Nickel toxicity to benthic organisms: The role of dissolved organic carbon, suspended solids, and route of exposure.

Nickel bioavailability is reduced in the presence of dissolved organic carbon (DOC), suspended solids (TSS), and other complexing ligands; however, no studies have examined the relative importance of Ni exposure through different compartments (water, sediment, food). Hyalella azteca and Lymnaea stagnalis were exposed to Ni-amended water, sediment, and food, either separately or in combination. Both organisms experienced survival and growth effects in several Ni compartment tests. The DOC amendments attenuated L. stagnalis Ni effects (survival, growth, and (62)Ni bioaccumulation), and presence of TSS exposures demonstrated both protective and synergistic effects on H. azteca and L. stagnalis. (62)Ni trophic transfer from food to H. azteca and L. stagnalis was negligible; however, bioaccumulating (62)Ni was attributed to (62)Ni-water ((62)Ni flux from food), (62)Ni-TSS, and (62)Ni-food. Overall, H. azteca and L. stagnalis Ni compartment toxicity increased in the following order: Ni-water >> Ni-sediment >> Ni-all (water, sediment, food) >> Ni-food.

Macroinvertebrate responses to nickel in multisystem exposures.

Metals introduced to sediments undergo a variety of complexation and partitioning changes that affect metal bioavailability. Using simultaneously extracted metal (SEM)/acid volatile sulfide (AVS) and organic carbon (f(OC)) models, the authors examined nickel (Ni) toxicity and bioavailability in 2 field studies (using streamside mesocosm and in situ colonization) and 1 laboratory study. The streamside mesocosm experiments indicated that benthic communities (Ephemeroptera, abundance, and taxa richness) responded negatively to increasing SEM(Ni) /AVS and (SEM(Ni) -AVS)/f(OC) models. In the in situ colonization study, taxa richness, abundance, and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa decreased with increasing SEM(Ni) and SEM(Ni)/AVS values. Nickel-spiked sediments were tested in the laboratory with indigenous field-collected mayflies (Anthopotamus verticis, Isonychia spp., and Stenonema spp) and a beetle (Psephenus herricki), and with laboratory-cultured Hyalella azteca and Chironomus dilutus. The amphipod H. azteca was the most sensitive organism tested, and the mayflies Anthopotamus verticis and Stenonema spp. were the most sensitive indigenous organisms to Ni-spiked sediments. These studies help discern which factors are important in determining Ni toxicity and bioavailability at the individual, population, and community levels.

Short-term macroinvertebrate recruitment and sediment accumulation: a novel field chamber approach.

Stream-deposited sediment is one of the major stressors affecting stream biota. Several methods exist to quantify stream sediment embeddedness, but they are relatively qualitative and operationally defined. The authors developed a short-term in situ embeddedness chamber method to measure aquatic insect recruitment and associated sediment accumulation in a more quantitative, better replicated manner. With sediment accumulation and aquatic insect recruitment as endpoints, three exposure periods were evaluated (4, 7, and 14 d) on a low-order stream (Honey Creek, New Carlisle, Ohio, USA) and a medium-order stream (Stillwater River, Covington, Ohio, USA). Chamber results show significant positive correlations between newly deposited fine sediment and insect recruitment. Embeddedness was also measured using the more conventional techniques of the Burns method and the U.S. Geological Survey National Water Quality Assessment Program method. This in situ chamber method allows for increased experimental options for assessing the stress of embeddedness and siltation on benthic communities and may prove useful for investigating the resilience of benthic communities after disturbances.

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.

Isonychia spp. and macroinvertebrate community responses to stressors in streams utilizing the benthic in situ toxicity identification evaluation (BiTIE) method.

Exposures of caged organisms in situ have proven to be a useful way to improve exposure realism and link to stressor effects in aquatic assessments of hazard or risk. A novel cage system, the benthic in situ toxicity identification evaluation (BiTIE), was developed for benthic macroinvertebrates (surrogate species, resident populations and communities) to separate low and high flow effects, and major chemical classes of stressors in streams. Three resin types were used to separate the chemical stressors in the streams Honey Creek and Little Beavercreek, Ohio, USA: Dowex Optipore (non-polar organics), zeolite (ammonia), and polywool (control). Isonychia spp. sensitivity was compared to Chironomus tentans, and no significant differences were found (p>0.05). Isonychia spp. growth (length) showed a stressor response in the zeolite treatments, and community testing revealed improved metric responses in the Dowex treatments. The BiTIE chamber system demonstrated stressor-response relationships using sublethal and multimetric endpoints.

Determining stressor presence in streams receiving urban and agricultural runoff: development of a benthic in situ toxicity identification evaluation method.

Determining toxicity in streams during storm-water runoff can be highly problematic because of the fluctuating exposures of a multitude of stressors and the difficulty of linking these dynamic exposures with biological effects. An underlying problem with assessing storm-water quality is determining if toxicity exists and then which contaminant is causing the toxicity. The goal of this research is to provide an alternative to standard toxicity testing methods by incorporating an in situ toxicity identification evaluation (TIE) approach. A benthic in situ TIE bioassay (BiTIE) was developed for separating key chemical classes of stressors in streams during both low- and high-flow events to help discern between point and nonpoint sources of pollution. This BiTIE method allows for chemical class fractionation through the use of resins, and these resins are relatively specific for removing nonpolar organics (Dowex Optipore), ammonia (zeolite), and polywool (control). Three indigenous aquatic insects, a mayfly (Isonychia spp.), a caddisfly (Hydropsyche spp.), and a water beetle (Psephenus herricki), were placed in BiTIE chambers that were filled with natural substrates. Acute 96-h exposures were conducted at Honey Creek, New Carlisle, Ohio, USA (reference site), and Little Beavercreek, Beavercreek, Ohio, USA (impaired site). At both sites, significant (p < 0.025) stressor responses were observed using multiple species with polywool or no resin (control) treatments exhibiting < 80% survival and resin treatments with >80% survival. The BiTIE method showed stressor-response relationships in both runoff and base flow events during 96-h exposures. The method appears useful for discerning stressors with indigenous species in situ.