EPA Science Panel Questions Data Used To Develop Level of Concern for Atrazine

FIFRA SAP Meeting on Atrazine

Key Development: Members of EPA scientific advisory panel question whether a level of concern for the presence of atrazine in water would adequately protect aquatic plants.

Impact: EPA will use the level of concern in a “national-scale” assessment of atrazine concentrations in water as a part of the registration review process.

What's Next: Registration review of atrazine is scheduled to begin in 2013.

By Patrick Ambrosio  

A panel of scientists expressed concern June 14 regarding the adequacy of data used by the Environmental Protection Agency to establish a level at which aquatic plants would not be affected by the widely used herbicide atrazine.

Several members of the Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) and the Food Quality Protection Act Science Review Board said they were skeptical that the data gathered from a series of microcosm and mesocosm studies was adequate to determine the aquatic plant community concentration equivalent level of concern (CE-LOC).

Microcosm and mesocosm studies, jointly referred to as “cosm studies,” are designed to mimic conditions in natural communities and ecosystems.

The panel's concerns about the assessment include the selection of studies to be included in the development of the LOC, the evaluation of the studies for exposure effects, and the focus on atrazine-only exposure.

EPA has determined the CE-LOC range for atrazine to be from 4-7 micrograms per liter (µg/L).

“Permanent or irreversible change” in aquatic plant community structure, function, or productivity would be expected at any freshwater or estuarine monitoring sites with a 60-day running average above 4 µg/L, according to an EPA report provided to the SAP.

EPA used the Plant Assemblage Toxicity Index (PATI), a methodology using single-species plant toxicity data and cosm studies, to estimate the LOC for atrazine. The PATI method will be utilized in a “national-scale assessment of atrazine concentrations in freshwater and estuarine ecosystems” as a part of the upcoming registration review of atrazine, according to agency documents.

EPA is scheduled to begin its registration review of atrazine in 2013.

Lack of Confidence in Data.

John Rodgers, professor of Forestry and Natural Resources at Clemson University, said additional studies are required because the data presented by EPA do not support the EC-LOC.

Rodgers said the cosm studies and single-species plant toxicity data used by the agency do not support the conclusion that there will be no effects below the EPA level of concern.

He cited a number of additional plausible hypotheses that need to be tested, including the susceptibility of some species at exposures lower than 4 µg/L.

Rodgers said if the SAP concluded that no effects can be expected below the LOC, it would prevent “needed studies” from being conducted in the future.

Anne Fetscher, senior scientist at the Southern California Coastal Water Research Project, said she had some issues with the source material for the cosm studies, including whether the studies were conducted in some communities that have already been “hammered” by atrazine exposure.

Fetscher said the assessment of aquatic plant exposure to atrazine is still “in flux,” and additional studies can be conducted based on questions raised by the SAP.

Michael Twiss, professor of biology at Clarkson University, agreed that he could not determine whether the 4-7 µg/L range was appropriate due to concerns with the underlying data used to support that range.

“I cannot really address the question without having confidence in those numbers,” Twiss said.

Experts Question Study Selection.

Kenneth Portier, director of statistics at the American Cancer Society, urged EPA to be very clear on the process for including and excluding particular cosm studies.

Portier said the development of a level of concern for atrazine comes down to “which cosms we want to use” and whether those studies are scored as illustrating an effect or no effect from exposure.

“One cosm in the wrong place” can shift the results of the study, Portier said.

Linda Young, professor of statistics at the University of Florida's Institute of Food and Agricultural Sciences, said although she viewed the EC-LOC range as “conservative,” the adjustment of several cosm studies shows the “sensitivity” of the data.

EPA said that under the PATI model, five endpoints previously classified as “no effect” were reclassified as “effect” under the revised analysis. This reclassification had a significant impact on the development of the EC-LOC, according to Young.

“I do not think we have a good measure of the uncertainty in this,” Young said.

Thomas La Point, director of the Institute of Applied Sciences at the University of North Texas, said the evaluation of key studies that are “right in the middle” of the effect/no effect classification is still “a work in progress.” The importance of the cosm studies in determining the LOC puts even more emphasis on making sure they are used correctly, according to La Point.

La Point called for “a few more focused cosm studies,” with altered concentrations and times of exposure, to better support the establishment of a LOC.

Atrazine-Only Exposure 'Not Realistic.'

Several members of the panel said EPA's analysis of effects was flawed because it ignored the synergistic effects of atrazine acting along with other potentially hazardous substances in nature.

William Effland, soil scientist at the Natural Resources Conservation Service, a branch of the Department of Agriculture, said it is important to recognize that the EPA atrazine assessment only looked at a single stressor to determine community effects.

“In the natural environment, exposure to just a single stressor like this is not realistic,” Effland said.

Stephen Klaine, director of the Clemson University Institute of Environmental Toxicology, said the analysis “seems flawed in real-world impacts” because atrazine is unlikely to be encountered in the environment in an isolated way. There is a possibility of synergistic effects that could “exacerbate” the toxicity of atrazine, according to Klaine.

Portier questioned how EPA will address reversible effects from atrazine exposure in determining whether an aquatic plant community is affected.

Portier said that while it is unlikely that any “major members” of the ecological community would be harmed at levels below the CE-LOC, exposure could harm some members in reversible ways. He questioned whether EPA would consider the entire community to be harmed if some members were harmed in reversible ways or if some members were eliminated, but their role was to be filled by other members of the community.

La Point agreed that additional discussion about reversible effects could be useful.

By Patrick Ambrosio  

EPA's report on the environmental fate and ecological risk assessment for atrazine is available at http://op.bna.com/env.nsf/r?Open=jstn-8van2d.