10.1. Measuring of water speeds and water expenses

In order to measure water expenses, we took the “speed-area” method, the most popular in the river hydro-metrics. While applying this method, we calculate an area of a stream cross section according to the depths measured, and water speeds (at certain points of an active cross section) are measured by hydro-metric rotators.

10.2. Taking of water samples for hydro-chemical tests

The samples of surface waters from the Dnipro basin were taken according to the standard methods generally accepted in hydro-chemical studies and environmental activity and related to ISO 5667-2-1991, "Water Quality. Manual on Taking Samples" and "Directions on taking samples for testing discharges and surface waters" approved by the Ministry of Natural Resources and Environmental Protection of Belarus Republic 16.02.1994.

The samples were taken in the middle of water flow at a depth of 0,5-0,6 m. The samples were of simple kind, that is, the necessary water volume was taken only once and the sample characterizes water contents at certain place and certain moment of time. For each sample and its duplicate, there were special records on taking samples. The sample and its duplicate were divided into six parts (vessels), each of which were separately marked and used for testing specific parameters. Examples of the records on surface water samples and the sample passports (test results) are presented in Appendix 1.2. The samples were not preserved or filtered because they were delivered to hydro-laboratories on the day of taking samples (they were filtered just before hydro-chemical testing, which was held on the day of taking these samples).

10.3. Taking samples of bottom sediments

The samples of bottom sediments were taken by a tube device for taking samples with a cross section of 54 см 2 according to ISO 5667-12-1995, "Water Quality. Manual on Taking Samples of Bottom Sediments". Before taking samples, we opened the device by rotating a rod and raising a flange to the upper position. Then we laid it on the bottom and pushed into the ground, afterwards by rotating the rod (in opposite direction) and lowering the flange, we closed the device tightly. After the device was taken out of water, the sample was removed by raising the flange - lack of tightness could end in falling out of sample. We took a mean sample and its duplicate from several devices, the height of sample column was ~10 cm. Samples were placed into plastic bags and marked. Every sample or its duplicate was accompanied by records on taking sample written just at the place, where they were taken (Appendix 3). Afterwards, samples were delivered to the central laboratory (in Minsk) for tests on metals, phenols and pesticides.

10.4. Taking samples for hydro-biological tests

Samples of phyto-plankton from a surface layer (0.3-0.5 m under the surface) were put directly into glass bottles of 0.5 l and fixed by the Utermel solution with adding formalin later. We obtained concentrated phyto-plankton in laboratory conditions by applying the sedimentation method.

Samples of zoo-plankton were got after filtration of 50 l of water, taken from a surface layer (0.2-0.5 m), through the qualitative plankton Apstein net (sieve № 70). The samples were fixed by 4% formalin solution.

Quantitative samples of zoo-bentos from dense river soils were taken by a tube device with a cross section of 54 см2. At every post, we took (depending on density of organisms) from three to five columns of ground, the height of which was 20-25 cm. Qualitative samples of zoo-bentos were taken by using hydro-biological scraper. Samples of macro-zoo-bentos were washed in a net of gas No.23. Afterwards the samples, washed out and containing sand, were sorted out. The routine was carried out while organisms were alive, then they were fixed by 4% formalin solution.

10.5. Taking samples for radio-nucleid testing

Taking samples of water and bottom sediments for radio-nucleid testing are practically the same as taking samples of bottom sediments for tests on heavy metals, phenols and pesticides (see the Parts 10.2 and 10.3).

10.6. Taking samples of fish tissues and organs

Fish was caught by fishing-nets at two posts: Dnipro river (boarder with Russia) and Sozh river (down stream Homel town). In both cases, we took samples of Bream liver, muscle tissues and fat. The samples were mean of several fishes.

10.7. Methods of analyzing hydro-chemical parameters

In order to determine hydro-chemical parameters, we used the methods of measurements described in "Manual on chemical analysis of surface waters of dry land", edited by Semenov, Hydrometeoizdat, Leningrad, 1977, "List of measurement methods, approved for implementation by the environmental control laboratories of institutions of Belarus Republic", vv.1-2, 1995-96, "Addition to the List of measurement…" vv.1-2, 1997. The methods, we used in each specific case, are presented in the Table 10.1.

The parameters, like pH, dissolved oxygen, temperature, transparence) were measured at the place of taking samples.

