Токсикологічна оцінка поверхневих вод та донних відкладів річки Устя методом біотестування

Abstract

Проведено оцінку рівнів токсичності різних ділянок річки Устя методом біотестування з використанням акваріумної водорості Vallisneria. Виявлено зростання токсичності донних відкладів у середній частині, а поверхневих вод – від верхів’я до гирла. Найбільш несприятлива токсикологічна ситуація виявлена в межах міста Рівне.

Проведена оценка уровней токсичности различных участков речки Устья методом биотестирования с использованием аквариумной водоросли Vallisneria. Отмечено возрастание уровня токсичности донных отложений от уровня «слабо токсичные» в истоке до уровня «высоко токсичные» в средней части речки. Поверхностные воды в верховье реки не проявили токсического действия на тест-обьект, а в устье реки характеризовались как «высоко токсичные». Наиболее неблагоприятная токсикологическая ситуация оказалась в пределах города Ровно. Использованный способ биотестирования может быть рекомендован для интегральной оценки токсичности гидроэкосистем перед проведением аналитического контроля химической природы загрязнений.

The author provides the toxicological evaluation results for the ecosystem of the Ustia River flowing through the territory of Zdolbuniv and Rivne districts of Rivne region. Due to a great number of natural and anthropogenic factors the river has some signs of degradation which are particularly acute in the urban areas of the watercourse. The researcher has observed the hydro-ecosystem conditions and conducted sampling for the tests in 6 control sections experiencing different levels of the anthropogenic load during the 2015 summer-autumn low-water period: site #1 – western outskirts of Ivachkiv village (upper river, natural background) site #2 – below the town of Zdolbuniv (impact of the wastewater discharge); control site #3 – within the town of Rivne, 100 metres below the dam of the Basiv Kut Lake (a control point is located below the Basiv Kut reservoir dam); site #4 – within the town of Rivne, near the central local market (impact of Rivne’s wastewater discharge); site #5 – the expanded area within the town of Rivne, near "La Riva" cafe (impact of Rivne’s wastewater discharge); site #6 – Orzhiv village, 0.1 km above the confluence into the Horyn River (a control point in the river mouth). In order to evaluate the toxicity of surface water and bottom sediments of the Ustia River the author used a cytophysiological method that records chloroplasts passing one or more divisions of the ocular micrometre and determines the speed of the cytoplasm as the ratio of the distance to the number of seconds during which the chloroplast covers this distance. Biotests were performed using of a test facility Vallisneria (R.Micheli ex. L. 1753). The researcher determined the rotary motion speed in 3-5 cells of each plant sample. Reliability criteria of the results were established as the deviation of the experimental data from control indices at a confidence interval R≤0,05 (by Student's t-test). In the research period river surface waters were non-toxic (group 1) in the areas near the discharge and within the town of Zdolbuniv. There was poor water toxicity (group 2) in the areas of the hydro-ecosystem that undergo the human impact of Rivne’s wastewater. On the contrary, surface waters of the river mouth (group 4) demonstrated high toxicity. Aqueous samples from bottom sediments have high toxicity (group 4) in all areas except the two alignments within the town of Rivne, where the toxicity of samples was weak (group 2). It is obvious that the increase of toxicity levels in aqueous samples from bottom sediments compared to surface waters toxicity of the Ustia River is directly linked to the accumulation of contaminants in the silt fractions of bottom sediments and their transition into the solution while sampling. This fact demonstrates the potential danger of pollution to the flow of surface waters of the river in certain circumstances (mechanical abuse of sediments, pH change in surface waters, acceleration of the river flow as a result of flood raising water levels etc.). The toxicity of bottom sediments was medium and high (groups 3-4) at the hydro-ecosystem sites with substantial anthropogenic pressure resulting from the deposition and accumulation of pollutants. The weak toxicity of bottom sediments (group 2) in headwater is driven by the lack of wastewater. Although the qualitative composition of the sediments in this area (near the discharge) contains large silt fraction, there is no adsorption of toxic contamination. The research has also discovered the weak toxicity of sediments in the river mouth where the analysis has also indicated high levels of toxicity in surface waters. In our opinion, this is a result of the pollution bulk removal together with the internal water flow towards the Horyn River. After all, this site is marked by relatively high levels of water and greater flow rate compared to the rest of the control sections. We assume that those peculiarities of the hydrological regime specific for this site of the hydro-ecosystem make the active sorption of pollutants of surface waters, in particular, by silt fraction of bottom sediments impossible. Thus, we observed the increase of the toxicity of bottom sediments in the middle part of the hydro-ecosystem. At the same time the toxicity of surface waters increases from headwaters to the mouth. The general toxicological situation is the most unfavourable in the site located in the town of Rivne (100 m below the dam of the Basiv Kut Lake): it demonstrates "high toxicity". Therefore, the toxicity of the whole bottom sediments and their water extracts reached the level of "high toxicity" and these indices were significantly higher compared to the toxicity of surface water. The only exception was the site in the mouth of the river. The explanation, mentioned above, can be further supplemented by an assumption that the toxicity of the hydro-ecosystem may also vary depending on such factors as surface water temperature and the intensity of production-destruction processes. The changes of the chloroplast speed which were tangible in the short period of time in experimental samples compared to the control data indicate that the Vallisneria cells are sensitive to the presence of toxins. Taking to consideration the ease of the plant cultivation and the representativeness of its cytophysiological changes, the biotesting method used in the experiment can be recommended for the integrated assessment of the hydro-ecosystem toxicity that should justify the necessity for an analytical control in order to determine the chemical nature of the pollution.