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.

Recent modeling has demonstrated that sediment supply is one of the primary environmental variables that will determine the sustainability of San Francisco Estuary tidal marshes over the next century as sea level rises. Therefore, understanding the environmental controls on sediment flux within the San Francisco Estuary is crucial for optimal planning and management of tidal marsh restoration. Herein, we present suspended-sediment flux estimates from water year (WY) 2009–2016 from the San Francisco Estuary to investigate the environmental controls and impact of the record 2013–2016 California drought. During the recent drought, sediment flux into Lower South Bay, the southernmost subembayment of the San Francisco Estuary, increased by 345% from 114 kt/year from WY 2009 to 2011 to 508 kt/year from WY 2014 to 2016, while local tributary sediment flux declined from 209 to 51 kt/year. Total annual sediment flux from WY 2009 to 2011 and 2014 to 2016 can be predicted by total annual freshwater inflow from the Sacramento-San Joaquin Delta (R2 = 0.83, p < 0.01), the primary source of freshwater input into the San Francisco Estuary. The volume of freshwater inflow from the Sacramento-San Joaquin Delta is hypothesized to affect shoal-to-channel density gradients that affect sediment flux from broad, typically more saline and turbid shoals, to the main tidal-channel seaward of Lower South Bay. During the drought, freshwater inflow from the Sacramento-San Joaquin Delta decreased, and replacement of typically more saline shoal water was reduced. As a result, landward-increasing cross-channel density gradients enhanced shoal-to-channel advective flux that increased sediment available for tidal dispersion and drove an increase in net-landward sediment flux into Lower South Bay.