The rest of parameters were measured in laboratory conditions whereas water samples were delivered within 24 hours to laboratories of the Ministry of Natural Resources and Environmental Protection and Hydromet of Belarus Republic. Examples of test records (post passports) are presented in the Appendix.

Tests on metals (iron, manganese, lead, aluminium, cadmium, arsenic, copper, chrome, zinc) were conducted in accordance with "Methods of measuring contents of metals by the atomically-absorb spectroscopy method, МВИ.МН-1137-99"; tests on mercury were conducted in accordance with "Methods of measuring mercury by the atomically-absorb spectroscopy of cold steams method, МВИ.МН-1138-99".

A sample for testing metals, delivered to laboratory, was divided into two parts. After special preparation, the first part was used for measuring contents of metals and mercury of general form. The second part, after filtration and preparation, was used for measuring contents of metals and mercury of soluble form. Suspended forms were measured according to the difference between contents of metals of general and dissolved forms.

Results of hydro-chemical tests of samples taken from surface waters of rivers of the Dnipro basin are presented in post passports (Appendices 3, 4) and in the joint Table 11.5, where we show the mean test data of samples and their duplicates.

During the expedition, we conducted comparative analysis (by different laboratories) of water samples taken from Sozh river in Homel town. Results of this analysis is presented in the Table 10.2. The samples were also delivered to Ukrainian laboratories for studies.

Table 10.1 Methods of measuring hydro-chemical parameters

10.8. Methods of testing bottom sediments

10.8.1. In order to conduct tests on metals contained in bottom sediments, we used Perken Elmer spectrometers: Simaa 6000 with a hydrid framing and Optima 3000 DV, optic-emissive spectrometer with inductively-connected plasma.

Simaa 6000, atomically-absorbing spectrometer, is equipped with electric-thermal atomizer, having a horizontal heater, and Seemann corrector of non-selective absorption. The heater includes the Lvov platform. In the heater, temperatures vary from the room temperature to 2600 degrees. The working spectral range is 190-860 nm. Registration limits of the device (3-sigma criterion) are 0.004 - 10 mkg/l (ppb) and depend on the nature of elements measured.

The working spectral range of Optima 3000 DV, optic-emissive spectrometer, includes a short-wave ultra-violet part (167-375nm) and a visible part of light (375-782nm). The device is equipped with a system of automatic control and data processing. Registration limits of the device (3-sigma criterion) are 0.03 - 30 mkg/l (ppb) and depend on the nature of elements measured.

Tests on metals (iron, manganese, lead, aluminium, cadmium, arsenic, copper, chrome, zinc), contained in bottom sediments, were carried out according to the methods of atomically-absorbing spectro-metrics and taking into account “Methods of measuring contents of metals by the atomically-absorbing spectroscopy method, МВИ.МН-1137-99”; tests on mercury were carried out taking into account “Methods of measuring mercury by the atomically-absorbing spectroscopy of cold steams method, МВИ.МН-1138-99" and the optic-emission spectroscopy method in accordance with “Methods of measuring metals in hard matrices by the optic-emissive spectrometric methods with inductively-connected plasma”, approved by the State Committee on Standards of Belarus Republic for applying in environmental activity. These methods are analogous to 7060А; 7131А; 7191; 7201; 7211; 7421; 7740; 7041; 7911; 7461; 7481; 7951; 7470; 7471А; 6010A of the US Environmental Protection Agency (US EPA).

The atomically-absorbing spectroscopy method for detection of metallic elements is based on measuring of resonance absorption of the light energy by atoms of the studied element. The method includes electric-thermal atomization of sample in a flow of inert gas and registration of the light of resonance wave length (of corresponding element), absorbed by the studied sample. The absorption degree corresponds to the content of the measured element in the studied sample; calculation is conducted according to the five-point calibrating curve.

A hydrid framing, inserted in the AAS (atomically-absorbing spectrometer) makes it possible to detect volatile elements of metals (Hg, As) by the method of cold steam. The method is based on chemical reduction of these elements, when they are closed in reactionary vessels, to atomic condition and then on blowing them out to an absorbing cell, where the light of corresponding wave is being absorbed and this absorption is registered.

The optic-emissive spectroscopy method for measuring metals is based on measuring emission of the studied element atoms in plasma by an optic spectrometer. A sample is dispersed and then transported into inductively-connected argon plasma, where the balanced dynamic processes of atomization and ionization take place; the processes are accompanied by the light energy emission, which is registered by a light-sensitive device (photo-diode matrix).

