Understanding the Relationship between Exposure and Effects

A key element in decision making will be to understand the relationship between the level of chemical exposure and the consequent risks to health or the environment. There are two main ways in which we can understand this relationship through the species sensitivity distribution (SSD) or the dose-response curve. The SSD is perhaps the more useful for environmental assessment because it integrates all species, whereas the dose response describes the cause-effect relationship for only one species. Nevertheless, the dose-response relationship could be a valuable tool for environmental assessment when the species described is either particularly sensitive, 

Environmental and Human Health Standards for Water and Soil 

FIGURE 2.3 Multicriteria decision analysis for assessing options for an environmental standard. 

MCDA allows the costs and practicality of meeting a standard to be accommodated in the final decision. This can be achieved by identifying the technological options for mitigating exposure, each of which would be associated with a different standard. They could include not only a do nothing option but also the application of different technologies or assumptions about the benefits that would follow from adopting best practice in some or all industry sectors. This may require stakeholder input to help focus attention on the most feasible abatement options. A preliminary analysis may usefully be shared with stakeholders so that they have an opportunity to comment and provide further information (e.g., to refine assumptions or prompt data collection to reduce uncertainty). 

The analysis need not be confined to the estimation of a standard that uses conventional methods of extrapolation (e.g., default assessment factors). It might usefully be accompanied by an analysis of the consequences of exceeding a particular standard. If a standard is proposed that sits within the range of available toxicological or ecotoxicological data or close to the lower limit of experimental data, then we should try to predict what impact an exceedance will have (e.g., excess cancer risk, proportion of species affected, or number of individuals affected). 

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