Air pollution tolerance index (apti)

Air pollution tolerance Index is been used in studies like Green belt development, traffic noise reduction and Pollution mitigation at roadside sites and around industries.

1. APTI Air Pollution Tolerance Index Sandeep Kumar Centre for Environment Science and Climate Resilient Agriculture ICAR-Indian Agricultural Research Institute New Delhi 110012

2. A large number of plant parameters have been used for this purpose, including visible foliar injury (Davis and Wilhour , 1976), leaf conductance (Winner, 1981), membrane permeability ( Farooq and Beg, 1980), ascorbic acid (Keller and Schwager , 1977), relative water content (Rat, 1979), chlorophyll content (Bell and Mudd , 1976), leaf-extract pH ( Chaudhary and Rao , 1977) and peroxidase activity (Eckert and Houston, 1982).

3. The sensitivity of plants and tolerance parameters varies with air pollutant level at the study area. Air pollution tolerance Index is been used in studies like Green belt development, traffic noise reduction and Pollution mitigation at roadside sites and around industries.

4. The Air pollution tolerance index is an empirical relation which evaluates the tolerance level of plant species towards air pollution from leaf biochemical parameters such as Leaf extract pH , relative water content of the leaf , ascorbic acid and total chlorophyll. The APTI is formulated by Singh and Rao (1991).

5. Ascorbic acid, through its reducing power, protects chloroplasts against SO2-induced H202, 02- and OH accumulation, and thus protects the enzymes of the CO 2 fixation cycle and chlorophyll from inactivation (Tanaka et al., 1982). Together with leaf pH, it plays a significant role in determining the SO2-sensitivity of plants ( Chaudhary and Rao , 1977; Rao , 1979).

6. Its reducing power is more at higher and less at lower pH values. Thus, it may be possible that ascorbic acid protects chloroplasts and chlorophyll functions from pollutants through its pH-dependent reducing power. Thus, the A(T+ P) part of the formula represents the potential of chloroplast to combat pollutants after their entry inside the plant.

7. The addition of RWC to A(T+ P) shows the capacity of the cell membrane to maintain its permeability under polluted conditions. Thus, this combination of four parameters is suggested as representing the best index of the susceptibility levels of plants under field conditions.

8. The categorization of the plant species is based on method of Singh and Rao (1983). The formula of APTI is given as APTI = Where, A = ascorbic acid content (mg/g) T = total Chlorophyll (mg/g) P = pH of leaf extract R =relative water content of leaf (%)

9. The plants are categorized according to APTI values plants Sensitive intermediate Moderately tolerant Tolerant Deciduous ˂ 14 15 - 19 20 - 24 ˃ 24 Evergreen ˂ 12 13 - 16 17 - 20 ˃ 20 Herbs ˂ 10 11 - 14 15 - 18 ˃ 18 Crop ˂ 16 17 - 29 - ˃ 29

10. Relative water content Relative turgidity is a direct measure of deficit in leaves. Relative water content indicates the capacity of the cell membrane to maintain its permeability under polluted conditions. Relative water content was estimated by Bars and Weatherley’s .   RWC = Where, FW = Fresh weight DW = Dry weight TW = Turgid weight Fresh weight was obtained by weighing the fresh leaves. The leaves were then immersed in water over night, blotted dry and then weighed to get the turgid weight. The leaves were than dried overnight in an oven at 70°C and reweighed to obtain the dry weight.

11. Leaf extract pH pH of the leaf extract signifies the tolerant capacity of the leaf species. Studies have shown that decline of pH during the presence of acidic pollutant, pH of leaf is found lowered in sensitive species than tolerant plants. Higher level of pH in leaf extract indicates that the plants are tolerant under polluted conditions. pH plays an important role in signifying the condition of plants with respect to the study area. pH is estimated followed by Singh and Rao’s procedure. 2g of the fresh leaves was homogenized in 20ml deionised water.

12. Ascorbic acid Take 5 ml of working standard into a 100 ml conical flask. Add 10 ml of 4% oxalic acid and titrate against the dye (V1 ml). End point is appeared as pink color which persists for a few minutes. The amount of the dye consumed is equivalent to the amount of ascorbic acid. Extract the sample (0.5 to 5 g, depending on sample) in 4% oxalic acid and make up to a known volume (100 ml) and centrifuge (5000 rpm for 20 min). Take out 5 ml of this supernatant and add 10 ml of 4% oxalic acid and titrate against the dye (V2 ml). Amount of ascorbic acid (mg/100g sample) = Where, V1 is volume of dye during first titration (ml) V2 is volume of dye during first titration (ml)

13. Total Chlorophyll content Take 1g of finely cut and well mixed samples of leaves into a clean mortar and pestle. Grind the leaves with addition of 20 ml 80% acetone until the color of leaves disappear (volume of acetone can vary). Centrifuge at 5000 rpm for 5 min and transfer the supernatant to a 100 ml volumetric flask. Make up volume to 100 ml with 80% acetone. Read the absorbance of the solution at 645 and 663nm against the solvent blank (80% acetone) Chlorophyll a (mg/g sample) = Chlorophyll b (mg/g sample) = Total chlorophyll (mg/g sample) = Where, A= Absorbance at specific wavelength V= Final volume of chlorophyll extract in 80% acetone (ml) W= Fresh weight of the tissue extracted (gm)

14. धन्यवाद