The origins of “micropollutants” are discussed and classified. It is suggested that assessing the risk and ensuring an acceptably low level of adverse effects from these substances requires information or control of three factors (exposure, toxicity and characteristics of the victim or organism) which combine to generate the toxic event. Methods of estimating exposure are discussed, especially environmental models. Ultimately, it should be possible to couple these models to toxicity data in a rational, rigorous manner to elucidate the extent of risk and control it to acceptable levels.