Technosols include soils dominated or strongly influenced by human-made materials. Similarly to natural soils, technogenic parent materials submitted to environmental factors undergo weathering and transformation processes. But the pedogenesis of the Technosols remains little known. With this aim in view, a Technosol developing on purely technogenic materials resulting from iron industry was thoroughly characterized in order to discuss pedogenetic evolution of this Technosol using knowledge about pedogenesis of natural soils. Materials and methods:The studied site was a former settling pond, where mainly sludge generated by wet cleaning of blast-furnace fumes was dumped until probably in the mid-20 th century. Thereafter the pond has been colonized by vegetation and is covered by a diversified forest. The soil was composed of contrasted layers. A 20 cm organic layer has developed at the surface. Samples were collected in the first two meters which are under root influence.Elemental composition, agronomic parameters, mineralogy as well as physical and hydraulic properties of the soil materials were characterized.

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International audienceLarge surface areas covered with man-made materials are subject to pedogenetic evolution. However, pedogenetic processes in the resulting Technosols are seldom fully assessed. This work was conducted to identify and characterize the processes occurring on deposits of industrial technogenic materials. A former settling pond of the iron and steel industry where a forest has established since termination of the industrial activity approximately 50 years ago was chosen. A 2-m deep pit was opened, and a series of layers of the soil profile were sampled. The macro- and micro-structure were studied, and soil samples were analysed for structural, chemical and mineralogical assessment (chemical analyses, X-ray diffraction, infrared and M¨ossbauer spectroscopies, scanning and transmission electron microscopies coupled with energy dispersion spectrometry). Results showed that the profile was composed of a succession of sub-horizontal layers arranged in two groups according to their structure and composition, linked to the composition of the industrial effluent. Group 1 was composed of iron-, carbonate- and aluminosilicate-rich layers exhibiting a compact structure. Group 2 contained manganese-rich layers with a friable structure. Pedogenetic processes of various intensities were detected at different depths. Besides an accumulation of organic matter at the surface, transformations of minerals were recorded all along the soil profile, with weathering, leaching and precipitation of new phases. Phenomena occurred primarily in specific zones, such as cracks and interfaces between two layers. In conclusion, the soil maintained characteristics of the original industrial material and displayed several stages of pedogenesis, which were controlled chronologically by climatic and biological factors

In cities, the strong heterogeneity of soils, added to the lack of standardized assessment methods, serves as a barrier to the estimation of their soil organic carbon content (SOC), soil organic carbon stocks (SOCS; kgC m) and soil organic carbon citywide totals (SOCCT; kgC). Are urban soils, even the subsoils and sealed soils, contributing to the global stock of C? To address this question, the SOCS and SOCCT of two cities, New York City (NYC) and Paris, were compared. In NYC, soil samples were collected with a pedological standardized method to 1 m depth. The bulk density (D) was measured; SOC and SOCS were calculated for 0-30 cm and 30-100 cm depths in open (unsealed) soils and sealed soils. In Paris, the samples were collected for 0-30 cm depth in open soils and sealed soils by different sampling methods. If SOC was measured, D had to be estimated using pedotransfer functions (PTFs) refitted from the literature on NYC data; hence, SOCS was estimated. Globally, SOCS for open soils were not significantly different between both cities (11.3 ± 11.5 kgC m in NYC; 9.9 ± 3.9 kgC m in Paris). Nevertheless, SOCS was lower in sealed soils (2.9 ± 2.6 kgC m in NYC and 3.4 ± 1.2 kgC m in Paris). The SOCCT was similar between both cities for 0-30 cm (3.8 TgC in NYC and 3.5 TgC in Paris) and was also significant for the 30-100 cm layer in NYC (5.8 TgC). A comparison with estimated SOCCT in agricultural and forest soils demonstrated that the city's open soils represent important pools of organic carbon (respectively 110.4% and 44.5% more C in NYC and Paris than in agricultural soils, for 0-30 cm depth). That was mainly observable for the 1 m depth (146.6% more C in NYC than in agricultural soils). The methodology to assess urban SOCS was also discussed.

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Background and Aims The widespread use of Rare Earth Elements (REEs) has resulted in localized soil pollution. Phytolacca americana L. has potential for REE phyto-extraction, but the related mechanism is not clear. Methods In this study, the uptake and fractionation of REEs, and the influence of REEs on biomass production was investigated in hydroponically grown plants. Furthermore, the effects of Ca 2+ and Al 3+ on REE uptake, and the role of organic acids in REE translocation were also examined. Results Results showed that biomass and accumulation of REEs in P. americana were enhanced at low REE concentrations, but inhibited at higher concentrations in solution. Significant heavy REE (HREE) enrichment was observed during the stem-to-leaf transport, with a quotient of ∑LREE/∑HREE decreasing from 0.75 to 0.23. Ca 2+ and Al 3+ treatments diminished REE accumulation. The ∑LREE/∑HREE ratio decreased from 0.84 to 0.62 with increasing input of Ca 2+ , but increased from 0.83 to 0.92 with higher Al addition. Conclusions LREEs appear to enter into the root of P. americana through Ca 2+ ion channels, whereas HREEs may share pathways with Al 3+. Finally, citrate plays an important role in the translocation of REEs in P. americana.

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