Daniel Arenas-Lago

The physiological mechanisms underlying the ability of Cistus monspeliensis L. from São Domingos mine to withstand high Zn concentrations in soils

Cistus monspeliensis L. is a species that grows spontaneously in contaminated mining areas from the Iberian Pyrite Belt. This species can have high concentrations of Zn in the shoots without visible signs of phytotoxicity. In order to understand the physiological mechanisms underlying this tolerance, C. monspeliensis was grown at several concentrations of Zn(2+) (0, 500, 1000, 1500, 2000µM) and the effects of this metal on plant development and on the defence mechanisms against oxidative stress were evaluated. Independently of the treatment, Zn was mainly retained in the roots. The plants with the highest concentrations of Zn showed toxicity symptoms such as chlorosis, low leaf size and decrease in biomass production. At 2000µM of Zn, the dry biomass of the shoots decreased significantly. High concentrations of Zn in shoots did not induce deficiencies of other nutrients, except Cu. Plants with high concentrations of Zn had low amounts of chlorophyll, anthocyanins and glutathione and high contents of H2O2. The highest concentrations of Zn in shoots of C. monspeliensis triggered defence mechanisms against oxidative stress, namely by triggering antioxidative enzyme activity and by direct reactive oxygen species (ROS) scavenging through carotenoids, that are unaffected by stress due to stabilisation by ascorbic acid.

Copper distribution in surface and subsurface soil horizons

The horizons of four natural soils were treated with Cu2+ in an acid medium to study the retention capacity of Cu. The possible mineralogical changes arising because of the treatment were also studied. The soil properties and characteristics with the greatest influence on the metal retention and its distribution among the different soil fractions were determined. Crystalline phases of each horizon were determined by X-ray diffraction (XDR). The morphology, structural distribution and particle chemical composition of soil samples were investigated using field emission scanning electron microscopy. Cu distribution in the different geochemical phases of the soil was studied using a sequential extraction. The treatment led to an increase in the amorphous phases and the formation of new crystalline phases, such as rouaite (Cu2(NO3)(OH)3) and nitratine (NaNO3). Cu was also found superficially sorbed on amorphous hydroxy compounds of Fe that interact with albite, muscovite and gibbsite, and also on spherical and curved particles of aluminium clays. The largest amount of Cu retained was in an exchangeable form, and the smallest amount associated with the crystalline Fe oxides and residual fraction. In the surface horizons, the predominant Cu retention process is complexation in organomineral associations, while in the subsurface horizons it is adsorption.

Limitations for revegetation in lead/zinc minesoils (NW Spain)

PurposeMetal mining is the main cause of soil contamination caused by heavy metals. Mine tailings and minespoils generally offer hostile environments for plant growth due to their low nutrient availability, low organic matter content, and high trace metal content. This study was carried out with the aim of characterizing the soils that have developed on the tailings from an abandoned lead and zinc mine in Galicia (NW Spain) and determining the soil factors that limit revegetation.Materials and methodsWe selected three zones: (a) the minespoils, (b) in the mining area, and (c) the settling pond, where the sludge from the flotation process was deposited. A control soil was also sampled outside of the mining area. We analyzed the physicochemical properties and metal levels in the mine spoil and soil samples we collected.Results and discussionThe results indicate that the main physical limitations of minesoils are their low effective depth, high porosity and stoniness, while the main chemical limitations are low organic matter content and low CEC and an imbalance between exchangeable cations. These minesoils are strongly affected by high Zn and Pb levels which hinder revegetation.ConclusionsAs high concentrations of toxic trace elements and a high pH are important factors in limiting the plant growth, the restoration procedure must overcome the oxidation processes by adding organic amendments that also contribute towards fixing heavy metals or by implanting spontaneous vegetation adapted to the mine conditions, such as common broom (Cytisus scoparius) or white birch (Betula celtiberica).

