Fundamental Properties of Chemicals

There are over two million known chemicals of which some 70 000 are presently in commercial use worldwide. These include metals, metal compounds, metalloids and an enormous variety of synthetic organic chemicals. Testing a new chemical for its likely adverse biological effects may cost from a few thousand US dollars for simple acute toxicity tests or laboratory measurement of bioconcentration potential to over one million US dollars for longer-term epidemiological studies on humans. Even then, in only 20% of all cases can health hazard assessments fulfil rigorous scientific and technical criteria (NRC, 1984). Furthermore, such testing procedures may not account adequately for the complex series of transformations undergone by chemicals once they are subjected to environmental processes. Thus, it is clear that some form of early screening is necessary, even if only to identify those chemicals likely to require further testing.