• Energy Research

The main limiting factor for cleaning-up contaminated soils with hyperaccumulator plants is the low production of aerial biomass and the number of successive crops needed to reach the objective of remediation. The aim of this study was to contribute to the determination of a fertilisation strategy to optimise soil metal phytoextraction by Thlaspi caerulescens. A pot experiment was conducted on an agricultural soil and on a contaminated soil from the vicinity of a former Pb/Zn smelter. The nitrogen (N) treatment consisted of 4 levels (0, 11, 21.5 and 31 mg N kg(-1) dry soil (DS)) added as NH4NO3. The highest N treatment was combined with 4 levels of phosphorus (P) (0, 20, 40 and 80 mg P kg(-1) DS as KH2PO4) and sulfur (S) additions (0, 10, 20 and 30 mg S kg(-1) DS as MgSO4). The highest N fertilisation contributed significantly to enhance biomass production of T. caerulescens and to decrease the concentration of Cd and Zn in the biomass. At constant N addition, P supply did not affect metal extraction by T. caerulescens but negatively affected plant health. Sulfur supply slightly increased phytoextraction of Cd. Our results show that N and S fertilisation might interact but further investigations on the effect of such interaction on Cd extraction efficiency are needed.

Technosols, soils subjected to a strong human influence and containing significant amounts of artefacts, are characteristic of the Anthropocene. In order to better apprehend their growing importance in our current environment, our knowledge of the evolution and fate of these soils must be improved. The aim of this article is to promote pedogenic modelling for Technosols by proposing an appropriate framework. The paper first defines the characteristics of Technosol pedogenesis, and then considers the requirements for its modelling in light of general concepts of pedogenesis, modelling tools and techniques, and 18 selected existing quantitative models. This mixed technical and conceptual analysis allows us to address at once the modelling approach, the choice of processes, the integration of control variables, the time scales, the spatial representation, and the data needed for such a framework. Technosol pedogenesis is characterised by the soils' anthropic creation, a young age, a climate globally favourable for soil evolution, a surprising level of biological activity, and mostly reactive artefacts as parent materials. Pedogenic processes observed in Technosols are similar to those occurring in more natural soils; however, they generally have fast kinetics and occur in unusual assemblages. We propose that the modelling framework for Technosol evolution should be based on the coupling of process-based models of soil functioning processes and accommodate the peculiar properties of technogenic materials. Our work also highlights modelling features needed for pedogenesis in general: development of biological and physical models, selection of a comprehensive energy unit, dual-time scale modelling, and multi-scale representation of the soil profile. We propose (i) an adaptation of existing energy metrics (entropy, exergy, emergy or EEMT), (ii) a dual-time scale approach, our original concept, based on resilience patterns in soil changes, and (iii) the development of an existing spatial representation. Constructed Technosols are a relevant experimental model which supplies reliable data on soil evolution, data which are required for the development of pedogenic models. Technosols are emblematic of the issues we face for the management of the soils of the Anthropocene. The design of a modelling framework for Technosol evolution should therefore bring interesting developments for pedogenic modelling in general.

Once previous industrial activity has ceased, brownfields are found in urban and suburban environments and managed in different ways ranging from being left untouched to total reconversion. These situations apply to large surface areas often impacted by residual diffuse pollution. Though significant and preventing any sensitive use, residual contamination does not necessarily require treatment. Moreover, conventional treatments show their technical and economic limits in these situations and gentle remediation options such as phytomanagement might appear more relevant to the management of those sites. Thus, these sites face up two major issues: managing moderate contamination levels and providing an alternative use of economic interest. This work proposes to assess a management strategy associating the phytoremediation of organic pollution along with the production of biomass for energy generation production. A 16-week controlled growth experiment was conducted on a soil substrate moderately impacted by multiple pollution (trace elements, mainly Zn and Pb, and hydrocarbons), by associating rhizodegradation with Medicago sativa or biomass production with Robinia pseudoacacia or Alnus incana in monocultures. The effect of a microbial inoculum amendment on the performances of these treatments was also evaluated. Results showed total hydrocarbons (TH), and to a lesser extent polycyclic aromatic hydrocarbons (PAH), concentrations decreased over time, whatever the plant cover. Good biomass production yields were achieved for both tree species in comparison with the control sample, even though R. pseudoacacia seemed to perform better. Furthermore, the quality of the biomass produced was in conformity with the thresholds set by the legislation concerning its use as a renewable energy source.

The aim of the present work is the assessment of the concentration, toxicity and phytoavailability of heavy metals in garden soils in the vicinity of three mines (A, B and C) in South of Morocco by using concurrently selective chemical extractions, MetPLATE a toxicity bioassay and plant growth experiments. The tailings materials containing very high concentrations of Mn, Cu and Co in mine A, Co, Mn, Cr and Ni in mine B and Cu and Zn in mine C. The high toxicity of tailings from mine C (86.7% inhibition) and moderate toxicity of tailings from mine B (51.0% inhibition) were mainly due to the relative high concentrations of soluble Cu and Zn. Nevertheless, the low metal toxicity observed in most garden soils was confirmed by the low metal concentrations in the soil water extracts. In all garden soils, Lactuca sativa L. and Lolium multiflorum L. contained in their shoots Cd, Co, Cr, Cu and Ni below toxic concentrations while Zn (in all soils) and Mn in two soils from mine A were accumulated at concentrations high enough to be considered phytotoxic. The low biomass produced on garden soils in the vicinity of mines B and C is explained by the relative low toxicity compared to mine A. Transfer factor values for Zn were higher than those found for Mn for both plant species, confirming that this element is present at lower bioavailable fraction in soil than Zn.

