In Belgium, Aclonifen has been encountered in surface water in concentrations that exceed the environmental quality standards (EQS). Therefore, 3 authorization holders (Bayer CropScience SA-NV, FMC Chemical s.r.l/b.v. and Globachem N.V.) committed themselves to analyze the available monitoring data (2011-2021), to try to identify any clear correlations with the use of Aclonifen-based products and to propose measures to reduce the number and level of exceedances.

Thresholds

Aclonifen is considered a priority substance under the Water Framework Directive, for which European water quality standards are available in Annex I of Directive 2013/39.

• The threshold for acute exposure in inland surface waters was set at 0.12 μg/L (MAC-EQS)
• The threshold for chronic exposure in inland surface waters was set at 0.12 μg/L (AA-EQS)

It should be noted that these EQS values are lower than the Regulatory Acceptable Concentration (RAC) value of 0.5 µg/L for the aquatic compartment, which is applied in product authorisation dossiers.

Use

Currently authorised products containing aclonifen are only intended for professional use. The use of aclonifen is in Belgium authorised in potatoes and some vegetables (peas, carrot and parsnip), with applications in spring season. In 2018 the list with authorised uses was extended with additional vegetables (field beans, celeriac, celery, Jerusalem artichoke, fennel, onion, shallot, garlic) and herbs (parsley, dill, coriander and common caraway) with application in spring and/or summer season. From 2021 onwards the use in winter cereals has been authorised, for which application takes place in autumn/winter. All uses concern spray applications during pre- or early post-emergence of the crops.

Properties of aclonifen

Due to the intrinsic properties of aclonifen, it is rather immobile and moderately to highly persistent in soil. The solubility of aclonifen in water is low. It is stable to hydrolysis in water and sediment, although it may, to some extent, be degraded by photolysis in the aquatic environment. The vapor pressure of aclonifen is low.

Considering these properties, aclonifen will probably not easily drain out of the soil, however, it will be very prone to erosion. Due to its rapid dissipation to and subsequent strong adsorption to the sediment, aclonifen can be transported and released in the water during strong currents or heavy rainfall. The contribution of long-range transport through air to surface water concentrations is considered to be insignificant.

Identification of possible emission routes to surface water

As aclonifen strongly adsorbs to soil, release to surface water via drainage is very unlikely. For the same reason, it will also be relatively more prone to erosion than run-off, though both these processes also depend strongly on the weather conditions and characteristics of the landscape.

Since aclonifen is applied by spraying, surface water contamination via spray drift can be a possible emission route. These emissions are countered by the following measures in place on the labels of the authorised products:

• for all uses a buffer zone of 10 to 20 m with respect to surface water should be adhered to, and for some authorisations the buffer zone is combined with an obligatory minimum percentage of drift reducing technique of 50% to 75%
• for all products the use is prohibited on erosion sensitive parcels unless anti-erosion measures are taken (Spe2)

Finally, point sources may be an important source of surface water contamination and could locally lead to significant exceedances. These are usually the consequence of bad agricultural practices, such as spilling or emptying tank mixtures or rinsing water in neighbouring water courses, or uncleaned spraying equipment unprotected from rain. A sewage treatment plant (STP) could also be a source for surface water contamination with pesticides. However, as aclonifen is not applied on hard surfaces, making the risk for run-off from large surfaces unlikely, the contribution of STPs is expected to be negligible.

Analysis

The number of monitoring stations in which the chronic threshold is exceeded is limited and does not show a clear trend in the last 5 years. Chronic exceedances are largely driven by 1 or 2 (consecutive) high exceedances of the acute threshold (MAC-EQS) in that monitoring station. The number of monitoring stations and measurements in which the MAC-EQS is exceeded increases from 2016 to 2021. This corresponds to an increase in the number of crops in which the application of aclonifen is allowed and coincides with an increase in sales volumes. Most of the acute exceedances take place at the end of spring or in early summer (April – July), corresponding to the application window for most of the authorised uses. Exceedances of the acute threshold in autumn appear in 2021, which coincides with the addition of the authorised use in winter cereals. Limited exceedances in the months outside of the application window (e.g., in August) could point to erosion of residual soil-bound aclonifen, or resuspension of sediment-bound aclonifen after (intense) rain events.

