Co-culture of Salix viminalis and Trifolium repens for the phytostabilisation of Pb and As in mine tailings amended with hardwood biochar.

Metal(loid) soil pollution causes environmental and health issues, and thus those sites need to be remediated. This can be done through phytostabilization, in combination with biochar amendment. The objectives were to investigate the potential of Salix viminalis L. associated with Trifolium repens L. for the phytostabilization of biochar-amended contaminated soils by assessing (1) the tolerance of both plants to metal(loid)s, through the biomass production, (2) the concentrations of metal(loid)s in plant parts and (3) the concentrations of metal(loid)s in soil pore water and percolation waters. Results showed that plant growth affected soil pore water Physico-chemical properties and metal(loid) mobility. When comparing the mono- and poly-cultures, although pH was higher with the polyculture than the monoculture, the decrease in Pb mobility did not differ. Moreover, the leachate analysis showed that As concentration in the soil particles leached from the soil was higher in the polyculture condition, while Pb concentration was the highest in the willow vegetated condition. Finally, willow dry weight was not affected by the presence of clover, while clover dry weight was lower when it was grown with willow. In conclusion, the results showed that the willow and clover polyculture was not better than the monoculture of these two species for the phytomanagement of a former mine site amended with biochar.

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

In phytomanagement approach the application of a combination of amendments is an option for remediating arsenic polluted areas and valorized biomass obtained. Various amendments can be used. Biochar has been shown to reduce metal(loid) availability, and increase soil fertility, while iron sulfate has a considerable As binding capacity, and poultry manure is a source of nutrients. A phytotoxicity test was performed by applying the three amendments (2% biochar, 0.15%, 0.30% and 0.45% iron sulfate and 0.4% poultry manure) to a former tin mine technosol, to investigate their effects on (i) soil pore water properties, (ii) metal(loid) immobilization and (iii) Phaseolus vulgaris L. growth, used as a bioindicator. Biochar addition alone did not affect soil properties or plant parameters. However, the addition of iron sulfate acidified the soil, decreased soil pore water As concentrations, and increased the ones of Fe and Pb. It also improved plant growth, and reduced As and Pb aerial and root concentrations. Finally, the addition of poultry manure had no effect on soil and plants. Based on our results, the combination of iron sulfate with biochar may be a solution for reducing soil toxicity of the Abbaretz mining technosol, improving its fertility, and thus ameliorating plant growth.Novelty statement:The work presented in this manuscript describes the effect of amendment application, i.e., biochar, chicken dung and/or iron sulfate, on soil properties, metals availability and dwarf bean growth, plant used as bioindicator.Our results showed that the combination of a low amount of iron sulfate with biochar is the strategy to reduce soil toxicity, improved its fertility and consequently authorizes plant growth.This study is one of the first describing the effects of combined amendments on a mining soil properties with focusing on metal(loid) mobility.

Effects of biochar, ochre and manure amendments associated with a metallicolous ecotype of Agrostis capillaris on As and Pb stabilization of a former mine technosol.

Metal(loid) soil pollution is a major environmental and health issue, requiring these areas to be remediated, for example through phytoremediation processes. In order to allow proper plant establishment and growth, amendments must be applied to highly contaminated and poorly fertile soils. Amendments are diverse, but many studies have shown the beneficial effects of biochar, manure and ochre, although studies on their combined use are scarce. Moreover, no studies have evaluated the effect of these combined amendments on endemic plant growth. Endemic plants growing on contaminated soils showed higher tolerance toward pollutants compared to plants coming from unpolluted areas. Therefore, the aim of the present study was to evaluate both the effect of amendments (single or combined) on the physicochemical properties of a former mining technosol, and the growth and metal(loid) accumulation ability of endemic Agrostis capillaris plants. This study revealed an improvement in the soil physicochemical properties following the application of amendments, with combined amendments showing better results than the application of just one. On top of this, Agrostis plants performed better on the amended technosols, especially the ones receiving manure, due to its high nutrient content. Finally, based on soil properties, plant growth and the metal(loid) accumulation profile, the use of biochar combined with manure seems to be the most appropriate treatment. Indeed, this treatment showed an improvement in both soil fertility and plant growth. Moreover, Agrostis plants grown in these conditions were among those showing higher root metal(loid) concentration associated with a lower translocation toward aerial parts.

