption. This contributes to perchlorates persistence in aquifer plumes, and confounds

1

environmental engineers because precipitation and sorption are ruled out as treatment options (Srinivasan, 2009). Perchlorate’s ionic radius is similar to that of the iodine anion. When in the bloodstream, perchlorate competes with iodine for uptake into the thyroid gland, which can ultimately reduce radioiodine uptake and disrupt the normal hormone secretion of the thyroid when ingested in large doses.

olubility. Perchlorates are commercially

q)

ommercial applicability of perchlorate

mics and Kinetics. Figure 2 epicts the ‘energy hump’ that reactants in a

Sviable as solid salts, in white or clear crystal form stored at ambient temperature. These salts fully dissociate in water (Equation 1) and some organic solvents, with solubility’s ranging from 2.06 x 104 to 2.10 x 106 mg/L in fresh water at 25ºC, and 1.00 x 101 to 1.82 x 106 mg/L in standard organic solvents (See Table 1). Log octanol-water partition coefficients (log Kow) are -5.84 for ammonium perchlorate, and -7.18 for

sodium and potassium perchlorates (Urbansky, 1998). Perchloric acid (HClO4) is miscible in water and has an octanol-water partition coefficient of -4.63 (EPA, 2008). Perchlorate is non-volatile and does not bind readily to mineral surfaces, which indicates that perchlorate will travel rapidly over soil with surface water runoff or be transported through soil with infiltration (ATDSR, 2008). Therefore, adsorption techniques used in water treatment plants are ruled out as a possible treatment option.

(1) NH4ClO4(s) water NH4+ (aq) + ClO4- (a

Subsequent discussion will talk about the ccontaining salts, but the following statement makes an important distinction: “Given that perchlorates completely dissociate at environmentally significant concentrations, their cations are, for all practical purposes, spectators in the aqueous fate of perchlorate. Therefore, the environmental fate of perchlorate salts is dominated by the perchlorate ion (ATDSR, 2008).” This property is important, because environmental engineers are concerned with the removal of perchlorate, and therefore the perchlorate anion, from the environment (especially drinking water sources). Research shows that this task is further complicated by the chemical kinetics of perchlorate. Thermodynadchemical reaction must surpass to become products. Perchlorate represents the highest oxidized form of chlorine (+7), and has a high reduction potential. Perchlorate can react explosively at high temperatures, and is a powerful oxidant when combined with fuel sources. Ammonium perchlorate, the most widely produced perchlorate salt, thermally decomposes at temperatures of 439ºC, and then combusts in a self-

Figure 1: Molecular Geometry of

butes

en

Perchlorate Perchlorates tetrahedron geometry contrito the large ionic volume and low charge density of ClO4

-. The negative charge is equally distributed among the 4 outer oxygatoms. Consequently, it is a poor complexing agent and highly soluble in aqueous environments, making it difficult to remediate by conventional methods. Image: CAS, 2009

2

propagating manner (CDTSC, 2005). Standard reduction potentials show that the reduction of perchlorate to (Eq. 2) chloride, or (Eq. 3) chlorate, is thermodynamically favorable (Urbansky, 1998).

- +(2) ClO4 + 8 H + 8 e- ↔ Cl- + 4 H2O -----E° = 1.287 V

3 2

perchlorate is ermodynamically favored to be easily

red

low vap

hloric Acid

(3) ClO4

- + 2 H+ + 2 e- ↔ ClO - + H O E° = 1.201 V

Though

thuced, it is highly non-reactive in aqueous

solution at ambient temperatures. “The low reactivity is a matter of kinetic lability rather than thermodynamic stability (Urbansky, 1998).” The activation energy needed to break down perchlorate is high: 123.8 kJ/mol below 240 ºC; 79.1 kJ/mol from 240 to 200 ºC; 307.1 kJ/mol between 400 and 440 ºC (ATDSR, 2008). This kinetic barrier is difficult for environmental engineers working towards remediation because typical reducing agents cannot reduce perchlorate economically (Urbansky, 1998).

Table 1 shows that all common perchlorate compounds have an extremely

or pressure, and do not volatize from water to air (Sellers, 2007). Therefore, air stripping is ruled out as a treatment option.

Perchlorate Compounds Ammonium Potas Sodium Percsium

Physical state at ambient temperature

White orthorhombic crystal

White orthorhombic deli stal quescent cry

Colorless orthorhombic cry ite stal or wh

crystalline powder Colorless liquid

Molecular weight (g/mol) 117.49 122.44 138.55 100.47

W at ater solubility (g/L 25oC) 200 2,096 15 Miscib water

Melting Point: 65.6 to Melting Point: 482 Melting Point: 400 Melting Point: -112

le in cold

Melting / Boiling point (oC) 439 Boiling Point: 19

Vapor pressure at 25oC (mm Hg) Not available 4.8 Not available 3.5

Specific gravity 1.95 2.52 2.53 1.664 Octanol-water partition

co ) efficient (log Kow-5.84 -7.18 -7.18 -4.63

Ve w Ve w Ve w V Sorption Capacity ry lo ry lo ry lo ery lowVolatility

Figure 2: Energy for a Chemical Reaction This general graph depicts the transgression of a chemical

as

low

reaction. In the case of perchlorate as a reactant, it hhigh activation energy, so it takes a large amount of energy to reach the “transition state”. Consequently, thereduction of perchlorate with typical reducers is too s(days to weeks) to be used in water treatment plants. Image: sparknotes.com/figures

This also implies the main path of perchlorate in the environment is aqueous, and the primary risk to

able 1: Physical and chemical properties of perc 05)

humans will be via ingestion. Perchlorate compounds are denser than water, a property that affects the transport of perchlorate in groundwater aquifer plumes. Table 1 also lists the specific gravities.

T hlorate (EPA, 2005 & IDTC, 20

3 Nonvolatile Nonvolatile Nonvolatile Nonvolatile

III. Common Commercial

recovered and recycled for use in

glass e

mes are difficult to gauge (ATDSR, 2008).

ate accounts for 90% of perchlorate production in the U.S.,

Applications The most widely used perchlorates

are in the form of solid salts, including ammonium, potassium, magnesium, sodium, and lithium perchlorate (see Table 2) . The Department of Defense (DOD), the National Aeronautics and Space Administration (NASA), and the defense industry have used perchlorate for decades in the manufacturing, testing, and firing of missiles and rockets. Their primary uses are as oxidants in combination with fuel sources. The approximate percentages sold for specific end users are 92% as an oxidizer, 7% as an explosive, and 1% for other uses (CDTSC, 2005). The DOD uses 6-8 million pounds of ammonium perchlorate annually, of which roughly 4 million pounds is

tching (ATDSR, 2008). Worldwide production of

perchlorates was less than 3.6 million total pounds up until 1940. However, with the onset of World War II, annual production of perchlorate increased to 36 million pounds, due to the increased demand for rocket and missile propellants. Advancements in space exploration technology and cold war innovations further increased demand. U.S. perchlorate production alone reached 50 million pounds annually by 1974, and in 1994 was estimated at around 22 million pounds, or 34% of capacity (ATDSR, 2008). Because perchlorate is considered a “strategic chemical” due to its military applications, and because the U.S. does not log perchlorate as a separate good on import/export logs, exact U.S. production and disposal volu

commercial applications such as blasting or Ammonium perchlor

Compound Chemical Formula

U.S. Production

in 1951-1997(million lb.)

Use

Ammonium perchlorate

NH4ClO4 609 Energetic booster in rocket fuel, used primarily by the DOD, national aeronautic space, and space administration. The high solubility of

NH4ClO4 makes this material useful as an intermediate for production of all other perchlorates by double metathesis reactions and controlled

crystallization (Kirk, 2004). Sodium

perchlorate NaClO4 20 Strong oxidizing agent used in the explosives and chemical industry

(Kirk, 2004).

Potassium perchlorate

KClO4 22 Solid oxidant for rocket production; also used in pyrotechnics (ATSDR, 2008).

Lithium perchlorate

LiClO4 No data found

Electrolyte in voltaic cells and batteries involving lithium anodes; thin film polymers used in certain electrochemical devices, may be doped

with lithium perchlorate to induce conductive properties; used as a synthetic of certain organic compounds (Seller et al, 2004).

Magnesium perchlorate

Mg(ClO4)2 0.7 Drying agent for industrial gases; electrolyte for magnesium batteries; used in synthesis of certain organic compounds (Kirk, 2004).

Perchloric acid

HClO4•2H2O No data found

Analytical reagent; used hot and concentrated as oxidizing and dehydrating agent (Merck, 1983).

