Long-term influence of a municipal solid waste compost on the functionality and biodiversity of a soil contaminated with potentially toxic elements

The use of organic amendments to restore the functionality and biodiversity of sites contaminated by potentially toxic elements (PTEs), such as abandoned mining lands, represents one of the most modern eco-sustainable strategies. Short-term laboratory-scale studies showed that compost from municipal solid waste (MSWC) can reduce PTEs mobility and increase soil fertility, functionality, and plant growth. However, its long-term impact in the open-field has been rarely evaluated (and is essentially unknown). For this purpose, different biochemical and microbial endpoints and plant diversity were evaluated six years after the addition of different MSWC amounts to a PTE-contaminated mine soil (i.e., Sb 416 mg·kg⁻¹; Pb 2653 mg·kg⁻¹ and Zn 7666 mg·kg⁻¹). The addition of increasing amounts of MSWC (i.e., 0.0 %; 1.5 %, 3.0 %, and 4.5 % w/w: T0, T1, T2, and T3, respectively) enhanced microbial respiration (e.g., ~ 5.1-fold in T3 compared to T0) as well as selected enzyme activities (e.g., dehydrogenase ~12-fold, β-glucosidase ~11-fold and urease ~4-fold in T3 compared to T0, respectively). Moreover, the bacterial communities of MSWC-treated soils showed a higher Shannon α-diversity index compared to T0. Surveys of the vegetation in the field identified 56 plant species, with therophytes as the dominant life form (61 %). Non-metric multidimensional scale and Permanova analysis revealed differences between the vegetation of the amended and control plots, but not between the plots amended with different MSWC amounts. Overall, MSWC addition can be an effective and long-lasting environmental management strategy to improve soil fertility and promote the restoration of (micro) biological function and diversity of PTE-contaminated soils.