Assessments of sediment contamination traditionally have focused on the solid phase and relied on total chemical concentration data versus sediment quality guidelines (SQG) for decision making. More commonly used SQGs are accurate about 70% of the time and vary with the chemical of concern. Effective risk management and remedy selection decisions are unlikely without first characterizing the pathways and compartments responsible for contaminant exposures. Together with the fate and transport of migrating sediment and groundwater contaminants, bioresponses from surficial sediments, upwelling groundwater, and sediment pore-water contaminants; from mobilization of sediment-bound contaminants; and from overlying surface waters need to be assessed. Coupling a suite of laboratory and field physical, chemical, and toxicity screening tools and assays to current Trident and UltraSeep Systems will lead to improved characterization of contaminant exposure and receptor effect linkages. Data from these multiple lines-of-evidence then can be integrated into a weight-of-evidence-based geographic information system (WOE-GIS), providing statistically based rankings of a site’s likely dominant physical and chemical stressors.
The objective of this project was to develop an efficient, accurate, and integrated approach for assessing ecosystem risk and recovery at contaminated sediment sites.
An integrated system—Sediment Ecosystem Assessment Protocol (SEAP)—incorporating rapid in situ hydrological, chemical, biological, and toxicological measurements was developed and tested at three field sites to simultaneously assess these interdependent processes and to better link exposure and effects measures. In situ toxicity and bioaccumulation test systems (SEA Ring system) were incorporated into the existing Trident and UltraSeep Systems (ESTCP project ER-200422). The Trident is a multisensor sediment probe device that is designed to rapidly identify groundwater-surface water (GSI) discharge zones and to sample pore water from these areas. The UltraSeep System provides the ability to directly and continuously quantify GSI discharge rates and collect flow proportional samples to quantify both water and chemical flux. The SEA Ring system allows for multiple species of ecologically relevant organisms to be deployed in three different exposures (overlying water, sediment-water interface, and bulk sediment) for approximately 2-day periods. In addition, passive sampling devices for detecting nonpolar organics and metals are also provided to detect exposures in overlying waters and through near-surface sediment depth profiles. The SEA Ring allowed for measurements of multiple endpoints, ranging from mortality to sublethal effects (e.g., feeding, tissue uptake, embryo development).
The SEAP method is unique. No other in situ systems exist that provide simultaneous exposures to multiple species in multiple exposure compartments and allow for co-existing collection of chemical data from each exposure compartment. The limitations are that it is non-standardized, requires specialized construction, may require a diver in deep waters, and is subject to vandalism and weather disruption.
The three field deployments showed that the integration of various endpoints and measures was useful in characterizing the test sites investigated. Toxicity, bioaccumulation, bulk chemistry, and bioavailability as deemed by pore water concentrations derived from uptake by passive samplers followed the expected gradient at Naval Base San Diego (NBSD) and suggested that hydrophobic organics (i.e., polycyclic aromatic hydrocarbons [PAHs]) might be important stressors, while bulk metals and diffusive gradient in thin film (DGT) concentrations appeared to be of less concern.
At Naval Air Station Pensacola, similar results were observed. However, the Trident and UltraSeep Systems were used to evaluate the potential for groundwater-surface water interactions to be contributing to historically defined effects at the southern end of the water body. Although groundwater was discharging into the surficial sediments, analysis of flow-weighted samples of the discharge revealed little to no chemical contamination associated with the infiltrating groundwater. Bulk chemistry, toxicity, and bioaccumulation, however, pointed to possible PAH-associated toxicity, which could have been exacerbated by ultraviolet photoinduced toxicity, explaining the difference between in situ and laboratory data for the shallow site.
The importance of continuous water quality sensing was clear at the Chollas Creek site, where diurnal drops in dissolved oxygen may have contributed to amphipod toxicity. That site, however, appears to be improving based on lower bulk chemical concentrations and toxicity than previously observed. This could be associated with recent restoration efforts upstream and reduced inputs of organophosphate pesticides, but the potential for temporal and spatial variability of results was noted.
The GIS WOE/weighted logistic regression (WLR) showed that stressor-response hypotheses generated by the spatial analyses can provide insight into the processes influencing local recovery or degradation, and provide guidance for corresponding remedial strategies if deemed necessary. Despite uncertainties in the NBSD study, a WOE/WLR-based ecological assessment of benthic survey and in situ toxicity field data was successfully applied to project data and effectively delineated screening-level stressor hypotheses for use in site management. The study results indicated that ecological risk and associated remediation strategies in the harbor would be best focused on the Chollas and Paleta Creek areas, as the dock area of the inner harbor had comparatively lower levels of risk. For areas with predicted ecological risk, pesticide exposure (represented as cumulative pesticide exposure) generally provided the greatest increase in ecological risk, pointing to this stressor source as a remediation priority.
In summary, the project met the stated objective to develop an efficient, accurate, and integrated approach for the assessment of ecosystem risk and recovery at sites where contaminated sediments exist, or previously existed. The SEA Ring proved quite versatile and was deployed in a wide range of habitats and conditions ranging from the Pacific to the Gulf of Mexico, one to ten meter depths (diverless), oligotrophic to eutrophic, cool to warm, and large to fine grained sediments. The data from the simultaneous exposure and effects measures over a wide range of contamination gradients provided accurate, short-term measures for ecological risk characterizations. These data were incorporated into a GIS WOE/WLR approach that statistically linked site physical and chemical stressors with adverse biological responses. This approach allows site managers to quickly and accurately determine areas of highest risk along with the stressors that may require remediation.
This project lays the foundation for certification of methods and development of a conceptual framework and user’s guide for improving the overall management of contaminated sediment sites. The screening assay approach enables assessment of many stations within a short time frame, and a straightforward, quantitatively based weight-of-evidence approach graphically demonstrates spatial and temporal displays of sediment quality and dominant stressor relationships with ecological risk. This integrated approach is expected to be useful not only for specific groundwater applications, but also for reducing the uncertainty of the risk assessment process by improving the linkage between chemical exposure and adverse biological responses, thus providing an improved decision making process.