Table 2: Estimated Annual Production and Use of Perchlorate Compounds

4

and is the largest component of solid rocket (~70%) and missile propellants (Lieberman et al, 2008). Being the only common perchlorate that does not leave behind a solid by-product as well as the ease of disposal from rocket encasings adds to its widespread use (CDTSC, 2005 & Atikovic, 2007). Solid rocket fuels that use perchlorate, as opposed to liquid fuels that use other oxidizers, can provide a high thrust for a low cost (ITRC, 2005). Average annual production rates for ammonia perchlorate between 1951 and 1997 estimated to be roughly 1.06 x 107 kg per year. The sole producer of ammonium perchlorate in North America is American Pacific Corporation (AMPAC) near Cedar City, Utah (ATDSR, 2008). Ammonium perchlorate is also used in small amounts in ammunition, mixed with sulfamic acid to produce smoke and dense fog for tactical military operations, and as a component of temporary adhesives used with steel and other metallic plates (ATDSR, 2008). Nitrate and perchlorate containing

ther Commercial Applications of

1998, the FDA approved the use of pota

common form of comme

cally during the 1950s and early 1960s, for the treatment

Chilean salt pepper is used in the production of fertilizer. The United States has been importing Chilean caliches since 1830, and the use continues today with the U.S. importing more than 75,000 tons containing 0.01% perchlorate annually between 2002 and 2004 for use mainly on tobacco, cotton, and some fruit crops (Seller et al, 2004). This accounts for approximately 1% of the total fertilizer used per year in the U.S. (ATDSR, 2008). OPerchlorate. While perchlorate’s major use is in the production of rocket propellant, munitions, explosives and fireworks, manufacturers also use perchlorate compounds in small amounts for some consumer products (see Table 3). Since 1976, over 14,000 patents have been issued for various perchlorate-containing materials

(Seller et al, 2004). Other uses of perchlorates include fireworks, road flares, matches, photography, etching and engraving, and blasting explosives used for mining and other civilian applications. Fireworks can contain up to 70% (wt) potassium or ammonium perchlorate, and over 221 million pounds of pyrotechnics were consumed in 2003 in the U.S. (Seller et al, 2004). Sodium perchlorate is employed in airbag inflator systems. Due to their low weight and high energy density, lithium and magnesium perchlorate have been used in batteries. Potassium perchlorate can be mixed with reactive metals such as zirconium or iron, and used in heat pellets to activate reserve battery cells (ATDSR, 2008).

Inssium perchlorate as an additive in

rubber gaskets of food containers. Ammonium, potassium, and sodium perchlorate have also been used as stimulants to increase the weight of poultry and other farm animals, and as weed killers and growth stimulants in leguminous plants (ATDSR, 2008).

Another rcially available perchlorate is

perchloric acid (HClO4). Applications include etching of liquid crystal displays, polymerization catalysis, critical electronics applications, and ore extraction. Perchloric acid is also used routinely for many industrial and testing laboratory chemical analyses, including isolation, separation, titration, deproteinization, dehydration, and as a solvent and oxidizing agent. Analytical chemists use perchlorates to adjust the ionic strength of aqueous metal solutions. Perchlorates are unreactive as a ligand (do not complex with metals) so they do not interfere with the chemical dynamics of the investigation (Urbansky, 1998)

Perchlorates used medi

5

6

eleases from commercial and natural applications

of hype

salivary glands. In addition, treatment to

IV. Commercial and Natural

atural Sources. Perchlorate occurs

ltpeter deposits contain concentrations

eleases from commercial and natural applications

of hype

salivary glands. In addition, treatment to

IV. Commercial and Natural

atural Sources. Perchlorate occurs

ltpeter deposits contain concentrations

Table 3: Estimated annual perchlorate r

rthyroidism, or Graves’ disease. In the United States, perchlorate is still used during medical imaging of the brain, blood, and placenta, in order to block radioiodine uptake in the thyroid, choroid plexus, and

le 3: Estimated annual perchlorate r

rthyroidism, or Graves’ disease. In the United States, perchlorate is still used during medical imaging of the brain, blood, and placenta, in order to block radioiodine uptake in the thyroid, choroid plexus, and

counter effects of the drug amiodarone on the thyroid includes potassium perchlorate (ATDSR, 2008).

counter effects of the drug amiodarone on the thyroid includes potassium perchlorate (ATDSR, 2008).

Application Est. Perchlorate Release (lb/year)

Additional Information Application Est. Perchlorate Release (lb/year)

Additional Information

Chilean

Production Production NNnaturally in the environment, but its exact origin and mechanisms of formation are not known. Isotopic ratios in the nitrate deposits suggest that perchlorate formed in the atmosphere by a process involving ozone as the oxidant (Brown, 2005). It has typically been discovered in high concentrations in the soils of arid climates. Historically, the largest known natural source of perchlorate is found in Atacama Desert in Chile, where

from 300 to 1,000 mg/kg in the soil. Natural perchlorate has been detected in the Bolivian Playa crust high in the Andes, at

naturally in the environment, but its exact origin and mechanisms of formation are not known. Isotopic ratios in the nitrate deposits suggest that perchlorate formed in the atmosphere by a process involving ozone as the oxidant (Brown, 2005). It has typically been discovered in high concentrations in the soils of arid climates. Historically, the largest known natural source of perchlorate is found in Atacama Desert in Chile, where

from 300 to 1,000 mg/kg in the soil. Natural perchlorate has been detected in the Bolivian Playa crust high in the Andes, at

sasa

concentrations of 500 mg/kg of soil (Seller et al, 2004). Research on perchlorate containing soils has concluded that perchlorate and nitrate co-occur naturally, so perchlorate is extracted from deposits of nitrate ores, and is distributed in sodium nitrate fertilizer. Dry deposits of perchlorate are also found naturally within potash (potassium ore deposit) in mines close to Carlsbad, New Mexico and in

concentrations of 500 mg/kg of soil (Seller et al, 2004). Research on perchlorate containing soils has concluded that perchlorate and nitrate co-occur naturally, so perchlorate is extracted from deposits of nitrate ores, and is distributed in sodium nitrate fertilizer. Dry deposits of perchlorate are also found naturally within potash (potassium ore deposit) in mines close to Carlsbad, New Mexico and in

nitrate fertilizer

15,000 About 75,000 tons of fertilizer including 0.01 (wt) % perchlorate was used annually between 2002 and 2004 (Seller et al., 2004).

F No nd . Concentrations as high as

ireworks data fou Environmental releases of perchlorate are difficult to predict due to variability in the decomposition of perchlorate during combustion44.2 μg/L have been observed in nearby surface waters following a fireworks display in Oklahoma (Wilkin et al, 2007).

Safety flares 240,000 Preliminary research indicates that unburned and burned flares can leach 3.6 g and 1.9 mg respectively perchlorate. Estimated 20-40 million flares used annually (Seller et al., 2004). Blasting agents used in coal mining, quarrying, and other uses can contain perchlorate up to 30 (wt) %. The U.S. produces around 2.5 million tons of

Blasting explosives

No data found

explosives annually (Seller et al., 2004). Environmental releases of perchlorate are difficult to predict due to variability in the decomposition of perchlorate during combustion. Wells at the Kennecott copper mines in Magna, Utah have measured 13 ng/L perchlorate (Urbansky, 1998).

Chemical Production

1,700 Electrochemical production of sodium chlorate can generate perchlorate as an impurity at 50-230 mg/kg chlorate. The annual consumption of sodium chlorate in the U.S. is around 1.2 million tons (Seller et al, 2004). Perchlorate released as a defoliant between 1991 and 2003 is estimated at around 20,000 lb (Seller et al, 2004).

Defoliant 1,600

central Canada. The concentrations of perchlorate in these deposits range from 25

ial Preparation. Sodium erchlorate is the most soluble salt, and

ClO3 → ClO4

formed y adding other salts to a sodium nitrate

+ M (aq) + X (aq) → ClO4 (s) ↓ + Na (aq) + X- (aq)

onate; M is magnesium, potassium, lithium, or

perchlorate. Perchlo

Waste Streams. Figure 3 shows a map of

to 2,700 mg/kg of soil. Reservoirs of natural perchlorate in the arid American southwest are estimated at up to 1 kg/ha (Seller et al, 2004). Industrptherefore the principal salt produced. The most common method of producing sodium perchlorate is electrolysis of an aqueous solution of sodium chloride, with the following two electron oxidation series (ATDSR, 2008): (4) Cl- → ClO2

- → - -

All other perchlorate compounds arebsolution, to selectively re-crystallize the perchlorate salts that are less soluble than sodium perchlorate: Na+ (aq) + ClO4

- (aq) + -

+M

where X is chloride, sulfate, or carb

ammonium; and MClO4 (s) is the desired perchlorate (ATDSR, 2008).

Degradation of other compounds is another way to produce

rate can be found as a breakdown product in solutions of sodium hypochlorite, which is used as a swimming pool disinfectant, and can be incidentally formed in corrosion control applications. The mechanism hypothesized for perchlorate formation commences with the initial degradation of hypochlorite to chlorate.

