Biochar-nanoparticle combinations enhance the biogeochemical recovery of a post-mining soil.

Here we addressed the capacity of distinct amendments to reduce arsenic (As), copper (Cu), selenium (Se) and zinc (Zn) associated risks and improve the biogeochemical functions of post-mining soil. To this, we examined nanoparticles (NPs) and/or biochar effects, combined with phytostabilization using Lolium perenne L. Soil samples were taken in a former metal mine surroundings. Ryegrass seeds were sown in pots containing different combinations of NPs (zero-valent iron (nZVI) or hydroxyapatite (nH)) (0 and 2 %), and biochar (0, 3 and 5 %). Plants were grown for 45 days and the plant yield and element accumulation were evaluated, also soil properties (element distribution within the soil fractions, fertility, and enzymatic activities associated with microbiota functionality and nutrient cycling) were determined. Results showed biochar-treated soil had a higher pH, and much higher organic carbon (C) content than control soil and NP-treated soils, and it revealed increased labile C, total N, and available P concentrations. Soil treatment with NP-biochar combinations increased exchangeable non-acid cation concentrations and reduced exchangeable Na%, improved soil fertility, reduced sodicity risk, and increased ryegrass biomass. Enzymatic activities, particularly dehydrogenase and glucosidase, increased upon the addition of biochar, and this effect was fostered by NPs. Most treatments led to a significant reduction of metal(loid)s contents in biomass, mitigating contamination risks. The two different NPs had similar effects in many parameters, nH outperformed nZVI in terms of increased nutrients, C content, and enzymatic activities. On the basis of our results, combined biochar-NP amendments use, specially nH, emerges as a potential post-mining soil restoration strategy.

Phytoremediation potential depends on the degree of soil pollution: a case study in an urban brownfield.

Phytoremediation is a cost-effective nature-based solution for brownfield reclamation. The choice of phytoextraction or phytostabilization strategies is highly relevant when planning full-scale treatments. A suitable approach to identify such species involves the evaluation of plants that grow spontaneously on the contaminated sites. Here, we sought to determine the phytoremediation potential of three spontaneous plant species, namely the trees Acer pseudoplatanus L (A. pseudoplatanus) and Betula celtiberica Rothm. & Vasc (B. celtiberica), and the shrub Buddleja davidii Franch (B. davidii), for the recovery of an urban brownfield. To determine the response of the species to the degree of contamination, we conducted soil and vegetation sampling inside and outside the site. The concentrations of As, Cu, and Zn in soil and plant samples were measured, and then various indexes related to phytoremediation were calculated. The translocation factor and transfer coefficient indicated that vegetation outside the brownfield had phytoextraction capacity while the same plants inside the brownfield revealed phytostabilization properties. Given our results, we propose that the selected species are suitable for phytostabilization strategies in areas with high concentrations of contaminants, whereas they could be used for phytoextraction only in soils with low or moderate levels of pollution.

Pyrolysis temperature influences the capacity of biochar to immobilize copper and arsenic in mining soil remediation.

Biochar is a promising material used for multiple remediation approaches, mainly in polluted soils. Its properties can differ depending on feedstock and pyrolysis temperature. In this context, we tested the capacity of three biochar products made from corncob, pyrolyzed at different temperatures (350, 500, and 650 °C), to remediate a mining soil affected by high levels of Cu and As. We performed an exhaustive characterization of the biochar. We found that biochar showed a higher surface area with increasing pyrolysis temperature, whereas high molecular weight PAHs were detected in biochar produced at the maximum temperature, thus indicating potential ecotoxicological risks. After the application of biochar to the soil, Cu was partially immobilized, especially when using that obtained at 500 °C. This effect is attributed to the structure of this material and an increase in soil pH and organic matter content. Conversely, As was increased in the soluble fraction for all three types of biochar but in a proportion that lacks relevance. On the whole, given its lower PAH content, higher Cu immobilization ratio, and an almost negligible increase in As availability, biochar obtained at 500 °C outperformed the other two products with respect to soil recovery. Of note, data on Cu and As availability were doubled-checked using two extraction methodologies. We propose that this operational approach for determining the most suitable pyrolysis temperature will find application in other soil remediation actions.

Effective bioremediation of soil from the Burgan oil field (Kuwait) using compost: A comprehensive hydrocarbon and DNA fingerprinting study.

