Guido Fellet

Application of biochar on mine tailings: Effects and perspectives for land reclamation

Mine tailings represent a source of toxic pollutants, mainly heavy metals, which may spread to the surrounding areas. Phytostabilization, a long-term and cost-effective rehabilitation strategy, can be achieved by promoting the establishment of vegetation to reduce the risk of pollutant transfer. In this work, the application of pyrolyzed biomass (biochar) was studied to evaluate the amelioration of the mine tailings properties for potential use as a phytostabilization technology. Four substrates were obtained by mixing the mine tailings from a dumping site in Cave del Predil (NE, Italy) with biochar from orchard prune residues at four dosages (0%, 1%, 5% and 10% biochar in the mine tailings). The physical and chemical properties were determined and the bioavailability and leachability of the contaminants were estimated. The pH, the nutrient retention in terms of cation exchange capacity and the water-holding capacity increased as the biochar content increased in the substrates and the bioavailability of Cd, Pb, Tl and Zn of the mine tailings decreased. The changes promoted by the biochar seem to be in favor of its use on mine wastes to help the establishment of a green cover in a phytostabilization process.

Elements uptake by metal accumulator species grown on mine tailings amended with three types of biochar

Mine tailings are of great concern due to the risk their toxic inorganic elements pose to the environment. The application of biochar as an amendment may be a solution to reduce the risk of pollutant diffusion. The main purpose of the research was to verify the effects of different types of biochar produced from different feedstocks (pruning residues, fir tree pellets and manure pellets) on changing the substrate conditions to promote plant growth for the phytostabilization of mine tailings. The SEM/EDX characterization showed different structures in terms of porosity and granulosity as well as the element composition. The plants used in the pot experiment were Anthyllis vulneraria subsp. polyphylla (Dc.) Nyman, Noccaea rotundifolium (L.) Moench subsp. cepaeifolium and Poa alpina L. subsp. alpina. The biochars were applied at three doses: 0, 1.5 and 3%dw. Although to different extents, the biochars induced significant changes of the substrates in terms of pH, EC, CEC and bioavailability of the metals. The biochar from manure pellets and pruning residues reduced shoot Cd and Pb accumulations. The former also led to a higher biomass production that peaked at the1.5% dose. Biochar has great potential as an amendment for phytoremediation but its effects depend on the type of feedstock it derives from. The characteristics of the substrate to be treated are crucial for the biochar selection.

Biochar addition to an arsenic contaminated soil increases arsenic concentrations in the pore water but reduces uptake to tomato plants (Solanum lycopersicum L.).

Arsenic (As) concentrations in soil, soil pore water and plant tissues were evaluated in a pot experiment following the transplantation of tomato (Solanum lycopersicum L.) plantlets to a heavily As contaminated mine soil (~6000 mg kg(-1) pseudo-total As) receiving an orchard prune residue biochar amendment, with and without NPK fertiliser. An in-vitro test was also performed to establish if tomato seeds were able to germinate in various proportions of biochar added to nutrient solution (MS). Biochar significantly increased arsenic concentrations in pore water (500 μg L(-1)-2000 μg L(-1)) whilst root and shoot concentrations were significantly reduced compared to the control without biochar. Fruit As concentrations were very low (<3 μg kg(-1)), indicating minimal toxicity and transfer risk. Fertilisation was required to significantly increase plant biomass above the control after biochar addition whilst plants transplanted to biochar only were heavily stunted and chlorotic. Given that increasing the amount of biochar added to nutrient solution in-vitro reduced seed germination by up to 40%, a lack of balanced nutrient provision from biochar could be concluded. In summary, solubility and mobility of As were increased by biochar addition to this soil, but uptake to plant was reduced, and toxicity-transfer risk was negligible. Therefore leaching rather than food chain transfer appears the most probable immediate consequence of biochar addition to As contaminated soils.

Toward the Standardization of Biochar Analysis: The COST Action TD1107 Interlaboratory Comparison

Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical-chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future.

Variation in Heavy Metal Accumulation and Genetic Diversity at a Regional Scale Among Metallicolous and Non-Metallicolous Populations of the Facultative Metallophyte Biscutella laevigata subsp. laevigata.

Biscutella laevigata is a facultative metallophyte, with populations on non-metalliferous and metalliferous soils. Some of its metallicolous populations have been shown to hyperaccumulate thallium or lead in nature. Only Tl hyperaccumulation has been experimentally confirmed. We aimed to compare the patterns of metal (hyper)accumulation and genetic diversity among populations of B. laevigata subsp. laevigata in NE Italy. None of the populations exhibited foliar hyperaccumulation of Cu, Zn, or Pb. The root-to-shoot accumulation rates for these metals were unchanged or decreased rather than enhanced in the metallicolous populations, in comparison with the non-metallicolous ones. Hyperaccumulation of Tl was confined to the population of the Cave del Predil mine. This population was genetically very distinct from the others, as demonstrated by AFLP-based cluster analysis. The two other mine populations did not surpass the threshold for Tl hyperaccumulation, but showed enhanced foliar Tl concentrations and root-to-shoot translocation rates, in comparison with the non-metallicolous populations. Genetic analysis suggested that adaptation to metalliferous soil must have been independently evolved in the metallicolous populations.

