Trace element concentrations in leachates and mustard plant tissue (Sinapis alba L.) after biochar application to temperate soils

High-carbon wood ash biochar for mine tailings restoration: A field assessment of planted tree performance and metals uptake

Unique properties of biochar render it appealing for revegetating and decontaminating historic, barren, and chemically complex mine tailings. Bottom ash from bioenergy facilities can contain high levels of charcoal residue, and thus qualify as a type of biochar; the wide availability of this material at low cost makes it of particular interest in the context of tailings remediation. Nevertheless, bottom ash is variable and often contains residual toxic metal/loids that could be phytoabsorbed into plant tissues. We implemented a replicated field trial on historic contaminated metal mine tailings in Northern Ontario (Canada) over a range of high‑carbon wood ash biochar (HCWAB) dosages (0-30 t/ha) to evaluate tree and substrate responses. Sapling survivorship and aboveground biomass growth were quantified over a 4-year period; substrate chemical parameters were measured using acid-digestion and ICP-MS, as well as ion exchange resin probes. To assess elemental composition of sapling tissues, we used electron probe microanalysis combined with laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) on intact samples across the range of dosages applied. Survival and growth of saplings peaked at mid-range ash dosages of 3-6 t/ha. Similarly, substrate ion availability of P, K, and Zn were stable at lower dosages, but increased above 6 t/ha. The trace amounts of toxic metal/loids of concern measured in wood ash (As, Cd, Cu, and Pb) did not result in significantly increased sapling tissue concentrations at low to moderate dosages, but in some cases tissue contaminant levels were elevated at the highest dosage examined (30 t/ha). Our findings highlight the potential for high‑carbon wood ash biochar to be used for metal mine restoration at low to moderate dosages.

Iron enriched quinoa biochar enhances Nickel phytoremediation potential of Helianthus annuus L. by its immobilization and attenuation of oxidative stress: implications for human health

The present study was performed to assess Ni-immobilization and the phytoremediation potential of sunflower by the application of quinoa stalks biochar (QSB) and its magnetic nanocomposite (MQSB). The QSB and MQSB were characterized with FTIR, SEM, EDX, and XRD to get an insight of their surface properties. Three-week-old seedlings of sunflower were transplanted to soil spiked with Ni (0, 15, 30, 60, 90 mg kg-1), QSB and MQSB (0, 1, and 2%) in the wire house under natural conditions. The results showed that increasing Ni levels inhibited sunflower growth and yield due to the high production of reactive oxygen species (ROS) and lipid peroxidation. Enzyme activities like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POX) also increased as Ni levels increased. However, the application of QSB and MQSB reduced Ni uptake, root-shoot, and shoot-seed translocation and decreased the generation of ROS, and lowered the activity of SOD, CAT, APX, and POX, leading to improved growth and yield, especially with MQSB. This was verified through SEM, EDX, XRD, and FTIR. It can be concluded that QSB and MQSB can effectively enhance Ni-tolerance in sunflowers and mitigate oxidative stress and human health risks.

Micronutrients and heavy metals in rice farms: the case of Ahvaz and Bawie Counties, Khuzestan Province, Iran

This study addressed micronutrients (Fe, Zn, Cu, Mn, Co) and heavy metals (As, Pb) in the soil and rice crop in Khuzestan Province, Iran. Twenty-eight composite soil and grain samples from the intended rice farms were garnered during harvest time. Concentrations of the elements in the samples and in the grains were, respectively, determined by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry device. The average concentration of As, Fe, Co, Cu, Mn, Pb, and Zn in soil of crop were 2.71, 20,065.8, 10.43, 22.28, 422.28, 5.85, and 47.07 mg/kg, respectively. The physicochemical properties of soil, bioconcentration factor, daily intakes, and health risk assessment of the elements were calculated. The results revealed that the area covered by alkaline saline soils is poor in micronutrients. Bioconcentration factor values of all elements were less than 1. Low levels of bioconcentration factor may be for low levels of nutrients in the soil and physicochemical conditions of the soil. Furthermore, the daily intake of Co (adults' group) and Fe and Zn (children group) was very low. Health risk assessment showed only adults are threatened by non-cancerous diseases due to excessive value of all the elements (HI = 2.53) and cancerous diseases caused by excessive As and Pb (2.86E-04 and 2.01E-05, respectively). Considering that Khuzestan Province is the fourth largest producer of rice in Iran, the lack of micronutrients and the presence of heavy metals in rice produced in the study area can adversely affect consumers. Further investigation is therefore a must in the region.