Perchlorate could also be an intermediate by-product from the interaction of two hypochlorite degradation pathways, for instance degradation to chlorate and degradation to oxygen and sodium chloride (MDEP, 2009).

known perchlorate users and table 4 shows some typical waste stream volumes. One of the advantages of ammonium perchlorate compared to other oxidizers is that it is easily washed out of old rocket boosters and can be reused in other commercial applications (after being re-crystallized). The washout operation generates wastewater that because of perchlorates low solubility and other properties persists in the environment for decades (Atikovic, 2007). Two methods of solid propellant disposal used in the past, open burning and hydro-mining, discharged perchlorate directly into the environment. With open burning, un-combusted fuel material was allowed to seep into the soil and water. Current practice is to collect unburned material and re-burn it “to ensure complete combustion of energetic material (ITRC, 2005).” Hydro-mining is a method of using high pressured water jets to wash out the rocket booster, so the hard ware can be recycled. Current practice it to capture and treat the waste streams prior to discharge (see section VIII), but in the past the waste water was discharged untreated to the ground or into retention pounds prone to leakage (USEPA, 2005). Measured perchlorate levels in ground and surface water near munitions and rocket fuel plants have been shown to range from 4000 mg/L to as high as 3700 mg/L (Urbansky, 1998).

7

State Location Suspected Source Type of Contamination Max. Conc. ppb

NV Kerr-McGee/BMI Henderson, Nevada

Perchlorate Manufacturing

Public Water System Monitoring Well Surface Water

24 3,700,000 120,000

NV PEPCON Henderson, Nevada

Perchlorate Manufacturing

(former)

Monitoring Well 600,000

CA Aerojet General Rancho Cordova, CA

Rocket Manufacturing

Public Water Supply Well Monitoring Well

260 640,000

CA Rialto-Colton Plume Rialto, CA

Fireworks Facility Flare Manufacturing Rocket Research and

Manufacturing

Public Water Supply Well 811

CA Stringfellow Superfund Site Glen

Avon, CA

Hazardous Waste Disposal Facility

Monitoring Well Private Well

682,000 37

IA Ewart, IA Unknown Source Livestock Well 29 NY Westhampton

Suffolk County, NY Unknown Source(s), possibly agricultural

Public Water Supply Well Monitoring Well

16 3,370

Figure 3: Locations of known users and manufacturers of perchlorate (USEPA, 2005)

Table 4: Selected perchlorate sources, releases and detections (Mayer, 2004)

8

Perchlorate can also be released into the environment at sites where perchlorate salts ar

rred from munitions manufa

urce

e used in manufacturing processes. As mentioned above, there is only one producer of ammonium perchlorate today, but there were many more that operated in the past but have now closed or ceased perchlorate production (see Table 4). Those former sites of manufacture are current locations of perchlorate plume tracking and remediation.

Other anthropogenic waste streams have occu

cturing & disposal and the launching of solid fuel launch vehicles. Natural waste streams may occur when sand or soil containing perchlorate erodes and by way of

run-off becomes mobile in the environment (ATSDR, 2008). Changes in land use patterns from natural settings to irrigated agricultural land are mobilizing natural deposits of perchlorate into surface and ground waters in these locations (Rao et al, 2007). In wet and humid climates that coincide with agricultural applications of imported perchlorate-containing fertilizers, there can be leaching from solid perchlorate at the soil surface (Seller et al, 2004). One study shows estimated so

strength of 1.4 x 105 kg/year for perchlorate released to the environment from road flares. If perchlorate is released into the air, it will eventually settle out, primarily in rainfall (ATSDR, 2008).

The US-EPA documents that 63 DOD sit

8) reports

te

’

DOD site prioritization began in 2004 to

t risk to

,

8).

but repre

leanup is underway as of

Table 5: Selected DOD sites with perchlorate detections (extracted from ITRC, 2005)

es or installations have detectable(meaning over the minimum detection range of .5 ppb-1 ppb) perchlorate concentrations in soil, and/or ground water. Racca et al (20056 installations had detections of over 4 ppb by 2007. A 2001 DOD survey of weapons systems containing perchloralisted 259 different munitions. There is also a ‘perchlorate replacement programunderway to replace perchlorate in some existing munitions when possible (ITRC, 2005).

determine which DOD establishments posed the greatesdrinking water contamination. Sites were evaluated based on reported detections over 4 ppb, whether or not perchlorate related activities had occurred at the siteand site proximity to drinking water wells (less than 1 mile, between 1 and 5, or greater than 5 miles) (Racca et al., 200

This list is not comprehensive, sentative of detections at select

DOD facilities. *) perchlorate c(

September, 2005.

State Installation Branch Type of Contamination

Perchlorate detection

(ppb)

CA Edwards Air Force Base*

Air Force GW 160,000

NM Holloman Air Force Base

Air Force SW 16,000

MA Aberdeen Proving Ground Army DW, GW 5, 24

AL Redstone Arsenal* Army GW 160,000

NM White Sands Missile Range Army GW 21,000

CA

Naval Air Weapons

Station, China Lake

Navy GW 560

MA Naval Surface

Warfare Center, Indian Head*

Navy SW 1,000

9

Transport in the Environment. As mentioned above perchlorate compounds are highly soluble in aqueous solution and the perchlorate ion does not bind to soil particles. Perchlorate has been released to the environment in solid form, as ammonium, sodium, potassium, and other perchlorate salts, as well as in liquid form. These concentrated releases form highly density perchlorate brines once in contact with moisture. In soil, the movement of perchlorate is a “function of the amount of water present. (ITRC, 2005)”

Flowers et al (2001) examined the behavior of perchlorate plumes in groundwater aquifers (see Figure 4). Their model assumed dense brine was released at a disposal site. Since a large density (1.11g/cm3) contrast exists between the concentrated brine and ambient groundwater, in the vadose zone the perchlorate solution will sink vertically by the force of gravity at the same velocity as water, and horizontally by way of capillary forces. As perchlorate disperses it begins to move faster than the average groundwater velocity (Flowers et al, 2001).

Figure 4: Fate and transport of perchlorate in groundwater aquifer and estimated residence time

(adapted from Flowers et al, 2001)

10

In arid regions perchlorate “may accumulate at various horizons in the soil due to evaporation of infiltrating rainfall that leached perchlorate from shallower depths. (ITRC, 2005)”

After subsurface migration in the vadose zone, the concentrated brine will pool on top of a low-permeability confining layer and eventually penetrate the layer byway of diffusion (at a lower velocity than in the vadose zone). Once confined in the low-permeability layer, perchlorate will become a long-term source of aquifer contamination (appx. 100 year retention time) because of mass-transfer limitations (Flowers et al, 2001). Even when perchlorate discharge at the surface is stopped, and the pool above the low-permeability layer stops growing, perchlorate will still diffuse back into the aquifer from the confining layer. They conclude that long-term pump and treatment

options would be an economically inefficient way to treat perchlorate, and that “isolating and removing the source” of contamination is recommended (Flowers et al, 2001).

As mentioned above, under ambient conditions perchlorate is kinetically stable and does not react or decompose. Biodegradation of perchlorate will not occur unless significant levels of organic carbon are present. Taking into account perchlorates high solubility, low sorption, and lack of degradation plumes tend to be large and persistent. For example, the perchlorate plume at the Stringfellow Superfund site (Figure 5) in California persists for 5 miles from the Pyrite Canyon to the Santa Ana River (Kenoyer et al, 2007.) According to the California-EPA, wastes from rocket fuel users/manufacturers were transported and dumped in unlined pounds for evaporation at Stringfellow throughout the years.

11

Figure 5: Schematic of Perchlorate Plume at Stringfellow Superfund Site (CDTSC, 2006)

18 ppb

12 ppb

Average of detected

perchlorate concentrations

Image: www.ccaej.org (Center for Community Action and Environmental Justice)

In addition, quarry blasting in Pyrite Canyon (since 1904) may have included explosives that contained perchlorate dust that was washed into the soil and creeks, and then into groundwater. Irrigation of the Glen Avon area may have occurred from sources such as the Colorado River, and many tons of nitrate fertilizer was used in the area during the twentieth century (CDTSC, 2006). Since these activities span over a century, and are all considered ‘possible’ sources, exact numbers on releases in the vicinity of the Stringfellow site are not available. However, current perchlorate concentrations measured in nearby groundwater wells are shown in the figure below.

An abstract from the American Geophysical Union’s fall 2007 meeting indicates that “groundwater perchlorate contamination is likely to increase in the future with more widespread flushing of naturally occurring perchlorate beneath cultivated regions.” Their study was motivated by the discovery of high

perchlorate concentrations (60ppb) in the Ogallala aquifer of the Texas southern High Plains. Their studied showed that perchlorate was found beneath natural grassland and shrub land ecosystems (2.7-7.2 ppb), and that its correlation with chloride concentrations suggests dry fallout and precipitation are the likely sources. Further, they determine that perchlorate plumes reach a maximum depth of 8.3 meters in a downward direction under rain fed agricultural areas, and again correlate perchlorate concentrations with chloride concentrations (Scanlon et al, 2007).

