Use of detergent additive, linear alkylbenzene sulfonate, as an indicator of wastewater input

to Oyster Pond, MA

Sarah Erskine

Wheaton College, Norton, MA

Maureen Conte

Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA

J.C. Weber

Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA

Semester in Environmental Science 2013

Abstract

Linear alkylbenzene sulfonate (LAS) is a common surfactant used in detergents

worldwide. A sediment core from Oyster Pond in Falmouth, Massachusetts was analyzed for

presence of LAS to determine if it could be used as an indicator of wastewater input to Oyster

Pond. Using the GC/MS, concentrations were found and compounds were identified. Septic

system samples were taken from a Standard Title V system to determine how much LAS would

be introduced to groundwater. No LAS was found in the most recent sediments due to septic

system treatment, but older sediment has concentrations high enough to be used as an

indicator.

Key Phrases

Wastewater Input; Anionic Surfactant; Oyster Pond; Linear Alkylbenzene Sulfonate; Septic

System

Key Words

Surfactant; LAS; Sediment; Indicator; Wastewater

Introduction

Surfactants are largely used worldwide in detergents and cleaning products. They have

hydrophilic heads and hydrophobic tails, their alignment in mixtures of two liquids decreases

surface tension and their structure helps bind to “dirty” compounds such as greases. Linear

alkylbenzene sulfonate (LAS) is the main surfactant used in detergents. LAS is an anionic

surfactant, with a sulfonate (R-SO3-) head and a hydrophobic tail with 10-14 carbon atoms (Fig.

1) (León, González-Mazo, Pajares, & Gómez-Parra, 2001). It biodegrades by ω-oxidation at a

terminal methyl group and β-cleavage (Eganhouse, Blumfield, & Kaplan, 1983).

LAS’s common use in households guarantees its presence in domestic wastewater.

Some LAS is removed during wastewater treatment, but even treated water contains significant

concentrations; an even higher concentration is present after treatment in septic systems

(McAvoy, White, Moore, & Rapaport, 1994; Tabor & Barber, 1996). LAS is further removed as it

travels through the aquifer and groundwater (Thurman, Barber, & LeBlanc, 1986). Since LAS

stays in the environment at measurable concentrations for decades, it can be helpful to look at

its presence in aquatic systems with significant wastewater input; in addition, there is a

possibility it could be used as an indicator of this wastewater input (Reiser, Toljander, Albrecht,

& Giger, 1997).

Concentration and Identification of LAS is possible through gas chromatography mass

spectroscopy (GC/MS), and provides reliable data but analysis by high performance liquid

chromatography (HPLC) is preferred because there is less possibility of error introduced during

derivatization and clean up (Ding & Fann, 2000; Kikuchi, Tokai, & Yoshida, 1986).

Methods

Site Description

Oyster Pond is a shallow pond located in Falmouth, MA (Fig. 2 ). It is composed of three

kettle ponds and has a total surface area of approximately 25 hectares (Wright-Pierce, 2013). It

is surrounded by residential homes and has a condominium complex on the northern end with

62 units and 27 septic systems. All buildings in the Oyster Pond watershed use septic systems,

none are on a sewer system (Wright-Pierce, 2013). A sediment core of 32cm was taken from

the northern end of the pond (Fig. 2). The sediment core was dated using the sedimentation

rate of 0.88cm/year in a nearby pond in Falmouth with similar physical characteristics (Keafer,

Buesseler, & Anderson, 1992).

Three, four liter, septic system samples were collected from a Standard Title V septic

system at the Massachusetts Alternative Septic System Test Center (MASSTC) from the main

influent channel, the septic tank, and the effluent from the leaching field. The system is dosed

at 450 gallons a day and the tank is 1000 gallons, giving a retention time of about 2.22 days.

The system was being treated with a stress test of three was loads created as a large

cycle of soap (Arm and Hammer Power Laundry Detergent, Clean Burst) and non-chlorine bleach

(Clorox 2 Stain Fighter and Color Booster, Original Scent) (Fig. 3). The laundry loads are created

as a large cycle with 12 gallons wash and 24 gallons rinse with about 108 gallons total for the

three loads. 108.5 grams of soap and 99 grams of non-chlorine bleach were added per large

load. These loads are added to a distribution system tank between the main influent and the

septic tank; this distribution system tank could not be sampled. The treatment was started

three days prior to sampling with a total of two large cycles, one on the morning of the day the

stress test was started, and one about 50 hours prior to sampling.

