VOLATILE SULFIDES AND THEIR TOXICITY IN FRESH-WATER SEDIMENTS

Three forms of volatile sulfides (free hydrogen sulfide, acid-volatile sulfides [AVS] and a new form, heat-volatile sulfides [HVS]), were me asured and their relationships discussed. Purging of some contaminated sediments with nitrogen at 22-degrees-C failed to remove all of the f ree H2S, even after 6h. With freshly H2S-spiked uncontaminated sedimen t, purging of H2S was complete after 2 h; however, if the spiked sedim ent was allowed to stand for 53 d, H2S continued to be purged, even af ter 43 h. The H2S likely originates from equilibrium reactions involvi ng reduced sulfur species in the sediment. Uncontaminated sediment spi ked with H2S was found to be highly toxic using a sediment-contact bio assay employing Photobacterium phosphoreum. Addition of Fe3+, which se questers the S2-, reduced the toxicity. Two other bioassays (ATP-TOX a nd Toxi-Chromotest), both involving a DMSO/methanol extract of the spi ked sediment, showed greatest toxicity with spiked sediment that had b een standing for 22 d. The results indicate that reduced sulfur specie s in sediment may be a cause of toxicity observed in contaminated anox ic sediments.