Mercurio En Peces

SEAFOOD NETWORK INFORMATION CENTER www.seafood.ucdavis.edu/pubs/mercury.html
Mercury in Seafood
Mercury is a naturally occurring metallic substance. Minute quantities of mercury are in air, water, soil, and all living matter. Mercury exists as both inorganic and organic forms, and the organic methyl mercury is the most toxic to humans.
Mercury vaporizes into the air from natural soildeposits. Rain washes mercury out of the air and returns it to rivers, lakes, oceans, and the soil. This cycle of vaporization and washing-out has probably taken place since the earth formed. Because plants and animals evolved in the earth's environment, all contain trace quantities of mercury.

Mercury and the Environment
Plants absorb mercury from the soil and air during normal growth. In somecases, plants concentrate mercury to small metal droplets. Some bacteria convert inorganic mercury to organic mercury compounds. Fish and animals may consume mercury containing bacteria. Some animals and vegetables convert organic mercury back to inorganic compounds.
This constant cycling of mercury from one form to another has gone on for eons without any recognizable toxic effect on the world'sfood supply. Our use of mercury has probably not significantly increased the mercury concentration in the oceans.
Awareness of Potential Dangerous Effects Increasing
Until the 1950's, we were only vaguely aware of the problems resulting from mercury misuse. Isolated events tragically demonstrated the potential dangers.
In 1953, an epidemic hit fishermen and their families in villages on Japan'sMinamata Bay. A number of people who were highly dependent on seafood showed signs of brain damage. Some of these cases were fatal. An investigation revealed that a local chemical plant was discharging organic mercury into the bay. The fish in the area absorbed the mercury and eventually passed it on to the villagers.
Authorities eliminated the source of pollution after finding the cause of theproblem. Mercury in the bay returned to normal levels, and once again the local fish were safe to eat.

Guidelines Established For Mercury in Food
The U.S. Food and Drug Administration (FDA) routinely analyzes foods for mercury. Almost all foods have mercury levels within the norms for natural environmental mercury content. Only some fish and fishery products have levels greater thanconsidered normal.
In 1969, FDA set a 0.5-part-per-million (ppm) action level as the maximum safe limit for total mercury in fish. Action levels represent the limit at or above which FDA will take legal action to remove a product from the market. FDA based this level on their investigations, and on Japanese and Swedish mercury poisoning experiences.
In 1979, FDA raised the mercury action level to 1ppm. FDA based this change in the action level in part on a National Marine Fisheries Service study. The study showed that a 1 ppm action level would adequately protect consumers.
In 1984, FDA switched from enforcing the mercury action level based on total mercury to a methyl mercury basis. The change occurred for two reasons. An acceptable test for methyl mercury was available, and evidenceindicated that methyl mercury was a small part of the total mercury in some fish.

Only Some Fish Exceed Limits
King mackerel, shark, swordfish, and tilefish are the four fish FDA found may have mercury levels above 1 part per million (ppm). These species accumulate mercury as they grow larger because they consume large amounts of small fish. All four combined add up to a very small amount (about1%) of the fish Americans eat. The average mercury level in the types of fish Americans eat is low – 0.086 ppm, weighted for consumption.
Commercial fishermen capture large fish at sea, far from any source of industrial pollution. The mercury in their system must come from natural sources. For years, we have probably eaten some fish with mercury levels above FDA's limit without harmful effects....