The bibliography for this article is at the very end of page two of this article.
In recent years a tremendous amount of research on mercury pollution has been conducted throughout the world. Scientists have shared their findings at several international conferences devoted to the subject. Research has focused on determining how much of the mercury in the environment can be attributed to industrial activities, and the consequential effects on human health.
According to case studies compiled by Canadian Government scientists, there is general consensus among internationally recognized scientists that annual mercury emissions have increased two to five fold within the last century, with anthropogenic emissions now surpassing natural emissions in the industrialized world. In areas of the Alaskan Arctic, where there is no industry, there is little difference between mercury concentration in the pre-industrial and present day layers in core samples of lake sediment. As long as pollutants remain undisturbed within the sediment, they tend to stay put and stack one layer upon another with the upper most layer being the youngest or most recently deposited layer. Through carbon dating and chemical analysis it is possible to determine how mercury level has varied over time.
Mercury from power plants, waste incinerators, smelting plants and natural sources is released into the air transported by air currents in a direction determined by prevailing winds. Particles of pollution such as mercury will eventually fall (most often in rain drops) and be deposited in soil or water. Airborne particles can travel hundreds and even thousands of miles. Dust from the eruption of Mount Saint Helens and radioactive particles from Chernobyl completely encircled the earth.
In an attempt to limit industrial contaminants, Pennsylvania and New Jersey have gone away from using coal fired power plants and implemented strict Maximum Achievable Control Technologies (MACT) regulations that require mercury-emitting plants to meet the highest level of emissions control that is presently achievable. As a result, both New Jersey and Pennsylvania have lowered mercury emissions from plants in those states. However, emissions from coal-fired plants in Illinois, Indiana, Ohio and West Virginia have increased significantly in recent years as a result of increased output of energy. In Detroit, Michigan mercury found in rain has been recorded at levels 65 times the level considered to be safe for humans. Pollution from the mid-western states is carried to Pennsylvania by prevailing winds, nullifying all of the improvements that Pennsylvania has made in its own power plants.
Recent studies estimate the annual global mercury pool (atmospheric) as high as 5000 tons while the total mercury content in the ocean is estimated at 10,800 tons. Research indicates that during the pre-industrial age, the global mercury pool contained 1,600 tons of mercury, while the ocean (mixed layers) had a total of 3,600 tons of mercury. This would suggest that the post-industrial level of mercury in global mercury pool is more than three time that of the pre- industrial level of mercury in the global mercury pool, and that the annual anthropogenic contribution to the global mercury pool is about 3,400 tons. Some studies have estimated the anthropogenic contribution of mercury into the atmosphere to be somewhat less than 3,400 tons/year, and the post-industrial level of mercury released into the global pool now closer to twice that of the annual amount that was released into the global mercury pool in during pre-industrial age. On the other hand, some researchers report finding suggesting that the post-industrial global mercury pool is greater than three times that of the pre-industrial global pool. Discounting the variation in exact numbers, few scientists will dispute the evidence that current industrial mercury pollution exceeds the mercury emitted from natural sources.
Mercury is a naturally occurring element. It is found predominately as cinnabar ore (HgS). Cinnabar is found in trace amounts in minerals and rocks, and in fossil fuels such as coal. As long as mercury remains undisturbed and imbedded in the rocks and fossils of the earth, it causes little problem for humans. If it is freed and enters the soil as a result of erosion, volcanoes or human activities, it can eventually find its way into the global pool of mercury through evaporation, vaporization, or more significantly through the burning of fossil fuel or combustion of municipal and medical waste. It is important to remember that industry does not manufacture mercury, but rather disrupts deposits of naturally occurring mercury thereby increasing human exposure to mercury.
Mercury causes most harm to the largest number of humans by entering the food chain. The mercury that is deposited in the oceans, lakes and rivers is converted into methyl mercury through microbial activities. Methyl mercury is fat-soluble. It enters the food chain and bio-accumulates in little fish that are eaten by larger fish that are eaten by humans. Mercury is not released from the body, but rather accumulates in the fatty tissue.
Children and fetuses are at greatest risk of suffering from the effects of mercury. The problem is that it is often hard to quantify the prenatal mercury exposure of a child who exhibits symptoms of mercury toxicity many months after the child is born.
As of 2002 43 states had warned residents to limit the number of freshwater fish that they consume. In one study more than 50% of the fresh water fish tested throughout the United States surpassed the limits of mercury considered safe enough to be consumed by children or women twice a week. It has been estimated that 1.2 million women of childbearing age in the United States regularly exceed the Reference Dose (an estimate of the daily exposure to a substance for humans that is assumed to be without appreciable risk) for mercury as established by the EPA. About 9-10% of these women are likely to be pregnant at any given year. That means that 100,000 pregnant women a year have exceeded the dose of mercury that is considered to be safe for fetuses. Federal agencies estimate that 600,000 U.S. children born each year have learning deficits from mercury exposure. Methylmercury is a particularly toxic form of mercury because it is fat soluble and therefore stored in the body. Current research indicates that there is no safe level for methyl mercury in the blood within the ranges of mercury measured in the studies. The lowest level studied was 1ppbillion. Presently 50% of the women in the United States of childbearing age have at least 1ppbillion methylmercury in their blood.
What do these numbers mean? Fetuses and children exposed to low levels of mercury are likely to suffer from neurological disorders, including lowered IQ and decreased functioning in attention, language, memory, fine motor skills and visual-spatial abilities. Higher levels of mercury have been found to cause mental retardation. In addition to neurological disorders, mercury has also been linked to lung and kidney damage and even death. EPA has determined that children born to women with a blood concentration of mercury above 5.8 parts per billion are at risk of these non-neurological adverse health effects. About 8% of women of childbearing age have blood levels of mercury that exceed 5.8parts per billion.
Children are not the only individuals at risk from mercury exposure. Recent published studies have demonstrated a relationship between methylmercury exposure and an increased risk of heart attacks and coronary disease in adult men. Mercury also has been shown to have an adverse effect on fertility and blood pressure regulation. Nearly all studies to date agree that the human effects of mercury exposure are irreversible.
If you need to cite this page, you can copy this text:
Roberta C. Barbalace. Mercury Pollution. EnvironmentalChemistry.com. April 12, 2004. Accessed on-line: 11/28/2023