Blanks and Standards for Standard Curve

I created two blank samples to run with my septic and sediment samples: one blank

sample of internal standard and one standard LAS mix. I spiked the LAS mix with 10µL of C8-LAS

internal standard. These two blanks were passed through the SAX column, derivatized, and

passed through all the columns for cleanup and the final filter in clean up. I ran these blanks on

the GC/MS with the rest of my samples.

I created five standards to use to make a standard curve. I filled 40mL glass vials with

the following volumes of LAS mix: 0.5mL, 1mL, 2mL, 3mL, and 4mL. The LAS was put in a drying

oven to evaporate off water in the mixture. I added 10µL of internal standard and transferred

to clean 13mm Pyrex test tubes with methanol. The standards were evaporated to dryness in

Savant on high heat for 20 minutes, reacted with 200µL thionyl chloride, and kept in a 95oC oven

for one hour. After the standards cooled to room temperature I added 200µL trifluoroethanol

and 200µL pyridine, and then put them in the 95oC oven to react for 20 minutes. I evaporated

the standards in the Savant for 20 minutes at medium heat to reduce volume to about 50µL. I

passed the standards through the alumina column with hexane/ethylacetate (1:1) and

evaporated to dryness. I resuspended the standards in 100µL methylene chloride and

transferred to a 2mL vial where I blew down to a volume of 50µL using zero nitrogen gas. I

transferred the standards to screw top v-vials and ran them on the GC/MS using the same

temperature program as with the samples.

Preparation for Extraction

I sectioned the Oyster Pond sediment core in one centimeter sections (Fig. 4). The top

several centimeters of the core were lose and had to be siphoned off. The sediment became

progressively firmer and denser as depth increased. Only 23 sections were obtained from the

32 centimeter core, meaning the sections were not exactly 1 centimeter, equation 1 was used to

adjust depths. I selected eight sections (1.4cm, 2.8cm, 4.2cm, 5.6cm, 13.9cm, 15.3cm, 23.7cm,

and 32.0cm) to represent the most recent sediments, the oldest sediment, and some

intermediates where the core looked somewhat different in color or texture. I loosely packed

these sections into labeled 40mL glass vials allowing for enough space for the expansion of

water when it froze. I placed small square of combusted aluminum foil over the top of the vial,

and punctured holes with a 23 gauge needle and screwed on the caps. I placed the samples in a

-30oC freezer.

After approximately 21 hours, I removed the samples from the freezer, and placed the

samples in the freeze drier. If any vials were cracked, I put them in an opened clean plastic bag

and then into the freeze drier vacuum flasks. To reduce any mixing of sediments from samples,

all vials from the same depth were put into the same flask with another set of samples from the

next depth (the 1.4cm vials with the 2.8 cm vials). I freeze dried the samples 48 hours.

After removing dried samples from the freeze drier, I combined vials of the same depth

on combusted aluminum foil and homogenized the sample. I removed roots, leaves, rocks, and

still frozen sediment from the sample, homogenized, and returned to the original 40 mL vials,

combining into as few vials as possible. I took care to not fill the vials more than half way and

took all samples’ weights. I kept a small subsample for CN and N15 analysis.

I filtered 50-500mL of the septic system samples through 47mm GF/F filters under

vacuum, filtering the cleanest sample first. I stored filtrate and filters in separate labeled 40mL

glass vials. I added 20mL methanol to the filters.

Extraction

I added 30mL of methanol to each vial with weighed out, freeze dried, sediment and

added a total of 10µL of C8-LAS internal standard to each depth. I ultrasonicated for 30 minutes

at an output power of 22%, centrifuged for 10 minutes at 1500rpm, and pipetted off methanol

taking care to not disturb the sediment and put the methanol into clean, labeled 40mL glass

vials. I added 20mL of methanol to the sediment and repeated untrasonication for 10 minutes

at an output of 22% and centrifuged for 10 minutes at 1500rpm, and finally pipetted off the

methanol and combined with the first 30mL of methanol.

