Ecological Evaluation Technical Guidance - State of New Jersey

silver, and zinc) that is extracted with the AVS. Recent literature suggests that Hgshould be included with the SEM components (USEPA, 1997c).The AVS present in sediment reacts with the SEM to form insoluble metalsulfides that are significantly less bioavailable for uptake by benthic organismsthan the corresponding free metals. For divalent metals, one mole of SEM willreact with one mole of AVS (although one mole of silver requires two moles ofAVS). Therefore, if the total concentration of AVS is greater than the totalconcentration of SEM, the SEM will likely all be bound as nontoxic metalsulfides. Conversely, if the total concentration of SEM is greater than the AVS,the excess fraction of the metals may exist as bioavailable free metals that couldcontribute to toxicity.Bulk sediment metals concentrations are a poor predictor of potential toxicity.The use of AVS/SEM ratios, along with organic carbon normalization has beenfound to be a better predictor of sediment toxicity. Earlier literature cites the ratioof ∑SEM to AVS (e.g. ∑SEM/AVS). More recent literature, however, expressthe difference between ∑SEM and AVS (e.g. ∑SEM-AVS). The advantages tousing ∑SEM-AVS is that the ratio does not get very large when AVS is very low,and that it can be modified to develop partitioning relationships that include otherphases such as TOC (Di Toro et al., 2005a,b). The use of the newer method ispreferred when evaluating divalent metal toxicity because it takes into account thepresence of TOC on a site-specific level.A recent study has indicated that measurement of AVS and SEM is notreproducible between laboratories (Hammerschmidt and Burton, 2010). Bysending four sediment samples to each of seven independent laboratories,demonstrated that measured concentrations of both AVS and SEM were highlyvariable. Measurement of AVS in the four samples varied between laboratoriesby factors of 70 to 3,500-fold. Measurement of SEM in the four samples variedbetween laboratories by factors of 17 to 60 fold. As a result, the calculation ofAVS/SEM ratios was highly uncertain.The interlaboratory variation in AVS/SEM was attributed to differences in theUSEPA-approved extraction methods (gravimetry, colorimetry, gaschromatographic photoionization, and ion-specific electrochemistry). Variabilitymay also be introduced through sample heterogeneity, and through oxidation ofreduced sulfur species between the times of collection and analysis. In addition,seasonal fluctuations in sediment chemistry can effect AVS/SEM measurements.A follow-up interlaboratory comparison was conducted by Brumbaugh et al.(2011) where AVS and SEM nickel concentrations were measured by fivelaboratories. In this study, the labs were aware of the planned interlaboratorycomparison and they were provided guidance for conducting sample preparation,analysis, and quality control measurements. The results of this study showed thatmeasurements of AVS and SEM-AVS can be reproducible among laboratories,thus emphasizing the need for consistent quality control procedures.While AVS/SEM is a potentially useful tool for assessing bioavailability andassociated toxicity of sediment metals, it should not be used as a stand-alone lineEcological Evaluation Technical Guidance Document 79Version 1.2 8/29/12