More than 100,000 chemicals have been registered or approved for commercial use in the US. For many of these chemicals, major information gaps limit evaluations of their potential risks, and environmental monitoring of these chemicals has not been required by regulatory agencies. Nevertheless, researchers and government agencies have begun to collect occurrence, fate, and toxicity data for a number of these chemicals.

As a result, a growing number of chemicals have been classified as contaminants of emerging concern (CECs), broadly defined as synthetic or naturally occurring chemicals that are not regulated or commonly monitored in the environment but have the potential to enter the environment and cause adverse ecological or human health impacts. The primary challenge for scientists and regulators is investigating and managing this ever-expanding number of emerging contaminants to ensure that they do not harm human and ecological health.

The Regional Monitoring Program for Water Quality in San Francisco Bay (RMP) has been investigating CECs since 2001, and established a formal workgroup to address the issue in 2006. The RMP Emerging Contaminants Workgroup (ECWG) includes representatives from RMP stakeholder groups, regional scientists, and an advisory panel of expert researchers that work together to address the Workgroup’s guiding management questions.

  • Which CECs have the potential to adversely impact beneficial uses in San Francisco Bay?
  • What are the sources, pathways and loadings leading to the presence of individual CECs or groups of CECs in the Bay?
  • What are the physical, chemical, and biological processes that may affect the transport and fate of individual CECs or groups of CECs in the Bay?
  • Have the concentrations of individual CECs or groups of CECs increased or decreased in the Bay?
  • Are they predicted to increase or decrease in the future?
  • What are the effects of management actions?

The overarching goal of the ECWG is to develop cost-effective strategies to identify and monitor CECs to support management actions to minimize impacts to the Bay. The ECWG guides an annual process of contaminant evaluation and long-term planning and optimization to respond to new RMP data and the rapidly evolving body of science on CECs.

Following this process over the past decade, the RMP has generated one of the world’s most comprehensive datasets for CECs in an estuarine ecosystem. While RMP stakeholders are the primary audience and user of RMP data and communications, the Program informs broader decision-making through outreach to state and federal agencies.

The RMP first published a formal CEC Strategy in 2013 as part of a continuous effort to refine approaches for supporting the management of CECs in San Francisco Bay. Periodic revision of the Strategy is essential given the rapid evolution of the science surrounding emerging contaminants; in 2017, the RMP completed its first revision of the RMP’s CEC Strategy. The Strategy consists of three major elements.

First, for CECs known to occur in the Bay, the RMP prioritizes CECs using a tiered risk-based framework. This prioritization framework guides future monitoring proposals for each of these contaminants, the results of which, in turn, provide key data to update evaluations of potential risk. The criteria listed below are used for placement in each tier.

High Concern • Bay occurrence data suggest a high probability of a moderate or high level effect on Bay wildlife (e.g., frequent detection at concentrations greater than the EC10, the effect concentration where 10% of the population exhibit a response, or another effects threshold). No CECs are currently assigned to this tier for the Bay.

Moderate Concern • Bay occurrence data suggest a high probability of a low level effect on Bay wildlife (e.g., frequent detection at concentrations greater than the predicted no effect concentration (PNEC) or no observed effect concentration (NOEC) but less than the EC10 or another low level effects threshold). CECs in this tier include: PFOS; fipronil; and nonylphenols and nonylphenol ethoxylates.

Low Concern • Bay occurrence data suggest a high probability of no effect on Bay wildlife (i.e., Bay concentrations are well below toxicity thresholds and potential toxicity to wildlife is sufficiently characterized). CECs in this tier include: pyrethroids (in the Bay - however, pyrethroids are a significant concern in Bay Area urban creeks); many pharmaceuticals and personal care products (PPCPs); hexabromocyclododecane (HBCD); and polybrominated dioxins and furans (PBDD/Fs). PBDEs, once considered a moderate concern for the Bay, have declined in response to management actions, and can now be classified as low concern CECs. 

Possible Concern • Uncertainty in measured or predicted Bay concentrations or in toxicity thresholds suggests uncertainty in the level of risk to Bay wildlife. CECs in this tier include: alternative flame retardants (including brominated, chlorinated, and phosphate compounds); bisphenol A; bis(2-ethylhexyl) phthalate (BEHP or DEHP) and butylbenzyl phthalate (BBzP); microplastic; tissue contaminants identified via recent broadscan study (2,2’-dichlorobenzil, dichloroanthracenes, 4-tert-butylamphetamine, methyl triclosan); other current use pesticides; poly- and perfluorinated alkyl substances (PFASs) other than PFOS; PCB-11; polyhalogenated carbazoles; short-chain chlorinated paraffins; and single-walled carbon nanotubes. 

The RMP review of a CEC may also indicate whether monitoring suggests levels are declining or increasing over time. Declines may be linked to specific management actions designed to prevent pollution, with continued monitoring appropriate for tracking recovery. Contaminants that have not been monitored with sufficient frequency to establish trends may still be expected to decline or increase due to known changes in manufacturing and use, or increases in population. Consideration of broader chemical or functional classes is an integral approach responsive to both manufacturing substitutions, market shifts, and data limitations.

The second element of the RMP CEC Strategy involves review of the scientific literature and other CEC monitoring programs as a means of identifying new CECs for which no Bay occurrence data yet exist. Initial monitoring to establish the presence of these newly identified CECs in the Bay is needed to evaluate the risks they may pose. Contaminants recently identified via this process include common fragrance ingredients and dyes.

Finally, the third element of the Strategy consists of exploratory techniques collectively referred to in this document as non-targeted monitoring. The RMP has conducted two types of non-targeted monitoring projects. The first, broadscan analyses of Bay samples, is designed to identify unexpected, previously unidentified CECs that are present in the Bay. The other, bioanalytical tools, is expected to establish protocols that can be used to evaluate whether Bay samples have the potential to elicit specifi c biological effects, such as estrogenic endocrine disruption, in exposed organisms.

The RMP’s multi-faceted approach to addressing the challenge of CECs is designed to be flexible and adaptive to new data from both the RMP and other sources. Based on the Strategy, a multi-year plan indicating monitoring and science priorities is outlined. A series of special studies are recommended for PFASs including the moderate concern PFOS, and a more limited range of studies are suggested for two other moderate concern contaminants, fipronil and nonylphenols and nonylphenol ethoxylates. Targeted special studies are also recommended for the following classes of compounds: alternative flame retardants, pharmaceuticals, plastic additives, personal care and cleaning product ingredients, and current use pesticides. Continued exploration of Bay matrices via non-targeted analysis is also suggested. Finally, recommendations for inclusion or exclusion of contaminant monitoring within routine RMP Status and Trends monitoring activities are also provided. 


Programs and Focus Areas: 
Clean Water Program
Bay Regional Monitoring Program
Contaminants of Emerging Concern
Data Services
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