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 controlling the bioavailability of sediment-associated metal was examined using the chronic saltwater benthic colonization test. Sediments were 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 surficial 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 cadmium/AVS treatment, measured simultaneously extracted metal (SEM(Cd)) was always less than AVS. Interstitial cadmium concentrations (<3-10 mu g/L) were less than those likely to cause biological effects. No significant biological effects were detected. In the nominal 0.8 cadmium/AVS treatment, measured SEM,, commonly exceeded AVS in the surficial 2.4 cm of sediment. Interstitial cadmium concentrations (24-157 mu g/L) were of likely toxicological significance to highly sensitive species. Shifts in the presence or absence over all taxa, and fewer macrobenthic polychaetes (Mediomastus ambiseta, Streblospio benedicti, and Podarke obscura) and unidentified meiofaunal nematodes, were observed. In the nominal 3.0 cadmium/AVS treatment, concentrations of SEM(Cd) were always greater than AVS throughout the sediment column. Interstitial cadmium ranged from 28,000 to 174,000 mu g/L. In addition to the effects above, these sediments were colonized by fewer macrobenthic species, polychaete species, and harpacticoids; had lower densities of diatoms; lacked bivalve molluscs; and exhibited other impacts. Over all treatments, the observed biological responses were consistent with SEM(Cd)/AVS ratios in surficial sediments and interstitial water cadmium concentrations.