Biochar decreases Cd mobility and rice (Oryza sativa L.) uptake by affecting soil iron and sulfur cycling

Biochar has been used as an amendment in Cd-contaminated soils. However, the mechanisms of which biochar reduce Cd mobility and rice (Oryza sativa L.) Cd uptake by modifying the iron and sulfur cycling in soil has rarely been addressed in the literature. A pot experiment has been carried out with two Cd-contaminated paddy soils (FG and DBS) from South China. Rice straw biochar (RSB) and rape straw biochar (RASB) pyrolyzed at 450 °C were applied at 0, 0.5, and 1% (w/w), respectively. The results showed that biochar amendment at a rate of 1% reduced grain Cd concentrations by 29.3-35.2%. Furthermore, biochar significantly reduced the Cd concentration of root, while the decline of Cd concentration by RASB treatment was higher than by RSB treatment. Root Cd in RASB_0.5 was significantly reduced by 56.4-51.8% compared to than that in RSB_0.5 at the maturing stage. Biochar reduced soil acid-soluble Cd by 15.9-25.3% with the increase of pH at the maturing stage in FG soil, and 30.1-59.3% by promoting soil into more reductive condition at the heading stage in DBS soil with higher contents of Fe and S. In addition, biochar impeded Cd transport from soil to rice roots by increasing the formation of iron plaque at the flooding stage. Owing to the influence of RASB₁, DCB-Cd concentration increased significantly, with 99.7% at the heading stage in FG soil and 237.9% at the tillering stage in DBS soil, respectively. Furthermore, RASB with a higher sulfur concentration had a more positive effect on Cd immobilization and iron plaque formation compared to RSB. As a conclusion, this study suggested that biochar might be able to promote the Cd immobilization by affecting the cycling of iron and sulfur in soil.

Biochar for agronomy, animal farming, anaerobic digestion, composting, water treatment, soil remediation, construction, energy storage, and carbon sequestration: a review

In the context of climate change and the circular economy, biochar has recently found many applications in various sectors as a versatile and recycled material. Here, we review application of biochar-based for carbon sink, covering agronomy, animal farming, anaerobic digestion, composting, environmental remediation, construction, and energy storage. The ultimate storage reservoirs for biochar are soils, civil infrastructure, and landfills. Biochar-based fertilisers, which combine traditional fertilisers with biochar as a nutrient carrier, are promising in agronomy. The use of biochar as a feed additive for animals shows benefits in terms of animal growth, gut microbiota, reduced enteric methane production, egg yield, and endo-toxicant mitigation. Biochar enhances anaerobic digestion operations, primarily for biogas generation and upgrading, performance and sustainability, and the mitigation of inhibitory impurities. In composts, biochar controls the release of greenhouse gases and enhances microbial activity. Co-composted biochar improves soil properties and enhances crop productivity. Pristine and engineered biochar can also be employed for water and soil remediation to remove pollutants. In construction, biochar can be added to cement or asphalt, thus conferring structural and functional advantages. Incorporating biochar in biocomposites improves insulation, electromagnetic radiation protection and moisture control. Finally, synthesising biochar-based materials for energy storage applications requires additional functionalisation.

Can combined compost and biochar application improve the quality of a highly weathered coastal savanna soil?

