One site in Grand County lake tests positive for beetle pesticides |

One site in Grand County lake tests positive for beetle pesticides

Tonya Bina
Grand County, Colorado

Tests studying the effects of tree-spray chemicals found both carbaryl and permethrin at one test site in a Grand County’, Colorado, lake.

The U.S. Geological Survey conducted the first set of sample testing for tree-spray chemicals on July 18 at Grand Lake, Shadow Mountain Dam, Granby Reservoir dam, Willow Creek Reservoir dam, Windy Gap Reservoir dam, the North Inlet and the Colorado River inlet to Shadow Mountain Reservoir. The Colorado Department of Public Health and Environment forwarded the results.

Sites were chemical-free except for the Colorado River inlet to Shadow Mountain Reservoir site, according to Grand County Water Quality Specialist Katherine Morris.

There, a carbaryl value of 0.6 micrograms per liter, or 6 one-billionths of the concentrated compound, was found.

A permethrin value of 0.14 micrograms per liter was also detected.

Permethrin and carbaryl are chemicals used in popular pine-beetle insecticides.

At those levels, they are not a “human health hazard,” but the positive results do create concern for freshwater invertebrates, according to Morris.

The level of permethrin detected, a chemical that does not break down as rapidly as carbaryl, could pose a disruption in the food chain by killing off one identified species of the water flea Daphnia Magna, a food source for Kokanee salmon and mysis shrimp, she said.

Triggered by the positive results, Morris re-tested the site on Aug. 23. Results showed the chemicals were no longer present due to chemical break-down or flush-out.

There are a variety of possibilities that would explain the higher concentration of chemical; Morris guessed someone handling the insecticides may have disposed of residue or excess chemical improperly.

Overspray, she guessed, wouldn’t have produced such values.

Designed specifically to break down, “these are not strongly persistent environmental chemicals,” Morris said. “They break down over time unlike pesticides of an historical note. That doesn’t mean they’re not strong; they need to be taken seriously.”

The “half lives” for compounds denote the rate of reduction over time and what percentage remains in water and soil.

“The ‘half life’ ensures it will degrade over time,” Morris said. Overspray that lands in soil breaks down halfway with the help of the sun in roughly three weeks. In soil with a lot of oxygen, the rate is from four to 72 days. In water, overspray breaks down halfway from about four days to two weeks.

Permethrin, Morris said, is more persistent and doesn’t enjoy as short a half-life as other insecticides. However, it is “not as stable as nasty chemicals of the past.”

The county plans to continue monitoring chemical levels in water sources.

Testing for pesticides may begin next April to see if chemicals are prevalent in runoff, and more tests are planned for before beetles begin to fly, around the height of spraying. Any positive results will be re-tested and explored “so that if someone is consistently misusing the chemicals, we will have a better chance of locating the area in which the misuse is occurring,” Morris said.

Operators of chemical sprays must follow labels as law and should be careful of overspray on hardscapes such as driveways and roofs.

Most labels give instruction on how far applicators must remain from water.

Absent label instructions, the rule of thumb is that applicators should stay at least 30 feet from water sources, Morris said.

” Tonya Bina can be reached at 887-3334 ext. 19603 or e-mail

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