An innovative combination of metagenomic profiling of microbial communities and GC-MS & Pyrolysis-GC-MS fingerprinting methods were used to assess the biodegradation of contaminated soil from the Burgan oil field in Kuwait. The soil was treated with (sludge) compost in microcosms to evaluate the feasibility of this material for bioremediation purposes. The most favourable trial showed a > 80% decrease in TPH, thereby indicating strong potential for full-scale application using a cost-effective technology and thus in line with the principles of the circular economy. The microbial study showed that compost addition enhanced the organic matter and nutrient content of the soil. However, the microorganisms in the compost did not seem to play a relevant role in bioremediation, meaning that compost amendments serve as a biostimulation rather than a bioaugmentation approach. The chemical study of the distinct oil fractions revealed rapidly biodegraded compounds (alkanes, alkyl-aromatics, etc.) and others that were much more refractory (hopanes, benzohopanes, etc.). Of note, although heavy fractions are usually considered recalcitrant to biodegradation, we observed incipient degradation of the asphaltene fraction by means of double-shot thermodesorption and pyrolysis. Finally, chemical fingerprinting also revealed that the treated soil contained some of the compounds found in the compost, such as coprostanol, cholesterol, and plant sterols. This observation would support the use of these compounds as proxies to monitor the effects of compost and to adjust dosages in real-scale bioremediation treatments.

Contrasting mobility of arsenic and copper in a mining soil: A comparative column leaching and pot testing approach.

The remediation of legacy metal(loid) contaminated soils in-situ relies on the addition of [organic] amendments to reduce the mobility and bioavailability of metal(loid)s, improve soil geochemical parameters and restore vegetation growth. Two vermicomposts of food and animal manure waste origin (V1 and V2) were amended to an arsenic (As) and copper (Cu) contaminated mine soil (≤1500 mg kg-1). Leaching columns and pot experiments evaluated copper and arsenic in soil pore waters, as well as pH, dissolved organic carbon (DOC) and phosphate (PO43-) concentrations. The uptake of As and Cu to ryegrass was also measured via the pot experiment, whilst recovered biochars from the column leaching test were measured for metal sorption at the termination of leaching. Vermicompost amendment to soil facilitated ryegrass growth which was entirely absent from the untreated soil in the pot test. All amendment combinations raised pore water pH by ∼4 units. Copper concentrations in pore waters from columns and pots showed steep reductions (∼1 mg L-1), as a result of V1 & V2 compared to untreated soil (∼500 mg L-1). Combined with an increase in DOC and PO43-, As was mobilised an order of magnitude by V1. Biochar furthest reduced Cu in pore waters from the columns to <0.1 mg L-1, as a result of surface sorption. The results of this study indicate that biochar can restrict the mobility of Cu from a contaminated mine soil after other amendment interventions have been used to promote revegetation. However, the case of As, biochar cannot counter the profound impact of vermicompost on arsenic mobility.

Short-term experiment for the in situ stabilization of a polluted soil using mining and biomass waste.

Mining and biomass waste were used to remediate a brownfield affected by As, Cd, Cu, Pb and Zn pollution in a pilot scale experiment, and a plant used for phytoremediation purposes was used as an indicator of possible toxicological effects. To carry out the experiments, plots in field conditions were treated with magnesite (mining waste), magnesite-sludge compost, and magnesite-biochar respectively, while untreated soil was used as a control. The plots were then irrigated and left for one week, after which seeds of the ryegrass Lolium perenne L. were sown. Soil properties such as metal(loid) availability, pH, phosphorus availability, total nitrogen, organic carbon, and nutrients were monitored for two months. Finally, the ryegrass was harvested and pollutant concentrations were analyzed in the aerial parts. Magnesite proved to be an excellent amendment for metal(loid) immobilization, although the notable increase in soil pH and Mg content inhibited plant growth. However, the application of magnesite in combination with the sludge compost (rich in N and P) favored plant growth and also immobilized metals, although As availability increased. In contrast, the analysis of plants in this treatment revealed lower As and metal concentrations than those grown in the untreated soil. In turn, the application of magnesite and biochar was also effective in reducing metal(loid) availability; however, the plants did not grow under these conditions, probably due to the low N and P content of biochar. In this regard, the combined application of mining waste and sludge compost emerges as a useful nature-based solution for soil remediation in the context of the circular economy.

Comparison of the effectiveness of biochar vs. magnesite amendments to immobilize metals and restore a polluted soil.

Here we addressed the remediation of a soil severely contaminated by Cu, Cd, Pb and Zn. In this regard, we tested the capacity of magnesite and biochar, inorganic and organic soil amendments, respectively, to reduce metal availability and improve soil properties. To this end, 1-kg pots containing the polluted soil were amended with either magnesite or biochar. Metal availability and soil properties were then measured at days 15 and 75. Also, to evaluate the impact of the two treatments on plant growth, we conducted experimental trials with Brassica juncea L. and compost addition. Both amendments, but particularly magnesite, markedly decreased metal availability. Soil properties were also enhanced, as reflected by increases in the cation exchangeable capacity. However, plant growth was inhibited by magnesite amendment. This observation could be attributable to an increase in soil pH and cation exchange capacity as well as a high Mg concentration. In contrast, biochar increased biomass production but decreased the quantity of metals recovered when the plants are harvested. In conclusion, on the basis of our results, we propose magnesite as a suitable approach for stabilizing contaminated soils (or even spoil heaps) where revegetation is not a priority. In contrast, although biochar has a lower, but still significant, capacity to immobilize metals, it can be used to restore natural soil properties and thus favor plant growth.

