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Published January 26 2011

North Dakota to continue monitoring pesticide levels found in Red

The North Dakota Department of Agriculture says it will continue to monitor three pesticides found last year in the Red River in concentrations approaching at-risk levels for fish and other aquatic life to see if the results repeat themselves.

Results of a statewide survey of streams and rivers were largely positive, but the detection of three pesticides – atrazine, bifenthrin and metolachlor – was noted as an area of concern that may warrant “risk mitigation measures” if pesticide levels persist.

“If we can repeat those results, we may give them a little bit more regulatory focus,” said Jim Gray, director of the department’s Pesticide, Feed and Fertilizer Division. “We may do some outreach to the users of those products and move from there.

“But in the short term, people should not be overly concerned,” he added. “They’re results from one year’s study.”

The state Health Department and U.S. Geological Survey conducted the survey, taking water samples from 33 sites from April through October.

Overall, the survey found North Dakota’s rivers and streams contained only trace amounts of nine commonly used products, Agriculture Commissioner Doug Goehring said.

“These results also show that current regulations, use restrictions and our enforcement strategy are effective in preventing contamination of surface water,” Goehring said in a news release.

The samples were sent to a lab in Oregon to be analyzed for 180 pesticides. The lab found trace levels of 2,4-D, atrazine, bentazon, bifenthrin, clopyralid, dicamba, diuron, MCPA and metolachlor.

Of the 43 detections, 29 were in the intensely farmed Red River Valley.

Atrazine and metolachlor were found in levels approaching the federal government’s “aquatic life benchmarks,” which are estimates of the concentrations at which pesticides are expected to harm aquatic life.

Here’s what the survey report had to say about each of the pesticides:

Atrazine

Atrazine is a broadleaf herbicide used primarily on corn. It was detected in late June in the Maple River at Mapleton, the Red River at Grand Forks and the Red River south of Harwood.

Concentrations ranged from 0.34 to 0.87 parts per billion (ppb) – close to the benchmark of 1 ppb. A 1976 study found that at the benchmark, algae exposed to atrazine for a week had a 41 to 98 percent reduction in chlorophyll production.

Atrazine “may be a concern for freshwater algae” in the Red, the report said.

Bifenthrin

Bifenthrin is an insecticide most commonly used on canola and soybeans, but it also may be used on corn, peas and grapes. Homeowners also use it on lawns and gardens.

It was detected in October in the Red River south of Harwood at a concentration of 0.13 ppb. There’s no benchmark for bifenthrin, but studies have shown it causes 50 percent mortality at 0.15 ppb for rainbow trout and at 0.35 ppb for bluegill, the report states.

“Based on available toxicity data, the department determined the bifenthrin concentration was near a level that could endanger freshwater fish,” the report states. “However, since this was a single bifenthrin detection at extremely low levels, the department is not overly concerned at this time.”

The report notes the Red River basin extends into Minnesota, and bifenthrin may also be used there.

Metolachlor

Metolachlor is used primarily on corn for grass and broadleaf weed control. It was detected four times in North Dakota: three times in the Red River and once in Medora.

Concentrations ranged from 0.39 to 0.91 ppb, close to the 1 ppb benchmark.

Gray said the federal government sets benchmarks extremely low for aquatic life and drinking water safety, and the survey samples were all within those guidelines.

“I think what it shows is our regulatory program is working, and I would say that the results are a positive,” he said.

This was the state’s second comprehensive surface water survey. The department hopes to continue doing them to build its data set and look for trends, Gray said.

Next year’s survey may include stationary bodies of water such as lakes and wetlands, he said.


Readers can reach Forum reporter Mike Nowatzki at (701) 241-5528