Pro-oxidant activity of vitamin C in drinking water ... - Ã bo Akademi

Review of the literatureFormation of free radicals during physiological conditions, for example OH • radicals, willset off a chain reaction between newly formed radicals and non-radicals. This chainreaction will not stop until two free radicals meet and react with each other.3. Drinking waterWater is necessary for all life and human cells consist of 80 percent water. Therefore,humans must drink water frequently to maintain their fluid requirement. Humans need todrink approximately 2 litres (8 glasses) of water every day to replenish the water that is lostfrom the body through urine, skin and the respiratory tract. However, only 0.3% of theEarth’s water supply is safe to drink. Only freshwater originating from rivers, lakes andunderground sources can be used for human consumption. In addition, freshwater frommany of these sources is unsuitable for human consumption, because of contaminants. Thecontaminants must be removed or adjusted to accepted threshold values.3.1. Drinking water impurities and Maximum Contaminant Level (MCL)Drinking water contains impurities from both natural and man-made sources. Gases,minerals, bacteria, metals and chemicals are examples of contaminants that have to beadjusted to accepted threshold values. This restriction of contaminants in drinking water isnecessary to protect public health and ensure a uniform standard for water qualitynationwide. Private water wells, on the other hand, are not regulated by drinking waterstandards. The owner of the well is responsible for testing, and if needed, treating the waterhimself, all to avoid health risks. The Maximum Contaminant Level (MCL) is the highestamount of a specific contaminant that is allowed in the drinking water. The MCL isnormally expressed in milligrams per litre (mg/l). 154, 155Contaminants fall into two categories, primary and secondary contaminants. The primarystandards serve as threshold value for the contaminant to avoid health problems.Radioactive elements, microbial pathogens and organic/inorganic chemicals are examplesof three classes of toxic pollutants that are classified as primary contaminants. Water plantsare obliged to follow MCL for primary contaminants.Secondary contaminants are regarded as contaminants that affect the aesthetic quality ofdrinking water, such as taste, colour, odour, pH and appearance. Chloride, sulphate,copper, iron, manganese, zinc etc. are all examples of secondary contaminants (Table 3).21