Cadmium Pollution and Its Impact on Human Health and Human Health
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Cadmium Pollution and Its Impact on Human Health and Environment 1. Introduction: Cadmium is a naturally occurring trace element, one of the important components in the earth crust and oceans, and present everywhere in our environment. It was first discovered in Germany in 1817 as a by-product of the zinc refining process. Its name is derived from the Latin cadmia and the Greek kadmeia. Industrial applications for cadmium were developed in the late 19 th and the early 20 th century. Cadmium sulfide based pigments were used as early as 1850 because of their brilliant red, orange and yellow colors and appeared prominently in the paintings of Vincent Van Gogh in the late 1800s. Thomas A. Edison in the United States and Waldemar Junger Sweden developed the first nickel-cadmium batteries early in the 20 th century. However the most significant early use of cadmium was a corrosion-protection coating on steel. Cadmium is recognized to produce toxic effects on humans. Because the use of cadmium by industry has greatly increased, the amount of cadmium we are exposed to via air, water and soil has increased to the extent that it has become a hazard to human health. Long term occupational exposure can cause adverse health effects on the lungs and kidneys. Under normal conditions, adverse human health effects have not been encountered from general population exposure to cadmium. 2. General chemistry : Cadmium is Natural. Cadmium (elemental symbol Cd) is a member, along with zinc and mercury, of group 12 (CAS IIB) of the periodic table of the elements. It is generally characterized as a soft, ductile, silver- white or bluish-white metal, and is listed as 64 th in relative abundance amongst the naturally occurring elements. Chemical properties of cadmium are shown in table-1. 1
Transcript
Cadmium Pollution and Its Impact on Human Health and Environment
1. Introduction: Cadmium is a naturally occurring trace element, one of the important components in the earth crust and oceans, and present everywhere in our environment. It was first discovered in Germany in 1817 as a by-product of the zinc refining process. Its name is derived from the Latin cadmia and the Greek kadmeia.Industrial applications for cadmium were developed in the late 19th and the early 20th century. Cadmium sulfide based pigments were used as early as 1850 because of their brilliant red, orange and yellow colors and appeared prominently in the paintings of Vincent Van Gogh in the late 1800s. Thomas A. Edison in the United States and Waldemar Junger Sweden developed the first nickel-cadmium batteries early in the 20th century. However the most significant early use of cadmium was a corrosion-protection coating on steel.Cadmium is recognized to produce toxic effects on humans. Because the use of cadmium by industry has greatly increased, the amount of cadmium we are exposed to via air, water and soil has increased to the extent that it has become a hazard to human health. Long term occupational exposure can cause adverse health effects on the lungs and kidneys. Under normal conditions, adverse human health effects have not been encountered from general population exposure to cadmium.
2. General chemistry : Cadmium is Natural. Cadmium (elemental symbol Cd) is a member, along with zinc and mercury, of group 12 (CAS IIB) of the periodic table of the elements. It is generally characterized as a soft, ductile, silver-white or bluish-white metal, and is listed as 64th in relative abundance amongst the naturally occurring elements. Chemical properties of cadmium are shown in table-1.
2.1 Chemical properties of cadmium:Table-1: Chemical properties of cadmium:1. Atomic number 482. Atomic mass 112.49 mol-1
3. Electro negativity according to Pauling
107
4. Density 807 gcm-1 at 20̊c5. Melting point 321̊c6. Boiling point 7670 ̊c
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Cadmium Pollution and Its Impact on Human Health and Environment
Cadmium Pollution and Its Impact on Human Health and Environment
3. Sources of cadmium: There are many sources of cadmium from which our environment and our bodies can be contaminated with cadmium. Cigarette smoke, refined foods, tea, coal burning, and shellfish are all definite sources. Contents and permissible limit of cadmium in soil, water, plants and animals are illustrated in the following table-3. Table-3: Contents of cadmium in soil, water, plant, and animals
Parameters ContentsSoils Total: 0.01-0.03 mgkg-1
Soluble:0.1-14.0 mgkg-1
Sea water 1.1×10-6 to 38×10-6 ml-1
Fresh water Reference:0.2 µgl-1
Plants 0.1-1.0mgkg-1
Reference plant 0.05mgkg-1
Animals 0.1-0.5mgkg-1
Muscle 0.14-3.2 mgkg-1
Bone 1.8mgkg-1
Blood 0.0053 mgdm-3
Urine 0.02 mgl-1
Sources: Pais and jones, 1997.3.1 Air:
Cadmium occurs as suspended particulate in air from burning coal and fossil fuel and used in the production of cement, battery, plastic, fertilizer, metal alloys, corrosion inhibitors, and other chemicals, pigments used in ceramics, paints in textiles and coatings, batteries, electronics and autos (Cook, 1994). Volcanic activity is the dominant natural source for cadmium pollution (Zoller, 1984). It enters the mainly from:
1. Combustion of domestic, hospital or industrial waste.2. Metal processing.3. Manufacture of cadmium products and cement.4. Mining and processing of copper, lead and zinc.
