Bioconcentration

Accumulation is the general term for any phenomenon associated with increasing the concentration of chemicals in a compartment relative to the surrounding phases. With regard to organisms, the accumulation processes are defined according to the mode of uptake of contaminants  

The potential of chemicals to bioaccumulate is generally characterized by the bioconcentration factor BCF, which serves as a measure of the compounds concentration in the organism concurrent with ambient concentrations under steady-state conditions (e.g. for aquatic environments)  

Most methods for experimental BCF determinations represent an assessment of the potential for accumulation. They do not account for specific environmental conditions, such as diflferences in the species exposed or the environmental bioavailability of the chemicals. The tests generally use fish as a model organism to serve as a predictor for bioconcentration in other aquatic species as well, and for bioaccumulation/biomagnification along aquatic foodwebs. Test guidelines for BCF in fish are available (e.g. OECD, 1981a), where the fish are exposed to the chemicals and from the concentrations in fish and water the BCF is obtained. The tests vary with respect to  

Several factors may contribute to the substantial variability observed in measured BCF values, which may range over several orders of magnitude for the same compound for example, for pentachlorobenzene, BCF values between 900 and 250 000 have been reported (e.g. Bruggeman et a/., 1984 Gobas, Shiu and Mackay, 1987 Hawker, 1990). The evident variability in experimental BCF data may arise from  

Species sensitivity the bioconcentration of xenobiotics in organisms varies with the size, lipid content, age, sex and lifespan of the species. 

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DDT is highly toxic to fish (LC q for trout and blue gill, 0.002—0.008 ppm), and it is only moderately toxic to birds (oral LD q mallard 1300 and pheasant >2240 mg/kg). However, widespread bird kills have resulted from bioconcentration of DDT through food chains, ie, from fish or earthworms. A significant environmental problem has resulted from the specific effects of DDE on eggshell formation in raptorial birds where accumulation has caused decreases in shell thickness of 10—15%, resulting in widespread breakage. 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

Environmental problems associated with PCBs are the result of a number of factors. Several open uses of PCBs have resulted in thein direct introduction into the environment, eg, organic diluents careless PCB disposal practices have resulted in significant releases into aquatic and marine ecosystems higher chlorinated PCBs are very stable in thein persistence in different environmental matrices and by a variety of processes (Fig. 1) PCBs are transported throughout the global ecosystem and preferentiaHy bioconcentrate in higher trophic levels of the food chain. 

Recent studies suggest that mercury can cause an instant decrease in the sperm viability of fish at concentrations comparable to those which are permitted in drinking water (1 /rg C ). The bioconcentration of the metal to levels in the testis considerably higher than this from water containing only 1/30 of permitted levels" suggests that current legal limits are much too high. 

Bioconcentration, Bio accumulation and Biomagnification. These aspects are determined by the physicochemical properties of a chemical, an organism s ability to excrete the chemical, the organism s lipid content and its trophic level. Bioconcentration relates to the difference between the environmental concentration and that of the body tissues. A high bioconcentration factor (BCF) predisposes to bioaccnmulation. The upper limit of bioaccnmulation is determined by lipid levels in the organism s tissues. Whether the resultant body burden causes biomagnification in the food chain depends upon the metabolic capabilities of the exposed organism. 

Tsuda T, Nakanishi H, Aoki S, Takebayashi J (1986) Bioconcentration of butyltin compounds by round crucian carp. Toxicology and Environmental Chemistry, 12 137-143. 

Estimates of bioconcentration factors, BCE, in aquatic organisms, based on calculations from water solubility and gave a log BCE of 1.80-2.89 (Kenaga 1980). Studies in outdoor ponds yielded log... 

BCF factors in fish ranging from 1.08 to 1.85, indicating that bioconcentration of methyl parathion is not an important fate process (Crossland and Bennett 1984). In another study, methyl parathion was added to the water of a carp-rearing pond and the concentration of methyl parathion was measured in water, soil, macrophytes, and carp over a 35-day period. Results showed that methyl parathion accumulated in macrophytes for 1 day and in carp for 3 days following exposure, and then dissipated. The concentrations of methyl parathion decreased in macrophytes by 94% by day 35 and by 98% in carp tissue by day 28 (Sabharwal and Belsare 1986). These data indicate the potential for biomagnification in the food chain is likely to be low because methyl parathion appears to be metabolized in aquatic organisms. 

Food Chain Bioaccumulation. There are a few studies to determine residues of methyl parathion in organisms in the environment. These have consistently shown low methyl parathion residues, indicating that methyl parathion does not bioconcentrate to a significant extent in aquatic organisms, plants, or animals (Crossland and Bennett 1984 Sabharwal and Belsare 1986). The methyl parathion that does get into organisms is rapidly degraded (Sabharwal and Belsare 1986). Some recent analyses of fish in a... 

EPA. 1981a. Acephate, aldicarb, carbophenothion, DBF, EPN, ethoprop, methyl parathion, and phorate Their acute and chronic toxicity, bioconcentration potential and persistence as related to marine environments. Gulf Breeze, FL U.S. Environmental Protection Agency, Environmental Research Laboratory. EPA-600/4-81/04L NTIS PB81-244477. 1-275. 

