ALLERGY: WATER POLLUTION

Apr
20
2009

Posted by: admin in Categories: Allergies.
Using Tags: Allergies

The level of pollutants in drinking water has been steadily rising in recent years. Pollutants run off the land into rivers or seep down through the soil into groundwater. Various purification measures are taken before the water reaches our taps, but these are never 100 per cent effective.

Agriculture makes the major contribution to water pollution. Nitrates, used as fertilizers, run off from the fields, and in several parts of Britain, tap-water regularly exceeds the EEC limit on nitrates. Although nitrates have received a lot of publicity, they are not as worrying as some of the other water pollutants. There are no clear signs that the nitrate levels found in drinking water are

damaging to health, except in newborn babies. As far as chemical-sensitive patients are concerned, nitrates are unlikely to be a problem.

Small amounts of pesticides also get into the water supply from farm use. In addition, there have been accidents in which large amounts of highly toxic pesticides such as dieldrin (now banned for agricultural use) have been emptied into drains or soakaways close to boreholes, causing major pollution of the groundwater below. Most water authorities do not systematically monitor drinking water for pesticides.

Oil from spillages may find its way into drinking water, but usually this is only in minute amounts. Organic solvents (see p164) also turn up in water supplies – a study by Imperial College, London, found the solvent trichloroethylene in 36 per cent of the 168 groundwater samples they tested. The level was higher than the limit set by the World Health Organization in 10 percent of the samples, and in one it was seven times the WHO limit. Other solvents are also found in groundwaters, usually as a result of factories discharging their waste solvents into drains or ditches. Very few of the water authorities systematically check their supplies for solvents or other industrial pollutants, and serious incidents of pollution may easily go undetected. Some of the chemicals used for purification also leave a residue in the water, but this is unlikely to be harmful as long as the correct amounts are being used.

Chlorine is added to water to kill bacteria and viruses that might otherwise cause disease. Unfortunately, chlorine readily reacts with certain organic molecules to produce chlorinated hydrocarbons. (The organic molecules may themselves be pollutants, or they may be produced by large amounts of waterweed, growing and then rotting down in reservoirs.) Some of these chlorinated hydrocarbons are carcinogenic, and they have occasionally turned up in drinking water.