3.2 Water:Unpolluted water contains very low levels of cadmium. Water may be contaminated by runoff from mines, smelters, industrial sites, coal ash or incinerator ash, with serious consequences, if the contaminated water is used to irrigate crops, as has
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Cadmium Pollution and Its Impact on Human Health and Environment
happened in japan. Cadmium in effluent water many result in accumulation in the sediment, from where it may be ingested by detritus feeders such as crabs or shellfish.
3.3 Soil:Most cadmium in nature occurs as an atomic substitution for zinc in zinc minerals, usually making up less than 1% of the mineral. Only a few relatively pure cadmium minerals are known. The best known of these is the mineral greenockite, but even these mineral forms rare and rather small crystals.Table-4: Typical levels of cadmium in environment and biological
materials:Material Cadmium content UnitAir borne:Industrial areasUrban areasRural areas
20-3000.1-500.003-4
ng∕m3
ng∕m3
ng∕m3
Wet precipitation:Industrial areasUrban areasRural areas
0.07-100.25-0.9<0.05-0.30
µg∕lµg∕lµg∕l
Natural waters and sediments:River waterEstuarine waterSea waterRiver sediments
Cadmium Pollution and Its Impact on Human Health and Environment
Cadmium in soils is derived from both natural and anthropogenic sources. The major factors governing cadmium speciation, adsorption and distribution in soils are pH, soluble organic matter content, hydrous metal oxide content, clay content and type, presence of organic and inorganic ligands, and competition from other metal ions (OECD 1994). The use of cadmium-containing fertilizers and sewage sludge is most often quoted as the primary reason for the increase in the cadmium content of soils over the last 20 to 30 years in Europe (Jensen and Bro-Rasmussen 1992). Atmospheric cadmium emissions deposition onto soils has generally decreased significantly over that same time period (Cook and Morrow 1995, Mukunoki and Fujimoto 1996). On the agricultural lands, the major sources of cadmium are:
1. Application of phosphate fertilizer (in which cadmium is trace impurity), and2. Atmosphere Deposition (Joardar, 2003).
4. Uses of cadmium :Cadmium is intentionally added to six major classes of products where it imparts distinct performance advantages and is present as an impurity in five major classes of products where its presence is regarded as an environmental disadvantage but which generally does not affect the performance of the product. The major intentional uses of cadmium are Ni-Cd batteries, cadmium pigments, cadmium stabilizers, cadmium coatings, cadmium alloys and cadmium electronic compounds such as cadmium telluride (CdTe). Trends in cadmium consumptions patterns from 2000 to 2005 are shown in figure-3 below:
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Cadmium Pollution and Its Impact on Human Health and Environment
Figure-3: Trends in cadmium consumption patterns.Sources: www.cadmium.org.
4.1 Patterns of Consumption:In recent years, the consumption pattern of cadmium in its various end use applications has increasingly shifted away from the traditional market areas of pigments, stabilizers and coatings to rapidly growing applications in Ni-Cd batteries. The relative distribution of cadmium uses is shown in figure-4.
Reference Year: 2003Figure-4: Relative distribution of cadmium uses.
Cadmium hydroxide is utilized as one of the two principal electrode materials in Ni-Cd batteries. Ni-Cd batteries are cost-effective well suited for high power applications, and have high cycle lives and excellent low temperature and high temperature performance relative to other battery chemistries (Morrow and Keating 1997).
4.3 Cadmium Pigments:Cadmium sulphide and cadmium sulphoselenide are utilized as bright yellow to deep red pigments in plastics, ceramics, glasses, enamels and artists colors. They are well known for their ability to withstand high temperature and high pressure without chalking or fading, and therefore are used in applications where high temperature or high pressure processing is required (Cook 1994).
Cadmium Pollution and Its Impact on Human Health and Environment
Cadmium-bearing stabilizers retard the degradation processes in polyvinylchloride (PVC) which occur upon exposure to heat and ultraviolet light. These stabilizers contain organic cadmium salts, usually carboxylates such as cadmium laureate or cadmium stearate, which ensure a long service life (Cadmium Association and Cadmium Council 1991).
4.5 Cadmium Coatings:Cadmium coatings are utilized on steel, aluminum, and certain other non-ferrous metal fasteners and moving parts to provide the best available combination of corrosion resistance, particularly in salt and alkali media, and lubricity or low coefficient of friction. In addition, cadmium coatings exhibit excellent plating characteristics on a wide variety of substrates, have good galvanic comparability with aluminum, and are readily solder able (Morrow 1996).