Intensity of the light energy emission (from atoms) depends on their content in a sample, quantitative calculations are conducted according to the five-point calibrating curve.

10.8.2. We measured phenols in bottom sediments with the help of HP 6890, gas chromatograph, with masses-selective detector and software developed by Hewlett-Packard, in accordance with “Methods of measuring semi-volatile organic substances by the chromatic-mass-spectrometry method with capillary column”, approved by the State Committee on Standards of Belarus Republic and being analogous to 8270 method of US EPA.

The chromic-mass-spectrometry method for detection of organic substances is based on division of studied components in a micro-capillary column of gas chromatograph and then they are detected by mass-spectrometer. Substances are being identified by comparing their mass-spectra to the spectra of standard substances. Quantitative calculations are carried out basing on the signal value of the main molecular ion of substance, measured in accordance with the inner standard, and using the five-point calibrating curve. A system of control and data processing is fully automatized. This method is accompanied by a mass-spectrum library for over 200 thousands of organic substances (including pesticides), which makes it possible to identify substances correctly (while conducting quantitative analysis) and also carry out qualitative analysis of sample components, which are not included in calibration.

While carrying out the tests, we used the HP-5MS, capillary quartz column (30m х0.5mm x 0.25mmc). The temperature program, we applied, was the following: an initial thermostat temperature is 40 degrees; a pause for 4 min; a rising temperature period: 10 degrees per minute up to 270 degrees; a pause for 10 min; an injector temperature is 250-300 degrees; a mass-detector temperature. We used helium (its flow speed was 30см /min) as a gas-carrier.

The measuring was carried out after some preparation of samples that included extraction of substances being measured with the help of organic solvent, then this extract had to be concentrated to1 ml.

10.8.3. We detected pesticides in bottom sediments by the HP 6890, gas chromatograph, equipped with a detector of electronic seizure and software, developed by Hewlett Packard, according to the 8081 method of US EPA. While carrying out the tests, we used the DB1701, capillary column, its length is 30 m, its inner diameter is 0.53 mm, its film thickness is 1 mmc. The temperature program, we applied, was the following: an initial thermostat temperature is 150 degrees; a pause for 30 sec; a rising temperature period: 5degrees per minute up to 250 degrees; a pause for 5 min; a temperature rise up to 270 degrees; a pause for 5 min.

We used helium (its permanent flow speed was 6,3 ml/mine) as a gas-carrier. For blowing detector, we applied an argon-methane mixture (95:5). The temperature of a feeding system was maintained at the level of 250 degrees, the temperature of the detector was maintained at the level of 290 degrees.

We conducted the device calibration according to 5 calibrating solutions with the following concentrations: 20, 50, 100, 200 and 500 ng/ml for each pesticide. The calibrating solutions were prepared from the standard pesticide solution of Hewlett-Packard. We recorded chromograms of prepared solutions under the conditions mentioned above. Peaks of components were integrated, then we developed graphs describing the dependence of the peak areas on components contents.

Samples of bottom sediments were tested after special preparation that included drying of samples, extraction of samples in order to get pesticides, as well as concentrating the extract to 1 ml.

The sample chromatograms were recorded under the same conditions as maintained while recording the chromatograms of the model mixtures for calibrating curve development. Peaks of chromatograms were automatically integrated and, basing on the peak areas, we calculated contents of the pesticides being measured in accordance with the method of external standard.

Quality control of the methods used for testing bottom sediments

The above-mentioned methods are characterized by continuos-successive measuring a series of identical matrix samples, including the samples for quality control:

1. An idle sample, that is clean ground;

2. A laboratory control sample, that is clean ground with mixture of control substances added (matrix control sample);

3. A working sample;

4. A working sample (parallel sample);

5. A working sample with mixture of control substances added;

6. A working sample with mixture of control substances added (parallel control sample).

All samples, as well as the quality control samples, were specially prepared and tested according to the methods in the following order: the quality control samples, ten samples, a sample for checking calibration, the rest samples of the series and again the quality control samples. Afterwards, we carried out comparative analyses of findings.

The test data obtained for an idle sample were used in order to conclude about cleanness of vessels and quality of the reagents used.

The test data obtained for a working sample and its duplicate were used in order to conclude about reproduction of the findings: any error did not exceed 10%.

The test data, obtained for a working sample with control addition and for a duplicate of working sample with control addition, were used in order to conclude about the impact of matrix or co-impacts of components, when they were extracted from samples. We did this because, for every method and every substance, we consider different errors permitted for the control substance extraction and for differences between the findings related to a sample and its duplicate.