Application of biochar, compost and ZVI nanoparticles for the remediation of As, Cu, Pb and Zn polluted soil.

Here we tested the capacity of zero valent iron nanoparticles (nZVI) combined with two organic amendments, namely, compost and biochar, to immobilize metal(oid)s such as As, Cu, Pb, and Zn. In addition, the effects of the amendments on the development of Brassica juncea L., a plant widely used for phytoremediation purposes, were also examined. To perform the experiments, pots containing polluted soil were treated with nZVI, compost-biochar, or a blend of compost-biochar-nZVI. Metal(oid)s availability and soil properties were evaluated after 15 and 75 days, and the height and weight of the plants were measured to determine development. The compost-biochar amendment showed excellent capacity to immobilize metals, but As availability was considerably increased. However, the addition of nZVI to the mixture corrected this effect considerably. In addition, soil treatment with nZVI alone led to a slight increase in Cu availability, which was not observed for the mixture with organic amendments. With respect to soil properties, the CEC and pH were enhanced by the compost-biochar amendment, thereby favoring plant growth. Nevertheless, the nanoparticles reduced the concentration of available P, which impaired plant growth to a certain extent. In conclusion, Fe-based nanoparticles combined with organic amendments emerge as powerful approaches to remediate soils contaminated by metals and metalloids.

Nanoremediation of As and metals polluted soils by means of graphene oxide nanoparticles.

The capacity of graphene oxide nanoparticles (nGOx) to reduce or increase As and metals availability in polluted soils was compared with that of zero valent iron nanoparticles (nZVI). The nanomaterials used in this study were characterized by X-ray techniques, CHNS-O analysis, dynamic light scattering, and microscopy procedures such as atomic force microscopy. To assess the capacity of these materials to immobilize pollutants, field samples of two soils were treated with nZVI and nGOx at a range of doses (0.2%, 1% and 5%). Availability tests were then performed. nGOx effectively immobilized Cu, Pb and Cd, but mobilized As and P (even at low doses), in the latter case irrespective of the simultaneous presence of high concentrations of metals. In turn, nZVI promoted notable immobilization results for As and Pb, a poorer result for Cd, and an increased availability for Cu. Soil pH and EC have been slightly affected by nGOx. On the whole, nGOx emerges as a promising option for mobilization/immobilization strategies for soil nanoremediation when combined with other techniques such as phytoremediation.

Contribution of fluorite mining waste to mercury contamination in coastal systems.

Samples from 13 beaches along the northern Spanish coast, a region with a history of heavy industries, were first screened to identify signs of pollution. High concentrations of Hg and Ba on Vega beach were found, both elements belong to the fluorite ore paragenesis, mined in the surroundings. Samples of beach and fluvial sediments, and nearby soils were collected in Vega beach area to address potential Hg pollution, fate and sources. Most samples showed a similar pollutants fingerprint to that of beach samples, especially those taken from white dunes, registering notable Hg concentrations. Hg was enriched in the finer fractions, and overall the main input was attributed to the mining waste discharged along the coast in the past. Although a specific risk assessment and study of the submerged sediments are advisable for this area, Hg bioavailability and methylation were low, thus indicating that this metal poses a reduced environmental risk.

Comparative effect of compost and technosol enhanced with biochar on the fertility of a degraded soil.

A large number of studies on the reclamation of mine soils focused on the problem caused by metals and did not explore in depth the issue of nutrients and vegetation after the application of organic materials. The aim of this study was to compare the effect of two treatments made of wastes and vegetated with Brassica juncea L. on the fertility of a settling pond mine soil. The first treatment was compost, biochar, and B. juncea (SCBP) and the second treatment was technosol, biochar, and B. juncea (STBP). This study evaluated the effect of the treatments on the soil nutrient concentrations and fertility conditions in the soil amendment mixtures, after 11 months of greenhouse experiment. Total carbon and nitrogen concentrations were higher in treatment SCBP than in treatment STBP after 7 months but, after 11 months, carbon concentration was higher in STBP. The used technosol could have forms of carbon more stable than compost, which could be released slower than in the compost-amended soils. Both compost and technosol mixed with biochar also increased the concentration of calcium, potassium, magnesium, and sodium in exchangeable form in the mine soil.

