Rafael Clemente

The effects of soil amendments on heavy metal bioavailability in two contaminated Mediterranean soils

Two heavy metal contaminated calcareous soils from the Mediterranean region of Spain were studied. One soil, from the province of Murcia, was characterised by very high total levels of Pb (1572 mg kg(-1)) and Zn (2602 mg kg(-1)), whilst the second, from Valencia, had elevated concentrations of Cu (72 mg kg(-1)) and Pb (190 mg kg(-1)). The effects of two contrasting organic amendments (fresh manure and mature compost) and the chelate ethylenediaminetetraacetic acid (EDTA) on soil fractionation of Cu, Fe, Mn, Pb and Zn, their uptake by plants and plant growth were determined. For Murcia soil, Brassica juncea (L.) Czern. was grown first, followed by radish (Raphanus sativus L.). For Valencia soil, Beta maritima L. was followed by radish. Bioavailability of metals was expressed in terms of concentrations extractable with 0.1 M CaCl2 or diethylenetriaminepentaacetic acid (DTPA). In the Murcia soil, heavy metal bioavailability was decreased more greatly by manure than by the highly-humified compost. EDTA (2 mmol kg(-1) soil) had only a limited effect on metal uptake by plants. The metal-solubilising effect of EDTA was shorter-lived in the less contaminated, more highly calcareous Valencia soil. When correlation coefficients were calculated for plant tissue and bioavailable metals, the clearest relationships were for Beta maritima and radish.

Efficiency of green waste compost and biochar soil amendments for reducing lead and copper mobility and uptake to ryegrass.

Green waste compost and biochar amendments were assessed for their assistance in regulating the mobility of copper (Cu) and lead (Pb) and the resultant uptake of these metals into vegetation. The amendments were mixed with a heavily Cu and Pb contaminated soil (600 and 21,000 mg kg(-1), respectively) from a former copper mine in Cheshire (UK), on a volume basis both singly and in combination in greenhouse pot trials. Ryegrass (Lolium perenne L. var. Cadix) was grown for the following 4 months during which biomass, metals in soil pore water and plant uptake were measured in three consecutive harvests. Very high Pb concentrations in pore water from untreated soil (>80 mg l(-1)) were reduced furthest by compost amendment (<5 mg l(-1)) whereas biochar was the more effective treatment at reducing pore water Cu concentrations. Duly, ryegrass shoot Cu levels were reduced and large, significant reductions in shoot Pb levels were observed after biochar and compost amendments, respectively during successive harvests. However, because green waste compost singly and in combination with biochar vividly enhanced biomass yields, harvestable amounts of Pb were only significantly reduced by the compost amendment which had reduced shoot Pb levels furthest. The low biomass of ryegrass with biochar amendment meant that this was the only amendment which did not significantly increase harvestable amounts of Cu. Therefore the two amendments have opposing metal specific suitability for treating this contaminated soil regarding whether it is a maximum reduction in plant tissue metal concentration or a maximum reduction in harvestable amount of metal that is required.

Assessing the influence of compost and biochar amendments on the mobility and toxicity of metals and arsenic in a naturally contaminated mine soil.

Amending contaminated soils with organic wastes can influence trace element mobility and toxicity. Soluble concentrations of metals and arsenic were measured in pore water and aqueous soil extracts following the amendment of a heavily contaminated mine soil with compost and biochar (10% v:v) in a pot experiment. Speciation modelling and toxicity assays (Vibrio fischeri luminescence inhibition and Lolium perenne germination) were performed to discriminate mechanisms controlling metal mobility and assess toxicity risk thereafter. Biochar reduced free metal concentrations furthest but dissolved organic carbon primarily controlled metal mobility after compost amendment. Individually, both amendments induced considerable solubilisation of arsenic to pore water (>2500 μg l(-1)) related to pH and soluble phosphate but combining amendments most effectively reduced toxicity due to simultaneous reductions in extractable metals and increases in soluble nutrients (P). Thus the measure-monitor-model approach taken determined that combining the amendments was most effective at mitigating attendant toxicity risk.

