2024-10-24 17:09:00
What are mercury and methylmercury?
Mercury is a metal present naturally in trace amounts in the environment. Essentially released from the earth’s crust into the air, it then disperses in soil, water and sediments. It also spreads in nature due to emissions generated by human activities: mining, metallurgy, processing of paper pulp, combustion of waste and fossil fuels in particular. Very volatile in its elemental form, mercury can transform into methylmercury following chemical reactions when it enters the aquatic compartment. This form is toxic, easily absorbed and accumulated by the body. Present at low concentrations in water or sediments, methylmercury can concentrate very strongly in aquatic organisms. Its content tends to rise along the food chain, each time one species eats another.
What are the health effects of methylmercury?
Methylmercury is toxic to the human central nervous system, particularly during in utero development and early childhood. This substance can thus cause mild behavioral disorders or developmental delays in children exposed in utero or after birth, even in the absence of signs of toxicity in the mother. This is why specific recommendations intended for pregnant or breastfeeding women, as well as children under 3 years old, have been defined.
What is the main source of exposure to methylmercury?
Fish consumption is the main source of human dietary exposure to methylmercury. The level of contamination of fish varies depending on the species. It tends to be higher in predatory and large predatory fish, which are higher on the food chain.
What are the consumption recommendations?
The risk linked to exposure to methylmercury does not generally constitute a major public health problem in mainland France. However, very regular consumers, both adults and children, of wild predatory fish (more than one serving per week) may have exposure levels exceeding the tolerable weekly intake determined by the European Food Safety Authority (EFSA). This dose corresponds to the quantity ingested per week beyond which health risks cannot be ruled out. In view of the nutritional benefits linked to the consumption of fish (essential fatty acids, proteins, vitamins, minerals and trace elements), the Agency recommends:
eat fish twice a week by combining an oily fish with a high content of omega-3 fatty acids (salmon, sardines, mackerel, herring) and another fish (hake, hake, cod, sole, etc.); to diversify the species of fish consumed and the places of supply (wild, farmed, fishing grounds, etc.).
For pregnant and breastfeeding women and young children (under 3 years), the Agency recommends taking special precautions:
limit the consumption of wild predatory fish, likely to be highly contaminated: tuna, bonito, skate, sea bream, sea bass, monkfish, emperor, halibut grenadier, sabrefish, pike, etc. avoid consuming the most contaminated “large predatory” fish: sharks, lampreys, swordfish, marlins (close to swordfish) and sikis (a variety of shark).
In an expertise carried out in 2019, the Agency issued specific recommendations for fish caught in New Caledonia. Indeed, certain deep-sea (pelagic) fish caught off the coast of this territory have high concentrations of methylmercury.
Beyond ANSES’s assessments and its recommendations, the situation of actual exposure of the population and different subgroups of this population to methylmercury is monitored by Public Health France as part of its biomonitoring mission. The study ESTEBAN (Health study on the environment, biomonitoring, physical activity and nutrition) thus reported in 2021 the results of biomonitoring of the French population for different metals, including methylmercury. These results make it possible both to assess the evolution over time and to situate the levels of impregnation of the population, which reflect exposure to these metals through all routes, including diet.
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Interview with Dr. Alice Thompson, Environmental Toxicologist
Interviewer: Thank you for joining us today, Dr. Thompson. To kick things off, could you explain what mercury and methylmercury are and how they differ?
Dr. Thompson: Absolutely, and thank you for having me. Mercury is a naturally occurring metal, found in trace amounts in the environment. It’s released from the earth’s crust into the atmosphere and can enter our ecosystems through various human activities, such as mining and burning fossil fuels. Methylmercury, on the other hand, is a more toxic form that is created when mercury undergoes chemical transformations, particularly in water. It accumulates in aquatic organisms and becomes more concentrated as it moves up the food chain.
Interviewer: That sounds concerning. What are the health effects of methylmercury, especially for vulnerable populations?
Dr. Thompson: Methylmercury is particularly harmful to the central nervous system. It can have serious impacts on the development of fetuses and young children, potentially leading to behavioral disorders and developmental delays. This is why pregnant and breastfeeding women, as well as young children under three, are given specific dietary recommendations regarding methylmercury exposure.
Interviewer: Speaking of exposure, what is the main source of methylmercury for people?
Dr. Thompson: The primary source of human exposure to methylmercury is through the consumption of fish. The level of contamination varies by species, with larger, predatory fish—such as shark or swordfish—having higher concentrations due to their position in the food chain.
Interviewer: Given these risks, what consumption recommendations do you suggest for fish-eaters?
Dr. Thompson: The European Food Safety Authority has set guidelines, advising that individuals eat fish twice a week. One serving should include oily fish high in omega-3 fatty acids, like salmon or sardines, paired with another type of fish, which is lower in mercury. While methylmercury exposure isn’t typically a major public health issue in mainland France, those who consume wild predatory fish more than once a week should be cautious of their intake.
Interviewer: Thank you, Dr. Thompson, for sharing your insights on this important topic. What’s one takeaway you’d like our audience to remember?
Dr. Thompson: I’d say the key takeaway is balance. Fish is a valuable source of nutrition, so it’s important to include it in your diet while being mindful of the species you choose. Awareness and moderation are essential for safe consumption.
Interviewer: Speaking of exposure, what is the main source of methylmercury for people?
Dr. Thompson: The primary source of human exposure to methylmercury is through the consumption of fish. The level of contamination varies by species; larger and predatory fish tend to have higher levels because they are further up the food chain and accumulate methylmercury over time. Common culprits include tuna, swordfish, and shark, which are known to be particularly high in methylmercury concentrations.
Interviewer: That’s important to know. What recommendations would you give regarding fish consumption, especially for those who regularly include fish in their diets?
Dr. Thompson: For most of the population, eating fish twice a week can be beneficial, as fish is a source of essential nutrients and omega-3 fatty acids. However, I advise diversifying the types of fish consumed and limiting the intake of wild predatory fish, especially for vulnerable groups like pregnant women, nursing mothers, and young children. They should avoid the most contaminated species to reduce their exposure to methylmercury.
Interviewer: Are there specific findings or studies that monitor exposure levels in populations, particularly in places like France?
Dr. Thompson: Yes, there have been significant efforts to monitor methylmercury exposure in population groups. For example, Public Health France coordinated the ESTEBAN study, which tracks environmental exposure to various metals, including methylmercury. This type of monitoring helps assess trends and determine whether current dietary guidelines are effectively protecting public health.
Interviewer: Thank you for sharing this insight, Dr. Thompson. It’s essential for our audience to understand both the risks of methylmercury and how to make informed dietary choices regarding fish consumption.
Dr. Thompson: Absolutely. Awareness and education are key to minimizing health risks while still enjoying the benefits of a balanced diet that includes fish. Thank you for having me.