EFFECTS OF QUARRYING ACTIVITIES ON SOIL QUALITY AND NUTRITIONAL COMPOSITION OF SELECTED VEGETABLES IN SOUTHEASTERN NIGERIA

This research work assessed the effects of quarrying activities on soil quality and nutritional composition of fluted pumpkin (Telferia occidentalis) and smooth pigweed (Amaranthus hybridus). Soil and vegetable samples were collected from three quarry and rock crushing sites. Soil samples were analyzed for various physicochemical parameters, soil nutrients and metals (NO3, PO4, Nitrate, Sulphate, Cu, Zn, Cr, Ni, Pb, Cd, Mg, Fe, Ca, Mn, K, Na) using standard analytical methods. Proximate composition and trace metal content of Telferia occidentalis and Amaranthus hybridus were also evaluated using Atomic Absorption Spectrophometer (ASS). Results obtained revealed deterioration of soil quality near the quarries, with significantly high levels of Cu, Zn, Ni, Pb, Cd, Fe and Mn recorded. In general, the mean concentration of heavy metals in soils from the rock quarries decreased in the order of: Fe>Mn>Cr>Pb>Cu>Ni>Zn>Cd. Values for Iron (Fe) in the soil samples ranged between 1667.36 ± 1.15 mg/kg in Quarry 1, 1635.03 ± 1.15 mg/kg in Quarry 2 and 1734.79 ± 11.55 mg/kg in Quarry 3. The average concentrations of Nickel (Ni) in soil samples collected from Quarries 1, 2 and 3 were 9.22 ± 0.06, 8.68 ± 0.08 and 7.53 ± 0.12 respectively. Soil Ni content was found to be higher than the WHO (2017) recommended limit of <1 mg/kg. Soil levels of TOC, NO3, PO4, Nitrate, Mg, Ca, K and Na were below the guidelines for maximum limit in soils. Proximate analysis of the vegetables cultivated in the quarry environs showed high contents of protein and dietary fibre. While the concentration of Ni was within permissible limit in the vegetables, Cr values exceeded recommended levels. Findings from this study indicate that residents of the quarry areas are exposed to contaminated soil and health risks associated with consumption of accumulated toxic contaminants in edible vegetables.