The Office of Pesticide Programs (OPP) Environmental Fate and Effects Division (EFED) has developed a tiered approach to determine the appropriate level of modeling needed to perform a risk assessment for a pesticide. This tiered approach is designed to minimize the amount of analysis required to evaluate any given chemical. Each of the tiers is designed to screen out pesticides by requiring higher, more complex levels of investigation only for those compounds that have not passed the previous tier. Each tier screens out a percentage of pesticides from having to undergo a more rigorous review prior to registration or reregistration. 'Passing' a given assessment tier indicates that there is a low possibility of risk to the aquatic environment. 'Failing' an assessment tier does not, however, necessarily mean the chemical is likely to cause environmental problems, merely that the assessment should continue on to the next higher assessment tier. The intent of this tiered modeling system is to produce only as thorough an analysis as is necessary for each pesticide, and thereby focus greatest resources and efforts toward areas of greatest potential ecological threat.

Title from title screen (viewed on March 4, 2008). "September 30, 2006." "EPA/600/R-06/095." Includes bibliographical references (page 37).