Some contaminants that enter biological systems are preferentially stored (usually in fat tissue) in organisms resulting in an accumulation over time. This process is called bioaccumulation (also biomagnification) – see image at right.
An organism at the base of a food web may contain low levels of a contaminant. Its consumer, however, will concentrate the contaminant as it consumes many individuals of its food source over its lifetime. With each step in the food web, these contaminants become increasingly concentrated as more are ingested and stored. The amount of contaminant accumulation is greater in food webs with more steps to the top predator. Therefore, the top predator in systems with longer food webs usually has higher contaminant concentrations than those with shorter food webs, all else being equal.
Image and Text Adapted from the Nile River Awareness Kit, Hatfield 2007
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