There is a strong correlation between the aclonifen concentrations in surface water and the surface of potatoes grown, pointing to the application in potatoes as an important contributor for aclonifen in surface water, and to lower extent also for vegetables, spices and ornamentals, particularly in the months May & June. For this last group, it is however not possible to distinguish between crops in which aclonifen is authorised and the other crops. Therefore, the application in potatoes indeed seems an important contributor for aclonifen in surface water.

Further, a clear link with precipitation was found, particularly in regions with high potato cover. The correlation was more outspoken in regions with a higher erosion risk. This indicates that, despite the mentioning on the SPe2 sentence on all authorised aclonifen-based products, erosion could be an important contributor to aclonifen in surface water. Nevertheless, as large rain events do not always result in higher aclonifen concentrations, the time lapse between the application and precipitation, precipitation intensity, soil type, and crop density may affect the consequences.

Based on the available data, no conclusions can be drawn on the role of spray drift in the observed exceedances. In case imposed buffer zones and/or drift reduction measures are not correctly adhered to, aclonifen may still end up in adjacent water bodies due to spray drift. 

Point sources (at the farm level) can also not be excluded, based on a correlation between the number of potato farms in a region and aclonifen concentrations (independent of the potato crop cover), and a link with precipitation in regions with a higher number of potato farms. Also, the magnitude of some MAC-EQS exceedances cannot be explained by run-off/erosion or even spray drift, though these can contribute to the total aclonifen concentration. Although we can assume they could be a significant factor, based on the available data no conclusions can be drawn on the extent of the contribution of spray drift or point sources in the observed exceedances.

Proposed emission reduction measures

Measures to avoid run-off and erosion

Measures that can be included as limitations on all existing and new product authorization certificates and which will in parallel also be included on the labels:

• Do not use aclonifen containing products if heavy rainfall or thunderstorms (≥ 25 mm/h and ≥ 50 mm/day) is predicted within 48 hours of application.
• Do not drain the water logging on the field in the direction of the water surface with temporary gullies.
• Obliged use of cross-dams in potato cultures on parcels with high sensitivity to erosion (please refer to pictures below for illustration). This higher sensitivity to erosion corresponds with the categories of very high erosion risk (purple fields) and high erosion risk (red fields) in Flanders & high sensitivity for erosion (code red and above) in Wallonia.
  
  
• In potato cultures, create ridges when possible perpendicular to water surfaces or perpendicular to the direction in which there is a run-off/erosion risk.

 

General awareness

Product stewardship actions to prevent point losses and diffuse losses:

• The industry should put efforts in stewardship campaigns to raise awareness among farmers on the triggers for and consequences of erosion, drift, point-contaminations, … This can be done via clarification of the measures on the label, leaflets, technical articles and by presenting these specialized measures in meetings with potato farmers / organizations to have them instituted in potato cultures.
• Relevant training institutions should include (obligatory) further training on the causes and consequences of environmental emissions in the Phytolicense training, e.g. as part of the additional training that needs to be followed to renew a Phytolicense.

Monitoring

The authorization holders would like to advise to continue the monitoring campaigns. The availability of monitoring data, sampled at the same location for several successive years with a regular interval, would greatly help to derive the origin of contaminations, to better understand the fate of aclonifen in the environment over a longer time frame, and to evaluate the effect of the proposed emission reduction measures. This could be combined with projects in smaller catchment areas, particularly at locations with threshold exceedances, in cooperation with the farmers, to focus on the identification of the entry routes.

Further, sampling of sediment at strategic timepoints and locations (e.g., in May-July on locations with regular exceedances) could indicate to what extent sediment is serving as a reservoir for aclonifen, which could be resuspended after (heavy) rain events.