Biomagnification: how DDT becomes concentrated as it passes through a food chain

The figure shows how DDT becomes concentrated in the tissues of organisms representing four successive trophic levels in a food chain.

The concentration effect occurs because DDT is metabolized and excreted much more slowly than the nutrients that are passed from one trophic level to the next. So DDT accumulates in the bodies (especially in fat). Thus most of the DDT ingested as part of gross production is still present in the net production that remains at that trophic level.

This is why the hazard of DDT to nontarget animals is particularly acute for those species living at the top of food chains.

For example, There is abundant evidence that some carnivores at the ends of longer food chains (e.g. ospreys, pelicans, falcons, and eagles) suffered serious declines in fecundity and hence in population size because of this phenomenon in the years before use of DDT was banned (1972) in the United States.
Link to more on DDT and its effects on wildlife.
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3 January 2001