As of October 2017, the Department of Health and Human Services (NDHHS), in cooperation with the Department of Environmental Quality (NDEQ), the Game and Parks Commission, and the Department of Agriculture, has issued fish consumption advisories for 141 waterbodies (13 stream segments and 128 lakes). States across the nation participate in this national sampling program, and the overall contaminant trends found in Nebraska are similar to those in other states.
The 2017 advisories are based on samples taken through 2016. Fish tissue samples are collected by the NDEQ, analyzed for mercury by the U.S. Environmental Protection Agency (U.S. EPA) and advisories are issued by the NDHHS. While mercury continues to be the major pollutant of concern in fish tissue statewide, previous monitoring included sampling and analysis for polychlorinated biphenols (PCBs). The NDEQ is committed to continuing monitoring for PCBs at those locations using a contract laboratory.
Fish tissue is collected and analyzed to assess human health risks associated with consumption using a risk-based assessment procedure. For non-cancer (noncarcinogenic) effects, such as those associated with exposure to mercury, the assessment procedure determines a Hazard Quotient for each contaminant. In addition to the concentration of a chemical contaminant found in fish tissue, this quotient is determined by taking into account an average body weight and ingestion rate for a consumer, and looks at how frequently (exposure frequency) and often (exposure duration), someone might eat fish from a particular waterbody.
If more than one contaminant is present in the fish tissue then the Hazard Quotients are summed to derive a Hazard Index. If the Hazard Index is less than 1.0, then adverse noncarcinogenic effects are not anticipated. If the Hazard Index equals or exceeds 1.0 then an advisory is issued.
For a contaminant that may also be associated with a potential cancer risk, the risk-based assessment procedure determines an estimated Cancer Risk. This estimate represents the probability of an individual developing cancer during their lifetime as a result of exposure to the potential carcinogen. If more than one potential carcinogen is present in fish tissue then the risk estimates are summed. Advisories are issued if the estimated Cancer Risk equals or exceeds 0.0001 (1 in 10,000).
Methylmercury is assessed using the Hazard Index approach, but Nebraska also limits the level of mercury in fish tissue to 0.215 milligrams (mg) methylmercury per kilogram (kg) of fish tissue. Therefore, for methylmercury, advisories are issued if the concentration in fish tissue equals or exceeds 0.215 mg/kg or if the Hazard Index exceeds 1.0. Exposure to high levels of mercury have been shown to adversely affect the developing nervous system, so women of child-bearing age, pregnant women, and children less than 15 years of age are the most sensitive to the effects of mercury.
Advisories remain in effect for a waterbody until it is re-sampled following a 6-year rotating basin monitoring approach. Re-sampled sites will be removed from the advisory list if fish tissue samples indicate contaminant levels below health risk criteria.
These advisories do not ban the consumption of fish from a particular waterbody but are designed to inform the public of how to safely prepare and eat what they catch, and provide suggested guidelines for limiting consumption. As a food source fish are a high quality protein, low in saturated fat, and high in omega-3 fatty acids, so anglers should not be discouraged from consuming fish in moderation.
Chemicals of primary concern in Nebraska and most other Midwest states include:
- Methylmercury (organic mercury) which occurs naturally and is released into the environment from mining operations, fossil fuel combustion, trash incineration, and industrial waste discharges.
- Polychlorinated biphenyl compounds (PCBs) prior to 1971 were used in heat transfer fluids, hydraulic fluids, lubricants, and wax extenders, and later in electrical transformers and capacitors.
NDEQ’s 2016 Data Assessment Report provides more detail on the sampling and analysis of fish tissue in Nebraska. A list of all waterbodies with advisories can be found at the link along with a map showing their locations.
Information on U.S. EPA Fish Advisories
Chemical Contaminants Found in Nebraska Fish Tissue
The State monitors waterbodies for PCBs and methylmercury two prevalent and persistent environmental contaminants. Newer regulations, chemical formulations, use restrictions, and other changes, have markedly improved the quality of surface water in Nebraska and throughout the nation.
Mercury is a naturally occurring metal that exists in several forms. The most common of which is methylmercury. Methylmercury can be found in water and soil, fish and shellfish. Methylmercury accumulates in fish tissue, primarily in older and larger predacious fish such as walleye, northern pike, and largemouth bass.
Exposure to high levels of methylmercury may adversely affect the developing nervous system. So young children and pregnant or nursing mothers are the populations most at risk. Advisories are issued to protect these very sensitive consumers.
U.S. Food and Drug Administration - What You Need to Know About Mercury in Fish and Shellfish
Agency for Toxic Substances and Disease Registry’s ToxFAQs for Mercury
Polychlorinated Biphenyls (PCBs)
PCBs are man-made chemicals that have been widely used in electrical equipment as coolants and lubricants (manufacturing stopped in 1977). Their presence in the environment is primarily due to improper disposal, leaks from electrical transformers, and incineration. They do not break down easily, so they persist in the environment for a very long time. PCBs can be found in water and soil, fish, meat and dairy products.
PCBs are stored in the fatty tissue and organs of fish. Therefore consumers can reduce their PCB intake by trimming all visible fat from the fish fillet and then grilling, broiling or baking the fillets in a way that allows remaining fat to drip or drain away.
PCBs are considered to be probable human carcinogens. Occupational studies and animal studies have both demonstrated that exposure to high levels of PCBs may be associated with the development of liver cancer.
Agency for Toxic Substances and Disease Registry’s ToxFAQs for PCBs