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“The global cycling of mercury, along with the processes of biomethylation and bioaccumulation, implies that humans must have consumed methylmercury in fish dating back to times before Homo sapiens evolved. It could be argued that environmental levels of mercury vapor were much higher in an earlier period of earth’s history when oxygen had not yet appeared in the atmosphere [i.e., the appearance an oxygen atmosphere was timed roughly to 2.45 to 2.22 billion years ago]. As levels of oxygen began to rise, increasing amounts of the vapor would be converted to the ionic form. Life forms at those Archean times [roughly 3.8 to 2.5 billion years ago] had to protect themselves not only from this new toxic gas, oxygen [i.e., because of its reactivity], but also from ionic mercury [i.e., Hg2+] pouring down in rainwater. Perhaps it is no coincidence that those proteins and antioxidant molecules present in today’s cellular machinery to protect against oxygen also are our main line of defense against mercury.Chicago Tribune: The simple question "Is fish safe to eat?" depends on many factors. What kinds of fish do you eat? How much do you eat? How often do you eat it? How much do you weigh? ... Shoppers have no way of knowing, for instance, if one piece of orange roughy in a supermarket display case has a widely different amount of mercury than the orange roughy fillet next to it. The same is true for canned tuna and many other kinds of fish. ... For example, 15 of the orange roughy samples the Tribune bought had high levels. The testing also indicates mercury levels can vary widely even within a given species. A sample of orange roughy from Dominick's in suburban Crestwood had seven times more mercury than a piece from Jewel on North Elston Avenue in Chicago. ... FDA officials said it is impractical to test individual swordfish to weed out those that are heavily contaminated. Issuing warnings is a better way to protect at-risk groups, such as young children and pregnant women, the officials said. "Rather than saying, `You can eat swordfish as long as it has been tested,' we're saying, `Don't eat those fish,'" Acheson said. Though it is unclear whether a single high-mercury meal could harm a fetus, experts say the developing nervous system is so sensitive to toxic substances that caution should prevail. "You only get one chance to develop a brain," Hightower said. (December 11, 2005) Response: Here, CT advances the somewhat sophistical notion that without implementation of impractical testing and labeling of every individual piece of fish sold in US markets or restaurants, any fetus may miss its “one chance to develop a brain.” Equally questionable is the “expert” claim of non-clarity regarding “whether a single high-mercury meal could harm a fetus.” It is highly doubtful that Dr. Jane Hightower – neither a toxicologist nor epidemiologist – would make such an extraordinary leap against the huge body of literature to the contrary (see Sec. 9). Such CT claims, here and throughout the series, compels the question as to how is it possible that thousands of generations of humans the world over have consumed large quantities of a variety of sea foods and still managed to escape a pandemic of brain damage? Ultra-trace levels of mercury have likely been present in fish and fish-eaters around persistent and current levels since either evolved. The data briefly presented in Sec. 1 and Sec. 8 clearly support the findings that fish and fish oil consumption is highly beneficial and that average Americans are far below optimal levels (1) consumed in other countries or (2) recommended by medical and nutrition professionals. The real benefits of fish consumption clearly far outweigh hyperbolic risk claims. Any such risk concerns need to be rationally evaluated on a case-by-case basis for extreme situations or consumption patterns. For example, a recent analysis by Carrington et al. (2004) suggests the optimal strategy for reducing MeHg exposure is to restrict fish consumption to no more than 12 ounces a week while avoiding the high-mercury species as recommended in the joint EPA/FDA fish advisories. Their analysis indicated that if the U.S. population took the further precautionary step of eating only the low-mercury species like shrimp, canned light tuna, salmon, pollock and catfish, even individuals with unusually high blood mercury could achieve reductions below a wide range of proposed safety standards, including the most stringent by EPA (see Figure 5 in Carrington et al. 2004). Pseudoscience calls for almost-zero risk tolerance in fish consumption is untenable and ignores the optimal approach taken by FDA in minimizing risk. In the above quote, the CT appears to blink at the principle of averages, failing to allow for the fact that occasionally crossing EPA’s stringent methylmercury threshold does not even faintly constitute a known health threat. According to EPA's own RfD definition, fish consumers would have to persistently beat incredible odds for randomly selecting only high-mercury content fish, day after day, for a lifetime to risk being “poisoned.” Practically, total public avoidance for occasionally eating a “high” mercury meal is unlikely, regardless of resources expended. Again, CT impugns the FDA as having purposely neglected its public health responsibilities, this time by comparing Canadian policy. CT appears to lament that the Canadian mercury actionable level (0.5 ppm) for prohibiting sale of commercial fish is twice as stringent as FDA (1 ppm). [As an aside, it should be noted that EPA's threshold advisory for freshwater fish is 0.3 ppm (see CSPP’s Making Sense of State Fish Advisories ). Also, see Sec. 17 highlighting the confusion in Representative Mark Kirk's "dear Colleague” letter suggesting that Canada banned the sales of walleyes above 0.5 ppm level while FDA has ignored the situation.] This