4.6 Alloys:Cadmium alloys include (a) electrical conductivity alloys, (b) heat conductivity alloys, and (c) electrical contact alloys.
4.7 Minor uses:In addition to the major uses of cadmium there are a wide variety of uses which consume only small amounts of cadmium. These minor uses, however, often have considerable technological and social importance.
5. Cadmium emissions: Cadmium emissions arise from two major source categories, natural sources and man-made or anthropogenic sources. Emissions occur to the three major compartments of the environment - air, water and soil, but there may be considerable transfer between the three compartments after initial deposition.
5.1 Natural Cadmium Emissions:Even though the average cadmium concentration in the earth's crust is generally placed between 0.1 and 0.5 ppm, much higher levels may accumulate in sedimentary rocks, and marine phosphates and phosphorites have been reported to contain levels as high as 500 ppm (Cook and Morrow 1995, WHO 1992). Volcanic activity is also a major natural source of cadmium release to the atmosphere, and estimates on the amount have been placed as high as 820 mt per year (WHO 1992, OECD 1994, Nriagu 1980, Nriagu 1989).
Cadmium Pollution and Its Impact on Human Health and Environment
5.2.1 Cadmium-Containing vs. Non-Cadmium Con Products:Man-made cadmium emissions arise either from the manufacture, use and disposal of products intentionally utilizing cadmium, or from the presence of cadmium as a natural but not functional impurity in non-cadmium containing products. In the former category of cadmium-containing products are included:
5.2.2 Factors in Anthropogenic Emissions Analyses:There are many studies which attempt to present a comprehensive overview of anthropogenic cadmium emissions to air, water and soil and their specific sources (Cook and Morrow, 1995). Examination of these analyses immediately indicates that there are three factors of primary importance in determining the levels of cadmium emissions. First, cadmium emission factors which are the amounts of cadmium emitted to the environment per unit of cadmium processed are generally much lower in the more technologically advanced regions of the world such as North America, Western Europe and Japan than in other regions (WHO 1992, Jackson and MacGillivray 1993, Nriagu and Pacyna 1988). Secondly, many countries have only partial data and often do not include significant cadmium emission sources particularly those where cadmium is not intentionally added. Third and most significantly, cadmium emissions have declined dramatically over the past thirty to forty years and are still declining today.
5.2.3 Point Sources vs. Diffuse Sources:Cadmium emissions may be considered as arising from either point sources such as large manufacturing or production facilities or from diffuse sources such as may occur from the use and disposal of products by many consumers over large areas. Emissions from point sources have been stringently regulated over the past twenty years, and cadmium emissions from point sources have decreased dramatically during that time period (Elgersma et al. 1992, Mukunoki and Fujimoto 1996, U.S. EPA 1996, Van Assche and Ciarletta 1992) as a result of these regulations and markedly improved emission control technology. Considerable progress is now being made in reduction of diffuse contamination from cadmium products through
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Cadmium Pollution and Its Impact on Human Health and Environment
collection and recycling programs of cadmium-containing products (Morrow 1997, Cook and Morrow 1995, Morrow and Keating 1997, Mukunoki and Fujimoto 1996).
5.2.4 Cadmium Emissions from Municipal Solid Waste Incineration:One of the concerns expressed by some is that increasing incineration of cadmium-containing products will eventually lead to increased cadmium emissions to the environment and increased risk to human health and the environment. While there are large differences from country to country in the amounts of municipal solid waste incinerated, from 10% to 90%, it is clear that modem state-of-the-art emission control devices on these incinerators result in a capture efficiency of better than 99% compared with previous estimates as low as 50% to 75% (Chandler 1996, OECD 1996). Finally, it must also be pointed out that there are many sources of cadmium in municipal solid waste, not just products to which cadmium has intentionally been added.
5.2.5 Partitioning of Cadmium Emissions to Compartments:Most of the studies cited above indicate that the vast majority of cadmium emissions, approximately 80% to 90%, partition initially to soils. The remaining 10% to 20% of anthropogenic cadmium emissions partition between air and water and depend largely on the type of source.
5.2.6 Anthropogenic Sources of Cadmium Emissions to Air Water and Soil:Cadmium emissions to air arise, in decreasing order of importance, from the combustion of fossil fuels, iron and steel production, non-ferrous metals production and municipal solid waste combustion (Cook and Morrow 1995, ERL 1990, Jackson and MacGillivray 1993, Jones et al. 1993, Van Assche and Ciarletta 1992). Cadmium emissions to water arise, in decreasing order of importance, from phosphate fertilizers, non-ferrous metals production, and the iron and steel industry (OECD 1994, ERL 1990, Van Assche and Ciarletta 1992). In the first case, the main inputs to agricultural soils which are of primary relevance to human exposure to cadmium arise from atmospheric deposition, sewage sludge application, and phosphate fertilizer application (Jensen and Bro-Rasmussen 1992, Van Assche and Ciarletta 1992).
