Interactive cytotoxicities of selected organic and inorganic substances to brown cells of Mercenaria mercenaria.

Toxicities of binary mixtures of Cu2+, Cd2+, benzo(a)pyrene [B(a)P] and N-ethylmaleimide (NEM) were screened using the in vitro neutral red (NR) assay to test the hypothesis that combined toxicity is more than or less than additive relative to the influence of each mixture constituent on toxicant uptake and brown cell lysosomal membrane stability. Significant cytotoxicity was observed at 25 mumol/L Cu2+, 500 mumol/L Cd2+ and 25 mumol/L NEM. B(a)P at 12 mumol/L exerted no toxicity under the conditions of the assay. Interactions between Cu2+ and NEM, between Cd2+ and NEM, and between Cd2+ and B(a)P significantly influenced brown cell survival. Comparison of observed joint toxicity with estimates made using a model of independent joint action indicates that interactive effects are less than additive in character. The 3-way interaction involving Cu2+, B(a)P, and NEM also affected brown cell survival to a statistically significant degree. However, the interactive cytotoxicity of this mixture is attributable mainly to the combined effect of Cu2+ and NEM. Results also indicate that new hypothesis and additional experimentation are needed to understand the interactive toxicity of mixture constituents.