A UK inquiry into common parasite treatments for pets finds their widespread use “is not supported by robust scientific evidence.”
The report says two of the chemicals often used for treatment are already banned in farming because they’re dangerous to insects like bees.
Given the meds’ toxicity, especially in water environments, and lack of information on how they affect humans, it recommends restrictions until their impact is measured.
The SMC asked experts to comment on use of the treatments in NZ, and their effects on our ecosystems.
Chloe McMenamin, Lecturer & Researcher in the School of Environmental and Animal Sciences, Unitec, comments:
“The current practice of selling flea and tick treatment products for pets freely over the counter for routine monthly use is increasingly difficult to justify given the weight of scientific evidence.
“This is also an emerging issue in Aotearoa New Zealand, and we should begin to open a dialogue about developing a plan before contamination escalates further.
“For the past four years I have been working alongside other researchers to investigate this issue from a New Zealand perspective. Our current research focuses on detecting flea and tick treatment chemicals – imidacloprid, fipronil, and fluralaner – in wastewater systems across the North Island of New Zealand. We found these chemicals at concentrations likely to cause ecological impact. Additionally, our testing indicates they are passing through the wastewater treatment process essentially unchanged.
“New international research shows that chemicals from common pet flea and tick treatments aren’t staying on our pets. Birds often line their nests with fur they collect from the ground, including moulted dog and cat fur, and that fur is carrying pesticide residues straight into the nest. Studies from the UK and Hungary have now found these chemicals not just in nest linings, but in unhatched eggs, dead chicks, and even the feathers of adult garden birds. Traces have also shown up in ponds where dogs regularly swim, at levels exceeding safety thresholds for aquatic life, for weeks after treatment.
“From a New Zealand perspective, I’d like to stress this isn’t a reason to stop protecting pets from parasites – but it does show these products don’t disappear once they’re applied. Their environmental footprint, and what it could mean for our indigenous avian species, deserve closer attention here in Aotearoa New Zealand. I recommend you speak to your veterinarian or animal health care about the options for supporting your pet’s health while also safeguarding our environment.”
“Agricultural pesticides undergo environmental risk assessment before use, but there are currently no equivalent requirements in Aotearoa New Zealand for these veterinary chemicals. This represents a clear gap in our regulatory framework.
“As we consider how to align with international trends on environmental protection, I believe this is an area where straightforward changes could deliver meaningful environmental benefit at relatively low cost.
“These changes include moving toward veterinarian-guided use rather than routine blanket treatment; addressing flea and tick issues through environmental and non-chemical management approaches rather than relying on chemical treatment alone; providing environmental contamination risk information upon dispensing, such as not bathing or swimming pets for the duration of the product’s action; and risk-based treatment – treating the pet only when parasites are present.”
Conflict of interest statement: Chloe has declared she has no conflicts of interest.
Dr Joanne Clapcott, President of the New Zealand Freshwater Sciences Society, comments:
“New Zealand’s rivers are already under pressure from well-established threats such as excess nutrients, sediment, habitat loss and climate change. This UK report highlights a potential additional pressure from pet parasite medications that is receiving increasing scientific attention overseas, but we simply don’t yet know how important this pathway is in New Zealand. The list of chemicals entering our waterways continues to grow faster than our understanding of their ecological effects.
“The response shouldn’t be to jump to conclusions or discourage responsible parasite treatment for pets. Instead, this is a reminder that we need sustained investment in freshwater monitoring and independent science so we can identify emerging contaminants early and understand their ecological significance alongside other pressures. Then we can make good evidence-based decisions about managing New Zealand’s freshwater.”
Conflict of interest statement: “No conflicts.”
Professor Melanie Kah, School of Environment, University of Auckland, comments:
Conflict of interest statement: Melanie has declared she has no conflicts of interest.
Siobhan Ellis, veterinarian, comments:
“This topic is important and valuable to be discussing. As a NZ veterinarian, we have been taught to treat fleas and parasites preventatively due to the risk they pose to humans and animals. Until now, how this impacts the environment has not been widely discussed.
