Naturally occurring hazards:
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Other elements in water
Other natural elements in water include calcium (Ca) and magnesium (Mg). Where the natural level is high (>200mg/ litre), the water is ‘hard’ and does not lather easily with soap. High levels are believed to be generally beneficial to health: for example, a large study1 in the United Kingdom (UK) found that cardiovascular (heart-related) mortality was 10-15% higher in ‘soft’ water areas with low levels of Ca and Mg. The protective effect on the cardiovascular system may be due to the greater solubility of harmful trace elements, such as lead, in soft water.
Copper is an essential trace element for human physiology: copper pipes may increase natural levels in water in water distribution systems. Thus levels high enough to cause illness are rarely due to natural contamination alone. Liver disease has been reported in India, for example, due to copper pipes leading from a well. Lead pipes were used for centuries in water distribution systems, until it was realised that, like copper, lead could dissolve in the water. While new distribution systems have used other materials, lead pipes still cause problems in water.
Aluminium is also present in all waters to some degree. It only represents a health hazard if there is a mishap in the water treatment process.
Sodium salts are widely found in the environment. Some waters contain a naturally high level, including water reclaimed from the sea. This is an increasingly important issue for communities drawing their water supply near coasts, and for arid regions. Water with high sodium levels may raise blood pressure slightly, and this is of particular concern in people with heart, liver, kidney and other diseases where salt intake has to be restricted.
Uranium is a naturally occurring radioactive element, found in most rocks and soils in small amounts (2-4 parts per million), as well as in the oceans. Large reserves of uranium have been identified in Australia, Brazil, Canada, Kazakhstan, Namibia, South Africa and USA. Uranium decays to form radium and the gas radon. Uranium ore has been mined since ancient times, for example to colour glass, but its main modern use is in the nuclear power industry. It enters water supplies via leaching from natural sources, from industrial and nuclear use, from combustion of coal and other fuels, and from phosphate fertilisers used in agriculture. It is likely that food is the main source of uranium intake in most areas. While the naturally occurring isotopes of uranium are not highly radioactive, it has toxic effects on humans and animals, particularly affecting the kidney. Adequate short and long-term studies on the chemical toxicity of uranium are not available and most epidemiological studies have focused on the more radioactive decay products of radium and radon. The WHO recommends a provisional guideline value in drinking water of 2-µg l-1.
Radon occurs naturally in ground water, particularly where there are granite rocks. It is a radioactive gas, which is released from water when it comes to the surface. In rocky areas it can present in houses at high concentrations, increasing the risk of lung cancer.
Naturally occurring hazards:
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