Annual Ring Analysis of Tamarindus indica Linn. As Indicator of Lead Increasing in Road Enviroment

Abstract

Lead in the road environment is spread almost exclusively by cars. Yearly increasing of traffic intensity will result in yearly increasing of lead accumulation in the road and adjacent areas. This study was taken to determine if Tamarindus indica Linn. Grown beside Rajdamnoen Nai road for many years, would reflect the higher lead accumulation in the successive annual rings; whether lead content in the annual rings could serve as biological indicator of lead in creasing in the road environment; and whether the variation in width of annual growth rings could constitute a rainfall almanac. Two tree samples of T. indica of at least 74 years old and 56.2 and 53.4 cm. in dimeter, were sawn off at 1.30 m. above ground level into two disks. The lead content of successive annual rings which covered 25 years from 1953-1977 was determined using dry ashing method and wet digestion in a mixture of nitric acid and perchloric acid. Analyses were made with an atomic absorption apectrophotometer. The variation in width of annual rings was measured employing cross-dating method. The fourth radius of the tree trunk which faced the road, showed the variation of lead content in the annual rings around 1.3-2.9 ppm. [dry weight] from 1953-1972. After 1972, lead level in the annual rings increased remarkably from 2.4 to 7.6 ppm. For the period 1953-1977, five year segments of more recently formed annual rings had a higher lead content than older ones. Hence, lead content in the annual rings of T. indica may serve as biological indicator of lead increasing in the road environment. However, many processes governing the radial transportation and deposition of lead within trees are poorly understood. The variation in width of growth rings which cover the period 1938-1977, could not constitute trees, crown pruning and the tree species.