This article throws light upon the top two microbiological methods used for estimating pollutants. The methods are: 1. Eco Taxonomical Method 2. Physicological-Biochemical Methods.
Microbiological Method # 1. Eco Taxonomical Method:
In these mainly two types of monitoring is done:
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(a) Single indicator method
(b) Community structure.
(a) Single indicator method:
When a water body receives any pollutant, its physic-chemical structure undergoes a change. The sensitive organism disappears while tolerant species take their place thus we identify organism in various types of pollution.
(b) Community Structure:
This approach involves monitoring the variation in the species richness or the no. of species present and the evenness of the relationship of no. of individuals per species, or the relationship between organisms of major group to correlate them with the degree of pollution.
Microbiological Method # 2. Physicological-Biochemical Methods:
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In this biological functions analysis, toxicity testing, avoidance studies are carried out. In all these the primary cases are taken of chlorophyll content, primary production of algae, and effect of pollution stress on A.T.P. generation, growth and egg production. Toxicity tests involves study of various concentration of the substances which will cause no or minimum hazard to aquatic ecosystem.
The fishes and aquatic animals avoid the area which is polluted and has effect on fertility, growth, susceptibility to disease. To study the behavioural pattern of species are known as avoidance studies.
Algae:
They are unicellular, having chlorophylls.
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Importance:
1. They produce as high as 25 gC/m / day in ideal conditions.
2. Natural waters which are deficient in number posses low populations of algae but additions of any kind of nutrient triggers their growth.
3. In biological treatment of waste water bacteria cause rapid mineralization of organic matter while the vital oxygen supplied by algae.
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4. Algae are known to indicate the level of pollution and are widely used throughout Europe and North America.
Types of Algae:
There are different types of algae: Phytoplankton, benthie, algae periphyton.
Only Phytoplankton is selected for this purpose:
Types:
Net plankton, Nano Plankton, Ultra Plankton.
Selection of sampling sites: bottom waste water lagoons etc.
Sampling:
Plankton net is (Fig. 5) is used for collection of planktons of bigger size. The amount of water filtered is calculated by formula.
V = Volume of water sample
r = Radius of nets orifices in m
D = Depth upto which the net has m
Preservation:
The sample is preserved in 4% formalin or Lugol’s solution.
Lugol’s solution can be prepared by dissolving 10 gm of KI (Neutral) in 20 ml of water and add 5 gm of twice sublimed Iodine. When solution is complete add 50 ml of water and 5 gm of sodium acetate or 10% acetic acid.
Counting:
For mirocystis a colony of several cells is counted to be as one unit. For oscillatoria each cell can be counted as one unit.
Haemocytometer (Fig.6) is a device for counting chamber. It is a glass slide which has a centrally located ‘H’ shaped groove. 2 prominent ridges come out of this groove, each containing 5 cubical chambers of length X breadth X depth as 1 mm x 1 mm × .1 mm. The central chamber is divided into 25 sub-chambers.
Calculation of Phytoplankton: (No. of phytoplankton in central) × 1014/concentration factor
Another device used for counting is Raftor Cell Method: In this the sample is placed in the Raftor cell (Fig. 7) and the indicator gives the signals which are counted.
No. of Plankton/ml = No. of organism counted/No. of replicates taken
Similar experiments are carried out with algae and exoplankton.
Thus the micro-biological diversity gives the signals for the various types of pollutants. For NO2 1500 signals are counted. In the same way for SO2 → 23,000 signals are counted.
Micro Chemical Analysis:
The term Micro chemical has been derived from the two words ‘Micro’ which means small and ‘Chemical’ means the organic or inorganic substances which can verify and quality and quantity of the material and also identify about the substances.
As we, know, there are various types of air pollutant, so the microchemical analysis is done. In this process a small amount of sample is taken and the reagents are added which give a dye color, which can be studied by colorimeter or spectrophotometer. There are various types of air pollutants.
They are as follows:
NO2, Ozone, SO2, CO, CH3Cl, CHCCl2, CHCl3 etc.
For the test of NO2:
When sulphanilic acid and N. ethylene diamine dichloride reacts together then they form a dye which can be studied under colorimeter. The graph is plotted which is in form of a straight line.
For the test of Ozone:
Ozone in the atmosphere is absorbed in a neutral buffered 10% KI solution. As a result is oxidized to iodine, the tri-iodide ion is determined by colorimeter. The latter part is recorded in the U.V. Spectrometer which is calibrated in parts per hundred million ozone.
For the test of SO2:
It is determined by reaction with iodide to form Iodine, which then reacts with hydrogen at cathode having a constant applied potential. The resulting polarization current tends to re-establish the hydrogen layer which is a measure of quantity of SO2 passing through cell. As SO2 gives a negative interference so by using colorimeter continuous analyzer procedure we can determine the SO2 concentration easily.
For the test of Carbon monoxide:
The air sample is taken in IR Photometer. The detector cell has a regular frequency by which the gaseous component expands and contracts. This expansion and contraction causes an oscillating movement of the diaphragm condenser. This electric signal can be determined and from this signal, the concentration of CO can be determined.