Environmental Trends 2002

Health and Environment

Status of Mercury in Freshwater Fish

Mean Mercury Concentration for Bull Trout and Lake Trout in British Columbia (parts per million wet weight)

SOURCE: Baker, R.F., 2002. Fish mercury database – 2001 British Columbia. Prepared by Aqualibrium Environmental Consulting, Vancouver for BC Hydro, Burnaby BC. NOTES: These data represent the most recent data available for the waterbody. All data are for 2000 except for Kinbasket (1995) and Arrow Reservoirs and Revelstoke Reservoir (1995). Data are size-adjusted to a 550 mm long fish.

Status of mercury in freshwater fish in British Columbia

• Both Bull Trout and Lake Trout feed at the top of the aquatic food chain. This means that mercury becomes more concentrated in their tissues than in species found lower on the food chain.

• In British Columbia, elevated levels of mercury in fish have resulted in three freshwater fish consumption advisories: Jack of Clubs Lake and Pinchi Lake (due to historic mining activities) and Williston Reservoir (due to mercury released during flooding when the reservoir was completed). (Comparable data for Jack of Clubs Lake was unavailable and so is not included in the above indicator).

• A fish consumption advisory is issued to minimize exposure to mercury by humans. Health risk is dependent upon the amount of fish eaten per meal, the frequency of fish meals, the mercury concentration of the fish eaten, and the body weight and gender of the consumer.

• The recommended guideline concentration for the commercial sale of fish in Canada is 0.5 parts per million. This does not apply to shark, swordfish, and fresh or frozen tuna that are considered delicacy items, not regularly consumed by the average individual.

Why is it important?

• Methyl mercury is the most toxic form of mercury and at high concentrations can affect nervous tissues of animals.

• Methyl mercury accumulates in fish, birds and mammals (bioaccumulation) and is found in higher concentrations in species near the top of the food chain (biomagnification).

• In addition to natural sources, human activities such as mining, and burning of fossil fuels and garbage contribute mercury to the environment. Also, mercury released from flooded soils and vegetation during reservoir creation, can cause mercury levels in fish to become elevated for about 20 to 30 years.

What is being done?

• There have been significant reductions in mercury emissions in Canada, particularly in base metal mining. Mercury used in the manufacture of chlorine and pesticides has mostly been eliminated. Releases from paints and batteries have also declined.

• The Canadian Council of Ministers of the Environment (CCME) has identified mercury as a priority issue. Canada-wide standards to regulate point-source mercury emissions are currently being developed.

For detailed information, including graph data, see In-Depth report [pdf].