Project Details Evaluation of food and feed safety implications of (altered) residues of pesticides applied on transgenic (GM) crops

Project No.:
Start Date:
01 January 2007
End Date:
29 February 2016
Division Name:
Chemistry and the Environment Division
Division No.:


The primary objectives of this project are:

  1. Update of past and future trends in GM Crops Production
  2. Definition/determination of the characteristics of specific agrochemical residues
  3. Evaluation of the health impact of (altered) agrochemical residues in edible crops, and
  4. Assessment of regulatory measures and food and feed safety requirements


The world wide area cultivated with GM crops has increased continuously over the last ten years, amounting to 90 million hectares in 2005, which, by comparison, equal the total areas of California, Nevada, and Utah. Most of these crops are grown in the United States, Argentina, Brazil, Canada, China, Australia, South Africa, and India.

These crops usually have been modified with either or both of two traits, i.e. herbicide resistance and insect resistance. While these traits are of agronomic and environmental importance, some experimental crops also possess traits geared towards consumer needs (e.g. high protein contents), which may in some cases also be combined with other agronomic traits. Moreover, crops with agronomic traits may find new applications, such as in the control of parasitic weeds that are sensitive towards herbicides applied to herbicide-resistant crops or insect-resistant crops with lowered mycotoxin contaminations caused by less insect infestation and less concomitant mould infection.

Herbicide and insect resistance traits are likely to influence the agrochemicals that are used on the crops with respect to quantities and nature of the chemicals, as well as the timing of applications. Subsequently, such changes may influence the nature and levels of residues present in the crops used for human and animal consumption. In addition, a number of pesticides have recently become generic, including broad-spectrum herbicides applied to GM crops, which may be offered in different formulations than the originally approved proprietary product. This may also have implications for the resultant residues levels in crops to which these pesticides are applied.

Another issue is the parallel usage of the same herbicides as weed control agents on GM crops and as crop desiccants (or defoliants) on conventional crops, i.e. potentially increasing both environmental and consumer exposure. Further as these herbicides can no longer be used as desiccant on GM crops, the further use of alternative chemicals as desiccants or defoliants is necessitated. In addition, the GM crops themselves may contain newly introduced transgenic products with pesticidal properties, such as “plant-incorporated protectants,” as regulated by the US EPA. These products may substitute for other pesticides and may have food safety considerations of their own.

In addition, the changed use patterns may affect the levels at which MRLs for residues of the pertinent pesticides in the GM crop commodities will be set. This raises the possibility of MRL disparities acting as irritants to trans-national trade in these commodities.

The team is also involved in another IUPAC project on the environmental impact of altered agrochemical use on GM crops; see project 2001-024-2-600.

The project will provide a greater attention to these global trends and especially on the MRLs to be set for residues of the pertinent pesticides applied on GM crops and commodities destined for the international trade. Accordingly, the project is to update the information gathered during the previous project, and to expand on the levels of residues of agrochemicals in GM crops, as well as the estimated exposure of humans and animals to these residues, and the MRLs to be set for the pertinent pesticides in these crops, touching on the issues of socio-economic importance, including international harmonization of regulatory thresholds and consumer concerns. In a broader sense, these data will be considered with regard to potential risks and benefits of GM crops compared to conventional crops.


June 2007 – project announcement published in Chem. Int. Jul/Aug 2007, p. 24

Dec 2010 – Team members gave presentations on the topic of the project at two events on crop protection that had been co-organized by IUPAC, including the Seventh International Workshop on Crop Protection Chemistry and Regulatory Harmonization in Beijing, PR China (October 2007; presentation by Dr Tanaka) and RACI 2010 and the 12th IUPAC International Congress of Pesticide Chemistry in Melbourne, Australia (July 2010; presentation by Dr Unsworth). Several team members also prepared a manuscript with a review of the knowledge on the altered profiles and levels of herbicides in transgenic herbicide-resistant crops as compared to residues in conventional crops.

The review focuses on the active ingredients of herbicides for which herbicide-resistant crops have already been commercialized, including active ingredients inhibiting acetolactate synthase (mainly imidizolinones and sulfonylureas), bromoxynil, glufosinate ammonium, and glyphosate. The knowledge on the metabolism of these herbicides and the resulting profile of herbicide metabolites within crop plants, both transgenic and non-transgenic, is reviewed, as well as the impact thereof on the definition of the residue employed by Codex Alimentarius Commission and national authorities. Also the impact on the setting of regulatory maximum residue limits (MRLs) is addressed. Based on the findings made in this review, no generalizations can be inferred on the impact of transgenic herbicide resistance on the profile and levels of herbicide residues in crops. In several but not all cases, the residue definition had to be changed by either Codex Alimentarius Commission or national authorities due the presence of newly formed metabolites. In addition, MRLs had to be changed in several cases due to higher levels of herbicide residues. Moreover, for some herbicide-crop combinations, no internationally harmonized residue definitions and MRLs have yet been established, and harmonization is therefore recommended. Besides herbicide-resistant crops, future work of the project team will also focus on pest-resistant crops.

Sept 2011 – The above mentioned manuscript has been accepted and published: Kleter, G.A., Unsworth, J.B., Harris, C.A. (2011) The impact of altered herbicide residues in transgenic herbicide-resistant crops on standard setting for herbicide residues. Pest Management Science, volume 67, issue 10, pages 1193-1210. doi: 10.1002/ps.2128

Last update 20110930