5.3 Anthropogenic Cadmium Emissions vs. Natural Cadmium Emissions:Earlier estimates of anthropogenic cadmium emissions vs. natural cadmium emissions had indicated approximately 8,000 to 10,000 mt per year for
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Cadmium Pollution and Its Impact on Human Health and Environment
anthropogenic emissions compared to 800 to 1,000 mt per year for natural cadmium emissions (Nriagu 1980, Nriagu 1989, WHO 1992).
6. Cadmium exposure and human health: It has been well established that excess cadmium exposure produces adverse health effects on human beings The relevant questions with regard to cadmium exposure are the total exposure levels and the principal factors which determine the levels of cadmium exposure and the adsorption rate of the ingested cadmium by the individual, other words, the pathways by which cadmium enters the food chain, the principal pathway of cadmium exposure for most human beings. Relative contribution of sources of cadmium human exposure is shown in Figure-5.
Figure-5: Relative contribution of sources of cadmium human exposureSources: www.cadmium.org
6.1 Principal Factors Which Determine Levels of Human Exposure:Humans normally absorb cadmium into the body either by ingestion or inhalation dermal exposure (uptake through the skin) is generally not regarded to be of significance (Lauwerys 1986). It is widely accepted (WHO 1992, ATSDR 1997) that approximately 2% to 6% of the cadmium ingested is actually taken up into the body. Factors influencing cadmium absorption are the form in which cadmium is present in the food, and the iron status of the exposed individual. The exception to this generalization is the cigarette smoker. One model for human cadmium intake (Van
Cadmium Pollution and Its Impact on Human Health and Environment
Assche 1998) has estimated that ingestion accounts for 95% of total cadmium intake in a non-smoker.
6.2 Human Intake of Cadmium:6.2.1. Ingestion:Much of the cadmium which enters the body by ingestion comes from terrestrial foods. This is to say, from plants grown in soil or meat from animals which have ingested plants grown in soil. Thus, directly or indirectly, it is the cadmium present in the soil and the transfer of this cadmium to food plants together with the cadmium deposited out of the atmosphere on edible plant parts which establishes the vast majority of human cadmium intake, Some have estimated that 98% of the ingested cadmium comes from terrestrial foods, while only 1% comes from aquatic foods such as fish and shellfish, and 1% arises from cadmium in drinking water (Van Assche 1998).
6.2.2. Cadmium Intake from Foods:Many studies have attempted to establish the average daily cadmium intake resulting from foods; In general, these studies show that the average daily diet for non-smokers living in uncontaminated areas is at present at the low end of the range of 10 to 25 µg of cadmium (Elinder 1985, OECD 1994, ATSDR 1997). The World Health Organisation (WHO) has established a provisional tolerable weekly intake (PTWI) for cadmium at 7 µg/kg of body weight. The average daily cadmium intake for the general population in the Western World has shown a distinct downward trend from 1970 through 1992 (Van Assche and Ciarletta 1992), a reduction presumed to be due to the marked decreases in direct atmospheric deposition of cadmium onto crops and soils. Monthly cadmium intake for the general population is shown in Figure-6.
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Cadmium Pollution and Its Impact on Human Health and Environment
Figure-6: Monthly cadmium intake for the general population.Sources: www.cadmium.org
6.2.3 Inhalation:Cadmium inhalation is a far smaller contributor to total cadmium body burden except, as previously noted, in the cases of smokers or some highly exposed workers of the past. Today, the inhalation route is well controlled in the occupational setting, and is well-controlled from point sources such as those which directly pertain to the non-ferrous, cadmium or cadmium products industries.
6.2.4. Cadmium Intake from Cigarette Smoking:Smokers absorb amounts of cadmium comparable to those from food, about 1 to 3 µg of cadmium per day, from the smoking of cigarettes. It has been reported that one cigarette contains about 1 - 2 µg of cadmium and that about 10% of the cadmium content is inhaled when the cigarette is smoked (WHO 1992). Cigarette smokers (WHO) are also occupationally exposed may increase their total cadmium intake even further.
6.2.5. Cadmium Intake from Occupational Exposure:Up to the l960s, very elevated cadmium in air exposure levels were measured in some workplaces, sometimes as high as 1 mg/m³. Since that time, workplace exposures and standards have decreased markedly so that most occupational exposure standards today are in the range from 2 to 50 µg/m³. The result has been that occupational exposures today are generally below 5 µg/m³, and most cadmium workers are exposed at levels which are considered to be safe (ATSDR 1997).
