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Chemical and Biological Species in Drinking Waters
The formula of water molecule is written as H2O, but only distilled water has this structure. Rain water, snow and ice are quite similar to distilled water. Water presents in nature contains, even if in traces, minerals very important for our health: salt and oligoelements dissolved during its way through the soil or it’s flowing in rocky streams. Calcium is one of the most common elements on the earth. It is essential in our body for teeth and bones formation, blood coagulation, right functioning of our nervous system. Calcium ions are contained in almost all spring, drinking water. Health effects caused by hard water, very rich in calcium and magnesium, are unknown. An excess in calcium can alter the water taste or cause scaling problems in pipes and household appliances. If we use a device for the reduction of the content of calcium and magnesium ions dissolved in water, it is important to see that the calcium content never goes under 60 mg/l.
Magnesium together with sodium and calcium is among the cations most commonly found in drinking water. In humans magnesium is important for many metabolic functions and for muscular and nervous activity. Its daily recommended intake is 150-500 mg. Sodium is an element very diffused on earth and in the biosphere, even if in nature it is almost never in its pure form, but mainly in form of salt (NaCl). Our body contains an average of 100 g of sodium which is an important metabolic regulator for nervous and muscular stimulations. The daily sodium chlorine intake is 20 mg. Due to our diet very rich in salt it is recommended to drink water with a sodic content lower than 20 mg/l, particularly for hypertensive people and children. The salt consumption in industrialized countries is considered much higher than the recommended levels (about 3.9 g/day on average). Drinking 2 litres of water containing 20 mg/l of sodium one reaches 40 mg that is about the 5% of the total intake. To reduce the daily sodium intake it would be more logical to change our nutrition: i.e. to eat only integral sea salt, more equilibrate and rich in mineral salts at home, and to avoid precooked food, always rich in refined salt.
Chromium is an important oligoelement for our organism, on condition that certain concentration is not exceeded and the element is not found in toxic or carcinogenic combinations that are always due to industrial pollution. At present there is no recommended daily intake limit for this element. Copper is an essential element for our health, but it is toxic at high concentration. A daily intake of 1.2 mg is recommended. Copper pollution in water can originate form copper pipes corrosion by soft, acidic water. Food rich in iron is very important, particularly for children and women in fertile age. The recommended daily intake is 10 mg. Iron is usually contained in low amount in drinking water. The WHO recommend a maximum of 0.3 mg/l the EEC of 0.2 mg/l. possible increasing (lower than 200 mg/l) are not to be considered harmful, even if they make the water not nice to drink and give an unpleasant reddish colour.
Chlorine is an important constituent of organic liquid and a daily intake of 7-15 g of NaCl is recommended. Food usually covers the recommended daily intake of 2-3 mg. An excessive concentration in water is not necessarily harmful, but originates the same problems as iron (unpleasant taste and colour). Though selenium is considered a toxic element when taken is high dosage, it is an important anti-oxidant as it is useful to attack free radicals for preventing aging. Its recommended daily intake by EEC is 40 picog. A possible lack of selenium can increase the risk of tumour and cardiovascular diseases.
In the opinion of many scientists fluorine is useful for the good health of bones and teeth, sometimes it is even essential, in others opinion it is unnecessary when you are adult. Fluorine is a halogen and the most electronegative of all the elements, so it reacts easily with most of the elements. In 1945 the addition of fluorine in drinking water began to be experimented in New York State, followed by Australia and some areas in UK, with the declared purpose of preventing dental caries in population. Water fluorination is prohibited in Belgium, Denmark, the Netherlands and France; in Spain and Germany local authorities handle every decision and in Italy there is no specific law on this matter.
Fluorine’s useful values for our body are very close to toxic values, so a dispense not aimed and personalized can cause high risk of overdosing and chronicle poisoning, with consequent skeleton deformation, spots on tooth enamel, osteosclerosis, neurological disorders, damages on the thyroids and even generation of tumours. According to some research, 10% of fluoride doesn’t deposit in teeth and bones, but harms kidneys. Fluorine has negative effects on the central nervous system, determining behaviour alterations, cognitive deficit, influencing on the foetus development even in concentration not harmful for the mother. The calcium fluoride presents in nature is very different from the sodium-silica-fluoride (Na2SiF6) added in drinking water, an industrial waste that is toxic and difficult to digest. People who are against fluorination of drinking water argue that it is a violence that does not count individual choice freedom, not to mention the individual tolerance limit.
Many toxic minerals are contained in water supplies, usually at high levels due to which treatment and potabilisation plants work to reduce these minerals to safe levels. Minerals can enter surface or ground water through natural sources, industrial sewage, and leakage from urban or agricultural areas, water pipes walls or even from domestic sources. The list of organic substances that one can find in industrial applications is exhaustive. Several of the inorganic species and their organic partners have been identified to be offending and disturbing species due to their complexation and chelation behaviour.
Phosphate in water originates from detergents and fertilisation and a level higher than 0.1 mg/l indicates pollution. Flora and fauna, very sensitive to phosphate presence, are the main victims. Sulphates are sulphuric acid salts combined with metallic ions. Water can naturally contain small quantities of sulphates, but they are mostly transferred in water bodies from the atmosphere and in the atmosphere form road traffic, industries and energy production. Sulphur oxidised in the air can come back on the soil as acid rain, causing serious environmental problems. Nitrates are the main source of nitrogen for plants and an essential constituent for nucleic acids and amino acids. A nitrates’ water content of about 10 mg/l is considered normal and natural. Its higher concentration is due to human operations (mauring and air pollution due to transportation. The problems resulting from excessive nitrate presence are due to the toxicity of nitrate for human body as nitrates are transformed in nitrites or in carcinogenic nitrosamines.
