In Belgium, MCPA is found in surface water in concentrations that exceed the environmental quality standards (EQS).

Therefore, Corteva and Nufarm committed to analyze the available monitoring data (2017-2019) in an effort to establish clear correlations with the use of MCPA-based products and to propose measures to reduce the number and level of exceedances.

Thresholds

To date, MCPA has not been considered a priority substance within the Water Framework Directive. There are no European water quality standards for this active substance. The current threshold values are established by the Belgian federal and regional authorities in consultation with the authorization holders and are based on available scientific data. The threshold values as proposed and calculated by Oekotoxzentrum, Switzerland were adopted.

• The threshold value for chronic exposure was set at 0.66 µg/L (AA-EQS)
• The threshold value for acute exposure was set at 6.4 µg/L (MAC-EQS)

Use

MCPA is currently approved for use in cereals, stone fruit, apple/pear, berries, ornamental plants and grassland. MCPA is commercially available in formulations containing only MCPA as the active ingredient, but also in mixtures with other active ingredients.

The allowed dosage of MCPA for a single application is 0.37 to 3.0 kg of active substance per hectare.

Properties of MCPA

MCPA (IUPAC name: 4-chloro-0-tolyoxyacetic acid) is a selective phenoxy acid herbicide. The active substance is very soluble in water. MCPA has a low adsorption in the soil and therefore does not adhere to the soil. MCPA has low volatility.

Identification of possible routes of emission

Given the high solubility of MCPA in water and the fact that it does not attach to soil particles, it is to be expected that MCPA is sensitive to leaching. MCPA is not, however, prone to erosion. Emission routes via the air can also be excluded due to the low volatility of the substance.

However, point source pollution can play an important role in the emission of MCPA into surface water through bad practices such as non-respecting the buffer zones and emptying and cleaning of spray equipment close to water or on hard surfaces

Analysis

Flanders

Over the period from 2017-2019, samples were taken from a total of 270 unique surface water monitoring sites in Flanders. This generated 2577 samples which were analyzed for MCPA residue. No MCPA residues were found in 1486 of these samples (58%). In 5% of the samples (130), the amount of MCPA residues found was higher than the AA-EQS value.

An arithmetic mean of the monthly average values (AMMA) that were found was calculated for each of the 277 monitoring sites. Since the AA-EQS value is a chronic standard, it makes more sense to compare it with an annual average. This AMMA value was thus compared with the AA-EQS of 0.66 µg/L. This showed that at 22 different monitoring sites the AMMA value was greater than the AA-EQS (8% of the total number of monitoring sites).

Wallonia

Over the same period from 2017-2019, a total of 236 unique surface water monitoring sites were sampled in Wallonia. This generated 4175 samples which were analyzed for MCPA residue. No residues of MCPA were found in 2912 samples (70%). 36 samples (0.86%) show an exceedance of the AA-EQS of 0.66 µg/L. An AMMA value was calculated for the 236 monitoring sites. For none of these monitoring sites the AMMA value was greater than the AA-EQS.

Conclusion

Temporal and spatial analysis of the MCPA surface water measurements from 2017-2019 show the following:

• Most peak MCPA concentrations were observed during the months of May and June, which coincides with the typical application period of MCPA.
• Where the AMMA concentration was greater than the AA-EQS, this was driven by a single, high peak concentration and not by a persistent, long-term high value of MCPA in surface water.
• All monitoring sites where the AMMA is greater than the AA-EQS were located in Flanders.
• There are no monitoring sites where the AMMA is greater than the AA-EQS in Wallonia
• The number of monitoring sites where the AMMA is greater than the AA-EQS decreased every year: 10 in 2019, 9 in 2018 and 5 in 2019
• About 36% of the monitoring sites where the AMMA was greater than the AA-EQS were located in the Yser basin (8 monitoring sites).
• At 3 surface water monitoring sites where the AMMA was greater than the AA-EQS, the determination was based on 1 single analytical result in a single given calendar year. If additional analytical results were available for that same calendar year, it is unlikely that the AMMA would have been greater than the AA-EQS.
• No correlation could be shown between heavy rainfall and the exceedances of the AA-EQS.

Based on a review of the agricultural setting and environmental conditions for these 22 monitoring sites where the AMMA is greater than the AA-EQS, point source emission (overspray) was identified as the most important emission route to surface water.

Several exceedance monitoring sites appear to be narrow streams and drainage ditches adjacent to a commercial agricultural field/grassland area with barely any space (less than 1 meter) between the presumed MCPA treated area and the water stream where the sampling was done.

Emission reduction measures

The following emission reduction measures will prevent a further discharge of MCPA into Belgian surface water:

• Since point source emissions and the minimum distance between the agricultural field and water flows are considered to be the main emission source of MCPA, it is proposed to standardize product labels of all plant protection products containing MCPA with regard to the minimum buffer zone to be used
  • Minimum buffer zone of 10 m with classic technique; OR
  • Minimum buffer zone of 5 m with 50% drift reducing nozzles

In order to be as efficient and transparent as possible, these measures should be included as a limitation in all existing and new authorizations for products based on MCPA.

• In addition to the change in the authorization certificates, the labels of plant protection products based on MCPA will contain following additional recommendations:
  • Do not spray when there is a risk of drift
  • Filling and cleaning of the tank should always be done away from water streams and ditches
  • Respect the prescribed buffer zones at all times. We recommend always maintaining a minimum buffer zone of 5 meters, even when the use of higher drift reducing nozzles allows for a lower buffer zone.
  • Do not spray when heavy rainfall is forecasted within 24 hours.

In addition to the changes to the authorizations and label recommendations for MCPA-based products, a stewardship campaign will help raise professional users’ awareness on the impact of incorrect application of plant production products in general.

With regard to the competent authority, it is important that monitoring campaigns  are continued. Especially in places where the threshold values are regularly exceeded.

The monitoring data will continue to be followed up. It is therefore important to sample at the same locations at regular intervals.