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  • Title: Evaluating the performance of diffusive gradients in thin films for predicting Ni sediment toxicity.
    Author: Costello DM, Burton GA, Hammerschmidt CR, Taulbee WK.
    Journal: Environ Sci Technol; 2012 Sep 18; 46(18):10239-46. PubMed ID: 22891754.
    Abstract:
    Diffusive gradients in thin films (DGTs) rapidly measure labile fractions of metal and are promoted as an assessment tool for bioavailability. Using macroinvertebrate community composition as a response, this study compared the predictive ability of DGT-measured Ni with acid volatile sulfide (AVS) and organic carbon (OC) corrected Ni [(SEM(Ni)-AVS)/f(OC)] and total Ni concentrations. In two experiments, sediments were amended with Ni and placed within either a streamside mesocosm or deployed in situ. DGT-measured Ni concentrations (C(DGT)) increased with increasing total Ni, were greater at depth, and decreased over time. Relationships between Ni C(DGT) and sediment geochemistry indicated a shift in Ni partitioning from AVS-bound to Fe- and Mn-associated Ni. In both experiments, DGT-measured Ni poorly predicted the invertebrate response to metal, whereas models that included total Ni or (SEM(Ni)-AVS)/f(OC) effectively predicted the invertebrate response for the streamside mesocosm and in situ experiments, respectively. C(DGT) overestimated the available Ni fraction, possibly due to sampling either nonbioavailable solid-phase Ni or Ni irrespective of cations competing at the biotic ligand. We suggest that C(DGT) cannot replace (SEM(Ni)-AVS)/f(OC) for predicting invertebrate response to sediment Ni, and greater understanding of metal species lability to DGTs is needed before assuming equivalence between bioavailable and DGT-labile metals in sediments.
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