Washing the Outdoors with Harmful Disinfectants?

By Gary Marcos | July 23, 2024

Have you ever noticed moss, mold, or algae growing on your driveway, roof, or deck? This problem can not only be unsightly, but it can also pose slip hazards and deteriorate building materials. Many homeowners and property managers turn to outdoor biocide products as a quick fix. Unfortunately, these products increasingly contain harmful quaternary ammonium compounds (QACs or quats) which can create much deeper problems for our health and environment. You can usually identify QACs by looking for ingredients ending with “nium chloride”. Some commonly used ones include dimethyl benzyl ammonium chloride or didecyl dimethyl ammonium chloride.

QACs are linked to skin, lung, immune, reproductive, developmental, and neurological harms in people. These chemicals also contribute to antibiotic resistance—a serious and growing global health problem. We’re already overusing them as disinfectants in indoor environments like homes, gyms, and schools. Spraying the outdoors with QACs will only pour gas on the fire.

Because I live in Washington in a damp climate, slippery moss tends to grow on my driveway. I also have a protected water area behind my house, so I was especially reluctant to use chemicals of emerging concern in this fragile environment. I researched alternatives such as acetic acid (i.e., vinegar) and sodium hypochlorite (i.e., bleach). I also looked into pressure washers for appropriate surfaces. Each of these solutions have their pros and cons, but none come with risks as serious or long-lasting as QACs.

In my locale, all the drainage from spraying these products on roofs and driveways can reach local ponds teeming with wildlife like frogs, garden snakes, and ducks. The runoff may eventually feed into groundwater and the larger lakes nearby (Lake Sammamish and Lake Washington). But this isn’t just a problem in the Pacific Northwest. Mold, moss, and algae growth is also a very common problem in the southern United States and many other parts of the world and unfortunately QAC concentrations in some aquatic ecosystems are already reported to be approaching protective toxicity thresholds.

While product manufacturers and governments need to do a better job at managing chemicals of concern, each of us can do our part to minimize harm before too much damage is done. I invite you to join me in my quest to quit the quats:

• My first choice is using 45% vinegar, which I dilute 1:1 with water. It requires a few applications over a week, but it is the most environmentally friendly option.
• For more demanding jobs, I turn to 6% bleach.

And remember that it is always a good idea to use personal protective equipment and test your solution on a small area first.