One of the most significant problems facing the water quality management field today is the translation of laboratory-derived aquatic toxicology criteria and standards to natural water field conditions. This problem is caused, in part, by the markedly different chemical environments that frequently exist in laboratory toxicity tests and the field. Normally, laboratory-developed water quality criteria are derived from bioassays in which the contaminant is presented to the organism in a completely or nearly completely available form or forms; however, under field conditions, many contaminants exist in a variety of forms only some of which are available to aquatic organisms.

Guidance is provided on how to use knowledge of the aqueous environmental chemistry of the contaminant or contaminants of concern to detect situations in which there may be markedly different toxicity levels under field and laboratory conditions. A hazard-assessment approach is outlined by which maximum use can be made of existing laboratory bioassay data and environmental chemistry in site-specific water quality evaluation.