Contamination

Contamination generally refers to the occurrence of some substance in the environment. The contaminant may be present in a larger concentration than normally occurs in the ambient environment. However, contamination is only said to occur when the concentration is smaller than that at which measurable biological or ecological damage can be demonstrated. Contamination is different from pollution, which is judged to occur when a chemical is present in the environment at a concentration greater than that required to cause damage to organisms. Pollution results in toxicity and ecological change, but contamination does not cause these effects because it involves sub-toxic exposures.

Chemicals that are commonly involved in toxic pollution include the gases sulfur dioxide and ozone, elements such as arsenic, copper, mercury, and nickel, pesticides of many kinds, and some naturally occurring biochemicals. In addition, large concentrations of nutrients such as phosphate and nitrate can cause eutrophication, another type of pollution. All of these pollution-causing chemicals can occur in the environment in concentrations that are smaller than those required to cause toxicity or other ecological damages. Under these circumstances the chemicals would be regarded as contaminants.

Modern analytical chemistry has become extraordinarily sophisticated. As a result, trace contamination by potentially toxic chemicals can often be measured in amounts that are much smaller than the thresholds of exposure, or dose, that are required to demonstrate physiological or ecological damage.