is an odd claim considering the FDA (and EPA) advocates the far more restrictive advisory of no consumption for the high-mercury fish species like swordfish, shark and fresh and frozen tuna steaks. Health Canada’s guidelines for high-mercury fish species state: “Certain fish species sold in Canada, namely, shark, swordfish, and fresh and frozen tuna, contain mercury at levels that are known to exceed the 0.5 ppm guideline. Mercury levels for these species generally remain between 0.5 and 1.5 ppm, allowing for occasional consumption. Therefore, these species (Note: not canned tuna) are exempted from the 0.5 ppm guideline and, in their case, another risk management strategy is followed, namely, issuance of advisories recommending appropriate restrictions on (amounts and frequencies of) consumption. In this way, these species can continue to be enjoyed by consumers as part of an occasional diet. Again, by advising total avoidance of high-mercury fish for pregnant women, FDA is more conservative, even though Health Canada’s legal limit for banning commercial fish is 2 times higher that the guideline set by the Canadian Food Inspection Agency. Freshwater Sport Fish How safe is freshwater sport fish consumption? First, an Electric Power Research Institute report of May 2003 assumed a large upper bound of 10% of all fish consumed in the U.S. being from “wild, freshwater fish.” However, utilizing statistics from the U.N. Food and Agriculture Organization, our macroeconomic estimate indicates that only about 0.5% of all fish consumed in the U.S. is from freshwater catch. For those concerned about mercury exposure consumption levels for freshwater fish, Fig. 4-A displays recent EPA exposure estimates from researchers at RTI International. The results clearly show that mean daily intake of MeHg from local freshwaters for the 38 eastern U.S. states - including Illinois - fall safely below EPA's recommended ingestion rate. These empirical findings confirm that alarmism over “toxic exposure” to MeHg from consumption of freshwater fish caught in U.S. lakes and rivers is largely unwarranted. Also, a collaborative project between the Wisconsin Department of Public Health and Maine’s Bureau of Health , assessing mercury awareness in 12 States, found that only 29% of the 3,015 women of childbearing age surveyed had eaten any sport-fish. Hair mercury levels [measured for 414 women in the sample] ranged from 0.005 to 4.62 ppm and were positively correlated to fish consumption rates (P<0.0001). Women who ate sport-caught fish did not have significantly higher hair mercury levels than others (mean 0.51 vs. 0.48 ppm). Among women who ate sport fish, advisory awareness had no effect on their mercury exposure. “Demographic indicators associated with higher hair mercury levels included residence in northeastern USA, marital status of married, college education, annual household income greater than $75,000, and Asian race.”  These researchers also documented that 50 women (12% of the 414 women sampled) had a hair mercury level greater than the 1 ppm safety guideline established by EPA’s MeHg RfD, and that most of these women did not consume sport-caught fish; their exposures are largely explained by consumption of commercially sold fish, including frequent meals of canned tuna.Additional research results were recently reported from Canada. Cole et al. (2004) reported relevant findings for anglers and sport-fish eaters from Ontario, Canada. Surveys among 176 anglers consuming their catch had a mean blood total mercury level of 2.8 ppb – well below EPA’s RfD of 5.8 ppb. These findings are also consistent with the estimates shown in Fig. 4-A, indicating that mercury exposure through the consumption of locally-caught freshwater fish is not a predominant route, when compared to commercial seafood. The authors concluded, “Given the nutritional and social benefits of fish consumption, prudent species and location choices should continue.” Similar results were reported by Morrissette et al. (2004) after monitoring actual blood and hair mercury exposures in pregnant women living in the region of the St. Lawrence lakes, St. Francois and St. Louis. Their analyses showed that “during pregnancy market fish (fresh, canned, and frozen) were more important sources of Hg exposure than were fish from the St. Lawrence River.” They concluded, “These results should be taken into account for future advisories and intervention strategies, which should consider Hg levels in different species from all sources in order to maximize the nutritional input from fish and minimize the toxic risk (emphasis added).” In other words, be smarter about advisories and stop scaring sport fish consumers. Also, these findings by Morrissette and colleagues are encouraging because they show that the primary mercury exposure path for these Canadian pregnant women was not from locally-caught fish. It is further encouraging to find that none of these pregnant Canadian women are significantly at risk from exposure to total, organic and inorganic mercury since all measured concentrations, including those notably more concentrated levels in cord blood, ranged from non-detectable to no more than 1.6 ppb, and total maternal hair mercury level below 0.3 ppm. Conclusion
All the above findings point to a relatively less important exposure risk through sport fish than the CT series suggests. This should have direct implications for active proposals by Illinois, Connecticut, Massachusetts, Minnesota, New Hampshire, New Jersey, North Carolina and Wisconsin calling for stringent cuts up to 90% on mercury emissions from local power plants. There is almost zero chance, even were 100% emission cuts achieved, that these states will be able to lower the methylmercury content in any of the popular fish consumed. This is more specifically examined under Sec. 5, 10, and 21. |
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