Written evidence from SongBird Survival (PPM0014)
Response to Environment and Climate Change Committee’s Inquiry into Pet Parasite Medication, May 2026
Response from SongBird Survival and Dr. Cannelle Tassin de Montaigu, Research Fellow at the University of Sussex.
This response draws on recent University of Sussex research, supported by SongBird Survival, which has identified a direct exposure pathway from pet parasiticides to wild birds through contaminated nest material.
Veterinary parasiticides, particularly fipronil and imidacloprid, have been found in bird nests across the UK and can transfer into eggs and chicks. These chemicals are widely used in flea treatments for cats and dogs, are highly toxic to invertebrates, and are also widely detected in rivers. The available evidence suggests that they are an important and still insufficiently recognised source of contamination in both terrestrial and aquatic ecosystems.
(Perkins et al., 2021; Wells and Collins, 2022; Tassin de Montaigu et al., 2025; 2026).
Recent UK research funded by charity SongBird Survival and completed by Dr Cannelle Tassin de Montaigu at University of Sussex has identified a direct and previously under-recognised pathway of exposure for birds. Pet hair treated with parasiticides is commonly incorporated into nests by small passerine birds such as blue tits and great tits, with an estimated 74% of examined Palearctic songbird species incorporating hair and fur into the lining of their nests (Harničárová and Adamík, 2016). A nationwide study of 103 nests found fipronil in 100% of samples and imidacloprid in 88%, demonstrating widespread contamination across the UK (Tassin de Montaigu et al., 2025). These findings indicate that exposure is not localised but occurring at a national scale.
Follow on research has demonstrated that these compounds can move beyond nest materials and into developing birds. Laboratory and field-based studies show that parasiticides can transfer from contaminated hair used in nest linings into eggs and chick tissues, confirming internal exposure during key developmental stages (Tassin de Montaigu et al., 2026).
Experimental work has provided important evidence of biological effects. In controlled studies where birds were offered fipronil-treated wool as nesting material, birds using treated material showed reduced fledging success compared to controls. This strengthens the evidence for a causal relationship between exposure and reproductive outcomes. While further work is needed to quantify population-level impacts, these findings demonstrate a plausible mechanism by which widespread environmental contamination could affect bird populations.
The primary substances of concern are therefore fipronil and imidacloprid, commonly used in spot-on treatments and flea collars for cats and dogs. Other compounds include permethrin and related pyrethroids, as well as newer treatments such as isoxazolines, although their environmental effects are not yet well understood. These chemicals are designed to kill invertebrates by disrupting the nervous system and are biologically active at very low concentrations.
These substances give rise to concern because they are persistent, bioactive at low doses, and highly toxic to non-target organisms, particularly insects and aquatic invertebrates. Notably, both fipronil and imidacloprid have already been heavily restricted or banned in agricultural use due to their environmental impacts yet continue to be widely used in companion animal treatments. This highlights a clear inconsistency in regulatory approaches across sectors.
Use of these treatments is widespread. Around 80% of the UK’s ~20 million cats and dogs receive parasiticide treatments annually, resulting in continuous release of residues into the environment at a national scale (PDSA, 2025).
There is also strong evidence of contamination in aquatic systems. Fipronil and imidacloprid have been widely detected in UK rivers and wastewater, in some cases at concentrations exceeding thresholds known to harm aquatic organisms (Perkins et al., 2021; Hadley et al., 2026). This demonstrates that these substances are entering the environment at scale and persisting across multiple ecosystems.
The strongest current evidence therefore infers that pet parasiticides which are used at very large scale are contaminating both terrestrial and aquatic environments and can directly expose wildlife. The emerging evidence from studies of birds is particularly important as it demonstrates a direct exposure pathway and measurable biological effects. Taken as a whole, the evidence points to these substances as a serious but still insufficiently recognised risk, particularly for invertebrates and insect-dependent species such as birds.
Pet parasiticides enter the environment through several pathways. The clearest evidence for terrestrial exposure comes from treated pet hair being incorporated into bird nests. Residues are also washed from treated animals during routine activities, entering wastewater systems and contributing to broader contamination of rivers and aquatic ecosystems. Collectively, these pathways represent both direct and indirect exposure routes for wildlife.
A key and previously under-recognised pathway is through the use of treated pet hair in bird nest construction. Many bird species, particularly small passerines such as blue tits and great tits, actively collect animal fur to line their nests. When pets have been treated with parasiticides, residues remain on their fur and are incorporated into nest material. Evidence shows that this results in widespread contamination of nests across the UK, with subsequent transfer of these compounds into eggs and chicks. This pathway represents a direct mechanism of exposure, through which chemicals designed to kill invertebrates are brought into close contact with birds during critical developmental stages.
Wastewater pathways also represent a route of substantial environmental contamination. Spot-on treatments spread across the animal’s coat and can be washed off during bathing, swimming, or exposure to rain, as well as through the washing of bedding and hands after application. These residues enter domestic wastewater systems and are discharged into rivers, where veterinary flea treatments have been identified as a significant source of fipronil and imidacloprid.
Additional dispersal occurs through shedding of contaminated hair and organic material into homes, gardens, and public spaces, where residues can enter soils, green spaces and waste streams. Pets may also transfer residues directly onto vegetation and surfaces outdoors, a pathway that is less quantified but still relevant. Because these compounds are highly toxic to invertebrates, their presence can also reduce insect abundance, with knock-on effects for food webs and insectivorous species.
