Levels of heavy metals on bark and fruit of trees in Benin City, Nigeria

Samples of bark of 29 trees of five different species were obtained from different locations in Benin City, Nigeria, where a traffic census was also conducted. The samples were analysed for trace heavy metals, lead, zinc, cadmium and copper. Rind or skin of some fruits obtained from the trees was also analysed for the metals. Levels of lead deposits in all cases, and zinc in a number of cases, were found to vary according to traffic volume; high levels (58·3–143·5 μg g^dash1 Pb, 26·8−102·7 μg g⁻¹ Zn) were recorded for areas of very high traffic volume and low levels (15·2−15·8 μg g⁻¹ Pb, 5·8−6·9 μg g⁻¹ Zn) for areas of low traffic volume. It was found that the rougher the tree bark, the higher the deposit for each species. There was no definite correlation between traffic volume and level of cadmium and copper deposits on the tree bark.