Threat to humans from pesticides in waterways declines, study finds

By Agri-Pulse staff

© Copyright Agri-Pulse Communications, Inc.



WASHINGTON, Sept. 17, 2014 - A new study by the U.S. Geological Survey found concentrations of pesticides in U.S. rivers and streams are less abundant in agricultural and mixed-land-use than in urban waters.

The study, “Pesticides in U.S. Streams and Rivers: Occurrence and Trends during 1992-2011,” also shows that risks to humans from pesticide tainted waterways has fallen, partly due to regulatory action and legal restrictions, while the threat to aquatic life is growing.

The study was published in the Environmental Science and Technology Journal. Researchers sampled water from 200 locations along U.S. rivers and streams to gather data on pesticide occurrence and potential significance for human and aquatic health.

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Many in the agricultural sector would take the reduction in its chemicals ending up in streams and waterways as a good sign. Dr. Mike Leggett, senior director of environmental policy for CropLife America, however, said he thought the study could have done a better sign of highlighting progress made in agriculture's chemical management practices.

“I was disappointed a little in how USGS portrayed a lot of the information. I thought there was a lot of good news in there that was kind buried,” Leggett said. “I thought there was a little too much doom and gloom.”

The “doom and gloom” Leggett referred to is the finding that concentrations of pesticides in many streams were found to be in excess of the threshold for aquatic health. The good news was the declining threat to human health.

The report compared findings from the first decade of the study to statistics from the second decade. It found that the proportion of agricultural and mixed-land-use streams with one or more pesticides that exceeded the aquatic life benchmark held steady or dropped from decade to decade, while urban streams jumped from 53 percent above the benchmark in the first decade to 90 percent during the second.

Researchers said that for pesticides assessed during both decades, the decrease in the proportion of streams exceeding aquatic life benchmarks was driven by regulator changes and market forces.

Leggett also called into question the very aquatic health benchmarks USGS used in the study, saying the authors never specifically declare parameters for the thresholds.

By the study's own admission, it also fails to test for many pesticides.

“Not all pesticides in use or all streams and rivers can be measured because of budget constraints, limitations of analytical methods, and the constant changes in pesticide use, including the phasing out of some and the introduction of others,” the study said. 

Instead, researchers said they assessed a “select subset” of the more than 400 different pesticides used in urban and agricultural settings in the last two decades. In that group, the study specifies that 123 pesticide compounds were analyzed between 2002-2011 and only 47 of those were also analyzed in 1992-2001.

“Clearly, some of the pesticides not included in the present assessment may add to overall occurrence and potential environmental significance,” according to the study.

Not included in the study was glyphosate, the application used in Roundup Ready crops and possibly the most commonly used herbicide on the market today. The study said it is “difficult and costly” to measure glyphosate, so data on environmental impact have been limited to smaller studies.

“A lot of what glyphosate replaced had really, really low use rates relative to glyphosate,” Leggett said, adding that glyphosate has a “short-lived” environmental impact. “It'll degrade pretty quickly over time, so even if it's going out at a higher rate than another chemical, it may not show up.”

Leggett said it was hard to determine which chemicals glyphosate replaced because of regional and crop-related factors.

The study was also somewhat limited in its scope. By only testing water samples, the study left out contaminants that could have resided in the sediment beneath the water or in the tissue of the water's aquatic life.

So what played the biggest role in the sharp increase in urban stream contamination? The study said it observed marked increases in two chemicals: fipronil and dichlorvos.

Fipronil is an insecticide used in more than 50 registered products, according to the National Pesticide Information Center. It was found to exceed its aquatic-life benchmark in 70 percent of urban streams, the study said. The EPA unsuccessfully sought to ban dichlorvos - which exceeded the aquatic life benchmark in about 45 percent of streams in the first decade of the study - from home use in 1995. The insecticide has similar applications as fipronil, and both are used in slow-release scenarios such as flea and tick collars for pets. The two chemicals can also be applied in a spray in a liquid pest control situation for residential, industrial, or agricultural use.

While agricultural producers have made great strides in precision technology such as improved applicator nozzles and automatic sprayer shutoff devices, Leggett said those recent improvements likely weren't a huge factor in a two-decade study, but he did say there was potential for further reductions as the technologies become more widespread. Instead, Leggett pointed to improved practices by producers as one of the biggest reasons for the drop in agricultural pesticides in the waterways.

“I think there's been a lot of awareness, a lot go into stewardship, a lot of work that's been done especially over the last 20 years on the farm relating to surface water and the potential impacts on surface water,” Leggett said. “A lot goes back to the farm and their overall awareness of how pesticides get used and what the implications are.”

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