Environmental Risk Assessment

Environmental risk assessments serve to evaluate the safety of unintended exposure of a plant protection product (PPP) to non-target organisms.  These include both of the previously described field scenarios (‘in-‘ and ‘off-‘), but spray drift is only considered for ‘off-field’ purposes.

The non-target ‘off-field’ organism scenarios considered, the role of spray drift in the core European assessment and the reference guidance are listed below:

* except secondary risk to fish-eating birds

It should be noted that although spray drift is not currently considered in an ‘off-field’ risk assessment for bees, birds & mammals and soil organisms, there are developing guidances for each area, which may necessitate utilisation of spray drift data in an ‘off-field’ risk assessment.  To allow for full awareness, towards future update, the following references are appropriate for these scenarios:

* Guidance is finalised and published, but not formally accepted for EU risk assessment

Source data
The source drift data for the core European environmental risk assessments is that published in BBA (2000), also represented in Rautmann et al (2001).  These data are represented graphically and via the use of regression equations, in order to quantify the necessary spray drift loading at specific distances from the treated crop (‘edge of field’).  For each crop+application scenario, the seasonal 90th percentile of drift probability should be used in the risk assessment.  This is achieved by reference to the standardised tables published in BBA (2000), an abbreviated version of which is shown below.  For multiple applications, the appropriate individual percentile, for a given distance, is shown and the cumulative percentile achieves the seasonal 90th percentile target.
Calculated Basic Drift Values (field crops)
Fruit crops, Grapevine, Hops, Vegetables, Ornamentals and Small fruit 

Basic drift values for one application in% of the application rate (90th percentile)

European Tier 1 Assessments

For NTA and NTTP risk assessments.  The off field exposure is calculated at 1m distance (arable/field crops) or 3m (orchards and vineyards) and is expressed as g/ha or ml/ha.  The appropriate drift value is entered into the standard equation:

Off-field exposure = Application rate * MAF * (drift factor / vegetation distribution factor, VDF)

 

Where:

  • MAF = Multiple Application Factor (from ESCORT 2)

  • Drift factor = % drift / 100

  • VDF = 10

 

For the aquatic risk assessment, a further refinement of the spray drift parameter is required.  This acknowledges that the width of the receiving water body (e.g. a pond) leads to the possibility for a biased value if the drift value nearest to, or furthest from, the edge of the treated field were to be used.  This is resolved by integrating the drift across the width of the water body to be assessed (ditch, stream and pond) and has been implemented in the FOCUS Drift Calculator, and in the FOCUS Surface Water tool.

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