Ecological risk assessment is the evaluation of the likelihood that adverse ecological effects result from exposure to one or more chemical or physical agents. Risk assessments are commonly used to support decisions about remediating spills or other contamination on closed or operating exploration and production (E&P) sites and refinery lands, and they may also be employed to site new infrastructure. In addition, risk assessments are a useful way to organise information and disclose effects to the public. (1) Most frameworks for ecological risk assessment include four stages:
- problem formulation;
- characterisation of exposure;
- characterisation of effects; and
- risk characterisation.
The US Environmental Protection Agency (USEPA) framework for ecological risk assessment (2) is depicted in Figure 1. The problem formulation is the planning stage of risk assessment, which entails a description of stressors (e.g. chemicals), assessment endpoints (valued ecological entities that are to be protected, e.g. plant production, wildlife population abundance), the spatial and temporal scope of assessment and a conceptual model of exposure pathways. The characterisation of exposure is the stage in which chemical concentrations or areas of disturbed land in the past, present or future are measured or modelled. The characterisation of effects can include doseresponse models, toxicity test results, ecological population model results or other exposure-response relationships. The risk characterisation is the stage in which the characterisations of exposure and effects are integrated and summarised, risk is estimated and uncertainties are calculated and discussed. Measurement methods and models for conducting risk assessments at contaminated sites have previously been published, (1) but risk assessment at petroleumcontaminated sites raises issues that necessitate the development of additional tools.
Figure 1: USEPA Ecological Risk Assesment Framework
- Measured levels of contamination may not correspond to bioavailable levels, and laboratory toxicity tests conducted with freshly added mixtures or single chemicals may not represent the toxicity of aged (weathered) mixtures of chemicals in the field.
- Population ecology may be more important than toxicology (the traditional basis of ecological risk assessment) in determining risk to wildlife.
- Habitat loss from physical stressors (e.g. brine scars, roads, wells) may be more important than toxicity from chemicals.
- Detailed, definitive ecological risk assessments may not be feasible for large tracts of land that have little contamination.
- Risk management may benefit from the consideration of relative net environmental advantages of ecological restoration and remediation.
Researchers at Oak Ridge National Laboratory (ORNL) and elsewhere have developed new tools for ecological risk assessment that are applicable at E&P sites, as well as many ‘downstream’ (i.e., refinery and pipeline) sites. Much of this work has been funded by the US Department of Energy National Petroleum Technology Office and has been undertaken in collaboration with the Petroleum Environmental Research Forum (www.perf.org).
In this article, some of the recent advances in ecological risk assessment tools for petroleum-contaminated sites are described, including general notions of bioavailability and plant uptake models for hydrocarbons and metals, wildlife population models that incorporate habitat disturbance and trophic relationships. Also discussed are ecotoxicity benchmarks and critical (habitat) patch size values, and a framework for net environmental benefit analysis.
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Environment
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