Biomagnifications

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. 

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. 

Kay SH. 1984. Potential for biomagnification of contaminants within marine and freshwater food webs. Vicksburg, MS Department of the Army, Waterways Experiment Station, Corps of Engineers. D-84-7. 

Biomagnification along terrestrial food chains is principally due to bioaccumulation from food, the principal source of most pollutants (Walker 1990b). In a few instances, the major route of uptake may be from air, from contact with contaminated surfaces, or from drinking water. The bioaccumulation factor (BAF) of a chemical is given by the following equation ... 

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... 

BCFs and BAFs measured before the steady state is reached have little value because they are dependent on the period of exposure of the organism to the chemical, and thus may greatly underestimate the degree of biomagnification that is possible. This statement should be qualified by the reservation that there may be situations in which the duration of exposure cannot be long enough for the steady state to be reached, for example, where the life span of an insect is very short. The principal processes of uptake and loss by different types of organisms are indicated in Table 4.1 (see also Box 4.2). 

The selection of these compounds was made on the grounds of their toxicity, environmental stability, and tendency to undergo biomagnification the intention was to move toward their removal from the natural environment. In the REACH proposals of the European Commission (EC published in 2003), a similar list of 12 POPs was drawn up, the only differences being the inclusion of hexachlorobiphenyl and chlordecone, and the exclusion of the by-products, dioxins, and furans. The objective of the EC directive is to ban the manufacture or marketing of these substances. It is interesting that no fewer than eight of these compounds, which are featured on both lists, are insecticides. 

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

Finally, an investigation of total DDT levels in seal (Phoca sibirica) from Lake Baikal, Russia (the largest lake in the world), during the 1990s showed substantial levels with evidence of strong biomagnification in this aquatic food chain (Lebedev et al. 1998). 

PCB mixtures were once used for a variety of purposes, and came to cause widespread environmental pollution. Over 100 different congeners are present in commercial products such as Aroclor 1248 and Aroclor 1254. PCBs are lipophilic, stable, and of low vapor pressure. Many of the more highly chlorinated PCBs are refractory, showing very strong biomagnification with movement along food chains. 

Both PCDDs and PCDEs are refractory lipophilic pollutants formed by the interaction of chlorophenols. They enter the environment as a consequence of their presence as impurities in pesticides, following certain industrial accidents, in effluents from pulp mills, and because of the incomplete combustion of PCB residues in furnaces. Although present at very low levels in the environment, some of them (e.g., 2,3,7,8-TCDD) are highly toxic and undergo biomagnification in food chains. 

PAHs can be bioconcentrated or bioaccumulated by certain aquatic invertebrates low in the food chain that lack the capacity for effective biotransformation (Walker and Livingstone 1992). Mollusks and Daphnia spp. are examples of organisms that readily bioconcentrate PAH. On the other hand, fish and other aquatic vertebrates readily biotransform PAH so, biomagnification does not extend up the food chain as it does in the case of persistent polychlorinated compounds. As noted earlier, P450-based monooxygenases are not well represented in mollusks and many other aquatic invertebrates (see Chapter 4, Section 4.2) so, this observation is not surprising. Oxidation catalyzed by P450 is the principal (perhaps the only) effective mechanism of primary metabolism of PAH. 

Biomagnification Increase in concentration of a chemical in living organisms with passage along a food chain. 

Borga, K., Gabrielsen, G.W., and Skaare, J.U. (2001). Biomagnification of organochlorines along a Barents sea food chain. Environmental Pollution 113, 187-198. 

Tissue extracts from 19 bald eagle Haliaectas leucocephalus) carcasses were examined to determine if biomagnification of TCDD had occurred in a manner similar to DDT. These carcasses came from the states of Alaska, Maine, North Dakota, Wisconsin, Michigan, Minnesota, Arkansas, Illinois, Missouri, Maryland, Virginia, Iowa, New York, New Jersey, and Florida between 1966 and 1971 and were collected and furnished by scientists at the Patuxent Wildlife Center, U.S. Department of the Interior, Laurel, Md. The samples were selected from these states to provide a widely dispersed sampling population. 

At the other extreme, if metabolism of the xenobiotic by the organism does not occur at all—or at insignificant rates—after exposure, the compound will be persistent in the organism, and may therefore be consumed by predators. This is relevant to biomagnification. 

Bowles KC, Apte SC, Maher WA, Kawei M, Smith R. 2001. Bioaccumulation and biomagnification of mercury in Lake Murray, Papua New Guinea. Can J Fish Aquat Sci 58 888-897. 

DesGranges J-L, Rodrigue J, Tardif B, Laperle M. 1998. Mercury accumulation and biomagnification in ospreys (Pandion haliaetus) in the James Bay and Hudson Bay regions of Quebec. Arch Environ Contam Toxicol 35 330-341. 

---