Though aluminium is very abundant on the earth, it is not important for human nutrition rather aluminium can have toxic effects even in small quantities. These effects occur in nervous system, but health effects originating from aluminium intake through water are still on debate. Aluminium concentration is usually lower than 200 mg/l in drinking water. If one drinks 1.5 litre of water per day, his/her daily intake from water is lower than 300 mg/day, a negligible amount if compared with the amount taken by nutrition (10-20 mg/day). There is no evidence that the aluminium assimilated through water is more soluble and more easily digestible, than the aluminium contained in food. Due to all these uncertainties at present there are no rules about its allowed concentration limits in drinking water, though the WHO recommends a concentration lower than 20 mg/l.
While arsenic can be toxic even in low amounts, the arsenic contained in food (amounts ranging from 0.01 to 1.5 mg/kg of dry weight) has a different influence: it carries out some positive metabolic function for our body. Its toxicity is strongly linked on the concentration. Lead is toxic even in small amounts for micro-organisms, interfering with haemoglobin formation and with the functionality of central nervous system. Lead is particularly harmful for children, who can suffer long term neurological and behavioural disorders. Major lead sources are paint, vehicle emissions, food and water. The European Directive about drinking water for human consumption 98/93/EC states that the maximum allowed lead concentration in drinking water should decrease from the actual 50 mg/l to 10 mg/l within 25 December 2013. The problem in Italy is that many pipes contain lead and acidic soft water, with low phosphate content. If this water lingers for long time in the pipes it can adsorb lead. Some precautions can be taken to lower lead content in drinking water:
We should flush the water before drinking it, since lingering water in pipes tends to accumulate more lead; to avoid water dissipation it is recommended to collect the flushed water in bottles and tanks for some subsequent uses. We must refrain from using hot tap water for cooking, since hot waters dissolve lead more easily than cold water. We should try to periodically remove clinker and slag from the pipes and use suitable ways for lead removal.
Cadmium, a highly toxic heavy metal, is considered carcinogen. Its harmful action is similar to the effect of lead and it can be released in drinking water by zinced iron pipes as Zinc always contains a small amount of cadmium. Mercury can or can not be toxic, depending on its chemical bonds. The WHO recommends that a daily intake of 0.3 mg/day for a 60 kg person may be considered under safe limits. Mercury can be released in ground water or in surface water by industrial waste water discharge in rivers and estuaries, by leakage from toxic landfill, by mercury emissions from volcanoes, seismic underground activity, incineration and fossil fuels combustion. The mercury released in the atmosphere is very light, so it can reach long distances from the source and fall again on the soil through rain, entering water bodies. However mercury is not commonly found as pollutant in our drinking water.
Asbestos can reach drinking water through natural sources, pipes built in a compound made of concrete and asbestos and from atmosphere. Hard water seems to bring to a lower asbestos loss compared to water poor in salts, which is much more corrosive. At present chlorination is the most used treatment to remove water bacteria which could cause health problems. The Italian law allows 30 mg/l of chlorine, while the guidelines of the European Directive indicate 1 mg/l and specify that the concentration should be as low as possible. According to international research the consumption of water containing compounds formed after the reaction between chlorine and microorganisms (trihalomethanes) can contribute to the increase of huro-genital tumours.
If you smell the chlorine odour typical of swimming pools when you open the tap, it is recommended to pour the water in a large tank and to leave it open or semi-open for about half an hour. Chlorine is in fact very volatile and tends to still on the water surface. To accelerate chlorine dispersion we can pour the water from a tank to another repetitively or mix very quickly.
Numerous organic compounds directly originate from plant or animal matter. For instance plastics are chemical organic compounds made of petrol, which originates from plants and animals.
Nowadays there are more than 100.000 chemical organic compounds, which include synthetic fertilizers, pesticides, herbicides, paints, dyes, flavours and pharmaceutical substances. Most of these compounds are toxic and many have been found in water reservoirs. VOC (Volatile Organic Compounds) are very dangerous, because they are adsorbed by the skin in contact with the water carrying them. If chlorine used for the water disinfection is in contact with these chemical organic compounds, the carcinogens trihalomethanes can form.
Phyto-pharmaceutical products are the most accused substances for ground water pollution. Here it will not be proper to spend too much time in the description of their use and abuse, but everybody should know cases of closed wells. Even if ground water pollution stopped immediately, an impossible thing to happen, it would take a long to soil and water to recover. Not very much is known about the harms of compounds of phyto-pharmaceuctics, but metabolites can be much more toxic than water.
Surfactants are the substances used in detergents to lower the surface tension of the water by allowing it to wet the clothes better. We all use substances containing surfactants, which are responsible for the pollution of the water we drink. They are also in cosmetics, anti freezing products, glues and colouring species. We can contribute to the reduction of this pollution source by using only the minimum necessary quantity or choosing biodegradable surfactants.
Microorganisms include bacteria, virus and parasite. Bacteria are carefully monitored in public water supplies, since they can be responsible for many health problems and their presence can be easily detected. Bacteria are easily killed by adding chlorine. Viruses are very abundant in water supplies as well. They are much more difficult to detect. Most viruses are killed by chlorination, and most of the viruses carried by water are too week to be harmful for humans. The third group of microorganisms commonly found in water are parasite. They are very resistant and can be found in tap water even if a treatment system is present. When drinking water has to be carried along long distances, the problem of a possible pollution occurs. This pollution can happen through the contact of water with porous surfaces or synthetic materials that are an ideal media for microorganisms. The risk occurs particularly in showers or Jacuzzis. The ideal environment for the bacteria of legionella phneumofila is included between 37 and 45 C.
About the Author
Dr. Badruddin khan teaches Chemistry in the University of Kashmir, Srinagar, India.
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