A 2007 study by Wilkin et al (2007) looked at perchlorate concentrations in a lake following fireworks displays. It concluded that before the fireworks displays, lake concentration of perchlorate rose from a mean value of .043 ppb to a maximum concentration of 44.2 ppb after the display. Perchlorate concentrations returned to previous levels within 20 to 80 days after the display, “with the rate of attenuation correlating to surface water temperature.”

Tronox Plume Management. Figure 6: Pathway of Tronox Plume in the Southwest

United States (USEPA, 2005) In mid-1997 the Metropolitan Water District of Southern California discovered perchlorate in the lower Colorado River and traced contamination to Lake Mead and the Las Vegas Wash (see Figure 6). Ultimately, the source of the perchlorate was traced to the Kerr McGee (now Tronox) Chemical Plant in Hendersen, Nevada (USEPA, 2005). Tronox ground water aquifer plume released about 900 to 1000 pounds per day (average) of perchlorate to Las Vegas Wash prior to controls being implemented (USEPA, 2005).

water contamination,

After revelations of the drinking

12

Tronox suspended the production of

trategy aims to capture

V. Environmental Occurrence

erchlorate Exposure in the United

ublic Water Systems. Current analytical

ddition to PWS’s that serve more than 10

previously assumed from the UCMR 1.

perchlorate and began remediation. The cost of remediation is 124 million dollars, and has resulted in a 90% decrease in perchlorate entering the LVW since 1999 (Aqueduct Mag., 2008).

Their control s and treat perchlorate on Tronox

property where it is most concentrated by means of a slurry wall, at a narrow subsurface channel between the plant and LVW, and near LVW where capture will have the most immediate impact on reducing releases to LVW. The Tronox releases described above, which ended up in Lake Mead and the lower Colorado River had an impact on the drinking water supply of 15 to 20 million people in Arizona, southern California, southern Nevada, Tribal nations and Mexico (USEPA, 2005). I PStates. The U.S. EPA has been tracking the manufacturing, use and release of perchlorate to the environment since the late 1990’s (Brandhuber, 2005). In addition, the DOD is currently in the process of going through historical records of possible perchlorate containing production processes to estimate the total amount of perchlorate that has been released throughout the century (ITRC, 2005). Occurrence mapping for perchlorate attempts to pinpoint the location of users and manufacturers of perchlorate (Figure 3), known or suspected releases of perchlorate into the environment (Figure 7), and its detection in public water systems (concs. > 4ppb, Figure 7). In addittion, its occurrence in food can be mapped from various studies, but establishing the cause and effect relationship between perchlorate releases and its pathway to food products is a challenge. Further, its occurrence in food is not related

to a federal drinking water limit for perchlorate. The occurrence maps that have been produced from studies by Brandhuber et al (2005) (occurrence in public drinking water systems) and the USEPA (2005) (users, manufacturers and releases) show that perchlorate is many times present in public water systems where no known or likely anthropogenic releases into the environment have occurred. Ptechniques have achieved detection limits as low as 0.5 ppb for perchlorate. In 1999 perchlorate was added to the EPA’s Unregulated Contaminant Monitoring List (UCML), and public water systems (PWSs) serving more than 10,000 people were required to monitor perchlorate levels beginning in 2001. As part of the EPA’s UCMR 1 program, conducted between 2001 and 2005, data was compiled from 34,331 samples collected at the entry points (where water goes from the source into the distribution system) of 3,865 of the nations PWSs. The minimum detection limit for the UCMR 1 program was 4 ppb, and perchlorate was detected in 637 (1.9%) of those samples, which equated to 160 (4.1%) of PWSs.

In a,000 people, 800 samples (2.3% of

the total) were taken from PWSs that serve populations less than 10,000. Therefore, the UCMR 1 accounted for roughly 80% of the U.S. population (Brandhuber et al, 2005). According to Russell et al (2009), a recent study (an update of Brandhuber et al (2005) to be published in AWWA Journal at the end of 2009) points out that because the UCMR 1 only accounted for 1.8% of small PWSs (pop. < 10,000) a “more complete sampling effort” is needed to fully assess perchlorate concentrations in those systems, and it is likely the levels are higher than

13

Figure 7: Suspected or known lorate releases and detections perch (Brandhuber, 2005).

Known perchlorate release Drinking Water Detections: 4µg/L < 10 µg/L >10 µg/L

igure 8: Percent of total U.S. perchlorate detections found in each state (Russell et al, 2009)

F

14

Of the positive detections, the perchlorate concentrations ranged from 4 ppb to more than 3.7 million ppb, with an average of 9.85 ppb. More than half of detections occurred in California and Texas (see Figure 8 above), with the highest concentrations found in Arkansas, California, Texas, Nevada and Utah. Figure 4 shows the share of total PWSs with perchlorate detections allotted to each state (and Puerto Rico). Figure 7 shows detections of perchlorate between 4bb and 10 ppb, and those above 10 ppb (Brandhuber et al (2005).

Table 6: Measured perchlorate concentration in common foods (compiled from FDA, 2004 & Jackson et al, 2005)

Food Exposure. Perchlorate is common in many foods. Table 6 and Table 7 list perchlorate concentrations found in food samples, and the relative source contribution of food to perchlorate in our diets. The relative source contribution will become important in the health section of this report when developing the subchronic health advisory. This report does not go into detail

concerning studies related to perchlorate in food, since it is not related to a federal standard for perchlorate in drinking water, and because the studies have found it hard to track sources of most perchlorate containing foods.

Occupational Exposure. In two widely cited occupational studies (Lamm et al, 1999 & Gibbs et al, 1998) there were no adverse health effects on factory workers exposed to perchlorate. While there was reduced iodine uptake, there was not any signs of hypothyroidism (i.e. no changes in TSH, T4, and T3 levels) (ATDSR, 2008). A more recent study, Bravermen et al (2005), found similar results. The study found that workers experienced a decrease in iodide uptake during their shifts when exposed to high doses, as well as fluctuations in T3 and

Table 7: Relative source contributions remaining for water based on TDS for various sub-groups (extracted

from US EPA, 2008)

Population Group

Food intake (ug/kg/day)

RfD remaining (ug/kg/day)

RSC for DW (% of RfD)

Infants .26-.29 041-.44 59%-63%

Children, 2yr .35-.39 .31-.35 44%-50%

Children, 6yr .25-.28 .42-.45 60%-64%

Children, 10 yr

.17-.20 .50-.53 71%-76%

Teen Girls .09-.11 .59-.61 84%-87%

Teen Boys .12-.14 .56-.58 80%-83%

Women, 25-30

.09-.11 .59-.61 84%-87%

Men, 25-30 .08-.11 .59-.62 84%-89%

Women, 40-45

.09-.11 .59-.61 84%-87%

Men, 40-45 .09-.11 .59-.61 84%-87%

Type of sample

Minimum (ppb)

Maximum (ppb)

Mean Perchlorate

(ppb)

Vegtables 2.38 228.25 19.43 Bottle water

0.45 0.56 ND

Cow milk 3.16 11.30 5.76 Fruit 0.85 144.48 ND Apple juice

1.39 3.45 2.15

Orange juice

2.27 3.15 2.59

Sweet Potatoes

0.85 2.07 1.24

Fish 12.22 17.70 6.61

15

T4 levels, but that these effects went away when the worker was away from the factory. They concluded that “long-term, intermittent, high exposure to ClO4- does not induce hypothyroidism or goiter in adults (Braverman et al, 2005).” These terms will be described in more detail in the Health Effects section of this report. In occupational settings, the main risk factor would be via inhalation. Finally, it is worth repeating that ammonium perchlorate is 90% of perchlorate sold, and all ammonium perchlorate produced occurs in a single production plant in Henderson, Nevada (as mentioned above). These studies were all carried out at that plant. Therefore, the implications of the numbers that follow would apply only for workers at that single plant, who would be experiencing the most frequent doses of perchlorate and maybe the only doses in the United States at any given time. Needless to say, a federal regulation for occupational exposure of perchlorate would be irrelevant.

“The median estimated absorbed dose was 0.167 mg/kg/day, equivalent to drinking approximately 2L of water containing 5 mg perchlorate/L. It should be mentioned that perchlorate workers are exposed during an unusual schedule of three 12-hour shifts followed by 3 days without exposure (long-time, intermittent exposure). Given the relatively short elimination half-life of chlorine in worker of approximately 8 hours (Lamm et al, 1999) perchlorate would not be expected to accumulate to levels that would cause thyroid problems (ATSDR, 2008).” No data were found on levels of perchlorate in ambient air, but workers at an ammonium perchlorate production facility who were exposed to perchlorate dust had single shift absorbed doses measured at 0.2–436 μg/kg, with a 35 μg/kg average. Cumulative lifetime doses for these workers over an average of 8.3 years ranged from 8,000 to 88,000 μg/kg (ATDSR, 2008).

