The Columbia River Basin is a priority watershed for states, tribes, federal agencies, and nonprofit organizations and was designated as a ‘critical ecosystem’ that warrants protection in the EPA's 2006-2011 Strategic Plan (USEPA 2006a). Past studies by EPA and others have found significant concentrations of toxic contaminants in fish and the waters they inhabit throughout the basin (USEPA 2009). However, the Mid-Columbia River main stem reach, between Bonneville Dam and Grand Coulee Dam, has never been assessed for concentrations of contaminants in fish tissue. This study of the Mid-Columbia River is an effort to fill this information void.
A spatially distributed probabilistic sample design was used to select 42 sample sites along the Mid-Columbia River main stem (MCR) to represent the entire 718 km (440 mile) reach. During the summers of 2008 and 2009, field crews collected two types of fish samples to represent both human health and ecological endpoints. Water quality and physical habitat data were also collected at each site. Fish tissue was analyzed for a variety of toxic contaminants. Water samples were analyzed for physical and chemical characteristics and trace elements.
Toxic contaminants were measured in fillet tissue for the human health endpoint and in whole fish tissue for the ecological endpoint. Using the probabilistic study design, the data were analyzed to produce statistical results that are expressed in terms of the extent of the Mid-Columbia reach (MCR). The results were also compared to literature screening values (SVs) to put the results in context for interpretation. Multiple contaminants were found to exceed SV concentrations. Mercury, PCBs, and DDTs were responsible for most of the exceedances of human health SVs. Trace elements and DDTs were responsible for most of the exceedances of ecological SVs.
Human Health Findings
Tissue contaminant concentrations in fish fillet samples were compared to four types of SVs. Cancer and non-cancer SVs were calculated for two different consumption rates, one representing the general public and one representing people who consume fish at a higher rate. All the contaminants that exceeded human health SVs in fillets were widely detected. However, some widely detected contaminants did not exceed any of these SVs. The following are general results on the extent and magnitude of contaminant concentrations relevant to human health SVs in fish fillet samples collected from the MCR.
- Mercury was detected in all fillet samples, representing 100% of the MCR length. Concentrations exceeded the non-cancer SVs for both the general and the high fish-consuming populations in most of the MCR.
- PCBs exceeded cancer SVs for both the general and the high fish-consuming populations throughout the MCR reach. Non-cancer SVs were exceeded for both types of consumers in a substantial proportion of the reach.
- Total DDTs and DDE exceeded cancer SVs for both the general and high fish-consuming populations in a substantial proportion of the MCR reach.
- Several of the other chlorinated pesticides were frequently detected in tissue samples. Only dieldrin exceeded both of the cancer SVs in a substantial proportion of the MCR reach. Heptachlor epoxide and hexachlorobenzene also exceeded the cancer SVs but to a lesser spatial extent.
- PBDEs were frequently detected in fillet samples, but did not exceed any of the SVs.
- Dioxins and furans were rarely detected. The dioxin congeners with available SVs were not detected in the samples.
Tissue contaminant concentrations in whole fish samples were also compared to available SVs. Three types of SVs were compared: piscivorous avian wildlife (kingfisher), piscivorous wildlife (mink and otter), and general aquatic species SVs. The avian SV are generally the lowest (most stringent) and therefore the ones most often exceeded in these tissue samples. The following are general descriptions of the extent and magnitude of contaminant concentrations in ecological SVs from whole fish samples collected from the MCR.
- Total DDTs and DDE exceeded both the kingfisher and general aquatic SVs in much of the MCR reach, while DDD exceedances for kingfisher were more limited in extent.
- Total chlordane exceeded the kingfisher SV in a small percent of the MCR length, and was the only other chlorinated pesticide with an SV exceedance.
- Total PBDEs exceeded the SV for American kestrels (a bird species) in a small percentage of the MCR reach.
- Mercury wildlife SVs were exceeded for kingfisher in much of the MCR reach, and for otter and mink in a smaller proportion.
- Several metals (zinc, copper, and selenium) exceeded the general aquatic SVs in most of the MCR reach, while others (nickel, arsenic, and lead) exceeded them in a smaller proportion of the river.
Conclusions and Recommendations
- Bioaccumulative contaminants are an ongoing problem in the Mid-Columbia River as in many other parts of the U.S. Nationally, the number of fish advisories for Hg, PCBs, and DDTs continues to increase (USEPA 2011).
- Elevated mercury concentrations are very similar to those found in rivers across the US. Likewise, PBDE levels were reflective of other large US river systems (Blocksom et al. 2010).
- MCR fish tissue concentration of DDTs stand out as being extremely elevated compared to what is found in the rest of the US, even in other agriculturally intense locations. Although DDTs and the other persistent chlorinated pesticides are likely related to historical agricultural applications, efforts can be made to reduce their mobilization and transport into the MCR. Improved land management practices have significantly reduced concentrations of DDT in fish tissue in some portions of the Columbia Basin (Washington Department of Ecology 2014).
- Important fish tissue contaminants of concern and their ranking are virtually the same for both the general and high fish consumers. This suggests the same triggers for improving environmental conditions/reducing contaminants are present regardless of the intensity of use of the fisheries resource.
- This study establishes a baseline for toxic contamination in fish tissue in the Mid-Columbia. Repeated at intervals, studies of this type would help to determine trends in contamination so that future assessments of the Columbia River will be able to provide more robust understanding of the relationship between contaminants and associated human activity, natural phenomena, and environmental change.
About this Report
This assessment does not evaluate risk. The purpose was to create a baseline understanding of toxic contamination in fish tissue in the Mid-Columbia. Continued assessments can help to determine trends in contamination and provide a more robust understanding of the relationship between contaminants and associated human activity, natural phenomena, and environmental change.
Both the states of Oregon and Washington maintain fish consumption advisories for the fish species included in this study. Salmon and steelhead were not included in this study, and are a recommended best choice according to the EPA and U.S. Food and Drug Administration.
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- Mid-Columbia River Fish Toxics Assessment (PDF)(164 pp, 10 MB, March 2017, EPA-910-R-17-002)