Using a strong anionic exchange cartridge from Agilent Technologies, I rinsed the column

with 5mL of methanol, making sure once the column did not dry at any point once it was wet

and to not exceed a drip rate of 2mL per minute (about three drops per second). I passed the

sample through and collected in a new labeled 40mL glass vial, rinsed with 2mL methanol and

collected into the same vial. To collect the LAS that was kept in the column, I passed through

5mL of 5% HCl in methanol and collected in a 13mm glass centrifuge tube.

I added 100µL of C8-LAS internal standard to the septic system filters in methanol. The

filters were untrasonicated at 22% output power for 30 minutes. After I pipetted off the

methanol into a clean labeled 40mL glass vial, I add 10mL of methanol to the filters and

repeated untrasonication for 30 minutes at 22% output power and the methanol pipetted off

and combined with the first 20mL of methanol.

The filtrate was extracted on C18-Disks from Supelco Inc. following their instructions

with slight modification (Supelco, 1994). I cleaned the disks by passing through 5mL of

methanol and drying for five minutes under vacuum. I then conditioned the disks under low

vacuum with 5mL methanol and 5mL Milli-Q water. A subsample was not passed through the

disk and kept for nitrate analysis. I dried the disk under vacuum for five minutes and extracted

analyte with 15-20mL of methanol, collected in a pear flask, and transferred to a clean labeled

40mL glass vial.

Derivatization

To derivatize my samples I followed methods by Reiser, Toljander, and Geiger (1997) and

Trehy, Gledhill, and Robert (1990) with slight modifications. I added 200µL of thionyl chloride to

samples and flushed with zero nitrogen gas for 30 seconds, and capped under nitrogen.

Samples were kept in 95oC oven for one hour and cooled to room temperature. I added 200µL

trifluoroethanol and 200µL pyridine, flushed with zero nitrogen gas for 30 seconds, and capped

under nitrogen. I kept samples in a 95oC oven for 20 minutes then evaporated down to about

50µL in Savant at medium heat for about 20 minutes.

Cleanup

Following Reiser et al. (1997) and Trehy et al. (1990) I cleaned up my samples. Using a

13cm column with approximately 1.5g alumina, I passed through my sample with 2mL

hexane/ethylacetate (1:1) and collected in a clean and labeled 13mm glass centrifuge tube. I

evaporated the samples to dryness in Savant under medium heat for 10-15 minutes then

resuspended in 50µL hexane/ethylacetate (1:1). Samples were then passed through a 13cm

column of 200µg copper powder on a bed of 0.5g alumina. I passed through my sample with

2mL hexane/ethylacetate (1:1) and collected in a clean and labeled 13mm glass centrifuge tube.

I evaporated to dryness in Savant under medium heat for 10 minutes and resuspended in 50µL

hexane. Samples were then passed through a 13cm column of about 1.0g silica gel with 5mL

hexane/ethylacetate (9:1). Samples were evaporated to dryness in Savant at medium heat for

30 minutes. I resuspended samples in 500µL methylene chloride and passed through fritted

extraction tubes with 4mm Millex-FH filters and collected into a labeled 2mL vial. I blew down

the samples with zero nitrogen gas and resuspended in 50µL methylene chloride and

transferred to 100mL screw top V-vials for analysis on GC/MS.

GC/MS

I injected 1-3µg of sample onto the GC/MS and ran a temperature program of 50oC for

two minutes, ramped to 200oC at 10oC per minute, then ramped to 320oC at 6oC per minute and

held at 320oC for 15 minutes.

Identification and Quantification

I used FID to make a standard curve from my standard samples and took

the average of the linear regression for each individual compound I could identify (Equation 2).

The standard deviation between the slopes and intercepts was small enough that it did not

seem to make a difference if I used, for example, the 2-C10 LAS to find the concentration of a

1/3-C11 LAS, this also allowed me to have a way to find concentrations of compounds that I did

not have in my LAS mix but did have in my sediment or septic samples.

