S-metolachlor: moving towards a ban on the main uses to preserve groundwater quality
ANSES undertook an expert appraisal on the risk of groundwater contamination by the herbicidal substance S-metolachlor and its metabolites. The appraisal showed that the estimated concentrations of the three metabolites metolachlor-ESA, metolachlor-OXA and metolachlor-NOA in groundwater are above the quality limit set by European legislation. To preserve the quality of water resources, ANSES is initiating a procedure to withdraw authorisation of the main uses of plant protection products containing S-metolachlor.
S-metolachlor is one of the most widely used herbicidal active substances in France. It degrades into metabolites that migrate into environmental media including soil, surface water and groundwater.
In tests of drinking water, the metabolites of S-metolachlor have frequently been detected at concentrations exceeding the quality standards.
In this context, the Agency collected all the data on levels of S-metolachlor metabolites in water (groundwater, surface water, and water distributed for human consumption) available through its phytopharmacovigilance scheme and published its report in 2021. Following this report, the Agency introduced restrictive measures in the marketing authorisations of S-metolachlor products, in particular a reduction in the maximum use rates for maize, sunflower, soybean and sorghum crops.
A specific expert appraisal on groundwater
To verify the impact of these changes in use, ANSES assessed the concentrations of S-metolachlor and its metabolites in groundwater. This assessment aimed to verify compliance with the criteria set by European legislation. It took into account the most recent data available on the substance and its metabolites. The Agency concluded that the estimated concentrations of the three metabolites of S-metolachlor (ESA, OXA, and NOA) in groundwater are above the threshold value defined in Regulation (EU) No 546/2011.
Therefore, despite the reduction in the maximum application rates for such products, ANSES points out a risk of groundwater becoming contaminated by the metabolites of S-metolachlor.
Intention to withdraw authorisation for the main uses
In light of this risk to the quality of water resources, ANSES is initiating a procedure to withdraw authorisation of the main uses of plant protection products containing the active substance S-metolachlor. This will reduce environmental contamination by this substance and thus help gradually restore the quality of groundwater.
Objectives and methodologies for assessing metabolites in groundwater and drinking water
Groundwater can be used to produce drinking water.
Assessments of metabolites in groundwater and drinking water have different objectives and therefore do not use the same methodology.
- Concerning groundwater, metabolites are assessed before authorisations are granted for plant protection products and the active substance. This assessment aims to verify that the quality of water resources is preserved when such products are used. It is carried out in accordance with the European regulations (Regulation (EC) No 1107/2009), which stipulate thresholds that must not be exceeded.
- For drinking water, the assessment aims to meet management needs when the quality limits provided for in the French regulations are exceeded. Management measures are taken to protect consumer health and are proportionate to the risks associated with the substances. They may include restrictions on their use.
Find out more about metabolites in drinking water in our article on pesticides in tap water.