A. Faz

Salinity increases mobility of heavy metals in soils

The effect of salinity induced by CaCl(2), MgCl(2), NaCl and Na(2)SO(4) on the mobility of Cu, Cd, Pb and Zn was studied. An increase of ionic strength by any salts promoted a higher release of Cd than the others metals. When CaCl(2) and NaCl were applied, Cd and Pb showed the highest degree of mobilization. When MgCl(2) was applied, Cd and Cu were mobilized the most. Finally, an increase of Na(2)SO(4) also promoted the strongest mobilization of Cd and Cu. As the total heavy metal content was higher, the percentage of Pb and Cu released upon salinization decreased, indicating that these metals are strongly bound to soil constituents. An increase of carbonates in the soil promoted a higher release of Pb for all used salts and for Zn when MgCl(2) and NaCl were used. This indicates that Pb and Zn are adsorbed on the surface of carbonate crystals. An increase of fine particles promoted a decrease of percentage of released Cd for all salts, indicating that Cd is strongly retained in the fine fractions. The main mechanism regulating Pb and Cd mobility was competition with Ca(2+) for sorption sites followed for metal chloro-complexation, association between the Cd/Pb-sulfates and competition with Mg(2+). The main mechanism regulating Cu mobility was the formation of Cu-sulfate, followed by competition with cations (Mg > Ca) and chloride. For Zn, competition with Ca(2+) for sorption sites was the most important process for its mobility; followed by Zn-sulfate association and, finally, chloride and competition with Mg with the same effect.

Identification of heavy metal sources by multivariable analysis in a typical Mediterranean city (SE Spain)

Problems associated with heavy metal characterization in the majority of sites are often due to multiple sources of pollution. This work presents the results through the use of advanced statistical techniques to identify sources of soil heavy metals in a typical Mediterranean city. The multivariable analysis performed on seven metals identified four sources controlling their variability. Cr, Mn, and Ni contents were associated to soil parent materials; Cd and Pb contents were related to anthropogenic activities, specifically industrial activities and traffic; Cu content is controlled by long-term application of inorganic fertilizers in agricultural areas. Finally, zinc concentration is associated to commercial and outdoor activities in the area. These results were supported by the fact that metals associated to parent material (Cr, Mn, and Ni) were better correlated with soil lithogenic properties, while anthropogenic metals were correlated with more variable soil constituents.

Stability, nutrient availability and hydrophobicity of biochars derived from manure, crop residues, and municipal solid waste for their use as soil amendments

We aimed to study the influence of feedstock properties, pyrolysis temperature and holding time on stability, nutrient contents and hydrophobicity of biochars derived from pig manure, crop residues and municipal solid waste. Biochars were prepared at 300 °C, 400 °C, 500 °C and 700 °C for 1 h, 2 h, 4 h and 5 h. All properties were influenced by feedstock except for pH and hydrophobicity. Temperature influenced all properties, whereas no effect of holding time was observed except for hydrophobicity and thermal stability. Increasing temperature increased aromatization and stability. Low temperatures provided higher cation exchange capacity and available nutrients, and lower salinity and alkalinity. Precipitation of phosphates and carbonates occurred with charring, explaining the decrease of available nutrients. Biochars produced at 300 °C showed high hydrophobity, which disappeared over 500 °C owing to the loss of labile aliphatic compounds. The high pH and carbonates contents at >500 °C resulted in suitable biochars for soil liming and decreasing soil metals availability.

Plant Cover and Soil Biochemical Properties in a Mine Tailing Pond Five Years After Application of Marble Wastes and Organic Amendments

Abstract Tailing ponds pose environmental hazards, such as toxic metals which can contaminate the surroundings through wind and water erosions and leaching. Various chemical and biochemical properties, together with extractable and soluble metals were measured five years after reclamation of a polluted soil affected by former mining activities. This abandoned mine site contains large amounts of Fe-oxyhydroxides, sulphates, and heavy metals. As a consequence, soils remain bare and the soil organic matter content is low ( −1 ). Marble waste, pig manure and sewage sludge were applied in 2004. Plant cover and richness, and soil chemical, biochemical and biological parameters were analysed five years later. Results showed that all soil biochemical properties as well as vegetation cover and richness were higher in treated soils than in the untreated contaminated plots (control), although organic matter, pH values and extractable metals concentrations were similar among treatments. Soluble cadmium and zinc were lower in the amended plots than in control. As a general pattern, soil amended with pig manure showed higher values of most biochemical properties compared to sewage sludge application, while the doses did not have a great effect, being only significant for β-glucosidase, phosphodiesterase and arylsulfatase. Significant correlations were found between vegetation cover, richness and soil biochemical properties, suggesting a high interdependence between plant colonization and reactivation of biogeochemical cycles during five years. This study confirms the high effectiveness of an initial application of the amendments tested to initialize the recovery of ecosystems in bare mine soils under Mediterranean semiarid conditions. This research also shows the high sensitivity of certain biochemical properties in order to evaluate soil quality and reactivation of nutrients cycles in reclaimed mine soils.

