The risk assessment for metal(loid)s in soil-slag mixing systems: Coupling sequential extraction, leaching tests, and...

The metals and metalloids (metal[loid]s) in the newly formed soil-slag mixing systems (SSMS), formed by the invasion of smelting slag into contaminated soils, may pose potential risks to environment and residents near the smelter sites. In this study, sequential extraction, leaching tests and in vitro bioaccessibility assays were conducted to assess the ecological and human health risk of metal(loid)s in SSMS. The results indicated that the contaminated soils and smelting slags were composed of more than 80 % silicate and oxide minerals, which served as the host phases for metal(loid)s in SSMS. Cd exhibited high mobility and availability, with its exchangeable fraction ranging from 0.15 % to 69.23 %. Leaching tests revealed high leachability and bioavailability of Cd, Mn and Zn. Moreover, metal(loid)s bioaccessibility varied amongst samples: 2.78-46.63 % of As, 11.87-95.25 % of Cd, 37.35-93.88 % of Mn, 1.97-87.84 % of Pb and 0-57.98 % of Zn. Risk assessment calculation results indicated potentially ecological risks posed by Cd, Mn, Pb, and Zn, and unfavorable carcinogenic risks associated with As and Cd, suggesting that remediation efforts were warranted. Overall, this study highlighted how the invasion of smelting slags can affect the accuracy of risk assessments, providing new guidance for risk control and environmental management at slag dumping sites.