Elevated mercury levels found in fish tissue from many state water bodies
The Oregon Health Authority (OHA) is issuing a statewide advisory for bass due to elevated levels of mercury found in fish tissue sampled from a number of water bodies across the state.
The fish consumption advisory affects bass in all water bodies statewide, including river systems.
"Fish are an important part of a healthy diet, especially migratory fish like salmon, steelhead and trout," said Dave Farrer, Ph.D., toxicologist in the Environmental Public Health Section at the OHA Public Health Division. "The elevated mercury levels we're talking about in bass are of concern to us, but there are some simple steps people can take to reduce their exposure to mercury when consuming bass."
Bass is the focus of the advisory because it is a resident species—it lives in one place its entire life—and is considered a top predator, eating other mercury-contaminated fish within an ecosystem. The longer bass live, the more mercury they accumulate. In addition, bass are found across the state in many popular fishing waters, and the amount of data the state has for this species is adequate to warrant a statewide advisory.
OHA recommends the following monthly meal allowances for bass from all water bodies across the state, including river systems:
- General population—Limit consumption to no more than six meals per month.
- At-risk populations—Limit consumption to no more than two meals per month.
Mercury was found at levels above established screening values. This means it is high enough to be of concern to human health if fish contaminated with mercury are not eaten in moderation. For reference, the screening values used by OHA when determining if the concentration of mercury found in fish tissue is a health risk are 0.2 mg/kg for at-risk populations (infants, children, and pregnant or breastfeeding women), and 0.6 mg/kg for the general public. Average total concentrations found in fish tissue from across the state ranged from 0.08 mg/kg to 0.86 mg/kg of mercury.
Tissue samples were taken from 62 bass from 11 water bodies across the state, including eight rivers, two reservoirs and one lake covering each region of the state, from 2008 through 2014.
The statewide advisory and recommended meal allowances cover those water bodies that do not currently have an individual advisory in place for resident fish, including bass. For a list of water bodies with an existing advisory, see the advisory table at HealthOregon.org/fishadv. People should follow the recommended meal allowances for fish from these individual water bodies, rather than the statewide meal allowance of six and two.
A meal is about the size and thickness of your hand; for children, a meal is about the size and thickness of a child's hand.
People who eat too much fish contaminated with mercury can suffer negative health effects over time, such as damage to organs, the nervous system and reproductive system. Fetuses, babies and small children are most vulnerable to the health effects of mercury and, if exposed to high levels, can suffer life-long learning and behavior problems. For this reason, OHA recommends that pregnant and nursing women, and women of childbearing age (18 to 45), follow the consumption recommendations closely. Anglers also should not give bass to others unless the recipients are aware of the mercury contamination issue and they understand the recommendations in the fish advisory.
Fish consumption advisories are issued when fish tissue data collected and analyzed verifies that a particular contaminant is over Oregon's established screening value for that contaminant. OHA has several advisories currently in place for mercury in resident fish including bass, although fish tissue in many water bodies has not been sampled and analyzed.
Because data for mercury in fish tissue is available for some, but not all, lakes across the state, and because environmental conditions are such that mercury is present in recreational waters and can accumulate in the fish that live there, OHA believes it is necessary to issue a statewide advisory to protect public health.
Issuing a statewide advisory helps prevent confusion and reduces the public's exposure to mercury when consuming bass from non-monitored water bodies.
The advisory is expected to remain in place for the foreseeable future because mercury can come from both natural and human-made sources, and is transported globally through air pollution. The monthly meal allowances represent the most consistent health protective recommendations possible based on available fish tissue data. Should more mercury data become available, OHA will evaluate those data and update this and other advisories as practical and necessary.
By issuing the advisory, health officials hope to increase the public's awareness of fish species they should avoid or limit consumption of, and those they can keep eating. While it is important for people to know about contaminants in fish, it is equally important to keep fish on the table. Health officials continue to encourage people, including pregnant women, to eat a variety of fish as part of a healthy diet. Migratory fish such as salmon and steelhead are an essential source of protein, omega-3 fatty acids and other nutrients, and are low in contaminants.
Visit HealthOregon.org/fishadv to learn more about why fish is good for you, and for other fish-related topics.