Application of amendments for the phytoremediation of a former mine technosol by endemic pioneer species: alder and birch seedlings.

Metal(loid) pollution of soils has important negative effects on the environment and human health. For the rehabilitation of these soils, some eco-innovative strategies, such as phytoremediation, could be chosen. This practice could establish a plant cover to reduce the toxicity of the pollutants and stabilize the soil, preventing soil erosion and water leaching; this technique is called phytoremediation. For this, plants need to be tolerant to the pollutants present; thus, phytoremediation can have better outcomes if endemic species of the polluted area are used. Finally, to further improve phytoremediation success, amendments can be applied to ameliorate soil conditions. Different amendments can be used, such as biochar, a good metal(loid) immobilizer, compost, a nutrient-rich product and iron sulfate, an efficient arsenic immobilizer. These amendments can either be applied alone or combined for further positive effects. In this context, a mesocosm experiment was performed to study the effects of three amendments, biochar, compost and iron sulfate, applied alone or combined to a former mine technosol, on the soil properties and the phytoremediation potential of two endemic species, Alnus sp. and Betula sp. Results showed that the different amendments reduced soil acidity and decreased metal(loid) mobility, thus improving plant growth. Both species were able to grow on the amended technosols, but alder seedlings had a much higher growth compared to birch seedlings. Finally, the combination of compost with biochar and/or iron sulfate and the establishment of endemic alder plants could be a solution to rehabilitate a former mine technosol.

Contrasted tolerance of Agrostis capillaris metallicolous and non-metallicolous ecotypes in the context of a mining technosol amended by biochar, compost and iron sulfate.

Metal(loid) contamination of soil, resulting from the mining activities, is a major issue worldwide, due to its negative effects on the environment and health. Therefore, these contaminated soils need to be remediated. One realistic method is the assisted phytostabilization, which aims at establishing a vegetation cover on the soil that will reduce metal(loid) bioavailability and spreading through the prevention of wind erosion and water leaching. In addition, amendments are applied to improve soil conditions and ameliorate plant growth. In this goal, biochar and compost showed good results in terms of amelioration of soil fertility and reduction in lead bioavailability. However, they usually have a negative effect on arsenic. On the contrary, iron sulfate showed capacity to reduce arsenic mobility through interaction with its iron hydroxides. Finally, the choice of the appropriate plant species is crucial for the success of assisted phytostabilization. One good option is to use endemic species, adapted to the metal(loid) stress, with a fast growth and large shoot and root systems. The aims of this study were to (1) evaluate the effects of applying biochar, compost and iron sulfate, alone or combined, to a former mine soil on the soil properties and Agrostis capillaris growth, and (2) assess the difference between two Agrostis capillaris ecotypes, an endemic metallicolous ecotype and a non-metallicolous ecotype. Results of the mesocosm experiment showed that amendment application improved soil properties, i.e., reduced soil acidity, increased nutrient availability and lower metal(loid) stress, the best being the combination biochar-compost-iron sulfate. These ameliorations allowed a better plant growth. Finally, the metallicolous ecotype performed better in terms of growth than the non-metallicolous one and could thus be used in an assisted phytostabilization process on the former mine site.

Fostering temporal crop diversification to reduce pesticide use.

Temporal crop diversification could reduce pesticide use by increasing the proportion of crops with low pesticide use (dilution effects) or enhancing the regulation of pests, weeds and diseases (regulation effects). Here, we use the French National DEPHY Network to compare pesticide use between 16 main crops (dilution effect) and to assess whether temporal crop taxonomic and functional diversification, as implemented in commercial farms specialized in arable field crops, could explain variability in total pesticide use within 16 main crops (regulation effect). The analyses are based on 14,556 crop observations belonging to 1334 contrasted cropping systems spanning the diversity of French climatic regions. We find that cropping systems with high temporal crop diversity generally include crops with low pesticide use. For several crops, total pesticide use is reduced under higher temporal crop functional diversity, temporal crop taxonomic diversity, or both. Higher cover crop frequency increases total pesticide use through an increase in herbicide use. Further studies are required to identify crop sequences that maximize regulation and dilution effects while achieving other facets of cropping system multiperformance.

