Assessing sediment recontamination from metals in stormwater.

Recontamination of sediments by stormwater is a major concern when evaluating the potential effectiveness of sediment remediation. Stormwater and sediment sampling were conducted in a mixed-use watershed at Paleta Creek in San Diego, CA to evaluate methods for assessing sediment recontamination by metals. Size-segregated stormwater contaminant loads with simultaneous receiving water and sediment measurements were used to identify dominant sources and contaminants with respect to their impact on sediment recontamination. Most of the stormwater contaminant loads of Cd, Cu, Pb, and Zn were associated with residential and highway sources from the upstream portions of the watershed and As, Ni and Hg were more significantly influenced by the downstream area of the watershed. Cd was strongly associated with large particles (>63 µm) and observed to settle in near shore areas with some attenuation due to mixing and dilution. Cu, in contrast, was associated more with the filtered fraction (<0.45 µm) and clay fraction (0.45-5 µm), resulting in less near shore sediment recontamination. Depositing sediment and other metals, particularly Cu and Hg, exhibited greater accumulation in settling traps than could be attributed to stormwater loads indicating the importance of other sources or resuspension of bay sediments on surficial sediment concentrations. Pb, Zn, Ni, and As showed influences of both stormwater and other sources. The study showed that measurement of size-segregated stormwater contaminant mass and concentrations combined with simultaneous measurements of deposition in sediment traps could differentiate between recontamination by stormwater and that of other sources.

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.

Review of thin-layer placement applications to enhance natural recovery of contaminated sediment.

This article provides a review of thin-layer placement applications to enhance the natural recovery of contaminated sediment. Three principal case studies are presented in which thin-layer placement has been implemented as a component of enhanced monitored natural recovery (EMNR). EMNR is defined as the application of engineered means such as thin-layer placement or broadcasting of capping material to accelerate natural recovery processes in locations not appropriate for application of monitored natural recovery (MNR) alone. Case studies examine factors affecting the implementation of EMNR, including the impact of site conditions on stable and successful thin-layer placement of clean sediment or other capping material, as well as the challenges in development and implementation of monitoring plans that chart progress toward achieving remedy success. Pilot-scale or demonstration studies of thin-layer placement of clean sand or sediment are subsequently assessed to highlight a range of potentially successful strategies for placement and post-placement monitoring. The primary difference between the pilot-scale or demonstration sites and the 3 primary EMNR case studies is that monitoring at the demonstration sites has focused more explicitly on understanding mechanisms of material placement and/or chemical migration, rather than assessing longer-term or more comprehensive remedial action objectives (RAOs) such as reductions in human health or ecological risk. All sites discussed in this review appear to have demonstrated reductions in the surface sediment concentration of at least some chemicals of concern following thin-layer placement; however, the achievement of human and ecological risk reduction has been inconsistent or is still under evaluation. Effective monitoring as an integral component of EMNR continues to represent a challenge. For cap material stability, monitoring typically focuses on surface sediment chemistry and the persistence of the cap material, whereas monitoring of ecological recovery tends to be limited or difficult and is not always correlated with successful placement of the thin-layer, especially in the short term. Recontamination of the newly placed cap material has been a relatively common occurrence in many of the sites considered herein, and has led to exceedance of remedial targets. However, in no case did recontamination return surface sediment chemical concentrations to pre-placement levels. Where the placement of cap material is stable and there is no evidence of chemical migration through the cap, recontamination signals a need to update conceptual site models to better reflect sediment and contaminant transport processes in areas in which EMNR has been implemented.

Critical tissue copper residues for marine bivalve (Mytilus galloprovincialis) and echinoderm (Strongylocentrotus purpuratus) embryonic development: conceptual, regulatory and environmental implications.

