The paper deals with the results of the phytoplankton investigations carried out in the 7 localities along the Yugoslav section of the Tisza river in the period of 13 Februar - 3 March 2000, after accidental pollution with the cyanide and heavy metals. Although certain decrease in the density of the phytoplankton and variation in the qualitative and quantitative composition were recorded, there are no significant differences in comparison with the data before accident. The short-term and possible long-term consequences were recognized, having in mind ability of algae to accumulate pollutants into their cells, and that algae are the first link on food chains. Since the content of pollutants increases with every next member in the chain, it is easy to assume cumulative effect of the all previous members.

In this paper a part of results of the wastewater quality control from the Thermal Power Plant "Kostolac", water from the rivers Danube and Mlava, and groudwaters near by (Serbia, Yugoslavia), is considered. In order to protect environment from the effects of hurtful substances make during working process of Thermal Power Plant "Kostolac" is especially does using solid fuel (coal), the Institute of Public Health of Serbia following an approved program checks upon the quality of groundwaters, water the rivers Danube and Mlava including the wastewater from the Thermal Power Plant "Kostolac", four times a year. The results of our research point out to the hurtful effects of the wastewater from Thermal Power Plant "Kostolac" on the groundwater.

To evaluate precision and reliability of recently introduced Metal Pollution Index as a method for metal pollution monitoring of surface waters, a series of toxicity tests with Daphnia magna have been undertaken. The sampling sites (the River Danube wetlands and Hydrosystem DTD (Danube - Tisza - Danube), Serbia, Yugoslavia) for this study have been chosen according to previously recorded high MPI values. Chemical characterization and WET (whole effluent toxicity) testing of selected waste waters at the chosen sampling sites, and the recipient water toxicity testing upstream and downstream the discharger evaluated the validity of MPI, and, on the other hand, discriminated the effects of background pollution. The results of acute and chronic toxicity tests of water and sediment corresponded well with MPI values, which leads to a conclusion that MPI could be regarded as a reliable and precise method for metal pollution monitoring of surface waters.

Low flows are a good measure of the waste water recipient self-purification capability. The regional statistical analysis is an objective way of assessment of the required low flows. This paper presents the principles and key phases of the regional statistical analysis. The advantages of this method are a reduction of the outliers influence and the assessment of low flows on ungauged streams and stream profiles. The method is illustrated with the results obtained by the required low flows regional statistical analysis in Serbia (Yugoslavia) with 59 hydrological gauge stations in the scope, which data has the same length of 39 years, from the year 1956 to 1994.

As a result of this study the overload by pollutants and low quality of canal water in the zone downstream of Vrbas and Srbobran towns (Serbia, Yugoslavia) has been recorded. Regarding to started work on demudification of canal bottom in the industrial zone of Vrbas town, in the course of 2000 the additional investigations of mud profile downstrean of wastewater discharge into the canal have been done. In the investigated mud samples the extremely high number of organotrophic bacteria was found (up to 1.7 x 10**10 cfu/ml), but also high number of conditionally pathogenic bacteria (opportunistic bacteria) was recorded. Also, the high number of fecal (thermo-tolerant) coliform bacteria (Escherichia coli and Klebsiella - Enterobacter - Citrobacter group of bacteria), as well as the presence of colifags was found. Such findings indicate possible bad consequences to the health of humans contacting this mud, as well as to the ground water quality, indirectly, via drainage water.

Drainage of industrial and communal effluents, directly into the water flow, as many hydrotechnical activities, significantly influence the schedule and balance of the processes that take place into water. In this paper, there are represented the results of systematic control of the water quality of the Danube river and DTD (Danube-Tisza-Danube) channel on the parts Vrbas-Bezdan and Becej-Bogojevo, at the control station network of the Republic Weather Bureau (the Republic of Serbia), for the period of 1991-1996. The results show that the most adverse influence of anthropogenic factor is on the part of the flow of the DTD (Danube-Tisza-Danube) channel from Vrbas to the flow into Tisza river.

Spectrophotometric method for determination of inorganic phosphate liberated in hydrolysis of ATP catalyzed by ATPase was modified in order to obtain faster procedure, which could also be used in none laboratory conditions. The modification has some advantages compared to the most used Pennial method: a) the reagents are stable for several months; b) the 45 min procedure of phosphomolibdate extraction by isobutanole-benzene is ommited, and the method is not dangerous for the analyst; c) color develops after 20 min. The method was tested on the determination of inorganic phosphate in the presence of cadmium nitrate as inhibitor of ATPase activity. The results were compared to the results obtained by Pennial method. The results obtained have shown some good agreements.

In our earlier work, we have shown that enzymes from rat brain synaptosomal membranes, Na(+)/K(+)-ATPase and Mg(2+)-ATPase, are promising biological components of a biosensor for lead detection. In this work, we represent our results of investigation with the same enzymes as biological components for the biosensor in presence of Hg(2+) ions in water. It was established that IC50 for Na(+)/K(+)-ATPase and Mg(2+)-ATPase is 6.9 and 5.5 x 10E-6 M, and the percentages of inhibition are 96% and 77% respectively. We concluded that these enzymes could be the base for developing biosensors for the presence of Hg(2+) ion in water. Since these enzymes maintain a stable activity for a longer period of time, they could be appropriate as components of biosensors for monitoring water quality.

MPI - Metal Pollution Index is being proposed with an aim improving the freshwater pollution control, monitoring and classification based on fish metal body burden. This is a simple mathematical model which enables presentation of Cd, Pb, Cu, Zn and Al fish liver concentration as a single value. After thorough studies of bioaccumulation, biomagnification and tissue distribution patterns, liver of Carassius auratus gibelio has been chosen as sentinel organ. Normal distribution and biological variation assessment is being achieved by using normalizers - reference values (liver concentrations of selected elements in fish from reference sites Vruje and Moharac micro water reservoirs, Serbia (Yugoslavia)). Selected representative sites have been evaluated according to new classification of freshwater ecosystem based on MPI values.