USDA: Transgenic Crops Can Improve Water Quality

When these bodies of water are used as drinking water sources, the contamination can mean increased treatment costs or a need to seek alternative sources of supply.

Farmer sprays herbicide on his field. (Photo credit unknown)

Residual amounts of these herbicides can have negative effects on aquatic ecosystems even at concentrations well below their drinking water standards.

When genetically modified, herbicide-tolerant, corn and soybean became commercially available in the 1990s it became possible to replace some of these residual herbicides with short half-life, contact herbicides that may be more environmentally benign.

By 2004 about 90 percent of the soybean crop grown in the United States was genetically modified for tolerance for the contact herbicide glyphosate known commercially as Roundup. Produced by Monsanto, it is currently the most widely used herbicide in the world.

To see how surface water was affected by these two different types of herbicides, U.S. Department of Agriculture, USDA, researchers compared losses when applied at normal rates to seven small watersheds planted with Roundup Ready soybean or with Liberty-Linked corn, by Bayer CropScience.

The study, conducted over four years at the USDA Agricultural Research Service North Appalachian Experimental Watershed near Coshocton, Ohio, showed much lower concentrations of the contact herbicides in runoff.

In their report, published in the March-April issue of the "Journal of Environmental Quality," soil scientists Martin Shipitalo and Lloyd Owens, and agricultural engineer Rob Malone demonstrated that loss of contact herbicides to surface water runoff was usually much less than that for the residual herbicides.

Averaged for all soybean crop years, loss of glyphosate, or Roundup, into the environment was about one-seventh that of the metribuzin and one half that of alachlor, residual herbicides it can replace.

In 2004, the states of New York, California, Connecticut, and Massachusetts petitioned the U.S. Environmental Protection Agency to add a tenfold safety factor for the protection of infants and children for the herbicides metribuzin and alachlor.

The states argued that once this factor is added, these herbicides no longer meet the safety standard, so they could not be used.

The EPA denied the states' petition.

Similarly, average loss of the contact herbicide glufosinate, or Liberty, was one-fourth that of atrazine, a residual corn herbicide it can replace.

Some studies have shown that atrazine can produce hermaphroditic frogs and male frogs with ovaries and eggs, although the level of exposure has varied in those studies.

One study of men who worked in a factory that produced atrazine found prostate cancer levels in those exposed to the chemical were 8.4 times higher than in the general population.

Project leader Martin Shipitalo said, “The concentrations of the contact herbicides in the runoff never exceeded their established or proposed drinking water standards while the residual herbicides frequently exceeded their standards, particularly in the first few runoff events after application.”

Concentrations of atrazine in runoff were up to 240 times greater than its drinking water standard while alachlor concentrations were up to 700 times greater than its standard.

The maximum glyphosate concentration noted was nearly four times less than its standard.

Glufosinate currently has no established standard, but was only detected at low concentrations and was below its detection limit 80 days after application.

In view of increased economic incentives to grow more corn and soybean for biofuel production, the results of this study suggest to farmers and the regulatory community that herbicide losses and concentrations in runoff can be reduced by planting herbicide-tolerant varieties of these crops and replacing some of the residual herbicides with the contact herbicides Roundup and Liberty.

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