Opinions and observations from environmental experts, activists, and luminaries
Environmental Toxins: A Focus on Mercury
What is a toxin? For one thing, it is a frightening term that invokes a sense of environmental concern and urgency.
Toxins are poisonous substances that threaten our environment, our livelihood and our very own existence. They can subtly take on many different shapes and forms, and even in minute quantities they endanger our survival. No amount of a toxin is truly ‘insignificant,’ for the process of bioaccumulation and subsequently, biomagnification exacerbates the effect of these substances on all trophic levels of the ecosystem.
We have introduced many types of toxins into the environment through industrial emissions, fertilizers, medications, oil spills, etc. In our efforts to improve our society and quality of life, we are have created anthropogenic agents of destruction. Now, we have reached a point where we cannot avoid these deleterious substances. They are everywhere.
Recent studies have shown that American girls are hitting puberty earlier (USA Today). An increasing number of scientists have linked this finding to hormone-disrupting chemicals in the environment. In this post, we will discuss a contaminant of concern to aquatic species and human beings: mercury.
Mercury Mercury is a naturally occurring element and is found in the Earth’s crust, oceans and in the atmosphere. Most of the mercury that is released into the atmosphere is derived from natural processes such as surface volcanic eruptions, deep-sea vents, underwater volcanoes, hot springs, evaporation from bodies of water and the soil, and erosion. Mercury is also released into the environment due to anthropogenic activities and industrial processes, such as the burning of municipal and hazardous waste, pulp and paper milling, the burning of coal and during the production of industrial chemicals (EPA, 2009). Airborne mercury has a long residence time; it is able to remain in the atmosphere for several years.
The Different Forms of Mercury and the Biogeochemical Cycle Mercury cycles through the environment in different forms, being subjected to complex physical and chemical changes. The three most common forms of mercury include metallic or elemental mercury, inorganic mercury compounds, and organic mercury compounds. Elemental or metallic mercury is the silvery white metal found as liquid at room temperature. It is used to produce chlorine gas and caustic soda and is most commonly used in thermometers, florescent light bulbs and in certain electrical switches. Mercury combines with other elements, such as sulfur, oxygen and chlorine to form inorganic mercury compounds, which appear as white or red powders or crystals. These compounds are used in certain antiseptics, disinfectants and medications. Inorganic mercury salts tend to be highly reactive and soluble, and can easily transform into airborne particles or gases that descend into the ground or into water. These particles are usually rapidly absorbed into aquifer solids, water-permeable materials such as soil or sediment, where they may dwell for hundreds of years. Particles that do not absorb into the soil vaporize and rise into the atmosphere. Inorganic mercury can readily combine with carbon in the environment to form organic mercury compounds, of which methylmercury is the most common. Natural transformations and environmental pathways of mercury are complex and there are a range of biogeochemical interactions that impact mercury in its different physical states and chemical forms.
When mercury circulates into lakes, rivers, marshes, and coastal ecosystems, microorganisms in the soil and water, primarily sulfate-reducing bacteria, convert the mercury into a more toxic form, methylmercury. Methylmercury has serious adverse health effects, posing threats to the immune system, altering genetic and enzyme systems, damaging the nervous system, including coordination and the senses of touch, taste, and sight. Methylmercury is especially harmful to developing embryos, which are five to ten times more sensitive than adults (USGS, 2000). The path of methylmercury intake is usually ingestion. Methylmercury is absorbed more readily and excreted more slowly than mercury in other forms.
Unlike elemental mercury, which quickly passes through and is eliminated by an organism, methylmercury accumulates in animal tissues. Because of biomagnification, methylmercury becomes more concentrated and more toxic as it moves up trophic levels in the food chain. By the time methyl-mercury has reached a top-level predator, such as a largemouth bass, it may have increased by as much as a million times from bacteria to fishes. The bioaccumulation effect is generally compounded the longer an organism lives, so that larger predatory game fish that tend to have a longer lifespan will likely have the highest mercury levels.
From a toxicological perspective, mercury is one of the most intriguing environmental contaminants that impact wildlife. In certain parts of the globe, concentrations of mercury in fish and wildlife are high enough to be a substantial risk to wildlife. This is a complex issue in causation field studies, however, because confounding factors possibly contributing to the studied biological effect are difficult to control. Scientists have discovered toxic effects in the field at concentrations of mercury that are toxic in the lab and thus, it is becoming clear that methylmercury is linked to toxicity and decline in wildlife populations. Methylmercury is particularly harmful to aquatic species. It is held tightly to fish protein when absorbed through the gills or when already contaminated food sources are eaten. According to the United States Geological Survey, methylmercury in carnivorous fish, such as freshwater bass, walleye and pike, and marine shark and swordfish, bioaccumulates up to a million times greater than levels in the water in which they live. Because many humans are omnivorous and at the top of the trophic level, many are exposed to methylmercury when consuming contaminated fish (USGS, 2000).
We need to learn more about toxins such as mercury in order to alter our diets and live healthier lifestyles. In upcoming posts, we will look closely at other anthropogenic contaminants.
