People are more concerned with acute effects of toxins in the environment such as hydrochloric acid being released from the early alkali industry, changes in the Great Lakes, lead in paint and gasoline as well as photochemical oxidants in Los Angeles and other large cities. These problems have obvious causes and damage done can be easily measured and quantified. Control measures are possible since sources can easily be identified. The delay between action and results is short since the effects of the contaminant are acute. While these acute problems must still be addressed in the future, the effects of pollutants must be considered in a wider ecological context.
Toxins act on ecological systems producing complex changes.
From this environmental complexity comes the problem of extrapolating laboratory results to the field. The effects of the pollutant are altered by such factors as age, nutritional and reproductive condition of the target. Chronic exposures to low concentrations of toxins must also be studied in detail. Invalidated statements have been made about the number of cancers with environmental causes. These are difficult to confirm experimentally, especially if there is a lag of many years between exposure and response.