Scientists from the Krasnoyarsk Science Center SB RAS for the first time studied the damage caused by man-made pollutants present in the bottom sediments of the river Yenisei; the study was carried out with the help of onions. The toxicity was estimated by observing the growth of roots; mutagenicity was analyzed through the number of cells with damaged chromosomes. The bio-tests did not show any increased toxicity in most of the bottom sediment samples; however, increased mutagenicity was observed in the samples from the Abakan channel. The results of the study are published in  the Siberian Ecological Journal.

Bottom sediments containing various organic and mineral particles are formed on the bottom of any water body, including rivers. Potentially toxic substances appearing in water due to the industrial activity of man are accumulated in the bottom sediments and can negatively influence the water ecosystem; they are also potentially dangerous for people. Such harmful substances  were earlier found by scientists in the bottom sediments of the river Yenisei.

The level of pollution for bottom sediments of natural water bodies is not regulated by law, while there are regulations for soils. To estimate the harmful potential of toxic substances it is not enough to estimate their content, their biological activity must also be analyzed. For this purpose, scientists are developing different methods of bio-testing.

The scientists from Krasnoyarsk for the first time used a bio test based on using onions to estimate the harmful effect of potentially toxic substances present in the bottom sediments of the river Yenisei on living organisms. The onion test has traditionally been used in the world to estimate  toxicity and mutagenicity of the environment. Toxicity is estimated by observing the root increment on the onion bulbs; mutagenicity – by the presence of cells with chromosome damaged in the root tips of onions.  

The bottom sediment samples were taken from 10 sites of the river stretch 100 km downstream from Krasnoyarsk and lower; this river stretch is affected by the million city with its industries and public utilities. After the pre-treatment the onion bulbs were planted into containers with the bottom sediments; after some days the root length was measured and samples of the root tips were taken for the analysis under the microscope.

In spite of the increased content of heavy metals, oil-products and man-made radionuclides which was observed in the samples, their toxicity level was not high since the length of the onion roots grown on all the bottom sediment samples was approximately the same. An increased percentage of cells with chromosome damage in the onion roots was recorded in a bottom sediment sample containing a mixture of organic and mineral pollutants taken in the Abakan channel. The results of the present study coincide with the results of earlier bio tests of the Yenisei bottom sediments carried out using the aquatic plant Canadian pondweed. The scientists made a conclusion that the onion test can be applied to estimate the quality of bottom sediments along with other biotests.

«Biotesting is an instrument which allows one to estimate the harmful potential of the whole complex of pollutants accumulated in bottom sediments.  We did not record high rates of toxicity and mutagenicity of the Yenisei bottom sediments with the help of the onion test. It can be indicative of a relatively low level of man-made pollution of the Yenisei bottom sediments. In most samples we did not find organic pollutants having high mutagenicity. Another possible reason is the insufficient sensitivity of onions to the type and level of the pollution in the bottom sediment samples», says the co-author of the paper Tatyana Zotina, Candidate of Biological Sciences, senior research associate of the Institute of Biophysics KSC SB RAS.

The present research is the result of the systematic work aimed at finding and developing more sensitive biotests. For example,  the test based on the aquatic plant Canadian pondweed , recently suggested by these scientists showed higher sensitivity to toxic and mutagenic substances present in the bottom sediments of the river Yenisei. Based on the results of biotesting, it is planned to develop regulations for the pollution levels for bottom sediments in natural water bodies. Such regulations are still absent in our country