Heavy metal bioavailability in a soil affected by mineral sulphides contamination following the mine spillage at Aznalcóllar (Spain).

A field experiment, lasting 14 months, was carried out in order to assess the effect of organic amendment and lime addition on the bioavailability of heavy metals in contaminated soils. The experiment took place in a soil affected by acid, highly toxic pyritic waste from the Aznalcóllar mine (Seville, Spain) in April 1998. The following treatments were applied (3 plots per treatment): cow manure, a mature compost, lime (to plots having pH < 4), and control without amendment. During the study two crops of Brassica juncea were grown, with two additions of each organic amendment. Throughout the study, the evolution of soil pH, total and available (DTPA-extractable) heavy metals content (Zn, Cu, Mn, Fe, Pb and Cd), electrical conductivity (EC), soluble sulphates and plant growth and heavy metal uptake were followed. The study indicates that: (1) soil acidification, due to the oxidation of metallic sulphides in the soil, increased heavy metal bioavailability; (2) liming succeeded in controlling the soil acidification; and (3) the organic materials generally promoted fixation of heavy metals in non-available soil fractions, with Cu bioavailability being particularly affected by the organic treatments.

Mobility of metals and metalloids in a multi-element contaminated soil 20 years after cessation of the pollution source activity

Knowledge of trace element concentrations and mobility is important in the ecotoxicological assessment of contaminated soils. We analysed soil pore water under field conditions to provide new insights into the mobility of residual contaminants in the surface 50 cm of a highly contaminated woodland soil. Cadmium and Zn were highly mobile in the acidic soil, concentrations increasing with depth in soil pore water, showing considerable downward mobility. High levels of surface organic matter restricted the solubility of Cu, Pb and Sb, with highest concentrations being found close to the surface. Dissolved organic carbon in pore water had a strong influence on mobility of Cu, Zn, Pb and Sb. Elevated As had moved from the organic surface horizons but was largely immobilised in deeper layers and associated with Fe and Al oxides. The measured differential mobility of pollutants in the present study is highly relevant to protection of groundwater and other receptors.

Mobility of arsenic, cadmium and zinc in a multi-element contaminated soil profile assessed by in-situ soil pore water sampling, column leaching and sequential extraction

Three methods for predicting element mobility in soils have been applied to an iron-rich soil, contaminated with arsenic, cadmium and zinc. Soils were collected from 0 to 30 cm, 30 to 70 cm and 70 to 100 cm depths in the field and soil pore water was collected at different depths from an adjacent 100 cm deep trench. Sequential extraction and a column leaching test in the laboratory were compared to element concentrations in pore water sampled directly from the field. Arsenic showed low extractability, low leachability and occurred at low concentrations in pore water samples. Cadmium and zinc were more labile and present in higher concentrations in pore water, increasing with soil depth. Pore water sampling gave the best indication of short term element mobility when field conditions were taken into account, but further extraction and leaching procedures produced a fuller picture of element dynamics, revealing highly labile Cd deep in the soil profile.

Relation between solution chemistry and morphology of SnO2-based thin films deposited by a pyrosol process

Abstract The chemical nature of precursors and morphology (surface aspect and preferred orientations) for SnO2 films deposited by a pyrosol process are examined for starting solutions containing either SnCl4 or SnCl2 · 2H2O dissolved in methanol. A study by comparison shows that molecules formed from SnCl4 deposit more easily than polymer molecules produced from SnCl2 · 2H2O. The addition of HC1 in this last solution modifies significantly the chemical nature of the molecule participating in film development as well as the growth rate. Electrical measurements of the solution resistivity as a function of HC1 concentration show a minimum in the equivalent conductivity which is directly correlated with a maximum in the growth rate. This is explained by the association of SnCl2 and HC1 to form neutral HSnCl3 molecules. A geometrical approach is then developed to describe the growth form of the film crystallites. For thin films deposited from SnCl2 · 2H2O, the crystallite faces consist of (101) corresponding to (110) preferred orientation. For SnCl4, the crystallites consist of 111 faces corresponding to a (200) preferred orientation. The presence of (101) and (301) twin planes is used to explain the observation of (301) (211) and (101) preferred orientations respectively. Lastly, the electrical and optical characteristics of the corresponding films are also reported.