Effects of compost and technosol amendments on metal concentrations in a mine soil planted with Brassica juncea L.

Mining activities often cause important impacts on soil and water quality. The main objective of this study was to evaluate the effect of amendments (compost and technosol made from waste) on metal concentrations in a mine soil planted with Brassica juncea. A greenhouse experiment with cylinder pots was carried out during 11 months. The mine soil was collected from the settling pond of the depleted copper mine of Touro (Galicia, Northwest Spain). A series of characteristics were analysed including soil pseudototal metal concentrations, soil CaCl2-extractable (phytoavailable) metal concentrations and metal concentrations in soil pore water. The results showed that at depth 0-15 cm SCP (mine soil + compost, grown with B. juncea) had a significantly lower CaCl2-extractable Cu, Pb, Ni and Zn concentration than STP (mine soil + technosol, grown with B. juncea) over the time (P < 0.05). At depths 15, 30 and 45 cm, STP and SCP had lower Cu pore water concentration than S over the time. The highest translocation factor (TF) values for all metals (Cu, Pb, Ni and Zn) were observed at time 1 (3 months) in the settling pond soils treated with technosol and B. juncea L. The conclusions of this experiment revealed that SCP compared to STP caused a higher reduction on Cu, Pb, Ni and Zn phytoavailable concentrations in the first depths.

Using compost and technosol combined with biochar and Brassica juncea L. to decrease the bioavailable metal concentration in soil from a copper mine settling pond.

One of the most important sources of pollution caused by metals, if not the most important, is mining. Metal pollution is covert, persistent and irreversible. For this reason, soil metal pollution has become a severe problem in many parts of the world. The aim of this study was to observe which combination of amendments (compost + biochar or technosol + biochar) combined with Brassica juncea L. was best at reducing the assimilable contents of Cu, and which also increased to a lesser extent the contents of other metals (Ni, Pb, Zn) found in these amendments. We also studied the phytoremediation capacity of brassicas in these amendments. The experiment was carried out using 45-cm-deep cylinders over and 11-month period, with soil from the settling pond in the depleted copper mine located in Touro (Galicia, north-west Spain). At depth 0-15 cm, the settling pond soil (S) had a higher CaCl2-extractable Cu, Pb, and Ni concentration, at the three time periods measured (time 1 = 3 months, time 2 = 7 months, time 3 = 11 months). The settling pond soil + technosol + biochar and vegetated with Brassica juncea L. (STBP) had the highest CaCl2-extractable concentrations of Zn over time. In general terms, the most effective treatment for reducing the phytoavailable contents of Cu, Pb, Ni and Zn was the treatment using compost +b iochar + Brassica juncea L. In the two treatments applied, Brassica juncea L. had a good phytostabilisation capacity.

Recovering a copper mine soil using organic amendments and phytomanagement with Brassica juncea L.

A 3-month greenhouse experiment was carried out for evaluating the effect of an amendment mixture and mustards on the chemical characteristics of a mine soil and the metal uptake by plants. A settling pond soil was amended with increasing percentages of a technosol and biochar mixture and vegetated with Brassica juncea L. Adding amendments and planting mustards increased the soil pH from 2.83 to 6.18 and the TSC from u.l to 131 g kg(-1) and generally reduced the CaCl2-extractable metal concentrations in the soil. However, the amendments increased the pseudo-total soil concentration of Ni from 9.27 to 31.9 mg kg(-1), Pb from 27.9 to 91.6 mg kg(-1) and Zn from 46.5 to 577 mg kg(-1). The technosol and biochar mixture increased the shoot biomass from 0.74 to 2.95 g and generally reduced the metal concentrations in plants, meaning B. juncea as a potential candidate for phytostabilization of mine soils.

Phytoremediating a copper mine soil with Brassica juncea L., compost and biochar.

The soils at a depleted copper mine in Touro (Galicia, Spain) are chemically degraded. In order to determine the effect of amendments and vegetation on the chemical characteristics of a mine soil and on the plant uptake of metals, a greenhouse experiment was carried out for 3 months. A settling pond soil was amended with different percentages of a compost and biochar mixture and vegetated with Brassica juncea L. The results showed that the untreated settling pond soil was polluted by Cu. Amendments and planting mustards decreased the pseudototal concentration of this metal, reduced the extreme soil acidity and increased the soil concentrations of C and TN. Both treatments also decreased the CaCl2-extractable Co, Cu and Ni concentrations. However, the amendments increased the pseudototal concentration of Zn in the soil, provided by the compost that was used. The results also showed that mustards extracted Ni efficiently from soils, suggesting that B. juncea L. is a good phytoextractor of Ni in mine soils.