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Drift Data in European Risk Assessments

Risk Assessments form the basis for European evaluation of Active Substance (AS) and Product registration applications.  The risk assessments are generally based upon agreed and harmonised approaches, supported by European, Zonal [ref EU Zonal process SANCO 13169/2010] and/or National Guidance and are under-pinned by high quality scientific data, which themselves will have been generated in accordance with EU legislation [ref 283/2013]. 

The assessment has two broad components – exposure and effects – the combination of which achieves a risk-based assessment approach.

Exposure is the term describing the route by which the product (or the chemical itself) comes into contact with the assessed organism or system.  Examples of primary exposure routes include over-spray and spray drift, both leading to direct contact exposure, whereas secondary exposure arises for example to mammalian tissues through ingestion or pollinators through nectar.

Representing and quantifying a ‘realistic worst-case’ exposure is critical to the assessment of risk.  The scenario to be assessed must be well understood and described, in order to represent modern agricultural practices and the extent, likelihood and frequency of exposure.

Effect is the term describing the results of scientific studies, across a relevant range of concentrations, which lead to an understanding of the impact on a test organism or system.  This may be determined through mortality or other, non-fatal, effects, such as leaf phytotoxicity, or behavioural anomalies.

Such studies are generally performed in the laboratory, at lower tiers of complexity, with a compromised, but realistic, representation of possible exposure mechanisms.  More complex (and by implication, more realistic) studies are performed, up to and including field and landscape-scale experiments.  The lower tiers (complexity) data provide endpoints for initial evaluations.  Higher tier studies provide the opportunity for use of refined endpoints and greater contextualisation of the system exposed.


The risk assessments themselves can consider two main scenarios, either ‘in-field’, which considers the exposure and effects within the target area treated (generally the crop to be protected), or ‘off-field’ which considers consequential exposure and effects beyond the perimeter of the target crop.  The contribution of spray drift, originating from product application to a target crop, is solely considered as an ‘off-field’ exposure route, and is discussed in more detail, below.  Note that other primary exposure routes are not considered here.


As discussed in more detail elsewhere [link], spray drift is described as the transfer of small spray droplets out of the target area.  According to two primary influences – droplet size (mass), boom height and wind speed – the droplets then move and deposit in the off-field landscape  Thus two exposure routes must be considered – airborne contact and deposition.  Risk assessments for a range of impacted organisms can then generated, using these exposure routes alongside established effect data.  The safety risk assessments are conducted for two community elements – humans and the environment.  Both have some commonality around the exposure component, but can be quite different in the scope and interpretation of the effect data.  These are described below.

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