29 No. 4
Altered Crop Protection Agent Residues in Transgenic Crops
Since the first large-scale commercial introduction of transgenic crops in 1996, the area cultivated with transgenic crops has increased continually, amounting to 102 million hectares worldwide in 2006. Most of the cultivated area is concentrated in the USA, followed by countries like Argentina, Brazil, Canada, Paraguay, China, India, and South Africa, in which the predominant transgenic crops for sale include soybean, maize, cotton, oilseed rape, and potato.
The two most prevalent traits linked with these crops, which are of environmental importance, are herbicide and insect resistance. Herbicide resistance greatly improves weed management and control, allowing herbicides (weed killers) to be applied “over the top” of the crop, eliminating the need for frequent and directed herbicide sprays between crop plants or mechanical removal of weeds. Many insect-resistant transgenic crops contain insect-killing proteins obtained from the soil bacterium Bacillus thuringiensis, which are toxic to certain insect species, but not to humans and domestic animals.
Both herbicide and insect resistance traits are likely to affect the nature and quantities of the applied pesticides. This can take the form of increased usage due to over-the-top application of herbicides on the transgenic crop, or of substitution or omission of other pesticides, as discussed in an ongoing IUPAC project (2001-024-2-600), which also considers the possible consequences of these changes on the environment.
The current project extends upon the previous project by considering the impact of transgenic crops on the use of pesticides and the level of pesticide residues on these crops, in particular. It is assumed that, in addition to the substitution of other pesticides that would otherwise have been applied and the change in the level of pesticide residues within a crop, the type of the transformed compounds of the applied pesticides may also differ. Further, besides the direct effects of pesticide application on transgenic crops, some indirect effects may also occur. Under normal practices, specific herbicides may serve as pre-harvest desiccants (i.e., agents that kill the green parts of the crops so that the harvest of seed or stolons is facilitated), while in the case of a herbicide-resistance trait, another chemical may be required for that purpose. This may lead to accumulation of chemical residues in the environment and also to dietary exposure of consumers to agrochemicals.
Thus, the introduction of transgenic crops and the altered nature and levels of residues of pesticides may also necessitate changing the regulatory Maximum Residue Limit (MRL) for a given pesticide in a particular crop. This, in turn, will have potential consequences for the international harmonization of MRLs, which is necessary for international trade and the movement of crop commodities.
These and other related issues, such as the risk assessment and risk management by authorities, will be considered by the proposed project on the evaluation of food and feed safety implications of (altered) residues of pesticides applied to transgenic crops. The project aims to use a coordinated approach, integrating the available information into a critical review of the potential technical, regulatory, and social implications linked with altered residues in transgenic crops.
The three-year project will be conducted by a team from IUPAC’s Division VI—Chemistry and the Environment. It will be led by Gijs Kleter and composed of Irene B. de Alleluia, Kevin Bodnaruk, Elizabeth Carazo, Caroline A Harris, Arata Katayama, Baruch Rubin, Yehuda Shevah, Gerry R. Stephenson, Carmen Tiu, and John Unsworth.
For more information and comments, contact the Task Group Chair Gijs A. Kleter <[email protected]>.
last modified 10 July 2007.
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