Evaluating the performance of diffusive gradients in thin films for predicting Ni sediment toxicity.

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.

A sediment ecotoxicity assessment platform for in situ measures of chemistry, bioaccumulation and toxicity. Part 1: System description and proof of concept.

In situ-based testing using aquatic organisms has been widely reported, but is often limited in scope and practical usefulness in making decisions on ecological risk and remediation. To provide this capability, an integrated deployment system, the Sediment Ecotoxicity Assessment (SEA) Ring was developed, which incorporates rapid in situ hydrological, chemical, bioaccumulation, and toxicological Lines-of-Evidence (LoE) for assessing sediment and overlying water contamination. The SEA Ring system allows for diver-assisted, or diverless, deployment of multiple species of ecologically relevant and indigenous organisms in three different exposures (overlying water, sediment-water interface, and bulk sediment) for periods ranging from two days to three weeks, in a range of water systems. Measured endpoints were both sublethal and lethal effects as well as bioaccumulation. In addition, integrated passive sampling devices for detecting nonpolar organics (solid phase micro-extraction fibers) and metals (diffusive gradients in thin films) provided gradient measures in overlying waters and surficial sediments.

A sediment ecotoxicity assessment platform for in situ measures of chemistry, bioaccumulation and toxicity. Part 2: Integrated application to a shallow estuary.

A comprehensive, weight-of-evidence based ecological risk assessment approach integrating laboratory and in situ bioaccumulation and toxicity testing, passive sampler devices, hydrological characterization tools, continuous water quality sensing, and multi-phase chemical analyses was evaluated. The test site used to demonstrate the approach was a shallow estuarine wetland where groundwater seepage and elevated organic and inorganic contaminants were of potential concern. Although groundwater was discharging into the surficial sediments, little to no chemical contamination was associated with the infiltrating groundwater. Results from bulk chemistry analysis, toxicity testing, and bioaccumulation, however, suggested possible PAH toxicity at one station, which might have been enhanced by UV photoactivation, explaining the differences between in situ and laboratory amphipod survival. Concurrently deployed PAH bioaccumulation on solid-phase micro-extraction fibers positively correlated (r(2) ≥ 0.977) with in situ PAH bioaccumulation in amphipods, attesting to their utility as biomimetics, and contributing to the overall improved linkage between exposure and effects demonstrated by this approach.

Effects of suspended solids and dissolved organic carbon on nickel toxicity.

Nickel (Ni) is a common and potentially toxic heavy metal in many fluvial ecosystems. We examined the potentially competitive and complementary roles of suspended sediment and a dissolved organic ligand, humate, in affecting the partitioning and toxicity of Ni to a model organism, Daphnia magna, in both batch and stream-recirculating flume (SRF) tests. Sediments included a fine-grained deposit, montmorillonite, and kaolinite. Survival of D. magna was unaffected by the range of suspended solids used in the present study (8-249 mg/L). However, exposure to suspended solids that were amended with Ni had a deleterious effect on test organism survival, which is attributed to partitioning of Ni into the aqueous phase. At comparable levels of dissolved Ni, survival of D. magna was reduced in tests with Ni-amended suspended solids compared to Ni-only aqueous exposures, suggesting potentiation between these two aquatic contaminants. Addition of humate attenuated toxicity to D. magna in both Ni-only and Ni-amended suspended sediment exposures. These results indicate that organic ligands and suspended solids have important functions in affecting the bioavailability and toxicity of Ni to aquatic organisms and should be incorporated into predictive models to protect ecosystem quality.