Heavy metal risk assessment on the consumption of Talinum triangulare grown on sewage dump site in University of Nigeria, Nsukka

Abstract

Consumers, in most cases, consider dark green and broad leaves as good or healthy quality leafy vegetables safe for human consumption, unfortunately most of these vegetables may be cultivated in soil rich in heavy metals from sewage. This study investigated the health risks of heavy metal build-up in vegetables Talinum triangulare grown on sewage dump site. Soil samples were collected at 15 cm with the aid of soil auger and vegetable samples were collected from sewage dumpsite and other samples from a farm where there were no sewage dumpsite served as control. The soil samples were collected at random to have a represented sample and analyzed for Physicochemical properties, pH, Total Nitrogen, Total phosphorus, Organic matter, total organic Carbon, and Exchangeable cations (K+, Mg+ and Na+) using a standard method and concentrations of the Heavy metals both in soils and vegetables, Cr, Zn, Pb, Cu, and Ni were analyze using Atomic Absorption Spectroscopy (AAS). The health risk from the consumption of these vegetables was calculated using standard methods and formula. The result showed a significant (p<0.05) increase in physicochemical properties for sewage soil, over the control. The pH of the Dump site and Control site were 5.19 and 6.95, respectively. The mean concentrations of metals (Cr, Zn, Pb, Cu, Ni) in the dump soil were 2.05, 1.03, 0.61, 0.58 and 0.42 mg/kg and in the control with no dump were 0.67, 0.07, 0.06, 0.20 and 0.24 mg/kg respectively. The mean values recorded were below the maximum permissible limit of metal in the soil by (WHO/FAO) with Cr (100), Zn (300), Pb (50), Cu (100) and Ni (50 mg/kg). The levels of Cr, Zn, Pb, Cu, and Ni in sewage dump Talinum triangulare were 2.04, 0.33, 0.37, 0.34, and 0.20 mg/kg and the control site were 0.01, 0.05, 0.00, 0.17, and 0.11 mg/kg respectively. However, the levels of Cr and Pb in the vegetable were above the levels recommended by WHO/FAO of Cr (0.3), Zn (27.3), Pb (0.3), Cu (3.0) and Ni (1.63 mg/kg) while Zn, Cu, and Ni were below the permissible limit for metals in vegetables. The values were all significant (p<0.05) compare to the controls samples for both vegetable and soil. The bioaccumulation factor showed that the vegetable exclude the element from soil. The HQ and HI shows that there is no harmful effect since the values obtain were less than >1. But continuous consumption can accumulate in the food chain especially for children. This study conclude that vegetables grown on sewage dumpsites are capable of accumulating high levels of heavy metals from contaminated and polluted soils with deleterious health effects.