The Biological Control of the Water and Soil Pollution, Based on Bioelectrical Response of a Freshwater Algae Cell

In most cases pollutants are unknown, so chemical analysis of the water (and soil as a water extraction) is difficult and expensive. On the other hand biological testing is the only method of integral determination of the water quality, as different environmental factors affect various physiological processes. Thus, the biological testing, as a first stage in ecological monitoring system, enables reduce expenditures. In addition it makes it possible to detect the combined effect of a several pollutants, present in water at the same time, even if each of them separately has not essential biological effect. In Plant Physiology Dept. of Belarussian State University the laboratory variant of device was created and tested. It consist of the bioblock, including as a main part the biosensor – giant freshwater algae cell Nitella flexilis, whose bioelectrical reaction in response to application of tested water is registered and analysed. The conducted tests shown, that the cells of freshwater algae Nitella flexilis are excellent testobjects for all monitoring and screening. The main characteristics of the method proposed: simplicity of test-object cultivation, preparation, assays and registration of information; quickness of obtaining the results (examination of one sample takes 10-20 min); information about the pollutant effect is obtained as the electric signal, that gives possibility to use computer processing of the data and to manage the biotest setup by computer; high sensitivity (in same cases 10 – 10 M of pollutant in the medium is enough to be detected by biotest). Introduction Now in biosphere there are more than 6 million of chemical compounds, which are mainly of anthropogenic origin and the quantity of them permanently increases. The emission points are the wastes of industrial release, of transportation, domestic waste, widely applicable in an agriculture pesticides. Only by chemico-analytical methods of monitoring is difficult, and frequently it is impossible to receive an enough complete picture of biological hazard of an environmental contamination because of the following reasons. • High costs and extensive labour needed to carry out chemical and other analyses (for instance, remote probing). • The limited number of maximum permissible concentrations (MPC) established for substances present in the air and water environments and the practical absence of such concentrations for soils. • The synergism in combined action of individual pollutants and the difference in their biological effects on the background of other substances (at present, the biosphere includes 6 .million individual chemical compounds, not to mention combinations of them). • The increased toxicity of substances in the process or their metabolic transformation by living systems (biotransformation) and biological accumulation. • The absence of evaluations of the biological soundness of the habitat in view of the phenomena mentioned above. Thus, depending on a concrete situation, the biological testing with necessity must either precede chemico-analytical one, or supplement it, but not change it completely. The purpose of presented work is to show an opportunity of biotesting of a water environment and soil on an example of one concrete biotest. The interaction of any substance with living system can be schematically represented according to the levels of structural organization as the following stages: a cellular membrane cell tissue organism. It is clear, that the most complete information can be received, using a test-object of a organism level. However long-run observation in this case is required, the registered parameters will have mainly qualitative character, the occurred changes, as a rule, will be irreversible (1, 2). However, in a number of cases a rapid diagnosis of situation, specially in systems of monitoring of quality surface and sewage waters, is indispensable. On the other hand, it is important to find out initial stages of pollution, that is the moment, when concentration of toxic substances yet does not produce irreversible changes in an organism. In this case most appropriate level of the test-object is the membranous cellular level. It is known, that all living cells are surrounded on the outside with a plasma membrane, which is a primary target affected by external physicochemical factors. The membranes are easily modified either directly being affected by many chemical compounds, or indirectly through disturbance of intracellular processes, which are responsible for maintenance of normal functioning of their structures, and thus, they are very sensitive to action of the chemical agents. The presence at an environment of chemical substances first of all causes the following changes in cell membranes characteristics: Ionic flows through a membrane; Membrane electrical potential; Electrical conductance (resistance) of a membrane. The outer cellular membranes include lipids, proteins, enzymatic complexes with rather various and very important functions, as a cell membrane is simultaneously both "a organ of sense " perceiving the information on changes of an environment and transmitting it to intracellular structures, and "a execution unit", which ensures adaptation of a cell to changes in environment. To the greatest extent these features inhere free living alga, for example, freshwater Characeae alga. To obtain more information and increase assessment accuracy two approaches can be developed: either to select the correspondent test-objects, or try to make as high as possible the number of independent parameters determined through the test procedures using a single test-object. The second approach would be more effective, reducing the labour costs and simplifying the procedures of biological testing, although the first approach is not eliminated. Thus, it is necessary to use the tests, which allow characterising the effect of pollutants by several independent parameters, which are determined simultaneously. At the same time, the realisation of conditions of independence parameters can be achieved with the greater probability when the used model representations are not empirical, but based on the established mechanisms, on which the observed changes are founded. Therefore it is expedient to elaborate scientific-founded methods of biotesting and to realise their in practice. Method of biotesting In our laboratory within many years with usage of electrophysiological methods the mechanisms of a ion transport through membranes of plant cells were studied (3, 4, 5). The gained experience has allowed to offer as a test-object for biotesting giant cells of freshwater Characeae alga Nitella flexilis. Two electrophysiological parameters are proposed for using in biotesting as independent ones. First thermodynamic – is a difference of electric potentials on a membrane, second kinetic electrical conductance (resistance) of a membrane. Both parameters are highly sensitive to a very great numbers of interactions, modifying a membrane. Procedure of biotesting: Let us consider one of our methods of biological testing, namely the method of electroalgological control. As a sensing element (biosensor) the cells of alga Nitella flexilis are used. The procedure of algae growing in laboratory conditions is very simple. Ports of algae thallus, having 3-5 internodes, and apical cells are planted out in glass vessels filled with a solution of artificial pond water with a rather simple composition: (KH2PO4, Mg (NO3)2, NaHCO3, CaCl2). The temperature of the nutrient solution is maintained within 20 to 25C, illumination is realized by luminescence lamp with a cycle of 16 hours light/8 darkness. A bioelectrical response has been selected as a test reaction since the presence of chemical-compounds in the environment causes modifications of such parameters as the difference of electrical potentials and the resistance of the cell. The experimental procedure used to measure these characteristics is implemented by means of the method of extra-cellular technique, which has been developed in our laboratory (Fig. 1). The 2nd or 3rd cell from the top are selected for the experiment. The cell is placed