Logan Reed
Fish and thimerosal-containing vaccines (TCV) are the primary sources of mercury exposure for the general population. Thimerosal, a mercury-containing compound, has been used as a preservative in vaccines since the 1930s to prevent bacterial and fungal contamination. While thimerosal contains ethylmercury, fish contain methylmercury, which is known to be toxic to humans at high exposure levels. Studies have shown that ethylmercury is cleared from the human body more quickly than methylmercury and is therefore less likely to cause harm. However, concerns have been raised about the potential risks of mercury exposure from both sources, especially for children and pregnant women.
| Characteristics | Values |
|---|---|
| Mercury in fish | Methylmercury, a known neurotoxin and cardiac toxin |
| Mercury in vaccines | Thimerosal, a mercury-based preservative, is added to some vaccines to prevent the growth of harmful microbes |
| Methylmercury toxicity | High exposure levels can be toxic to humans |
| Ethylmercury toxicity | Ethylmercury is cleared from the human body more quickly than methylmercury and is therefore less likely to be harmful |
| Thimerosal toxicity | Studies have found no evidence of harm caused by thimerosal exposure, including no link to autism or neuropsychological delays |
| Fish consumption benefits | Provides nutrients and omega-3s, which can decrease the risk of a heart attack |
| Mercury exposure from fish | The more fish consumed, the higher the mercury exposure; certain fish are higher in mercury, such as swordfish and shark |
| Mercury exposure from vaccines | Exposure from vaccines is minor compared to fish consumption; the amount of mercury in a flu shot is roughly equivalent to the amount in a can of tuna |
| Thimerosal usage | The use of thimerosal in vaccines has declined due to reformulation and the development of single-dose presentations |
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What You'll Learn
Mercury levels in predatory fish
Mercury is a naturally occurring heavy metal found in the earth's crust, air, soil, and water. It is released into the environment through various natural and anthropogenic processes, including industrial activities such as burning coal. Mercury can enter freshwater systems through point sources, like spills or leaks, and extended flooding.
Methylmercury, the organic form of mercury, is highly toxic and can accumulate in the bodies of fish. This accumulation occurs because fish absorb methylmercury from their diet, primarily by consuming algae or smaller fish that already contain the toxin. The older the fish, the more mercury it may have accumulated. This process is called bioaccumulation or biomagnification, resulting in higher concentrations of mercury in predatory fish that consume smaller fish.
Predatory fish, such as swordfish, sharks, and tuna, have been found to contain higher levels of mercury due to their position in the food chain. The larger and longer-lived a fish is, the higher the potential mercury concentration. This is because the mercury consumed accumulates and becomes more concentrated as it moves up the food chain.
Consuming predatory fish with high mercury levels can be detrimental to human health. Methylmercury is a neurotoxin and cardiac toxin, increasing the risk of heart attacks and causing damage to the nervous system, particularly in developing fetuses, infants, and young children. Prolonged or excessive consumption of mercury-contaminated fish can lead to cognitive and developmental issues, impacting learning, memory, and overall neurological function.
Therefore, it is crucial to strike a balance between the nutritional benefits of fish consumption and the risks posed by mercury. Certain predatory fish, such as salmon, sardines, and anchovies, have relatively low mercury levels due to their dietary preferences for plankton and smaller organisms lower in the food chain. Additionally, their shorter lifespans and migratory behaviors contribute to lower mercury accumulation.
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Thimerosal in vaccines
Thimerosal is a mercury-based preservative that has been used in vaccines since the 1930s to prevent microbial growth. It is added to vials of vaccines that contain more than one dose (multi-dose vials) to prevent the growth of germs like bacteria and fungi. The introduction of bacteria and fungi can occur when a syringe needle enters a vial during vaccine preparation, potentially causing severe local reactions, serious illness, or even death. Thimerosal contains ethylmercury, which is cleared from the human body more quickly than methylmercury (found in certain kinds of fish) and is therefore less likely to cause harm.
Thimerosal was removed from childhood vaccines in the United States in 2001, although it is still present in some multi-dose flu vaccines. This change began in 1999 as a precautionary measure to minimize overall exposure to mercury during early development, not because thimerosal was proven unsafe. Multiple well-conducted scientific studies have found no evidence that thimerosal in vaccines causes harm, except for minor reactions like redness or swelling at the injection site. Major health organizations, including the FDA, CDC, and WHO, continue to support the safety of vaccines containing thimerosal.
Despite this, concerns have been raised about the potential link between thimerosal-containing vaccines and autism. However, extensive research has failed to establish a causal relationship between the two. A 2010 study by the CDC found that prenatal and infant exposure to thimerosal-containing vaccines did not increase the risk for autism spectrum disorder (ASD). Additionally, even after thimerosal was removed from childhood vaccines, autism rates continued to rise, contradicting the hypothesis that thimerosal causes autism.
It is important to note that dietary exposure to mercury through fish consumption can also be harmful. While fish provide valuable nutrients like omega-3s, they also contain methylmercury, a known neurotoxin and cardiac toxin. Eating half a can of tuna, for example, exposes an individual to the same amount of mercury as one hundred thimerosal-containing vaccines. Therefore, while concerns about mercury exposure from vaccines are understandable, it is important to consider the relative risks and benefits of both vaccine and fish consumption.
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Methylmercury exposure guidelines
Methylmercury is a hazardous substance that is of particular concern with regard to environmental health. It is a known neurotoxin and cardiac toxin. Methylmercury is formed when inorganic mercury circulating in the general environment is dissolved into freshwater and seawater. It then bioaccumulates in fish and shellfish. For example, large predatory fish are more likely to have high levels of mercury as a result of eating many smaller fish.
