Ecological risk assessment development

A number of EIA theorists believe in incorporating formal RA methods into EIA as a way to cope with uncertainties, especially in impact prediction where a formal framework for ecological risk assessment (EcoRA) is already developed. It includes three generic phases problem formulation, analysis, and risk characterization followed by risk management. The analysis phase includes an exposure assessment and an ecological effects assessment (see, e.g., US EPA (1998)). 

Ecological risk assessment in EIA is to evaluate the probability that adverse ecological effects will occur as a result of exposure to stressors2 related to a proposed development and the magnitude of these adverse effects (Smrchek and Zeeman, 1998 US EPA, 1998 Demidova, 2002). A lion s share of site-specific EcoRAs were concerned with chemical stressors—industrial chemicals and pesticides. 

Uncertainty analysis is increasingly used in ecological risk assessment and was the subject of an earlier Pellston workshop (Warren-Hicks and Moore 1998). The US Environmental Protection Agency (USEPA) has developed general principles for the use of Monte Carlo methods (USEPA 1997), which provide one of several approaches to incorporating variability and uncertainty in risk assessment. 

The Pellston workshop in February 2002, which produced this book, aimed to develop guidance and increased consensus on the use of uncertainty analysis methods in ecological risk assessment. The workshop focused on pesticides, and used case studies on pesticides, because of the urgent need created by the rapid move to using probabilistic methods in pesticide risk assessment. However, it was anticipated that the conclusions would also be highly relevant to other stressors, especially other contaminants. 

Suter GW II. 1999. Developing conceptnal models for complex ecological risk assessments. Human Ecol Risk Assess 5 375-396. 

The overall ecological risk assessment process is shown in Figure 28.1 and includes three primary phases (1) problem formulation, (2) analysis, and (3) risk characterization. Problem formulation includes the development of a conceptual model... 

Causality is the relationship between cause (one or more stressors) and effect (assessment end point response to one or more stressors). Without a sound basis for linking cause and effect, uncertainty in the conclusions of an ecological risk assessment will be high. Developing causal relationships is especially important for risk assessments driven by observed adverse ecological effects such as fish kills or long-term declines... 

Grapentine, L., Anderson, J., Boyd, D., Burton, G.A., DeBarros, C., Johnson, G., Marvin, C., Milani, D., Painter, S., Pascoe, T., Reynoldson, T., Richman, L., Solomon, K. and Chapman, P.M. (2002) A decision making framework for sediment assessment developed for the Great Lakes, Human and Ecological Risk Assessment 8, 1641-1655. 

The basic features of ecological risk assessment schemes are very similar throughout the world. Usually, one focuses on effects (concentration or dose response information), exposure, and risk characterization. The following paragraphs summarize how extrapolation practices can be developed in such a way that a consistent pattern emerges. 

Whenever appropriate, and in line with the probabilistic concept of risk, probability distributions are used in ecological risk assessment of mixtures. This applies to the assessment of exposure (e.g., the probabilistic application of multimedia fate models see Hertwich et al. 1999 Ragas et al. 1999 MacLeod et al. 2002), as well as to the assessment of effects, especially the SSD approach. Recent developments (both conceptually and practically) suggest that joint probability assessments (looking at exposure and effects distributions simultaneously) are applied more frequently. This relates to the refined questions being posed, but also to theory development (e.g., Aldenberg et al. 2002) and technical facilitation by software (e.g., Van Vlaardingen et al. 2004). 

When it comes to mixtures, an important development is the use of the internal dose as a dose metric, particularly in human assessments. The internal dose is either measured directly or modeled using PBPK models, for example, as a blood or a target tissue concentration. Application of an internal dose metric makes it possible to account for 1) interindividual variability in toxicokinetics, 2) temporal variations in exposure patterns, and 3) interactions between substances during absorption, metabolism, and transport. In ecological risk assessment, internal doses are sometimes measured but rarely modeled with PBPK models. The awareness is growing that the internal dose is a useful metric but the use in formal risk assessment procedures is still limited, for separate compounds as well as for mixtures. 

In both human and ecological risk assessment, there is considerable scientific latitude to develop novel methods (e.g., those that exist in only one of the subdisciplines could be useful in the other one) and to refine approaches (e.g., by considering complex reaction networks and more specific attention for modes of action). The refinements are needed to... 

There are many concepts in use for the assessment of risks or impacts of chemical mixtures, both for human and ecological risk assessment. Many of these concepts are identical or similar in both disciplines, for example, whole mixture tests, (partial) mixture characterization, mixture fractionation, and the concepts of CA and RA (or I A). The regulatory application and implementation of bioassays for uncharacterized whole mixtures is typical for the field of ecological risk assessment. The human field is leading in the development and application of process-based mixture models such as PBTK and BRN models and qualitative binary weight-of-evidence (BINWOE) methods. Mixture assessment methods from human and ecological problem definition contexts should be further compared, and the comparison results should be used to improve methods. 

In both human and ecological risk assessment, there is considerable scientific latitude to develop novel methods (e.g., those that exist in only one of the subdisciplines could be useful in the other one) and to refine approaches (e.g., by considering complex reaction networks and more specific attention for modes of action). The refinements are needed to improve the scientific evidence that is available for underpinning risk assessments. Several key issues in risk assessment of chemical mixtures were identified, that is, exposure assessment of mixtures (e.g., mixture fate and sequential exposure), the concept of sufficient similarity (requires clear criteria), mixture interactions, QSARs, uncertainty assessment, and the perception of mixture risks. Resolving these key issues will significantly improve risk assessment of chemical mixtures. 

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