The Regional Monitoring Program for Water Quality in San Francisco Bay (RMP) has recently focused attention on better characterization of contaminants in nearshore “margin” areas of San Francisco Bay. The margins of the Lower South Bay are mudflats and shallow regions that receive direct discharges of stormwater and wastewater; as a result, they may have higher levels of urban contaminants than the open Bay. In the summer of 2017, the RMP collected samples of margin sediment in the South and Lower South Bay for analysis of legacy contaminants. The studydescribed here leveraged that sampling effort by adding monitoring of sediment and water for two additional sets of emerging contaminants: 1) current-use pesticides; and 2) fragrance ingredients including the polycyclic musk galaxolide, as well as a range of other commonly detected emerging contaminants linked to toxicity concerns such as endocrine disruption.
A number of current-use pesticides were observed in margin samples. Bifenthrin, a current-use pesticide commonly detected in freshwater sediments at concentrations associated with aquatic invertebrate toxicity, was present in 3 of 12 sites at concentrations ranging from 1.3 to 1.7 μg/kg dry weight (dw). Eighteen pesticides were detected in filtered water samples, and none were detected in suspended sediment. Three of these pesticides—carbendazim, fipronil, and imidacloprid—were detected in some samples at concentrations greater than U.S. Environmental Protection Agency (USEPA) aquatic life benchmarks for freshwater settings.
Among fragrance ingredients and other emerging contaminants, a total of 16 compounds were detected in bed sediment, with five compounds detected in at least half of the samples. Four compounds were detected at concentrations comparable to or greater than available ecotoxicology thresholds, including the fragrance ingredients indole and camphor, as well as 4-methylphenol and 4-n-nonylphenol. A total of 18 distinct compounds were detected in water samples, with one, an organophosphate ester (OPE) known as tris(1,3-dichloroisopropyl) phosphate or TDCPP, exceeding a protective ecotoxicity threshold.
Evaluation of the results for individual contaminants relative to available toxicity thresholds generally supported existing classifications within the RMP’s Tiered Risk-based Framework for emerging contaminants. Among pesticides, findings were consistent with fipronil and imidacloprid as Moderate Concerns for the Bay, pyrethroids as Low Concern for the Bay (this class is considered a High Concern in tributaries), and other current-use pesticides as Possible Concerns for the Bay.
Fragrance ingredients were generally found at levels indicative of minimal or Low Concern. One exception, indole, a fragrance ingredient that is also produced naturally and used as a fecal indicator, is considered a Possible Concern for the Bay. Another emerging contaminant with natural and anthropogenic sources, 4-methylphenol, may also be considered a Possible Concern. Detections of TDCPP and other OPEs, used as flame retardants and plastic additives, were consistent with classification of this class as a Moderate Concern for the Bay. Likewise, detections of 4-n-nonylphenol were consistent with the current designation of alkylphenols and alkylphenol ethoxylates as a Moderate Concern for the Bay.