Mahony, A.; Arnold, W.; Miller, E.; Méndez, M.; Sutton, R. 2024. Investigation of quaternary ammonium compounds (QACs) in wastewater effluent, influent, biosolids and environmental matrices in San Francisco Bay. SFEI Contribution No. 1196. San Francisco Estuary Institute: Richmond, CA.

Quaternary ammonium compounds (QACs) are surfactants widely used in a variety of consumer products, particularly as antimicrobials. The COVID-19 pandemic has increased use of products containing QACs. This is of concern because QACs can be toxic to aquatic life at low concentrations. This study was undertaken to evaluate the concentrations of 21 QACs in municipal wastewater influent, effluent, and biosolids from three treatment plants in the San Francisco Bay Area. The QACs detected in wastewater influent in the highest concentrations are those commonly used as antimicrobials in disinfectant products, indicating that disinfectants are likely a large source of QACs to wastewater. While wastewater treatment removed QACs in the aqueous phase, as evidenced by much lower concentrations in effluents than influents, total levels present in treated effluent were still on the order of hundreds of ng/L to low μg/L. High amounts of QACs were found sorbed to biosolids, which could provide another environmental release route.

QACs were also observed in San Francisco Bay water, sediment, and urban stormwater runoff samples collected as part of ongoing monitoring by the Regional Monitoring Program for Water Quality in San Francisco Bay (RMP). Wastewater effluents and stormwater runoff are both pathways for QACs to enter San Francisco Bay. We classify QACs as a Possible Concern for the Bay in the RMP’s tiered risk-based framework for emerging contaminants, based primarily on the limited number of ambient Bay samples analyzed, and recommend additional screening of Bay water in the future.

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