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Title: PREDICTED IMPACT OF TRANSGENIC, HERBICIDE-TOLERANT CORN ON DRINKING WATER QUALITY IN VULNERABLE WATERSHEDS OF THE MID-WESTERN USA

Author
item Wauchope, Robert - Don
item ESTES, T - STONE ENVIRONMENTAL
item JONES, R - AVENTIS CROP SCIENCE
item BAKER, J - IOWA STATE UNIV.
item HORNSBY, A - UNIV. OF FLORIDA
item GUSTAFSON, D - MONSANTO

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2001
Publication Date: 12/1/2001
Citation: WAUCHOPE, R.D., ESTES, T.L., JONES, R., BAKER, J.L., HORNSBY, A.G., GUSTAFSON, D.I. PREDICTED IMPACT OF TRANSGENIC, HERBICIDE-TOLERANT CORN ON DRINKING WATER QUALITY IN VULNERABLE WATERSHEDS OF THE MID-WESTERN USA. PEST MANAGEMENT SCIENCE. 58:146-160. 2001.

Interpretive Summary: Roundup Ready and Libery-Link corn are grown on perhaps 10% of the corn acreage in the US, with the companies projecting that market share should grow to 25%. These genetically-engineered crops are resistant to glyphosate and glufosinate herbicides, respectfully, allowing those herbicides to be used and reducing the amounts of traditionally heavily-used herbicides such as alachlor and atrazine. Because alachlor and atrazine have been detected in many of the nations important drinking water resources, it appears that the use of these GMO crops could be significant in reducing this widespread contamination or perhaps replacing one set of contaminants with another. In this study we used a computer simulation that the Environmental Protection Agency's uses to estimate water contamination by pesticides and compared the long-term contamination potential for the different herbicide combinations in three corn-belt watersheds. The model shows that the newer herbicides are both less contamination- prone, and since they are also less toxic to humans they should be much less important as drinking water contaminants. The results indicate that these GMO crops could help solve the herbicide drinking water contamination problem.

Technical Abstract: We selected three settings representative of vulnerable corn-region watersheds, and used the PRZM-EXAMS model with the Index Reservoir scenario to predict corn herbicide concentrations in the reservoirs as a function of herbicide properties, use pattern, and site characteristics and weather in the watersheds. We compared herbicide application scenarios including pre-plant atrazine and alachlor applications with a glyphosate pre-plant application, and scenarios in which only glyphosate or glufosinate postemergent herbicides were used, with corn genetically modified to be resistant to them. In almost all years a single runoff event dominated the input into the reservoir and annual average pesticide concentrations are highly correlated with annual maximum daily values. The modeled concentrations were generally higher than those observed in monitoring data. Because of their lower post-emergent application rates and greater soil sorptivity, glyphosate and glufosinate loads in runoff were generally 1/5 to 1/10 those of atrazine and alachlor. These model results indicate that the replacement of pre-emergent corn herbicides with the post-emergent herbicides allowed by genetic modification of crops would dramatically reduce herbicide concentrations in vulnerable watersheds. Given the lower chronic mammalian toxicity of these compounds, risks to human populations through drinking water would also be reduced.