SETAC Spotlight: Bird-Brained? Migratory Bird Risk Assessment

CEA presented 1 platform and 9 posters at SETAC Seville in May 2024. We will be showcasing each of these presentations in a series of ‘SETAC Spotlight’ articles. This week it is:

SETAC Spotlight: Bird-Brained? Migratory Bird Risk Assessment According to the New EFSA (2023) Bird and Mammal Guidance

Authors: Helena Crosland, Amy Brooks, Emma Russell

Cambridge Environmental Assessments, RSK ADAS, Boxworth UK

The new EFSA guidance document on the Risk Assessment for Birds and Mammals (EFSA 2023) contains several chapters dedicated to the choice of acute and chronic endpoints for use in ecotoxicology risk assessment. Amongst these, chapter 5.2.9. “Special consideration for migratory birds” is a small section of the guidance, amounting to less than a single page, but with the potential to have significant implications for the avian risk assessment for some substances.

Why migratory birds?

Why do migratory birds require specific consideration in the new guidance document? The reason behind EFSA’s concern appears to be the particular life traits of migratory birds and the sensitivity of these traits to certain Modes of Action (MOAs), as well as their potential for exposure to pesticide residues.

Migratory birds perform hyperphagia i.e. pre-migratory fattening through excessive eating in order to fuel their intensive migratory flights. They may make use of farmland for this purpose, and/or use farmland as a stopover to refuel during migration. There is therefore the possibility of high exposure to pesticide residues. Cognitive processes such as orientation and navigation are very important for migratory success. The Bird and Mammal guidance (EFSA 2023) therefore raises concerns over the sensitivity of migratory birds to neurotoxic pesticides, and in particular neurotoxic insecticides (e.g. nicotinic acetylcholine receptor (nAChR) agonists or acetylcholinesterase (AChE) inhibitors) which may disrupt cognitive function and therefore migratory success. The guidance also raises concerns with chemicals which show an effect on weight-gain in studies. These effects may cause a reduction in populations if birds are not able to successfully migrate to feeding or mating grounds.

Migratory birds may be particularly at risk from neurotoxic insecticides e.g. nicotinic acetylcholine receptor (nAChR) agonists or acetylcholinesterase (AChE) inhibitors. Birds may use farmland as a stopover and refuelling source, and therefore may be exposed to pesticide residues. Effects on cognitive and motor functions could result in issues with refuelling, orientation and navigation, and therefore migratory success.

What is the migratory bird risk assessment?

What does the migratory bird risk assessment entail? Chapter 5.2.9 of EFSA (2023) is a short section of the guidance, which does not present a strongly structured risk assessment, and leaves several questions unanswered.

Here we provide a summary of our understanding of the assessment, as well as highlighting the areas which we believe require further consideration and clarification.

Mode of action (MoA)

What we know:

The assessment requires a consideration of whether the substance in question is known to have a neurotoxic MoA. AChE inhibitors and nicotinic acetylcholine receptor (nAChR) agonists are specifically mentioned, but it is stated that it should also be checked if the substance has “other neurotoxic mechanisms”. If this is the case then further steps are required.

What isn’t clear:

It is not explained what “other neurotoxic mechanisms” are, nor how we can identify them. It is not known whether it is likely for substances where the main MoA is not neurotoxic to have unintentionally neurotoxic effects which could impact migratory birds. Finally, it is not explicitly stated that the absence of any known neurotoxic MoA precludes the need for further assessment. If a substance is not listed as having a neurotoxic MoA (for example, if a neurotoxic MoA is not elucidated in the human health risk assessment), does this mean that one must ‘go looking’ for neurotoxic effects in the bird/mammal data?

Passerine data

What we know:

If a neurotoxic MoA is identified, then it should be checked if lab data on passerine species is available. This is sometimes the case if studies have been performed for regulatory regimes outside of the EU. The purpose of this is to compare the sensitivity of passerine and non-passerine birds (standard test species) to “see whether the reproductive risk assessment… with the use of a standard assessment factor of 5 is assumed to adequately cover possible effects on migratory birds”.

What isn’t clear:

The focus here is on acute data (as passerine studies are only likely to be available on the acute scale), but we consider sub-lethal effects to be more relevant for the risk to migratory birds. Using this as a proxy may not be very useful. In addition, there may be natural variation in the sensitivity of passerines versus non-passerines, which may not relate to migration. But it is not clear whether any research has been done on this.

Mammal data

What we know:

When specific data on passerines are not available, the guidance states that the mammalian data package should be considered, with particular attention to neurotoxicity studies and primary effects on body weight. One should then compare the range of doses where effects occur in mammal and bird studies to determine if this allows us to conclude that the chronic bird endpoint is adequately protective of migratory birds.

What isn’t clear:

It is not clear if consideration of mammal data is always needed when passerine data is not available, or whether we can stop earlier in the process if there is no indication of a neurotoxic MoA from the human health assessment. It is also questioned how appropriate it is to use mammal data to conclude the risk to migratory birds – is this too big of a leap?

Additional conservativeness

What we know:

Finally, according to the guidance, if effects do not occur at similar doses between birds and mammals, then additional conservativeness should be explored. This could be by the use of an assessment factor, or by explaining the potential risks to migratory birds to the risk managers. It is stated that additional vertebrate testing should not be performed.

What isn’t clear:

It is not clear what sort of assessment factor should be applied to the risk assessment, nor how appropriate the proposed additional conservative options are. It is not currently possible to determine if the proposed assessment strategy for migratory birds would over- or under-estimate the risk to migratory birds.

Final thoughts

It is possible that the migratory bird assessment presented in the EFSA (2023) guidance will only impact neurotoxic insecticides with known neurotoxic MoAs (which therefore have the potential to negatively affect bird migratory success). However, it is currently unclear whether the assessment will also impact any other substances where neurotoxic effects cannot be excluded (and the requirements for excluding a substance are vague). It is also not currently clear whether the proposed scheme is protective of the potential risks to migratory birds, or whether it is overly conservative – potentially implementing additional restrictions where they are not required. The impact of this element of the new EFSA (2023) guidance will likely only become apparent once the guidance is implemented and submissions to regulators have been attempted.

You can download the full poster (as presented at SETAC Seville in May 2024) on this topic here.

If you would like to discuss the potential impact of the migratory bird assessment, feel free to contact us.