Food Chain/Web

Bioaccumulation refers to the tendency of persistent hydrophobics and other chemicals such as methyl mercury to be stored in the fatty tissues of organisms. When these compounds are spilled into the environment they are rapidly absorbed by organisms in food webs. It is estimated that 99% of pesticides do not reach the target pest which means the chemical ends up in the general environment. If these pesticides are hydrophobic they build in the tissues of non-pest organisms.

Once inside the fatty tissues of an organism, persistent hydrophobics are not excreted easily. There are excretion mechanisms in most species. But each time the organism is exposed to the contaminant, more is taken in and deposited in the fatty tissues, accumulating progressively. Bioaccumulation is particularly acute in long-lived species because the period during which they bioaccumulate is longer. This is why some governments do not recommend consuming fish over a certain age or size because the older and larger they get, the more contaminated they are likely to be.