Measurements of acid volatile sulfide and simultaneously extracted metals are irreproducible among laboratories

Abstract

Partitioning with solid phases is a principal control on availability and associated toxicity of metals to aquatic biota. In anoxicsediments, environmentally active fractions of sulfide and associated metals are defined operationally as acid-volatile sulfide (AVS) andsimultaneously extracted metals (SEM). Ratios of these chemical parameters are often used in establishing equilibrium partitioningsediment benchmarks for toxicity and, therefore, require analytical accuracy to be useful. To investigate the reproducibility and accuracyof AVS and SEM measurements, we distributed subsamples of four physicochemically disparate stream sediments to seven independentlaboratories, including our own, for analysis of both AVS and SEM (Cd, Cu, Pb, Ni, and Zn). Synthesis of these results shows that AVSvaried from 70 to 3,500× and SEM ranged from 17 to 60× mong laboratories for each of the four sediments. Inadequate detection limitsfor AVS precluded calculation of SEM:AVS ratios for two of the deposits, whereas the ratio varied more than 50-fold among laboratoriesfor the other two sediments. This work highlights the need for improved quality control and standardization of methods for determinationof AVS and SEM in sediments, and suggests that predictions of metal toxicity in sediments can be laboratory specific, which raisesconcerns on the use of the AVS:SEM model for risk assessments and regulatory decisions. © 2010 SETAC.