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- Toxics in Aquatic Life
- Indicator
- Contaminants in Pacific herring
- Vital Sign Indicator
- Chemical Concentration Wet Weight (ng/g wet weight)
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By 2030, 95% of the samples gathered across Puget Sound habitats exhibit a declining trend of contaminant levels, or are below thresholds of concern for species or human health.
By 2050, 95% of the samples gathered across Puget Sound habitats exhibit contaminant levels below thresholds of concern for species or human health and show no increasing trends.
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Natasha Winnacott
- Contributing Partners
- Last Updated
- 10/22/2025 16:42:05
The contaminants in Pacific herring indicator tracks the concentration of PCBs and PBDEs in herring whole bodies. The levels of these persistent organic pollutants (POPs) in herring signal harmful concentrations in this species, but also the extent of contamination in the pelagic food web. POPs threaten the health of herring and other forage fish, the health of the fish, wildlife and humans who consume them, and the overall productivity of the pelagic habitat.
Pacific herring are a keystone species in the pelagic (open-water) food web, serving as important prey for virtually all large predatory fish and fish-eating seabirds, and most marine mammals in Puget Sound. Herring have a high fat content and accumulate persistent organic pollutants (POPs) that may be present in the pelagic food web because of the propensity of these contaminants to accumulate in lipid-rich tissues. As such, they are likely to accumulate contaminants from their environment and reflect regional spatial patterns of contamination.
It is difficult to measure contaminants directly in many larger pelagic predators (e.g., southern resident orcas). Herring provide a more practical approach for measuring contaminants in the pelagic food web because they are abundant and relatively easy to capture and process in the laboratory. Moreover, we sample young adult herring that integrate contaminant conditions in the food web over a relatively short period of time (2-3 years), which means that management actions designed to reduce POP loadings to the ecosystem should be observed quickly.
- PCB and PBDE concentrations continue to exceed adverse fish health effects thresholds in Pacific herring samples from two of the five monitored stocks (Port Orchard/Madison and Squaxin) but not for herring collected from three less contaminated stocks (Quilcene/Dabob Bay, Semiahmoo Bay and Cherry Point). Overall, PCB and PBDE concentrations are decreasing (see Interpretation of Results for more details). Thus, we determine this indicator is BELOW TARGET but GETTING BETTER.
- PCB and PBDE concentrations that exceed the adverse fish health effects thresholds may impair herring growth, health and subsequent survival, limiting food supply to predators that rely on them.
- PCBs and PBDEs in herring are transferred up the food chain to their predators, including Chinook salmon, and ultimately to Southern Resident killer whales (SRKW) who feed on salmon. This results in high enough PCB levels in both Chinook salmon and SRKW to negatively impact their recovery.
- Monitoring Program
Washington State Department of Fish and Wildlife, Toxics Biological Observation System
- Data Source
Washington State Department of Fish and Wildlife, Toxics Biological Observation System (unpublished data); Winnacott, N. H. F., L. B. Harding, K. Hayes, and S. M. O’Neill. 2025. Contaminants in Pacific Herring, 2020 Status and Trends Report, Washington Department of Fish and Wildlife, Olympia, Washington.
This update presents contaminant results for five herring stocks selected to cover a wide area of Puget Sound from its Southern Basin (Squaxin Pass), into its Central Basin (Port Orchard/Madison), northward to the Strait of Georgia (Semiahmoo Bay and Cherry Point), and westward to Hood Canal (Quilcene/Dabob). As used herein, the term “stock” refers to a biologically meaningful unit of herring population recognized by the Washington Department of Fish and Wildlife (WDFW). Stocks are defined by the herring’s predictable and consistent use of specific spawning habitats. WDFW currently recognizes 21 spawning stocks in Puget Sound and the Strait of Juan de Fuca. Herring are sampled during their spawning season (January to June, depending on stock) using either gill (tangle) nets targeting fish on nearshore spawning grounds, or midwater trawls targeting predictable pre-spawning aggregations offshore of spawning grounds.
PCBs and PBDEs are measured directly in the herring's whole body (see West et al., 2017 for detailed analysis methods). Composite samples of 5-10 individual herring were created for chemical analysis. The resulting values reflect the mean concentration of contaminants in herring and allows an assessment of how much toxic contaminants predators (or humans) may be exposed to when consuming herring whole-bodies.