Overall, the evidence demonstrates that pet parasiticides are dispersed through a combination of direct exposure (e.g. into bird nests), wastewater contamination, and broader environmental distribution processes. These pathways operate simultaneously and at scale, explaining the widespread detection of these chemicals across UK ecosystems. The evidence from bird nests is particularly important because it demonstrates a direct and widespread pathway of exposure for wild birds and therefore provides a critical insight into how these chemicals move through terrestrial ecosystems.
There is currently no clear evidence that alternative parasiticides carry a lower environmental risk. The more credible alternative is therefore not simple substitution, but more selective use based on veterinary assessment.
Many pets are treated routinely throughout the year regardless of their actual level of parasite exposure. A more selective approach, guided by veterinary assessment of factors such as lifestyle, seasonality and local parasite prevalence, could reduce unnecessary chemical use while maintaining animal health.
Some newer products, including isoxazolines such as fluralaner and afoxolaner, are increasingly used as alternatives to older compounds such as fipronil and imidacloprid. However, there is still very limited published evidence on their environmental fate, persistence and effects on non-target species. This means they cannot yet be assumed to represent a safer option.
Non-chemical or lower-impact approaches, including improved parasite monitoring, hygiene measures and more targeted treatment strategies, may also help reduce reliance on parasiticides in some contexts. However, their effectiveness and environmental benefit are not yet well established at scale.
In summary, there is no straightforward replacement that can currently be safely assumed to have little or no environmental impact. The most effective approach is likely to combine reduced and more targeted use with stronger environmental assessment of both existing and alternative products. Without this, there is a significant risk that environmental harm will continue through substitution rather than reduction.
Any answer to this question needs to weigh the benefits of parasite control for animal and public health against the potential risks associated with widespread pesticide exposure. A more selective approach to parasiticide use could help reduce environmental contamination while maintaining appropriate protection against fleas, ticks and related diseases.
Reducing the use of parasiticides without suitable alternative strategies could increase animal and human exposure to fleas, ticks and some tick-borne or zoonotic diseases. However, the level of risk is not uniform and depends on factors such as geography, season, pet lifestyle and local parasite prevalence. Current practice often involves routine prophylactic treatment regardless of individual risk, which may result in unnecessary chemical use. A more selective approach, guided by veterinary assessment, would allow these risks to be managed more proportionately.
At the same time, pet owners are being directly exposed to these chemicals through contact with treated animals and through residues in the home environment, including dust, bedding and soft furnishings. Children may be more likely to encounter these residues because of their close contact with pets and household surfaces. There is some toxicological evidence that compounds such as fipronil and imidacloprid can affect mammalian systems in laboratory studies, but the implications of typical real-world exposure in humans remain uncertain.
Important uncertainties remain regarding chronic low-dose exposure, combined exposure to multiple compounds, indoor accumulation, and possible developmental effects in children.
Both under-use and over-use of parasiticides carry risks. A more selective approach is therefore likely to be the most proportionate way to reduce environmental and potential human health risks while maintaining effective parasite control.
There is a need to balance the benefits of parasite control for animal and public health with the potential risks associated with widespread pesticide exposure. A shift towards more targeted and evidence-based use of parasiticides could reduce environmental contamination while maintaining appropriate protection against parasites and associated diseases.
Reducing the environmental and human health risks associated with pet parasiticides depends upon stronger regulation, risk-based prescribing, clearer product guidance, better public information and guidance, and improved environmental monitoring. Current systems do not adequately assess or manage the cumulative impacts of these widely used chemicals, so their effects on ecosystems may be drastically underestimated.
One priority should be to strengthen environmental risk assessment. Companion animal medicines are not subject to the same depth of environmental scrutiny as those used on livestock, and the long-term fate and ecological effects of these compounds are not always fully assessed before widespread use. Stronger requirements would help ensure that both existing and newly developed products are evaluated more robustly.
Clearer product labelling and owner guidance are also needed. Current information often provides little detail on environmental risk, and some advice appears inconsistent with the available evidence. More accurate guidance on bathing, swimming, bedding and post-treatment handling would help reduce unintentional contamination of waterways and households.
There is also a need for greater public awareness and veterinary stewardship. Many pet owners are unlikely to realise that these chemicals can enter the environment through everyday activities such as washing treated pets, cleaning bedding, or allowing animals to enter water. Better communication from manufacturers, retailers and veterinary professionals could support more informed and responsible use.
Finally, improved environmental monitoring and regulatory consistency are needed. Systematic surveillance of veterinary parasiticides in rivers, soils, wildlife and urban environments would help quantify contamination and assess whether interventions are working. Greater alignment across regulatory frameworks would also be appropriate, given that some of these compounds are subject to strict restrictions in agriculture but continue to be widely used in companion animal treatments.
Risk reduction will depend on a coordinated approach that combines stronger assessment, better information for users, improved monitoring, and more consistent regulation. Without these changes, current patterns of use are likely to continue contributing to environmental contamination and potential human exposure.
Several knowledge gaps remain, such as the effectiveness and environmental impact of alternative treatments; the long-term monitoring of veterinary medicine residues in the environment; and the potential mechanisms of transfer of these chemicals both inside and outside of the household.
We also believe the primary issue is not simply the lack of knowledge, but rather the absence of a Phase II environmental risk assessment for pet parasiticides. Therefore, the environmental exposure, persistence, ecotoxicity, and long-term ecological consequences are not adequately investigated. As a result, compounds like fipronil and imidacloprid continue to be extensively applied to millions of pets despite the plethora of evidence regarding their negative effects on the environment.
These gaps mean that current environmental risk assessments do not fully reflect the scale, persistence, and complexity of real-world exposure. Addressing them will require a combination of improved risk assessment frameworks, targeted research on ecological impacts, and strengthened monitoring systems. Without this, there is a high likelihood that environmental risks will continue to be underestimated.
References
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