What Makes Mercury a Problem?
A heavy metal called mercury can be naturally found in soil, water, and the air. There are three main types of mercury in nature: organic, inorganic, and elemental or metallic. Consuming fish and shellfish can expose one to low levels of mercury absorbed by these animals due to water pollution. The organic form of mercury, known as methylmercury, can accumulate in the human body as time passes. Methylmercury, at particular levels, can cause serious illnesses.
What Occurs When Someone Is Exposed to Mercury?
Based on the exposure route and the kind of mercury it will be absorbed by the body. Inhaled mercury is absorbed at a greater rate than the mercury that is consumed. However, methylmercury will be absorbed easily, regardless of the exposure route. Mercury can pass through the placental and blood-brain barriers in both elemental and methyl forms. The adult and fetal brain are the essential intended targets for elemental mercury, and the brain and kidneys are the essential target structures for methylmercury. Mercury may accumulate in the brain, central nervous system, liver, and nearly every organ of the body, although the kidneys retain the greatest amount of any form of mercury within the body. Mercury accumulates in the human body because it is excreted through urine and feces at a lower rate than the intake. Accumulated mercury will be found in breast milk, resulting in greater levels of mercury in infants. Since mercury can cross the placental barrier, the fetus may also get exposed to higher concentrations of mercury.
How Are Fish Exposed to Methylmercury?
Fish is considered an essential food because of its immense health benefits owing to the omega-3 fatty acids, vitamin D, B2 (riboflavin), and several essential minerals. It is also considered one of the best foods to prevent the impact of aging and promote skin health. However, it is important to note the nutrition facts that need to be considered while consuming certain fish varieties that may contain moderate to higher amounts of mercury. Consuming these varieties of fish cannot only possibly raise the level of mercury in the body but is also an absolute contraindication, according to the United States Food and Drug Administration (FDA), for pregnant and breastfeeding women.
Larger fish and some species of fish, such as shellfish, are known to absorb the methylmercury dissolved in water bodies because of human activities, such as the burning of coal and industrial pollution, which in turn lead to environmental pollution. In large fishes, methylmercury can usually pose the threat of human toxicity. Additionally, individuals who work in industries such as coal mining, for instance, may also be subjected to the ill effects of methylmercury exposure and poisoning. Methylmercury is demonstrated by scientific research to be toxic to the human central nervous system (CNS), that is, the brain and spinal cord, including the CNS of unborn babies and young infants, thus causing an irreversible form of CNS damage. This kind of CNS damage in infants and children is mainly due to methylmercury exposure during pregnancy or breastfeeding.
Why Is Fish Ideally Contraindicated in Pregnant or Nursing Individuals?
Though many varieties of fish may contain some traces of mercury content, for healthy individuals, there are absolutely no contraindications to consuming fish even regularly. Also, for most individuals, the trace amounts of mercury consumed from fish do not pose a health issue as such, nor interfere with the minerals and vitamins they get from fish consumption. However, some fish species have higher amounts of mercury that may prove fatal and have the highest risk of causing damage to a developing fetus or a newborn infant. That is why the United States Food and Drug Administration advises pregnant and nursing mothers to refrain from consuming any variety of fish in their diet during this time.
Methylmercury poisoning may produce adverse effects such as cerebral palsy, deafness, blindness, impairment in cognitive functions, impaired pulmonary functions, growth issues, and microcephaly (an infant's small head). Even for women planning to conceive, nutritionists always advise them to avoid consuming fish, even in mild or moderate amounts. According to the recommendations by the FDA, pregnant women and younger children below six years of age should not consume more than two servings of fish each week and must ideally consume a variety of fish with lower mercury content.
What Are the Large Fish Varieties Exposed to Mercury?
Several varieties of large fish usually comprise a higher level of mercury content that can be unintentionally consumed by human beings in the process of biomagnification (mercury concentrations in larger, predatory fish can be up to ten times greater than in the fish they eat). Through the food chain. This can prove life-threatening or potentially dangerous because the mercury levels are exceeded in the human body. For the given list of large fish, the recommended serving for healthy individuals, according to the US Food and Drug Administration, is not to consume more than two to three servings of these types of fish every month. On the other hand, it is advisable for nutrition experts that pregnant, nursing women, children, or even younger adults who would be easily prone to mercury poisoning should entirely avoid them.
These large fish groups are as follows:
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Grouper.
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Sea Bass.
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Mackerel.
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Croaker.
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Sablefish.
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Perch.
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Tuna.
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Bluefish.
Also, there are varieties of large fish that are completely contraindicated for consumption by the FDA because of their high mercury levels and potential risk of causing mercury poisoning. Even a small serving of these fish, because of their size and the mercury content in them, is still capable of causing mercury excess. Hence, the FDA recommends that adults and children completely avoid eating these varieties of fish. These fishes include:
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King mackerel.
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Orange roughy.
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Shark.
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Swordfish.
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Tilefish (the Gulf of Mexico).
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Marlin.
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Tuna (Big eye).
What Varieties of Fish Have Moderate Mercury Content?
Fish containing moderate levels of mercury content would be safe to consume in moderation, preferably around six or less than five servings per month. The FDA recommended that pregnant and nursing women, as well as younger children and infants, avoid eating or consuming the following fish with moderate mercury content:
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Cod (Alaskan).
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Halibut.
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Lobster.
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Mahi Mahi.
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Monkfish.
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Bass (saltwater, striped, black).
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Buffalo Fish.
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Carp.
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Perch (freshwater).
What Varieties of Fish Have Low Mercury Content?
According to the FDA, several fish varieties tend to have only minimal or low levels of mercury content. Therefore, the consumption of these varieties is considered safe for around two to three servings a week by healthy individuals, excluding the risk-prone groups such as pregnant, nursing women, and younger children. Though these groups should ideally not consume larger amounts, if low mercury fish are consumed by these risk groups, they should consume only around 12 ounces or two servings every week. These varieties of fish include:
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Clam.
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Crab.
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Crayfish.
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Croaker (Atlantic).
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Flounder.
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Haddock.
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Hake.
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Herring.
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Mackerel (North Atlantic, Chub).
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Mullet.
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Oyster.
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Perch.
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Pollock.
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Salmon.
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Anchovies.
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Catfish.
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Sardine.
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Scallop.
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Shrimp.
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Sole.
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Squid.
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Tilapia.
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Trout.
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Whitefish.
Conclusion
The traces of methylmercury or organic mercury in water bodies can be found in various fish varieties. The consumption of these fishes can predispose mercury poisoning, mercury toxicity, or food poisoning in high-risk groups, such as pregnant and breastfeeding mothers and younger children. Methylmercury has a detrimental central nervous system (CNS) impact on these groups. Therefore, the FDA strictly discourages the consumption of fish containing high mercury content and only recommends low or moderate mercury-containing fish to be consumed with less than two servings per week, especially for high-risk groups.