To determine whether the contaminants are likely to harm herring, the PCB and PBDE concentrations in fish tissues were compared to adverse fish health effects thresholds. These thresholds are typically a numerical value established experimentally and published in the scientific literature. They are a documented level, above which fish health would be predicted to be harmed by exposure to the chemicals. If herring contain either PCBs or PBDEs above the fish health threshold, we predict health impairments in a portion of those fish that may affect their survival. Current levels for PCBs are 220 ng/g for increased risk of fish mortality and 100 ng/g for increased risk of impairments to fish growth (Berninger and Tillitt 2019). The current levels for PBDEs are 9.8 ng/g for increased risk of disease susceptibility in fish and 34 ng/g for increased risk of altered thyroid function in fish based on interpretations of studies by Arkoosh et al. (2013 and 2018) and the approach described in O’Neill et al. (2015) and Chen et al. (2018). Because composite samples were analyzed – the resulting value represents the mean of 5 individual herring and thus dampens the variability that comes from analyzing individual samples. In addition, fish health effects thresholds are typically a numerical value established experimentally based on individual, whole body samples. As such, caution should be taken when comparing modeling results of mean composites samples to these individual based thresholds.
Models were created to evaluate long-term PCB and PBDE time trends in herring with the goal of providing insight into how contaminant trends have changed over time in the herring stocks sampled in Puget Sound. These modeling efforts focused on four of the five monitored herring stocks (Squaxin Pass, Port Orchard/Madison, Semiahmoo, and Cherry Point) because they had sufficient data to evaluate time trends in PCBs and PBDEs. Separate models were created to relate either PCBs or PBDEs to location and year to evaluate how toxic concentrations vary by herring stock (location) over time. For PCB’s, a generalized linear model (GLM) was used which related PCB concentrations to the interaction between location and year. This model was fit with a gamma distribution and a log link to ensure that the data met the assumption of normality. The emtrends function (R package “emmeans”; Lenth 2024) was used to calculate the slope, standard error and 95% confidence intervals for each site. Sites were considered significant if the 95% confidence interval of the slope estimate for a site did not encompass zero.
For PBDEs data, initial modeling diagnostics indicated the GLM (describe above) was not a suitable model because there were patterns in the residuals versus the year covariate. As a result, generalized linear mixed effects models (GLMMs) were explored that related log10-transformed PBDE concentrations to the interaction between year and location with a random intercept for year to allow for variability in PBDE concentrations by year across herring stocks.
For both the GLM fit to PCB concentrations and the GLMM fit to PBDE concentrations, model assumptions (normally distributed residuals and homogeneity of variance) were visually assessed using normal Q-Q plots, residuals vs. fitted, residuals vs. covariates, and histogram of residuals. Results were plotted using predicted fitted lines through time at each site for PCBs and PBDEs. Each line includes a manually calculated 95% confidence intervals and fish health thresholds outlined above.
- Critical Definitions
Persistent Organic Pollutant (POP): a type of organic chemical that is toxic, and resistant to environmental and biological degradation, such that they persist in the environment longer than other types of contaminants. POPs typically accumulate in organisms and once in the food web, tend to remain there and increase in concentration (biomagnify) up the food chain from prey to predators.
Polychlorinated biphenyls (PCBs): are a group of synthetic (man-made) chemicals consisting of 209 compounds, or congeners, each containing a unique number and position of chlorine atoms attached to two phenyl (aromatic) rings. These typically oily compounds were designed for various industrial and residential products and uses (transformers, cable insulation, caulking and plastics) and industrial products typically consist of complex mixtures of congeners. PCBs were largely banned in the US by 1979, but they are still found in materials produced before the ban, as unintentional byproducts of manufacturing, and in small amounts (<50 parts per million), still allowed in newly manufactured products. PCBs are classified as a Persistent Organic Pollutant (POP) because they are resistant to most forms of degradation, and once released to the environment, they can bioaccumulate in organisms and cause adverse health impacts in wildlife and humans.
Polybrominated diphenyl ethers (PBDEs): are a group of synthetic (man-made) chemicals consisting of 209 compounds, or congeners (similar to PCBs), although each containing a unique number and position of bromine atoms surrounding two phenyl-ether rings. PBDEs were designed primarily as flame-retardants to prevent or slow the spread of fire in products ranging from electronics and furniture to clothing. In 2008, Washington state banned the sale of select PBDE mixtures, however they can still be found in materials produced before the ban. PBDEs are classified as a POP, because once released to the environment are resistant to degradation, bioaccumulate in organisms and have adverse health impacts in wildlife and humans.
The current status of this indicator is reported as “below 2030 target”, because PCBs exceeded the fish mortality and growth thresholds in some herring samples collected at Port Orchard/Madison and the fish growth threshold only in some herring samples collected at Squaxin. For PBDEs, some herring samples from Port Orchard/Madison and Squaxin exceeded the fish disease threshold, while the thyroid alteration threshold for PBDEs was not exceeded by any of the stocks. Herring collected from Quilcene/Dabob and Semiahmoo stocks in 2020 and Cherry Point in 2018 were below all PCB and PBDE fish health thresholds (Figure 2).
