ANALYSIS OF ACID-VOLATILE SULFIDE (AVS) AND SIMULTANEOUSLY EXTRACTED METALS (SEM) FOR THE ESTIMATION OF POTENTIAL TOXICITY IN AQUATIC SEDIMENTS

Acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) are operationally defined methods for the analysis of sulfide and asso ciated metals in aquatic sediments. The SEM-to-AVS ratio has been usef ul in explaining the results of bioassay tests of metal toxicants. Thi s paper describes apparatus that can be used in the evolution of sulfi de from sediments and a method for the analysis of the evolved sulfide and the liberated metal. The method was studied with respect to gas f low rate, digestion time, and acid concentration. Liberated and trappe d sulfide was determined by a colorimetric method of analysis. Using t he apparatus and conditions described in this paper, the colorimetric method of analysis is capable of detecting AVS at concentrations norma lly encountered with a recovery of sulfide of at least 90%. High preci sion is possible if this apparatus is used. The limit of detection of the method is approximately 0.01 mumol/g dry sediment. We added 6 M HC l to produce a final concentration of approximately 1 M for the releas e of the AVS and SEM from unheated samples. We found that sulfide was not released from pyrite (FeS2) or copper sulfide (CuS) under these co nditions. The liberation of copper from the two studied sediments indi cates that copper was probably associated with another phase in these sediments. AVS is stable for several weeks in refrigerated or frozen s amples.