VI. Health Effects

The main health concern regarding the perchlorate ion is its ability, when in the human blood stream, to inhibit the uptake of iodide by the thyroid. The EPA considers this inhibition the mode of action rather than the adverse affect. Srinivasan et al (2009) states that the mode of action is considered the factors that cause the inhibition of iodide uptake, and the potential adverse health affect is hypothyroidism. The flow chart to the left, adapted from Seller et al (2007), illustrates this distinction (see Figure 9). The EPA’s reference dose for perchlorate and all discussion regarding exposure to vulnerable groups is always referring to the mode of

action, and not the adverse health affect. In this respect, perchlorate is treated differently than other ‘candidate contaminants’ that the EPA evaluates for regulation (US EPA, 2008). Therefore, since the reference dose of perchlorate is not based on the adverse health effect, but a precursor to the adverse health effect, it can be considered an added safety factor to protect vulnerable groups (see Figure 12).

It is important to point out that the available clinical studies in many cases show that perchlorate affects thyroid functioning (ie. iodide uptake inhibition) while exposure is occurring, but no study has proven any long term adverse health

16

Figure 9: Perchlorate mode of action and adverse affect when ingested (adapted from Seller et al, 2007)

effects of perchlorate at doses that are likely to be consumed by humans from drinking water or food supplies. This section will discuss further important human studies over the past ten years, the relevance of animal studies, and finally potentially vulnerable groups of the human population. Perchlorate and Thyroid Function. When idodide uptake is reduced, one or more steps in the synthesis and secretion of thyroid hormones can be interrupted, resulting in subnormal levels of T3 (triiodothyronine) and T4 (thyroxin) and an associated compensatory increase in secretion of TSH (thyroid stimulating hormone). Perchlorate has been found to induce this precursor to the adverse effect (iodide uptake inhibition) and subsequent adverse affect in humans when administered at doses much higher than those found in the environment (greater than 500 ppb). The perchlorate ion, because of its similarity to iodide in ionic size and charge, competes with iodide for uptake into the thyroid gland by the sodium-iodide symporter, a transport mechanism in the membranes of thyroid cells. This competitive inhibition results in reduce production of the thyroid hormones T3 and T4 and a consequent increase in THS where thyroid, pituitary and hypothalamus are involved (see figure 10) (ATDSR, 2008).

Mode of Action

Subsequent events include decreases in serum T4 and T3. In mice studies, this decrease has led to the potential for altered neurodevelopment if observed in either mothers, fetuses or neonates, and increase in serum TSH leading to the potential for thyroid hyperplasia and tumors (ATDSR, 2008). The repeat observation of thyroid effects such as alterations of hormones, increase thyroid weight, and alterations of thyroid histopathology from a large number of rat studies on perchlorate provide supporting evidence for the propose mode-of-action, and confirms that the

Adverse Affect

perturbation of thyroid hormone economy as the primary biological effect of perchlorate in rats (CDTSC, 2005) Human Studies. In the US Department of Health and Human Service’s Toxicological Profile for Perchlorate, studies are summarized that aimed to determine “does-response relationships at low doses of and to define no-effect level of exposure to perchlorate (ATSDR, 2008).”

17

Their summary concludes that no study thus far has shown perchlorate to cause adverse health effects in humans at doses encountered in the environment. G. Charnley (2009), Srinivasan et al (2009), and Hagstrom (2006) back up this claim with their summaries.

Figure 10: The thyroid and its role in hormone secretion (image: www.clarion.com)

Greer et al (2002) conducted the

most widely cited study (under the auspices of the National Academy of Sciences), one that is also the basis for the EPA’s perchlorate reference dose (RfD). 37 human volunteers were separated into four groups and served drinking water amounting to 0.007, 0.02, 0.1, and .5 mg/kg-day levels of perchlorate for 14 days. Using various statistical measures of radioiodine uptake inhibition they determined a true no effect level of 5.2 and 6.4 µg/kg-day measured 8 and 24 hours after exposure, respectively. For comparison, this would correspond to a drinking water supply concentration of about 180 and 220 µg/L (ppb), respectively. The levels detected in U.S. drinking water supplies generally range from 5-20 µg/L as seen in section IV (Greer et al (2002).

Reports released by the Environmental Working Group (a non-profit

based in Washington D.C.) are cited widely in the blogosphere and in newspapers, would indicate that perchlorate has been determined highly dangerous to women with low iodide levels, and that the lack of a Federal perchlorate regulation is a result of Defense Department lobbyists and other special interests. The keystone study cited in this sphere of information is a 2005 CDC report that establishes a positive relationship between iodide deficient women, perchlorate levels in their urine, increasing serum concentrations of TSH, and decreasing serum concentrations of T4 (ie. perchlorate was a predictor for the imbalance of these hormones in iodine deficient women).

The study (Blount et al, 2006) evaluated the relationship between levels of perchlorate in the urine and serum levels of TSH and T4 in 2,299 men and women (>11 years old). The study concluded that in women with urinary iodine < 100µg/L, perchlorate was a predictor of T4 and TSH. A previous study on women in Chile (avg. iodine 269µg/L) exposed to perchlorate concentrations of up to 114 µg/L showed no adverse affect, but their iodine concentrations were sufficient. However, the Blount study recognized that the low levels of perchlorate that produced the adverse affect in iodide deficient women did not produce adverse affects in numerous previous studies. As they put it: “(The adverse affects of this study) are found at perchlorate exposure levels that were unanticipated based on previous studies (Blount et al, 2006).” Furthermore, they establish a predictor, but the change in T4 and TSH was still within the healthy range for a human being. Finally, a New York Times article quotes the author of the CDC study as follows: “The study did not establish a cause-and-effect relationship but pointed to a need for more research (Goodman, 2009).”

18

In addition, and something these researchers seemed to have over looked or at least considered, is that an iodine deficiency in and of itself is a cause of hypothyroidism, with or without the perchlorate. Any online medical dictionary will explicitly state the main adverse affect of iodine deficiency is hypothyroidism. The CDC study removed 91 women from a total of 1,226 because they had reported a history of hypothyroidism. This indicates that the authors assumed that the majority of women with a thyroid disorder or out of the ordinary T4 and TSH have been diagnosed. They do not offer a justification for that assumption. The authors controlled for many variables that could also be positive predictors of T4 or TSH, but none of those include low iodide levels. The authors also state that the World Health Organization defines sufficient iodine intake as 100µg/L or more. So by concluding that women with iodide levels below the accepted standard showed the typical adverse affect of low iodide content, the authors are stating the obvious.

Animal Studies. Most of the concern about perchlorate’s possible adverse effect on human health stems from extensive research on animals where perchlorate doses have instigated hypothyroidism and tumors. Generally, the animals in these studies are given doses 10-times or more the amount likely to be encountered by humans in the environment (Srinivasan, 2009). Rats and mice are used because in some cases their response mechanisms to perchlorate would be similar to humans. Specifically, rats and humans have thyroids that function similarly, and the mode of action of perchlorate (i.e., iodide uptake inhibition) is analogous. However, the main difference between human and animals represented in the studies is the dose-response relationships. In humans, perchlorate dosages must occur over a longer period of

time than in rats to affect the circulation of T4 and T3 hormones (ATSDR, 2008). There are also physiological differences between rats and humans related to the pituitary thyroid axis, which “makes rats inappropriate for quantifying predicted changes in humans for risk assessment purposes (Srinivasan, 2009).”

In the June 2009 Environmental Health Perspectives there is a discussion of an article by Gilbert et al (2008) in which he claims neurological development effects of perchlorate in drinking water consumed by adult rats. Though the discussion is not peer reviewed, it is a discourse about a peer reviewed article between the authors of the article, and employees from Novice who were contracted to assess the claims of the article. While they go back and forth about implications of the article, they both agree on one thing: “…the purpose of our study was not to emulate human exposures to perchlorate.” The study found a reduction in synaptic functioning at a dose of 4.5 mg/kg-day, which is much higher than the maximum concentration of .5 mg/kg-day in Greer’s study (Gilbert et al, 2009). At-risk subpopulations. The main concern and basis of the perchlorate regulatory debate is on possible congenital effects. Since fetuses of hypothyroidic women are at a greater risk for abnormal growth and development, the concern is that perchlorate induced hypothyroidism will produce the same effects. “(According the National Research Council) because the fetus depends on an adequate supply of maternal thyroid hormone for its central nervous system development during the first trimester of pregnancy, iodide uptake inhibition from low-level perchlorate exposure has been identified as a concern in connection with increasing the risk of neurodevelopmental impairment in fetuses of high-risk mothers (USEPA, 2008).”

