Toxic pollution

A toxic substance is any substance which has the capability of injuring or killing animal or plant life, even when present in relatively low quantities. Many plants and animals produce toxins as a means or defense from predators, or even, in a few cases, as a means of attack. In a few places, natural toxins have been deliberately used by humans for centuries as a means to capture fish. Pacific islanders have used roots from the Derris plant and toxins from the skin of sea cucumbers in this way to stun fish.

Since the industrial revolution a massive range of natural and synthetic products, including many toxins, have been created. Large quantities of these are released, deliberately, accidentally, or even as unmeasured waste products into the environment. Such materials have widely different survival times. Some may be rapidly broken down, whilst others may persist for years or decades, or, in the case of radioactive materials, even millennia.

Natural processes may help in the breakdown of some toxins, but they can also be responsible for their concentration through the food-chains. This is particularly the case for those compounds which cannot be broken down. Filter feeders can greatly concentrate particular compounds in their bodies, whilst long-lived organisms, or species which are high in the food chain often build up remarkably high concentrations of extremely rare compounds and become a considerable hazard to human health should they be ingested.