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Cadmium Pollution and Its Impact on Human Health and Environment
Extensive preventative hygiene programs and medical follow-up programs have been developed to control the risk related to cadmium exposure at the workplace (ACGIH 1996, OSHA 1992, Lauwerys 1986).
6.3. Human Health Effects of Cadmium:The kidney is the critical target organ for the general population as well as for occupationally exposed populations. Cadmium is known to accumulate in the human kidney for a relatively long time, from 20 to 30 years, and, at high doses, is also known to produce health effects on the respiratory system and has been associated with bone disease.
6.3.1 General Population:Ingestion of cadmium in food is the major source of cadmium for non-smokers. Average daily intakes from food in non-contaminated areas is at the lower end of the 10 to 25 µg range of which approximately 0.5 to 1.0 µg is actually retained in the body. Uptake of cadmium from smoking could more than double that amount.Individuals (WHO) consume large amounts of these materials might thus at first seem to be at increased risk. Thus, individuals (WHO) ingest large amounts of sunflower seeds may invest up to 100 µg cadmium per day, yet these individuals do not have levels of cadmium in blood or urine which are higher than individuals with far lower levels of cadmium intake (Reeves et al. 1997).
6.3.2 Occupationally Exposed Populations:Occupational exposure to cadmium is mainly by inhalation but also may include additional intakes through food, tobacco, and poor personal hygiene practices. Acute poisoning by inhalation may lead to respiratory manifestations such as severe bronchial and pulmonary irritation, subacute pneumonitis, lung emphysema, and, in the most severe situations, death from pulmonary oedema may occur (Lauwerys, 1986). Chronic obstructive airway disease has been associated with long-term high-level occupational exposure by inhalation (WHO 1992, OECD 1994). For chronic cadmium exposure, effects occur mainly on the kidneys, lungs, and bones. A relationship has been established between cadmium air exposure and proteinuria (WHO 1992, OECD 1994). However, recent work has demonstrated that these effects are reversible at low exposure levels once the cadmium exposure has been removed or reduced (Roels et al. 1997).
6.4. Sources of Human Cadmium Exposure:
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Cadmium Pollution and Its Impact on Human Health and Environment
While sources of cadmium emissions to the environment have been listed in some detail in this report and others (Cook and Morrow 1995, WHO 1992, OECD 1994), there have been very few attempts to partition human cadmium exposure to its various sources. Van Assche (Van Assche and Ciarletta 1992) has developed a model for cadmium exposure for human beings and allocated this exposure to the various sources. The analysis acknowledges that most human cadmium exposure comes from ingestion of food, and most of that arises from the uptake of cadmium by plants from fertilizers, sewage sludge, manure and atmospheric deposition, specifically, the model estimated that the relative importance of various cadmium sources to human exposure is as follows (Van Assche 1998):
7. Level of cadmium in the environment: Cadmium levels in the environment vary widely. As stated above, cadmium emissions to the environment are normally transported continually between the three main environmental compartments, air, water and soils, but a steady state flux is probably achieved and the general levels can reasonably well be established.
7.1 Cadmium in Air:Three distinct categories may be recognized with respect to cadmium-in-air concentrations - cadmium in ambient air, cadmium air levels in occupational exposure situations, and cadmium in air from the smoking of tobacco. Cadmium in ambient air represents, by far, the majority of total airborne cadmium. Inputs from all three categories may affect human cadmium intake and human health, but the levels and the transfer mechanisms to humans are substantially different for the three.
7.1.1 Cadmium in Ambient Air:
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Cadmium Pollution and Its Impact on Human Health and Environment
Ambient air cadmium concentrations have generally been estimated to range from 0.1 to 5 ng/m³ in rural areas, from 2 to 15 ng/m³ in urban areas, and from 15 to 150 ng/m³ in industrialized areas (Elinder 1985, WHO 1992, OECD 1994) although some much lower values have been noted in extremely remote areas and some much higher values have been recorded in the past near uncontrolled industrial sources.
7.1.2 Cadmium in Occupational Environments:Cadmium air concentrations may be elevated in certain industrial settings, but these exposures are closely controlled today by national occupational exposure standards. Occupational exposure standards which were formerly set at 100 to 200 µg/m³ are now specified at 2 to 50 µg/m³ along with requirements to maintain biological indicators such as cadmium-in-blood and cadmium-in-urine below certain levels to assure no adverse human health effects from cadmium occupational exposure (International Labor Organization 1991, ACGIH 1996, OSHA 1992).
7.1.3 Cadmium in Tobacco Smoke:Tobacco leaves naturally accumulate and concentrate relatively high levels of cadmium, and therefore smoking of tobacco is an important source of air cadmium exposure for smokers. It has been reported that one cigarette contains about 0.5 - 2 µg of cadmium and that about 10% of the cadmium content is inhaled when the cigarette is smoked (Elinder 1985, WHO 1992).
