Assessment of an ecological quality of surface water is necessary for effective protection, abatement and successive revitalisation of river ecosystems. This quality is primarily given by biological impact of surface water pollution. Substances contained in pollution are frequently toxic to aquatic organisms. Risk of chronic impact of surface water pollution is very often underestimated due to hidden long time action of pollutants. Proper estimation of the risk is not possible from results of chemical analyses and data of substances' toxicity. Chemical analyses are not able to detect all substances presented in water including the products of reactions between them. In addition, a simultaneous presence of substances can modify their final effect on aquatic organisms. Therefore, a complex method of assessment of toxic risk of surface water pollution based on ecotoxicological approach was developed. The toxic risk of surface water pollution is determined from results of evaluation of toxic risk of organic part and inorganic part of surface water pollution. Resultant degree of toxic risk of total pollution is given by the highest degree detected in any part of the water pollution. Presented method, which is routinely used for monitoring in the Czech part of the Odra river basin, was fully standardised and published in the form of the Czech branch technical norm of water management (TNV) in the year 2000.

T G Masaryk Water Research Institute Prague Ostrava Branch Office Macharova 5 702 00 Ostrava Czech Republic

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A method for screening for the risk of chronic effects of surface water pollution