The Use of Field-Based Data and Weight-of-Evidence to Develop Water Quality Criteria: Current Framework and Status

Water quality criteria have typically been developed using laboratory-based studies in which the effect of a single substance on a biotic endpoint (e.g., reproduction, growth, survival) is quantified and used to determine levels that do not affect designated uses. However, given the suite of environmental variables and confounding factors that affect biota in natural systems, researchers, stakeholders, and permit holders have questioned the appropriateness of laboratory-based measures of toxicity for developing water quality criteria. Methods in which field data can be used for deriving criteria have been proposed and applied, but questions remain as to whether these methods are sufficiently robust for purposes of implementing regulatory standards. This white paper provides an update on the current state of science regarding field-based criteria development. Specifically, it:

• Provides a basic overview of the laboratory-based methods typically used to develop water quality criteria.
• Describes field-based methods that have been proposed and/or used to develop water quality criteria.
• Illustrates several challenges associated with using field data for the derivation of water quality criteria.

Understanding the state of the science will apprise members of changes to water quality criteria development processes, and inform industry response to outcomes from related studies and proposed criteria.