Effects of Cerium and Titanium Oxide Nanoparticles in Soil on the Nutrient Composition of Barley (Hordeum vulgare L.) Kernels

The implications of metal nanoparticles (MeNPs) are still unknown for many food crops. The purpose of this study was to evaluate the effects of cerium oxide (nCeO2) and titanium oxide (nTiO2) nanoparticles in soil at 0, 500 and 1000 mg·kg−1 on the nutritional parameters of barley (Hordeum vulgare L.) kernels. Mineral nutrients, amylose, β-glucans, amino acid and crude protein (CP) concentrations were measured in kernels. Whole flour samples were analyzed by ICP-AES/MS, HPLC and Elemental CHNS Analyzer. Results showed that Ce and Ti accumulation under MeNPs treatments did not differ from the control treatment. However, nCeO2 and nTiO2 had an impact on composition and nutritional quality of barley kernels in contrasting ways. Both MeNPs left β-glucans unaffected but reduced amylose content by approximately 21%. Most amino acids and CP increased. Among amino acids, lysine followed by proline saw the largest increase (51% and 37%, respectively). Potassium and S were both negatively impacted by MeNPs, while B was only affected by 500 mg nCeO2·kg−1. On the contrary Zn and Mn concentrations were improved by 500 mg nTiO2·kg−1, and Ca by both nTiO2 treatments. Generally, our findings demonstrated that kernels are negatively affected by nCeO2 while nTiO2 can potentially have beneficial effects. However, both MeNPs have the potential to negatively impact malt and feed production.

Phytoremediation and Biochar Application as an Amendment

Biochar is a charcoal-like carbonized organic material, but unlike charcoal, it is added to soils to improve their properties and to store carbon. It has received worldwide attention since the discovery of the fertile terra preta, which is an anthropogenic type of soil enriched in organic matter derived from charred residues. Biochar is characterized by a large surface area, a high porosity, and a high cation exchange capacity, determined to a large extent by source materials and pyrolysis temperatures. Owing to its properties, its amendment to contaminated soils has been considered for the immobilization of organic and inorganic contaminants. The application of biochar in soil can however also have an undesired effect, e.g., by decreasing the efficacy of pesticides, slowing the degradation of organic contaminants, and introducing contaminants such as PAH, PCB, and dioxins. This indicates a trade-off between the beneficial effects of biochar as a soil amendment and the introduction of new risks. Furthermore, the mechanisms of contaminant retention by biochar need to be investigated in more detail before biochar can be applied on a broad scale to manage soil pollution in a safe and sustainable way.

Agronomy towards the Green Economy. Optimization of metal phytoextraction

Traditional techniques for remediation of polluted soils are based on a physical-chemical approach; such techniques are expensive, have adverse effects on soil quality and are often highly expensive. In the scenario of the Green Economy , low cost and impact technologies should be promoted. Phytotechnologies are remediation technologies that use plants for the containment, degradation or removal of contaminants from polluted matrices for the restoration of degraded ecosystems. The process of phytoextraction is substantially based on plant-soil interactions that involves the mass transfer of an inorganic pollutant from the bulk soil to the plant biomass. This implies that the management of the two elements of the system (plant and soil) should have effects on the efficiency of the process. As phytoremediation is essentially an agronomic approach, its success depends ultimately on standard agronomic practices. The present paper aims give an overview on the role of agronomy in the optimization of metal phytoextraction is focused.

Using Chelator-Buffered Nutrient Solutions to Limit Ni Phytoavailability to the Ni-Hyperaccumulator Alyssum murale

Abstract Nickel (Ni) is essential for all plants due to its role in urease activation. Demonstration of Ni essentiality has required exceptional effort to purify nutrient solutions to remove Ni; thus, an improved technique would make study of Ni deficiency more available to diverse researchers. As part of our research on Ni hyperaccumulation by plants, we developed chelator-buffered nutrient solutions with very low buffered activity of free Ni2+, and tested growth of Alyssum murale (Goldentuft Madwort), A. corsicum (Madwort), A. montanum (Mountain Alyssum) and Lycopersicon esculentum (Tomato). We used a modified Hoagland nutrient solution with 2 mM Mg and 1 mM Ca to simulate serpentine soil solutions. We could use hydroxyethyl-ethylene-diaminetriacetate (HEDTA) to achieve Ni2+ activity levels as low as 10-16 M, and cyclohexane-ethylenediamine-tetraacetate (CDTA) to supply higher activities of buffered Ni2+ compared with HEDTA; however, we were unable to obtain proof of induced Ni-deficiency, even with urea-N supply in a 6-week growth period, apparently because seeds supplied enough Ni for growth. Yields were somewhat reduced at lower Ni activity by the end of the test period, but strong deficiency symptoms did not occur, apparently due to the supply of Ni from hyperaccumulator species seeds (contained 7000–9000 mg Ni kg-1). Chelator buffering supplied controlled levels of Ni2+ for all test species; very low plant Ni levels were attained when seed Ni was low. Reaching clear and strong Ni deficiency appears to require longer growing periods, using seed with exceedingly low initial endogenous Ni, or species possessing higher Ni requirements.

Phytoremediation of soils polluted by heavy metals and metalloids using crops: (i) the state of the art

Phytoremediation has a strong potential as a natural, solar-energy driven remediation approach for the treatment of soils and sediments polluted. Research has focused several aspects of the process of uptake, translocation and storage of heavy metals in plants. However we can not predict when the technique could find practical application on large scale. Beyond the evaluation of the best suited species, little has been inquired on the multiple aspects of the agronomic management of phytoextraction. This review provides a synthesis of current knowledge on phytoextraction of metals from soils and their accumulation in plants.