7.2 Cadmium in Water:The average cadmium content in the world's oceans has variously been reported as low as <5 ng/L (WHO 1992) and 5-20 ng/L (OECD 1994, Jensen and Bro-Rasmussen 1992) to as high as 110 ng/L (CRC 1996), 1 00 ng/L (Cook and Morrow 1995) and 10 to 100 ng/L (Elinder 1985). Higher levels have been noted around certain coastal areas (Elinder 1985) and variations of cadmium concentration with the ocean depth, presumably due to patterns of nutrient concentrations, have also been measured (WHO 1992, OECD 1994).
7.3. Cadmium in soil:7.3.1 Sources:Cadmium in soils is derived from both natural and anthropogenic sources. Natural sources include underlying bedrock or transported parent material such as glacial till and alluvium. Anthropogenic input of cadmium to soils occurs by aerial deposition and sewage sludge, manure and phosphate fertilizer application. The major factors
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Cadmium Pollution and Its Impact on Human Health and Environment
governing cadmium speciation, adsorption and distribution in soils are pH, soluble organic matter content, hydrous metal oxide content, clay content and type, presence of organic and inorganic ligands, and competition from other metal ions (OECD 1994). The use of cadmium-containing fertilizers and sewage sludge is most often quoted as the primary reason for the increase in the cadmium content of soils over the last 20 to 30 years in Europe (Jensen and Bro-Rasmussen 1992).
7.3.2 Cadmium Levels in Soils:The average natural abundance of cadmium in the earth's crust has most often been reported from 0.1 to 0.5 ppm, but much higher and much lower values have also been cited depending on a large number of factors.
7.3.3 Cadmium Emissions to SoilsCadmium in soils must be distinctly classified in three separate areas with regard to their relative effects on human health and the environment. These three areas are agricultural soils, non-agricultural soils, and controlled landfills. Cadmium in controlled landfalls is virtually immobile, and is unlikely to have any effect on human health or the environment simply because it is so well contained (Eggenberger and Waber 1998, NUS 1987).
7.3.4 Cadmium in Agricultural Soils:Numerous agencies have focused upon the presence of cadmium in agricultural soils, the means by which agricultural soils may be enriched by cadmium. Except in cases of extreme contamination, the concentration of cadmium in soils is not the primary determinant of cadmium in the human diet.
7.3.5 Cadmium Levels in Foodstuffs:Cadmium levels can vary widely in various types of foodstuffs. Leafy vegetables such as lettuce and spinach and certain staples such as potatoes and grain foods exhibit relatively high values from 30 to 150 ppb. Peanuts, soybeans and sunflower seeds also exhibit naturally high values of cadmium with seemingly no adverse health effects. Meat and fish normally contain lower cadmium contents, from 5 to 40 ppb. Animal offal such as kidney and liver can exhibit extraordinarily high cadmium values, up to 1,000 ppb, as these are the organs in animals where cadmium concentrates (WHO 1992, ATSDR 1997). There are strong indications that cadmium levels in foodstuffs have substantially decreased during the past several decades due to the progressive control of cadmium emissions to the environment (Van Assche and Ciarletta 1993, Watanabe et al. 1993, Watanabe et al. 1994).
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Cadmium Pollution and Its Impact on Human Health and Environment
7.3.6 Cadmium Contamination of Agricultural Soils:In the past, there have been examples of marked cadmium contamination in areas where food has been grown. This was particularly so for rice crops in Japan in the 1950s and 1960s where cadmium concentrations from 200 to 2,000 ppb were found (Elinder 1985).
7.3.7Cadmium contamination in Bangladesh soils:Available data on the impact of industrial pollution in Bangladesh especially on soils and crops and the mobility in the human food chain are quite limited. No systematic research work has yet been done on the amelioration of heavy metal uptake into crops from polluted soils. During the course of the research work-“Amelioration of Heavy Metals from Contaminated Soils of Hazaribagh and Tejgaon Areas from Bangladesh Using Red Mud” by Chamon et al., (2009) in the Department of Soil, Water and Environment, University of Dhaka, Dhaka, Bangladesh., oxides of iron (as red mud) were tested as additives in two contaminated soil of Bangladesh, in order to remediate heavy metals from those soil.Pot experiments were conducted with heavy metals contaminated soil (0-15 cm depth) from Tejgaon industrial and Hazaribagh tannery areas. The characteristics of Tejgaon and Hazaribagh soil are given in Table-5.
Table-5.: The characteristics of Tejgaon and Hazaribagh SoilParameter Tejgaon soil Hazaribagh soilpH 5.67 7.08%C 8.24 1.02%N 0.74 0.16P(mg/kg) 415 229K(mg/kg0 243 213Cd (mg/kg) 2.6 0.08Texture Clay loam Clay loam
Source: Chamon et al., 2009.
