Many Southern California sportfish have elevated levels of mercury, PCBs


Mar 11, 2001
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Many Southern California sportfish have elevated levels of mercury, PCBs


Fish in many freshwater lakes and reservoirs tested in Southern California have highly elevated levels of mercury and some fish also have high levels of PCBs (polychlorinated biphenyls), according to a report issued by the State Water Resources Control Board in May. The levels are high enough to set off alarm bells for health officials, but anglers arent being asked to stop eating their catch.


The report gives data from the first year of a two-year study being conducted by the SWRCB and represents the largest survey ever done on contaminants in sportfish from the state's lakes and reservoirs. The first year of data showed methylmecury and PCB levels in commonly consumed sportfish -- catfish, largemouth bass, bullhead, and carp -- are likely to be very high in many waters, and anglers should be prudent about eating these fish and follow some simple, common-sense guidelines until the Office of Environmental Health Hazard Assessment (OEHHA) gets more data that might lead to official health advisories and warnings.

"It's a red flag, for sure, but it's not a storm warning," said Dave Clegern, a spokesman for the SWRCB. "People should be concerned, but not panicked. We certainly don't want to discourage people from eating fish because it is an important part of a healthy diet."

The preliminary results show that it's very likely that many, if not most, of the major fishing reservoirs in the region have levels of mercury that eventually will require some health advisories.

For example, Lake Silverwood's largemouth bass were found to have .48 to .49 parts per million (ppm) of mercury in their muscle flesh. The OEHHA threshold for a recommendation of no more than three servings per week is just .07 ppm, and OEHHA would consider recommending no consumption if levels exceed .44 ppm, which the Silverwood fish did. Sante Fe Reservoir's bass had levels at 59 ppm, Hansen Dam bass were at .49 ppm, and Lake Piru at .46 ppm. Castaic, Casitas, and Pyramid all had levels between .29 ppm and .39 ppm in their bass during this preliminary testing.

For PCBs, OEHHA recommends that no fish be consumed if the levels are 120 parts per billion (ppb), and the threshold level when no more than three servings per week are recommended is only 3.6 ppb. Pyramid Lake has PCB levels as high as 416 ppb in brown bullhead, and largemouth bass levels were 66 ppb. Silverwood Lake's largemouth bass had levels from 55 ppb to 131 ppb, with the higher number in bigger, older fish.

Are these numbers alarming to health officials?

"We sort of lead with, "fish are good food" because of the potential for health benefits [by eating fish], but you just need to make some smart choices," said Dr. Robert Brodberg with OEHHA.

Dr. Susan Klasing, also with OEHHA, explained that anglers need to know the problems associated with both mercury and PCB consumption and just be smart about how much fish they eat, how often, the size and species of fish, and what parts of the fish are eaten. Anglers need to be cautious until the public health agency has more data.

"With methylmercury, the part of the population we're really trying to protect is the fetus -- and women who might become pregnant," said Klasing. Mercury affects the fetus and children's neurological development as their brain grows, and studies have shown that children exposed to mercury in the fetus and early years can have problems, sometimes serious, at high exposure levels.

Mercury stays in the body a long time. While it is shed slowly, its half-life is 40 to 70 days. High levels can remain in your system more than a year after initial consumption, which is why most warnings talk about limiting the number of servings per week, so levels don't continue to build up in a person's system. In cases where mercury levels become too high, even adults can begin noticing initial symptoms, such as numbness and tingling extremities. But most anglers who have an occasional meal of fish, at even the highest levels of mercury in this study, will not face problems. Pregnant women or women likely to become pregnant would be wise to avoid fish from most local waters for the duration of pregnancy and while nursing, and young children also face far more risks than adults.

Anglers can also avoid some mercury by sticking with smaller fish for the table or focusing on species that are not at the top of the food chain. Striped bass, largemouth bass, and other predatory fish that make a living eating smaller fish, accumulate more mercury than fish like bluegill, carp, or even catfish. Young bass have less than old bass. At Santa Fe Reservoir, bass had mercury levels of 59 ppm, while carp in the same water had levels at .12 to .16 ppm. At the Castaic Lake lagoon, the bass had .18 ppm mercury readings, but the redear had between .02 and .03 ppm, below the threshold level.

Mercury appears to be widespread in Southern California waters, likely spread in the atmosphere from industrial and mining operations around the world, but local watersheds with mining operations also seem to have more mercury than other waters thanks to runoff. Lakes at higher elevations and smaller, isolated lakes that don't receive water from major water projects or significant runoff also seem to have lower levels of mercury.

PCBs are known carcinogens (cancer-causing) and emerging studies are showing they can also have neurological impacts on humans. They are dangerous at very low levels, with health recommendations at parts-per-billion levels rather than parts-per-million. PCBs also stay in the human system longer than mercury. But anglers can avoid most PCBs in fish by not eating fatty tissue and skin, where PCBs accumulate. Fatty fish with marbled flesh (like carp), make this task more difficult. While predators seem to accumulate more mercury than insect and bottom feeders, PCBs build up more in bottom-feeding fish, with carp and catfish generally having higher levels than bass and stripers.

The good news is that PCBs showed up less in the testing than mercury, but it seemed to be pervasive in Southern California, more than in other regions of the state. PCBs are known to concentrate in areas where there has been historic use and maintenance of electrical equipment, and there is far more in and around urban centers.

OEHHA's Brodberg said that anglers who ate "a lot of striped bass every week" from a water known to have high mercury levels was pushing the envelope, but that anglers that fished in different waters and ate a variety of fish species and sizes were less likely to have problems.

The initial year of the monitoring program can best be described as a well-designed, shotgun-approach to testing, with waters selected from throughout the state that represent groups of similar lakes and reservoirs, and then the fish most-likely to accumulate contaminants in these waters were tested. The preliminary data likely represents a worst-case scenario for each water, but the fish sampled are also very representative of the types of fish anglers are likely to pursue and eat. Anglers need to take precautions now while more data is being evaluated and collected.

"The survey has shown us where we need to focus in the future," said Clegern with the SWRCB. "This problem is not going to go away."

The first-year report is from data gathered in 2007. In that year, the study team collected over 6,000 fish from 150 lakes and reservoirs statewide. The team sampled another 130 lakes in 2008. Results from this second round and a more in depth analysis of possible trends will be available in a final report early in 2010.

For anglers who want to look up individual lake data on places they fish, all this information is in the 295-page study's appendix, and the full report is available on-line at this website: State Water Resources Control Board

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