Soil fertility decline is a major constraint to crop production in sub-Saharan Africa. The positive effect of biochar and compost applications on soil fertility has been reported by many authors. In this study, a 30-day laboratory incubation experiment was done using 120 g samples each of a Haplic acrisol amended with corn cob biochar (cbio), rice husk biochar (rbio), coconut husk biochar (coco300 and coco700) or poultry manure compost (compost); and co- composted rice husk biochar (rcocomp) or co-composted corn cob biochar (cococomp) at rates of 1 % w/w amendment: soil, respectively. Other treatments in the study were combined poultry manure compost and corn cob biochar or rice husk biochar (1 % compost + 1% biochar: 1% soil w/w), respectively, to examine their effects on basal soil respiration, soil pH; soil microbial carbon; cation exchange capacity; total organic carbon, total nitrogen and available nitrogen concentration. Biochar and compost applied solely or together, and composted biochar increased soil pH by 0.28-2.29 pH units compared to the un-amended control. Basal respiration from the sole compost or composted rice husk, or corn cob biochar or combined biochar and compost were higher than the un-amended control, which was similar to that from the biochar only treatments. TOC in the sole compost and combined corn cob biochar and compost treatments were up to 37% and 117% higher, respectively, than the control. Combined application of rice husk biochar and compost increased MBC by 132% while sole compost addition increased MBC by 247%, respectively, compared to the control. In conclusion, the study demonstrated that sole or combined application of compost and biochar, or composted biochar improved soil quality parameters such as soil pH and MBC, and promoted soil C stabilization through enhanced TOC and reduced soil C loss through basal respiration.

Aluminum toxicity in plants and its possible mitigation in acid soils by biochar: A review

Toxicity of aluminum (Al) is a serious problem for agricultural plants, especially due to excessive soil acidification caused by continuous intensive agriculture and modified environmental conditions related with global climate change. Decreased root elongation and shoot growth, reduced biomass production, nutrient imbalance and altered physiological and metabolic processes are responsible for lower yield and crop quality and therefore, decreased variability and productivity of the land. Recently, biochar is gaining popularity for ameliorating metal toxicity in soils. However, there is a lack of comprehensive information regarding the effects of biochar and its functioning. Multiple mechanisms are involved in ameliorating Al toxicity in which inherent properties of biochar influencing Al adsorption, absorption, complexation, cation exchange and electrostatic interaction are considered to play major roles. Modification of biochar to enhance these mechanisms might hold the key for long term solution. Present review indicates gaps for further research. Long term field studies are needed to understand the effects of biochar on Al toxicity.

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.

Does biochar inhibit the bioavailability and bioaccumulation of As and Cd in co-contaminated soils? A meta-analysis

Biochar, an effective and low-cost amendment for immobilizing heavy metals, has been extensively studied. However, the simultaneous inhibition effects of biochar on the plant uptake for arsenic (As) and cadmium (Cd) in co-contaminated soils are still ambiguous due to their distinct environmental behaviors. A meta-analysis was conducted to quantitatively assess the effects using 1030 individual observations from 52 articles. On average, biochar application significantly decreased the bioavailability of Cd in soils by 50.12%, while slightly increased the bioavailability of As in soils by 2.39%. The more instructive result is that biochar application could also simultaneously reduce the concentration of As and Cd in plants by 25.48% and 38.66%, respectively. The orders of the decreased percentage of As and Cd in various tissues were root < stem< leaf < grain, and root < leaf < stem < grain, respectively. According to the analysis of critical factors, manure biochar, low pyrolysis temperature (at <400 °C), low application rate (<2%), and high SOC (>30 g/kg) were more conducive to reduce the bioaccumulation of As and Cd simultaneously in co-contaminated soils. Pristine and modified biochar could inhibit As and Cd accumulation in crops, but their efficiencies need to be further improved to ensure the safety of crop productions. Overall, the meta-analysis suggests that biochar has the potential to remedy the As and Cd co-contaminated soils.

The Use of Biochar and Pyrolysed Materials to Improve Water Quality through Microcystin Sorption Separation

Harmful algal blooms have increased globally with warming of aquatic environments and increased eutrophication. Proliferation of cyanobacteria (blue-green algae) and the subsequent flux of toxic extracellular microcystins present threats to public and ecosystem health and challenges for remediation and management. Although methods exist, there is currently a need for more environmentally friendly and economically and technologically feasible sorbents. Biochar has been proposed in this regard because of its high porosity, chemical stability, and notable sorption efficiency for removing of cyanotoxins. In light of worsening cyanobacterial blooms and recent research advances, this review provides a timely assessment of microcystin removal strategies focusing on the most pertinent chemical and physical sorbent properties responsible for effective removal of various pollutants from wastewater, liquid wastes, and aqueous solutions. The pyrolysis process is then evaluated for the first time as a method for sorbent production for microcystin removal, considering the suitability and sorption efficiencies of pyrolysed materials and biochar. Inefficiencies and high costs of conventional methods can be avoided through the use of pyrolysis. The significant potential of biochar for microcystin removal is determined by feedstock type, pyrolysis conditions, and the physiochemical properties produced. This review informs future research and development of pyrolysed materials for the treatment of microcystin contaminated aquatic environments.

