30 No. 2
On the Environmental Impact of Altered Pesticide Use on Transgenic Crops
by Gijs A. Kleter
Modern biotechnology has enabled the introduction of “foreign” genes into crop plants, leading to the creation of “transgenic” plants and providing a new method for conveying properties of interest to plants. Since the first large-scale introduction of transgenic crops a little more than 10 years ago, the area planted with these crops has been steadily growing, reaching 102 million hectares in 2006. Most of these plants are crops of high economic value and carry either one or both of two traits: herbicide resistance and insect resistance. Popular examples of these transgenic crops are glyphosate (herbicide)-resistant soy and corn borer (insect)-resistant maize.
Herbicide resistance allows for over-the-top application of herbicides (weed killers), contrary to the need to apply other herbicides to the soil as a preventive measure. In addition, herbicide resistance provides an alternative to mechanical weed removal, such as plowing, in areas where minimum tillage is practiced. Adoption of herbicide resistant crops is likely to change the use of herbicides on a particular crop, perhaps leading to an increase in use of the associated herbicide. Insect resistance in crops, on the other hand, is likely to reduce the use of externally applied pesticides.
Currently, there is a trend toward sustainable agriculture. Therefore, the question is what is the environmental impact from changes in pesticide usage on transgenic crops. Various sources have reported the changes in pesticide quantities used on transgenic crops as compared to conventional crops. Pesticides have different environmental profiles, such as dose-response relationships in toxicity and environmental dissemination and persistence. The changes in quantities of pesticides used should, therefore, be put into perspective in order to assess the potential environmental impact of these changes.
From 2002 until 2007, IUPAC has sponsored a project called Impact of Transgenic Crops on the Use of Agrochemicals and the Environment (2001-024-2-600). During the project, data have been collected on the quantities of pesticide used on transgenic crops and on conventional crops. These data have been obtained from various sources, particularly from reports by institutions that regularly carry out surveys, such as the National Center for Food and Agricultural Policy (NCFAP) and the United States Department of Agriculture. In addition, data have been collected, when available, on the associated environmental impacts of these pesticides. The project team has also applied a universal environmental indicator for pesticide use (i.e., the environmental impact quotient [EIQ]).
The outcomes of these studies have been published in three peer-reviewed journal articles and in various contributions to conference proceedings. (See reference list below.) In addition, the results of the project have also been disseminated through conference presentations and an evening seminar at the IUPAC-JSPS pesticide congress in Kobe, Japan, in August 2006.
It is also worth mentioning that the work of a Canadian member of the project received widespread media attention, including a radio interview. His inventory showed that between 1996–2000, herbicide use on Canadian canola substantially changed, concomitant with the introduction of three herbicide-resistant types of canola, of which two are transgenic and one conventional. The results show that the change towards the herbicides used on herbicide-resistant crops has led to a substantial decrease (i.e., by 36.8 percent) in the EIQ.
The team has also applied the EIQ to NCFAP data on pesticides used on transgenic crops and the alternatives applied to conventional crops, including soy, maize, cotton, and canola, in the USA for different years. In particular, the data on herbicides used on herbicide-resistant crops are relatively detailed, including alternative herbicide programs adapted to each American state. The outcomes for the various years are consistent in that they show, in general, that quantities and environmental impacts from pesticides applied to transgenic crops are reduced. Interestingly, conventional herbicides, particularly modern, low-rate herbicides, occasionally show a favorable environmental impact as well. In addition, the data also show a shift toward certain pesticides, in particular to glyphosate in glyphosate-resistant soy at the expense of other conventional herbicides.
Cotton is a crop that typically receives multiple pesticide sprays each season. Interestingly, insect resistance not only reduces the number of sprays towards certain target insects, but also saves non-target beneficial insects, such as predators of other pests. Insect-resistant cotton, therefore, lends itself to incorporation into integrated pest management programs.
A prospective study has considered the potential implications of the adoption of glyphosate-resistant crops in Europe, where limited adoption has taken place so far. The data in general show that reductions in quantities of herbicides applied to beets and canola can be achieved, although soy may require slightly more herbicide. The environmental consequences of the herbicide used on glyphosate-resistant crops are similar to, or less negative than, those of herbicides applied to conventional crops, depending on the parameters considered or the method used for prediction.
In conclusion, the review of collected data and calculations performed by the team show that, in general, adoption of herbicide- and insect-resistant crops lead to less environmental impacts from pesticides applied to these crops. This conclusion is relevant to both risk assessment of transgenic crops and the pesticides applied to them, as well as to risk policy regarding the adoption of these crops. In a follow-up project sponsored by IUPAC, the investigations will focus on the consequences of altered pesticide use on pesticide residues on transgenic crops, particularly with respect to the impact on regulatory issues and consumer exposure to pesticides, shifting the focus from the environment to consumption.
The task group members were as follows: Raj Bhula, Kevin Bodnaruk, Elizabeth Carazo, Allan S Felsot, Caroline Harris, Arata Katayama, Harry Kuiper, Kenneth D. Racke, Baruch Rubin, Yehuda Shevah, Gerald R. Stephenson, Keiji Tanaka, John Unsworth, Don Wauchope, and Sue-Sun Wong. Gijs Kleter was the chair.
T.A. Brimner, G.J. Gallivan, and G.R. Stephenson, “Influence of Herbicide-Resistant Canola on the Environmental Impact of Weed Management.” Pest Management Science 61:47–52 (2005).
G.A. Kleter, R. Bhula, K. Bodnaruk, E. Carazo, A.S. Felsot, C.A. Harris, A. Katayama, H.A. Kuiper, K.D. Racke, B. Rubin, Y. Shevah, G.R. Stephenson, K. Tanaka, J. Unsworth, R.D. Wauchope, and S.S. Wong, “Altered Pesticide Use on Transgenic Crops and the Associated General Impact from an Environmental Perspective.” Pest Management Science, 63:1107–1115 (2007).
G.A. Kleter, C. Harris, G. Stephenson, and J. Unsworth, “Comparison of Herbicide Regimes and the Associated Potential Environmental Effects of Glyphosate-Resistant Crops vs. What they Replace in Europe.” Pest Management Science, 64:479–488 (2008);
References for conference proceedings are available on the project web page.
Gijs A. Kleter <[email protected]> is at the National Institute for Quality Control of Agriculture in Wageningen, Netherlands.
last modified 24 March 2008.
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