The future direction of ecological risk assessment in the United States: reflecting on the U.S. Environmental Protection Agency's "Examination of risk assessment practices and principles".

As part of an agency evaluation of the development of risk assessment tools, the U.S. Environmental Protection Agency (U.S. EPA) issued a staff paper in March 2004 describing the current state of practices and policies regarding risk assessment from the agency's perspective. The staff paper provided a rationale for the agency's positions regarding technical topics frequently the subject of comments or complaints. Considerations relevant to ecological risk assessment were included, primarily in a single chapter focused on this topic. This commentary highlights four technical issues important to the advancement of ecological risk assessment practice and discusses how some of the points raised by the U.S. EPA in the staff paper have significance to ecological risk assessors. Discussion regarding incorporating population- and community-level analysis into risk assessments and the apparent reluctance of the U.S. EPA to adopt advances in this area is provided. Also, continuing inconsistencies in the body weight scaling of toxicity values between human health and ecological risk assessment practices are discussed. Ideas for refining the calculation of exposure point concentrations for ecological receptors and the progression between screening steps and comprehensive risk assessment are also discussed.