I used the areas of the ion 91 peaks as my areas for LAS peaks with the

same retention time, since 91 is an ion in an LAS compound. I used the internal standard to

normalize the areas of the 91 peaks then used the standard curve equation to convert the area

to concentration.

To be able to compare concentrations from sediments to concentrations from a septic system I

used CHN analysis to put concentrations in terms of grams of Carbon.

Results

LAS in Septic Systems

The septic system shows an increase in nitrate, with a change in concentration of three

orders of magnitude from influent to effluent (Table 1). LAS does not show an increase or

decrease in total concentration from influent through to effluent. Total LAS is highest in influent

and lowest in the tank (Fig. 5). Partitioning between dissolved LAS and LAS bound to suspended

particulates are similar between influent and effluent, and a much higher percentage of

suspended particulate attributed to the partitioning in the tank (Fig. 5). Chain length

distribution for dissolved LAS shows similar patterns between the influent and effluent with C13

as the least abundant chain length and C11 and C12 as the highest (Fig. 6). The tank shows a

different distribution compared to the influent and effluent and favors shorter chain lengths

with a highest abundance of C10 then C11 and C12 and no C13 (Fig. 6). All septic system

samples show the same general pattern of distribution across chain lengths for suspended

particulate-bound LAS with relatively even percentages of C10, C11, and C13 and the majority of

LAS from C12 (Fig. 6).

LAS in Sediments

Total LAS in sediments shows no LAS until sample depth 13.9cm (approximate year 2001)

with a concentration ranging from 2.74 to 17.06µgLAS/gC between 2001 and 1985 (Fig. 7). A

chain length of 12 carbons is the highest concentration across most depths with a 13 carbon

chain as the lowest concentrations (Fig.8). Distribution of chain length is similar between the

years 1992 and 2000 and similar between the years 2001 and 1985 (Fig. 9). 2001 and 1985 have

a higher percentage of shorter chain lengths compared to 2000 and 1992, where 2000 and 1992

have the majority of their chain lengths C12 (Fig. 9). The distribution of chain length in 2001 and

1985 is closer to the distribution of chain lengths seen in the septic tank sample and the

distribution in 2000 and 1992 have a distribution closer to that of the septic influent and

effluent (Fig. 6, 9). There is no obvious pattern between distributions of group position in the

sediment samples (Fig. 10).

Stable Isotopes

N15 and C13 isotope analyses run on the septic system samples show lightest carbon

and heaviest nitrogen in the influent and heaviest carbon and lightest nitrogen in the effluent

with the tank’s values in between (Fig. 11). I am hesitant about the negative δ15N values (Fig.

11) . The sediments shows isotopic values more similar to fresh water in the more recent

sediment and more similar to saltwater in the older sediments (Fig. 12). There is no similarity

between the septic tank stable isotopes and the sediment stable isotopes (Fig. 11, 12). The

nitrogen shows a pattern somewhat like the pattern seen in total LAS concentration through

depth (Fig. 7, 13). There is no obvious correlation between the 15N values for the septic system

and Oyster Pond (Fig. 11, 13).

Discussion

LAS in septic systems

My results show the important partitioning between dissolved LAS and LAS bound to

suspended particulates at different stages in a Standard Title V system (Fig. 5). I expect this

partitioning between the samples to be due to the characteristics of the stages of the septic

system. Since only aqueous samples were taken, any LAS in the sludge in the septic tank was

not accounted for, the only particulate-bound LAS was suspended particulate. Doing this

experiment again it would be insightful to look at the LAS content in the sludge or biofilm. I

believe the characteristics of the way water flows through the septic system is also an important

factor in the partitioning seen between the samples. Influent and effluent have more water

movement so there is a higher chance of LAS staying dissolved in the water rather than

adsorbing onto particulates where as in the tank the water becomes more stagnant and solids

separate out of the wastewater. Stagnant water and this separation between solids and liquids

are most likely the reasons why we see a higher percentage of suspended particulate bound LAS

in the tank. I believe the higher presence of biofilm in the septic tank is the reason for the lower

concentration of LAS because LAS biodegrades much more quickly in the presence of biofilm

(Takada, Mutoh, Tomita, Miyadzu, & Ogura, 1994). Once again I think it would be helpful to see

the LAS presence in the sludge or the biofilm to support this theory and to see if it could make

up for the drop in total LAS concentration seen from the influent to the tank and the increase

from the tank to the effluent (Fig.5).