8. Effects of cadmium: 8.1. Effects of cadmium on human health:
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Cadmium Pollution and Its Impact on Human Health and Environment
Cadmium is a pollutant which has strong negative effects on human and animal health. Inhalation of cadmium fumes or particles can be life threatening, and although acute pulmonary effects and deaths are uncommon, sporadic cases still occur. Cadmium exposure may cause kidney damage. The first sign of the renal lesion is usually a tubular dysfunction, evidenced by an increased excretion of low molecular weight proteins.Acute exposure to cadmium fumes may cause flu like symptoms including chills, fever, and muscle ache. More severe exposures can cause trachea-bronchitis, pneumonitis, and pulmonary edema. Symptoms of inflammation may start hours after the exposure and include cough, dryness and irritation of the nose and throat, headache, dizziness, weakness, fever, chills, and chest pain. Chronic exposure to cadmium is associated with kidney damage, bone damage, cancer, low birth weight, spontaneous abortion, and many other ailments.Inhaling cadmium-laden dust quickly leads to respiratory tract and kidney problems which can be fatal (often from renal failure). Ingestion of any significant amount of cadmium causes immediate poisoning and damage to the liver and the kidneys. Compounds containing cadmium are also carcinogenic.The study of health effects of cadmium with respect to the cardiovascular system and calcium metabolism disproved the hypothesis that exposure to cadmium would lead to an increase in blood pressure and in the prevalence of hypertension and other cardiovascular diseases. On the other hand, there was a positive relationship between urinary cadmium (Cd-U) and both serum alkaline phosphatase activity and urinary excretion of calcium. The regression coefficients obtained after adjustment for significant co-variants indicated that, when Cd-U increased two-fold, serum alkaline phosphatase and urinary calcium rose by 4% and 0.25 mmol/24 h, respectively. These findings suggest that calcium metabolism is gradually affected as cadmium accumulates in the body.Cadmium derives its toxicological properties from its chemical similarity to zinc an essential micronutrient for plants, animals and humans. Cadmium is bio persistent and, once absorbed by an organism, remains resident for many years (over decades for humans) although it is eventually excreted. Other patients lose their sense of smell (anosmia).Sources: medicaljournal.blogspot.com
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Cadmium Pollution and Its Impact on Human Health and Environment
The effects of cadmium on human health is shown in figure-7
Figure-7: The effect of cadmium on human health.Sources: www.cadmium.org.
“Itai itai”disease:Itai-itai disease (“ouch-ouch sickness"), was the documented case of mass cadmium poisoning in the Jintsu River Valley region, Toyama Prefecture, Japan, starting around 1912. The cadmium poisoning caused softening of the bones and kidney failure. The disease is named for the severe pains (Japanese: itai) caused in the joints and spine. The term "itai-itai disease" was coined by locals. The cadmium was released into rivers by mining companies in the mountains. The mining companies were successfully sued for the damage. Itai-itai disease is known as one of the Four Big Pollution Diseases of Japan.In this disease, some of the Zn+2 ions in the bones are apparently replaced by Cd+2
ions, since they have the same charge and virtually the same size (figure-8). The bones become porous, and can subsequently fracture and collapse. The intake of
Cadmium Pollution and Its Impact on Human Health and Environment
cadmium by itaiitai sufferers was estimated at about 600 micrograms per day, which is about 10 times the average ingestion of North America.
Cd+2
Figure-8: Pathway of Cd+2 in human body (De, 2000).Sources: De, A.K., 2000.
8.2. Effects of cadmium on environment:Naturally a very large amount of cadmium is released into the environment, about 25,000 tons a year. About half of this cadmium is released into rivers through weathering of rocks and some cadmium is released into air through forest fires and volcanoes. The rest of the cadmium is released through human activities, such as manufacturing.Cadmium can be transported over great distances when it is absorbed by sludge. This cadmium-rich sludge can pollute surface waters as well as soils.Cadmium strongly adsorbs to organic matter in soils. When cadmium is present in soils it can be extremely dangerous, as the uptake through food will increase. Soils
20
Free Cd+2 Inhalation (µg) Ingestion
Exchange with Zn containing enzymes
to alter
Birds completely with metallo thionine protein
Kidney 1%
99% eliminated
Renal dysfunctio Anemi
aHyper
tensionBone
marrow Cancer
Cadmium Pollution and Its Impact on Human Health and Environment
that are acidified enhance the cadmium uptake by plants. This is a potential danger to the animals that are dependent upon the plants for survival. Cadmium can accumulate in their bodies, especially when they eat multiple plants. Cows may have large amounts of cadmium in their kidneys due to this.In aquatic ecosystems cadmium can bio accumulate in mussels, oysters, shrimps, lobsters and fish. The susceptibility to cadmium can vary greatly between aquatic organisms. Salt-water organisms are known to be more resistant to cadmium poisoning than freshwater organisms.Animals eating or drinking cadmium sometimes get high blood-pressures, liver disease and nerve or brain damage.Sources: www.lenntech.com.
