Physicochemical properties and ecological and human-health risk assessment of soil-like material excavated from a stabilised municipal solid waste landfill on the Xizang Plateau

Abstract Landfill mining is promoted to reclaim land and recover resources from legacy waste, but re-use of its fine, humus-rich fraction, soil-like material (SLM), is constrained by scarce information on its properties and risks at high altitudes. We characterised SLM excavated at 0–5 m depths from the stabilised Lhasa municipal solid waste landfill (Xizang, 3,670 m a.s.l.) and assessed heavy metal contamination, ecological risk and human-health risk using contamination factors, geoaccumulation indices, Hakanson's potential ecological risk index and the USEPA exposure model, with 20,000 Monte Carlo iterations. SLM accounted for 61.2 ± 4.6% of the excavated waste and was slightly alkaline (pH 7.76–8.11), strongly humified and nutrient-rich (SOM 47.5–96.6 g kg⁻¹; available K 978–2,541 mg kg⁻¹; humic-acid/fulvic-acid ratio 5.0). Mean metal concentrations met the Chinese agricultural screening values (GB 15618 − 2018), but Cr, Cd and Hg were enriched 2.2–3.3-fold over the local background, giving a potential ecological risk index of 215.8 (moderate hazard) dominated by Hg (60.5%) and Cd (30.2%). Non-carcinogenic risk exceeded the USEPA threshold only for children (HI = 1.55; Cr 70%, As 22%); Monte Carlo gave an 85% probability that the child HI exceeds unity, whereas total carcinogenic risk (2.1 × 10⁻⁵ for adults; 3.1 × 10⁻⁵ for children) remained acceptable in over 99.5% of simulations. SLM is therefore unsuitable for direct agricultural or residential use but suitable for non-food biomass, landscaping substrates and landfill cover after blending and monitoring of Hg, Cd and Cr speciation.