The quality of drinking water is a concern for people worldwide. Although in many areas of the world contaminated drinking water often carries pathogens such as those that cause cholera, in developed countries the most common concern is contamination of water by heavy metal compounds. Perhaps the most notorious and dangerous among such contaminants is mercury, the only metal that is present in its natural form as a liquid, allowing it to mix freely with water supplies once exposed.
Identification
In most developed nations environmental agencies closely monitor the quality of drinking water. In the United States the Safe Water Drinking Act charged the Environmental Protection Agency with identifying safe levels of mercury in drinking water. The threshold for mercury in water potentially causing health problems was set at two parts per billion, meaning that for every kilogram of drinking water there is only one microgram of mercury present.
Potential
Mercury is a highly toxic element that has the potential to cause a wide range of symptoms and medical conditions. Though accumulating enough mercury to cause systemic toxicity through drinking contaminated water is a relatively rare cause of mercury poising, conditions that could result if contaminated water is consumed include anxiety, tremors, insomnia, memory problems and irritation. All of these symptoms are caused by mercury's ability to damage brain and nervous tissue. Additional conditions that may result from exposure to toxic levels of mercury are kidney damage, lung damage and disruption of the gastrointestinal system.
Sources
Dangerous levels of mercury in drinking water can arise from multiple sources. Mercury is widely used in industrial processes and can be found in many common household items such as fluorescent light bulbs, batteries and medical equipment. If improperly disposed of, such items may contaminate the local water supply. Mercury is also released into the atmosphere by the burning of fossil fuels and in natural processes such as forest fires and volcanic eruptions. Mercury in the atmosphere may eventually make its way into a body of water or into the soil, where it may become exposed to groundwater.
Types
Regardless of its source, once mercury is absorbed into water it is turned into the chemical compound methylmercury by bacteria. However, mercury that has been used in industrial processes has often been converted into the chemical compound mercury oxide. Mercury that leeches into the water supply from sources such as batteries will be in this form. Compared to methylmercury, mercury oxide is not considered to be very toxic. This is because methylmercury more easily reaches the brain and central nervous system once present in the human body, though mercury oxide may still cause kidney damage at sufficient levels.
Considerations
Though a common concern is the safety of drinking water, especially as regards the level of highly toxic compounds such as mercury, a much larger potential for poisoning is present in contaminated foodstuffs. Methylmercury in large bodies of water is readily absorbed by fish and other marine animals. With increasing body size and age a marine animal usually contains increased levels of mercury as well. Mercury levels in fish and other wildlife consumed by humans has not reached a level where it is considered hazardous by environmental agencies across the board, but it may be a good idea for the health-conscious consumer to investigate the amounts of mercury found in foods they commonly consume in order to be aware of what they are putting into their body.
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