Chlorinated paraffins are a class of mixtures of chlorinated hydrocarbons that are produced and used globally at high volumes for various consumer and industrial applications. Chlorinated paraffins are composed of short-chain (SCCPs), medium-chain (MCCPs), and long-chain compounds (LCCPs), with all having characteristics of persistence, bioaccumulation, and toxicity. These compounds are now ubiquitously detected in urban settings and contaminate a range of wildlife species.

The present study examined archived sediment from San Francisco Bay for 63 chlorinated paraffin compounds to understand their presence and potential impacts to wildlife. Analysis of samples from 10 sites collected across four sampling efforts (2014-2020) did not detect any chlorinated paraffins. The summed reporting limits for SCCPs, MCCPs, and LCCPs (76, 91, and 140 ng/g, respectively), which serve as a proxy for the maximum concentration that could potentially be present in Bay sediment, are significantly lower than the available ecotoxicity thresholds for chlorinated paraffins in sediment from the Canadian Federal Water Quality Guidelines (1.8, 5.4, and 100 mg/kg dw, for SCCPs, MCCPs, and LCCPs, respectively).

Results from this study support classification of chlorinated paraffins as a Low Concern for the Bay under the tiered risk-based framework developed by the Regional Monitoring Program for Water Quality in San Francisco Bay (RMP). No additional monitoring is planned at this time.