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Development of a Methodology for the Derivation of Aquatic Plant Water Quality Criteria
Thursby, G. AND M. Lewis. Development of a Methodology for the Derivation of Aquatic Plant Water Quality Criteria. US EPA Office of Research and Development, Washington, DC, EPA/600/R-18/025, 2018.
This report provides information for the Office of Water in support of their efforts to establish guidelines for the derivation of Aquatic Life Criteria for plants.
Aquatic plants form the base of most aquatic food chains, comprise biodiversity-building habitats and are functionally important in carbon assimilation and oxygen evolution. The USEPA, as stated in the Clean Water Act, establishes criterion values for various pollutants found in the waters of the United States. These criteria serve as guidance for States and Tribes to use in developing their water quality standards. The current Office of Water (OW) methodology for deriving criteria is in the Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses. These OW guidelines focus primarily on deriving criteria based on animal toxicity data. Data for aquatic plants; however, has recently become important due to the need to address the particular modes of action of herbicides. In the EPA guidelines, an acute criterion results from using acute toxicity data for animals. A chronic criterion uses the most sensitive of the final chronic value for animals or the final plant value (FPV). There are some limitations associated with using the FPV because of an insufficient description of minimum data requirements for plants within the 1985 Guidelines. This report provides a means to evaluate small toxicity data sets to estimate the value of additional data. The method relies on the observed and expected ratio of toxicity values for the least and most sensitive species in a given data set. We do not recommend minimum data requirements based on a fixed number of test species, or a particular list of desirable species to include. The recommendations rely on guidance for examining he overall quality and representativeness of the sensitivity distribution with any available data. We show that using only the recommended five aquatic plant species from EPAs requirements under the Federal Insecticide, Fungicide and Rodenticide Act as a starting point, a reasonable estimate of the aquatic plant sensitivity distribution is possible.