The test data obtained for a laboratory control sample, that is the certified sample which includes the substances being measured, were used in order to conclude about accuracy of measurements and quality of sample preparations. Any error (related to detection of substances) did not exceed 10 % of the value certified.

While applying the measurement coefficients (taken from the methods and related to quality control), we considered all measurements, carried out for this series of samples, correct. Otherwise, we excluded error sources and repeated the method routine.

The test data, obtained for bottom sediments (total 30 samples) taken from rivers of the Dnipro basin, are presented in post passports (Appendix) and in the joint Table 11.6, which includes the mean test data calculated for samples and their duplicates.

10.9. Methods for testing fish

Tests on contents of metals and pesticides in fish were carried out according to the above-mentioned methods and after the samples were specially prepared.

For testing metals, fish was prepared in accordance with the standards 26929-94, Raw Materials and Food Products, Sample Preparation, Mineralization for Testing Contents of Toxic Elements.

For testing pesticides, fish was prepared in accordance with the Methods for Testing Micro-Quantities of Pesticides Contained in Food Products, Forage and Environment, Compilers are М.А.Кlisenko, А.А.Кalinina, Reference book, 2 volumes. Moscow, "Kolos" Publishing House, 1992.

The test data are presented in a fish passport (Appendix) and in the joint Table of Part 11.

10.10. Methods of hydro-biological tests

While testing phyto-plankton, we calculated numbers of water plants in Fuchs-Rosental chamber by filling it three times and then taking a mean value. For trichomes, cenobias and colonies, we calculated numbers of cells. Bio-masses were determined by calculating volumes of water plants according to generally accepted methods.

Quantitative processing of zoo-plankton samples was carried out in Bogorov chamber by total calculation of organisms in several parts of sample, and then by studying the whole sample in order to find single species and measure lengths of zoo-plankters, to calculate individual masses of organisms of all species according to parameters of masses-lengths correspondence. Weight of the коловратки was determined according to literary sources. Bio-masses of zoo-plankton were calculated by multiplying an individual weight of organisms of each kind by their number.

Bio-masses of separate macro-zoo-bentos organisms or groups were determined by weighing them after drying them off on a sheet of filter paper to the condition when there were no wet spots, then we calculated the bio-masses for 1 м 2 bottom area. Quantities and bio-masses of big molluscs were not taken into account while testing quantitative samples.

In order to assess quality of surface waters and bottom sediments (by testing phyto- and zoo-plankton communities), we used the saprobe index by Pantle and Bukke modified by Sladechek and the index of species variety by Shannon. The corresponding bio-identification was carried out according to the generally accepted methods of Woodywiss biotic indices (on taxonomic variety and revealing values of hydrobionts) and to the index by Goodnight-Whitley (on relative number of Oligochaeta).

Water quality classification (on hydro-biological parameters) was carried out in accordance with the standards 17.1.3.07.82.

10.11. Methods for testing radionuclied and strontium-90 in bottom sediments

Samples were prepared for measurements in the following way: weighing in wet condition; drying; homogenization; weighing in dried condition; putting into container for measuring; determination of geometry.

Samples of bottom sediments were dried off (under ventilation) in the ШЖН-1, drying box, the temperature was 70 degrees. The samples, while drying, from time to time (approximately every 1-1.5 h), were stirred by clean scalpel. After stirring, the scalpel was cleaned, rubbed with alcohol, washed with water several times and wiped dry.

After it was dried off, the sample was crushed by a porcelain pestle in a porcelain mortar and thoroughly stirred to homogenous condition. After processing every sample, all tools and vessels were thoroughly washed (starting with water, weak solution of hydro-chloric acid, water, soapy water, water and alcohol).

We put samples of bottom sediments into container for measuring (by gamma-spectrometer) with the help of clean scalpel or little shovel. Afterwards the sample form was changed according to the certain geometry.

In order to determine a composition of gamma-radiating radio-nucleids, contained in samples, and their activity, we used the ADCAM-100, semi-conductive gamma-spectrometer, produced by the ORTEC, USA. The detector was of GEM-80205 kind. Strontium-90, contained in samples of bottom sediments, was detected according to standard methods. A strontium-bearer was measured by an atomically-absorbing spectro-photo-meter. Radio-metrical measurements were conducted with the help of the РУБ-01П1 device.

