Selected Heavy Metals as Indices of Atmospheric Pollution in African Locust Bean (Parkia biglobosa) Tree Barks

Metallurgical industries are pollution “hot spots” for emission of dust, particulates of heavy metals and gaseous contaminants at levels that can be injurious to man and environment. The atmospheric levels of selected heavy metals around Ajaokuta Steel Company Nigeria were assessed using barks of Parkia biglobosa trees. The tree barks were randomly collected during wet and dry seasons, sorted and digested according to standard methods. Heavy metals were analysed using flame atomic absorption spectrophotometer (Unicam 969, UK). The mean concentrations (mg/kg) of metals in P. biglobosa tree barks were 33.23±5.03, 12.98±1.24, 3.65±0.69, 1.65±0.36, 1.20±1.16, 0.55±0.10 and 0.33±0.16 for Zn, Mn, Pb, Cu, Ni, Cr and Cd respectively. The concentration distribution sequence in barks are in the order Zn > Mn > Pb > Cu > Ni > Cr > Cd. Zn with the highest level ranged between 26.39±5.24 and 40.93±4.64 mg kg^-1 relative to other metals. There was significant difference (p<0.005) between metals’ concentration in tree barks during the dry and the wet seasons, with Zn and Mn showing about 5-15% variation, while corresponding values for Cd, Cr and Pb were not significantly different.