Potential human health risk assessment of heavy metals intake via consumption of some leafy vegetables obtained from four market in Lagos Metropolis, Nigeria

Abstract

This work investigated six heavy metals (Pb, Cr, Zn, Cd, Ni and Cu) accumulation in five popular leafy vegetables: Telferia occidentalis (fluted pumpkin), Talinum triangulare (waterleaf), Ocimum gratissimum (scent leaves), Celosia argentea (plumed cockscomb), and Amaranthus viridis (slender amaranth) obtained from 4 popular markets in Lagos metropolis using an atomic absorption spectrophotometer (AAS), and evaluate the human health risks of their consumption. Heavy metals content in vegetables across the markets ranged as follow; Cd (0.05 – 0.20 mg/kg); Pb (0.34 – 5.44 mg/kg), Zn (4.21 – 20.80 mg/kg), Cr (0.25 – 1.51 mg/kg), Ni (0.13 – 2.91 mg/kg) and Cu (2.34 – 14.08 mg/kg). The concentrations of all metals are quite generally lower than the permissible levels by FAO/WHO in vegetables except for Pb. Statistical analysis of levels of the studied metals in A. viridis, T. occidentalis, C. argentea, and O. gratissimum in all the markets sample showed significant differences in levels of Zn, Cr, Cu and Ni (p<0.05). To assess the the health risk of the inhabitants of Lagos and the environs due to heavy metal intake from these vegetables consumption., the daily intake of metals (DIM), health risk index (HRI), and target hazard quotient (THQ) were calculated. The daily intake of metals in vegetables species for Zn (0.51 – 1.46 mg/kg) and Ni (0.05 – 0.22 mg/kg) are significantly lower than the recommended daily intake of metals and the upper tolerable daily intake level (UL). However, DIM of Cd (0.004 – 0.017 mg/kg) and Pb (0.046 – 0.182 mg/kg) exceed the recommended DIM but fall within the upper tolerable daily level. Cr (0.048 – 0.082 mg/kg) is lower than the recommended oral reference dose (RFD) of 1.5 mg/kg (USEPA, 2010). The THQ values range showed that Cd was 0.048 – 0.192, Pb was 0.150 – 0.587, Zn was 0.021 – 0.190, Cr was 0.0001 – 0.001, Ni was 0.050 – 0.120 and Cu was 0.148 – 0.239. This result reflected the risk associated with exposure for the period of life expectancy considered, and the inhabitants are highly exposed to health risks associated to these metals in the order Pb > Cu > Cd > Ni > Zn > Cr. The THQ in all metals is less than 1 in all the vegetables species; therefore, it does not pose serious health risk concern. However, vegetable consumption was just one part of food consumption, the potential health risks for residents might actually be higher than in this study when other routes of heavy metals intake are considered.

Keywords: Heavy Metals, leafy vegetable, daily intake of metals, health risk index, target hazard quotient (THQ), zinc, lead, chromium, cadmium, nickel, copper