While fish are an excellent source of protein, they sometimes contain chemicals that could pose health risks to humans. When contaminant levels are known to be unsafe, consumption advisories are recommended to limit consumption of particular species of fish caught in certain places. The advisories typically provide recommendations based on the size of the person consuming the fish and on whether they are pregnant, planning on being pregnant, or nursing.
Fish tissue analyses performed on fish from Denver Lakes resulted in fish consumption advisories for two lakes, Berkeley and Rocky Mountain. Advisories for consumption of large mouth bass were posted for these lakes in March 2006 based on elevated fish tissue mercury levels. The advisory will stay in place until future sampling demonstrates acceptable fish tissue mercury levels for human consumption.
This site provides a summary of mercury and how it impacts humans via fish consumption under the following topics:
General Information on Mercury
- Mercury is a naturally occurring element in the environment (volcanoes, etc) and is also released into the air through industrial pollution; In the U.S., coal-fired power plants are the largest industrial source of mercury emissions.
- Mercury air pollution comes from local, regional, and global sources. We do not yet have a good understanding of how much mercury comes from inside or outside of Colorado.
- Mercury that is deposited from the atmosphere accumulates in water bodies. Bacteria in the water cause chemical changes that transform mercury into methylmercury.
- Fish absorb the methylmercury as they feed in these waters. The amount of methylmercury in fish depends on what the fish eat, how long they live, and how high up the food chain they are.
- Fish and shellfish are the main sources of methylmercury exposure to humans.
- General advisories have been issued by the Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) for consumption of fish and shell fish, with particular focus on children less than 15 and pregnant women.
- Local fish advisories are typically posted by state regulatory agencies as more is learned about contaminants in fish within their state.
- At least 43 states have issued mercury-based fish consumption advisories.
Mercury in the Aquatic Environment
- Like many environmental contaminants, mercury can bioaccumulate. Bioaccumulation is the process by which organisms take up contaminants more rapidly than their bodies can eliminate them, thus the amount of mercury in their body accumulates over time.
- The food source for organisms higher on the food chain is progressively more concentrated in mercury and other contaminants. This results in increased bioaccumulation rates at the top of the food chain. The bioaccumulation effect is generally compounded the longer an organism lives, so that larger predatory game fish will likely have the highest mercury levels.
- Mercury concentrates in the muscle tissue of fish. Unlike some contaminants that concentrate in the skin and fat, mercury can not be filleted or cooked out of consumable game fish.
Risk Posed to Humans by Excessive Amounts of Mercury
- While research shows that most people's fish consumption does not cause a health concern, high levels of mercury in the bloodstream of unborn babies and young children may affect their neurological system.
- The FDA and the EPA released an advisory that if followed should keep an individual's mercury consumption below levels that have been shown to cause harm.
- The advisories for Berkeley and Rocky Mountain Lakes applies only to consumption of large mouth bass (a large predator).
- There are currently 11 fish consumption advisories posted within the state of Colorado
Large-mouth Bass
What is Denver's DEH Doing?
- DEH initiated tissue analysis of Berkeley Lake fish after measuring elevated arsenic concentrations in the water.
- Follow-up sampling by the Colorado Department of Public Health & Environment (CDPHE) found acceptable arsenic-tissue concentrations but elevated mercury-tissue concentrations.
- DEH will continue to monitor water and sediment concentrations and coordinate with the CDPHE and Colorado Division of Wildlife for follow-up sampling of fish tissue in Berkeley and Rocky Mountain Lakes, and fish tissue in the other Denver Lakes.
- Criteria suggested by the CDPHE for lake selection for fish tissue analyses includes the amount of fishing pressure on a lake, and evidence based on other information (such as water or sediment monitoring results) suggesting a potential risk.
Useful Links
- U.S. Environmental Protection Agency
- Colorado Department of Public Health and Environment