Potentially harmful elements and their health implications in cultivable soils and food crops around lead-zinc mines in Ishiagu, Southeastern Nigeria

Abstract

This study assessed the concentrations of potentially harmful elements (Cu, Pb, Zn, Mo, Ni, Co, Cd, Cr, Mn and As) in agricultural soils and plants (tubers, fruity and leafy vegetables) and their possible health risk implications on human in the lead-zinc mining districts of Ishiagu, Nigeria. The concentration of potentially harmful elements in the soils varies according to the order Pb > Mn > Zn > Co > Cu > Ni > Cr > Cd > As > Mo. The potential ecological risk assessments show that the agricultural soils are contaminated by Pb, Zn and Cd and exceeded recommended limits. The concentration of Pb and to some extent Zn, Cr and Cd are higher in the leafy vegetables compared to the tubers and exceeded EU and WHO/FAO maximum allowable limits. Plant concentration factor (PCF) was identified to be higher in Cd, followed by Zn > Cu > Mo > Cr > Ni > Pb > Mn > Co > As. The Daily In-Take of Metals (DIM) values for the PHEs through the ingestion of tubers, fruit, and leafy vegetables were generally below 1; the sequence of DIM values for adults and children for all the plants studied in the order: Zn > Mn > Pb > Cu > Cr > Ni > Cd > As; also, the DIM values were higher for the children compared to the adults, in consistent with the observation of previous workers. The DIM values for Pb, Mn and Cd for all the plants exceeded the USEPA IRIS (2006) threshold limits. The health risk indices indicate that Pb, Mn and Cd contamination in the food crops have greater potential to pose serious health risk to the consumers, including decrease in immune system and dysfunction of vital organs, rise in Pb levels in the blood of children, kidney damage and development of carcinogenic cells in the body, with more prevalence in the leafy vegetables. Development and implementation of effective monitoring and regulation of the activities of mining industries and land use types in the area, massive sensitization campaign for the inhabitants and miners on mining best practices, are recommended for reducing these negative effects of mining in the environment; application of lime-rich soils can be adopted to limit the mobility of the PHEs to some extent.