Technosols, soils subjected to a strong human influence and containing significant amounts of artefacts, are characteristic of the Anthropocene. In order to better apprehend their growing importance in our current environment, our knowledge of the evolution and fate of these soils must be improved. The aim of this article is to promote pedogenic modelling for Technosols by proposing an appropriate framework. The paper first defines the characteristics of Technosol pedogenesis, and then considers the requirements for its modelling in light of general concepts of pedogenesis, modelling tools and techniques, and 18 selected existing quantitative models. This mixed technical and conceptual analysis allows us to address at once the modelling approach, the choice of processes, the integration of control variables, the time scales, the spatial representation, and the data needed for such a framework. Technosol pedogenesis is characterised by the soils' anthropic creation, a young age, a climate globally favourable for soil evolution, a surprising level of biological activity, and mostly reactive artefacts as parent materials. Pedogenic processes observed in Technosols are similar to those occurring in more natural soils; however, they generally have fast kinetics and occur in unusual assemblages. We propose that the modelling framework for Technosol evolution should be based on the coupling of process-based models of soil functioning processes and accommodate the peculiar properties of technogenic materials. Our work also highlights modelling features needed for pedogenesis in general: development of biological and physical models, selection of a comprehensive energy unit, dual-time scale modelling, and multi-scale representation of the soil profile. We propose (i) an adaptation of existing energy metrics (entropy, exergy, emergy or EEMT), (ii) a dual-time scale approach, our original concept, based on resilience patterns in soil changes, and (iii) the development of an existing spatial representation. Constructed Technosols are a relevant experimental model which supplies reliable data on soil evolution, data which are required for the development of pedogenic models. Technosols are emblematic of the issues we face for the management of the soils of the Anthropocene. The design of a modelling framework for Technosol evolution should therefore bring interesting developments for pedogenic modelling in general.

This work was undertaken to measure the in situ phytoextraction of zinc using a former zinc-smelter site where metallophyte plants have been growing for 30 years. The site exhibited a gradient in the total metal concentration in the upper horizon (from 3230 to 8530 mg Zn kg(-1)). Soils were sampled from four different sectors (I-IV), and plant shoots were harvested, identified, their biomass weighed and analysed for zinc. The results showed that three plant species were dominant on the site, including Arabidopsis halleri (cress), Armeria maritima (seathrift), and Arrhenatherum elatius (fromental). A. maritima was the predominant species according to the biomass production on the most polluted sector 1. As the concentration of metals in soils decreased. A. maritima disappeared and A. halleri increased. The biomass of A. elatius was the highest on the less polluted soils. Concentrations in zinc in the aerial parts of plants varied from 73 (sector IV) to 6269 mg kg(-1) DM (sector 1). The concentration of Zn in A. halleri decreased with the decrease in concentration of zinc in soil. Phytoextraction was calculated from the biomass and its concentration of metal. It was at a maximum in sector III with a high contribution of A. halleri and A. elatius and reached 10 kg Zn ha(-1), a promising amount for phytoextraction considering the absence of any agricultural practices. In sector 1, phytoextraction was four times lower despite a 2.6 times higher concentration of Zn in the upper horizon. In conclusion, phytoextraction was strongly dependent on the concentration of the available metal in soils which may limit the growth of plants, and favour tolerant but low biomass plant species such as A. maritima.

Thlaspi caerulescens is known to hyperaccumulate high quantities of Cd with Cd concentrations up to 3000 mg kg(-1) in some populations from south of France. However, within these populations, the Cd concentrations can vary widely from plant to plant in a way that appears to be not entirely due to variations in soil Cd. The aim of this work was to investigate the variability in the Cd uptake ability of individual plants within a population and among seedlings grown from seeds from a single plant. Ten populations of T. caerulescens plants were selected from four locations (V: Viviez; SF: Saint Félix-de-Pallières; LB: Le Bleymard; CMA: Col du Mas de l'Air) depending of the extent and soil homogeneity of the site. One population from CMA consisted of the progeny of a single maternal plant. Hundred plants of each population were grown for three months in the same homogeneous and lightly Cd-polluted soil (about 20 mg total Cd kg(-1) dry soil). Cadmium uptake behavior of the plants was monitored by labeling the soil with 109Cd. To allow partial plant destruction, radioanalysis was performed on the largest leaf of each plant as an indicator of the total Cd concentration in plant shoots. Results showed significant differences in biomass production and Cd uptake by T. caerulescens between sites and between populations within sites. We observed a wide intra-population variation in biomass, Cd concentration and total Cd uptake. For these properties, 1 to 5 percents of the plants in each population varied by more than a factor of two from the mean values. The mean Cd uptake by the single-plant population from CMA was more than 40% higher than for the population at large. T. caerulescens would respond to traditional selection methods, which would significantly improve the phytoextraction of Cd.