Assessment of Vehicular Emissions Effect on Some Heavy Metal Content of Hyptis Suaveolens (L.) Found along Zaria-Giwa Road, Kaduna State, Nigeria

Abstract

Studies on lead, cadmium, copper and zinc content in different parts of Hyptis suaveolens was carried out along Zaria-Giwa road, Kaduna state, Nigeria. The different organs of the plants (roots, stems and leaves) were collected at four different locations namely: Ahmadu Bello University Teaching Hospital (ABUTH), National Animal Production Research Institute (NAPRI Shika), Marabar Guga and along Ahmadu Bello University Dam Quarters (control), which were characterized by dense, high, medium and low traffic densities respectively. The samples were collected at distances of 0, 5, 10, 20, 40 and 100 m away from the edge of the road. Atomic absorption spectrophotometer (A.A.S.) was used in the determination of the metal ions concentration in the samples. The data obtained were subjected to Analysis of Variance (ANOVA), Pearson correlation was employed in determining the correlation between the heavy metals in the soil and the different organs of the plants. The heavy metals had higher concentration at roadside (0) m and this decreased progressively with increase in distance away from the roadside. However, the region of higher concentration was mostly at 0 and 5 m from the roadside. The ranges of the metal concentrations in H. suaveolens were: Pb (11.52-24.31 mg/kg), Cd (1.45-3.39 mg/kg), Cu (4.41-22.35 mg/kg) and Zn (11.43-68.77 mg/kg). Highest metal concentrations in H. suaveolens were recorded at ABUTH, however, the high level of Pb and Cd were observed in the roots while Cu and Zn were observed in leaves. The concentrations of the heavy metals in all the organs of the plant were in the order of: Zn > Pb > Cu > Cd. Heavy metal concentrations in the plant samples from ABU Dam quarters (control) were significantly lower than those of other locations. In conclusion, distance from the roadside and vehicular densities of the sampled locations had a significant effect on the lead, cadmium, copper and zinc concentrations in the different organs H. suaveolens. Also, there was a significant positive relationship between the heavy metal concentrations in the soil and the different organs of the plant