AQUEOUS-PHASE, PORE-WATER, AND SEDIMENT-PHASE CADMIUM - TOXICITY RELATIONSHIPS FOR A MEIOBENTHIC COPEPOD

Comparative effects of aqueous-, pore-water-, and sediment-phase cadmi um on mortality of an infaunal laboratory-cultured copepod, Amphiascus tenuiremis, were determined using acute 96-h bioassays. Experimental design included five cadmium concentrations, three replicates per conc entration, and 50 adult copepods per replicate for each of the exposur es. Exposures included cadmium solubilized in seawater only (aqueous), whole sediment (i.e., pore water and sediment), and pore water only. In addition, two whole-sediment bioassays were compared in which pore- water cadmium concentrations were altered experimentally but sediment concentrations remained the same. Results of these experiments showed that for Amphiascus tenuiremis, cadmium is most toxic in the aqueous p hase, less toxic in the pore-water phase, and least toxic in the sedim ent-bound phase. The lowered toxicity of cadmium in the pore water was most likely due to complexation of cadmium with DOC, because concentr ations of DOC were six times higher in the pore-water phase than in th e aqueous phase. In whole sediments, pore-water-phase cadmium was the primary source of acute toxicity, as sediment-associated cadmium contr ibuted negligible effects.