I think water flow characteristics could also be the reason for the difference in chain

length distribution between the septic samples (Fig. 6). According to the “distance principle,”

LAS compounds with longer chain lengths with break down more readily than those with shorter

chain lengths (Swisher, 1987). With the higher presence of biofilm and solids in the septic tank,

I assume that more LAS is degrading, meaning a lower presence of longer chains.

LAS in sediments

Further investigation into the absence of LAS in the upper sediments led to the discovery

that Treetops Condominiums treats their 27 septic systems monthly with the product Septic

Doctor Tablet from Caldwell Environmental (Fig. 7). This product guarantees the digestion of

greases and other problem wastes, and since LAS is strongly associated with greases and has a

similar molecular structure, I believe that the tablets also degrade LAS (Fig. 14) (Caldwell

Environmental Inc., n.d.). Another core should be sampled with sections between 5.6 and

13.9cm to see tablet addition’s direct effect.

Chain length concentrations through depth increases and decreases in the same pattern

indicating the differences between years are not a product of analysis (Fig. 8). I believe that

water flow could once again be the reason for the observed distributions (Fig. 9). Increased flow

or flushing of Oyster Pond could cause distributions similar to septic tank influent and effluent

where longer chains are more abundant than shorter chains (Fig. 6). Large storms occurred in

1991 and 1999 and could be the reason for the distributions seen in 1992 and 2000.

Distribution of location of benzene group did not show any discernable patterns (Fig.10).

Stable Isotopes

The close similarity between the most recent sediment and its difference compared to

the deeper sediments shows that the Septic Doctor Tablet could be altering 13C input to Oyster

Pond, but it does not seem like it has significantly altered the 15N input (Fig. 11, 12). The similar

pattern seen between the total LAS concentration and the 15N values shows a possible

correlation between LAS and wastewater input since 15N is often used as an indicator (Fig. 7, 13)

(Valiela, 1995).

Conclusions

With Treetop Condominiums’ septic system treatment, LAS cannot be used as an

indicator of wastewater input to Oyster Pond for recent sediment, but high enough

concentrations of LAS are present in deeper sediments and can be used as an indicator. Further

research should be done with a deeper core and historical data of water use to determine an

equation of converting the concentration of LAS in sediments to what wastewater input would

have been.

Acknowledgements

I thank my advisors Maureen Conte and J. C. Weber for their guidance and help

throughout the project. I thank Richard McHorney, Becky Leone, Lauren Wind, Kelsey Gosselin,

and Tyler Ueltschi for help collecting and sectioning my sediment core. I thank Ken Foreman for

running Semester in Environmental Science (SES). I thank Wendi Buesseler and the rest of the

Oyster Pond Environmental Trust (OPET) for help finding a sampling location and putting the

pieces together. I thank Keith Mroczka and the Massachusetts Alternative Septic System Test

Center (MASSTC) for access to and endless information on septic systems. I thank Fiona Jevon,

Alice Carter, and Sarah Nalven for countless advice. I thank Wheaton College. I thank the

Marine Biological Laboratory and the Ecosystems Center for funding and use of equipment.

Literature Cited

CaldwellEnvironmentalInc. (n.d.). Septic Doctor Tablets. Retrieved December 06, 2013, from http://www.caldwellenvironmental.com/products/septic-doctor-tablets/

Ding, W.-H., & Fann, J. C. . (2000). Determination of linear alkylbenzenesulfonates in sediments using pressurized liquid extraction and ion-pair derivatization gas chromatography-mass spectrometry. Analytica Chimica Acta, 408(1-2), 291–297. doi:10.1016/S0003-2670(99)00870-3

Eganhouse, R. P., Blumfield, D. L., & Kaplan, I. R. (1983). Long-chain alkylbenzenes as molecular tracers of domestic wastes in the marine environment. Environmental science & technology, 17(9), 523–30. doi:10.1021/es00115a006

