Safety risk analysis of high dosage of phosphogypsum in limestone soil and yellow soil: a case study of potted amaranth

The safe management and sustainable utilization of phosphogypsum (PG) tailings in Guizhou, China, represent a pressing issue. High dosage incorporation of PG into karst soil has emerged as a promising approach. This method not only addresses the long-term storage issue of substantial PG tailings but also has the potential to enhance soil fertility. However, its safety risks to soil and food chain remain unclear. Through pot experiments, we incorporated 10-20% PG into limestone soil and yellow soil from the Karst region. The findings indicated significant increases in soil organic carbon (from 4.12% to 7.87%), and total salts (from 2.80 g/kg to 36.65 g/kg). Additionally, the concentration of potentially toxic elements (PTEs) in the soil did not exceed the established safety standards. The dry weight of Amaranthus tricolor showed a notable increase (from 0.01 g/plant to 0.78 g/plant), although the concentrations of Cu, Zn, and Cr exceeded permissible limits. Furthermore, the pH of the PG-added yellow soil increased significantly (from 5.40 to 6.03), whereas the pH of the limestone soil decreased notably (from 7.18 to 6.93). The microbial diversity analysis revealed PG had a more profound impact on the structural changes in bacterial and fungal communities within the yellow soil compared to the limestone soil, significantly influenced bacterial community composition, reducing saprophytic fungi and plant pathogens within the fungal community. The relative abundance of Bacteroidota and Firmicutes increased significantly in the yellow soil samples, while that of Proteobacteria and Acidobacteria decreased notably. In conclusion, high dosage PG utilization has the potential to enhance soil nutrients and optimize microbial community structures, thereby promoting plant growth. However, it may also lead to PTEs' accumulation, posing potential risks to food chain and ecological security. The study provides basic data for evaluating the environmental and ecological impacts of high dosage PG utilization in karst soils.