Patterns in Toxicity of Sublethal Mixtures of Metals and Organic Chemicals Determined by Microtox® and by DNA, RNA, and Protein Content of Fathead Minnows (Pimephales promelas)

Abstract

Combinations of copper (0–90 μg/1) and zinc (0–1200 μg/L) acted in an additive fashion when tested by Microtox®, decreasing the luminescence of the marine bacterium Photobacterium phosphoreum after a 30-min exposure. Acetophenone (0–18 mg/L) combined with diethylene glycof (0–40 g/L) had less-than-additive effects, as did acetophenone–zinc combinations. In contrast, less-than-additive action of copper (0–150 μg/L) and zinc (0–1500 μg/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.