2008-2009 National Rivers and Streams Assessment Fish Tissue Study
Beginning in 2008, EPA has conducted a series of fish contamination studies as part of the Agency’s National Rivers and Streams Assessments that occur in five-year cycles. The 2008-2009 National Rivers and Streams Assessment (NRSA) Fish Tissue Study is the first statistically based national assessment of contaminants in fish from U.S. rivers. Each NRSA fish contamination study involves collection of recreational fish species from randomly selected river sites and analysis of fillet tissue for a variety of chemicals to evaluate the potential health impacts for people who eat fish.
Sampling sites for the 2008-2009 NRSA Fish Tissue Study were randomly selected in rivers across the lower 48 states. Site selection for this study included rivers that are 5th order or greater in size (based on Strahler stream order) with a permanent fish population and flowing water during the study period from May through September (also referred to as perennial rivers). Only freshwater portions of tidal rivers were included in the study. A statistically representative set of 542 river sites (164 urban river sites and 378 nonurban river sites) were sampled for the 2008-2009 NRSA Fish Tissue Study.
Fish Sample Collection
Field crews used primarily electrofishing gear to collect fish composite samples from the 542 river sites sampled for the 2008-2009 NRSA Fish Tissue Study. A routine fish composite sample consisted of five fish that met the following criteria:
- All fish in the composite sample are of the same species.
- The fish species in the composite sample is commonly consumed by people.
- All fish in the composite sample either meet legal requirements of harvestable size for the sampled river or are at least of consumable size.
- All fish in the composite sample are similar in size, so that the smallest fish in the composite sample is not less than 75% of the total length of the largest fish in the composite sample.
- All fish in the composite sample are collected at the same time.
Various species of fish were collected for the 2008-2009 NRSA Fish Tissue Study. The three most frequently caught species were Smallmouth Bass, Largemouth Bass, and Channel Catfish. These three fish species accounted for 56% of the fish composite samples collected for this study.
Fillet Tissue Sample Preparation
Field crews shipped whole fish samples collected for the 2008-2009 NRSA Fish Tissue Study to a laboratory designated by EPA for preparation of fillet tissue composite samples. Experienced laboratory staff filleted the fish (removing scales but retaining the skin and the belly flap on each fillet) and homogenized the fillet tissue in a strictly controlled environment to avoid contaminating the fish tissue samples. The homogenized fillet composite samples were divided into fillet tissue aliquots containing adequate tissue for each type of chemical analysis before being shipped to laboratories under contract to EPA to analyze the fillet composite samples for the chemical contaminants included in the study.
Fillet Tissue Sample Analysis
Laboratories analyzed the 2008-2009 NRSA fillet tissue samples for the following chemical contaminants:
- Mercury (total)
- Selenium (total)
- Polychlorinated biphenyls or PCBs (21 congeners)
- Polybrominated diphenyl ethers or PBDEs (8 congeners)
- Pesticides (21 compounds)
- Per- and polyfluoroalkyl substances or PFAS (13 compounds)
An EPA laboratory and a commercial laboratory used the techniques are listed for analysis of the 2008-2009 NRSA Fish Tissue Study fillet samples for these chemical contaminants:
- Mercury: DMA, or Direct Mercury Analyzer, refers to an instrument that determines the mercury concentration in an environmental sample (for example, fish tissue) by thermal decomposition, amalgamation, and atomic absorption spectrophotometry. The sample is heated in a high-temperature furnace in an oxygen atmosphere to break down the sample and release any mercury. The mercury is swept from the furnace into an amalgamator that traps the mercury. The amalgamator is subsequently heated to release mercury vapor, which is introduced into an absorbance cell, where it is measured by an atomic absorption spectrophotometer at a wavelength of 253.7 nm and reported as a concentration in the sample. (EPA laboratory)
- Selenium: ICP/AES, or inductively coupled plasma-atomic emission spectroscopy, refers to an analytical technique for determining the concentrations of metals and metalloids (such as selenium) in an environmental sample. The sample is digested in a strong acid solution and an aliquot of the digestate is introduced into the instrument, where a high-temperature plasma excites the metal ions. As those atoms return to their unexcited (ground) state, they emit light at a specific wavelength that is measured by the instrument and reported as a concentration in the sample. (EPA laboratory)
- PCBs, PBDEs, and Pesticides: GC/ECD, or gas chromatography-electron capture detection, refers to an instrument for determining the concentrations of various organic compounds that contain halogen atoms, such as chlorine or bromine (for example, polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers) in an environmental sample. The sample is extracted with an organic solvent and an aliquot of the extract is introduced into the gas chromatograph, where the individual compounds are separated from one another before being introduced into the detector. The electron capture detector responds to the presence of any electrophilic atom, such as chlorine or bromine, and the response is measured by the instrument and reported as a concentration in the sample. (EPA laboratory)
- PFAS: HPLC-MS/MS, or high performance liquid chromatography-tandem mass spectrometry refers to an instrument for determining concentrations of various organic compounds, such as per- and polyfluoroalkyl substances (PFAS) in an environmental sample. The sample is digested in an alkaline solution of methanol and an aliquot of the digestate is introduced into the liquid chromatograph, where the individual PFAS compounds are separated from one another before being introduced into the detector. Two mass spectrometers, operating in tandem, monitor specific mass fragments that are characteristic of each PFAS compound and the response is reported as a concentration in the sample. (commercial laboratory)
Results and Data
All results for the fillet tissue concentrations are reported on a wet weight basis. Fish samples collected from the 542 river sites yielded 541 fillet sample results for mercury and selenium (one sample had insufficient fillet tissue for analyses of these metals), 540 fillet sample results for PCBs, PBDEs, and pesticides (two samples had insufficient fillet tissue for analyses of these organic chemicals), and 162 fillet sample results for PFAS (only fillet samples from urban river sites were analyzed for PFAS). Of the fish fillet samples analyzed for the 2008-2009 NRSA, 100% contained detectable levels of mercury and selenium, and 98.7% contained detectable levels of total DDT.
Analytical and field sampling data for each 2008-2009 NRSA Fish Tissue Study chemical contaminant are provided, along with a data dictionary that describes the contents of each data file.
- Mercury Data (xlsx)
- Selenium Data (pdf)
- PCB Data (xlsx)
- PBDE Data (xlsx)
- Pesticide Data (xlsx)
- PFAS Data (xlsx)
- Data Dictionary