Introduction

An ecological risk assessment (ERA) may be described as ‘a process that evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors’ (USEPA 1992, 1998). Arguably the most common stressors are chemical contaminants, and regulatory authorities in many countries around the world use ERA schemes to determine whether chemical contaminants are impacting on ecological systems. The USA, the Netherlands, Canada, Australia, New Zealand and the UK have all spent considerable resources developing ERAs for use under their respective regulatory regimes. But, although each country has developed its ERA schemes for its own specific regulatory needs, the approach taken is broadly similar for all ERAs.

The largest programme of work to develop ERA frameworks is that of the United States Environmental Protection Agency (USEPA), which started in the mid 1980s. Typically, the USEPA ERA follows three basic steps: problem formulation, analysis and risk characterization (USEPA 1998). The ERA process has been further adapted for use at EPA Superfund sites, to include eight specific steps, from screening level evaluations to full site investigations and risk management (USEPA 1999). Marking ten years of use in the United States, the USEPA has recently assessed how well the ERA guidelines have worked, identifying strengths and weaknesses (see Dale et al. 2008; Kapustka 2008; Suter & Cormier 2008).