Immobilization of heavy metal in contaminated mine technosols using biochar: A phytomanagement strategy

Soil contamination by metal(loid)s is one of the most important environmental problem. It leads to loss of environment biodiversity and soil functions and can have harmful effects on human health. Therefore, contaminated soils could be remediated, using phytomanagement. Indeed, plant growth will improve soil conditions while accumulating metal(loid)s and modifying their mobility. However, due to the poor fertility and high metal(loid)s levels of these soils, amendments, like biochar, has to be applied. Phytomanagement is a technique for rehabilitating these soils and reducing the spread of pollutants. To this end, it is advisable to stabilize the mobility of pollutants in the soil before planting plants. Biochar, produced by the pyrolysis of biomass under low oxygen conditions, has gathered attention in the last few years due to its capability to reduce metal(loid)s bioavailability and mobility in soils, as well as its beneficial effects on soil fertility. Indeed, biochar amendment to polluted soil induced usually an increase of pH, water holding capacity, and nutrient contents, associated with a decrease of metal(loid)s concentrations in soil pore water, through sorption on biochar. We tested different biochar concentrations from different wood feedstock in mesocosm and then on a field experimental plot presenting a significant arsenic (500 to 1000 mg/kg) and lead (15000 to 20000 mg/kg) pollution. Biochar from hardwood feedstock and more particularly the one obtained from bark and presenting the finest grain size (Lebrun et al. 2018) has shown good efficiency by reducing the availability of lead in soil pore water by more than 90% and keeping arsenic levels in the soil pore water below critical environmental concentrations. For the all plant species tested (Phaseolus, Populus, Salix, Ailanthus altissima, Alnus, Agrostis, and Trifolium) in biochar amended soils we show that biochar has allowed the establishment of a dense vegetation whereas until then the soils were bare and unsuitable for any plant development (Lebrun et al 2019, Nandillon et al 2019). Please click Additional Files below to see the full abstract

The Potential of Clover Green Amendment, Associated with Biochar, Activated Carbon or Ochre, for the Phytoremediation, Using Populus x. canescens, of a Former Mine Technosol

Metal(loid) soil pollution resulting from past and present mine activities is a serious environmental and health issues worldwide. Therefore, the remediation of those polluted areas has been a growing research interest over the last decades, especially the assisted phytoremediation. In this study, a pot experiment was set up, using a former mine technosol, highly polluted by As and Pb, to which biochar, activated carbon, or ochre was applied, alone or in combination to clover green amendment. Following amendment application, Populus x. canescens cuttings were planted. Results showed that all four amendments reduced soil acidity. However only the first three amendments immobilized As and Pb, while the green amendment drastically mobilized those two pollutants and none of the amendments improved plant growth. In conclusion, the association of clover green amendment to biochar, activated carbon, or ochre did not appear as an efficient remediation strategy in this case; although the aging of the amendments and degradation of the green amendment in the soil with time could have positive outcomes

The reduction of the As and Pb phytotoxicity of a former mine technosol depends on the amendment type and properties

International audienceIn remediation of metal(loid) polluted soils, it is crucial to improve soil conditions and reduce metalloid) toxicity to permit plant growth. To do that, amendments, such as biochar, activated carbon, and redmud, can be applied to the soil. Their effects are dependent on their type and properties. The aims of this study were thus to evaluate the potential of diverse biochars, activated carbons, and redmuds to reduce phytotoxicity of a former mine technosol polluted with As and Pb. Two pots experiments were set up. The first one applied on Pontgibaud technosol ten biochars, eight activated carbons, and three redmuds, at 2% for the biochars and activated carbons and 1% for the redmud. Soil pore water properties (pH, electrical conductivity), metal(loid) mobility, and Phaseolus vulgaris growth were monitored. In a second experiment, the five best amendments, one redmud associated with two biochars and two activated carbons, selected based on their ability to improve soil conditions, immobilize metal(loid)s and improve plant growth, were applied. The same plant species was used and soil and plant parameters were measured. Results demonstrated that not all amendments were capable of ameliorating soil conditions and reducing soil phytotoxicity. Moreover, the five selected amendments (biochars from oak bark sapwood and bamboo, activated carbons from vegetal feedstock chemically activated and physically activated, modified redmud) showed good sorption capacity towards Pb, with maximum sorption capacity between 63 and 217 mg g(-1), depending on the amendment, and their combined application led to better soil properties improvement than the single amendments. However, plant growth was only ameliorated further than a single application in the redmud-biochar combination but not in the association of redmud with activated carbon. This study is one of the first to deliver a rapid phytotoxicity test screening demonstrating that redmud associated with particular biochar could be beneficial in reducing the phytotoxicity of technosol polluted with As and Pb and thus allow plant growth and a phytomanagement process