Methylmercury exposure occurs mainly through inhalation of elemental mercury vapours during industrial processes and through the consumption of contaminated fish and shellfish. Fish consumption provides nutrients, but all fish also provide methylmercury. The more fish we eat, the more omega-3s we get, but the more mercury we get, too.
There is a particular threat to the development of the child in utero and early in life. Infants in the womb can be exposed to methylmercury when their mothers eat fish and shellfish that contain methylmercury. This exposure can adversely affect unborn infants' growing brains and nervous systems. These systems may be more vulnerable to methylmercury than the brains and nervous systems of adults. Children exposed to methylmercury while in the womb can experience impacts to their cognitive thinking, memory, attention, language, fine motor skills, and visual spatial skills.
In addition, high exposure to inorganic mercury may result in damage to the gastrointestinal tract, the nervous system, and the kidneys. Both inorganic and organic mercury are absorbed through the gastrointestinal tract and affect other systems through this route. Symptoms of high exposure to inorganic mercury include muscle weakness.
The Joint FAO/WHO Expert Committee on Food Additives has proposed to prepare additional fish and shellfish intake recommendations for consumers based on the quantified evaluation of the hazardousness of methylmercury contained in fish and shellfish. The starting point of methylmercury exposure management is inorganic mercury in the general environment, but food intake through methylation is the main exposure source.
In the United States, federal guidelines keep as much methylmercury as possible out of the environment and food, but over a lifetime, everyone is exposed to some methylmercury. If you are concerned about your exposure to methylmercury, you should consult your physician.
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Mercury poisoning in humans
Mercury is a naturally occurring element found in the earth's crust, air, soil, and water. It is toxic to humans and can cause mercury poisoning, which can lead to severe health issues and even death. Methylmercury and ethylmercury are the two types of mercury that people are exposed to. Methylmercury is commonly found in certain kinds of fish and shellfish, while ethylmercury is derived from Thimerosal, a mercury-based preservative previously used in vaccines.
Methylmercury is a powerful neurotoxin that can accumulate in the bodies of people who consume fish and shellfish with high levels of this toxin in their tissues. High exposure to methylmercury can cause adverse health effects, including muscle weakness, nausea, nervousness, numbness, and neurological issues. Infants in the womb can also be exposed to methylmercury when their mothers consume fish and shellfish containing high levels of this toxin.
Ethylmercury, on the other hand, is derived from Thimerosal, which was once used as a preservative in vaccines to prevent bacterial and fungal contamination. While ethylmercury stays in the body for a shorter time than methylmercury, concerns have been raised about its potential impact on child development and the increase in autism prevalence. However, studies have not found a causal link between Thimerosal-containing vaccines and autism.
To prevent mercury poisoning, it is essential to limit exposure to mercury by making dietary and environmental changes. Pregnant women, in particular, should be cautious about consuming fish with high mercury levels. Additionally, safe alternatives to mercury-containing medical devices, such as thermometers and blood pressure machines, should be used to reduce the risk of exposure.
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Sources of mercury emissions
Mercury emissions are a global issue that transcend national and continental boundaries. Once released into the atmosphere, mercury can travel thousands of miles before settling back on earth through rainfall or dry gaseous form. Mercury is a potent neurotoxin that poses a significant threat to human health, especially the development of children in utero and early life.
There are two types of mercury emissions: natural sources and anthropogenic (human-caused) sources. Natural sources of mercury emissions include volcanic eruptions, emissions from the ocean, geothermal springs, geologic deposits, and weathering of rocks. While mercury occurs naturally in the earth's crust, human activities have significantly increased its presence in the environment, leading to widespread global mercury pollution.
Anthropogenic sources of mercury emissions are estimated at approximately 2220 metric tons per year. The largest contributor to these emissions is artisanal and small-scale gold mining (ASGM), accounting for 37.7% of the total. This is followed by stationary combustion of coal (21%), non-ferrous metals production (15%), and cement production (11%). The use of mercury in gold mining and the burning of coal for power and heat are particularly hazardous to human health.
Mercury released into the air eventually settles into bodies of water, such as lakes and streams, or onto land. Microorganisms in water bodies can transform inorganic mercury into methylmercury, which then bioaccumulates in fish and shellfish. Large predatory fish that consume smaller fish tend to have higher levels of mercury. As a result, the consumption of contaminated fish and shellfish is a primary source of human exposure to mercury.
In addition to mining and coal combustion, other human-related sources of mercury emissions include waste incineration, industrial processes, and the use of mercury in products and raw materials. Mercury released from broken containers or damaged products can evaporate, leading to inhalation risks in poorly ventilated indoor spaces. Mercury is also used in small amounts as a preservative in some vaccines, but this form, known as ethylmercury, does not pose a health risk.
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Frequently asked questions
Yes, the levels of mercury in fish are higher than in vaccines. A single serving of canned tuna contains as much mercury as 100 thimerosal-containing vaccines.
Thimerosal is a mercury-containing preservative that has been used in vaccines since the 1930s to prevent the growth of harmful microbes. It is also known as an organomercurial and is approximately 50% mercury by weight.
Thimerosal is added to vaccines to prevent the growth of bacteria and fungi, which can cause illness or even death. It has a long record of safe and effective use, and there is no data or evidence of any harm caused by the level of exposure from vaccines.
No, there is no link between thimerosal-containing vaccines and autism. This has been supported by several epidemiologic studies, including a review by the Immunization Safety Review Committee of the Institute of Medicine in 2004.
Yes, it is safe to receive vaccines with thimerosal. Studies have shown that exposure to thimerosal does not cause signs and symptoms consistent with mercury toxicity. The half-life of ethylmercury derived from thimerosal is much shorter than that of methylmercury found in fish, and it does not accumulate in the blood.
