Biomagnification
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Biomagnification: property of a chemical to be concentrated along the food chain. This requires that the chemical is not easily degraded chemically or biologically, and that it is bound to organisms or tissues so that it is carried from one species to the next species using it as its food. Lipid-soluble, poorly water-soluble chemicals are bioaccumulated by e.g. phytoplankton (plankton of plant character such as algae), this is consumed by animal plankton, this by invertebrates, further by fish and finally by seals. If the lipid-soluble chemical is very persistent, its concentration will increase stepwise at each level. That is why the species at the "top" of a feeding pyramid suffer most of persistent environmental chemicals. Chlorination of organic chemicals often increases both their persistence and their lipid solubility. Therefore PCBs and dioxins are bioaccumulated and biomagnified especially well. Increasing number of chlorines increases both lipid solubility and biomagnification. However, the optimal biomagnification capacity is at about 6 chlorines, probably because higher chlorinated congeners (esp. octa-) are so poorly water soluble that their bioavailability is low. Human beings are also at the top of the food chain, but because of the variety of foods from different sources humans consume, as compared with seals or eagles, bioaccumulation to humans is not so great.[1]