Toxins are poisonous substances that threaten our environment, our livelihood and our very own existence. They can subtly take on many different shapes and forms, and even in minute quantities they endanger our survival. No amount of a toxin is truly ‘insignificant,’ for the process of bioaccumulation and subsequently, biomagnification exacerbates the effect of these substances on all trophic levels of the ecosystem.
We have introduced many types of toxins into the environment through industrial emissions, fertilizers, medications, oil spills, etc. In our efforts to improve our society and quality of life, we are have created anthropogenic agents of destruction. Now, we have reached a point where we cannot avoid these deleterious substances. They are everywhere.
Recent studies have shown that American girls are hitting puberty earlier (USA Today). An increasing number of scientists have linked this finding to hormone-disrupting chemicals in the environment. In this post, we will discuss a contaminant of concern to aquatic species and human beings: mercury.
Mercury Mercury is a naturally occurring element and is found in the Earth’s crust, oceans and in the atmosphere. Most of the mercury that is released into the atmosphere is derived from natural processes such as surface volcanic eruptions, deep-sea vents, underwater volcanoes, hot springs, evaporation from bodies of water and the soil, and erosion. Mercury is also released into the environment due to anthropogenic activities and industrial processes, such as the burning of municipal and hazardous waste, pulp and paper milling, the burning of coal and during the production of industrial chemicals (EPA, 2009). Airborne mercury has a long residence time; it is able to remain in the atmosphere for several years.
The Different Forms of Mercury and the Biogeochemical Cycle Mercury cycles through the environment in different forms, being subjected to complex physical and chemical changes. The three most common forms of mercury include metallic or elemental mercury, inorganic mercury compounds, and organic mercury compounds. Elemental or metallic mercury is the silvery white metal found as liquid at room temperature. It is used to produce chlorine gas and caustic soda and is most commonly used in thermometers, florescent light bulbs and in certain electrical switches. Mercury combines with other elements, such as sulfur, oxygen and chlorine to form inorganic mercury compounds, which appear as white or red powders or crystals. These compounds are used in certain antiseptics, disinfectants and medications. Inorganic mercury salts tend to be highly reactive and soluble, and can easily transform into airborne particles or gases that descend into the ground or into water. These particles are usually rapidly absorbed into aquifer solids, water-permeable materials such as soil or sediment, where they may dwell for hundreds of years. Particles that do not absorb into the soil vaporize and rise into the atmosphere. Inorganic mercury can readily combine with carbon in the environment to form organic mercury compounds, of which methylmercury is the most common. Natural transformations and environmental pathways of mercury are complex and there are a range of biogeochemical interactions that impact mercury in its different physical states and chemical forms.
When mercury circulates into lakes, rivers, marshes, and coastal ecosystems, microorganisms in the soil and water, primarily sulfate-reducing bacteria, convert the mercury into a more toxic form, methylmercury. Methylmercury has serious adverse health effects, posing threats to the immune system, altering genetic and enzyme systems, damaging the nervous system, including coordination and the senses of touch, taste, and sight. Methylmercury is especially harmful to developing embryos, which are five to ten times more sensitive than adults (USGS, 2000). The path of methylmercury intake is usually ingestion. Methylmercury is absorbed more readily and excreted more slowly than mercury in other forms.
Unlike elemental mercury, which quickly passes through and is eliminated by an organism, methylmercury accumulates in animal tissues. Because of biomagnification, methylmercury becomes more concentrated and more toxic as it moves up trophic levels in the food chain. By the time methyl-mercury has reached a top-level predator, such as a largemouth bass, it may have increased by as much as a million times from bacteria to fishes. The bioaccumulation effect is generally compounded the longer an organism lives, so that larger predatory game fish that tend to have a longer lifespan will likely have the highest mercury levels.
From a toxicological perspective, mercury is one of the most intriguing environmental contaminants that impact wildlife. In certain parts of the globe, concentrations of mercury in fish and wildlife are high enough to be a substantial risk to wildlife. This is a complex issue in causation field studies, however, because confounding factors possibly contributing to the studied biological effect are difficult to control. Scientists have discovered toxic effects in the field at concentrations of mercury that are toxic in the lab and thus, it is becoming clear that methylmercury is linked to toxicity and decline in wildlife populations. Methylmercury is particularly harmful to aquatic species. It is held tightly to fish protein when absorbed through the gills or when already contaminated food sources are eaten. According to the United States Geological Survey, methylmercury in carnivorous fish, such as freshwater bass, walleye and pike, and marine shark and swordfish, bioaccumulates up to a million times greater than levels in the water in which they live. Because many humans are omnivorous and at the top of the trophic level, many are exposed to methylmercury when consuming contaminated fish (USGS, 2000).
We need to learn more about toxins such as mercury in order to alter our diets and live healthier lifestyles. In upcoming posts, we will look closely at other anthropogenic contaminants.
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Kamini Doobay is a recent graduate from Barnard College of Columbia University. She is currently doing clinical research in the field of rheumatology at Hospital for Special Surgery, NY. Along with her interest in medicine and public health, she is passionate about
...Kamini Doobay is a recent graduate from Barnard College of Columbia University. She is currently doing clinical research in the field of rheumatology at Hospital for Special Surgery, NY. Along with her interest in medicine and public health, she is passionate about environmental conservation and its relationship with religion and spirituality.
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