Keafer, B. A., Buesseler, K. O., & Anderson, Do. M. (1992). Burial of living dinoflagellate cysts in estuarine and nearshore sediments. Marine Micropaleontology, 20(2), 147–161. Retrieved from http://dx.doi.org/10.1016/0377-8398(92)90004-4

Kikuchi, M., Tokai, A., & Yoshida, T. (1986). Determination of trace levels of linear alkylbenzenesulfonates in the marine environment by high-performance liquid chromatography. Water Research, 20(5), 643–650. doi:10.1016/0043-1354(86)90029-1

León, V. M., González-Mazo, E., Pajares, J. M. F., & Gómez-Parra, A. (2001). Vertical distribution profiles of linear alkylbenzene sulfonates and their long-chain intermediate degradation products in coastal marine sediments. Environmental Toxicology and Chemistry, 20(10), 2171–2178. doi:10.1002/etc.5620201006

McAvoy, D. C., White, C. E., Moore, B. L., & Rapaport, R. A. (1994). Chemical fate and transport in a domestic septic system: Sorption and transport of anionic and cationic surfactants. Environmental Toxicology and Chemistry, 13(2), 213–221. doi:10.1002/etc.5620130205

Reiser, R., Toljander, H., Albrecht, A., & Giger, W. (1997). Alkylbenzenesulfonates in Recent Lake Sediment as Molecular Markers for the Environmental Behavior of Detergent-Derived Chemicals. In Robert P. Eganhouse (Ed.), Molecular Markers in Environmental Geochemistry (pp. 196–212). Wahington, D.C: American Chemical Society.

Reiser, R., Toljander, H. O., & Giger, W. (1997). Determination of alkylbenzenesulfonates in recent sediments by gas chromatography/mass spectrometry. Analytical chemistry, 69(23), 4923–30. doi:10.1021/ac970407v

Supelco. (1994). ENVI-Disk Instructions. Bellefonte, PA.

Swisher, R. D. (1987). Surfactant Biodegredation (Second.). New York, New York: Marcel Dekker Inc. Retrieved from http://books.google.com/books?hl=en&lr=&id=G56_-

HYey9IC&oi=fnd&pg=PR5&dq=Swisher+Surfactant+Biodegredation&ots=5ApXhOd70H&sig=HXLwHY2QBl9CS4qsznjsOPDmD-8#v=onepage&q=distance principle&f=false

Tabor, C. F., & Barber, L. B. (1996). Fate of Linear Alkylbenzene Sulfonate in the Mississippi River. Environmental Science & Technology, 30(1), 161–171. doi:10.1021/es950210p

Takada, H., Mutoh, K., Tomita, N., Miyadzu, T., & Ogura, N. (1994). Rapid removal of linear alkylbenzenesulfonates (LAS) by attached biofilm in an urban shallow stream. Water Research, 28(9), 1953–1960. Retrieved from http://www.sciencedirect.com/science/article/pii/0043135494901708

Thurman, E. M., Barber, L. B., & LeBlanc, D. (1986). Movement and fate of detergents in groundwater: A field study. Journal of Contaminant Hydrology, 1, 143–161.

Trehy, M. L., Gledhill, W. E., & Robert, G. O. (1990). Determination of linear alkylbenzenesulfonates and dialkyltetralinsulfonates in water and sediment by gas chromatography/mass spectrometry. Analytical chemistry, 62, 2581–2586.

Valiela, I. (1995). Marine Ecological Processes (Second.). Springer.

Wright-Pierce. (2013). Oyster Pond Needs Assessment DRAFT August 2013 Prepared for the Town of Falmouth. Falmouth, MA.

Figures and Tables

Figure 1. Linear alklybenzene sulfonate (LAS) is an anionic surfactant with a hydrophilic

head and hydrophobic tail of 10-14 carbon atoms where x+y=n and n+2 is the

length of the carbon tail.

Figure 2. Oyster Pond, Falmouth, MA. Sampling site marked by a yellow circle and the

approximate location of Treetops Condominiums marked by a red outline. Map

courtesy of Google Maps.

