Pest control for pets: taking a look beneath the surface 


Our household pets are subject to the possibility of catching fleas or picking up ticks. These pests not only irritate them but can lead to diseases being transferred and the pet’s health deteriorating. Luckily this can be prevented by using pest medication like spot-on flea or tick treatment. The medication contains chemicals that kill the fleas and ticks, but these chemicals are also damaging to aquatic environments which is where these chemicals end up via down the drain contamination. 

Anyone with a cat or dog will know the most common flea treatment is applying a small amount of medication to the back of the animals’ neck and letting it soak in. This type of treatment contains fipronil and imidacloprid. These chemicals were banned by the EU and UK from 2018 onwards and even before this there was no recorded use of either in the UK from 2016. They were previously used in agriculture as pesticides however, they had negative impacts on insects that were not the intended target for example pollinators like the honeybee. The risk of these chemicals is not unknown, and a study published by Spurgeon et al. highlighted fipronil as the contaminant of highest concern to UK surface waters. 

Analysing the wash off they found that chemicals were present in every type of wastewater for at least a month

If the chemicals are banned from agriculture, then how are they still entering UK water and being detected in UK water waste? This can be explained by unintentional down the drain contamination by pet owners. The University of Sussex and Imperial College London wanted to investigate the presence of contaminants further and completed a study with 98 dogs on flea medication. The application of the flea treatment to dogs’ fur and skin leads to the chemicals spreading quickly. When you apply the treatment to the dog you then may stroke the dogs’ fur later that day or even later that week, this transfers the chemicals spreading to your hands which you then wash.

The chemicals also end up on the dogs’ bed which at some point will also be washed. Fipronil and imidacloprid can stay on the dogs’ skin for over a week after application so when you wash your dog some of it comes off then and goes down the drain. The study aimed to control some of these factors like providing all the dogs with a fresh identical bed and owners with the same hand soap. They collected the wash off from owners washing their dogs, their hands, and the dogs’ beds. Analysing the wash off they found that the chemicals were present in every type of wastewater for at least a month (this was the length of the study). The levels were highest in the first 5 days of the dogs receiving the treatment and the wastewater with highest levels was the direct washing of the dogs. 

There are numerous negative effects that these contaminants can have on aquatic environments which is where most of the wastewater ends up as even water treatment does not remove all the contaminants. For example, research papers by Möhler (2004) and Margarido (2013) show that fipronil can introduce an excess of reactive oxygen species into the cells of fishes that they do not have sufficient enzymes to resolve the presence of a reactive species. The unchecked presence of these reactive oxygen species can lead to cell death. As in insects the chemical also binds to the GABA receptors on fish cells, these receptors are needed for correct neurological function in vertebrates.  Despite these negative effects there are no highly effective alternatives that can be used on cats and dogs as flea treatment. Thus, research in this field must continue and investment should be made to improve water treatment effectiveness. 

Image: Nick Allen via Wikimedia Commons

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