Figure 2. Status (2020 data) of total PCBs and PBDEs in four herring stocks from Puget Sound, WA. Cherry Point data (* symbol in plot) is from 2018 since no herring samples were collected here in 2020. Median concentrations for each stock are shown as a solid horizontal line inside the box plot. Box ends represent the 25th and 75th percentile concentrations and diamonds represent the 5th (lower) and 95th (upper) percentile concentrations. The color of the box for each stock is determined by whether the upper diamond is below fish health thresholds (blue), above one fish health threshold (yellow), or above two fish health thresholds (red; shown as dashed lines; 220 ng/g for increased risk of fish mortality, and 100 ng/g for increased risk of fish growth impairments [PCBs] and 9.8 ng/g for increased risk of disease susceptibility in fish, and 34 ng/g for increased risk of altered thyroid function in fish [PBDEs]).
Modeling results for the GLM relating PCB concentrations in herring to the interaction between location and year show a statistically significant declining PCB trend in all four stocks at an average rate of 1.95% (± 0.445%) to 3.08% (± 0.445%) per year (Figure 3; Table 1). In 2020, the predicted mean concentrations of PCBs in herring were below the fish mortality threshold in all herring stocks, while levels exceeded the fish growth and reproduction threshold only at Port Orchard/Madison and Squaxin (Figure 3).
Figure 3. Generalized linear model results from the effect of stock and time (year; x-axis) on PCB concentrations in herring (y-axis). Fitted regression lines of PCB concentrations as a function of the interaction between stock and time. Colored lines correspond to PCB concentrations in each of the four stocks (Cherry Point (green), Port Orchard/Madison (blue), Semiahmoo (red), and Squaxin (purple)). Shaded regions are the 95% confidence intervals. Dashed lines indicate the adverse fish health effects thresholds. Each point represents PCB concentrations in a composite herring sample (5-10 individuals).
Table 1. Results from the generalized linear model that relates PCB concentrations in herring as a function of the interaction between sample collection date (year) and herring stock. Mean year trend is the estimated mean slope for year in each stock with the corresponding standard error, degrees of freedom (df) and 95% confidence levels. Significant (confidence intervals upper and lower bounds do not encompass zero) Mean Year Trend results in bold.
|
Stock |
Mean Year Trend |
Standard Error |
df |
Lower Confidence Level |
Upper Confidence Level |
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Semiahmoo |
-0.0227 |
0.00455 |
463 |
-0.0316 |
-0.0138 |
|
Cherry Point |
-0.0308 |
0.00628 |
463 |
-0.0432 |
-0.0185 |
|
Port Orchard/Madison |
-0.0195 |
0.00445 |
463 |
-0.0282 |
-0.0108 |
|
Squaxin |
-0.0304 |
0.00455 |
463 |
-0.0394 |
-0.0215 |
Modeling results using the GLMM for the PBDE data indicate that there is a negative interaction between year and location among all four herring stocks monitored. The trend in this interaction varies at each site, but overall PBDE concentrations declined across all sites monitored for this study. The interaction is significant in the Cherry Point and Squaxin stocks (Cherry Point slopes = -0.0291 ± 0.0070, p < 0.05; Squaxin slopes = -0.0421 ± 0.0123, p < 0.05), while it was not significant in the Port Orchard/Madison and Semiahmoo stocks (Port Orchard/Madison slopes = -0.0370 ± 0.0123, p > 0.05; Semiahmoo slopes = -0.0336 ± 0.0125, p > 0.05) (Figure 4). Variability in the slope for year explained less than half of the variance in the data (r2total = 0.8522, of which r2fixed = 0.7635).
Figure 4. Generalized linear mixed effect model results from the effect of stock and time (year; x-axis) on PBDE concentrations (y-axis) in herring. Fitted regression lines of PBDE concentrations as a function of the interaction between stock and year with a random intercept for year. Colored lines correspond to PBDE concentrations for each of the four stocks (Cherry Point (red), Port Orchard/Madison (green), Semiahmoo (blue), and Squaxin (purple)). Shaded regions are the 95% confidence intervals. Dashed lines indicate the adverse fish health effects threshold. Each point represents PBDE concentrations in a composite herring sample (5-10 individuals).
