In Belgium, diflufenican has been encountered in surface water in concentrations that exceed the environmental quality standards (EQS). Therefore, 8 authorization holders (Bayer CropScience SA-NV, Globachem NV, Q-chem NV, UPL Europe LTD, Adama Registrations B.V., BASF Belgium, Sharda Cropchem Espana S.L. and Rotam Agrochemical Europe LTD) committed themselves to analyze the available monitoring data (2009-2018), to try to identify any clear correlations with the use of diflufenican-based products and to propose measures to reduce the number and level of exceedances.

Threshold values

To date, diflufenican is not considered a priority substance under the Water Framework Directive. There are no European water quality standards for this active ingredient. The current thresholds are established by the Belgian federal and regional authorities in consultation with the authorization holders, and are based on publicly available data in line with the Technical Guidance for Deriving Environmental Quality Standards (Guidance Document No 27, 2018).

• The threshold for acute exposure was set at 0,05 μg/L (MAC-EQS)
• The threshold for chronic exposure was set at 0,03 μg/L (AA-EQS)

Uses

The currently authorized diflufenican-based products are all intended for professional use, however, until 2018 several products containing diflufenican for non-professional use were on the market. In practice, the use of diflufenican from 2009 until 2018 consisted of its use in cereals, orchards, ornamental plants, permanently uncropped soil and covered not cultivable soil (including railway tracks) and – to a lesser extent - potatoes.

Properties of the active substance

On the basis of the properties of the active substance, it can be concluded that diflufenican degrades very slowly in the soil. Furthermore, its adsorption to soil particles is very high. Therefore, diflufenican will not drain easily out of the soil, e.g. following heavy rainfall, but will be very prone to erosion of soil particles to which diflufenican has adsorbed. In addition, long-range transport of this compound in surface water should be duly considered, since this active substance degrades very slowly in water and photolytic degradation is negligible. Based on the negligible potential for volatilization from plant and soil surface (low volatility, adsorption to soil), it is considered that exposure to air and therefore long-range transport through air is insignificant for diflufenican.

Identification of possible emission routes

Considering the low water solubility and strong adsorption potential to soil of diflufenican, it can be expected that the substance is more prone to erosion than to runoff. Spray drift is not identified as a major source of emission for diflufenican.

Also point sources can play an important role in the emission to surface water due to bad practices such as overspray, emptying and cleaning of spraying equipment on hard surfaces.

Analysis

In general, a clear reduction in the number of locations and measurements with exceedances can be observed over the period 2009 – 2018. This reduction could be due to several restrictions in the use of diflufenican-based products, mainly for non-professional users. Further, campaigns from national and regional authorities and a prohibition for general use of plant protection products on communal grounds from 2015 probably had an important effect on the amount of pesticides applied for non-agricultural applications and subsequent release of diflufenican to surface water. Despite these restrictions, there are still exceedances observed in 2018 in a considerable number of monitored locations. An in-depth analysis was performed to understand if the observed exceedances could be related to land use, erosion and/or weather patterns. It was difficult to link exceedances of acute or chronic thresholds with a specific use, as most of the relevant crops cover almost the whole region. The links between precipitation data and diflufenican concentrations should be interpreted with care as several factors and uncertainties have their influence (f. ex. intensity and duration of rain showers, different geographical locations of weather stations and monitoring locations, …). Even though the portion of diflufenican found in surface water due to erosion cannot be distinguished from other sources, encouraging and enforcing measures to avoid erosion and a prohibition of the use of diflufenican based products on plots with high or very high erosion risk (SPe2 sentence) could have a positive effect on diflufenican concentrations in surface water, particularly in hilly regions, which are usually more prone to erosion.

Overall, it can be concluded that the general trend of the diflufenican concentrations in surface water is decreasing in recent years, both in frequency and level of exceedances. This could demonstrate that the measures taken since 2015-2016 (e.g. use restrictions) already have a positive effect. In order to further reduce the release of diflufenican to surface water, several emission reduction measures are proposed by the authorisation holders.

Emission reduction measures

Following emission reduction measures will avoid further release of diflufenican in Belgian surface water:

• As erosion is likely an important source of diflufenican to surface waters, it is proposed to prohibit the use of the product on soils prone to erosion, unless precautions are taken to avoid erosion. Therefore, the SPe2 sentence (To protect aquatic organisms the product cannot be used on erosion-sensitive parcels. For the Flemish Region and the Brussels Capital Region, this applies to parcels classified as “sterk erosiegevoelig”. For the Walloon Region, this corresponds to parcels identified with an R-code. In case precautionary measures against erosion are taken, as laid down in the regional legislations, the use can be allowed.) should be included on all authorization certificates and labels of diflufenican-based products for agricultural use.
• In several of the basins with threshold exceedances in recent years, railway tracks were present in the vicinity of water ways. To avoid release to neighboring water bodies from the use on railway tracks, the use of diflufenican on railway tracks should be completely prohibited.
• The use of diflufenican-based products needs to be limited:
  • Agricultural use:
    • Annual crops: maximum 1 application of a diflufenican-based product per crop.
    • Perennial crops: maximum 1 application of a diflufenican-based product per 12 months.
  • Non-agricultural use: maximum 1 application of a diflufenican-based product per 12 months. In addition, the window of application should be limited to “March-June”.

In order to be as efficient and transparent as possible, these measures should be included as limitations on all existing and new product authorization certificates. Further, discussion is needed on how to control the implementation of these measures. This is considered a very important step to ensure the proposed measures are correctly followed.

Further, a stewardship campaign will help to further increase the awareness of professional users on the impact of their behavior.

Towards the competent authorities, the authorization holders would like to advise to continue the monitoring campaigns, particularly at locations with regular threshold exceedances. The availability of monitoring data, sampled at the same location for several successive years with a regular interval (max. one month), would greatly help to derive the origin of contaminations, to better understand the behavior of diflufenican in the environment over a longer time frame, and to evaluate the effect of the proposed emission reduction measures.

The authorization holders trust that the above measures and stewardship actions will lead to further emission reductions of diflufenican in Belgian surface waters.