EPA has significantly raised the level at which the agency believes atrazine harms aquatic plants, potentially helping some farmers who rely on the weedkiller.

EPA's Office of Pesticide Programs on Monday announced a new concentration equivalent level of concern, or CE-LOC, which is “the level at which atrazine is expected to adversely affect aquatic plants,” The CE-LOC is also important because it is the level "that triggers required monitoring and/or mitigation to protect aquatic plant communities.”   

The previous CE-LOC of 3.4 parts per billion (ppb) was way too low, atrazine manufacturer Syngenta and grower groups have argued for years, contending that EPA was relying on flawed studies.

EPA has now raised it to 9.7 ppb, following a report from a scientific advisory panel that recommended excluding the studies in question, which EPA did in coming up with the new water quality level.

In its update Monday, OPP said it would use the new CE-LOC “to develop a revised regulatory decision to help protect aquatic plants as well as fish, invertebrates, and amphibians.”

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That will mean modifying proposed mitigation measures that grower groups have said would make it extremely difficult to use atrazine. EPA previously proposed requiring sorghum, field corn and sweet corn growers in watersheds with atrazine levels above 3.4 ppb (about 18% of all watersheds in the U.S.) to choose from a “picklist” of practices — among them cover crops, contour buffer strips, terrace farming or field borders — depending on the crop.

OPP said the new water quality level would result in removal of “millions of acres of land from the 2022 map of watersheds that were expected to exceed the level of concern.” At the same time, “a much smaller number of acres in other areas of the country” would have to mitigate for their use of atrazine.

Watersheds with levels above 9,.7 ppb, however, still cover a broad swath of the middle of the country, according to the map included in an EPA document explaining the recalculation of the CE-LOC. (See above.)

EPA could not immediately say how many acres are in watersheds covered by the new CE-LOC. 

Syngenta said it was examining the decision.

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