Study: Toxic Substances in Flea Control Products Remain in the Home

Last spring, at the initiative of the Hollands Noorderkwartier Water Board (HHNK), the municipality of Uitgeest, and the municipality of Heemskerk, the campaign “Take Care of Your Pet and Your Garden, and Protect Nature” was launched. The campaign helps residents become more mindful of their use of products such as flea treatments for dogs and cats. Many people are unaware that the toxic substances in these products can linger in their homes and indirectly end up in surface water. A preliminary study of nearly fifty households in Uitgeest and Heemskerk shows that toxic substances do indeed linger in homes.

One component of the campaign was an exploratory survey of households to determine which substances pets carry on their bodies—for example, through the use of flea control products. These substances can end up in surface water via hair and dust. By gaining a better understanding of this, we can work more effectively toward clean surface water for people, animals, and nature. Residents of Heemskerk and Uitgeest who own a dog or cat could participate in the citizen science study by submitting a dust and hair sample.

Survey Results

The Velt association conducted the study. The results show that chemicals from flea and tick treatments remain indoors. The five most commonly detected chemicals indoors are imidacloprid, fipronil, dinotefuran, pyriproxyfen, and selamectin. These chemicals are commonly found in flea and tick treatments. Imidacloprid and fipronil were banned in agriculture in the European Union years ago because they are too harmful to humans and the environment. HHNK has observed that imidacloprid, which causes bee mortality, is still present in surface water. This study shows that the use of this substance in pets may explain its continued presence in the water. At the same time, further research is needed to better understand the exact extent of this contribution. For the full research report, visit:www.hhnk.nl/doemee.

Every contribution to cleaner water counts

The substances detected are of concern to the water board because previous studies have shown that veterinary drugs can enter surface water through hair, fur runoff, and treated animals swimming. This study shows that such substances are present in homes and can therefore serve as a source for further dispersal into the environment. Water Board Member Jos Beemsterboer, portfolio holder for integrated water management in rural areas: “We frequently encounter these toxins in water quality measurements, sometimes in concentrations that are too high. Many residents are unaware that these types of substances are also found in consumer products. With this campaign, we have brought this issue to the public’s attention. Use chemicals responsibly and only when necessary, and choose products with the least possible impact on the environment. Only if everyone—the water board, other government agencies, agriculture, industry, and residents—does their part can we improve water quality.”

Tips for Pet Owners

  • Only treat a pet with flea medication when it is truly necessary;
  • Prevent a flea infestation: check dogs and cats weekly with a flea comb
  • Wash the blankets and pillows from sleeping areas regularly at 60 degrees;
  • It's better to choose a short-acting pill rather than long-acting pipettes or collars;
  • Wear disposable gloves while handling the product and dispose of them with general waste;
  • Do not let dogs swim for the first few days, and do not bathe the pet after administering the medication;
  • Collect the hair while combing and dispose of it with the general waste;
  • Clean up the feces and dispose of it with the general waste.

For more tips, visit the campaign website:www.hhnk.nl/doemee. There, you can also sign up for a webinar with a veterinarian on responsible parasite control for pets, which will take place on November 10, 2026.

Pilot Project in the Uitgeester- and Heemskerkerbroek Polder

Photo: Xander van Ommen (for Velt)

The study is part of a pilot project in the Uitgeester- and Heemskerkerbroek polder aimed at improving water quality. In February 2023, HHNK, the municipalities of Heemskerk and Uitgeest, the province of North Holland, the KAVB, LTO, Glastuinbouw Nederland, Landschap Noord-Holland, and PWN signed a letter of intent to collaborate on ensuring clean surface water in the Uitgeester and Heemskerkerbroek polder. This led to a package of measures, some of which have been implemented or are currently being implemented. For example, a water retention area with a purification function was recently completed in the Heemskerkerduin. There are also ambitious plans for an ecological corridor from Heemskerk toward Uitgeest and for the redevelopment of a park in Heemskerk’s “ centre ” area to enhance connectivity and the experience of water. In addition, the agricultural sector is taking steps to implement measures within its own operational processes to limit the emission of nutrients and crop protection products. Finally, farmers and land managers have begun maintaining their ditches to provide more space for ecological development within the water system. For more information, see the Uitgeester- and Heemskerkerbroek Pilot page.