Biomagnifications, PCBs

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. 

Henny CJ, Kaiser JL, Grove RA, Bentley VR, Elliott JE. 2003. Biomagnification factors (fish to osprey eggs from Willamette River, Oregon, U.S.A.) for PCDDs, PCDFs, PCBs and OC pesticides. Environ Monit Assess 84 275-315. 

Macdonald, C.R., R.J. Norstrom, and R. Turle. 1992. Application of pattern recognition techniques to assessment of biomagnification and sources of polychlorinate multicomponent pollutants, such as PCBs, PCDDs, and PCDFs. Chemosphere 25 129-134. 

The biomagnification of polychlorinated biphenyls (PCBs) in the Great Lakes of North America is illustrated by the following residue values available from Environment Canada, a report published by the Canadian government, and other sources. 

Thus, the biomagnification for this substance in the food chain, beginning with phytoplankton and ending with the herring gull, is nearly 50,000-fold. Domestic animals and humans may eat fish from the Great Lakes, resulting in PCB residues in these species as well. 

As PCB production increased, more concerns were raised about the health and environmental effects of PCBs, which entered the environment through leakage, production processes, and improper disposal. The persistence and lipophilicity of PCBs resulted in its biomagnification in the environment (see DDT). Problems associated with PCB contamination in wildlife include deformities, tumors, disruption in the endocrine and reproduction systems, and death. Human exposure to PCBs occurs through environmental and occupational routes. The primary exposure... 

Figure 10.9 Example of a food chain biomagnification of PCB52 (2,2 ,5,5 ,-tetrachIorobiphenyI). Concentrations in parts per billion (ppb, i.e., fig L 1 or fig kg 1, respectively) of this PCB in each phase of two food chains (i) from water to phytoplankton to herbivorous mysids to carnivorous small fish to carnivorous large fish, and (ii) from bed sediments to de-trivorous amphipods to carnivorous small fish to carnivorous large fish. Data from a study of Lake Ontario (Oliver and Nimi, 1988) assuming all organisms were 80% water content to convert all concentrations to a dry-weight basis.

The biomagnification LOE involves determining concentrations of contaminants such as DDT, PCBs, dioxins, TBT, and methyl mercury in benthic invertebrates or fish. This LOE only applies to those few organic contaminants that actually biomagnify. Concentrations are compared to reference areas or literature-based toxicity reference values (TRVs) and assessed via food chain bioaccumulation models (Grapentine et ah, 2002). 

Regardless of one s position in this debate, it is apparent that the use of compounds that show persistence in the environment must be carefully examined and monitored. Any compound that is persistent and hydrophobic (lipophilic or fat soluble) will be subject to the process of biomagnification and may present special problems. In addition to DDT and other chlorinated pesticides, another example is provided by the polychlorinated biphenyls (PCBs). These compounds have two benzene rings bonded together, with varying numbers of chlorines substituted on the rings. One example is provided by the following structure ... 

PCBs are so chemically inert that they were extensively used as heat transfer fluids in large electrical transformers, along with other uses. Of course, when they escaped into the environment, they exhibited the two troublesome qualities of persistence and biomagnification. Because PCBs are now suspected carcinogens, they are no longer manufactured in the United States. However, they are now widely distributed in the environment. Furthermore, there is the problem of disposing of the large number of electrical devices that contain these compounds. 

Helm, P. A., Gewurtz, S. B., et al (2008) Occurrence and biomagnification of polychlorinated naphthalenes and non- and mono-ortho PCBs in Lake Ontario sediment and biota. Environmental Science and Technology, 42(4) 1024-1031. 

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