mineral impuritiesReading time:
Some of these impurities will affect the organoleptic qualities of water, its appearance or behaviour through the mains distribution network. However, these impurities will not have any marked effect on consumer health whereas other impurities are acknowledged to be deleterious.
impurities that do not have a noticeable effect on health
Alongside colour, this is the first parameter that is immediately perceived by the consumer. Excess turbidity will cause the water to be rejected by the consumer. Turbidity also has to be eliminated on other grounds:
- to ensure water is properly disinfected;
- to eliminate pollution adsorbed by suspended solids (heavy metals, etc.);
- to prevent the formation of deposits in the mains distribution network.
Colour can be the result of certain mineral impurities (iron, etc.) but more often than not, it is caused by some dissolved organic matter (humic and fulvic acids). Colour has to be eliminated in order to make the water pleasant to drink. Eliminating colour involves eliminating some unwanted organic matter such as the precursors of haloform or trihalomethane ( THM ) compounds.
Calcium hardness and alkalinity contribute to water’s carbonate balance in conjunction with pH and dissolved carbonic acid (see neutralisation – remineralisation). The aim is to distribute a balanced water in order to prevent network corrosion or scaling. Too many sulphates will affect the flavour of the water and may, when Mg is present, give it laxative properties. Too many chlorides will also have an adverse effect on water taste and render it corrosive.
Iron and manganese can cause coloration and deposits in the system. These deposits can cause corrosion. Additionally, they affect the water’s organoleptic properties as do other metals: copper, aluminium and zinc.
H2S is indicative of anaerobic conditions and of an oxidation-reduction potential which is too low; it causes unpleasant odours and may initiate corrosion. It must be eliminated.
Ammonium does not have any noticeable effect on consumer health but when present in surface water, it does indicate the presence of pollution. In deep water, ammonium may also be caused by the reducing conditions prevailing in the medium. Ammonium must be eliminated from water intended for consumption because it interferes with chlorination (formation of chloramines) and is a nutrient that can promote the proliferation of some bacteria in mains distribution networks.
impurities that affect health
Discharged in IWW, cadmium, chromium, copper, nickel, lead and mercury especially must be removed from water (please refer to current standards WHO, European Union, USEPA, etc. standards).
These heavy metals are generally adsorbed by suspended solids present in raw water and eliminating these suspended solids is usually enough to remove the heavy metals. Heavy metals may also be dissolved in water and require a suitable pH so that they can be eliminated as hydroxides after coagulation and flocculation.
In some cases, these metals can be chelated either by natural organic matter (e.g. mercury) or by pollutants. The treatment used must then be capable of destroying or eliminating this complex.
Nitrate levels are generally found to be on the increase in raw water and, therefore, they must be eliminated when they rise above 50 mg NO3·L–1, because they cause methemoglobinemia (or cyanosis) in infants and even cancer.
Although asbestos has been recognised as carcinogenic when inhaled, the carcinogenic effect of asbestos fibres contained in drinking water is not proven. However, it is advisable that they be eliminated as much as possible because these fibres could be entrained in water vapour (boiling water, showers etc.). Good turbidity reduction levels also ensure that asbestos fibres are adequately removed.
The use of soda or sodium chloride for water softening through does lead to an increased level of sodium in water. A high levels of sodium to favour high blood pressure.
Too much fluorine will cause tooth enamel staining and bone fluorosis. Fluorine levels have to be reduced using a specific treatment when they exceed approximately 1 mg·L–1.
Suspected of affecting blood composition, the WHO (1994) and the European Parliament (1998) have limited its presence in drinking water to 5 µg· L–1.
Naturally present in some water, arsenic causes skin cancers and possibly other forms of cancer and even circulation problems; permissible arsenic levels in water intended for consumption are constantly being reduced (provisionally: 10 µg· L–1).
Usually natural in origin, this metal could cause cardio-vascular problems and its presence in drinking water has now been regulated (magnitude: 0.7 mg·L–1).
In most cases, boron is injected in limited amounts viaUWW and IWW. In principle, boron contained in freshwater only reaches excessively high levels under the natural influences prevailing in some regions. However, the widespread use of borates in detergents is causing this situation to change. The effects of boron are still under much discussion. Nevertheless, as a precautionary measure, the European directive (1998) has restricted boron to 1 mg·L–1, l whereas the WHO (1998) recommends 0.5 mg·L–1.
Very widespread but toxic to Man, affecting the liver, nails and hair, the levels of selenium in drinking water have been limited to 10 µg· L–1 (WHO, EU, …).
means used to study impacts on health
It is difficult to assess the effect of a particular product direct on Man. Accidents caused by the acute toxicity of some products that are lethal (= poisoning) can be controlled. Epidemiological studies can also be undertaken with the aim of correlating the ingestion of certain products with mortality and with the risk of cancer or of other illnesses.
However, given the number of factors that can exist in each individual’s surroundings and also population mobility in modern life, epidemiological studies are long, costly and frequently produce results that are often debatable. Therefore, preference should be given to experimental methods.
In order to improve our knowledge of the effects of various pollutants on consumer health, studies and experiments are not carried out direct on Man but on some animals whose sensitivity has been demonstrated to be close to that of Man. The results obtained are then extrapolated to Man using models that reproduce, as best as possible, the transition from animals to Man.
The effects of a pollutant observed on different animals can be defined in various ways:
- acute toxicity : it is rapidly fatal in animals. LD 50 expresses the lethal dose that will kill 50% of individuals within a given timescale (e.g. 24 hours); a similar concept is used to define a lethal concentration (LC 50);
- chronic toxicity : an individual’s metabolism is capable of withstanding, without any risk, a maximum dose ingested daily throughout his life: that is the ADI beyond which the risk of death increases;
- cytotoxicity : studies can be carried out on cell cultures instead of constituted living organisms; the product under investigation causes a certain percentage of the cells involved to die. We can then define cytotoxicity;
- mutagenicity : the ingestion of a product likely to cause mutations (structural changes in some genes) that might be hereditary, affecting all or part of cells in living beings. The danger of mutagenicity exists irrespective of the dose ingested. The risk is low when the dose ingested is low and rises as the ingested dose increases;
- carcinogenic effect :the individual’s exposure to the product under investigation or its ingestion by the individual, can result in the appearance of a malignant tumour. As in the case of the mutagenic effect, a carcinogenic effect will exist regardless of the dose ingested.