Symptoms of toxic effects ordinarily don’t occur unless one exceeds the RfD by a fairly wide margin for an extended period. Facts: This statement is wrong in two ways. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely. The site is secure. All of the children were found to have mercury levels below the EPA's public safety limit of 5.8 nanograms per milliliter (ng/mL). Exposure is most likely to occur during mining, production, and transportation of mercury, as well as mining and refining of gold and silver ores. And it overstates the actual Reference Level by a factor of 10. The period the Reference Dose applies to is therefore a pregnancy and the first few years of life. Mercury levels in fish are expressed in parts per million; see FDA data on levels in different fish and shellfish. The definition of safe exposure is the Reference Dose. (Since a deciliter is one-tenth of a liter, this is the same as saying the limit is 58 micrograms per liter.) This claim is based on another major conceptual error. Some experts in mercury toxicity believe that an RfD at least 50 percent lower would be fully justified by the available evidence. The RfD expresses the amount of mercury that can be safely consumed per unit of body weight, each day. But as exposure increases above the RfD, risk increases, and the “reasonable certainty of no harm” becomes less certain. When the EPA set the Reference Dose, it began with a level of mercury in blood that had a statistically significant adverse effect on children’s cognitive development, in the best-designed epidemiological study. The bottom line: The RfD, the current definition of safe exposure, was based on evidence that was available when it was set, in 1999. For many people, under most conditions, a single meal of high-mercury fish, now and then, is unlikely to be harmful. Are Mercury Warnings Bad for Public Health? Most people are exposed to low levels of mercury, often through chronic exposure (continuous or intermittent long term contact). Because most Americans don’t eat fish every day, the EPA and FDA have addressed methylmercury exposure averaged over a week’s time. and three times a week without going over the maximum acceptable mercury intake amount for an average pregnant woman Swordfish: 0.976 pm x 170 grams =166 micrograms Flounder: 0.050 ppm x 170 grams = 9 micrograms An “uncertainty factor” is not a “safety margin.” An uncertainty factor is applied to account for unavoidable scientific uncertainties. The FDA has set a limit of 1 part per million of mercury in fish for human consumption. For copper, the action level is 1.3 mg/L, and for lead is 0.015 mg/L. This safety standard is called the Reference Dose, abbreviated RfD. N/A-data not available. High mercury exposure results in permanent nervous system and kidney damage. Facts: The seafood lobby uses this fable to suggest that consumers don’t need to be concerned about short-term high exposure to methylmercury. [See also advice on canned white/albacore tuna via the "Mercury webpage"] 1 mg/kg: The edible portion of escolar, orange roughy, marlin, fresh and frozen tuna, shark, and swordfish While the RfD defines “reasonable certainty of no harm,” some uncertainty still remains within that “reasonable certainty.” The RfD protects different individuals to different degrees, and for some, the margin between the RfD and a potentially harmful exposure is undoubtedly quite narrow. Sometimes they explain that they know the actual reference level is 5.8 micrograms per liter, but because “there is a 10-fold safety margin built into the RfD,” the actual “safe” level is 58 micrograms per liter. Gulf of Mexico tilefish: 1.45 ppm x 170 grams = 246 micrograms. 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