Heavy metal content and toxicity of mine and quarry soils

PurposeSoils formed in metallic mines and serpentinite quarries, among other unfavourable features, have high levels of heavy metals. They can release into the environment causing surface and subsurface water contamination, uptake by plants, their accumulation in the food chain and adverse effects on living organisms. In this work, we studied the magnitude of the soils’ toxic effects not only on spontaneous plants but also on two species with phytoremediation potential.Materials and methodsSeveral soils from two different exploitations were selected: a lead and zinc mine and a serpentinite quarry. Soils were characterized, and the pseudo-total and extractable contents of Co, Cr and Ni in soils from a serpentinite quarry were determined. The Cd, Pb and Zn pseudo-total and extractable contents were determined in soils developed in the Pb/Zn abandoned mine. Using a biotest, the chronic toxicity of the soil samples on higher plants was determined. Festuca ovina L., Cytisus scoparius (L.) Link., Sinapis alba L. and Brassica juncea L. were selected, the first two because they are spontaneous plants in the study areas and the last two because they have heavy metal phytoremediation potential.Results and discussionPseudo-total contents of Co, Cr and Ni in the serpentinite quarry soils and of Zn, Pb and Cd in the Zn/Pb mine soils exceed generic reference levels. CaCl2 is the reactant that extracts the highest proportion of Co, Cr and Ni in the quarry soils and EDTA the largest proportion of Pb Zn and Cd content in the mine soils. The germination index values based on seed germination and root elongation bioassays revealed increasing plant sensitivity to the mine soils in the following order: B. juncea < S. alba < F. ovina < C. scoparius. The wide range of GI values indicates that the response of test plants to soil heavy metals depended on their concentrations and soil characteristics, especially pH and organic matter content.ConclusionsThe pollution index indicates severe Cd, Pb and Zn contamination in the mine soils, as well as high Cr and Ni and moderate Co contamination in the serpentinite quarry soils. The performed biotests were suitable for identifying toxic soils and showed that the studied soils are toxic to the spontaneous plants, more to C. scoparius than to F. ovina. They also indicate that the mine soils are more toxic than the quarry soils for both species.

Validation of TOF-SIMS and FE-SEM/EDS Techniques Combined with Sorption and Desorption Experiments to Check Competitive and Individual Pb2+ and Cd2+ Association with Components of B Soil Horizons

Sorption and desorption experiments were performed by the batch method on the B horizons of five natural soils: Umbric Cambisol, Endoleptic Luvisol, Mollic Umbrisol, Dystric Umbrisol, and Dystric Fluvisol. Individual and competitive sorption and desorption capacity and hysteresis were determined. The results showed that Pb2+ was sorbed and retained in a greater quantity than Cd2+ and that the hysteresis of the first was greater than that of the second. The most influential characteristics of the sorption and retention of Pb2+ were pH, ECEC, Fe and Mn oxides and clay contents. For Cd2+ they were mainly pH and, to a lesser extent, Mn oxides and clay content. The combined use of TOF-SIMS, FE-SEM/EDS and sorption and desorption analyses was suitable for achieving a better understanding of the interaction between soil components and the two heavy metals. They show the preferential association of Pb2+ with vermiculite, chlorite, Fe and Mn oxides, and of Cd2+ with the same components, although to a much lesser extent and intensity. This was due to the latter’s higher mobility as it competed unfavourably with the Pb2+ sorption sites. TOF-SIMS and FE-SEM/EDS techniques confirmed the results of the sorption experiments, and also provided valuable information on whether the soil components (individually or in association) retain Cd2+ and / or Pb2+; this could help to propose effective measures for the remediation of contaminated soils.

Pollution and risk assessment of potential hazardous elements in a shooting range soils (NW Spain)

Pollution at shooting ranges is an issue of growing importance. Accumulation in soils of potentially harmful elements (PHEs) from ammunitions used is a major environmental risk. The total and available (extraction with 0.01 M CaCl2 and DTPA) content of As, Cd, Cu, Ni, Pb, Sb and Zn were evaluated in 10 soils from a shooting range for military use (Leon, Spain). The results showed that, among the studied pollutants, Pb is the element present in highest concentration (13.83-4451.57 mg kg-1), followed by Sb (1.80-96.10 mg kg-1), Cu (4.50-88.52 mg kg-1), As (13.24-62.47 mg kg-1), Zn (13.31-46.19 mg kg-1), Ni (11.53-46.30 mg kg-1) and Cd (0.30-1.00 mg kg-1). The strong soil acidity, its medium organic matter content and low proportion of clay, favor a high availability of these PHEs, particularly Pb and Cu. Although impact mitigation measures, such as collecting cartridges whenever a round of shots is fired in the shooting range, the pollution assessment indicates that performances should improve in the berm. The application of organic amendments, or nanomaterials, could help reduce the PHEs availability and avoid the contamination of adjacent areas.

