Dietary assimilation of cadmium associated with bacterial exopolymer sediment coatings by the estuarine amphipod \u3cem\u3eLeptocheirus plumulosus\u3c/em\u3e: effects of Cd concentration and salinity

Bacterial extracellular substances (also known as exopolysaccharides, or EPS) may serve as vectors for trophic transfer of metals in benthic systems because these ubiquitous sediment coatings can sorb high concentrations of toxic metals, and because many benthic invertebrates assimilate EPS sediment coatings upon ingestion. We conducted 3 sets of experiments to determine the assimilative bioavailability of EPS-associated Cd to the benthic amphipod Leptocheirus plumulosus as a function of Cd concentration and salinity. Bioavailability was measured as L. plumulosus Cd assimilation efficiency (AE) from EPS-coated silica (EPS●Si) and from uncoated silica (NC●Si) using modified pulse-chase methods with the gamma-emitting radioisotope 109Cd. Cd AE was significantly greater from NC●Si than from EPS●Si at 7.5%, but not at 2.5 or 25%. Overall, Cd AE from EPS●Si was between 15.1 and 21.5%. Because EPS●Si sorbed more Cd than NC●Si, EPS coatings magnified the amount of Cd amphipods accumulated at each salinity by up to a factor of 10. Salinity did not directly affect Cd AE from EPS●Si, but because Cd●EPS partitioning increased with decreasing salinity, amphipods accumulated more Cd from EPS at the lowest Cd●EPS incubation salinity (2.5%) than at higher salinities (7.5 and 25%). Finally, Cd concentration in EPS exhibited an inverse relationship with Cd AE at 2.5%, but not at 25%. Specifically, Cd AE was 12 times greater at 1 compared with 10µg Cd µg-1 EPS. Together, these results show that estuarine benthos can accumulate Cd from EPS sediment coatings, but that the degree to which this phenomenon occurs is dependent upon seawater salinity and Cd concentration in EPS

Development of a bioavailability‐based risk assessment approach for nickel in freshwater sediments

To assess nickel (Ni) toxicity and behavior in freshwater sediments, a large‐scale laboratory and field sediment testing program was conducted. The program used an integrative testing strategy to generate scientifically based threshold values for Ni in sediments and to develop integrated equilibrium partitioning‐based bioavailability models for assessing risks of Ni to benthic ecosystems. The sediment testing program was a multi‐institutional collaboration that involved extensive laboratory testing, field validation of laboratory findings, characterization of Ni behavior in natural and laboratory conditions, and examination of solid phase Ni speciation in sediments. The laboratory testing initiative was conducted in 3 phases to satisfy the following objectives: 1) evaluate various methods for spiking sediments with Ni to optimize the relevance of sediment Ni exposures; 2) generate reliable ecotoxicity data by conducting standardized chronic ecotoxicity tests using 9 benthic species in sediments with low and high Ni binding capacity; and, 3) examine sediment bioavailability relationships by conducting chronic ecotoxicity testing in sediments that showed broad ranges of acid volatile sulfides, organic C, and Fe. A subset of 6 Ni‐spiked sediments was deployed in the field to examine benthic colonization and community effects. The sediment testing program yielded a broad, high quality data set that was used to develop a Species Sensitivity Distribution for benthic organisms in various sediment types, a reasonable worst case predicted no‐effect concentration for Ni in sediment (PNECsediment), and predictive models for bioavailability and toxicity of Ni in freshwater sediments. A bioavailability‐based approach was developed using the ecotoxicity data and bioavailability models generated through the research program. The tiered approach can be used to fulfill the outstanding obligations under the European Union (EU) Existing Substances Risk Assessment, EU Registration, Evaluation, Authorisation, and Regulation of Chemicals (REACH), and other global regulatory initiatives. Integr Environ Assess Manag 2016;12:735–746. © 2015 SETACKey PointsA comprehensive, representative sediment toxicity database is available to support risk assessment of Ni in freshwater sediments.Sediment Ni ecotoxicity data were gathered from studies that used spiking approaches that resulted in Ni‐enriched sediments resembling naturally contaminated sediments, thus increasing their relevance.Bioavailability of Ni in sediments, which is controlled by acid volatile sulfides (AVS), varies among different species, with actively bioturbating species showing a lower slope in the relationship between decreasing toxicity with increasing AVS.A bioavailability‐based, tiered approach is presented, where the first tier involves comparison of ambient total Ni concentrations with a RWC threshold value of 136 mg Ni/kg. Site‐specific AVS can be used to calculate a site‐specific threshold if ambient Ni is greater than 136 mg Ni/kg.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134197/1/ieam1720.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134197/2/ieam1720_am.pd

A review of nickel toxicity to marine and estuarine tropical biota with particular reference to the South East Asian and Melanesian region

The South East Asian Melanesian (SEAM) region contains the world\u27s largest deposits of nickel lateritic ores. Environmental impacts may occur if mining operations are not adequately managed. Effects data for tropical ecosystems are required to assess risks of contaminant exposure and to derive water quality guidelines (WQG) to manage these risks. Currently, risk assessment tools and WQGs for the tropics are limited due to the sparse research on how contaminants impact tropical biota. As part of a larger project to develop appropriate risk assessment tools to ensure sustainable nickel production in SEAM, nickel effects data were required. The aim of this review was to compile data on the effects of nickel on tropical marine, estuarine, pelagic and benthic species, with a particular focus on SEAM. There were limited high quality chronic nickel toxicity data for tropical marine species, and even fewer for those relevant to SEAM. Of the data available, the most sensitive SEAM species to nickel were a sea urchin, copepod and anemone. There is a significant lack of high quality chronic data for several ecologically important taxonomic groups including cnidarians, molluscs, crustaceans, echinoderms, macroalgae and fish. No high quality chronic nickel toxicity data were available for estuarine waters or marine and estuarine sediments. The very sparse toxicity data for tropical species limits our ability to conduct robust ecological risk assessment and may require additional data generation or read-across from similar species in other databases (e.g. temperate) to fill data gaps. Recommendations on testing priorities to fill these data gaps are presented