19

VII: Regulation

Perchlorate Regulation in the United States. Figure 11 illustrates the history of perchlorate regulation at the Federal level. Because debate exists regarding its health effects at environmentally present doses, there is not a federal drinking water limit established for perchlorate. California and Massachusetts are the only two states to establish an enforceable regulation for perchlorate, as shown in Table 8. The Safe Drinking Water Act was amended in 1996 to include section 1412, which mandates the EPA to evaluate at least five contaminants from its candidate list every 5 years and determine whether or not they require

Federal regulation (US EPA, 2009). “The U.S. Congress is considering two pieces of legislation, one that would compel the US EPA to establish a drinking water standard for perchlorate and one that would compel US EPA to determine whether perchlorate should be regulated (G. Charnely, 2008).”

According to the EPA, in order to regulate a contaminant three conditions must be met:

1) The contaminant may have an adverse affect on human health.

2) The contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems with a frequency and at levels of public health concern.

3) Regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by the public water system.

Table 8: State Drinking Water Regulations (USEPA, 2008) 

Enforceable Regulations Advisory Levels in Other States 

Massachusetts 2 

ppb 

4‐51 ppb 

California  

6 ppb 

Figure 11: Progression of Perchlorate Regulation at the Federal level in the United States (self-generated graphic)

20

Sub population  Body Weight 

Drinking Water Consumption 

RSC From Drinking 

Water as % RfD 

Potential HA level 

Women of Childbearing 

Age 

70 kg  2 liters  84‐87%  21 µg/L 

Pregnant Women 

70 kg  2 liters  62%  15 µg/L 

RfD =NOAEL

UF

DWEL =RfD x BW

DWI Subchronic HA = DWEL x RSC

RfD = 7 µg/kg/day = 0.7 µg/kg/day

10

DWEL = 0.7 µg/kg/day x 70

kg = 24.5 µg/L 2 L/day

Subchronic HA = 24.5 µg/L x 0.62 = 0.0152 µg/L (rounded 15 µg/L)

Figure 12: Quantification and calculations for toxicological effects of perchlorate (self generated from USEPA, 2008)

RfD = Reference Dose (mg/kg bw/day) DWEL = Drinking Water Equivalent Level RSC = Relative Source Contribution NOAEL = No Adverse Effect Level (mg/kg bw/day) UF = Uncertainty factor established for vulnerable subpopulations BW= Assumed body weight of an adult (70 kg) DWI = Assumed daily water consumption for an adult (2 L/day)

Table 9: Relative source contributions of perchlorate in drinking water for vulnerable subpopulations (USEPA, 2008)

21

22

In October, 2008 the EPA determined perchlorate did not meet the 2nd and 3rd conditions, and asked for public feedback. They received nearly 33,000 public comments, but as of October, 2009 have not made a final determination on a federal regulation. Currently, there is a Federal Register notice asking for “comment on a broader range of alternatives” for evaluating all available data on conditions 1 thru 3. 2005 Reference Dose & 2009 Health Advisory. The EPA assigned a Reference Dose (RfD) of 0.007 mg/kg/day for perchlorate recommended by the National Research Council (NRC, 2005) based off of the NOEL from Greer et al (2002). A composite uncertainty factor (UF) of 10 was used to protect the fetuses of pregnant woman who might have hypothyroidism or iodide deficiency. The RfD represents the maximum safe oral dose of a noncarcinogenic substance that can be consumed by a human. To correlate this dose with drinking water safety, a Drinking Water Equivalent Level (DWEL) is established, which is the concentration of a contaminant in drinking water that will have no adverse effect. The DWEL assumes that a 70 kg adult drinks 2 L of water per day with no exposure from other sources. Hence, 24.5 ppb (µg/L) is the DWEL recommended by the US-EPA in their integrated risk information system (see Figure 12) (Gu et al, 2006). The 2009 interim health advisory covers a period of more than 30 days, but less than one year. The subchronic health advisory is directed towards the fetuses of iodine deficient pregnant women, and includes a relative source contribution from drinking water of 62% specifically for pregnant women, as their food intake varies from non-pregnant women and other populations (see Table 9). The EPA used the

90th percentile rather than mean food exposure data “to ensure that the interim HA protects highly exposed pregnant women and their fetuses (USEPA, 2008).” VIII: Treatment Options

In order for the EPA to set a regulation for a contaminant they must assess and put forth the most economical remediation and treatment technologies. The perchlorate treatment technologies can be classified according the environmental setting of perchlorate. The treatments in this section will separate the perchlorate from the medium of interest or degrade it. The physical and chemical properties, cost, feasibility and source of the contamination will dictate which treatment is the best. Table 10 summarizes the technologies discussed in this section and their range of effective treatments. Ion exchange. Ion exchange (IX) is the most common used ion exchange. Ion exchange is a physical-chemical process in which charged functional groups, resins, on the surface of a solid attracted and thereby remove ions from water via electrostatic forces. Resins are macroporous of which contain positively charge surface functional group sorbed with counter ions, usually Cl־ anions. When it is exposed to a solution that contains ions like perchlorate, the ions in solution will enter the ion exchange, in exchange for Cl־ from the resin bead, see figure 13 (Chiang, 2005).

Table 10: Applicability of common treatment technologies (adapted from Seller, 2007)

Figure 13: Schematic representation of the ion exchange between perchlorate and chloride (extracted from Gu, 2006) Ion exchange technology can use multiple beds in series to reduce the need for bed regeneration; beds first in the series (lead beds) require regeneration first, and fresh beds can be added at the end of the series

(lag beds). Using multiple beds can also allow continuous operation because some beds can be regenerated while others continue to treat water, see figure 14 (EPA, 2005).

Type of

treatment Technology Soil Water

Effective treatment

concentration (ppb)

Separation Ion exchange ● 10-100,000

GAC ● 1-10 Membrane filtration ● 10-5,000

Destruction

Bioreactors ● 100-10,000 In situ

biodegradation ● ● 100-500,000

Thermal destruction ● ● 10-10,000 Electrochemical

destruction ● 1-10

Iron particles ● Phytoremediation ● ● 100-10,000 Catalytic reactor ● 10-1,000

23

Figure 14: Ion exchange treatment for perchlorate removal (Extracted from EPA, 2005)

Granular Activate Carbon (GAC). It is one of the oldest means of treatment water process. GAC is a granular porous that has a sorption capacity of contaminant as perchlorate. Thus, liquid phase carbon adsorption using granular activated carbon (GAC) is an ex situ technology to remove perchlorate from contaminated groundwater and surface water. The mechanism of perchlorate sorption is not well understood. Conceptually, perchlorate interacts with the positively charged surfaces of the GAC particles rather than adsorbing to the inner surfaces of pores in the GAC as would a large organic molecule. See figure 14 and swap ion exchange resin for a sorbent zone. Nevertheless, GAC has a comparatively

small treatment capacity for perchlorate removal, and research is underway to identify methods to improve the treatment capacity of a GAC system for perchlorate removal, including use of “tailored GAC (Srinivasan 2009).”

Rapid Small-Scale Column Test (RSSCT) were dry packed with virgin activate carbon. Water passes onto virgin GAC utilizing RSSCTs containing (180 x 250 µm) GAC. The challenge for tailored GAC is the regeneration of the medium because it can be regenerated. Hence, any spent tailored GAC must be removed for disposal. It can be used organic clay and zeolites instead of GAC (Gu, 2006).

Membrane Filtration. Membrane filtration treatment includes reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and electrodialysis (ED). Process based on membrane, water is forced through a semi-permeable membrane while dissolved salts are unable to pass through the membrane.

Two streams are produced in the membrane process, see figure 15: the filtrate or permeate which is nearly deionized water and the brine concentrate or rejectate, which contains all reject salts or dissolved material including perchlorate.

24

Figure 15: Schematic representation of a membrane filtration system for the treatment of perchlorate, adapted from (Gu 2006). Bioreactors. A bioreactor is a situ biological treatment system that degrades contaminants in extract groundwater using microorganisms. Biological treatment can be aerobic, or anaerobic. Anaerobic system is used to treat perchlorate. The microorganisms are facultative anaerobes and they can use electron acceptor other than dissolved oxygen such as: nitrate, perchlorate and sulfate. The dissimilatory perchlorate reducing bacteria (DPRB) has a perchlorate reduction pathway consisting of two key enzymes perchlorate reductase and chlorite dismutase. These two enzymes govern the following anaerobic reduction process (EPA, 2006).

24 2OClClO +→ −−

The first enzymatic step of the pathway, perchlorate reduction to chlorite, is performed by perchlorate reductase. The chlorite produced is subsequently converted to chloride and oxygen, this conversion is done by chlorite dismutase, see figure 16.

