EFFECTS OF ACID-VOLATILE SULFIDE ON ZINC BIOAVAILABILITY AND TOXICITYTO BENTHIC MACROINVERTEBRATES - A SPIKED-SEDIMENT FIELD EXPERIMENT

Acid-volatile sulfide (AVS) has been proposed as the primary normaliza tion phase for the development of sediment quality criteria for certai n cationic metals. This study was designed to assist in this developme nt by providing necessary field data on the relationships among season , AVS concentrations, and zinc bioavailability and toxicity in freshwa ter sediments. Zinc was spiked into uncontaminated sediments collected from a local pond, creating five simultaneously extracted metal (SEM) concentrations ranging from 0.8 to 12.0 mu mol/g dry weight. The spik ed sediments were transferred to 4-L plastic trays, returned to the bo ttom of the pond, and sampled on five dates during 1993-1994. Results revealed a pronounced increase in AVS concentration with increasing zi nc concentration. Acid-volatile sulfide concentrations in zinc-spiked sediments displayed only minor seasonal variation but were lowest in s urficial (0-2 cm) sediments. Acid-volatile sulfide concentrations alwa ys exceeded SEM concentrations at less than or equal to 6.0 pmol SEM/g ; only at 12.0 mu mol SEM/g did SEM/AVS ratios exceed 1.0. Zinc was ra rely detected in pore water at any treatment and never at concentratio ns which should have posed a hazard to benthic macroinvertebrates. No substantial effect on colonization of zinc-spiked sediments by benthic macroinvertebrates was observed. Only oligochaetes (Naididae) were si gnificantly reduced in abundance at the high zinc treatment, although reductions were occasionally evident for other taxa. Lack of noteworth y pore-water zinc concentrations and lack of associated, ecologically meaningful effects were attributed to the increase in AVS levels obser ved with increasing SEM zinc sediment concentration. The increases in AVS theoretically resulted from a replacement of natural iron and mang anese sulfides with the more stable zinc sulfide complex.