Recent research raises this question as studies show environmental contamination with flea products. The flea products identified are potent insecticides so their presence in the wider environment endangers the insect population. So how important is this?

The VMD (Veterinary Medicines Directorate) regulates the use of veterinary medicines in the UK. In light of the recent findings, the VMD has commissioned a PhD at the University of Sussex to study the environmental impact of commonly used flea treatments used in dogs, cats, rabbits and ferrets. (1)

New research has raised concerns

Recent studies have found that two products routinely used for flea prevention and treatment are present in high levels in English rivers and household dust in the homes of treated pets. These products, fipronil and imidacloprid, are highly potent insecticides so they pose a considerable risk to insect populations and animals higher up the food chain. A European Commission review in 2018 showed that the global insect population is falling and that environmental contamination with insecticides may be a contributing factor. 

So far, only fipronil and imidacloprid are being investigated. Both products have been banned from agricultural use since 2017 and 2018 respectively because of environmental contamination. However, insecticide use in non-food animals has not been regulated in the UK. It was thought that the small quantities used on individual animals carried an insignificant risk. However, recent studies suggest this is not true. 

How big is the problem?

Monthly, year-round preventative treatments are currently used in a large proportion of the 10.9 million cats and 9.9 million dogs in the UK. This results in an accumulation of the chemicals in the environment. 

These chemicals are very effective insecticides, so low levels pose a risk to insect populations. The effects of fipronil on bee populations are widely reported. One study (2) measured the amount of fipronil in household dust in the homes of treated pets. The results showed that 1 gram of dust contained enough fipronil to kill over 750 bees(3). Further research is needed to assess whether the fipronil found is active and killing insects or whether it becomes inactivated in dust.

A 2017 study (4) found fipronil in 99% of samples in 20 English rivers. The levels were above safety limits according to Canadian water safety data. We have no official limits for these chemicals in the UK currently. In fact, levels of fipronil were found to be 5 times higher than the safety limit. While levels of fipronil sulphone, a powerful breakdown product of fipronil were found to be 38 times higher. This is believed to be because of environmental contamination from swimming dogs, bathing dogs, washing pet bedding and owner’s hands after stroking treated pets. Further research is necessary to prove how the chemicals reach water courses. 

Another 2017 study carried out by Buglife looked at imidacloprid levels in urban UK rivers (5). Imidacloprid was found in 66% of the rivers sampled, with levels above the toxic limit in 7 of the 20 rivers. This study found the highest levels in water drained from urban areas suggesting pet treatments were the source of contamination rather than farmland. 

Flea-free but harming the environment

The team investigating these findings at the University of Sussex believe that the widespread use of flea products is causing environmental harm. They recommend considering regulation, perhaps moving some products to a prescription-only category, a thorough assessment of the environmental impact and reconsidering year-round treatment. Fleas are not as prevalent in winter although central heating in our homes means that they can survive and continue to lay many eggs that can hatch to infest the home. Fleas are often responsible for skin disease in domestic pets with human transmission occurring in infected homes. Prevention of home infestations and skin disease has driven the use of year-round parasite control. This has been recommended to promote good health for our pets. 

This new information means that as pet owners and vets we need to carefully consider how best to protect our pets, homes and the environment. 

  1. Perkins R. “Are pet parasite products harming the environment more than we think?” (2020) Vet Record. September issue:197
  2. Mahler BJ, Van Metre PC, Wilson JT, et al. “Fipronil and its degradates in indoor and outdoor dust”. (2009) Environmental Science Technology 43:5665– 70
  1. Tingle CCD, Rother JA, Dewhurst CF, et al. (2003) “Fipronil: environmental fate, ecotoxicology, and human health concerns”. Rev Environmental Contamination Toxicology 176:1–66
  2. Teerlink J, Hernandez J, Budd R. “Fipronil washoff to municipal wastewater from dogs treated with spot-on products”. (2017) Sci Total Environ 599– 600:960–6

Shardlow M. “Neonicotinoid insecticides in British freshwaters”. (2017) (accessed 19 November 2020)