Variation in the sensitivity of aquatic species in relation to the classification of environmental pollutants.

Differences in species sensitivity to toxicants can be substantial. In this study this among-species variation in sensitivity was analyzed in relation to chemical's mode of action. Chemicals were classified as: non-polar narcotics, polar narcotics, reactive compounds and specifically acting compounds. Acute toxicity data of aquatic species were derived from the literature. Levels of enhanced toxicity, averaged over all species, and interspecies variation in sensitivity were analyzed for 35 chemicals, with data ranging from 12 to 62 aquatic species per compound. Non-polar and polar narcotic chemicals demonstrate the smallest variation in sensitivity and have levels of toxicity, which are highly predictable on the basis of their hydrophobicity. Reactive and specifically acting compounds can be much more toxic than predicted and variation in species sensitivity can be as large as 10(5) to 10(6). In general, the larger this interspecies variation the more asymmetric is the toxicity distribution due to extremely sensitive species. Reactive and specifically acting compounds pose a potentially larger risk for species in ecosystems than polar and non-polar narcotic compounds. They will need more testing to derive precisely equal estimates of safe environmental concentrations.