Assisted phytoremediation of a former mine soil using biochar and iron sulphate: Effects on As soil immobilization and accumulation in three Salicaceae species

Metal(loid) accumulation in soils, is of increasing concern because of the potential human health risks. Therefore, metal(loid) contaminated sites need rehabilitation. It is becoming increasingly popular to use phytoremediation methods for the reclamation of sites containing metal(loid)s. However, plant establishment and growth on contaminated soils can be difficult due to high metal(loid) concentrations and poor fertility conditions. Consequently, amendments, like biochar and iron sulphate, must be applied. Biochar, obtained from plant biomass or animal wastes pyrolyzed under minimal oxygen supply, showed beneficial effects on soil properties and plant growth. Iron sulphate can effectively immobilize anions, thus mitigating metal(loid) toxicity and hence promoting plant development. This study aimed to assess the effect of two different modalities of biochar amendment application (top third of the tube and all tube height) combined with iron sulphate addition on the physico-chemical properties of a mining polluted soil and the growth and metal(loid) uptake of three Salicaceae species. A 1.5 year mesocosm experiment under field condition was conducted using a former tin mine contaminated by arsenic, amended with biochar and iron sulphate and vegetated with three Salicaceae species. Results showed that the combination of biochar and iron sulphate improved soil characteristics by increasing pH and electrical conductivity and reducing soil pore water metal(loid) concentrations. Between the two biochar application methods, the addition of biochar on the all tube height showed better results. But for such contaminated soil, biochar, in combination with iron sulphate, had no positive effect on plant growth, for all species tested and especially when incorporating on the top third of the tube. Finally, S. purpurea presented high root metal(loid) concentrations associated to the better growth compared to P. euramericana and S. viminalis, making it a better candidate for phytostabilization of the studied soil.

Contrasting effects of biochar and hydrothermally treated coal gangue on leachability, bioavailability, speciation and accumulation of heavy metals by rapeseed in copper mine tailings

The purpose of this research was to examine the influence of hydrothermally treated coal gangue (HTCG) with and without biochar (BC) on the leaching, bioavailability, and redistribution of chemical fractions of heavy metals (HMs) in copper mine tailing (Cu-MT). An increase in pH, water holding capacity (WHC) and soil organic carbon (SOC) were observed due to the addition of BC in combination with raw coal gangue (RCG) and HTCG. A high Cu and other HMs concentration in pore water (PW) and amended Cu-MT were reduced by the combination of BC with RCG and/or HTCG, whereas individual application of RCG slightly increased the Cu, Cd, and Zn leaching and bioavailability, compared to the unamended Cu-MT. Sequential extractions results showed a reduction in the exchangeable fraction of Cu, Cd, Pb, and Zn and elevation in the residual fraction following the addition of BC-2% and BC-HTCG. However, individual application of RCG slightly increased the Cu, Cd, and Zn exchangeable fractions assessed by chemical extraction method. Rapeseed was grown for the following 45 days during which physiological parameters, metal uptake transfer rate (TR), bioconcentration factor (BCF), and translocation factor (TF) were measured after harvesting. In the case of plant biomass, no significant difference between applied amendments was observed for the fresh biomass (FBM) and dry biomass (DBM) of shoots and roots of rapeseed. However, BC-2% and BC-HTCG presented the lowest HMs uptake, TR, BCF (BCF_root and BCF_shoot), and TF for Cu, Cd, Cr, Ni, Pb, and Zn in rapeseed among the other amendments compared to the unamended Cu-MT. Overall, these findings are indicative that using biochar in combination with RCG and/or HTCG led to a larger reduction in HMs leaching and bioavailability, due to their higher sorption capacity and could be a suitable remediation strategy for heavy metals in a Cu-MT.

