Purpose Constructed soils are Technosols resulting from the deliberate combination of various artefacts. Similarly to natural soils, technogenic parent materials are transformed by pedogenic factors contributing to their evolution. This work was conducted to study the first stages of the pedogenesis of constructed soils. Materials and methods Two soils were constructed in lysimetric plots (10 × 10 m) using an engineering process by the combination of paper-mill sludge, thermally treated soil material and green waste compost. Evolution of the soil profiles, composition of soils and leachates were studied for 3 years. Results and discussion A strong evolution of the profiles was observed over the 3 years with rapid changes in the number and characteristics of the horizons. Significant changes in chemical weathering (decarbonatisation) and physical status (aggregation), i.e. processes similar to those occurring in natural soils were observed. Other processes specific to the technogenic materials were recorded, e.g. massive dissolution of gypsum or drainage of constitutive water. Apart from constructed Technosols classification, prediction was made on their future pedogenic evolution. Conclusions Constructed Technosols made of finely divided reactive organic and mineral compounds were observed to evolve quickly. Evidences of original pedogenic processes have been highlighted that could be considered as a general diagnostic characteristic of Technosols. Finally, some considerations about the application of the World Reference Base for Soil Resources to the classification of Technosols are proposed, taking into account some aspects of their pedogenesis that have been highlighted by our work.

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Due to human activities, large volumes of soils are contaminated with organic pollutants such as polycyclic aromatic hydrocarbons, and very often by metallic pollutants as well. Multipolluted soils are therefore a key concern for remediation. This work presents a long-term evaluation of the fate and environmental impact of the organic and metallic contaminants of an industrially polluted soil under natural and plant-assisted conditions. A field trial was followed for four years according to six treatments in four replicates: unplanted, planted with alfalfa with or without mycorrhizal inoculation, planted with Noccaea caerulescens, naturally colonized by indigenous plants, and thermally treated soil planted with alfalfa. Leaching water volumes and composition, PAH concentrations in soil and solutions, soil fauna and microbial diversity, soil and solution toxicity using standardized bioassays, plant biomass, mycorrhizal colonization, were monitored. Results showed that plant cover alone did not affect total contaminant concentrations in soil. However, it was most efficient in improving the contamination impact on the environment and in increasing the biological diversity. Leaching water quality remained an issue because of its high toxicity shown by micro-algae testing. In this matter, prior treatment of the soil by thermal desorption proved to be the only effective treatment.

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