Uptake and inhibition studies were used to evaluate mechanisms of uptake of Ni(2+), Cd(2+), and B(a)P in the brown cells of M. mercenaria. Brown cells contain one or more vesicles that have been shown to be lysosomes. Cd(2+), Ni(2+), and B(a)P accumulation by brown cells was concentration-dependent and independent of time and temperature at 5 C. Metabolic inhibitors such as carbonyl cyanide-m-chlorophenyl hydrazone and NaF did not inhibit their uptake. N-ethylmaleimide facilitated Ni(2+) and Cd(2+) uptake, but inhibited B(a)P uptake. Buthionine-(S,R)-sulfoximine inhibited Ni(2+), Cd(2+), and B(a)P uptake in a dose-dependent manner, and diethylmaleate had no effect on Cd(2+) and B(a)P uptake, but increased Ni(2+) uptake. Chloroquine and copper, which accumulate in lysosomes, inhibited Ni(2+), Cd(2+), and B(a)P uptake. Verapamil inhibited Ni(2+) and B(a)P uptake, whereas it increased Cd uptake. The authors' results suggest that the brown cells of M. mercenaria are capable of accumulation of soluble foreign material and that membrane sulfhydrl groups, glutathione, and Cd(2+) channels are active in these processes. (Copyright (c) 1992 Elsevier Science Publishers Ltd, England.)