Effect of mine tailing on the spatial variability of soil nematodes from lead pollution in La Union (Spain)

The Cartagena-La Union mining district, exploited since the end of the 3rd century BC, was one of the world's largest lead producers in the 19th century. Although activity ceased in 1991, today mining residues pose a huge pollution problem. This study characterises lead contents (total and DPTA) and other soil parameters (N, P, K, pH, SOM, CaCO3, granulometric fraction, etc.) using multivariate geostatistical methods in relation to nematode diversity. In this work, trophic groups and metabolic footprints of soil nematodes were measured using 193 samples from the mining, natural and agricultural areas in this district. We explored the relationship between soil health and nematode communities. High lead concentrations were quantified: mean 8,500 mg kg(-1) for total and 340 mg kg(-1) for DPTA in this mining area. Although nematode diversity was broad (81 taxa), their diversity, abundance and metabolic footprints significantly reduced in the mining area. Significant differences in the nematode community structure were observed, and the relative abundance of predators was sensitive to mine and agricultural activities, whilst omnivores reduced only in the agricultural area, and bacterial feeders exhibited a differential response to both anthropogenic disturbances. The total abundance of nematodes, trophic groups and c-p groups correlated negatively with soil Pb contents, and a positive relationship was found with SOM and N, P and K contents.

Potential use of gypsum and lime rich industrial by-products for induced reduction of Pb, Zn and Ni leachability in an acid soil

This study evaluates the potential use of four industrial by-products (phosphogypsum (PG), red gypsum (RG), sugar foam (SF), and ashes from biomass combustion (ACB)), applied at two rates in single and combined amendments to reduce the mobility and availability of Pb, Zn and Ni in a metal-spiked acid soil. Leaching experiments were done to estimate leachability indexes and assess their effectiveness. Most of the treatments significantly reduced the metal leachability although only a few were effective for all metals. Based on principal component and cluster analysis, sugar foam (SF) and a mixture of RG and ACB (RG+ACB), both applied at high rate, were selected as first choices to reduce mobility and availability of the three metals. Metal sorption mechanisms involved in the reduction of their leachability were identified using scanning electron microscopy. In the SF-treated samples, the metals were found associated to amorphous Al-hydroxy polymers deposited on phyllosilicates and organic matter particles. In the (RG+ACB)-treated samples, Pb, Zn, and traces of Ni were found associated to Fe/Ti oxide phases with a significant concentration of S, suggesting the formation of metal-sulfate ternary complexes.

Assessment of the use of industrial by-products for induced reduction of As, and Se potential leachability in an acid soil

Four industrial by-products (phosphogypsum, PG; red gypsum, RG; sugar foam, SF and ashes from the combustion of biomass, ACB) were evaluated as possible amendments for reducing the leachability and bioavailability of As and Se in a metalloid-spiked acidic soil. The treatments were applied as single, double and triple amendments and at two different rates. The effectiveness of the treatments was evaluated after a series of leaching experiments using a chelating agent (DTPA solution) or a weak acidification (acetic acid at pH 4.93). The most effective treatments (ACB and RG, both applied at high rate) were identified by means of Cluster Analysis using the leachability indexes. Different sorption mechanisms involved in the overall reduction of metalloid leachability were identified using scanning electron microscopy (SEM-BSE and SEM-EDS). In the ACB-treated samples, Se was found associated to organic matter aggregates and to Fe compounds. In the RG-treated samples, EDS analyses showed that As and Se were associated to Fe/Ti (hydr)oxides phases which are present not only in the by-product as maghemite and rutile, but also in the soil as hematite and goethite. In addition, the application of RG induced the formation of non-crystalline Al-hydroxy polymers with As and Se in their composition.

Surface Instability of Serpentine in Aqueous Suspensions

The electrokinetic behavior and stability of aqueous suspensions containing serpentine minerals of different deposits have been studied. Crystallochemical analyses carried out by X-ray diffraction, IR spectroscopy, TEM, DTA/TG, and XRF revealed that all samples are lizardite-type serpentines with a similar chemical composition. It has been determined that the electrokinetic behavior of lizardite aqueous suspensions is mainly a function of the Mg/Si atomic ratio on surface. So, the low isoelectric point observed in some samples has been linked to values of this ratio lower than that of the ideal lizardite (Mg/Si=1.5). Dissolution studies have shown that the removal of Mg cations from the solid at speeds faster than that theoretically expected (Mg/Si=1.5), i.e., incongruent dissolution, is responsible for the enrichment of Si cations on surface. Therefore, it has been clearly established that the surface charge value developed in the lizardite/aqueous electrical interface is a function of the lizardite surface alteration grade. Copyright 2000 Academic Press.