Fish Tissue Monitoring Program

Why NDEE Does this Monitoring

Each year fish samples are collected from numerous streams and lakes across Nebraska to determine their suitability for human consumption. This is important because certain contaminants bio-accumulate in fish tissue and, when eaten, can cause an increased risk for human health problems. In waterbodies where contaminant levels in fish are of concern, “fish consumption advisories” are issued.

These advisories do not ban the consumption of fish from a particular waterbody. Rather, advisories 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 omega-3 fatty acid food source, so anglers should not be discouraged from consuming fish in moderation.

History of the Fish Tissue Program

Fish tissue sampling in Nebraska was initiated in the late 1970s, primarily to identify potential pollution concerns throughout the State. Monitoring efforts were focused on whole fish samples collected on large rivers near the bottom of their drainage areas. In the late 1980s, more emphasis was placed on evaluating human health concerns and the Department began analyzing the fillet portions from fish that are most-often consumed. These efforts have continued to the present day.

Where is the Monitoring Conducted?

Monitoring is generally conducted at locations where most fishing occurs, therefore the risk to human health is greatest. Fish species targeted for collection included those that are most frequently sought by fisherman, such as: catfish, largemouth bass, walleye, crappie, and even carp.

From July 1 to September 30 each year, the Department collects fish samples from approximately 40-50 pre-selected streams and publicly owned lakes in two or three of Nebraska’s 13 major river basins (see the map above for basin divisions and historic sampling locations).

Fish tissue sampling activities are rotated through all 13 basins on a six-year cycle. In addition, fish samples are collected every two years at five locations termed “trend sites.”

These five trend sites have been monitored for more than 16 years in an effort to identify long-term changes in fish contaminant levels, if present.

What is Monitored?

Fish tissue samples are analyzed for a variety of parameters including: heavy metals, pesticides and other organic compounds. Of primary concern of the parameters screened are:

• polychlorinated biphenyl compounds (i.e., PCBs – prior to 1971, they were used in heat transfer fluids, hydraulic fluids, lubricants, and wax extenders, and later in electrical transformers and capacitors);
• methyl mercury (i.e., organic mercury – occurs naturally and is released into the environment from mining operations, fossil fuel combustion, refuse incineration, and industrial waste discharges); and
• dieldrin (i.e., a breakdown product of the insecticide Aldrin, generally used on corn prior to 1974).

How are the Data Used?

Fish tissue data collected are used to assess human health risks utilizing a risk-based assessment procedure. For non-cancer (noncarcinogenic) effects the assessment procedure results in a Hazard Quotient value for each contaminant and takes into account an average body weight, ingestion rate, exposure frequency and duration, and percent absorption of contaminants. 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 cancer risk, the risk-based assessment procedure results in a Cancer Risk estimate that 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).

While mercury (methylmercury) is a contaminant accounted for in the HI, Nebraska also utilizes a fish tissue residue criterion in place of a water column criterion for the protection of human health. Nebraska’s tissue residue criterion represents the mercury (0.215 mg/kg) concentration in fish tissue that should not be exceeded on the basis of a consumption rate of eight ounces (0.227 kg) per week. Advisories are issued if the mercury concentration in fish tissue equals or exceeds the tissue residue criterion of 0.215 mg/kg. 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.

Currently the Nebraska Department of Health and Human Services (NDHHS), in cooperation with the NDEE, the Nebraska Game and Parks Commission (NGPC), and the Nebraska Department of Agriculture (NDA), issues fish consumption advisories for waterbodies where high concentrations of contaminants may indicate a health risk for consumers. Waterbodies where sampling has revealed exceedances of health risk criteria and subsequent consumption advisories have been issued will be re-sampled following the 6-year rotating basin monitoring approach. Re-sampled sites will be removed from the advisory list if their respective samples indicate contaminant levels below health risk criteria.

Fish tissue data are also utilized to assess impairment of Nebraska’s waterbodies. Where fish consumption advisories exist, the NDEE places those waters on the State’s Section 303(d) List of Impaired Waterbodies with regard to aquatic life. Nebraska does not have an assigned beneficial use of “fish consumption” in Title 117 Surface Water Quality Standards, therefore the assumption is made that if contaminant loads to fish can affect human health, it is probable that these contaminants can impact aquatic life health.