Pb, Zn, and Cu levels in tree barks as indicator of atmospheric pollution

Barks of seven species of trees were sampled at 32 locations having different pollution levels in Abeokuta, Nigeria. The concentrations of Pb, Zn, and Cu were determined by atomic absorption spectrometry. The Pb and Zn contents, 1.9-159.8 and 16.5-659.1 micrograms g-1, dry weight respectively, correlate with traffic volume, indicating pollution from anthropogenic sources. The results obtained for Cu, 4.2-20.7 micrograms g-1, dry weight, though lower, were still significant but did not show any correlation with traffic density. The study also confirms the suitability of Azadirachta indica (Dogoyaro--a very popular local tree) as a suitable bio-indicator of aerial fallout of heavy metals.