Discussion
Pacific herring provide a long-term and Sound-wide perspective on PCBs and PBDEs in Puget Sound’s pelagic food web. Results indicate that both PCB and PBDE concentrations in herring are declining at sampling locations used for this study. Despite this, PCB concentrations in herring remain high enough to impact fish health at the Central and South Puget Sound sites (Port Orchard/Madison and Squaxin). This indicates that the pelagic food web in the Central and South Basins of Puget Sound continue to be contaminated at levels of concern for herring health. As a result, there is a risk for reduced prey availability as well as transfer of these persistent chemicals up the food chain to Chinook salmon, fish-eating seabirds, and marine mammals including Southern Resident killer whales. West et al. (2011a) reported high levels of PCBs in Pacific krill from Elliott Bay, sampled near the Lower Duwamish Waterway Superfund site. Krill and similar species are a primary prey for herring, and the biomagnification of PCBs from krill to herring is likely a primary pathway for PCBs entering the pelagic food web via plankton. PCB distribution patterns in Chinook salmon (O’Neill and West 2009) and adult gadoid codfishes (Pacific hake and walleye pollock; West et al., 2011b), both of which are herring predators, provide a weight of evidence pointing to the Central and South Basins as hot spots for PCBs in the pelagic food web.
Although PBDEs have declined broadly in Puget Sound’s pelagic marine food web, concentrations are above the fish health threshold for increased risk to disease in the Central and South Sound stocks (Port Orchard/Madison and Squaxin). PBDE contamination at levels of concern have also been reported in seaward-migrating juvenile Chinook salmon in lower-river estuarine habitats of the Snohomish and Nisqually Rivers (see juvenile Chinook Vital Sign Indicator). This again points to increased risk of PBDE biomagnification in the food web here. O’Neill et al. (2020) and Gipe and Hobbs (2025) identified wastewater treatment plant (WWTP) discharges in the Snohomish River as the likely source of PBDEs to juvenile Chinook in that system. These results suggest that timing and proximity of discharges with salmon migration in a restricted water body (river) may be key factors in the exposure of fish to chemicals discharged by WWTPs. In addition, these results exemplify the importance of monitoring a diversity of indicator species covering different habitats to fully understand the impact of chemical contamination in the Puget Sound ecosystem.
PCBs and PBDEs remain below fish health thresholds in the two Southern Strait of Georgia stocks monitored for this study (Cherry Point and Semiahmoo). Herring were not collected from the Cherry Point stock during the 2020 sampling event due to the COVID 19 lockdowns. Despite the lack of samples from the Cherry Point stock in 2020, time trend analysis shows a declining trend in both PCB and PBDE concentrations here (Figure 3&4). In addition, PCBs in herring from these stocks have not exceeded the fish adverse health effects threshold over the past 20 years (Figure 3&4). Currently, PCB and PBDE concentrations can be considered low enough to pose low health risks in most fish in these stocks based on the current adverse fish health effects thresholds.
An evaluation of the pathways of PCBs and PBDEs from their terrestrial sources to aquatic habitats may help to focus or prioritize remediation efforts. Osterberg and Pelletier (2015) reported stormwater (“surface runoff" in their Table 3) as the greatest loading pathway for PCBs to the Central and South Basins, with lesser amounts attributable to wastewater from WWTP and to atmospheric deposition. In contrast, WWTPs have been identified as being the primary pathway through which PBDEs move from their terrestrial sources to Puget Sound waters (Osterberg and Pelletier 2015). Stormwater was the dominant loading pathway for PCBs in Elliott Bay and Commencement Bay, two highly urbanized embayment's in the Central Basin, both containing PCB Superfund sites. With stormwater loading of PCBs 13 to 20 times greater than either atmospheric deposition or WWTPs in these PCB-contaminated bays, a focus on stormwater pathway overall, and Superfund sites in particular, seems appropriate.
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The manufacture and sale of PCBs in the US and many other countries was largely banned in 1979 and several aquatic ecosystems world-wide have exhibited PCB declines in biota since that time (e.g., Nyberg et al., 2015). Though PCB concentrations are declining in herring from stocks monitored for this study, concentrations at the Central and South Sound sites Port Orchard/Madison and Squaxin are still above health thresholds for PCBs and the rate of decline is roughly half the rate for PBDEs over the same time period. The significant and far-reaching consequences of this contamination raise a red flag for focusing attention on reducing PCB inputs to the Puget Sound ecosystem.
The steady decline of PBDE levels in most monitored herring stocks in marine waters in both urbanized and less urbanized basins suggests management actions to reduce inputs of these chemicals to Puget Sound have been effective. This not only highlights the value of effectiveness monitoring for evaluating the efficacy of pollution mitigation actions but also prompts questions about which actions have been responsible for the recovery.
Targeted PBDE actions in the past 20 years include both statutory and voluntary PBDE controls on production and use of these chemicals in Washington State. These may have resulted in reducing PBDEs at their source, thereby reducing PBDEs in their primary pathways to Puget Sound. Kim et al. (2013) reported a strong correlation between PBDEs and total suspended solids (TSS) from a review of 20 Canadian WWTPs, which prompts questions about whether changes in treated wastewater effluent in Puget Sound during this period may also have helped to reduce the mass of PBDEs entering Puget Sound.
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- Reporting Instructions
No Subcategories for this Puget Sound Indicator.