CHRONIC EFFECT OF CADMIUM IN SEDIMENTS ON COLONIZATION BY BENTHIC MARINE ORGANISMS - AN EVALUATION OF THE ROLE OF INTERSTITIAL CADMIUM AND ACID-VOLATILE SULFIDE IN BIOLOGICAL AVAILABILITY

The role of interstitial cadmium and acid-volatile sulfide (AVS) in co ntrolling the bioavailability of sediment-associated metal was examine d using the chronic saltwater benthic colonization test. Sediments wer e spiked to achieve nominal cadmium/AVS molar ratios of 0.0 (control), 0.1, 0.8, and 3.0 in this 118-d test. Oxidation of AVS in the surfici al 2.4 cm within 2 to 4 weeks resulted in sulfide profiles similar to those occurring naturally in local sediments. In the nominal 0.1 cadmi um/AVS treatment, measured simultaneously extracted metal (SEM(Cd)) wa s always less than AVS. Interstitial cadmium concentrations (<3-10 mu g/L) were less than those likely to cause biological effects. No signi ficant biological effects were detected. In the nominal 0.8 cadmium/AV S treatment, measured SEM,, commonly exceeded AVS in the surficial 2.4 cm of sediment. Interstitial cadmium concentrations (24-157 mu g/L) w ere of likely toxicological significance to highly sensitive species. Shifts in the presence or absence over all taxa, and fewer macrobenthi c polychaetes (Mediomastus ambiseta, Streblospio benedicti, and Podark e obscura) and unidentified meiofaunal nematodes, were observed. In th e nominal 3.0 cadmium/AVS treatment, concentrations of SEM(Cd) were al ways greater than AVS throughout the sediment column. Interstitial cad mium ranged from 28,000 to 174,000 mu g/L. In addition to the effects above, these sediments were colonized by fewer macrobenthic species, p olychaete species, and harpacticoids; had lower densities of diatoms; lacked bivalve molluscs; and exhibited other impacts. Over all treatme nts, the observed biological responses were consistent with SEM(Cd)/AV S ratios in surficial sediments and interstitial water cadmium concent rations.