Critical tissue copper (Cu) residues associated with adverse effects on embryo-larval development were determined for the Mediterranean mussel (Mytilus galloprovincialis) and purple sea urchin (Strongylocentrotus purpuratus) following laboratory exposure to Cu-spiked seawater collected from San Diego Bay, California, USA. Whole body no-observed-effect-residues (NOER) were similar, with means of 21 and 23 microg g(-1) dw, for M. galloprovincialis and S. purpuratus, respectively. Mean whole body median effect residues (ER50) were 49 and 142 microg g(-1) dw for M. galloprovincialis and S. purpuratus, respectively. The difference in ER50s between species was reduced to a factor of <2 when expressed as soft tissue residues. Coefficients of variation among whole body-ER50s were 3-fold lower than median waterborne effect concentrations (EC50) for both species exposed to samples varying in water quality characteristics. This suggests that tissue concentrations were a better predictor of toxicity than water concentrations. The CBRs described herein do not differentiate between the internal Cu concentrations that are metabolically available and those that are accumulated and then detoxified. They do appear, however, to be well enough related to the level of accumulation at the site of action of toxicity that they serve as useful surrogates for the copper concentration that affects embryonic development of the species tested. Results presented have potentially important implications for a variety of monitoring and assessment strategies. These include regulatory approaches for deriving saltwater ambient water quality criteria for Cu, contributions towards the development of a saltwater biotic ligand model, the conceptual approach of using CBRs, and ecological risk assessment.

Effects of dissolved and complexed copper on heterotrophic bacterial production in San Diego bay.

Bacterial abundance and production, free (uncomplexed) copper ion concentration, total dissolved copper concentration, dissolved organic carbon (DOC), total suspended solids (TSS), and chlorophyll a were measured over the course of 1 year in a series of 27 sample "Boxes" established within San Diego Bay. Water was collected through a trace metal-clean system so that each Box's sample was a composite of all the surface water in that Box. Bacterial production, chlorophyll a, TSS, DOC, and dissolved copper all generally increased from Box 1 at the mouth of the Bay to Box 27 in the South or back Bay. Free copper ion concentration generally decreased from Box 1 to Box 27 presumably due to increasing complexation capacity within natural waters. Based on correlations between TSS, chlorophyll a, bacterial production or DOC and the ratio of dissolved to free Cu ion, both DOC and particulate (bacteria and algae) fractions were potentially responsible for copper complexation, each at different times of the year. CuCl2 was added to bacterial production assays from 0 to 10 microg L(-1) to assess acute copper toxicity to the natural microbial assemblage. Interestingly, copper toxicity appeared to increase with decreases in free copper from the mouth of the Bay to the back Bay. This contrasts the free-ion activity model in which higher complexation capacity should afford greater copper protection. When cell-specific growth rates were calculated, faster growing bacteria (i.e. toward the back Bay) appeared to be more susceptible to free copper toxicity. The protecting effect of natural dissolved organic material (DOM) concentrated by tangential flow ultrafiltration (>1 kDa), illite and kaolinite minerals, and glutathione (a metal chelator excreted by algae under copper stress) was assessed in bacterial production assays. Only DOM concentrate offered any significant protection to bacterial production under increased copper concentrations. Although the potential copper protecting agents were allowed to interact with added copper before natural bacteria were added to production assays, there may be a temporal dose-response relationship that accounts for higher toxicity in short production assays. Regardless, it appears that effective natural complexation of copper in the back portions of San Diego Bay limits exposure of native bacterial assemblages to free copper ion, resulting in higher bacterial production.

Use of laboratory toxicity tests with bivalve and echinoderm embryos to evaluate the bioavailability of copper in San Diego Bay, California, USA.

Copper concentrations in parts of San Diego Bay (CA, USA) exceed ambient water quality criteria (WQC; currently 3.1 microg/L dissolved, U.S. Environmental Protection Agency [U.S. EPA]). In order to better understand the bioavailability of copper to water-column organisms in the bay, toxicity tests were performed with copper added to surface water collected from various sites in the estuary over a three-year period. The species and endpoints used, bivalve and echinoderm embryo-larval development, are among the most sensitive in the U.S. EPA's national toxicity dataset, which is used to derive WQC. No toxicity was observed in ambient bay water samples, as indicated by high proportions of normally developed larvae in control treatments, averaging 93+/-5% across all sites and all sampling events. Median effects concentrations (EC50), obtained by copper spiking of ambient water samples, ranged from 1.7 to 3.4 times lower at sites located near the mouth compared to sites near the back of the bay. These data indicate a gradient in complexation capacity increasing from the mouth to the back of the bay, which is consistent with similar trends in dissolved organic carbon and total suspended solids. For the bay as a whole, estimates for total recoverable and dissolved water-effect ratios (WER) ranged from 2.07 to 2.27 and 1.54 to 1.67, respectively. Water-effect ratios of this magnitude suggest that adoption of a somewhat higher site-specific WQC for San Diego Bay still would achieve the level of protection that is intended by the WQC guidelines.