10. Treatment technology: Treatment of soils contaminated by trace metals is classically based on the application of lime and phosphates and the addition of organic matter (Kabata and Pendias, 1992). Immobilization of Cd in soil by either synthetic or natural zeolites reduced the Cd contents of plant tissues (Chlopecka and Adriano, 1996). In soil, heavy metal can be sorbed and immobilized by a large variety of substances, such as the different iron oxides and clay minerals (Tiller et al., 1984). Studies have
Cadmium Pollution and Its Impact on Human Health and Environment
shown that Fe oxides have a binding performance for specific metals (Yong et al., 1992), which becomes important when high levels of several metals are applied to soils. With high concentrations of metals added, the capacity of specific sorption sites (strongly bound metals) could be exceeded and the metal cations would compete with the bulk cations for adsorption sites. Rule and Martin (1999) reported that bio solids treated with Fe-RichTM (Fe-Rich Trace Metals) sorbed significantly more of all metals.For example, during the course of the research work-“Amelioration of Heavy Metals from Contaminated Soils of Hazaribagh and Tejgaon Areas from Bangladesh Using Red Mud” by Chamon et al. (2009) in the Department of Soil, Water and Environment, University of Dhaka, Dhaka, Bangladesh., oxides of iron (as red mud) were tested as additives in two contaminated soil of Bangladesh, in order to remediate heavy metals from those soil.The experiment showed that in principle, the taken measures i.e. application of red mud and selection of plant species ameliorated plant growth and/or heavy metal toxicity. Applied in small amounts, the ferric oxides, present in red mud led to an increase in biomass production and improved yield for tomato plants and caused significant reductions of soil to plant transfer of Cd. Heavy metal uptake into tomato plants was significantly ameliorated in both soils.The treatment technology is shown in following table-6.Table-6: Treatment technology in different route of exposure.
NOTE! PREVENT DISPERSION OF DUST! STRICT HYGIENE!
General First Aid: IN ALL CASES CONSULT A DOCTOR!
Route of Exposure
Symptoms First Aid
InhalationCough. Headache. Symptoms may be delayed (see Notes).
Fresh air rest. Half-upright position. Artificial respiration if indicated. Refer for medical attention.
Skin Remove contaminated clothes. Rinse and then wash skin with water and soap.
Eyes Redness. Pain. First rinse with plenty of water for several minutes (remove
22
Cadmium Pollution and Its Impact on Human Health and Environment
contact lenses if easily possible) then takes to a doctor.
Sources: medicaljournal.blogspot.com. And www.banglajol.info
Cadmium can be efficiently removed from source of waters by lime softening and coagulation with ferric sulphate. Lime softening removes over 98% of an initial cadmium concentration of 0.03mg∕l in the pH range 8.5 to 11.3; ferric sulphate coagulation removes more than 90% above pH 8, but only 30% at pH 7. Alum coagulation removes less than 50% in the pH range 6.5 to 8.3. Ion exchange is used industrially to remove cadmium from waste waters, and it has been reported that a home ion exchange water softener removes 99% of the cadmium present in drinking water. Reverse osmosis has also been reported capable of removing 90% or more of the cadmium present in drinking water (ottaway, 1980).
11. Conclusion: It has been clearly demonstrated that cadmium concentrations in agricultural soil, wheat, and human kidneys have increased significantly during the last century. Although there is no clear evidence of a further increase in the concentrations of cadmium in diets, blood, urine, and human kidneys, there is a tendency towards an increase for each medium. Taken together, it seems likely that the human exposure to cadmium continues to increase. This assumption is supported by the reported ongoing increases in concentrations of cadmium in soil and pig kidney.The recovery of cadmium from cadmium products through recycling programs not only ensures that cadmium will be kept out of the waste stream and out of the environment, but it also conserves valuable natural resources as well. Attempts to ban or restrict cadmium products are considered unnecessary, taking into account the ever decreasing human cadmium intake level which is already below the WHO standard, and the very small relative contribution of cadmium products in this respect. Rather than restricting products, it is argued that the European Union should co-operate with and encourage the industry’s voluntary product stewardship initiatives to cooct and recycle cadmium containing products, which would contribute to the sustainable and safe use of cadmium in modern society.
23
Cadmium Pollution and Its Impact on Human Health and Environment
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Cadmium Pollution and Its Impact on Human Health and Environment
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