International Journal of Environmental Science and Development

Abstract—Use of vegetation as a bioindicator of atmospheric heavy metal accumulation has received more attention worldwide due to the fact that this method has been found to be effective, cheap and simple to use. This study aims to find out the levels of heavy metals found in tree bark layers and to test the factors (exposed sides of tree to traffic and size of tree trunk) that affect atmospheric heavy metal accumulation in the bark of Cassia fistula, which is a common tree commonly found along the road sides and planted for shading and decoration. In order to provide the necessary information with regard to using a native tree species as a bioindicator, heavy metals emitted from road traffic including Cr, Cu, Fe, Ni, Pb and Zn were investigated. The results showed that only Cu, Fe and Zn were detected. Their concentrations were highest in the cork layer, decreased in the second (chlorenchyma), third (phloem) layers and increased in the innermost layer (vascular cambium). Heavy metals found on the outer most layer of bark definitely came from atmospheric pollution due to direct exposure to the environment. However, the concentrations in the vascular cambium were higher than in the chlorenchyma and phloem. This is probably due to some diffusion that took place in the xylem, which is connected to the cambium layer. Concerning the factors affecting the heavy metal accumulation in the tree bark, the size of Cassia fistula tree trunks (5 - 30 cm) was not significantly correlated (p > 0.05) with the heavy metal concentrations found in the bark. This was also true of the sides of the exposure of the tree in relation to the traffic source. This means that the bark sampling can be done easily without any limitations with regard to the size of tree trunk and direction of exposure.

Index Terms—Tree bark, heavy metal, bioindicator, Cassia fistula, atmospheric pollution.

Rungruang Janta and Munetsugu Kawashima are with Environmental Science Program, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand (e-mail: rrjanta@yahoo.com).
Somporn Chantara is with Environmental Science Program, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand. Somporn Chantara is also with Chemistry Department, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand (e-mail: somporn.chantara@cmu.ac.th).
Angkhana Inta is with the Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
Kenichi Satake is with the Faculty of Geo-Environmental Science, Rissho University, Saitama 3600194, Japan.

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Cite: Rungruang Janta, Somporn Chantara, Angkhana Inta, Munetsugu Kawashima, and Kenichi Satake, "Levels of Road Traffic Heavy Metals in Tree Bark Layers of Cassia fistula Tree," International Journal of Environmental Science and Development vol. 7, no. 5, pp. 385-388, 2016.