Transforming Lead-Contaminated Soil into Fertile Land by Recycling Phosphogypsum

Abstract

The presence of lead (Pb) in soil affects the environment and public health and causes serious issues as it is persistent, toxic, and bioaccumulates in the food chain. Traditional soil lead remediation methods are expensive and scale poorly. In this study, we explore an integrated and sustainable approach to remediation that combines phosphate-solubilizing fungal bioremediation with chemical stabilization. The bioremediation uses Aspergillus niger, while the chemical stabilization uses phosphogypsum, an industrial waste product from phosphate fertilizers. A 60-day laboratory study was conducted to assess the effects of fungal inoculation and phosphogypsum amendment, and their combination, on Pb-contaminated soil (300 mg/kg Pb).  Lead bioavailability was determined using diethylene triamine penta-acetic acid (DTPA) extraction and subsequent measurement by atomic absorption spectrophotometry. Treatment results showed significant lead bioavailability reduction, and the combined approach was the most effective, with an estimated 65% reduction of Pb following 60 days of treatment. Enhanced reduction is due to bioaccumulation, organic acid production of the fungus, and lead biosorption which, in combination with phosphogypsum, precipitates lead into stable minerals, such as pyromorphite. Additionally, the integrated treatment improved soil biological activity and stability. The findings highlight the potential of this bio-chemical approach as a cost-effective, scalable, and environmentally sound solution for rehabilitating lead-contaminated soils while promoting circular economy principles through industrial waste reutilization, particularly in regions affected by heavy metal pollution such as Iraq.