Remediation of Cd-contaminated soils by GWC application, evaluated in terms of Cd immobilization, enzyme activities, and pakchoi cabbage uptake

Compost (mainly composed of cow manure, horse manure, chicken manure, and straw) has turned out to be effective in remediation of heavy metal-contaminated soil. However, in recent years, the effects of green waste compost (GWC) on plant growth and the immobilization of heavy metal cadmium (Cd) in the soil have not been clearly studied. We considered the effects of different GWC ratios on the growth of pakchoi cabbage, soil physical and chemical properties, total and availability of Cd content, and soil enzyme activity. The results showed that organic matter, total nitrogen, available phosphorus, and available potassium in the soil gradually put in place over the increase of compost proportion and showed a significant difference. Dehydrogenase, urease, and catalase activities grew by 380, 35, and 32% under the treatment of T10, respectively. The increase of enzyme activity indirectly reflects the enhancement of self-purification ability of contaminated soil. The addition of GWC improved soil quality, leading to a significant increase in soil nutrients, and in biomass and chlorophyll content of pakchoi cabbage. The decrease of Cd availability led to a significant reduction of Cd content in pakchoi cabbage, with a 30-36% reduction of Cd content in roots and a 43-69% reduction in leaf. The BCF of leaves decreased from 0.62 to 0.22, and the TF decreased from 0.94 to 0.46, indicating that the addition of GWC reduced the mobility of Cd to pakchoi cabbage leaves. The result is decreased in Cd content in edible parts of pakchoi cabbage.

The role of biochar in organic waste composting and soil improvement: A review

Large amounts of organic wastes, which pose a severe threat to the environment, can be thermally pyrolyzed to produce biochar. Biochar has many potential uses owing to its unique physicochemical properties and attracts increasing attentions. Therefore, this review focuses on the agronomic functions of biochar used as compost additives and soil amendments. As a compost additive, biochar provides multiple benefits including improving composting performance and humification process, enhancing microbial activities, reducing greenhouse gas and NH₄ emissions, immobilizing heavy metals and organic pollutants. As a soil amendment, biochar shows a good performance in improving soil properties and plant growth, alleviating drought and salinity stresses, interacting with heavy metals and organic pollutants and changing their fate of being uptaken from soils to plants. Furthermore, combined application of biochar and compost shows a good performance and a high agricultural value when applied to soils. Objectively and undeniably, there are still negative or ineffective cases of biochar amendment on crop yield and heavy metal immobilization, which is worthy of further attention. The medium-long term field monitoring of biochar-specific agricultural functions, as well as the exploration of wider sources for biochar feedstocks, are still needed.

Potential use of biochar, compost and iron grit associated with Trifolium repens to stabilize Pb and As on a multi-contaminated technosol

Vegetation cover can be used in the phytomanagement of polluted areas by adding value to abandoned sites and reducing the dispersion of pollutants by erosion. Appropriate amendments, that allow both efficient plant growth and the immobilization of contaminants in the soil must be chosen in order to optimize the efficiency of this process. We used a mining technosol mainly contaminated by arsenic (1068 mg kg^-1) and lead (23387 mg kg^-1) to study the effect of three amendments (biochar, compost and iron grit) on (i) physico-chemical properties of the soil and soil pore water, (ii) metal(loid) mobility, bioavailability and bioaccessibility (CaCl₂ and Simple Bioaccessibility Extraction Test (SBET)), and (iii) the capability of Trifolium repens to germinate and grow. All the amendments used increased the pH and electrical conductivity of the SPW, resulting in a 90% decrease in the concentration of lead in the soil pore water (SPW). We also demonstrated a decrease in Pb phytoavailability. The amendments allowed the establishment of a plant cover, although the addition of iron grit alone did not allow any clover germination. For the Pontgibaud technosol, the combination of the three amendments resulted in a significant decrease in As and Pb concentrations in clover tissues, mainly in the aerial organs. The amendments also made it possible for some of them to halve the phytoavailable fraction of arsenic. However, for compost, both the As concentrations in the SPW, and the bioavailable fraction of As increased. All the amendments used had contrasting effects on the bioaccessible fractions of metal(loid)s. The most efficient amendment combination was the addition of 5% biochar and 5% compost.

