Accumulation of Lead (Pb) in the Lichen Thallus of Mahogany Trees in Medan City Road

Abstract

Rapid growth of vehicles in Medan, Indonesia, is one of the causes in the increasing of air pollution, in which approximately 85% is contributed merely by vehicles. On the other hand, the use of lead-based fuel in motor vehicle increases the air contamination in Medan. This study aimed to obtain an accumulation of lead (Pb) in the thallus of lichens in mahogany trees in four different locations in Medan, Sumatera Utara, Indonesia, in which the lichens act as a bioindicator of air contamination as well as measuring the lichen’s lead correlation and traffic densities. Purposive sampling location was determined based on the traffic density level with different air pollutions; the location which was far from traffic circulation was used as the control. The analysis of Pb was conducted using atomic absorption spectrophotometry (AAS). The data were analyzed descriptively to discover and compare Pb accumulation between each location with different traffic density levels. The result showed that there were 11 species of 7 genera and 7 families with two types of the thallus (foliose and crustose) in mahogany trees. The traffic density level influenced the diversity of lichens as the traffic density was quite significant with the number of lichen types. The levels of Pb and traffic density correlated very significantly at the level of α = 0.01 for Parmelia saxatilis, Lepraria incana, and Pertusaria amara type, while Opegrapha atra had a significant correlation. The accumulation of Pb in the thallus of Pertusaria amara ranged from 5.23 to 15.07 μg/g, whereas medium in Lepraria incana ranged from 1.19 to 4.88 μg/g. Thus, Pertusaria amara which had greater Pb level than Lepraria incana had the potential as a resistant bioindicator. The correlation analysis of Pb levels and traffic density showed that Pertusaria amara had a significantly high correlation compared with Parmelia plumbea, Parmelia glabratula, and Graphis scripta. Furthermore, Lecanora conizaeoides was a tolerant bioindicator of air pollution whereas Parmelia saxatilis had the potential to be a tolerant bioindicator.