The rhizosphere of Salix viminalis plants after a phytostabilization process assisted by biochar, compost, and iron grit: chemical and (micro)-biological analyses.

Amendments, such as biochar, compost, and iron grit, used in phytostabilization studies, showed positive effects on soil physico-chemical properties, plant growth, and the microbial community. However, assisted phytostabilization studies do not always focus on the rhizosphere area where soil, plants, and microorganisms are affected by the amendments and plants and microorganisms can also interact with each other. The aims of this study were to evaluate the effects of amendment application on the exudation of organic acids by Salix viminalis plant roots, as well as the effects of amendments and plant development on the soil CHNS contents and the microbial community activity and diversity, assessed by measuring enzyme activities and using Biolog EcoPlatesTM tests and next-generation sequencing analyses. The results of the mesocosm experiment showed that soil C, H, and N contents were increased by amendment application, especially biochar and compost, while the one of S decreased. Enzyme activities, microbial activity, and diversity were also increased by the addition of amendments, except iron grit alone. Finally, the quantity of organic acids exuded by roots were little affected by amendments, which could in part explain the reduced effect of plant development on soil chemical and microbiological parameters. In conclusion, this study showed in particular that biochar and compost were beneficial for the soil CHN contents and the microbial community while affecting poorly Salix viminalis root exudates.

Evaluation of direct and biochar carrier-based inoculation of Bacillus sp. on As- and Pb-contaminated technosol: effect on metal(loid) availability, Salix viminalis growth, and soil microbial diversity/activity.

Phytomanagement manipulates the soil-plant system to lower the risk posed by contaminated soils. In this process, the addition of amendments, such as biochar, and bacteria can improve the fertility of poor contaminated soils and consequently ameliorate plant growth. A number of studies based on the inoculation of soil with microorganisms of the genus Bacillus, previously isolated from contaminated sites, revealed positive effects on soil properties and plant growth. Furthermore, when the Bacillus isolates were used in association with biochar, better results were obtained, as biochar can ameliorate soil properties and serve as habitat for microorganisms. Accordingly, a mesocosm study was set-up using a mining technosol amended with biochar and inoculated with an endogenous Bacillus isolate, to evaluate the effect of inoculation on soil properties, metal(loid) immobilization, and Salix viminalis growth. Two inoculation methods were compared: (1) direct inoculation of bacteria (Bacillus sp.) and (2) inoculation using biochar as a carrier. Results showed that the Bacillus isolate modified soil properties and ameliorated plant growth, while having a reduced effect on metal(loid) accumulation. The microbial activity was also stimulated, and the community composition was shifted, more importantly when biochar was used as a carrier. In conclusion, this research revealed an improvement of the plant growth and microbial activity after the addition of the endogenous bacterium to the analyzed former mining soil, with better results recorded when a carrier was used.

Biochar and compost effects on the remediative capacities of Oxalis pes-caprae L. growing on mining technosol polluted by Pb and As.

Selection of plant species with a great remediating capacity and a high biomass production is an important step for depolluting soils especially mine soils. Hyperaccumulators are used in phytoextraction for extracting metals from soil to roots and to translocate them to aerial parts. While in phytostabilization that usually requires amendment, metals are accumulated in the plant roots. The purpose of this study is to investigate Oxalis pes-caprae L. tolerance to Pb and As from Pontgibaud mine soil in France amended with compost and/or biochar. Oxalis bulbils were harvested in three sites located around Algiers: (1) an agricultural land in Reghaïa, (2) an area planted with Pines at the USTHB university campus, and (3) the polluted bank of the El Harrach river. The small and medium bulbil sizes were selected from each locality. Concerning the experimental soil, five mixtures of Pontgibaud technosol (P) with amendments compost (C) and biochar (Bc) were prepared: PC, PBc5, PBc10, PBc5 C, PBcC (w/w). The results indicate that amendments alter the soil physico-chemical characteristics and the mobility of metal(loid)s. They also reveal that As and Pb are differently distributed in plant organs. Medium bulbils especially from El Harrach river and the university campus have shown a better growth. Seedlings growth rate has been the highest in Pontgibaud amended with PC and the lowest in PBc10.

