Info

Source: LaGrega et al. (2001); original source D. W. Connell (1990), Bioaccumulation of Xenobiotic Compounds, CRC Press, Boca Raton, FL.

Note that KB in this case should be interpreted as an accumulation factor for ingestion alone. More generally, bioaccumulation includes all sources of contaminants.

18.7.4 Food Chain Transfer and Biomagnification

A bioaccumulation model such as equation (18.34) can be applied separately to each trophic level in an ecosystem, with the food at one level being the organism concentration at the lower level:

Here Ci is the concentration of toxin in the organisms of trophic level i, Ci-1 is the concentration of the next-lower trophic level, KCi is the bioconcentration factor for trophic level i, and KBi is the bioaccumulation factor for trophic level i.

For example, suppose that the environmental concentration of a toxic substance is 1 mg/kg and KC = KB = 10 for all trophic levels. The primary producers will have a concentration of 10 mg/kg due to bioconcentration alone. The herbivores will have C = 10 • 1 + 10 • 10 = 110 mg/kg. The concentration in carnivores will be C = 10 • 1 + 10 • 110 = 1110 mg/kg. Secondary carnivores will have a concentration 11,110 mg/kg.

An increase of tissue concentration of a toxic substance with increasing trophic level is called biomagnification. Figure 18.9 illustrates the relationship for two food chains. Substances that bioaccumulate also tend to biomagnify. Thus, the tendency to biomagnify is usually also related to the KOW. However, a low rate of elimination, especially by biotransformation, is also necessary. These conditions are particularly true for chlorinated organics. Biomagnification can produce extremely high body burdens in organisms at

Pesticide: DDD Water 0.02 ppm

Pesticide: Toxaphene Water 0.2 ppm

Plankton 5.3 ppm; x265

Planktonic crustaceans 73 ppm; x365

Planktonic crustaceans 73 ppm; x365

Small fish 10.0 ppm; x500

Small fish 10.0 ppm; x500

Goldfish 200 ppm; x1,000

Goldfish 200 ppm; x1,000

1,700 ppm; x85,000

Predator fish

1,700 ppm; x85,000

Predator fish

1,700 ppm; x8,500

Pelican

1,700 ppm; x8,500

Figure 18.9 Biomagnification of two organochlorine pesticides in aquatic food chains.

TABLE 18.6 Thoman's Food Chain Multipliers

Log Kow

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