Occurrence of humic substances in waters

Humic matters are present in almost all natural waters. They are extracted from soil and peat. The solubility of the constituents of the soil humus depends on the type of soil, period of contact with water, pH of the water and its composition, and depending on such factors, the humic materials are present as either true or colloid solutions. In waters from peat moors the concentration of humic matters is usually tens of mg 1 . In some stationary waters as much as 500 mg 1 can be found. In waters from peat moors a low pH is typical (it can be lower than 4), high oxidation potential and the presence of iron, manganese and ammonia nitrogen (anaerobic processes). Iron and other metals are present in an organic complex form and they are difficult to remove [52, 53]. 

Humic matters cause a deterioration of the sensory properties of water, giving rise to a yellow to brown colour of the water and an unpleasant odour. The intensity of colour increases with increasing pH. 

The presence of humic matters in drinking, service and industrial waters is undesirable on account of these properties. Their colour, for example, can impair the quality of some products, e.g. of textil and paper industries. 

They are of small detrimental significance from the viewpoint of hygiene. The toxicity limit for warm-blooded animals is about 100 mg 1 in drinking water. 

With regard to chlorination, the lowest possible content of humic matters in waters intended for drinking is desirable for water treatment. Many papers currently deal with the study of the structure of humic matters. For example, the authors of the study [54] have characterized the humins of sediments on the basis of their alkaline hydrolysis whose products were separated via gas chromatography or GC-MS technique. Another study 

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