Hormesis responses of free and immobilized light-emitting bacteria.

The stimulatory effect of sublethal or low concentrations of toxic chemicals on organismal metabolism, referred to as hormesis, has been found to be common in the widely used Vibrio fischeri luminescence bioassay. In addition to the "normal" type alpha, we have demonstrated type beta and, possibly, type gamma, dose-response curves in free and immobilized V. fischeri bioassays developed. Understanding and utilizing data from hormesis responses are necessary in determining the toxicity of chemicals, singly or in complex mixtures, to natural biota without imposing excessive penalties to dischargers. At the same time, care must be taken not to relax environmental standards. This can only arise by fully investigating and understanding the role of hormesis in toxicity data used for risk assessment.