Mobility, bioaccessibility and toxicity of potentially toxic elements in a contaminated soil treated with municipal solid waste compost

Abstract

The aim of this study was to assess the influence of a municipal solid waste compost (MSWC) on the mobility, bioaccessibility and toxicity of several potentially toxic elements (PTE), i.e. Pb (15,383 mg kg−1), Zn (4076 mg kg−1), Cu (181 mg kg−1), Sb (109 mg kg−1), Cd (67 mg kg−1) and As (49 mg kg−1), present in a contaminated sub-acidic soil (pH = 5.93).The addition of MSWC at 2 and 4% rates significantly decreased the labile fractions of PTE (with the exception of Cu and As) and at the same time increased the residual fractions of Zn and Sb. In-vitro tests also showed that compost amendment was able to decrease Cd and Cu gastric bioaccessibility, with respect to untreated soil (−19 and 13% of Cd and Cu in MSWC-4% respectively), while a significant increase of As intestinal bioaccessibility was recorded. This increment was attributed to the pH rise (up to 7.0) during the in-vitro intestinal phase, which likely favoured a release of the arsenic non-specifically bonded to MSWC. Soil enzyme activities, i.e. dehydrogenase and β-glucosidase, were significantly enhanced in MSWC-amended soils (i.e. up to ~6.0 and 1.4 times higher in MSWC-4% than in control soil, respectively), as well as soil basal respiration, and the potential metabolic activity and catabolic versatility of soil microbial communities (as assessed by the Biolog ecoplate community level physiological profile).Overall, the results obtained suggested that MSWC, particularly at 4% rate, could be useful to stabilise PTE in sub-acidic contaminated soils and to increase the microbial activity and functionality in these latter soils.