Ecological and human health risks assessment of heavy metals in vegetables grown in palm oil mill effluents irrigated farmland

This study evaluated the impact of heavy metal contents in vegetables grown in a palm oil mill effluents (POME) irrigated farmland on the biomes and well-being of humans that consume the vegetables. In this study, POME, a soil sample from POME irrigated farmland, and selected vegetables were evaluated. The results showed high cadmium (Cd), chromium (Cr), lead (Pb), nickel (Ni),) and arsenic (As) and lower zinc (Zn) and copper (Cu) concentrations in POME relative to their respective permissible limits. The soil irrigated with POME had elevated levels of metals, comparable to the control soil, whereas vegetable growing in POME irrigated farmland contained increased amounts of most of the heavy metals above their respective permissible levels in edible vegetables. The plant concentration factors (PCF) of heavy metals detected in the vegetables were less than one except for V. amygdalina with PCF>1 for cobalt. The pollution load index of Cd, Cr, Cu, Co, and As in the POME soil were above 50, while high enrichment factors were obtained for Cd, Cr, Pd, Co, and arsenic. The geoaccumulation index indicated that the POME soil was strongly contaminated by Zn, Fe, Pb, Mn, Ni and extremely contaminated with Cd, Cr, Zn, Cu, and Co. The metals levels ingested daily from the vegetables were low, comparable to their respective oral reference doses except for Mn in V. amygdalina and As in most of the vegetables. There was a high target hazard quotient for Mn, and As in most of the vegetables with hazard index (H.I.) >1 in each of the vegetables and increased cancer risk for Cd, Cr, Pb, Ni and As toxicity coupled with very high total cancer risks. These findings show that irrigation of farmlands with POME raises the heavy metal levels in vegetables and the risk of heavy metal toxicity.