Lichens

Lichens are indicators of Heavy metal pollution Dr.Abida Begum, Department of chemistry, P.E.S School of Engineering, Bangalore, Email: [email protected]

Introduction Lichens are small, non-vascular plants consisting of a fungus and an alga growing together in one tissue. The most commonly known lichens are those that are found on the bark of trees, or the reindeer lichens growing on the ground, but many other species grow on rocks, fences, roofs, tombstones, and other man-made objects. Even though some lichens are extremely tough and grow in very inhospitable habitats, they are also notoriously sensitive to air pollutants, primarily sulfur dioxide and heavy metals. Lichen deserts, a phenomenon where lichens disappear from cities, were described over a hundred years ago and determined to be caused by sulfur pollution. Lichens are especially sensitive to air pollutants because they have no outer impermeable layer of tissue to exclude gases and particles that impair their metabolism. Consequently, accumulation of pollutants is greater than it is in the foliage of vascular plants, which have impermeable cuticles. Lichens accumulate unusually large amounts of deposits, including heavy metals, which eventually reach toxic concentrations. Lichens are therefore excellent bioindicators and biomonitors. As bioindicators, the presence/absence of sensitive species is used to look for distribution patterns that reflect pollutant deposition. Voids in distributions may indicate whether lichens have died out due to heavy metals and/or sulfur oxide pollution. These observations are determined by conducting taxonomic inventories or surveys, which include sampling many species in many localities in the study area. Lichens that do not die out, but are still present and are known to accumulate trace elements are used to indicate patterns of deposition. Common species that are found in most localities are used to facilitate collecting enough samples geographically. Many lichens are collected in bulk in a locality to avoid collecting an anomalous sample that might falsely suggest that a hot spot is present. The samples are typically cleaned of extraneous material, not washed, ground to a fine powder, and analyzed chemically for elements of interest. Typically, both nutritional and anthropogenic elements are included to evaluate the health of the lichens as well as for enabling a geographic study of deposition.

Data collection and analysis Lichens from all the available tree species were collected from Agara lake during February 2008. The lichens were carefully removed from the bark

snapper blade and were oven-dried to a constant weight at 80°C. The dried lichen samples (three replicates) were then powdered (0.5g) for further metal analysis. Lichen samples were extracted and analysed with (aqua regia) a mixture of concentrated HCl and HNO3 (3:1) and digested to 80°C, few drops of perchloric acid is added. The mixture was filtered through Whatman filter paper No. 42. The filtrate was diluted to the desired volume with de-ionised water. The total concentrations of Cr, Pb, Fe, Zn, Ni and Cu in the filtrate were determined by atomic adsorption spectrometer Different concentrations dissolved in distilled water

of the air-dried Soil Samples

were analysed for

pH, Alkalinity,

CO2 and

Dissolved Oxygen. Table showing Heavy Metal Concentration in Litchens species of Agara lake Lichen Species

Heavy Metal Concentration µg g–1 dry weight Cr

Pb

Fe

Zn

Cu

Ni

C. candelaris (L.) Laundon

23.50

1.55

7556

95.76

23.72

460.01

D. consimilis (Stirton) Awasthi G. scripta (L.) Ach.

22.5

21.92

7081

198.14

22.32

453.70

35.59

12.30

863

384.55

10.06

600.76

leucosorodes Nyl.

14.4

49.15

7085

79.86

21.25

460.01

P. cocoes (Swartz) Nyl.

15.36

10.40

9795

224.6

19.32

600.54

D. aegialita (Afz. in Ach.) Moore L. perplexa Brodo

2.44

2.44

7281

322.39

20.21

720.34

24.26

19.32

265

531.5

7.37

644.10

picture Showing Heavy metal level in Litchen Species

1.C. candelaris (L.) Laundon 2. D. consimilis (Stirton) Awasthi 3. G. scripta (L.) Ach. 4. leucosorodes Nyl. 5. P. cocoes (Swartz) Nyl. 6. D. aegialita (Afz. in Ach.) Moore 7. L. perplexa Brodo

Results and Discussion

The heavy metal analysis of (Table) various species of lichens collected, analysed and identified in the Agara Lake is reported. It is observed that the heavy metal pollution is maximum and above permissible limits in Agara Lake due to heavy sewage and municipal discharge(untreated).

Conclusions Monitoring of heavy metals through Litchen Species provides efficient way to

assess

the

qualitative

and

quantitative

differences

in

metal

concentrations at distinct locations and on local and landscape scales. Under the present ecological conditions the heavy metal load is significant in Hosur Road, Bangalore. The studies on lichens with particular reference to impact of air pollutants on them are valuable to society and a well established scientific endeavor. This work should be supported wherever possible. Academia, government, industry, and the public are all involved and affected by this.