Speciation, bioavailability and human health risk of heavy metals in soil and spinach (amaranthus spp.) in Kano Metropolis, Northwestern-Nigeria

Abstract

The rapid population growth and industrialization affected the environment momentously and one of the most noteworthy impacts is the toxicological effect of toxic chemical pollutants. The noxiousness of toxic heavy metals to ecosystem rests on their biochemical form therefore, measuring their chemical status gives more information than the determination of the concentration. This research aimed at assessing the chemical forms of heavy metals and ecological effects. Eight soil and spinach samples were collected using point composite sampling method. The soil was analyzed using five stages of sequential extraction methods. The results were subjected to statistical analysis to carry out a descriptive and inferential statistic. The results revealed that significant fraction of the heavy metals exist in carbonate bond form (63.57%) which is accessible to plant, then residual (11.46%), Fe – Mn oxide (9.39%), organically bond (8.12%) and, exchangeable form (7.53%), furthermore, Ni (100.02 mg kg-1) and, Pb (29.02 mg kg-1) have the highest concentration in the spinach. The bioavailability of chemical pollutants ranked in this direction as: Ni > Cd > Pb > Zn & Cu > Cr. The high potential of non-carcinogenic effect by Ni and the carcinogenic effect in the area due to elevated values of risk proportion and risk guide. The available form of heavy metals is present in substantial proportion and consequently, there is serious threat with regard to the carcinogenic effect.