Figure 3. Soap and non-chlorine bleach used for stress test of septic system sampled from

MASSTC.

Figure 4. Core sectioning was done by pushing the sediment core up into an empty core

(A) and using a spackling knife to cut and remove one centimeter sections by

sliding the spackling knife between the sediment core and the empty core (B).

The sectioned sediment was then moved from the spackling knife to a labeled

40mL glass vial (C). If sediment was not solid enough, the centimeter sections

were siphoned off.

Figure 5. Partitioning between total concentrations of LAS compounds in aqueous samples

from a septic system as dissolved LAS and LAS bound to suspended particulates.

Figure 6. Distribution of LAS compounds based on carbon chain length. Dissolved LAS in

aqueous samples from septic system (A) and suspended particulate bound LAS in

aqueous samples from septic system (B).

Figure 7. Concentrations of total LAS compounds versus depth with approximate age of

sediment based on a sedimentation rate of 0.88cm per year.

Figure 8. Concentration of LAS compounds based on carbon chain length in sediments of

approximate years from Oyster Pond core.

Figure 9. Distribution of LAS compounds based on carbon chain length in sediment core

from Oyster Pond.

Figure 10. Distribution of LAS compounds in years based on carbon chain length and

position of benzene sulfonate group identified in mass spectrum from GC/MS.

Figure 11. Stable isotope composition of aqueous septic system samples.

Figure 12. Sediment stable isotope values from Oyster Pond sediment core. Data points are

labeled with depth and approximate age of sediment.

Figure 13. Stable isotope 15N through depth of Oyster Pond sediment core.

Figure 14. Grease and LAS molecules join together because of their similar structures.

Table 1. Nitrate concentrations of aqueous samples from a Standard Title V septic system.

Equation 1. actual depth = section*(32/23)

Equation 2. y = 0.00002088x + 0.00123941

Figure 1. Linear alklybenzene sulfonate (LAS) is an anionic surfactant with a hydrophilic head

and hydrophobic tail of 10-14 carbon atoms where x+y=n and n+2 is the length of the carbon

tail.

Figure 2. Oyster Pond, Falmouth, MA. Sampling site marked by a yellow circle and the

approximate location of Treetops Condominiums marked by a red outline. Map courtesy of

Google Maps.

Figure 3. Soap and non-chlorine bleach used for stress test of septic system sampled from

MASSTC.

Figure 4. Core sectioning was done by pushing the sediment core up into an empty core (A) and

using a spackling knife to cut and remove one centimeter sections by sliding the spackling knife

between the sediment core and the empty core (B). The sectioned sediment was then moved

from the spackling knife to a labeled 40mL glass vial (C). If sediment was not solid enough, the

centimeter sections were siphoned off.

Figure 5. Partitioning between total concentrations of LAS compounds in aqueous samples from

a septic system as dissolved LAS and LAS bound to suspended particulates.

Figure 6. Distribution of LAS compounds based on carbon chain length. Dissolved LAS in

aqueous samples from septic system (A) and suspended particulate bound LAS in aqueous

samples from septic system (B).

A B

Figure 7. Concentrations of total LAS compounds in Oyster Pond core versus depth with

approximate age of sediment based on a sedimentation rate of 0.88cm per year.

Figure 8. Concentration of LAS compounds based on carbon chain length in sediments of

approximate years from Oyster Pond core.

Figure 9. Distribution of LAS compounds based on carbon chain length in sediment core from

Oyster Pond.

Figure 10. Distribution of LAS compounds in years based on carbon chain length and position of

benzene sulfonate group identified in mass spectrum from GC/MS.

Figure 11. Stable isotope composition of aqueous septic system samples.

Figure 12. Sediment stable isotope values from Oyster Pond sediment core. Data points are

labeled with depth and approximate age of sediment.

Figure 13. Stable isotope 15N through depth of Oyster Pond sediment core.

Figure 14. Grease and LAS molecules join together because of their similar structures.

Influent Tank Effluent

NO3 (µM)

0.0612 0.348 8.98

Table 1. Nitrate concentrations of aqueous samples from a Standard Title V septic system.