PREDICTING CHRONIC TOXICITY OF SEDIMENTS SPIKED WITH ZINC - AN EVALUATION OF THE ACID-VOLATILE SULFIDE MODEL USING A LIFE-CYCLE TEST WITH THE MIDGE CHIRONOMUS-TENTANS

The development of sediment quality criteria for the cationic metals c admium, copper, lead, nickel, and zinc has focused on the use of acid- volatile sulfide (AVS) as the primary normalization phase for predicti ng interstitial pore-water concentrations and bioavailability of the m etals. To date, most of the research in support of AVS in this context has utilized short-term laboratory exposures, with a relative paucity of information pertaining to long-term exposures. The purpose of this study, therefore, was to investigate the use of AVS as a predictor of metal toxicity to a benthic organism in a long-term laboratory exposu re. Clean sediment was spiked with zinc to obtain nominal treatments r anging from -2.34 to 58.5 mu g/g dry weight with respect to the molar difference between simultaneously extracted metal (SEM) and AVS. The t est was initiated with newly hatched larvae of the midge Chironomus te ntans and carried through one complete generation (56 d) during which survival, growth, emergence, and reproduction were monitored. When the molar difference between SEM and AVS (i.e., SEM - AVS) was <0, the co ncentration of zinc in the sediment interstitial water was low and no adverse effects were observed for any of the biological endpoints meas ured. Conversely, when SEM - AVS exceeded 0, a dose-dependent increase in the relative concentration of zinc in the pore water was detected. However, the absolute concentration of pore-water zinc at each treatm ent declined over the course of the study, corresponding to an increas e in sediment AVS and to a loss of zinc due to diffusion into the over lying water, which was renewed twice daily. Only when SEM - AVS exceed ed 0 were significant reductions in survival, growth, emergence, and r eproduction observed. Together, the chemical and biological data from this study compare favorably with observations made in short-term expo sures and thus support the use of AVS as a normalization phase for pre dicting toxicity in metal-contaminated sediments.