Heavy metal concentrations in soils and two vegetable crops (Corchorus olitorius and Solanum nigrum L.), their transfer from soil to vegetables and potential human health risks assessment at selected urban market gardens of Yaoundé, Cameroon

Soil contamination by heavy metals has received considerable attention in recent years. In this study, heavy metal accumulation in two vegetable crops (Corchorus olitorius and Solanum nigrum L.) was studied. Assessment of soil properties and seven heavy metals (Zn, Cu, Cd, Ni, Pb, Cr and Mn) in soils and vegetables was done. Heavy metal transfer from soil to plant parts, translocation from roots to leaves and estimated potential health risks of heavy metal to humans via consumption of vegetable crops were studied. The ANOVA test showed that variations in the soil characteristics and heavy metal concentrations were statistically significant at level 0.05. Pearson correlation coefficients showed that the concentration of heavy metals has significant relationships with some soil properties like cation exchange capacity (CEC), organic carbon (OC) and soil texture. Bioconcentration factor (BCF) for both leaves and roots for Zn, Cu, Cd, Ni Cr and Mn were found to be greater than one, indicating the hyperaccumulation nature of vegetables. High translocation (TF) from root to leaves (TF>1) was recorded for Zn, Cu, Cd and Mn. The Health Risk Index (HRI) was found generally less than 1, suggesting that it is not risky for the Yaoundé city inhabitants to consume vegetable crops, except for Cd and Mn in Solanum nigrum L. Total Hazard Health Risk Index (THRI) expressed to know the overall harmful effects on health posed by several heavy metals taken together showed that the value for vegetables studied was higher than 1, suggesting the probability of adverse effects. The health risk is likely to occur for vegetable consumers.