Heavy Metal Toxicity in Fish

Any metallic element with high density and toxicity at modest concentrations is considered a heavy metal, reports Lenntech, an organization formed in 1993 by alumni from the Technical University of Delft, the Netherlands, to develop environmentally responsible air purification and water treatment systems. Heavy metals include mercury, arsenic, lead and chromium. As components of the planet's crust, these metals resist degradation. To a limited extent, they slip into the body through the atmosphere, water and food. Intake of heavy metals in greater concentrations can lead to poisoning. For example, toxic mercury exposure from eating fish poses a public health issue.

Heavy Metal Toxicity

• Because heavy metals accumulate in tissues over a period of time---i.e., stored faster than excreted---they can lead to poisoning and severe health problems, according to Lenntech. In contrast to trace elements such as selenium (antioxidant), heavy metals have no biological function in the body.

Mercury

• While diets should include fish as part of a nutritional regimen, this protein source rich in omega-3 fatty acids also contains traces of mercury, as put forth by the Environmental Protection Agency. Mercury, a metal that exhibits several forms, combines with carbon to form organic compounds. The most familiar one is methylmercury, which is created by microorganisms found in soil and water, reports the Agency for Toxic Substances and Disease Registry. In turn, methylmercury accumulates in the tissues of fish.

  As many as 60,000 children in the United States may be impacted by mercury toxicity, according to a 2001 study by the National Academy of Sciences. In 2002, an environmental organization reproached the U.S. Food and Drug Administration (FDA) for not warning the public about mercury exposure from tuna. California sued five supermarkets in 2003 for the failure to warn customers regarding potential mercury contamination from shark, tuna and swordfish, reports the EPA.

Health Risks

• Poisoning due to mercury can cause injury not only to the brain and kidneys but also to a growing fetus. In particular, the nervous system is vulnerable to many forms of mercury, reports the Agency for Toxic Substances and Disease Registry. If the metal seeps into the brain, the effects include tremors, irritability, difficulties with memory and distortions in hearing and vision.

  According to the EPA, the dangers of mercury poisoning from eating fish are not a major concern. The risk depends on the amount of fish intake coupled with levels of mercury in the fish. As a preventive measure, the EPA and FDA recommend that infants, pregnant women and nursing mothers avoid specific types of fish and only eat fish that are low in mercury.

Chromium

• Another toxic heavy metal, chromium builds up in aquatic organisms and animals. While minimal exposure to chromium can cause ulceration and skin irritation, exposure over the long term can damage nerve tissue and the liver, reports Lenntech.

Testing for Heavy Metal Toxicity

• Current lab technology can gauge heavy metals in the body, according to Mount Rainer Clinic. Laboratories such as LabCorp or Quest Diagnostics (located in urban centers throughout the United States) can perform whole blood tests. Results appear in reports that employ EPA and Occupational Safety and Health Administration (OSHA)-approved ranges of reference.