PATTERNS IN TOXICITY OF SUBLETHAL MIXTURES OF METALS AND ORGANIC-CHEMICALS DETERMINED BY MICROTOX(R) AND BY DNA, RNA, AND PROTEIN-CONTENT OF FATHEAD MINNOWS (PIMEPHALES-PROMELAS)

Combinations of copper (0-90 mu g/L) and zinc (0-1200 mu g/L) acted in an additive fashion when tested by Microtox(R), decreasing the luminescence of the marine bacterium Photobacterium phosphoreum after a 30-min exposure. Acetophenone (0-18 mg/L) combined with diethylene glycol (0-40 g/L) had less-than-additive effects, as did acetophenone-zinc combinations. In contrast, less-than-additive action of copper (0-150 mu g/L) and zinc (0-1500 mu g/L) was apparent from DNA, RNA, and protein contents of newly hatched fathead minnows (Pimephales promelas) exposed for 4 d. The highest copper-zinc combinations caused dramatic decreases in DNA, RNA, and protein contents of fish to 35, 8, and 46% of control levels, respectively. Although most joint effects were less-than-additive, independent action and antagonism were observed for some combinations of toxicants, and the type of action usually changed as proportions of toxicants were altered. Isobole mapping of response surfaces gave a useful overall picture of joint action for all concentrations tested, was favoured as a method of illustrating the results, and provided the interpretations given above.