Because of pesticides, mining and other human pursuits, heavy metal levels have increased in fresh and saltwater fish populations. Though the human body tolerates a certain amount of heavy metals before damage occurs, consuming large quantities of contaminated food can pose health threats. Toxic exposure can lead to difficulty thinking and focusing, lethargy, nausea and decreased motor coordination. Talk to your doctor about your fish consumption, following his advice to reduce your risk of overexposure.
Heavy Metals
Heavy metals are natural elements that are five times denser than water. Found abundantly in nature, small quantities of certain metals such as zinc, copper and iron are essential to a healthy body. Overexposure through ingestion, skin contact or respiration can cause metals to accumulate in body tissues and organs such as the liver. Heavy metals can disrupt physiological processes, affecting brain function, heart and circulatory system as well as your nervous system. The most commonly encountered heavy metals are arsenic, iron, cadmium, aluminum, lead and mercury.
Heavy Metals in Fish
Aquatic organisms born in the same environment as their parents are exposed to heavy metals both maternally and environmentally, increasing their mortality rate, according to an April 2011 article in the journal Environmental Science and Technology. Metals also build up in the food chain from the grasses and plankton to the smaller fish, which are consumed by larger fish. Bivalves such as clams and mussels are filter feeders, pulling in large quantities of contaminated water. In a May 2006 survey from the Food Standards Agency, bivalves were found to contain high levels of arsenic, cadmium and aluminum. Cadmium and arsenic were also highest in samples of crab meat, while the highest levels of mercury were found in skipjack tuna and swordfish.
Heavy Metal Effects
Symptoms of acute toxicity can include cramping, nausea, disorientation, headaches, difficulty breathing or impaired cognitive, motor, and language skills. Chronic exposure happens over time, and is characterized by fatigue, nervousness, learning difficulties, feeling ill and disruption in cognitive, motor or language skills. Though acute symptoms are easier to discern, chronic heavy metal exposure is similar to other disease symptoms, making them difficult to diagnose.
Effects from Fish Consumption
The effects of heavy metal exposure from eating fish varies, depending on the amount of fish and metals consumed. Fish is a major source of methyl mercury exposure, according to a 2003 study published in the British Medical Bulletin. Though the population is not at great risk, groups with high fish consumption "may attain blood levels associated with a low risk of neurological damage to adults," according to the study. Pregnant women are at increased risk of harming the fetus when consuming contaminated foods. If you are pregnant, limit your intake of shark, swordfish and tuna as well as fish taken from polluted waters. Choose instead, sardines, anchovies, catfish and certain types of salmon, which are lower in mercury.
References
- Life Extension: Heavy Metal Toxicity
- "International Journal of Environmental Science and Technology"; Bioaccumulation of Heavy Metals ,,,; R. Vinodhini, M. Narayanan; March 2008
- "Environmental Science and Technology"; Interactive Effects of Maternal and Dietary Mercury Exposure Have Latent and Lethal Consequences for Amphibian Larvae; C.M. Bergeron, et al.; April 2011
- Food Standard Agency; Survey of Metals and Other Elements in Processed Fish and Shellfish; May 2006
- "British Medical Bulletin"; Hazards of Heavy Metal Contamination; L. Jarup; 2003
- Food and Drug Administration: Mercury Levels in Commercial Fish and Shellfish
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