25

Organic carbon

e-

e-

CO2

ClO2-

Cl-O2

H2O

ClO4-/ClO3

-

Figure 16: Enzymatic pathway of the dissimilatory perchlorate reducing bacteria (DPRB), adapted from (Gu 2006). More than 30 different strains of perchlorate-degrading microbes have been identified, with many classified in the Proteobacteria class of the bacteria kingdom. Soil and groundwater samplings have confirmed the pervasiveness of perchlorate-reducing bacteria (EPA 2005).

In situ biodegradation (ISB). ISB comes together hydrogeology, chemistry, engineering and microbiology into an approach for planned and controlled microbial degradation of perchlorate. ISB normally involves nutrients to the subsurface to promote the biodegradation of the perchlorate by the DPRB. The electron donors can be substance based on carbon such as: alcohols, organic acids, or sugars.

As in bioreactor, bacteria use perchlorate as electron acceptor (Srinivasan 2009). ISB has reduced perchlorate concentrations less than 4 μg/L in groundwater (EPA 2005).

Thermal Destruction. This process can remove perchlorate from soil to the vapor phase and subsequently destroy it. Remove perchlorate from soil requires temperatures between 315 to 650 ºC. This technology is also time depending because perchlorate volatilizes over a period of time once a target temperature is achieved. The exhaust from this system is accumulated by an air cleaning system and heated to temperatures of approximately 816 ºC to destroy it completely. It can treat samples with concentration from 1 to 110 µg/kg. It can reduce to 4 µg/kg, if the sample is more this concentration (Seller 2006).

Electrochemical destruction and Iron particles. This process reduces perchlorate into chloride ion. When a cell has nickel electrode and a platinum counter electrode

in concentrated solutions of hypochlorous acid is been reduced. Titanium metal is also used as a chemical reductant to remove perchlorate in water. The activation of

26

titanium was achieved by eliminating the localized surface oxide film using electrochemically induced pitting corrosion. The titanium metal ions in the vicinity of the pits results in a higher rate of perchlorate reduction. The surface of the bare Ti inside the pits induces further electrochemical reactions and causes faster rate of chloride oxidation to chlorine by increasing the current (Srinivasan 2009).

Stabilized elemental iron nanoparticles can remove perchlorate knowing that temperature played a critical role in perchlorate degradation process. Perchlorate removal is achieved by iron particle at temperature around 200 ºC (Srinivasan 2009). Phytoremediation. Phytoremediation is in situ mechanism that uses plants to remove

contaminants by natural processes occurring within the plant body. This process for perchlorate removal gain attention in the late 1990s, and it was considered for surface, groundwater and soil. The process, see figure 17, ahs two mechanisms: rhizosphere degradation where the perchlorate is present in soil adheres to the root system of the plant. The root system contains various microbial communities that, thus, provide biomass to biodegrade perchlorate. Second mechanism is phytoaccumulation or phytoextraction. Shoots and trees take up and harvest the perchlorate and the perchlorate is accumulated in leaves as a result of evapotranspiration. The water is evaporated but the perchlorate not, hence, under anoxic conditions certain microorganism can degrade perchlorate.

Figure 17: Phytoremediation of perchlorate. This process is an emerging technology for perchlorate remediation (taken from EPA 2005). Catalytic reactor. This technology uses hydrogen gas to reduce perchlorate completely to chloride has been reported. Methylthrioxorhenium is added to combine with 5% Pd-carbon powder. Metallic iron and goethite (FeO·OH) or other metal are

also used to reduced perchlorate. Perchlorate absorbs ultraviolet (UV) light in the wavelength range shorter than 185 nanometers, and consequently UV light can be used to catalyze the reduction reaction (seller 2007).

27

Cost Implications of Regulating Perchlorate

The American Water Works Association (AWWA) published in March, 2009 the first report on the national cost implications of regulating perchlorate with a maximum contaminant level (MCL) at the national level (Russell et al, 2009). If the Federal Government implemented a MCL of 4µg/L, 3.4% of public water systems (PWS) would be affected, and the net present value (NPV) of compliance costs would be 2.1 billion USD. An MCL of 24µg/L would affect 1% of PWS’s, and the NPV for compliance would be 100 million USD. See Table 11.

According to the AWWA, the national cost for perchlorate remediation would be cheaper than previous contaminant regulations in the United States, but “…a small number of systems are carrying this cost burden and the cost implications to an individual system having to install perchlorate treatment would likely be significant (Russell et al, 2009).” They also say that if Congress decides to pursue a federal regulation for perchlorate in the future, this report will be a “key building block” for subsequent discussions of national cost.

Conclusions

Perchlorate is an environmental contaminant which can cause negative health affects at high doses, especially to the fetuses of iodine deficient pregnant women. While the cost of implementing a federal drinking water standard is low compared to previous limits, the cost would fall upon a few individuals. Clearly, there are many stakeholders and we hope the political process serves both sides of the debate fairly. If a regulation is put in place, we would recommend the ion exchange method as the most reliable and capable of removing perchlorate from public water systems.

Table 11: National Cost of Federal Regulation 

MCL  % PWS affected 

Cost (USD) 

4 ppb 

3.4  2.1 billion 

24 ppb 

1  100 million 

28

References ATDSR. (2008). Toxicological Profile for

Perchlorates. U.S. Department of Health and Human Services.Agency for Toxic Substances and Disease Registry. CAS#: 10034: 81-8, 7778 : 74-7, 7790 : 98-9, 7601 : 89-0, 7791 : 03-9

Atikovic, E., Suidan, M. T., & Maloney, S. W.

(2008). Anaerobic treatment of army ammunition production wastewater containing perchlorate and RDX. Chemosphere, 72, 1643-1648.

Blount, B.C., J.L. Pirkle, J.D. Osterloh, L.

Valentin-Blasini, and K.L. Caldwell. 2006. Urinary perchlorate and thyroid hormone levels in adolescent and adult men and women living in the United States. Environmental Health Perspectives.114 (12): 1865-1871

Brandhuber, P., & Clark, S. (2005). Perchlorate

occurrence mapping. American Water Works Association.

Braverman, L. E., Pearce, E. N., He, X., Pino,

S., Seeley, M., Beck, B., et al. (2006). Effects of six moneths of daily low-dose perchlorate exposure on thyroid function in healthy volunteers. The Journal of Clinical Endocrinology & Metabolism, 91(7): 2721-2724.

Braverman, L. E., He, X., Pino, S., Cross, M.,

Magnani, B., Lamm, S. H., et al. (2005). The effect of perchlorate, thiocyanate, and nitrate on thyroid function in workers exposed to perchlorate long-term. The Jounral of Clinical Endocrinology & Metabolism. 90 (2).

Brown, G. M., & Gu, B. (2006). The chemistry

of perchlorate in the environment. In Springer Science. Business Media INC (Ed.), Perchlorate: Environmental occurrence, interactions and treatment

Chemistry Department of Moscow State University. Activation energy graph. Retrieved September 12, 2009. http://www.chem.msu.su/eng/teaching/Kinetics-online/chapter6e_ad.html Chiang, K. and Megonnell, M. (2005). Ion

exchange technologies for perchlorate removal are evolving. Water World, 21.

Columbia Analytical Services, I. (2009).

Perchlorate geometry images. Retrieved: September 12, 2009 .http://www.caslab.com/Perchlorate-Testing/

Canas, J. E., Patel, R., Tian, K., & Anderson, T.

A. (2006). Development of an extraction method for perchlorate. Journal of Environmental Monitoring, 8: 399-405.

Capuco, A. V., Rice, C. P., Baldwin, R. L.,

Bannerman, D., Paape, M. J., Hare, W. R., et al. (2005). Fate of dietary perchlorate in lactating dairy cows: Relevance to animal health and levels in milk supply. PNAS. 102 (45): 16152-16157.

CDTSC (2006). Stringfellow Superfund Site

Perchlorate Update. California Department of Toxic Substances Control. Fact Sheet: December 2006. Retrieved: October 12, 2009. http://www.dtsc.ca.gov/SiteCleanup/Projects/upload/Stringfellow_FS_Perchlorate_Update_1206.pdf

CDTSC. (2005). Chemistry and Toxicology of

Perchlorate: Section 2. California Department of Toxic Substances Control. Pp. 2-15 Retrieved: September 12, 2009. http://www.dtsc.ca.gov/LawsRegsPolicies/Regs/upload/HWMP_WS_dPerch-Sec2.pdf.

29

Charnley, G. Perchlorate. (2009). Overview of

risks and regulations. Food and Chemical Toxicology, 46: 2307

Dasgupta, P. K., P. K. Martinelango, A. Jackson,

K. Tian, R.W. Tock, & S. Rajagopalan. (2005). The Origin of Naturally Occurring Perchlorate: The Role of Atmospheric Processes. Environmental Science and Technology, 39(6): 1569–1575.