Phytostabilization of Zn and Cd in Mine Soil Using Corn in Combination with Biochars and Manure-Based Compost

Mining activities could produce a large volume of spoils, waste rocks, and tailings, which are usually deposited at the surface and become a source of metal pollution. Phytostabilization of the mine spoils could limit the spread of these heavy metals. Phytostabilization can be enhanced by using soil amendments such as manure-based biochars capable of immobilizing metal(loid)s when combined with plant species that are tolerant of high levels of contaminants while simultaneously improving properties of mine soils. However, the use of manure-based biochars and other organic amendments for mine spoil remediation are still unclear. In this greenhouse study, we evaluated the interactive effect of biochar additions (BA) with or without the manure-based compost (MBC) on the shoots biomass (SBY), roots biomass (RBY), uptake, and bioconcentration factor (BCF) of Zn and Cd in corn (Zea mays L.) grown in mine soil. Biochar additions consisting of beef cattle manure (BCM); poultry litter (PL); and lodge pole pine (LPP) were applied at 0, 2.5, and 5.0% (w/w) in combination with different rates (0, 2.5, and 5.0%, w/w) of MBC, respectively. Shoots and roots uptake of Cd and Zn were significantly affected by BA, MBC, and the interaction of BA and MBC. Corn plants that received 2.5% PL and 2.5% BCM had the greatest Cd and Zn shoot uptake, respectively. Corn plants with 5% BCM had the greatest Cd and Zn root uptake. When averaged across BA, the greatest BCF for Cd in the shoot of 92.3 was from the application of BCM and the least BCF was from the application of PL (72.8). Our results suggest that the incorporation of biochar enhanced phytostabilization of Cd and Zn with concentrations of water-soluble Cd and Zn lowest in soils amended with manure-based biochars while improving the biomass productivity of corn. Overall, the phytostabilization technique and biochar additions have the potential to be combined in the remediation of heavy metals polluted soils.

Insights on limits of detection, precision and accuracy in TXRF analysis of trace and major elements in environmental solid suspensions

In this work, the analytical capability of the total reflection X-ray fluorescence technique with the S2 PICOFOX spectrometer was investigated. A set of certified reference materials was prepared as solid particulate for TXRF analysis. Experimental data of sensitivity, limits of detection and recovery for many elements were obtained. Good sensitivity and limits of detection with a good recovery range of around 90-110% were achieved. Thus, the TXRF technique exhibits a good analytical potential for its applicability on different materials.

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.

Improved quinoa growth, physiological response, and seed nutritional quality in three soils having different stresses by the application of acidified biochar and compost

Quinoa (Chenopodium quinoa Willd.) is a traditional Andean agronomical resilient seed crop having immense significance in terms of high nutritional qualities and its tolerance against various abiotic stresses. However, finite work has been executed to evaluate the growth, physiological, chemical, biochemical, antioxidant properties, and mineral nutrients bioavailability of quinoa under abiotic stresses. Depending on the consistency in the stability of pH, intended rate of S was selected from four rates (0.1, 0.2, 0.3, 0.4 and 0.5% S) for the acidification of biochar and compost in the presence of Thiobacillus thiooxidans by pH value of 4. All three soils were amended with 1% (w/w) acidified biochar (BC_A) and compost (CO_A). Results revealed that selective plant growth, yield, physiological, chemical and biochemical improved significantly by the application of BC_A in all stressed soils. Antioxidants in quinoa fresh leaves increased in the order of control > CO_A > BC_A, while reactive oxygen species decreased in the order of control < CO_A < BC_A. A significant reduction in anti-nutrients (phytate and polyphenols) was observed in all stressed soils with the application of BC_A. Moreover, incorporation of CO_A and BC_A reduced the pH of rhizosphere soil by 0.4-1.6 units in all stressed soils, while only BC_A in bulk soil decreased pH significantly by 0.3 units. These results demonstrate that BC_A was more effective than CO_A to enhance the bioavailability, translocation of essential nutrients from the soil to plant and their enhanced bioavailability in the seed.

