By Sierra Garcis, San Francisco Estuary Institute
Even though most Bay Area residents couldn’t name a quaternary ammonium compound, or QAC, they have encountered them. That’s because the antimicrobial chemicals have soared in popularity since the COVID-19 pandemic, and end up in San Francisco Bay via sewage systems and stormwater runoff in such large amounts that scientists consider them a possible threat to Bay water quality.
A new study now finds that wastewater treatment plants remove 98% of QACs on average from wastewater, and includes data from San Francisco Bay. However, the treatment transfers significant portions of the chemicals from water to the solid waste instead of breaking them down. Of the twelve plants studied, only one truly broke down nearly all the QACs—and it used a costlier treatment method.
QACs might be a problem not only for Californian farmers encouraged to use treated sewage as fertilizer, but also for the wastewater treatment process itself.
“It’s an antimicrobial agent, and a lot of what cleans wastewater are bacteria themselves,” says Miguel Méndez, an author of the new study and SFEI scientist. “So once [QACs] reach a certain threshold, it’s killing those good bacteria that we want to clean the water and degrading the treatment process.”
Although only 2% of the QACs in the sewage system may flow out to the Bay, that may still be too much to adequately protect water quality.
“We have already observed levels that exceed more protective standards for aquatic life,” says Rebecca Sutton, the lead scientist on emerging contaminants at SFEI. The Regional Monitoring Program for Water Quality hasn’t yet collected enough samples to say what that means for the Bay, but classify QACs as a possible concern pending more data. High enough levels of QACs in the Bay could damage growth or even kill wildlife like fish and crustaceans.
Overuse of QACs can also harm human health. They’ve been linked to skin and respiratory irritation as well as potential reproductive and developmental harm, and could contribute to the growing trend of resistance to products and drugs designed to kill microbes. Many health experts have urged reducing unnecessary disinfectant use in situations where soap can suffice, or using safer alternatives when disinfecting. Sutton supports the focus on using fewer QACs to address both health and environmental concerns.
“More [wastewater] treatment is not the answer,” she says. “Preventing the chemicals from getting into wastewater in the first place is more effective.”
Learn More About Products With QACs: San Francisco Environment Department Safer Clean
About QACs
- Quaternary ammonium compounds (QACs) are antimicrobial chemicals.
- QACs like benzalkonium chloride are ingredients in some disinfectant wipes, sprays, and other products. (Non-QAC disinfectants include alcohols, hydrogen peroxide, and citric acid.)
- QACs in disinfectant products can end up in San Francisco Bay after passing through wastewater treatment systems.
