3.2.1 Codification and Institutional History In the United States requirement for risk assessments is written into a considerable volume of legislation and regulation. There is likewise a significant amount of EPA documentation specifying some of the technical details as well as general guidance on how a risk assessment should be carried out. Much of this documentation is specifically directed at human health risk assessments, since it is acknowledged that ecological risk assessment is at a less formalized stage of development. Nevertheless, this documentation for human health risk assessment does provide a framework for some official guidance of practice, if only by analogy. And there is a draft Ecological Risk Guidelines (U.S. EPA, 1996). Other relevant official, or quasi-official, documents include: 1992 US EPA Exposure Assessment Guidelines 1992 US EPA Risk Assessment Council Guidance 1994 US National Academy of Sciences, Science and Judgment in Risk Assessment 1995 US EPA Policy for Risk Characterization 1997 US EPA Policy for Use of Probabilistic Analysis in Risk Assessment, Guiding Principles for Monte Carlo Analysis