Authors: Sarah Priestly1, Gabe Weyman2 and Amy Brooks1
1Cambridge Environmental Assessments; 2Gabe Weyman Consulting Ltd
The risks to birds and mammals from potential exposure to plant protection products (PPPs) are currently assessed in the EU using the EFSA (2009) guidance. A new version of this guidance document (GD) was published in February 2023 (EFSA 2023).
There are a number of areas that have changed in the new GD compared to the 2009 version, so to avoid a very lengthy news article, we are posting articles on particular topics. Our first article was on toxicity endpoints and time-weighted average factors (fTWA). Now we are looking at the concept of the terrestrial area of interest (TAI)…
In the current birds and mammals GD (EFSA 2009), exposure is only considered in the treated crop area, and any risks from exposure outside of this area are covered by this worst case, in-crop risk assessment. However, small mammal GMS’ (Generic Model Species) are assumed not to be present in-crop at early growth stages of many crops, due to lack of vegetative cover, though they may be present in nearby off-crop areas. In the updated GD, EFSA addresses the risk to these small mammals with the inclusion of a new off-crop risk assessment scenario called the Terrestrial Area of Interest (TAI). The terminology “off-crop” is deliberately avoided due to past variable interpretation.
According to the EFSA (2023) GD:
It is up to Member State risk managers to consider the location of the TAI in their Member State considering, amongst others, field structures and agronomic conditions. For the purposes of performing a quantitative exposure assessment, a TAI can also be considered as the area at a set distance from the sprayer. This is in line with the current approach for other non-target organisms such as non-target arthropods and non-target terrestrial plants.
To summarise, to calculate the exposure to small mammals in the TAI, the application rate (kg a.s./ha) is adjusted by the spray drift % at a minimum distance from the spray equipment:
- For standard horizontal sprayers, the default distance at Tier 1 is 1 m
- For sideward sprayers and air blast equipment, the default distance at Tier 1 is 3 m
- To mitigate the risk to mammals using no-spray buffer zones, the no-spray zone must be between the TAI and the sprayer.
In the EFSA calculator tool, the spray drift value must be manually entered. Spray drift values are given in Appendix I of the GD but these may change in future or differ at national level so have not been incorporated into the calculator tool. The relevant spray drift value depends upon the type of crop, the type of sprayer and the number of applications. Essentially, they are the same as those used for other areas of the terrestrial risk assessment, such as non-target arthropods.
Appendix I of the EFSA GD also gives the following information:
“…interception by plants in the Terrestrial Area of Interest (TAI) has not been previously considered. However, the WG considered that it would be a reasonable approach to also apply half of the crop interception in grass to account for plant interception in TAI. This means that deposition to soil surface food items is assumed to always be 55% irrespective of the crop growth stage but deposition to weeds/plants/foliar-dwelling arthropods, etc. is 100%. It is acknowledged that the interception by plants in the TAI area will vary significantly. However, since plant coverage is key for the small mammal GMS for which the risk assessment is being performed, the WG considered that it was reasonable to assume plant interception in the TAI.”
Therefore, the crop interception applied to dietary food items is not crop or growth-stage dependent, and will thus be the same for all crop-uses. In all cases, the feeding guilds used for TAI scenarios are small insectivorous, small herbivorous and granivorous mammals (the latter always being the GMS with 6 g bodyweight, regardless of the in-crop GMS). So, in fact, the TAI risk assessment always has the same three GMS scenarios and the outcome is only dependent on the use pattern (application rate, number of applications, application interval) and drift rate entered. For the same use pattern and drift rate, the TAI outcome is therefore always the same regardless of the crop. Of the 3 GMS’, the small herbivorous mammal is always the worst case; i.e. lowest TER values.
This can be observed in the example risk assessment below, for which a single application of 10 kg/ha of ‘Molecule X’ is applied to potatoes, amenity grassland, spring cereals and vines. The toxicity exposure ratios (TERs) for potatoes, amenity grassland, and spring cereals are all the same as the spray drift is 2.77% for all three, whereas the TER values for vines are lower as the spray drift is 8.02%. In this example, the TERrepro values for small herbivorous mammal fail for all 4 uses, and for granivorous for vines.
Overall, the addition of the TAI scenario does not appear to add significant amounts of time to the risk assessment process given that it is quite simple in the end, and the calculator tool performs the assessment automatically. It is unclear at this stage how frequently the TAI risk assessment will fail but, given the low exposure rates (resulting from spray drift), it might only be of concern for small herbivorous mammals for those products with low reproductive toxicity endpoints that are used either at high application rates or applied multiple times in a season. In addition to refinements commonly used for in-crop scenarios (e.g. diet refinement or refined DT50 on diet items (the latter only if fTWA can be used – see our previous article)), refinement can be made with drift reduction measures (e.g. buffers or nozzles).
If you would like to know more about how the TAI risk assessment may impact your ongoing or future bird and mammal risk assessments, please get in touch.
Enjoyed this article? Avoid missing out on our future news articles by signing up – you can select which topics you are interested in and can unsubscribe at any time.