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

Soil 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.

Effect of Fe-functionalized biochar on toxicity of a technosol contaminated by Pb and As: sorption and phytotoxicity tests.

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. However, biochar has been shown efficient in sorbing cation pollutants, like Pb, but present a low sorption capacity towards anions like As. This contrasted behavior poses a problem, as most polluted soils are multi-contaminated, with both cation and anion pollutants. One of the solutions to overcome such problem is to functionalize biochar, by modifying its surface. However, most studies actually focused on functionalization effect on metal(loid)s sorption towards batch experiments, and only a few dealt with modified biochar incorporation to the soil. Therefore, this study aimed (i) to assess the sorption capacity of hardwood biochars, harboring different particle sizes, towards Pb and As; (ii) to evaluate the effect of a Fe-functionalization on Pb and As sorption; and (iii) to validate the results, in a phytotoxicity test using Phaseolus vulgaris as bioindicator plant. The batch experiments showed that all four biochars were able to efficiently sorb Pb, the fine biochars showing higher sorption values than the coarse biochars. As sorption was very low. Fe-coating increased As sorption value, while having no effect on Pb sorption. However, when incorporated in the soil, Fe-coated biochar did not improve soil physico-chemical properties compared to the pristine biochar; especially, it did not reduce As soil pore water concentrations. Finally, bean plant did not show differences in terms of biomass production between the two biochars incorporated into polluted soil, demonstrating that Fe-functionalization did not improve biochar capacity to decrease soil toxicity.

Assisted phytostabilization of a multicontaminated mine technosol using biochar amendment: Early stage evaluation of biochar feedstock and particle size effects on As and Pb accumulation of two Salicaceae species (Salix viminalis and Populus euramericana).

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 phytoremediation. 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. This study was performed on a former mine technosol contaminated by As and Pb and aimed to study (i) the effect of biochar on soil physico-chemical properties and plant phytostabilization potential (ii) biochar feedstock and particle size effects. In this goal, a mesocosm experiment was set up using four different biochars, obtained from two feedstocks (lightwood and pinewood) and harboring two particle sizes (inf. 0.1 mm and 0.2-0.4 mm) and two Salicaceae species. Soil and soil pore water physico-chemical properties as well as plant growth and metal(loid)s distribution were assessed. The results showed that biochar was efficient in improving soil physico-chemical properties and reducing Pb soil pore water concentrations. This amelioration allowed plant growth and increased dry weight production of both species. Regarding metal(loid)s distribution, willow and poplar showed an As and Pb accumulation in roots and low translocation towards edible parts, i.e stems and leaves, which shows a phytostabilization potential. Finally, the 2 biochar parameters, feedstock and particle size, only affected soil and soil pore water physico-chemical properties while having no effect on plant growth.

Cd, Pb, and Zn mobility and (bio)availability in contaminated soils from a former smelting site amended with biochar.

Biochar is a potential candidate for the remediation of metal(loid)-contaminated soils. However, the mechanisms of contaminant-biochar retention and release depend on the amount of soil contaminants and physicochemical characteristics, as well as the durability of the biochar contaminant complex, which may be related to the pyrolysis process parameters. The objective of the present study was to evaluate, in a former contaminated smelting site, the impact of two doses of wood biochar (2 and 5% w/w) on metal immobilization and/or phytoavailability and their effectiveness in promoting plant growth in mesocosm experiments. Different soil mixtures were investigated. The main physicochemical parameters and the Cd, Pb, and Zn contents were determined in soil and in soil pore water. Additionally, the growth, dry weight, and metal concentrations were analyzed in the different dwarf bean plant (Phaseolus vulgaris L.) organs tested. Results showed that the addition of biochar at two doses (2 and 5%) improved soil conditions by increasing soil pH, electrical conductivity, and water holding capacity. Furthermore, the application of biochar (5%) to metal-contaminated soil reduced Cd, Pb, and Zn mobility and availability, and hence their accumulation in the different P. vulgaris L. organs. In conclusion, the data clearly demonstrated that biochar application can be effectively used for Cd, Pb, and Zn immobilization, thereby reducing their bioavailability and phytotoxicity.