Waste or substrate for metal hyperaccumulating plants - The potential of phytomining on waste incineration bottom ash

Phytomining could represent an innovative low-cost technology for the selective recovery of valuable trace elements from secondary resources. In this context the potential of phytomining from waste incineration bottom ash was tested in a pot experiment. Fresh bottom ash was acidified, leached to reduce salinity and amended with organic material to obtain a suitable substrate for plant growth. Two hyperaccumulator species, Alyssum serpyllifolium subsp. lusitanicum and Sedum plumbizincicola as well as three metal tolerant species, Brassica napus, B. juncea and Nicotiana tabacum were tested for their phytomining potential on the pre-treated and amended bottom ashes from municipal solid waste and hazardous waste incineration. The hyperaccumulators had severe difficulties to establish on the bottom ash and to produce sufficient biomass, likely due to salinity and Cu toxicity. Nevertheless, concentrations of Ni in A. serpyllifolium and Zn in S. plumbizincicola were high, but total metal removal was limited by the low biomass production and was clearly less than on metalliferous soils. The Brassica species proved to be more tolerant to salinity and high Cu concentrations and produced considerably higher biomass, but total metal removal was limited by rather low shoot concentrations. The observed limitations of the phytomining process along with currently low market prices of Ni and Zn suggest that further optimisation of the process is required in order to make phytomining economically feasible on the tested waste incineration bottom ashes.

Risks and benefits of marginal biomass-derived biochars for plant growth

In this study, 19 biochars from marginal biomass, representing all major biomass groups (woody materials, grass, an aquatic plant, anthropogenic wastes) were investigated regarding their content of available potentially toxic elements (PTEs) and nutrients (determined by NH4NO3-extractions) and their effects on cress (Lepidium sativum) seedling growth. The objective was to assess the potential and actual effects of biochar with increased PTE content on plant growth in the context of use in soil amendments and growing media. It showed that the percentage of available PTEs was highest for biochars produced at the highest treatment temperature (HTT) of 750°C. On average, however, for all 19 biochars, the percentage availability of Cu, Cr, Ni and Zn (<1.5% for all) was similar to the percentage availability reported in the literature for the same elements in soils at similar pH values which is a highly important finding. Most biochars exceeded German soil threshold values for NH4NO3-extractable PTEs, such as Zn (by up to 25-fold), As and Cd. Despite this, cress seedling growth tests with 5% biochar in sand did not show any correlations between inhibitory effects (observed in 5 of the 19 biochars) and the available PTE concentrations. Instead, the available K concentration and biochar pH were highly significantly, negatively correlated with seedling growth (K: p<0.001, pH: p=0.004). K had the highest available concentration of all elements and the highest percentage availability (47.7±19.7% of the total K was available). Consequently, available K contributed most to the osmotic pressure and high pH which negatively affected the seedlings. Although a potential risk if some of these marginal biomass-derived biochar were applied at high concentrations, e.g. 5% (>100tha(-1)), when applied at agriculturally realistic application rates (1-10tha(-1)), the resulting smaller increases in pH and available K concentration may actually be beneficial for plant growth.

Carbon mineralization and nutrient availability in calcareous sandy soils amended with woody waste biochar

Many studies have reported the positive effect of biochar on soil carbon sequestration and soil fertility improvement in acidic soils. However, biochar may have different impacts on calcareous sandy soils. A 90-day incubation experiment was conducted to quantify the effects of woody waste biochar (10 g kg(-1)) on CO2-C emissions, K2SO4-extractable C and macro-(N, P and K) and micro-(Fe, Mn, Zn and Cu) nutrient availability in the presence or absence of poultry manure (5 g kg(-1) soil). The following six treatments were applied: (1) conocarpus (Conocarpus erectus L.) waste (CW), (2) conocarpus biochar (BC), (3) poultry manure (PM), (4) PM+CW, (5) PM+BC and (6) untreated soil (CK). Poultry manure increased CO2-C emissions and K2SO4-extractable C, and the highest increases in CO2-C emission rate and cumulative CO2-C and K2SO4-extractable C were observed for the PM+CW treatment. On the contrary, treatments with BC halted the CO2-C emission rate, indicating that the contribution of BC to CO2-C emissions is negligible compared with the soils amended with CW and PM. Furthermore, the combined addition of PM+BC increased available N, P and K compared with the PM or BC treatments. Overall, the incorporation of biochar into calcareous soils might have benefits in carbon sequestration and soil fertility improvement.

