Silent Rivers
By Jeff Gill

In 1962, Rachel Carson published her seminal book A Silent Spring. In it, she exposed the devastating environmental damage caused by the pesticide DDT and challenged the misinformation from industry, together with the lack of questioning by public bodies. In 2025, it appears we still haven’t learnt to stop the damage caused to the environment by pesticides, as our rivers fall ever more silent under this continuing chemical assault. As a pet owner, I have a dog, it’s the black one in the photo. I was shocked to realise that I was part of the problem when I discovered the pollution of our rivers by the pesticides in the popular Spot-On pet medicines that are used to treat fleas and ticks.
This is what I found out. The pesticides fipronil and imidacloprid are still authorised for use in pet medicines in spite of them being banned for agricultural use nearly ten years ago. This is largely because barely any environmental risk assessment takes place by our regulators, as it is assumed that the pesticides are unlikely to enter the environment in any quantity. But assumptions can be dangerous, especially when you consider there are over 10 million dogs and over 10 million cats in the UK. The dodgy assumptions are weakened further when, on top of the vast number of pets, an aggressive pet med marketing strategy is designed to entice and often frighten pet owners to use as many of these products as often as possible and for as long as possible.
“Driven by innovation and profit, the pharmaceutical and chemical industry require marketing authorisation to get their products onto the market as quickly as possible. The regulatory authorities rely on industry to ensure that their products are safe and effective, in other words, to mark their own homework. Technology today is far more reliable and predictive of human health and environmental impact than ever before. The challenge facing society today is government inertia to amend regulatory requirements in line with 21st-century evidence-based test methods”.
Dr Andre Menache MRCVS PVA – Progressive Veterinary Association
Industry misinformation exposed all those years ago by Rachel Carson still exists today and is evidenced by the strategies to boost sales. Marketing claims fly in the face of the advice coming from responsible vets and ignore the science. For example, organisations like Vet Sustain and the PVA champion a ‘One Health’ approach (see below) and disagree with the practice of applying routine monthly prophylactic use of these Spot-On treatments regardless of need. Instead, like many others, they advocate a risk/need-based approach, contextualised is the phrase often used, as well as the use of environmentally safer or better still safe alternatives.
So, given all this, just how wrong have those assumptions made by our regulator proved to be? For our aquatic life, the answer is disastrous because this is what we now know and why it matters. To start with, there is the question of how do pesticides in Spot-On pet treatments which are applied in the household get into our rivers in the first place? The image below drawn from extensive research, shows how this happens. Since this was published in 2021, the suggested but at that stage unconfirmed additional pathways have also been confirmed. {Thanks to Dr Rose Perkins and Sussex University for the image)

So that’s how pet product pesticides get into our rivers but to what extent is this a problem for aquatic life? Just how many rivers are affected and what concentrations are being found? Environment Agency data from 2018 found extensive contamination of many English Rivers with fipronil and imidacloprid being found in at least two-thirds of the samples (99% in the case of Fipronil). Further monitoring in 2024 concluded that the levels of these two chemicals was now way above the PNEC, this being the predicted no effect concentration. As a result, the Environment Agency has identified these two pesticides as top of their list of priority concerns as well as confirming the source from pet medicines, all of which is supported by independent research. Other published studies have ranked fipronil as the organic pollutant posing the greatest threat to English waterways and ranked imidacloprid (a neonicotinoid) as the highest-risk organic contaminant in London’s waterways. So online retailers like, for example, Amazon and Pet Drugs Online have a lot to answer for, and yet in spite of these levels of pollution, they still continue to drive booming sales of products like Itch Flea©, Frontline©, Advantage©, Bob Martin Plus© to name a few.
Are pet owners aware of this problem? A study by Imperial College London of ponds on Hampstead Heath, see the image below, confirmed not only pet pesticide levels at way above risk thresholds but also that most dog owners were not aware of the problem. It did, however, find that many dog owners would choose safer alternatives if they knew what was going on.

Taking a deeper dive into our increasingly silent rivers we know that Mayfly nymphs are amongst some of the aquatic invertebrates most vulnerable to these two chemicals. You only need to speak with trout anglers in national parks like Exmoor to find out what they think about this pollution. One resident on Exmoor told me that “These pet medicines containing pesticides are poisoning the pristine waters of the rivers Barle and Exe and killing off the insects and water life that used to sustain the migratory fish like Atlantic salmon, native trout and local bird life”.

You might expect rivers in our National Parks to do better than most but not so. As it turns out they are the most heavily polluted compared with urban rivers when it comes to human pharmaceuticals. Add the pet medicines to this, and yes fipronil and imidacloprid are being found at alarming levels in the small rivers on Exmoor, then this is an eco-toxic timebomb poisoning our rivers and risks silencing them for good.
As well as invertebrates and the knock effect on fish stocks and river-dwelling birds like dippers and kingfishers, there is increasing concern for my personal favourites, the otters that rely on a healthy ecosystem to survive and thrive. As apex predators, they can be a keystone indicator of river health.
But our rivers can’t speak up for themselves, so what can we do about all this? One thing is for pet owners like me who love their pets and who love nature to explore alternative approaches. For example, consider environmentally safe tick repellents like Cedarcide© (made from all-natural cedar oil and smells great!). Talk to your vet and ask about some of the oral medicines that are potentially safer, as well as assess the level of risk your pet might be exposed to, for instance are ticks an all-year-round issue where you walk your dog or very seasonal?
“Risk-based parasite control in pets means tailoring parasite prevention to each animal’s lifestyle and infection risk, instead of giving routine treatments to every pet. This approach balances animal, human and environmental considerations, reducing unnecessary drug use, limiting side-effects, slowing resistance development, and helping protect the environment.”
Dr Rosemary Perkins BVSc CertSAOpth PhD MRCVS

We can also challenge the industry to clean up their act. For example, put feedback about environmental damage into reviews, talk to store managers in supermarkets and other retail outlets (The Co-op and Waitrose have stopped selling these products) and write to the mighty Amazon and the like. If your vet happens to be part of the IVC Evidensia chain, then ask them about the environmentally irresponsible marketing practice of Pet Drugs Online which is owned by this global vet group.
At the government level, there is increasing awareness of the problem and of public concerns. As a result, there are small signs that DEFRA ministers are beginning to listen and the regulatory bodies like the VMD that are accountable to DEFRA are taking tiny steps although handicapped by the powerful lobby from the vet medicines industry. Talk to your MP and let them know not enough is being done nor at a pace in keeping with the data and research. We can collectively start to drown out the big pharma lobby with noise of our own. Taking action, which surely is what River Action is all about.