Kenaga EE. 1980. Predicted bioconcentration factors and soil sorption coefficients of pesticides and other chemicals. Ecotoxicol Environ Safety 4 26-38. 

Schimmel SC, Gamas RE, Patrick JM, et al. 1983. Acute toxicity, bioconcentration and persistence of AC 222,705, benthiocarb, chlorpyrifos, fenvalerate, methyl parathion and permethrin in the estuarine environment. J Agric Food Chem 31 104-113. 

Bioconcentration Factor (BCE)—The quotient of the concentration of a chemical in aquatic organisms at a specific time or during a discrete time period of exposure divided by the concentration in the surrounding water at the same time or during the same period. 

Endosulfan is released to the environment mainly as the result of its use as an insecticide. Significant contamination is limited to areas where endosulfan is manufactured, formulated, applied, or disposed of. The compound partitions to the atmosphere and to soils and sediments. Endosulfan can be transported over long distances in the atmosphere, but the compound is relatively immobile in soils. It is transformed by hydrolysis to the diol and by microorganisms to a number of different metabolites. It is bioconcentrated only to low levels and does not biomagnify in terrestrial or aquatic food chains. 

Endosulfan does not bioaccumulate to high concentrations in terrestrial or aquatic ecosystems. In aquatic ecosystems, residue levels in fish generally peak within 7 days to 2 weeks of continuous exposure to endosulfan. Maximum bioconcentration factors (BCFs) are usually less than 3,000, and residues are eliminated within 2 weeks of transfer to clean water (NRCC 1975). A maximum BCE of 600 was reported for a-endosulfan in mussel tissue (Ernst 1977). In a similar study, endosulfan, isomers not specified, had a measured BCE of 22.5 in mussel tissue (Roberts 1972). Tissue concentrations of a-endosulfan fell rapidly upon transfer of the organisms to fresh seawater for example, a depuration half-life of 34 hours (Ernst 1977). Higher BCFs were reported for whole-body and edible tissues of striped mullet (maximum BCF=2,755) after 28 days of exposure to endosulfan in seawater (Schimmel et al. 1977). However, tissue concentrations decreased to undetectable levels 48 hours after the organisms were transferred to uncontaminated seawater. Similarly, a BCE of 2,650 was obtained for zebra fish exposed to 0.3 pg/L of endosulfan for 21 days in a flow-through aquarium (Toledo and Jonsson 1992). It was noted that endosulfan depuration by fish was rapid, with approximately 81% total endosulfan eliminated within 120 hours when the fish were placed in a tank of water containing no endosulfan. 

The results of metabolism studies with laboratory animals and livestock indicate that endosulfan does not bioconcentrate in fatty tissues and milk. Lactating sheep administered radiolabeled endosulfan produced milk containing less than 2% of the label. Endosulfan sulfate was the major metabolite in milk (Gorbach et al. 1968). A half-life of about 4 days was reported for endosulfan metabolites in milk from survivors of a dairy herd accidentally exposed to acutely toxic concentrations of endosulfan endosulfan sulfate accounted for the bulk of the residues detected in the milk (Braun and Lobb 1976). No endosulfan residues were detected in the fatty tissue of beef cattle grazed on endosulfan-treated pastures for 31-36 days (detection limits of 10 ppm for endosulfan, 40 ppm for endosulfan diol) the animals began grazing 7 days after treatment of the pastures. Some residues were detected in the fatty tissue of one animal administered 1.1 mg/kg/day of endosulfan in the diet for 60 days. No endosulfan residues were... 

Food Chain Bioaccumulation. Endosulfan is bioconcentrated by aquatic organisms (Ernst 1977 Novak and Ahmad 1989 NRCC 1975 Roberts 1972 Schimmel et al. 1977) but not by plants or animals (ERA 1982a). The compound is metabolized by terrestrial (Coleman and Dolinger 1982 El Beit et al. 1981c Martens 1977 NRCC 1975) and aquatic organisms (Cotham and Bidleman 1989), and it does not biomagnify to any great extent in terrestrial or aquatic food chains (HSDB 1999). No additional information on the bioaccumulation of endosulfan is needed at this time. 

BCF = bioconcentration factor, 270 L/kg for alpha-, beta-endosulfan, and endosulfan sulfate WCR = water consumption rate, set at 2 L/day... 

Ernst W. 1977. Determination of the bioconcentration potential of marine organism- A steady state approach. I. Bioconcentration data for seven chlorinated pesticides in mussels(mytilus edulis) and their relation to solubility data. Chemosphere 11 731 -740. 

Schimmel SC, Patrick JM Jr, Wilson AJ Jr. 1977. Acute toxicity to and bioconcentration of endosulfan by estuarine animals. In Mayer EL, Hamelink JL, eds. Aquatic toxicology and hazard evaluation, ASTM STP 634. Philadelphia, PA American Society for Testing and Materials, 241-252. 

Biomagnification along aquatic food chains may be the consequence of bioconcentration as well as bioaccumulation. Aquatic vertebrates and invertebrates can absorb pollutants from ambient water bottom feeders can take up pollutants from sediments. The bioconcentration factor (BCF) of a chemical absorbed directly from water is defined as... 

Some models for predicting bioconcentration and biomagnification are presented in Box 4.1. 

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