Issue 6: Chemical

It is important to be aware of the distinction between pollution and contamination. Contamination should be used where a chemical is present in a given sample with no evidence of harm, whereas pollution is used in cases where the presence of a chemical is causing environmental harm. Any chemical can become a pollutant in water if it is present at a high enough concentration.

Despite the fact that any chemical can be a pollutant, certain chemicals have been identified by regulation or by international agreement as being ‘priority chemicals for control’. Such chemicals are generally selected using the following criteria:

· The chemicals are frequently found by monitoring programmes

· They are toxic at low concentrations

· They bioaccumulate

· They are persistent

· They are carcinogens

Chemical pollution from industrial sources is one of the major types of anthropogenic stress. Industrial pollution can reduce the health of ecosystems. The toll can be direct, e.g. immediate declines in productivity or in the value of the goods produced (such as the loss of fish stocks after the Exxon Valdez spill). Or it may be indirect, e.g. the weakening of the assimilative capacity. The latter can gradually sap productivity or result in catastrophic change or collapse (such as the transformation of the Black Sea.) Just as with a depressed immune system, when their regulation mechanisms are compromised, ecosystems cannot cope with what would normally be minor stresses.

GIWA definition

Chemical pollution refers to the adverse effects of chemical contaminants released to water bodies as a result of human activities.

Environmental impacts

1. Reproductive dysfunction in aquatic organisms

2. Behavioral dysfunction in aquatic organisms

3. Modified community structure

4. Increased mortality of aquatic organisms

5. Immunosupression in aquatic organisms

Indicators

The following are environmental impact indicators for the chemical issue.

Select the environmental impact indicators that are relevant from the list below and input data into the appropriate indicator sheets.

Pollution

Biological effects

Biological

Proxy indicator of chemical pollution