Carbon mineralization, microbial activity and metal dynamics in tailing ponds amended with pig slurry and marble waste

A field experiment was set up in Cartagena-La Unión Mining District, SE Spain, aimed at evaluating the short-term effects of pig slurry (PS) amendment alone and together with marble waste (MW) on organic matter mineralization, microbial activity and stabilization of heavy metals in two tailing ponds. These structures pose environmental risk owing to high metals contents, low organic matter and nutrients, and null vegetation. Carbon mineralization, exchangeable metals and microbiological properties were monitored during 67 d. The application of amendments led to a rapid decrease of exchangeable metals concentrations, except for Cu, with decreases up to 98%, 75% and 97% for Cd, Pb and Zn, respectively. The combined addition of MW+PS was the treatment with greater reduction in metals concentrations. The addition of PS caused a significant increase in respiration rates, although in MW+PS plots respiration was lower than in PS plots. The mineralized C from the pig slurry was low, approximately 25-30% and 4-12% for PS and MW+PS treatments, respectively. Soluble carbon (Csol), microbial biomass carbon (MBC) and β-galactosidase and β-glucosidase activities increased after the application of the organic amendment. However, after 3d these parameters started a decreasing trend reaching similar values than control from approximately day 25 for Csol and MBC. The PS treatment promoted highest values in enzyme activities, which remained high upon time. Arylesterase activity increased in the MW+PS treatment. Thus, the remediation techniques used improved soil microbiological status and reduced metal availability. The combined application of PS+MW reduced the degradability of the organic compounds.

Evaluation of heavy metal availability prior to an in situ soil phytoremediation program

Metal mobility and the fractionation of elements and thus the biological uptake of Zn, Pb and Cd by plants were investigated using a simplified analytical procedure for soluble and bioavailable metals using a four-step sequential extraction procedure. Results showed that there was a low proportion of immediately soluble metals, as well as a high proportion of metals that could be released and would so be available for plant uptake. In the sequential extraction procedure, considering the total partition, there was a large proportion of Pb, Cd and Zn extracted in a readily mobile form. In acidic soils the content of metals in ready mobile form (exchangeable-bound to carbonates as well as to Fe and Mn oxides) and bound to organic matter constitutes an important source of potentially available elements. The same pattern was observed in alkaline soils, where almost 80% of the metals could be remobilized and be potentially available to plants. Knowing the metal partitioning and mobility of heavy metals it is very important for evaluating the phytoremediation efficiency.

Influence of population density on the concentration and speciation of metals in the soil and street dust from urban areas

Street dust and soil from high, medium and low populated cities and natural area were analysed for selected physical-chemical properties, total and chemical speciation of Zn, Pb, Cu, Cr, Cd, Co, Ni to understand the influence of human activities on metal accumulation and mobility in the environment. The pH, salinity, carbonates and organic carbon contents were similar between soil and dust from the same city. Population density increases dust/soil salinity but has no influence on metals concentrations in soils. Increases in metal concentrations with population density were observed in dusts. Cu, Zn, Pb, Cr can be mobilized more easily from dust compared to the soil. In addition, population density increase the percentage of Pb and Zn associated to reducible and carbonate phase in the dust. The behaviour of metals except Cd in soil is mainly affected by physico-chemical properties, while total metal influenced the speciation except Cr and Ni in dusts.

Selection of Autochthonous Plant Species from SE Spain for Soil Lead Phytoremediation Purposes

Mining activity in SE of Spain, in the west Mediterranean coast, originated more than two millenniums ago. It has generated huge areas affected by heavy metals contamination, especially of lead, which is possibly one of the most important. Investigations related to the selection of autochthonous plant taxa from a typical Spanish Mediterranean area, useful for phytoextraction and phytostabilization purposes in these polluted areas are shown. Under these edaphoclimatic conditions 12 interesting species were considered, from them six taxa were chosen for further studies. Some plant species have been proposed either for phytoextraction or phytostabilization purposes. Recommendations for further research have been discussed.

High altitude artisanal small-scale gold mines are hot spots for Mercury in soils and plants.

Mercury releases from artisanal and small-scale gold mines (ASGM) condense and settle on plants, soils and water bodies. We collected soil and plant samples to add knowledge to the likely transfer of Hg from soils into plants and eventually predict Hg accumulation in livestock around ASGM in Bolivia. Mean contents of Hg in soils range from 0.5 to 48.6 mg Hg kg(-1) soil (5× to 60× more compared to control sites) and exceeded the soil Hg threshold levels in some European countries. The Hg contents ranged from 0.6 to 18 and 0.2 to 28.3 mg Hg kg(-1) leaf and root, respectively. The high Hg in Poaceae and Rosaceae may elevate Hg accumulation into the food chain because llama and alpaca solely thrive on these plants for food. Erosion of soils around ASGM in Bolivia contributes to the Hg contamination in lower reaches of the Amazon basin.

Speciation of arsenic in bulk and rhizosphere soils from artisanal cooperative mines in Bolivia.

Soils near artisanal and small-scale gold mines (ASGM) have high arsenic (As) contents due to the presence of arsenopyrite in gold ores and accelerated accumulations due to mine wastes disposal practices and other mining activities. We determined the content and speciation to understand the fate and environmental risks of As accumulations in 24 bulk and 12 rhizosphere soil samples collected in the Virgen Del Rosario and the Rayo Rojo cooperative mines in the highlands of Bolivia. Mean total As contents in bulk and rhizosphere soils ranged from 13 to 64 mg kg(-1) and exceeded the soil environmental quality guidelines of Canada. Rhizosphere soils always contained at least twice the As contents in the bulk soil. Elemental mapping using 4×5 μm synchrotron-generated X-ray micro-beam revealed As accumulations in areas enriched with Fe. Results of As-X-ray Absorption Near Edge Spectroscopy (As-XANES) showed that only As(V) species was detectable in all samples regardless of As contents, size fractions and types of vegetation. Although the toxicity of As(V) is less than As(III), we suggest that As uptake of commonly-grazed vegetation by alpaca and llama must be determined to fully understand the environmental risks of high As in soils near ASGM in Bolivia. In addition, knowledge on the speciation of the As bio-accessible fraction will provide another useful information to better understand the fate and transfer of As from soils into the food chain in environments associated with the ASGM in Bolivia and other parts of the world.