Semi-conductive gamma-spectrometers are used for measuring activity of environmental samples presented in three-dimensional form, while the activity of radio-nucleids, being measured, varies from 2 to 10⁵ Bc. Such spectrometers make it possible to measure the activity (for samples presented in three-dimensional form) by photon radiation within the energy range of 0,07-3 MeV; the following are errors of measurements, while the trust probability is 0,95:

30 - 50 % within the range of 2 - 10 Bc,

20 - 30 % within the range of 10 - 100 Bc,

15 - 20 % within the range of 102 - 105 Bc.

The time of sample measuring was determined according to the activity of the radio-nucleid being measured and to the standards ensuring accuracy of such measurements.

11.1. Water speeds and expenses

The water speeds and areas of cross sections were measured at 20 posts (3 of which were additional). The data on water expenses, calculated according to the measurement figures, and the data - related to the 4 posts (the Dnipro river up stream Mohylyov town, the Dnipro river down stream Rechitza town, the Prypyat river down stream Mozyr town and the Dnipro river down stream Komarin town), where water expenses were calculated taking into account correlations between areas of water collection - are presented in the Table 11.1. Information on water expenses at boundary posts (the Table 11.2) fully corresponds to the analogous data, obtained by Ukrainian expedition.

If we compare the monitoring data of many years (the Table 11.3), we can see that, during the expedition period, for all the posts without exception, water expenses exceeded the water expenses of the calculation October (for calculations, we regarded a year of low water), and, for majority of posts, they were close to the mean data of a long term.

Table 11.1 Results of hydro-metric measurements in the Dnipro basin

Table 11.3 Actual data on water expenses of rivers at the measurement posts

11.3. The summary beta-activity and contents of caesium-137 in bottom sediments

The measurement data on the summary beta-activity and contents of Cs-137 in the bottom sediments, taken from Belarussian rivers, are presented in the Table 11.7.

For the current period, the summary beta-activity has been formed mostly by beta-radiation of potassium-40 beta-rays and caesium-137. Contents of other beta-emitters, in the ground and bottom sediments, are not as significant as of the above-mentioned elements.

The content of potassium-40 in bottom sediments of the Dnipro river, at the places where samples were taken, is 330-390 Bk/kg of dry weight. The only exception was the sample that included the fine disperse clay minerals, it was taken up stream Orsha town, in the right bank shore, where the potassium-40 content is the highest of all other samples of bottom sediments and makes up 518 Bk/kg of dry weight of bottom sediments. The part of potassium in the summary beta-activity of this sample is 99,8%.

The content of potassium-40 in sandy bottom sediments of Sozh river, down stream Homel town, is less than in sandy-silty bottom sediments of the same river up stream Krichev town. But, as far as near Homel town, the bottom sediments are heavily polluted by caesium-137, in the second case, the summary beta-activity is higher than in the first one (the summary activity of that sample is the highest of all tested samples and makes up 640 Bk/kg of dry weight).

The bottom sediments from Iput river near Demyanka village, up stream Dobrush town, were presented as washed up fine-grained sand, from which, most likely, potassium and a part of fine-disperse clay minerals (the potassium-40 bearers) were de-sorbed, so the potassium-40 contents of that sample was only 96 Bk/kg (for the Ubort river, the corresponding figures were 36 Bk/kg). However, the summary beta-activity was rather high because of significant contamination by caesium-137.

The lowest summary beta-activity was registered (in the decreasing order) for the bottom sediments of Goryn, Stviga and Ubort rivers; the minimum amount of potassium was found in the bottom sediments of the Ubort river (36 Bk/kg).

As we can see in the Table 11.7, the bottom sediments contamination by caesium-137 correlates with the polluted waters around the places where the samples were taken. For instance, the contents of caesium-137 in the bottom sediments of Dnipro river, up stream Orsha town, where waters are practically clean of radio-caesium, do not exceed 0,7 Bk/kg, then going down stream, the contents of radio-caesium rise from 5,3 Bk/kg, near Mohylyov town, to 10,3 Bk/kg, near Komarin town situated in the area, were contamination is 5-15 Ki/кm2. These differences are even more clear if we talk about the bottom sediments of the Sozh river: from 4,6 Bk/kg near Krichev town (less 1 Ki/km2) to 271,7 Bk/kg near Homel town. The maximum caesium-137 content was registered for the bottom sediments taken from the Iput river, up stream Dobrush town (Demyanki village), which can be explained by the fact that the area is contaminated by caesium (over 40 Ki/кm2). The sample was taken at a shallow place of the left bank of Iput river, which “catches” the highly active hard flow, taken away from a watershed.

