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Total and hexavalent chromium [Cr(VI)] were measured in sediment and sediment porewater in the lower Hackensack River (NJ) to assess the relationship between sediment geochemistry and chromium speciation, which in turn controls the mobility, bioavailability, and toxicity of chromium. Between 2003 and 2005, >100 surface (0 to 15 cm) sediment samples were tested for total chromium and Cr(VI), acid-volatile sulfides (AVS), ferrous iron (Fe(II)), divalent manganese (Mn(II)), ammonia, and organic carbon. Sediment porewater samples were collected by centrifugation or using in situ samplers colocated with the collection of sediments. In whole sediments, total chromium and Cr(VI) concentrations ranged from 5 to 9190 mg/kg dry weight (dw) and from <0.47 to 31 mg/kg dw, respectively. Sediment porewater concentrations ranged from <10 to 83 microg/l for total chromium; Cr(VI) was not detected in sediment porewater (n = 78). Concentrations of AVS (ranging between <10.6 to 4178 mg/kg) and other geochemistry measurements indicated anoxic, reducing conditions in the majority of sediment samples. In polychaetes (Nereis virens) and clams (Macoma nasuta) exposed in the laboratory for 28 days to sediments contained between 135 and 1780 mg/kg dw total chromium, concentrations in whole tissues after 24-hour depuration ranged between 1.2 and 14.8 mg/kg wet weight (ww; median 1.6 mg/kg ww) total chromium. In whole tissues of indigenous polychaetes collected from the sediment, tissue concentrations of total chromium ranged between 1.0 and 37.5 mg/kg ww (median = 2.1 mg/kg ww). Chromium concentrations in whole tissues of animals exposed in the field or in the laboratory showed no relationship with total chromium or Cr(VI) concentrations in the sediment. There were no statistical differences among animals exposed to sediments from site and reference locations. The results of this study are consistent with sediment studies conducted elsewhere indicating low chromium bioavailability in sediment under reducing conditions. This study also highlights the importance of sediment geochemistry and in situ porewater measurements to understand the ecological significance of chromium in sediment and the potential for human health and ecological exposures.

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A Sediment Quality Triad (SQT) study consisting of chemical characterization in sediment, sediment toxicity and bioaccumulation testing, and benthic community assessments was performed in the Lower Hackensack River, New Jersey. Chemistry data in sediment and porewater were evaluated based on the equilibrium partitioning approach and other published information to investigate the potential for chemical effects on benthic organisms and communities. Relationships were supported by laboratory toxicity and bioaccumulation experiments to characterize chemical effects and bioavailability. Benthic community results were evaluated using a regional, multimetric benthic index of biotic integrity and four heterogeneity indices. Evidence of slight benthic community impairment was observed in five of nine sediment sample stations. Severe lethal toxicity to amphipods (Leptocheirus plumulosus) occurred in four of these five stations. Although elevated total chromium concentrations in sediment (as high as 1900 mg/kg) were the rationale for conducting the investigation, toxicity was strongly associated with concentrations of polycyclic aromatic hydrocarbons (PAHs) rather than total chromium. PAH toxic units (SigmaPAH TU) in sediment and SigmaPAH concentrations in laboratory organisms from the bioaccumulation experiment showed a clear dose-response relationship with toxicity, with 0% survival observed in sediments in which SigmaPAH TU > 1-2 and SigmaPAH concentrations in Macoma nasuta were >2 micromol/g, lipid weight. Metals detected in sediment and porewater, with the possible exception of copper, did not correlate with either toxicity or levels in tissue, likely because acid-volatile sulfide levels exceeded concentrations of simultaneous extracted metals at all sample locations. The study reinforces the value of using multiple lines of evidence approaches such as the SQT and the importance of augmenting chemical and biological analyses with modeling and/or other approaches to evaluate chemical bioavailability and toxicity of sediments.