1.2 Pollutants and bioaccumulation
The term ‘pollutant’ is a very wide-ranging term. When the introduction or action of something into any environment causes harm, it is considered a pollutant. This could be a harmful chemical such as smoke from a chimney, or it could be a more subtle and transient effect such as floodlights at an evening football match preventing stargazing.
There are many examples of how society has responded to pollution, such as the removal of lead in petrol, which affected human health, or the banning of chlorofluorocarbons (CFCs), which damaged the ozone layer. In both of these cases (i.e. lead and CFCs), when the pollution source was removed, the levels of them in the environment reduced and consequently so have the effects – albeit with a time delay.
By definition, persistent pollutants such as PBDEs do not break down, so continued introduction of even minute levels into an environment leads to accumulation and perhaps magnification of potential harm. For example, at a landfill site the PBDE level is likely to increase with time. Animals around that landfill may ingest PBDEs directly, but this bioaccumulation (intake and concentration of the chemical in their tissues) may be so small that it does not cause problems to any particular animal. However, a predator such as a cat might eat dozens of rats that live around the landfill, so it would receive the combined dose that each of these rats had within it. If this dose were subsequently absorbed by the cat, then the resulting accumulated level could be significantly more harmful. This concentration of pollutants at higher levels in the food chain is called biomagnification, and the result is that higher predators can be poisoned and suffer harm while animals at lower levels in the food chain are apparently unaffected.