“I agree with the call for more research and data, and to increase education to vets on the impact of these products to the environment. Flea and worm treatments do provide a known health benefit to both pets and humans, and prevention can be important, as treating once the problem is established can be difficult and require more intensive chemicals.
“Additionally, the two products that are highlighted (Fipronil and Imidacloprid) are falling out of favour with NZ vets for newer products, and much less is known about the environmental impact of these new products.
“It would also be useful to have research that compares the environmental impact of spot-on treatments (those applied to the skin) with oral treatments. Current recommendations from vets are often based on ease of administering the treatment and considerations like the bathing routine of the pets, but if more was known about the environmental impacts between these two formulations, this could be factored into these suggestions.
“I think before any changes are implemented in NZ, we should have our own research done. The NZ environment is very different due to less densely populated cities that would reduce contamination, and a possible higher need for flea control due to the warmer climate that favours flea growth.”
Conflict of interest statement: “I am working for a veterinary pharmaceutical start up (not flea/ parasite treatment related).”
Our colleagues at the UK SMC have also gathered comments. A small selection follows.
Prof Oliver Jones, Professor of Chemistry, RMIT University, Australia said:
“This is an interesting and balanced report. The evidence that medications designed to treat things like fleas and ticks in our pets get into the environment is very strong. The consequences of their presence are less clear. While the risk of harm to humans and pets is low, it is certainly possible that these compounds may have unintended consequences on the environment by killing aquatic invertebrates and other species. The key word, however, is “may”. The evidence at this stage is largely circumstantial. Just because something can cause harm does not automatically mean that it does so. As noted in the report, there are many types of contaminants in rivers that might affect things that live there, so how do we know which is worst, or where to focus our efforts? This requires careful thought.
“Prophylactic treatment of pets for fleas and ticks is not a bad thing in itself. If you don’t treat an animal until after it is infected, you are potentially causing suffering that could be avoided. Treating pets early also stops their owners from getting infected. What this report shows is that this practice is not without risk. The committee’s overall suggestions of getting more data on the amount of these compounds that are used and avoiding unnecessary treatments are sensible. The unenviable task regulators have is to try to balance the risks of not treating pets for parasites early enough against the potential negative effects on the environment of doing so.”
Conflict of interest statement: “I have previously published research on pesticides in food and the environment. I have in the past received funds from the Environment Protection Authority Victoria and various Australian Water utilities for research into environmental pollution.”
Prof Leon Barron, Professor of Analytical & Environmental Sciences, Imperial College London, UK, said:
“We’ve tested thousands of water samples and aquatic organisms across most UK waterways and coastal areas and these products come up consistently as posing the worst risk to aquatic life.
“As a cat owner, who used spot-on products myself until 2022, I couldn’t initially reconcile this tiny drop on the back of our cat’s neck at home with the concentrations we were seeing in the environment. The fact is that the vast majority of this is coming from household wastewater. After you use it, it washes off the pet, contaminates your skin, clothes, upholstery, and floors. When these are washed, it ends up down the drain and out into the environment.
“Wastewater treatment is ineffective at removing some of them, so it isn’t just the raw sewage spills we’re talking about, it’s also in the water that’s been treated.
“While upgrading water treatment technology can be a solution, a more immediate solution is reducing how we use them. Talk to your vet and see if your animal is at risk of ticks and fleas and whether you actually need them. There’s got to be a better balance, which maintains health of our pets while also protecting the environment.”
Conflict of interest statement: “I am one of the founding members of the PREPP team at Imperial’s Grantham Institute for Climate Change and the Environment studying this issue and I supplied written evidence to the Environment and Climate Change Committee for this inquiry. I am Chair of the Royal Society of Chemistry interest group on separation science. Projects in my lab have been co-funded by industry, including agrochemical and pharmaceutical industry partners, as well as the UK government. None of these work in the pet parasiticide industry sector that I know of.”