Silvia Martínez-Martínez

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.

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.

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.

Metal content and environmental risk assessment around high-altitude mine sites

Gold mining activities in Apolobamba area, northwest of La Paz, Bolivia have created serious environmental concern and great risk to human health. The current methods used to extract gold are too primitive resulting in metal contamination of soil and water. The objectives of this study were to: (1) determine the degree of metal pollution, and (2) assess the risk to human health and environment in the Apolobamba area. Soil, water, sediment samples, and mine spills were collected and analyzed. Metals including Pb, Cu, Zn, Cd, and Hg concentrations were higher in surface soils than in subsurface soils indicating active atmospheric deposition of metals. Sediment samples had elevated levels of metals probably from mine spills discharged into the Sunchulli River. Surface soils in the Sunchulli community show the highest levels of Pb and Hg in all soil samples and may pose a risk to the health of the human population and environment.

Soil fertility status and nutrients provided to spring barley (Hordeum distichon L.) by pig slurry

Nutrient recycling using pig slurry is a common agricultural practice to manage the ever-increasing amounts of wastes from the pig industry. This study was conducted in the southeast of Spain to quantify the enrichments in major (N, P, K, Mg) and minor (Zn, Fe, Cu, and Mn) nutrients in soils amended with D1-170 kg N ha-1 (European Union legislated dose) or D2-340 kg N ha-1, and understand the influence of pig slurry on yield and nutrient uptake in two crop seasons of spring barley (Hordeum distichon L.) Compared to control, D2 increased NO3--N by 11.4X to 109 mg kg-1, Olsen-P by 6.9X to 423 mg kg-1, exchange K (2.5X to 1.6 cmol+ kg-1), Mg (1.7X to 1.8 cmol+ kg-1), diethylene-triamine pentaacetic acid (DTPA)-Zn (94X to 18.2 mg kg-1), and Fe (2X to 11.3 mg kg-1). Available NO3--N, Olsen-P, and DTPA-Zn have the best correlations with crop yield and nutrient uptake. These results indicate that the assessment of soil fertility status at 1-mo after pig slurry addition provides a good indicator for potential yield and uptake of barley. However, it is suggested that leachates should be monitored to effectively manage potential releases of nitrate and phosphate into the environment.

Syrian Bean-Caper (Zygophyllum fabago L.) Improves Organic Matter and Other Properties of Mine Wastes Deposits

The omni-presence of Zygophyllum fabago L. (Syrian bean-caper) natural colonies in post mining areas prompted us to investigate its contributions to reclamation of mine wastes deposits′ in southeast Spain. Select plant-related (edaphic) characteristics and bio- and water soluble-Cd, Cu, Pb and Zn in rhizosphere of Z. fabagowere compared to deposits one year since application of pig slurry and marble waste. Total N in rhizosphere increased up to a factor of 20X (339 vs 17 mg N kg−1) in El Gorguel and 27X (85 vs 3.1 mg N kg−1) in El Lirio sites. Organic matter accumulation in rhizosphere from litter and roots of Z. fabagoincreased organic C from 6.6 to 19.5 g kg−1in El Gorguel and from 2.1 to 5.7 g kg−1 in El Lirio in one year. Dissolution of inorganic C takes place due to organic acids from root exudates of Z. fabago. Reduction in bio-available Cd, Cu, Pb, and Zn in rhizosphere of Z. fabagoat El Lirio is attributed to increase in pH from 5.3 to 7.7 through marble waste addition, although increased cation exchange capacity may also have played a role. Addition of marble waste to encourage colonization by Z. fabagoin acidic mine wastes deposits was recommended.

Bioaugmentaton in Technosols created in abandoned pyritic tailings can contribute to enhance soil C sequestration and plant colonization

Creation of Technosols in combination with phytostabilization may be a sustainable strategy to minimize the environmental and human health hazards derived from mine tailings. Bioaugmentation can facilitate plant establishment and growth for efficient phytostabilization. In order to assess if bioaugmentation can increase soil quality and fertility, decrease metal(loid) mobility and accelerate plant colonization, a one-year field experiment was designed with creation of Technosols in two tailings ponds with different pH (acidic (AT) and neutral (NT)), with addition of marble waste (MaW) and two organic materials (pig manure (PM) and sewage sludge (SS), without or with inoculation of effective microorganisms (EM) at three rates. Results showed that MaW was the main factor responsible for maintaining pH ~7 in AT and ~8 in NT, decreasing salinity, and decreasing the soluble fraction of metals (70-99%). The soluble fraction of As decreased ~45% in AT, related to increases in pH up to neutrality, while increased ~90% in NT with PM due to pH>8 and higher content of organic compounds. The addition of PM and SS significantly increased soil organic C (SOC), nutrient contents and microbial biomass and activity in both tailings, being PM more effective. However, a positive priming effect was observed in NT with SS addition likely due to higher C/N ratio and lack of nutrients. There was a significant effect of EM rate on inorganic C, SOC, N, K and microbial biomass and activity, with higher values as rate increased. Vegetation richness and density directly increased with increasing EM rate. Multivariate analyses showed that the most important properties contributing to increase richness and plant density were microbial biomass and N. Thus, bioaugmentation contributed to soil C sequestration (as organic and inorganic C) and soil fertility, related to high soil microbial biomass and activity, which facilitated an effective colonization of vegetation.

Suitability of Different Mediterranean Plants for Phytoremediation of Mine Soils Affected with Cadmium

Mine residues dumped on the environment as overburden or tailings ponds show environmental and human health hazards by the transfer of heavy metals through erosion or leaching. The objective of this study was to assess the potential use of different Mediterranean plant species for phytostabilization or phytoextraction of cadmium in acidic mine residues. For this purpose, a reclamation strategy was carried out in a mine tailing based on the use of phytoremediation aided with three different amendments (pig slurry, pig manure, and marble waste). –Six Mediterranean species were introduced: Lygeum spartum, Atriplex halimus, Helichrysum stoechas, Dittrichia viscosa, Piptatherum miliaceum, and Limonium cossonianum. Soil and plant samples were collected 24 months after remediation works. Results showed that the characteristics of the mine residue improved with the reclamation developed, with increased pH, organic matter and fertility, and decreased salinity. The extractable and exchangeable fractions of Cd decreased 85 % and 96 %, respectively. The tested species (except for A. halimus and L. cossonianum) may be potential candidates for the objectives of Cd phytostabilization since they showed low translocation and bioaccumulation factors. P. miliaceum was the best candidate owing to its lower translocation and bioaccumulation factors, higher biomass, and higher colonization of the area. A. halimus seems a potential candidate for phytoextraction rather than for phytostabilization of soil Cd, with high translocation and bioaccumulation factors, high biomass, and fast growth.