Mercury has been leeching into Clear Lake for thousands of years and it”s not only in Clear Lake. Upper and Lower Blue Lakes, Lake Pillsbury and Indian Valley Lake also contain mercury.
Tons of literature has been written about the effects of mercury on the fish and wildlife, including humans, but it would take a physics degree from Harvard to understand most of it. In fact, most of the fishermen who visit Clear Lake don”t know how much fish they can consume or even if it”s safe to eat a single fish.
The type of mercury that”s dangerous to humans is methylmercury. Once mercury is deposited in lakes, rivers and oceans, it is converted to methylmercury by aquatic organisms. Humans are exposed to it when they eat fish.
Plankton and insects can ingest the mercury bacteria and in turn are eaten by the smaller invertebrates. The methylmercury is then passed up the food chain to the fish. In fish, the mercury normally accumulates in the muscle tissue located on the side of the fish. That”s where the fillets come from.
The amount of mercury in a fish accumulates over time. In other words, the larger and older a fish, the more mercury it has absorbed into its tissue.
Methylmercury can affect humans in several ways. According to the Environmental Protection Agency (EPA), in fetuses, infants and children, the primary health effect of methylmercury is impaired neurological development. Methylmercury exposure in the womb, which can result from a mother”s consumption of fish and shellfish that contains methylmercury, can adversely affect a baby”s growing brain and nervous system. Also, impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methylmercury in the womb.
The big question is, are most the fish in Lake County lakes infected with methylmercury and how many of them can we eat?
Human fish consumption advisories have been in place at Clear Lake since 1986. In March of this year the state Office of Environmental Health Hazard Assessment (OEHHA) upgraded its guidelines for eating fish from lakes in Lake County. These include recommendations that pregnant or nursing women, women anticipating becoming pregnant, or children under 6 should not consume fish out of Clear Lake.
For all other groups of consumers, no more than 1 pound of fish should be consumed per month of largemouth bass or channel catfish. Children 6-15 years of age should eat no more than one-half the amounts indicated for adults.
For fish caught in Lake Pillsbury, the OEHHA guidelines are that pregnant women or nursing women and children under the age of 6 eat only one trout per week and no bass or bluegill. Women over the age of 45 and men over 17 can eat three servings of trout per week but no bass or bluegill.
The OEHHA has placed no specific guidelines on eating fish from Indian Valley Reservoir or Upper and Lower Blue Lakes. However, the general OEHHA guidelines on eating fish should be followed.
Lake County has thousands of people that are classified as senior citizens. These seniors are older than 50. Since most of the methylmercury poisoning has an effect on neurological functions of younger humans younger than 17, is it safe for these seniors to eat the fish?
Actually there have been very few studies on the effect of methylmercury on adults of non-child bearing age. In fact, scientists disagree if it has any effect at all, and then it depends on how much fish is eaten. However, OEHHA recommendations place restricted fish consumption for all women over the age of 45 and men over 17. The reason the age for women is 45 is because they can still become pregnant.
Largemouth bass and catfish are the two fish that have the highest mercury contamination in Lake County. In Clear Lake, the bass in the Clearlake Oaks arm have the highest level of mercury, the reason being that the Sulfur Bank mine is in the Oaks arm. It”s rare for a bass to swim the length of the lake and most live out their lifetimes within a mile.
The lowest level was found in the north end of the lake. But bass tournaments change that equation. Hundreds of bass are caught in the Oaks arm during tournaments and transported to Lakeport area to be weighed and then released. These bass spend the rest of their lives near the release site and could have elevated mercury levels.
Actually with the exception of crappie and catfish, few fish are eaten from Clear Lake. A study done by the Department of Fish and Game (DFG) a few years ago showed that anglers released 85 percent of all the fish caught in Clear Lake and that includes bass, crappie and catfish.