Using Ca3(PO4)2 nanoparticles to reduce metal mobility in shooting range soils.

Shooting activities are a very important source of contamination as they are commonly detected high concentrations of Pb in the soils from these facilities. Different remediation methods imply the immobilization of the pollutants by decreasing their mobility and availability and nanotechnology is a promising technique in this field. The effectiveness of calcium phosphate nanoparticles (CPNs) in the remediation of small-arms firing range and trap shooting range soils is evaluated in this work. The operationally defined extractable content of Pb, Cu and Zn is determined together with the interaction of the pollutants with the nanomaterials. Soil samples were treated with the CPNs and after the treatment the extractable contents of Cu, Pb and Zn decrease. To check the retention by the nanoparticles TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometry) and HR-TEM-EDS (High Resolution Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy) techniques were applied. The association of Pb and Cu to the CPNs was demonstrated by TOF-SIMS although it also indicated that not all the Pb and Cu contents are linked to the nanoparticles. By means of HR-TEM/EDS it was made out the filamentous shape and the size (50-150nm long and 20-40nm wide) of the CPNs together with their elemental composition (Ca, P and O). The CPNs were identified in treated soil samples together with signals of metals. The decrease on metal extractability detected is, in part, due to the association with CPNs but still more investigation is needed regarding mobility and availability of potentially hazardous elements in soils treated with nanoparticles.

A Multianalytical Approach for the Assessment of Toxic Element Distribution in Soils From Mine and Quarry Areas

Mining activities and serpentinite quarrying may result in negative effects on the environment, as significant amounts of potential hazardous elements (PHEs) remain in a hostile environment that limits proper organism development. Their total or pseudototal contents in soils are generally used as an initial reference but normally they are not a good predictor for availability, because in most cases only a fraction is mobile and/or available. For assessing actual availability, mobility or toxicity of pollutants, different approximations are used, but no universally applicable approach has yet been established. A combination of different techniques is effective for identifying the soil sorbents for PHEs and for assessing their distribution and association with different geochemical phases. This provides more information about the interactions between pollutants and soil solid phases necessary for appropriate risk assessment and for taking proper corrective measures.

Cd2+, Cu2+, and Pb2+ sorption, desorption and migration in Fluvisols

The aim of this work was to assess and compare the mono and bimetallic Cd2+, Cu2+ and Pb2+ sorption and desorption capacities as well as the sorption hysteresis in two different types of Fluvisols. The migration of cations through the profiles was evaluated, along with the dependence on soil properties of mono and bimetallic Cd2+, Cu2+ and Pb2+ fixation, hysteresis and mobility. Sorption irreversibility and migration of the studied cations through the profiles were evaluated, by means of hysteresis and migration indexes calculated from retention capacity values (Kr) proposed and validated in a previous work. The results showed that the sorption and retention capacities of the A horizons were higher than those of C and that the individual sorption and retention capacities were greater than the competitive capacities. The highest values of sorption and retention capacities were those for Pb2+, followed by Cu2+ and Cd2+. Mn oxides, organic matter and, consequently, ECEC were the components and properties that most highly influenced Pb2+ monometal and competitive sorption and retention. Cd2+ did not interfere with Pb2+ or Cu2+ sorption and retention. Organic matter content was only correlated with the sorption hysteresis of Pb2+, in accordance with the high Pb2+fixation capacity of in this component and its lower capacity to retain Cu2+ and Cd2+. Tidalic Fluvisols retained only 0.4 and 0.2% of added Cd2+ when competing with Cu2+ and Pb2+, respectively. However, more than 60% of the added Pb2+, and over 47% of the added Cu2+ were retained. The Pb2+ retained in competition with Cu2+ was 98.2 in TF and 47% in the Umbric Fluvisol, whereas the retained Cu2+ was 93.8 and 29.9% respectively. These retention and Cd2+ mobility indicated that there is a possibility of heavy metals transferring to subsurface waters and, through these, of contamination and even of these metals entering the food chain.