Saturday, 15 July 2006

Effect of Anthropogenic Wastes on Heavy Metal Mobility after 6 Months of Stabilization.

Andrea Zanuzzi and Angel Faz. Universidad Politécnica de Cartagena, Paseo de Alfonso XIII, 48, Cartagena, 30203, Spain

The intense mining activity carried out in Cartagena-La Unión Mountain, Southeast Spain, caused extremely high accumulation of heavy metals in soils. Among remediation technologies, phytostabilization is an effective method to rehabilitate mine lands. However, the properties of mining soils, such as high metal concentrations, sheet erosion, drought, compaction and shortage of essential nutrients, make them a poor medium for plant growth. Therefore for stabilizing these mining areas, utilizing tolerant populations together with fertilizers and carbonates application, which provide plant nutrients and reduce acid drainage and heavy metal mobilization and toxicity, has been selected as a feasible remediation method. The aim of this research was therefore to assess the effect of marble wastes (carbonates) and pig slurries and sewage sludge on some soil properties and characteristics, such as pH, electrical conductivity (EC), nitrogen and organic carbon contents and heavy metals' bioavailability and solubility. For that purpose, two representative mining ponds were selected and 20 square field plots (4 m2 each) were located in each pond. Three different doses of organic amendments, such as pig slurries and sewage sludge, and one dose of marble wastes (carbonate) for each pond, were added. A positive effect of amendments after 6 months of stabilization was observed. There was an increment of pH, nitrogen, organic carbon and carbonates contents as a result of marble wastes and organic amendments addition. There was also an increment of EC in Brunita pond, but there was a reduction in Lirio pond; which could be related with pH raising and its influence on soluble salts. Conversely, there was a reduction of Zn, Pb and Cd solubility and bioavailability, except for bioavailable Pb in Lirio pond, and an increment of Cu mobility. There were significant differences among blank and amended soils for soluble and bioavailable Pb, Cd, and Zn except for bioavailable Pb in Lirio pond and bioavailable Cd and Zn in Brunita pond. Otherwise, there were significant differences among pig slurries doses and sewage sludge treatments for bioavailable Cu in both ponds, and for soluble Cu in Brunita pond. In the case of soluble Cu, there were significant differences among blank and pig slurries amended soils in both ponds. These results showed that there was an immobilizing effect for Zn, Pb and Cd due to liming and perhaps because of organic amendment addition due to complexation and immobilization processes. Organic matter could reduce metal toxicity changing bioavailable forms to other less bioavailable forms. However, the increase of Pb bioavailability in Lirio pond could be related to the addition of organic matter with high proportion of soluble compounds which could amplify the solubility of heavy metals in short term; or with the establishment of organic-metallic compounds that could increase the solubility of some heavy metals at high soil pH. And the increment of Cu mobility could be associated to compounds of low molecular weight applied with sewage sludge and pig slurries that may increase Cu bioavailability and solubility. Therefore, the addition of organic amendments in combination with carbonates raises pH and reduces heavy metal bioavailability and solubility, promoting the stabilization of the studied mine lands.

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