Biochar Application Rate: Improving Soil Fertility and Linum usitatissimum Growth on an Arsenic and Lead Contaminated Technosol

International audienceThe remediation of metal(loid) contaminated sites often requires the application of an amendment, such as biochar. Biochar is the product of biomass pyrolysis and has been shown to reduce soil acidity, immobilize metal(loid)s and thus ameliorate plant growth. The beneficial effects of biochar are usually higher at a higher dose. However, an excessive dose can have negative outcomes due to nutrient loss. The application of an amendment to the soil comes at a financial cost, especially if the contaminated area is large, and therefore the optimum dose must be determined. In addition, to overcome the cost of biochar application, the use of a plant with economic benefits, such as flax, can be a suitable option. In this context, a mesocosm study, on a former mining soil polluted by As and Pb was performed, using flax and biochar applied at increasing concentrations. Results showed an increase in soil pH and the immobilization of Pb with increasing biochar doses. These ameliorations led to better plant growth. A higher biochar dose increased plant growth up to a 3% application rate, from which point dry weight no longer increased.Metal(loid) concentrations decreased between 1 and 3% biochar, and then increased at higher doses. It can thus be concluded that with 3% biochar, soil properties are ameliorated, metal(loid)s are immobilized, and plant growth increases, and a higher biochar application rate does not bring about better outcomes. Therefore, a 3% biochar application dose seems to be the best application dose to improve soil conditions and plant growth at a lower cost

Mixing ratio and Nitrogen fertilization drive synergistic effects between biochar and compost

International audienceCompost and biochar mixtures used to replace mineral N fertilisers in agricultural systems showed contrasting results, especially when applied in combination. We hypothesised that their effect may depend on the mixing ratio between the two components. The aim of our study was to determine if varying ratios of biochar/compost mixtures in presence or absence of chemical nitrogen (N) fertilisation influence ryegrass growth and nutrient uptake. To this end, we set up a pot experiment with an agricultural soil amended with five compost and biochar mixtures differentiated by their mixing ratio. We followed soil fertility parameters and ryegrass growth over three harvests.Results showed that the addition of amendments improved nutrient availability. The highest nutrient availability was observed with pure compost. Despite their high C/N ratios, biochar and compost increased N availability while preventing its microbial immobilisation. Biomass and nutrient uptake by plants were improved by amendments, but were dependent on the biochar/compost ratio. Addition of a mixture containing less biochar than compost (30% biochar/70% compost, on a dry weight basis) showed highest plant growth response and nutrient uptake as compared to the chemical N fertilisation. In addition, the beneficial effects of biochar and compost on plant growth were strengthened by N fertiliser. All in all, we demonstrated the synergistic effects between biochar and compost, which were predominantly driven by the mixing ratio between those two materials, and highlighted their potential use as a sustainable alternative to chemical fertilisers

Effect of biochar, iron sulfate and poultry manure application on the phytotoxicity of a former tin mine

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Biochar effect associated with compost and iron to promote Pb and As soil stabilization and Salix viminalis L. growth

International audienceSoil pollution by metal(loid)s is one of the most significant problems in Europe. To remediate and potentially rehabilitate these contaminated sites, phytoremediation procedures are being put into place, often using amendments to help offset the extreme conditions of such soils. The aim of this study was to define the best amendment to use on the field. This was done by studying how the addition of three different amendments (biochar, compost and iron grit), alone or in combination, could affect: (i) soil physico-chemical properties, (ii) Salix viminalis growth, and (iii) metal(loid) stabilization. A 69 day-mesocosm study was thus set up using a former mine technosol, the three amendments applied alone or combined, and S. viminalis cuttings. The results showed that biochar and/or compost improved the soil fertility and the soil pore water characteristics, with reductions of acidity, metal(loid) mobility and toxicity, while iron grit amendment presented negative effects on such parameters. Such ameliorations allowed better plant growth and higher biomass production. In addition, stress indicators (leaf pigment content and root guaiacol peroxidase activity) showed a reduction in plant stress following biochar and/or compost application. Finally, among the different treatments, the use of compost or a biochar-compost combination showed better results in terms of improvement of soil conditions, increase in plant growth and reduced translocation of metal(loid)s towards upper parts, making these two treatments a valuable option for a field trial