Role of phosphorous mining in mobilization and bioaccessibility of heavy metals in soil-plant system: Abbottabad, Pakistan

Abstract

Indiscriminate anthropogenic activities have considerably changed biogeochemical balance of naturally occurring heavy metals and posed serious threat to the environment. The phosphate rock (PR) mine is typically exploited for phosphorus fertilizers in Pakistan. It is mainly composed of phosphorous and minutely of many other elements like heavy metals (HM). This was the first attempt to evaluate the impacts of phosphate rock mining on soil and crop system adjoining PR mining near Abbottabad by growing maize plants due to mountainous nature of the study area. Exchangeable and water soluble forms of the HM were determined in phosphate rock. Results showed a significant increase in the concentration of HM in soil and plant samples. The heavy metal concentrations in soil samples varied in the order of Pb > Cr > Ni > Zn > Cd. The magnitude of metal species in soil samples decreased with the increasing distance from the mine irrespective of the kind of element. Maximum concentration of each metal was found at 20 m distance while minimum at 100 m distance from the mine. Phosphate mining enhanced HM concentrations in all parts of the maize plants. Plant parts differed in HM accumulation in the order: root > shoot > grain. The fields nearer to the PR site showed higher HM concentrations in plant parts. The results revealed that maize plants showed TF > 1.0 for Cd, while TF values for other heavy metals are Pb > Zn > Ni > Cr. Biological accumulation factor was higher for Cd, Pb, and Zn as compared with Cr and Ni. The results show that growing crops near PR mines is producing tangible impacts on soil-plant system thereby entering food chain and affecting the human and animal health.