FDA, United State Food and Drug

Administration. 2004. Exploring Data on Perchlorate in Food, Office of Plant and Dairy Food.

Flower, T.C., and J.R. Hunt. (2000). “Long-

Term Release of Perchlorate as a Potential Source of Groundwater Contamination,” Chap. 17 in Perchlorate in the Environment, E.T. Urbansky, ed. New York: Kluwer/Plenum.

GAO. (2007). Government Accountability

Office. EPA Does Not Systematically Track Incidents of Contamination. Testimony Before the Subcommittee on Environment and Hazardous Materials, House Committee on Energy and Commerce. Perchlorate.

Gibbs JP, Ahmad R, Crump KS, Houk DP,

Leveille TS, Findley JE, Francis M. 1998. Evaluation of population with occupational exposure to airborne ammonium perchlorate for possible acute or chronic effects on thyroid function. J Occup Environ Med 40:1072-1082

Goodman, S. (2009). New findings spur EPA to

rethink perchlorate regulation. New York Times, Retrieved: August 6, 2009

Greer, M. A., Goodman, G., Pleus, R. C., and

Greer, S. E. (2002). Health effects assessment for environmental

perchlorate contamination: The dose response for inhibition of thyroid radioiodine uptake in humans. Environmental Health Perspectives. 110 (9): 927.

Gu, Baohua and Coates, John. (2006).

Perchlorate. Environmental Occurrence, Interactions and Treatment. Springer edition. 1st. New York, NY.

Hagstrom, E. L. (2006). Perchlorate: A

scientific, legal, and economic assessment. Lawyers & Judges Oublishing Company, Inc.

Hurley, J. A., & Air Force Research Laboratory.

(2001). Ammonium perchlorate treatment technology development. US Environmental Protection Agency.

ITRC. (2005). Interstate Technology &

Regulatory Council. Perchlorate: Overview of Issues, Status, and Remedial Option. PERCHLORATE-1. Washington, D.C.: Interstate Technology and Regulatory Council, Perchlorate Team. Retrieved October 2009. http://www.itrcweb.org

Jackson, W. A., Joseph, Preethi; Laxman,

Patil; Tan, Kui; Kmith, Philip N; Yu, Lu; and Anderson, Todd A. 2005. Perchlorate Accumulation in Forage and Edible Vegetation. Jour. Agricu. Food Chem. 53:369-373.

Kenoyer, G. J., Nuttall, H. E., Paulson, R.,

Wolfenden, A., & Aldern, J. (2007). Fate and transport of perchlorate at california's stringfellow superfund site. Eos Trans. AGU. 88 (52).

Kirk-Othmer Encyclopedia of Chemical

Technology. (2004). 5th. John Wiley & Sons. New Jersey.

Lamm, SH., LE. Braverman, FX. Li, K.

Richman, S. Pino, and G. Howearth.

30

(1999). Thyroid health status of ammonium perchlorate in workers: a cross-sectional occupational health study. J Occup. Environ Med. 41:248-260.

Lieberman, Tony M., and Robert C. Borden,

Ph.D. 2008. Natural Attenuation of Perchlorate in Groundwater: Processes, Tools and Monitoring Techniques. Defense Technical Information Center. Environmental Security Technology Certification Program: Project ER-0428. Retrieved: September 12, 2009. http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA495522&Location=U2&doc=GetTRDoc.pdf.

Mayer, Kevin (EPA Region 9). 2004.

“Perchlorate in the Environment.” Presentation at American Chemical Society Meeting, Agricultural Chemical Division, Anaheim, CA. March 31

MDEP. (2006). The occurrence and sources of

Perchlorate in Massachusetts. Massachusetts Department of Environmental Protection. Retrieved: September 20, 2009. http://www.mass.gov/dep/cleanup/sites/percsour.doc

Merck Index, The (1983). 10th. Merck & Co.,

Inc. New Jersey. Motzer, William E. 2001. “Perchlorate:

Problems, Detection, and Solutions.” Environmental Forensics. 2: 301 – 311.

Politzer, P., & Lane, P. (1998). Energetics of ammonium perchlorate decomposition steps. Journal of Molecular Structure. 454: 229-235.

Racca, Laurie, Clare Mendelsohn, John Russell,

Shannon Cunniff, Frederick Moss, and Baha Zarah. (2008). Attention to Protocol, How a State/Federal Partnership Defused Tensions over Perchlorate. EM Magazine. Air and Waste Management Association.

Rao, Balaji, Anderson, Todd A., Orris, Greta J.,

Rainwater, Ken A., Rajagopalan, Srinath, Sandvig, Renee M., Scanlon, Bridget R., Stonestrom, David A., Walvoord, Michelle A., and Jackson, W. Andrew. (2007). Widespread Natural Perchlorate in Unsaturated Zones of the Southwest United States. Environ. Sci. Technol., 41(13): 4522–4528.

Russell, C. G., Roberson, A. J., Chowdhury, Z.,

& Mcguire, M. J. (2009). National cost implications of a perchlorate regulation. Journal of American Water Works Association.101 (3): 54.

Sanchez, C. A., Crump, K. S., Krieger, R. I.,

Khandaker, N. R., & Gibbs, J. P. (2005). Perchlorate and nitrate in leafy vegetables of north america. Environmental Science and Technology. 39 (24): 391-9397.

Seller, Kathleen., William Alsop, Stephen

Clough, Marilyn Hoyt, Barbara Pugh, Joseph Robb, and Katherine Weeks. (2007). Perchlorate Environmental Problems and Solutions. Taylor & Francis Group. 1st. New York.

Scanlon, Bridget R., Robert C. Reedy, W.

Andrew Jackson, and Balaji Rao. (2008). Mobilization of Naturally Occurring Perchlorate Related to Land-Use Change in the Southern High Plains, Texas. Environ. Sci. Technol., 42(23): 8648–8653.

Srinivasan, Asha, and Thiruvenkatachari

Viraraghavan. 2009. Perchlorate: Health Effects and Technologies for Its Removal from Water Resources. Int. J. Environ. Res. Public Health, 6:1418-1442.

Urbansky, Edward T. 1998.Perchlorate

Chemistry: Implications for Analysis and Remediation. Bioremediation Journal. 2:81-95.

31

32

US Environmental Protection Agency-Waste Management Division. Perchlorate monitoring results: Henderson, nevada to the lower colorodo riverUS Environmental Protection Agency.

US EPA. (2008). Interim drinking water health

advisory for perchlorate No. EPA 822-R-08-025). Washington DC: Office of Science and Technology, Office of Water.

U.S. EPA (1998a). Perchlorate Environmental

Contamination: Toxicological Review and Risk Characterization Based on

Emerging Information (External Review Draft). Office of Research and Development, Washington, D.C. NCEA-1-0503.

U.S. EPA (2001). Survey of fertilizers and

related materials for perchlorate. Final report. U.S. Environmental Protection Agency Office of Research and Development, Cincinnati, OH. Report no. EPA/600/R-01/049.

U.S. EPA. (2005). Perchlorate monitoring

results: Henderson, Nevada to the lower Colorodo River. U.S. Environmental Protection Agency, Waste Management Division.

U.S. EPA. (2008). Emerging Contaminant:

Perchlorate. Fact Sheet. Environmental Protection Agency.

https://www.clu-in.org/download/contaminantfocus/epa542f07003.pdf. September 16, 2009.

USEPA (US Environmental Protection Agency),

2009. Drinking Water: Perchlorate Supplemental Request for Comments. Notice. Fed. Reg., 74:183:48541

USEPA (US Environmental Protection Agency),

2008. Drinking Water: Preliminary Regulatory Determination on Perchlorate. Notice. Fed. Reg., 73:198:60262

USEPA (US Environmental Protection Agency),

2008. Drinking Water: Regulatory Determination Regarding Contaminants on the Second Drinking Water Contaminant Candidate List. Notice. Fed. Reg., 73:147:44251

USEPA (US Environmental Protection Agency),

2005. “Perchlorate Treatment Technolgy Update.” Federal Facilities Forum Issue Paper

USEPA (US Environmental Protection Agency),

2005. Perchlorate Monitoring Results: Henderson, Nevada to the Lower Colorado River. US Environmental Protection Agency, Region 9. Waste Management Division.

Valentine, Nzengung, A., Wang, Chuhua, and

Harvey, Greg. (1999). Plant-Mediated Transformation of Perchlorate into Chloride. Environ. Sci. Technol. 33(9): 1470–1478.

Wilkin, Richard T., Dennis D. Fine, and Nicole

G. Burnett. (2007). Perchlorate Behavior in a Municipal Lake Following Fireworks Displays. Environ. Sci. Technol., 41: 3966-3971.

110th Congress 1st Session. (2007). Perchlorate:

health and environmental impacts of unregulated exposure. Hearing Before the Subcommittee on Environment and Hazardous Materials of the Committee on Energy and Commerce. House of Representatives.