The Mussel Watch California pilot study on contaminants of emerging concern (CECs): Synthesis and next steps

•Most targeted CECs were infrequently detected in coastal bivalves in California.•Detectable CECs were more prevalent at urban and storm water influenced locations.•Selected CECs should be monitored in Mytilus and using passive sampling devices.•Multiple agencies partnered to expand coastal water quality monitoring statewide.•This pioneering study will inform monitoring in California and across the nation.

A multiagency pilot study on mussels (Mytilus spp.) collected at 68 stations in California revealed that 98% of targeted contaminants of emerging concern (CECs) were infrequently detectable at concentrations ⩽1 ng/g. Selected chemicals found in commercial and consumer products were more frequently detected at mean concentrations up to 470 ng/g dry wt. The number of CECs detected and their concentrations were greatest for stations categorized as urban or influenced by storm water discharge. Exposure to a broader suite of CECs was also characterized by passive sampling devices (PSDs), with estimated water concentrations of hydrophobic compounds correlated with Mytilus concentrations. The results underscore the need for focused CEC monitoring in coastal ecosystems and suggest that PSDs are complementary to bivalves in assessing water quality. Moreover, the partnership established among participating agencies led to increased spatial coverage, an expanded list of analytes and a more efficient use of available resources.