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 anoxic sediments, environmentally active fractions of sulfide and associated metals are defined operationally as acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM). Ratios of these chemical parameters are often used in establishing equilibrium partitioning sediment benchmarks for toxicity and, therefore, require analytical accuracy to be useful. To investigate the reproducibility and accuracy of AVS and SEM measurements, we distributed subsamples of four physicochemically disparate stream sediments to seven independent laboratories, including our own, for analysis of both AVS and SEM (Cd, Cu, Pb, Ni, and Zn). Synthesis of these results shows that AVS varied from 70 to 3,500x and SEM ranged from 17 to 60x among laboratories for each of the four sediments. Inadequate detection limits for AVS precluded calculation of SEM:AVS ratios for two of the deposits, whereas the ratio varied more than 50-fold among laboratories for the other two sediments. This work highlights the need for improved quality control and standardization of methods for determination of AVS and SEM in sediments, and suggests that predictions of metal toxicity in sediments can be laboratory specific, which raises concerns on the use of the AVS:SEM model for risk assessments and regulatory decisions.

Performance and sensitivity of rapid sublethal sediment toxicity tests with the amphipod Melita plumulosa and copepod Nitocra spinipes

“…However, during the tests the 1 to 3 mm surface layer of the sediments were observed to become light brown in color, compared to the grayer color of the sediments beneath, indicating that oxygen in the overlying water was most likely causing the oxidation of AVS in the surface layer. While it is recognized that the AVS concentrations in sediments can vary considerably and that all methods are subject to analytical artifacts [38], the rapid AVS method used in the present study was more likely to partially underestimate rather than overestimate the amount of AVS in the samples [30]. Although most metal sulfide phases oxidize more slowly than the iron and manganese sulfides, which are expected to make up the bulk of the AVS [39], we have determined previously that much of the AVS in the surface sediment may be oxidized during 10-d toxicity tests (Stuart Simpson, CSIRO, unpublished results).…”

Copper Sediment Toxicity and Partitioning during Oxidation in a Flow-Through Flume

“…14,15 Sulfide was determined colorimetrically 14 and Cu SEM was measured by ICP−MS. Oxidized Fe (amorphous and crystalline) and associated Cu was measured with selective extractions.…”

The Application of Solar Cells in the Electrokinetic Remediation of Metal Contaminated Sediments

“…Therefore, in this paper we determined the contents of the acid-volatile sulphide and simultaneously extracted metals. AVS is considered an important factor in affecting the bioavailability of most divalent metals having a high affinity with sulphides (Allen et al, 1993;Peng et al, 2009;Hammerschmidt and Burton, 2010;Hou et al, 2013), and R [SEM] is often used as a proxy for prediction of trace metal toxicity in the sedimentary environment (Di Toro et al, 1992;Lee et al, 2000;Teuchies et al, 2013). Experimental studies have revealed that there are no adverse effects or impacts on organisms when R [SEM] / [AVS] , 1.…”