Miscellaneous additives can enhance plant uptake and affect geochemical fractions of copper in a heavily polluted riparian grassland soil

The problem of copper (Cu) pollution in riverine ecosystems is world-wide and has significant environmental, eco-toxicological, and agricultural relevance. We assessed the suitability and effectiveness of application rate of 1% of activated charcoal, bentonite, biochar, cement kiln dust, chitosan, coal fly ash, limestone, nano-hydroxyapatite, organo-clay, sugar beet factory lime, and zeolite as soil amendments together with rapeseed as bioenergy crop as a possible remediation option for a heavily Cu polluted floodplain soil (total Cu=3041.9mgkg(-1)) that has a very high proportion of sorbed/carbonate fraction (484.6mgkg(-1)) and potential mobile fraction of Cu (1611.9mgkg(-1)). Application changed distribution of Cu among geochemical fractions: alkaline materials lead to increased carbonate bounded fraction and the acid rhizosphere zone might cause release of this Cu. Thus, mobilization of Cu and uptake of Cu by rapeseed were increased compared to the control (except for organo-clay) under the prevailing conditions.

Trace element biogeochemistry in the soil-water-plant system of a temperate agricultural soil amended with different biochars

Various biochar (BC) types have been investigated as soil amendment; however, information on their effects on trace element (TE) biogeochemistry in the soil-water-plant system is still scarce. In the present study, we determined aqua-regia (AR) and water-extractable TEs of four BC types (woodchips (WC), wheat straw (WS), vineyard pruning (VP), pyrolyzed at 525 °C, of which VP was also pyrolyzed at 400 °C) and studied their effects on TE concentrations in leachates and mustard (Sinapis alba L.) tissue in a greenhouse pot experiment. We used an acidic, sandy agricultural soil and a BC application rate of 3% (w/w). Our results show that contents and extractability of TEs in the BCs and effectuated changes of TE biogeochemistry in the soil-water-plant system strongly varied among the different BC types. High AR-digestable Cu was found in VP and high B contents in WC. WS had the highest impact on TEs in leachates showing increased concentrations of As, Cd, Mo, and Se, whereas WC application resulted in enhanced leaching of B. All BC types increased Mo and decreased Cu concentrations in the plant tissue; however, they showed diverging effects on Cu in the leachates with decreased concentrations for WC and WS, but increased concentrations for both VPs. Our results demonstrate that BCs may release TEs into the soil-water-plant system. A BC-induced liming effect in acidic soils may lead to decreased plant uptake of cationic TEs, including Pb and Cd, but may enhance the mobility of anionic TEs like Mo and As. We also found that BCs with high salt contents (e.g., straw-based BCs) may lead to increased mobility of both anionic and cationic TEs in the short term.

Utilization of biochar sorbents for Cd²⁺, Zn²⁺, and Cu²⁺ ions separation from aqueous solutions: comparative study

The objective of this study was to study the utilization of two different woody-derived biochars for Cd(2+), Zn(2+), and Cu(2+) ions separation from aqueous solutions. Physicochemical characterization confirmed the main differences in sorbent surface area and cation-exchange capacity. The maximum cadmium, zinc, and copper sorption capacities were 1.99, 0.97, and 2.50 mg g(-1) for biochar (BC) A; 7.80, 2.23, and 3.65 mg g(-1) for BC B. Sorption processes can be affected by time and pH. The most of sorbed cadmium and zinc were bound on exchangeable fractions and copper oxidizable fractions. Chemical modification and FT-IR analyses confirmed the crucial roles of hydroxyl and mainly carboxyl functional groups in sorption processes of Cd(2+), Zn(2+), and Cu(2+) ions by BC A and BC B. The garden wood rests with leaf mass-derived biochar can be utilized as an effective sorbent for bivalent ions.