Quaternary ammonia compounds in disinfectant products: evaluating the potential for promoting antibiotic resistance and disrupting wastewater treatment plant performance

Quaternary ammonium compounds (QACs) are a class of compounds that were widely used as disinfectants during the COVID-19 pandemic and continue to be used as disinfecting agents. After consumer usage, QAC concentrations are diluted in wastewater as they enter wastewater treatment plants. At sub-inhibitory concentrations, QACs may have unintended repercussions, including increased antibiotic resistance and inhibition of process performance in wastewater treatment plants. This review first summarizes how QACs inhibit bacteria and then highlights the mechanisms by which QACs can promote antibiotic resistance in general. Reported environmental concentrations of QACs are compared to concentrations that are suspected to impact antibiotic resistance, and the role QACs may have on antibiotic resistance proliferation in wastewater treatment is addressed. Finally, the specific impacts that QACs can have on biological wastewater processes (activated sludge and anaerobic digestion) are reviewed. We highlight key research gaps along with recommendations for future research. Of particular interest, research is needed to elucidate the relationship between the chemical structure of QACs and impacts on antibiotic resistance as well as process performance in wastewater treatment plants. Finally, the ability to mitigate (reverse) these impacts if QACs are removed needs to be determined.