Use of ecotoxicity test and ecoscores to improve the management of polluted soils: case of a secondary lead smelter plant

International audienceWith the rise of sustainable development, rehabilitation of brownfield sites located in urban areas has become a major concern. Management of contaminated soils in relation with environmental and sanitary risk concerns is therefore a strong aim needing the development of both useful tools for risk assessment and sustainable remediation techniques. For soils polluted by metals and metalloids (MTE), the criteria for landfilling are currently not based on ecotoxicological tests but on total MTE concentrations and leaching tests. In this study, the ecotoxicity of leachates from MTE polluted soils sampled from an industrial site recycling lead-acid batteries were evaluated by using both modified Escherichia coli strains with luminescence modulated by metals and normalized Daphnia magna and Alivibrio fischeri bioassays. The results were clearly related to the type of microorganisms (crustacean, different strains of bacteria) whose sensitivity varied. Ecotoxicity was also different according to sample location on the site, total concentrations and physico-chemical properties of each soil. For comparison, standard leaching tests were also performed. Potentially phytoavailable fraction of MTE in soils and physico-chemical measures were finally performed in order to highlight the mechanisms. The results demonstrated that the use of a panel of microorganisms is suitable for hazard classification of polluted soils. In addition, calculated eco-scores permit to rank the polluted soils according to their potentially of dangerousness. Influence of soil and MTE characteristics on MTE mobility and ecotoxicity was also highlighted

Opportunities and challenges in the use of coal fly ash for soil improvements – a review

Coal fly ash (CFA), a by-product of coal combustion has been regarded as a problematic solid waste, mainly due to its potentially toxic trace elements, PTEs (e.g. Cd, Cr, Ni, Pb) and organic compounds (e.g. PCBs, PAHs) content. However, CFA is a useful source of essential plant nutrients (e.g. Ca, Mg, K, P, S, B, Fe, Cu and Zn). Uncontrolled land disposal of CFA is likely to cause undesirable changes in soil conditions, including contamination with PTEs, PAHs and PCBs. Prudent CFA land application offers considerable opportunities, particularly for nutrient supplementation, pH correction and ameliorating soil physical conditions (soil compaction, water retention and drainage). Since CFA contains little or no N and organic carbon, and CFA-borne P is not readily plant available, a mixture of CFA and manure or sewage sludge (SS) is better suited than CFA alone. Additionally, land application of such a mixture can mitigate the mobility of SS-borne PTEs, which is known to increase following cessation of SS application. Research analysis further shows that application of alkaline CFA with or without other amendments can help remediate at least marginally metal contaminated soils by immobilisation of mobile metal forms. CFA land application with SS or other source of organic carbon, N and P can help effectively reclaim/restore mining-affected lands. Given the variability in the nature and composition of CFA (pH, macro- and micro-nutrients) and that of soil (pH, texture and fertility), the choice of CFA (acidic or alkaline and its application rate) needs to consider the properties and problems of the soil. CFA can also be used as a low cost sorbent for the removal of organic and inorganic contaminants from wastewater streams; the disposal of spent CFA however can pose further challenges. Problems in CFA use as a soil amendment occur when it results in undesirable change in soil pH, imbalance in nutrient supply, boron toxicity in plants, excess supply of sulphate and PTEs. These problems, however, are usually associated with excess or inappropriate CFA applications. The levels of PAHs and PCBs in CFA are generally low; their effects on soil biota, uptake by plants and soil persistence, however, need to be assessed. In spite of this, co-application of CFA with manure or SS to land enhances its effectiveness in soil improvements

Comparative analysis of Cd and Zn impacts on root distribution and morphology of Lolium perenne and Trifolium repens: implications for phytostabilization

Backgrounds and aims The phytostabilization potential of plants is a direct function of their root systems. An experimental design was developed to investigate the impact of Cd and Zn on the root distribution and morphology of Lolium perenne and Trifolium repens. Methods Seedlings were transplanted into columns filled with washed quartz and irrigated daily with Cdor Zn-containing nutrient solutions during 1 month. Root biomass, root length density (RLD) and diameter were subsequently quantified as a function of depth. Pot experiments were also performed to quantify metal, lignin and structural polysaccharides concentrations as well as cell viability. Results Lolium perenne accumulated Cd and Zn in the roots whereas T. repens was unable to restrict heavy metal translocation. Cadmium and Zn reduced rooting depth and RLDbut induced thick shoot-borne roots in L. perenne. Cd-induced root swelling was related to lignification occurring in the exodermis and parenchyma of central cylinder. Hemicelluloses and lignin did not play a key role in root metal retention. Cadmium slightly reduced mean root cell viability whereas Zn increased this parameter in comparison to Cd. Conclusions Even though plant species like Lolium perenne and Trifolium repens may appear suitable for a phytostabilization scheme based on their shoot metal tolerance, exposure to toxic heavy metals drastically impairs their root distribution. This could jeopardize the setting up of phytostabilization trials. The metal-induced alterations of root system properties are clearly metal- and speciesspecific. At sites polluted with multiple metals, it is therefore recommended to first test their impact on the root system of multiple plant species so as to select the most appropriate species for each site

Seed Priming of Trifolium repens L. Improved Germination and Early Seedling Growth on Heavy Metal-Contaminated Soil

Abstract Seed priming effects on Trifolium repens were analysed both in Petri dishes and in two soils (one unpolluted soil and a soil polluted with Cd and Zn). Priming treatments were performed with gibberellic acid 0.1 mM at 22 °C during 12 h or with polyethylene glycol (−6.7 MPa) at 10 °C during 72 h. Both priming treatments increased the germination speed and the final germination percentages in the presence of 100 μM CdCl2 or 1 mM ZnSO4. Flow cytometry analysis demonstrated that the positive effect of priming was not related with any advancement of the cell cycle in embryos. Seed imbibition occurred faster for primed seeds than for control seeds. X-ray and electronic microscopy analysis suggested that circular depressions on the seed coat, in addition to tissue detachments inside the seed, could be linked to the higher rate of imbibition. Priming treatments had no significant impact on the behaviour of seedlings cultivated on nonpolluted soil while they improved seedling emergence and growth on polluted soil. The two priming treatments reduced Zn accumulation. Priming with gibberellic acid increased Cd accumulation by young seedlings while priming with polyethylene glycol reduced it. Priming improved the light phase of photosynthesis and strengthened the antioxidant system of stressed seedlings. Optimal priming treatment may thus be recommended as efficient tools to facilitate revegetation of former mining area