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Improving Representation, Management and Mitigation of Spray Drift for Plant Protection Products in Arable Crops

Draft Risk Assessment Workshop

Context and scope

Spray drift measurements are performed under a range of reference conditions to assess the amount of applied spray volume blown downwind of a treated area and deposited on the soil surface next to the field. Differences arise between assessments and these are related to the choice of standard reference conditions for tests. Reference conditions are detailed in ISO 22369 but include some scope for flexibility/variation in the environmental characteristics at the point of application (wind speed, temperature, humidity), application settings (nozzle height, travel speed), crop and landscape influences (bare ground / grass versus crop, choice of crop) and measurement standards (choice of collector, relationship of measurement to edge of field/end nozzle location (Huijsmans & van de Zande, 2011; van de Zande et al., 2015). Differences also arise between highly standardized assessments conducted in wind tunnels and those made under field conditions. Within the SETAC MAgPIE WG, it was concluded that harmonization of testing standards beyond ISO 22369 would be more effectively addressed independently via spray physics expert working groups.

In order to move forward and develop a more complete understanding of spray drift to improve the regulatory basis for risk assessment, a series of workshops has been initiated to facilitate efforts in a number of areas:

  • Assemble a database of the existing spray drift trials for boom sprayers; review state of knowledge; statistically analyse and interpret available data and highlight areas where protocol-derived differences may warrant further targeted trial investigations  

  • Develop a targeted programme of trials to better understand and quantify differences emerging from measurement methodology and choices (e.g., choice of collector, framework of drift deposition collection, role of crop)

  • Use information from above to develop proposals for standardized framework of measurement going forward to investigate key drivers or influences on drift (e.g., crop and landscape characteristics/morphology)

  • Use information from above to support further interpretation of existing spray drift trials to develop a more complete and coherent picture of spray drift (e.g., by generating a standard set of trials against which drift models can be calibrated and validated)

  • Determine which collector type best represents the actual deposition capture by the relevant risk assessment compartment (e.g., surface water v. bare ground v. turf, etc.) 

  • Develop a path forward for a role for mathematical modelling as a higher tier basis for risk assessment refinement

Funding for experimental work to support these activities has been supplied by ECPA.

These immediate goals would have the aim of arriving at a better understanding of the differences arising between drift trials, causes for these differences, and the extent to which they may then be quantified and predicted to rationalize apparently contrasting results as a means of addressing uncertainty.

Ultimately, it is proposed that a body of understanding should be developed that would make the best use of a large and valuable heritage of research on spray drift developed in the past to work towards the longer term goal of facilitating greater flexibility with drift representation through mathematical modelling of drift arising from boom applications.

Representation of spray drift affects a range of forms of risk assessment (aquatic, non-target terrestrial plants, non-target arthropods, bystander exposure etc.). It is considered essential that a significant component of this work includes liaison with other workshops (e.g.,NTTP) and ecotoxicology expertise to ensure coherence and awareness of developments. There is also a necessity to ensure deliverables from the workshop are practically grounded for regulatory implementation and thus specific workgroups are envisaged focusing on awareness raising, implications of refined representation and practicality of implementation in each form of risk assessment. Finally, as a direct follow-up action from SETAC MAgPIE, it is recommended that a specific work group is established to  provide European regulatory authorities with an expanded and secure toolbox of risk mitigation measures. This action is considered an essential parallel component of the workshop in order to better ensure efficient transition to a new framework of drift representation is coupled with options to accommodate change. In some cases it is envisaged that this may require policy realignment and, thus, a high degree of regulatory participation and awareness would be sought.

Objectives of this workshop:

1.     Review, statistically analyse,  and interpret available spray drift database;


2.     Highlight deficiencies, limitations and uncertainties;


3.     Develop targeted framework of drift trials to address key issues arising;


4.     Reinterpret available data with aim of assisting with development of more comprehensive harmonised drift representations;


5.     Evaluate options for enhanced mathematical modelling to support improved risk assessment;


6.     Evaluate impact in diverse risk assessment domains;


7. Consider options for implementation and improved/expanded risk management and mitigation to accommodate revised representation

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