To examine equilibrium‐partitioning model predictions of interstitial water concentrations of fluoranthene as part of the equilibrium‐partitioning (EqP) approach to sediment quality criteria development, the bioavailability (toxicity) of fluoranthene‐amended sediment (a nonpolar organic compound) to Hyalella azteca, Daphnia magna, and Chironomus tentans was determined. Fluoranthene was added to three freshwater sediments with similar organic carbon content (0.44‐0.50%). Although sediments were from divergent sources (Water Research Field Station [WRFS], Trinity River [TR], and Lake Fork [LF]), sediment physical and chemical characteristics did not vary appreciably, leading us to hypothesize (based on EqP theory) that fluoranthene‐amended sediment toxicity would not vary between sediments. Predicted interstitial water concentrations from the equilibrium‐partitioning model were similar to measured interstitial water concentrations for WRFS and TR sediment, but the model underpredicted measured values for LF sediment by a factor of two. EC50s for Daphnia magna, Hyalella azteca, and Chironomus tentans in interstitial water were a factor of two to five greater for LF than for WRFS and TR sediments. Factors other than organic carbon content of sediments (e.g., dissolved organic carbon content in interstitial water) probably contributed to the variability in bioavailability of fluoranthene. Based on 10‐d sediment toxicity tests with Hyalella azteca, Daphnia magna, and Chironomus tentans, organic carbon‐normalized sediment concentrations were better predictors of toxicity than interstitial water and bulk sediment fluoranthene concentrations. In 10‐d aqueous‐phase tests with fluoranthene, Chironomus tentans and Hyalella azteca were twice as sensitive as Daphnia magna. The response of freshwater organisms to fluoranthene‐amended sediment was similar to that of marine organisms exposed to fluoranthene in other studies. The EqP approach for sediment‐quality criteria accurately predicted sediment toxicity for WRFS and TR sediments but not for LF sediment, indicating the model may be overly protective for some bottom sediments. Factors other than organic carbon content may be important in affecting neutral organic compound bioavailability.

Estimating ecological risks associated with contaminants in the environment requires accurate characterization of the exposure of organisms to potentially toxic materials. Because organisms integrate contaminant exposure over space and time, estimating exposure concentrations reflective of actual exposures is a complex task. Quantification of spatial components of environmental exposure can utilize computerized Geographic Information Systems (GIS) as a central tool. The GIS was used to evaluate ecological risks to terrestrial receptors at a National Priorities List (NPL) site where dieldrin was one of the contaminants. The CIS was applied directly to estimating spatially weighted exposure concentrations within organisms' foraging, or exposure ranges. Moreover, CIS was also used for comparing exposure concentrations to "benchmark" concentrations and subsequent presentation of the results in a three-dimensional "risk surface" format. The three-dimensional risk surfaces were then superimposed on site-specific maps to serve as effective visual representations of site-specific quantified ecological risks and, as such, provide an effective risk-management decision-making tool. As an integral part of this approach, GIS serves as an interactive tool for assessing the effectiveness of proposed remedial alternatives by facilitating evaluation of effects of various remediation scenarios. This capability can be used to optimize remedial costs, benefits, and impacts.

Estimating ecological risks associated with contaminants in the environment requires accurate characterization of the exposure of organisms to potentially toxic materials. Because organisms integrate contaminant exposure over space and time, estimating exposure concentrations reflective of actual exposures is a complex task. Quantification of spatial components of environmental exposure can utilize computerized Geographic Information Systems (GIS) as a central tool. The GIS was used to evaluate ecological risks to terrestrial receptors at a National Priorities List (NPL) site where dieldrin was one of the contaminants. The GIS was applied directly to estimating spatially weighted exposure concentrations within organisms' foraging, or exposure ranges. Moreover, GIS was also used for comparing exposure concentrations to “benchmark” concentrations and subsequent presentation of the results in a three‐dimensional “risk surface” format. The three‐dimensional risk surfaces were then superimposed on site‐specific maps to serve as effective visual representations of site‐specific quantified ecological risks and, as such, provide an effective risk‐management decision‐making tool. As an integral part of this approach, GIS serves as an interactive tool for assessing the effectiveness of proposed remedial alternatives by facilitating evaluation of effects of various remediation scenarios. This capability can be used to optimize remedial costs, benefits, and impacts.

No abstract

Ecological risk assessment for bioaccumulative chemicals at hazardous waste sites like Rocky Mountain Arsenal (RMA) is challenging, particularly when the site is large and is characterized by heterogeneous environments and patterns of contamination. Because RMA is an National Priorities List site and a future wildlife refuge, an effective and practical risk assessment approach was required. This approach includes methods to estimate contaminant concentrations below detection limits, spatial and temporal integration, bioaccumulation, and toxicity criteria. Validation of the quantitative risk assessment approach was achieved through comparisons of observed versus predicted tissue concentration values, as well as evaluation of ecological endpoints relative to wildlife health. The results of the assessment based on this approach provide a realistic representation of observed conditions at RMA, and provide quantitative conclusions that are consistent with qualitative observations of the health and diversity of biota at RMA. In addition to supporting baseline risk assessment, the approach provides a useful framework for evaluation of future risk management alternatives.

No abstract

No abstract