CEA presented 16 posters at SETAC Dublin in April/May 2023. We will be showcasing each of these presentations in a series of ‘SETAC Spotlight’ articles. This week it is:

Time weighted average factor (fTWA) assessments for birds and mammals under the new bird and mammal guidance – experiences to date

Authors: Amy Brooks1, Helena Crosland1 and Alan Lawrence2
1Cambridge Environmental Assessments; 2Alan Lawrence Ltd

The potential risks to wild birds and mammals from foraging in areas treated with pesticides must be assessed in the EU under Regulation (EC) 1107/2009. Currently, the risk assessment is performed using the EFSA (2009) guidance, but this is in the process of being revised, with a new guidance being released by EFSA in 2023 but not yet noted within the EU. Within the new guidance, a number of changes have been made compared to the EFSA (2009) guidance, including the use of time-weighted average factors (fTWA) in reproductive risk assessments.

Under EFSA (2009), fTWAs could be used for reproductive risk assessments, with a default value of 0.53 being applied (relating to a DT50 of 10 days and an averaging period of 21 days) to dietary items such as crop plants, weeds, insects, etc where foliar uses of pesticides were proposed. The assumption behind this was that the toxic effects observed in reproductive toxicity studies were driven predominantly by long-term, rather than short-term, exposure, and therefore residue decline over time could be taken into account in the risk assessment. Conversely, if effects were expected to be driven by the initial maximum level of exposure, then taking into account residue decline over time (and thus a Ftwa) would not be appropriate.

Under the new guidance (EFSA 2023), the fTWA is no longer used by default in the reproductive risk assessment for birds and mammals. Instead, an assessment must be made as to its appropriateness based on the effects observed in the mammalian and avian toxicity studies. This poster presents our experiences to date in performing these assessments, highlighting potential issues and where further clarity of guidance is recommended where relevant.

If you would like to discuss any of the topics raised in this article, feel free to contact us.

The poster is available for free download.

You can find all of the other posters that CEA presented at SETAC Dublin here. You can also find all of our publications from previous conferences and links to journal articles we have authored on our library page.

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