Stabilising fluoride in contaminated soils with monocalcium phosphate and municipal solid waste compost: microbial, biochemical and plant growth impact

This study evaluated the influence of a municipal solid waste compost (MSWC) and monocalcium phosphate (MCP), alone or combined, on the mobility, toxicity, bioavailability and health risk of fluoride (1000 mg F−·kg−1) in an artificially polluted soil (pH 7.85). The addition of MCP (0.2% w/w) and MSWC (1% w/w) (alone and combined) to the contaminated soil reduced water-soluble (e.g. by more than 50% in MCP and MCP + MSWC-treated soils) and exchangeable F− fractions and increased the residual one. The addition of MSWC and MSWC + MCP to the contaminated soil significantly increased microbial biomass C (SMB-C; 1.3–3.6-fold) while all treatments increased the abundance of culturable heterotrophic bacteria (up to twofold in MSWC + MCP). Overall, dehydrogenase, β-glucosidase, urease and phosphomonoesterase activities were enhanced in treated soils and positively correlated with SMB-C, but not with labile F−. All treatments increased carrot yield (up to 3.4-fold in MSWC + MCP), while bean growth was significantly enhanced only by MCP and MCP + MSWC (~ twofold). The opposite trend applied for F− uptake which was especially reduced in the edible part of carrot after soil amendment. A limited influence of MCP and MSWC on hazard quotient (HQ), due to bean and carrot consumption, was also recorded (i.e. HQ generally > 1). Results suggest that MCP and MSWC can be used in the recovery of soil chemical, microbial and biochemical status of F-rich agricultural soils. They also indicate that the bean and carrot cultivars employed in this study are likely unsuitable in such soils due to high F− uptake in edible parts.