What are the health issues and environmental challenges presented by herbicide-tolerant varieties?

Herbicide-tolerant varieties (HTVs) are crop varieties that have been developed to be intentionally tolerant to specific herbicides. They have the advantage of allowing targeted herbicide applications on plots under cultivation once the weeds have emerged.

HTVs can be obtained by different techniques:

• conventional variety selection, wich consists in identifying plants that are naturally tolerant to herbicides and cross-breeding them with existing varieties;
• mutagenesis, wich is a laboratory technique that accelerates the creation of mutations in a plant's genome in order to induce tolerances. Two types of mutagenesis exist:
  • random mutagenesis, which is older, and consists in exposing the plant (in vivo) or some of its cells (in vitro) to physicale or chemical agents causing random mutations in the genome;
  • site-directed mutagenesis, which is more recent, and uses molecular biology tools to induce mutations in targeted sequences

It should be noted that while it is also possible to obtain herbicide-tolerant varieties through transgenesis, this article only deals with HTVs obtained through the above techniques.

In France, HTVs were first developed in the late 1990s for chicory, then in the 2000s for maize, and between 2010 and 2012 for rapeseed and sunflower, which now account for the main uses of HTVs. According to the data collected, land planted with HTVs of oilseeds in 2017 accounted for 27% of the sunflower crop area (about 160,000 ha) and 2% of the rapeseed crop area (about 30,000 ha). The total area planted with HTVs of sunflower and rapeseed seems to have reached a plateau as it has not risen since 2017.

Directive 2001/18/EC of the European Parliament and of the Council dated 12 March 2001,  which governs the deliberate release into the environment of genetically modified organisms, provides an exemption from premarket risk assessment for organisms obtained through mutagenesis. Therefore, HTVs currently fall under the same regulatory framework as traditional plant varieties. However, following the ruling of the Court of Justice of the European Union of 25 July 2018 (case C-528/16) and the decision of the Council of State of 7 February 2020, it is possible that the status of HTVs will change.

The subject of HTVs is especially complex and highly politicised. It is a burning issue at the crossroads of GMOs and pesticides, reflecting two conflicting views of agriculture.

On the one hand, opponents of HTVs point to the risk of increased herbicide use, and of the development of resistance to the substances used. They also criticise the lack of transparency and traceability of the use of these varieties and consider HTVs to be "hidden GMOs". Furthermore, they would prefer a change to farming practices as an agronomic solution to weed control problems, rather than promoting an intensive cropping model.

On the other hand, proponents of HTVs see them as a technical solution for targeted field-by-field weed control (especially ragweed, which is an invasive species and causes serious allergies in the population), thereby enabling the rational use of chemical herbicides.

In France, the HTVs of sunflower and rapeseed on the market are all tolerant to herbicidal active substances of the acetolactate synthase (ALS) inhibitor class. This chemical class is also used for weed control on cereal plots included in crop rotations with rapeseed and/or sunflower.

After analysing the cultivation practices, ANSES confirmed the increased risk of development of weed resistance to ALS-inhibiting herbicides in HTVs of sunflower. For the plots surveyed in 2017, it demonstrated:

• more intense herbicide use in plots planted with HTVs compared to conventional crops;
• short crop rotations (2-3 years) resulting in a higher frequency of use of the same chemical class from one year to the next, for both HTVs and conventional crops;
• a lower diversity of chemicals used in HTV plots for pre-emergence weed control.

In its expert appraisal report (PDF) published in March 2020, ANSES stressed that the limitations of the data collected in terms of their quantity and quality did not enable it to reach a decision on potential adverse effects or to carry out an a posteriori health risk assessment. In its 2021 report it gives methodological guidelines for further studies on the effects of HTVs. ANSES has also carried out some preliminary analyses.

ANSES notably tested an indicator that compares the health risks associated with farmers' exposure depending on whether asunflower crop is an HTV or non-HTV, based on use data from the Ministry of Agriculture's 2017 "plant protection products-arable crops" survey. The results of these tests suggest that the value of the risk indicator for the non-HTV group is higher than that of the HTV group. These findings can be explained by the use of more active substances with more unfavourable toxicological profiles to control weeds in non-HTV plots. A collective expert appraisal including the selection of a robust risk indicator will need to be conducted to confirm or infirm these initial results.

Regarding the risks related to the consumption of foods containing pesticides residues used on HTVs of crops, the sampling protocol of the national plans for monitoring pesticide residues cannot currently distinguish between HTV and non-HTV crops. Moreover, the active substances associated with HTVs are currently not effectively screened for in harvested products and in foodstuffs. At this stage, therefore, it is not possible to analyse the risk to human health from dietary exposure.

The limitations pointed out in ANSES’s 2020 expert appraisal report (see above) mean that it is not possible to carry out a risk assessment for the environment.

In its 2021 report, the Agency has proposed methodological guidelines for assessing environmental effects. A preliminary analysis, based on an environmental risk indicator and pesticide use data, suggested that the impacts of weed control practices on aquatic organisms such as fish or aquatic plants may be greater for non-HTV crops. However, in order to more realistically take account of the exposure of aquatic organisms to pesticides and evaluate the associated risks, water contamination data should be used rather than pesticide use data. To do this, the Agency has recommended a number of measures to strengthen monitoring of the impact of HTVs on water quality, using existing networks.

There is currently no indicator in the French and European catalogues of crop species and varieties that can be used to easily identify HTVs. The lack of traceability of HTV seeds makes it impossible to monitor either how these varieties are used or the associated cultivation practices. In order to rectify this situation, the Agency recommends setting up a monitoring scheme for HTV seeds. This would help develop knowledge on cultivation practices and increase the surveillance of residues from herbicides associated with HTVs.

ANSES also recommends conducting a study of several HTVs of sunflower in order to determine whether specific pesticide residues are formed. The Agency then recommends conducting a specific monitoring campaign within the Ministry of Agriculture’s monitoring and control plans. This would allow a more comprehensive comparative study of the risks associated with dietary exposure to be conducted.