As the Table 11.6 shows, the bottom sediments of the rivers, flowing in the contaminated territories, contain significant amounts of caesium-137. Whereas, in the bottom sediments, up to 20% of radio-caesium are presented in the solvent and changeable forms, they should be regarded as potential sources of secondary contamination for surface waters. Additional amounts of radio-caesium are delivered to the surface waters from bottom sediments as a result of floods, pumping water for technical needs or other purposes; and this fact has to be taken into account while developing the water protection activities.

There were no radio-active elements detected in the fish samples.

Table 11.7 The summary beta-activity and contents of caesium in bottom sediments

11.2 Hydro-chemical parameters of water quality

Hydro-chemical parameters of water quality were determined for 21 posts. At every post, we registered 33 indicators, 10 of which were on heavy metals of suspended and dissolved forms. Characteristics of surface water quality (according to hydro-chemical parameters), related to the water taken from the Dnipro river, Prypyat river and their tributaries, are presented in the Tables 11.4…11.5.

Dnipro River

The upper part of Dnipro river (the posts 1 and 2, from the border with Russia to Orsha town inclusive) can be considered relatively clean. As to the main components, we did not register any cases when the permissible standards were exceeded. As to manganese, the exceeded permissible standards can be, probably, explained by natural factors; and as to copper, neither here nor at any other post of the Dnipro river, Prypyat river or their tributaries, we take this fact into account, so far as, in Belarus Republic, the current standards exceed the analogous ones of the European countries in 10…100 times. While entering Belarus Republic (the border with Russia), the water quality corresponds to the water quality measured for the Dnipro river down stream Orsha town; and as to some parameters (like ammonium nitrogen, СВАП, silicon and others), the figures were even worse, this fact can be regarded as an indirect evidence of insignificant impact of the concentrated pollution sources, produced on the Dnipro environment in this area.

The pollution content in surface waters of the Dnipro river rises going with the stream. Near Mohylyov town (the posts 3 and 4), apart from manganese and copper, we registered the exceeded standards on the ammonium nitrogen and nitrite nitrogen substances, phenols and oil products (the Table 11.4), which are surely related to the human activity; the same was registered on iron but the reason of this has a natural character. Such pollution contents do not change to Rechitza town, where discharges of local hydrolitic plant (together with the municipal discharges) make the parameter, related to the BOD-5, to exceed the standards too. At boundary posts of Dnipro river (Loeve and Komarin towns), the pollution level of surface waters lowers, the standards are exceeded only on copper and zinc, which happens down stream Loeve town.

Berezina River

For the studied period, the Berezina river can be considered moderately polluted. However, the Svisloch river, tributary of the Berezina river, is the most polluted river of all studied rivers of the Dnipro basin. The considerable pollution, produced by Minsk city, has caused an essential excess in the ammonium and nitrite nitrogen contents (over 10 times of the standards), as well as in the phosphates, the BOD, oil products, manganese, copper and zinc contents.

Sozh River

Surface waters of Sozh river and Iput river, its tributary, are moderately polluted. For the studied period, we registered excessive (to some extent) contents of nitrogen and heavy metals (manganese, copper, zinc, iron) and of the SURFACTANTS (Iput river).

Prypyat River

While entering Belarus Republic, the Prypyat water was characterized by excessive contents of phosphates. The iron excess, as everywhere, can be, probably, explained by natural factors. Down stream Pinsk town, we registered growing pollution by phosphates. Besides, the standards were exceeded as to the BOD-5 too. Going down streasm, the pollution level of Prypyat river slightly lowers, but the municipal and industrial discharges of Mozyr town raise it once more; and while leaving Belarus Republic (the post 17), the water was characterized by excessive contents of ammonium nitrogen, manganese, copper and iron.

Entering Belarus Republic, the right-bank tributaries of Prypyat river (Styr, Goryn, Stviga and Ubort) are already polluted by ammonium nitrogen (Stviga and Ubort rivers), phosphates (Styr and Goryn rivers), the СВАП (Goryn and Ubort rivers); this fact, most likely, relates to the pollution carried from agricultural territories of Ukraine.

Comparative analysis of the results, obtained by hydro-chemical research into the rivers of Dnipro basin, and the annual monitoring data, collected by Hydromet in 1999, shows that the data, got by the expedition, is representative