Over the last decades, European rivers have mostly shared the same fate. Until the mid 1980s many of them were in rather bad shape. Nobody would have thought about using the waters for recreation. However, continuous efforts over the last three decades have achieved success and today's water quality has changed to the better. This obvious change in water quality, which was proved by investigations done on the basis of the European Directive 2000/60/EC framework for Community action in the field of water policy, made people consider using the rivers for recreation or irrigation. In the present study a Central European River was investigated from hygienic perspectives (faecal indicators), and its toxicological status was examined - both of which are parameters which are not included in the Directive 2000/60/EC. The pivotal question was whether these parameters provide essential and additional information about the river's status and its quality. In general, the monthly values for all sampling points from the toxicological tests correlated with the determined physical and chemical statuses according to the national water management plan. Once, however, the toxicological values did increase significantly. This detection of a single toxicological burst within a year of observation underlines the applicability of the tests as screening methods for the detection of toxic substances. Moreover, our microbiological investigations show high numbers of faecal indicators and Salmonellae. These results are not consistent with the apparently good quality of the river. Therefore faecal indicators, which are directly related to the discharge of waste water, should be an integral part of the procedure of water classification.
In order to determine the impact of sunlight on the reduction rate of indicator bacteria, bathing waters of different turbidity were artificially contaminated with indicator bacteria and exposed to sunlight. The reduction rates determined for the indicator bacteria showed a significant correlation with radiation intensity and, thus, also the time of day as well as the turbidity of the water. Under conditions of strong radiation intensity and low water turbidity (< 5 FTU), indicator bacteria were eliminated within 1-2 h of contamination with an initial concentration of 10(5) CFU/mL. Moreover, differences between different indicator bacteria were found. Enterococcus faecalis proved to be significantly more resistant to sunlight than the other indicator bacteria tested (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus). The results of the present study, namely the complete elimination of indicator bacteria within a few hours, showed that sunlight, given an appropriate intensity and good water transparency, was the most important factor in the reduction of hygienically-relevant microorganisms in surface waters and, thus, also in small-scale bathing ponds.
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