Effects of compost, pig slurry and lime on trace element solubility and toxicity in two soils differently affected by mining activities.

The use of organic wastes as amendments in heavy metal-polluted soils is an ecological integrated option for their recycling. The potential use of alperujo (solid olive-mill waste) compost and pig slurry in phytoremediation strategies has been studied, evaluating their short-term effects on soil health. An aerobic incubation experiment was carried out using an acid mine spoil based soil and a low OM soil from the mining area of La Unión (Murcia, Spain). Arsenic and heavy metal solubility in amended and non-amended soils, and microbial parameters were evaluated and related to a phytotoxicity test. The organic amendments provoked an enlargement of the microbial community (compost increased biomass-C from non detected values to 35 μg g(-1) in the mine spoil soil, and doubled control values in the low OM soil) and an intensification of its activity (including a twofold increase in nitrification), and significantly enhanced seed germination (increased cress germination by 25% in the mine spoil soil). Organic amendments increased Zn and Pb EDTA-extractable concentrations, and raised As solubility due to the influence of factors such as pH changes, phosphate concentration, and the nature of the organic matter of the amendments. Compost, thanks to the greater persistence of its organic matter in soil, could be recommended for its use in (phyto)stabilisation strategies. However, pig slurry boosted inorganic N content and did not significantly enhance As extractability in soil, so its use could be specifically recommended in As polluted soils.

The use of a halophytic plant species and organic amendments for the remediation of a trace elements-contaminated soil under semi-arid conditions.

The halophytic shrub Atriplex halimus L. was used in a field phytoremediation experiment in a semi-arid area highly contaminated by trace elements (As, Cd, Cu, Mn, Pb and Zn) within the Sierra Minera of La Unión-Cartagena (SE Spain). The effects of compost and pig slurry on soil conditions and plant growth were determined. The amendments (particularly compost) only slightly affected trace element concentrations in soil pore water or their availability to the plants, increased soil nutrient and organic matter levels and favoured the development of a sustainable soil microbial biomass (effects that were enhanced by the presence of A. halimus) as well as, especially for slurry, increasing A. halimus biomass and ground cover. With regard to the minimisation of trace elements concentrations in the above-ground plant parts, the effectiveness of both amendments was greatest 12-16 months after their incorporation. The findings demonstrate the potential of A. halimus, particularly in combination with an organic amendment, for the challenging task of the phytostabilisation of contaminated soils in (semi-)arid areas and suggest the need for an ecotoxicological evaluation of the remediated soils. However, the ability of A. halimus to accumulate Zn and Cd in the shoot may limit its use to moderately-contaminated sites.

Rhombohedral-scalenohedral calcite transition produced by adjusting the solution electrical conductivity in the system Ca(OH)2-CO2-H2O.

This work is aimed to investigate the effects of the adjustment of the electrical conductivity (kappa25) during the semicontinuous carbonation of Ca(OH)2 suspension (slaked lime) on the morphology of the precipitated calcite (CaCO3) particles. The experiments were carried out at 30, 45, and 60 degrees C. A gradual morphological change from rhombohedral to scalenohedral shapes was produced with an increase of kappa25 from 1 to 7 mS/cm at each temperature. The explanation of this morphological change is given in terms of the increase of both the supersaturation and the ratio between concentrations of charged species containing calcium and carbonate ([Ca]ch/[CO3]ch) in the aqueous phase as the kappa25 set-point increases, prior to the precipitation process. In addition to the rise of the supersaturation this change most probably takes place because the increase of the [Ca]ch/[CO3]ch ratio affects the growth rate of the rhombohedral {104} and scalenohedral {21-1} faces in a different manner: (i) favoring the equality between the surface coverage of Ca2+ and CO3(2-) on the stoichiometric {104} face, thus enhancing the formation of CaCO3(0) growth units and then its growth rate and (ii) inhibiting the growth of the {21-1} face by adsorption of the excess calcium species.