In the years 2005-2010 concentrations of organic substances in the water flow Čaradice brook were evaluated. For their determination we used an indirect method based on the oxidation of organic matter by potassium dichromate, which is known as chemical oxygen demand by potassium dichromate (CODcr), which are oxidized almost all organic substances contained in the water. The watercourse springs in the mountains of Pohronský Inovec in the southern foot of Drienka hill and it is the right tributary of the Hron River, into which mouth near the village Kozárovce. Its length is 11.1 km. Samples of the water in a longitudinal profile of the watercourse were carried out from six sampling sites, on a regular basis, in the second decade of the month. The places of taking samples were localized to include all real sources causing the pollution of watercourse. Seasonal regularity of dynamics of concentrations of organic substances during the whole monitored period is not reflected. The average concentration of CODcr in the monitored period ranged from 56.55 (2005) to 66.48 (2006) mg O2 dm-3. For the whole period represented value of 64.11 mg O2 dm-3. Depending on the time of sampling the lowest average concentration for the whole monitored period in winter were recorded, with a minimum value in February (57.08 mg O2 dm-3). The highest average concentrations in summer were found, with maximum value in July (72.64 mg O2 dm-3). Increase of values of chemical oxygen demand in the summer period is probably related to increasing water temperature, accumulation of organic matter and its intense microbial decomposition. Effect of sampling sites was as significant as the influence of the month. The highest average value for the whole monitored period was in sampling sites situated near Čaradice village (61.33 mg O2 mg-3) and Kozárovce village (61.71 mg O2 mg-3), which can be considered as major source of organic pollution of water by sewage waste water. The second most significant increase near the water reservoir was found. Can be assumed that the increase in the values of CODcr in that sampling site is probably related to the release of organic matter from sediment in the water reservoir, into which they got from the basin of the water flow. In the regulation of the Government of the Slovak republic No. 269/2010 Coll. the recommended value for CODcr is 35 mg O2 dm-3. Calculated values of 90-th percentile (P90) of this indicator in all sampling locations were higher than the recommended value of government regulations.

organic substances, Slovak Republic, water flow, water quality.

Presentation: oral