The concentration, distribution and health risk from potentially toxic elements in the soil - plant - water system developed on black shales in SE Nigeria

Potentially toxic elements (PTEs) are present in some natural geological materials and the black shales of southeastern Nigeria provides an example of this. The concentration and distribution of these PTEs such as Cd and Pb in shale rocks and soil-water-plant systems are spatially examined in this study. Geochemical surveys were undertaken in 6 shale formations. Some PTEs are highly enriched in the black shales (Mo, Se, Tl, and Zn) and soils (As, Cd, Cr, Cu and Zn). Acknowledged pollution indices revealed various levels of soil, water and crop plants contamination by PTEs. Distribution of PTEs may be attributed to differences in geochemical nature of shale formations and degree of weathering. The concentrations may also be modified by varying degree of pedogenetic processes that may lead to mobility and redistribution of PTEs in soil. Health risk assessment of the population, based on the Hazard quotients (HQ) and indices (HI), identified minimal or no risk for drinking water consumption in the area. The cancer risk from As for individuals exposed through the soil and stream water pathways did not exceed the acceptable risk of 1 in 10,000 set for regulatory purposes. This study has provided data for the development, demobilization and implementation of a monitoring system and management of PTEs from shale bedrock.