An Approach to Quantifying Spatial Components of Exposure for Ecological Risk Assessment

Abstract

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.

The Potential for the Use of Agent-Based Models in Ecotoxicology

“…As shown earlier there are indications that the magnitude and effect of pesticide exposure on populations are influenced by the spatial structure of contamination in the landscape and habitat location [53][54][55]. Even so, the use of nonspatial approaches is still common when characterizing exposures and effects of pesticide stresses.…”

Developing a Field of Landscape Ecotoxicology

“…Other spatially explicit models have been developed by integrating models of agricultural nonpoint-source pollution with the GIS, which locates relevant physical features of watersheds for investigating the ecological consequences of various farming practices (e.g., Brusven and Walker 1995). Clifford et al (1995) integrated maps of dieldrin contamination in soils at a Superfund site, tissue concentrations, and food-web information to estimate exposure across the foraging range for various organisms. These spatially and temporally weighted exposures were compared to benchmark concentrations to derive spatially explicit estimates of risk.…”

An approach for estimating ecological risks from organochlorine pesticides to terrestrial organisms at rocky mountain arsenal

“…Thus, the co-located distributions procedure is an excellent predictor of what was actually observed, and the resultant BAFs do not, therefore, contribute substantially to assessment uncertainty. Besides BAF, uncertainty was identified (but not quantified) for a number of the RMA risk assessment components (Clifford et al, 1995). In general, Clifford et al (1995) found that the risk assessment analysis was not biased or likely to greatly affect the validity of quantitative or qualitative conclusions.…”

“…Hum The extrapolation methodology deemed most appropriate for the assignment of soil concentration values for the heterogeneously contaminated environment of RMA was the Thiessen (also known as Vbronoi) polygon technique [for details see Clifford et al (1995)]. This procedure utilized Geographic Information Systems software (Environmental Systems Research Institute, 1989) to divide the site into a mutually exclusive and collectively exhaustive set of polygons such that each polygonal region contains a single sample value.…”