Objects & methods of researches
Objects of researches
Students of Lyceum learned the content of zinc and manganese in the birch leaves and in mosses that were collected on the areas of Shelekhov and Arshan by theyself. Other students studied the needles of the pine-trees as the indicators of the pollution of the environment. Why were these the objects chosen?
1. We compared to per cents content of zinc and manganese in the clean birch leaves with per cent of content of zinc and manganese content in the dirty birch leaves gathered at the suburbs of Shelekhov and at Arshan (background sample). We find out that the birch leaves growing in the fields near the Irkutsk Aluminium plant contain zinc in twice more and manganese almost in ten times than the background leaves contain. What are the reasons of that fact?
2. Mosses belong to the plants that are the most sensitive for the pollution of habitat. That’s why they may be chosen for the object of analysis.
3. Xeromorphos needles of pine-tree have low gas resistance for some reasons:a. A needle has a long lifetime. It is constantly exposed by the influence of gases during its lifetime.
b. A needle has a high sickness rate in comparison with deciduous species.Process of needle forming and rise brakes because of pollutant influence. Because of it needle lifetime decreases to 2-3 years and in individual cases – to one year while it reaches to 6-9 years in young inviolate pine forests. Chlorosis and necrosis of assimilated plant organs belong to outside changes that are the results of man-caused pollutant influence. These features are of a big interest of diagnostic counse.
The plants that have been chosen for research are members of different departments like Mosses, Gymnospermae and Angiospermae. That gives us a possibility to learn not only the chemical composition of these plants but their taxonomy. That’s why our researches have a complex character.
In order to perennial observations for condition of plant components of biogeocenoses five monitoring areas (or sub territories) were placed. They had a square of 400 square meters and identical plant dominants and soils. Three control areas were placed around Shelekhov and two background areas – around Arshan settlement. On these areas total geobotanical and soil descriptions were done, samples of plants and soils were taken for chemical analyses. Common sampless were prepared by chair of botany and analytical researches were done by chair of physical methods of analysis of Irkutsk State University.Method of researches of birch leaves and mosses
Roentgen-spectral fluorescent method of analysis (RSFA) was used for the determination of the chemical composition of the mosses and content of the chemical elements in the birch leaves.
Distinguishing feature of a modern RSFA is that it is used for the determination of elements in the biological objects and for the control of the pollution of the environment. In comparison with other physical methods of analysis (such as an atomic absorptive, an emissive spectral, a neutron activation) when apparatus with the energy spectrum decomposition is used RSFA has the following advantages:
1. A possibility to determine a big number of elements at the same time:
2. A conservation of the research sample’s materials that gives us the possibility for its second analysis by different methods:
3. A slight man-hours for analysis, an easy spectrum treatment, a possibility to use computers for the calculation of the concentration:
4. This method falls for automation easily.
The last two advantages are the most important for the realization of mass analyses.
Preliminary researches have showed that Mn, Fe, Zn, Nb Pb, Sr in the mosses may be determined by RSFA. So the aim of the present work is to elaborate the system of the Roentgen-fluorescent determination of Zn and Mn in the mosses that have a high rate of content of Zn and Mn rather than the content of other listed elements.
Five samples of mosses and birch leaves were selected for the realization of the researches in different places. The first two samples were selected in Arshan settlement. The second sample — at the suburb of Shelekhov at a distance of 3 km from the industrial zone, the third sample was selected at a distance of about 6 km from the industrial zone and the forth sample — at a distance of 0.5 km from Irkutsk Aluminium Plant. Samples that had been taken in Arshan were named as a background. The samples that have been selected at the suburb of Shelekhov were named as control. In other words not only influence of nature facts were estimated by them but also the influence of environment for the content of Zn and Mn.
Clean and dirty birch leaves and moss were analyzed independently after another. It was done for determination of the ways of Zn and Mn penetration in plant’s organism (from the soil or the atmosphere). Each sample of the clean and dirty birch leaves was analysed four times.Apparatus
The researches were led by the roentgen fluorescent spectrometer VRA-30 that is produced by the firm “Carl Zeiss”. This spectrometer has one scanning channel and is completed by three roentgen pipes with different anodes (tungsten, rhodium and chrome). X-radiation decomposes into the spectrum using crystal-analysers LiF(200), LiF(220), PE, ADP, KAP, Si by Soller method.
Scintillation and flowing proportional counters are used for the registration of the radiation. The first one is used for K- radiation measuring of elements that have numbers Z>25 and for the radiation measuring of L-series of the elements with Z>60. The second one is used for X-radiation measuring of the elements those are from 9K to 29Cu and for K-radiation measuring of the elements with Z<60. All process of the regulation, measuring and inside control of the device are led by inside microcomputer.
During the experiments K-radiation activity was being registered under the conditions that the tension of the roentgen pipe was 40 kV, current strength was 40 kA, exposition lasted for 60 seconds and crystal-analyser LiF(200) and scintillation detector were used. K-lines of Zn and Mn were the analytical lines.Method of research of pine-tree needles
The system that had been published in the book “Ecological monitoring” by F. Snakin (Moscow, 1996) was used for needles research. Observations had been continued for 3 years (2000, 2001, 2002). 10 branches of pine-tree that was 2 years old were selected from 10 trees on each area then general number of needles, numbers of healthy and injured needles were calculated.
There were chosen 3 classes of needles injury (or necrosis):
1. Needles without spots or healthy,
2. Needles with a few small spots,
3. Needles with a lot of black and yellow spots and completely yellow needles (or dried needles).