Cat and dog flea treatments harm river life

Companion animal flea treatment pesticides, fipronil and imidacloprid, are ending up in rivers where they harm marine wildlife and insects such as dragonflies, mayflies and beetles. Fipronil is the main ingredient in the well known and well used Frontline flea treatment for cats. It’s an insecticide which disrupts the insect’s central nervous system causing them to die. This problem has been known about for a while as I wrote about it in Jan 2018. Message to the manufacturers: TAKE REMEDIAL ACTION PLEASE.

Flea treatment insecticides pollute rivers and streams
Flea treatment insecticides pollute rivers and streams. I have pointed to the chemical concerned.
Two useful tags. Click either to see the articles:- Toxic to cats | Dangers to cats
Fipronil in cat and dog spot on flea treatments
Fipronil in cat and dog spot on flea treatments is killing river wildlife. Image (annotated) in public domain.

Bathing – dog owners more to blame?

It is believed that the chemical is getting into river systems after cats and dogs have been bathed or their bedding cleaned. Traces of the chemical on bedding is washed into the drainage system and thence to rivers. That’s the theory. I suspect that dog owners are more to blame that cat owners as dogs are bathed often whereas cats are very rarely bathed.


Researchers at Sussex University, in testing samples of river water collected by the Environment Agency, found that concentrations of fipronil and imidacloprid “often far exceeded accepted safety limits”. The study concerns the UK and the worst affected rivers were the Nene in the East of England, the Test in Hampshire and the Waveney on the boundary of Suffolk and Norfolk. The highest levels of pollution were found just downstream of sewage treatment works.

In 98% of samples, fipronil was detected while the average concentration was 5.3 times the safe limit according to The Times report of Tuesday, November 17, 2020. The research was funded by the Veterinary Medicines Directorate.

The study was published in Science of the Total Environment. Dave Goulson, co-author of the study, said, “Studies have shown both pesticides to be associated with declines in the abundance of aquatic invertebrate communities”.

He found it deeply troubling that rivers are being routinely and catastrophically contaminated by these chemicals and their “toxic breakdown products”.

Pesticides banned in agriculture

These pesticides are banned in the agricultural sector but are still permitted for pet treatments.

Many products

There are 66 veterinary products containing fipronil in the UK and 21 containing imidacloprid. Some of the products can be bought off the counter at supermarkets and pharmacies and online. Others can only be purchased with a prescription from a veterinarian.


Matt Shardlow, cheif executive of Buglife referred to fipronil as a ‘highly toxic nerve agent’ and that the overpollution of “all water bodies” is shocking. A full investigation needs to take place into the impact of these pesticides on the environment. Clearly, other domestic animal flea treatments need to be included in such an investigation.


There is no automatic need to apply pesticides to pets on the advice of vets. Veterinarians tend to sell and promote the use of pesticides as skin parasite treatments for companion animals without asking pertinent questions about whether they are genuinely needed. I have never applied spot-on pesticide treatments to the cat that I have lived with. I flea comb my cat very frequently and I don’t have a flea problem. Why do people think they need to apply this treatment willy-nilly as a matter of course when it might not be needed? Think of alternative ways of proceeding such as physical checks and keeping the home clean and free of fleas.


Frontline say that people shouldn’t touch the chemical i.e. the insecticide because it is dangerous to touch. And yet we put it on our cats. Strange, don’t you think? We have known about this problem of insecticides polluting rivers for a while now but nothing has happened. It is deeply troubling that we are using a strong insecticide to protect our cats and dogs from fleas while at the same time achieving the opposite with respect to river wildlife. It is simply unacceptable. Looking after our pets can be quite destructive of nature and the environment. It isn’t just parasite treatments such as Frontline and and other products such as Advantage illustrated above. Both the manufacture of cat litter and its disposal harms the environment. We talking about millions of tonnes of the stuff. The numbers are vast. It doesn’t surprise me that these pesticides end up in rivers when you consider the huge quantities being used by consumers.

The manufacturers involved in supplying pet products of all kinds have shown an irresponsible attitude towards environment and I would argue their attitude is not always responsible in terms of the health and welfare of companion animals either. Their priorities are financial profit and shareholder dividends. I’d like to see an improvement in attitude which demonstrates a concern for nature and the environment which I think would benefit these big businesses as today consumers are far more switched on to environmental issues thanks to the coronavirus pandemic and global warming. It is time for them to step up to the plate and become environmentally responsible.

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