Chelate-assisted phytoextraction of heavy metals in a soil contaminated with a pyritic sludge.

The occurrence of many polluted areas as that affected by the accident of the Aznalcóllar pyrite mine has promoted phytoremediation as a technology able to reduce the risk of heavy metal contamination at low cost. White lupin plant has been considered a good candidate for phytoremediation. We studied the capacity of several complexing agents to improve the ability of white lupin for heavy metal phytoremediation in soils with multi-elemental pollution from acid pyritic sludge. Solution-soil interaction was studied and pot experiments with sludge-affected soil were carried out to this end. The interaction experiments indicated that EDTA and NTA were more efficient than malate and citrate in solubilizing metals (Fe, Mn, Cu, Zn, Cd), with minimum differences between EDTA and NTA. The pot trial showed that NTA was able to mobilize toxic elements from sludge-polluted soil and hence increasing their concentrations in plant (Mn, Cu, Zn, As, Cd). However, the NTA treatment promoted an increase of toxic elements concentrations, especially for As, Cd, Pb, in the lixiviates exceeding the maximum permissible levels, so a careful management of chelate is necessary.

Risk assessment of an abandoned pyrite mine in Spain based on direct toxicity assays.

This research reports the risk assessment of an abandoned pyrite mine using direct toxicity assays of soil and groundwater samples taken at the site. The toxicity of As and heavy metals from mining soils to soil and aquatic organisms was studied using the Multispecies Soil System (MS-3) in soil columns. Ecotoxicological assessment was performed with soil samples diluted with a control soil at concentrations of 12.5, 25, 50 and 100% test soil/soil (w/w). In this way, changes in the mobility and bioavailability of soil contaminants due to changes in geochemical soil properties via soil dilution were studied. The toxicity of water samples was tested on algae and Daphnia magna. The assessment of the mining area indicated that the current presence of As and heavy metals at the site may cause injuries to soil and aquatic organisms in the entire research area. Moreover, this investigation demonstrated that changes in geochemical conditions can increase the availability of arsenic and, consequently, the environmental risk of these soils. A good correlation was not found between toxicity parameters and the concentrations of soil contaminants based on total and extracted element concentrations. This finding reinforces the usefulness of direct toxicity assays for evaluating environmental risk.

Screening risk assessment tools for assessing the environmental impact in an abandoned pyritic mine in Spain.

This paper describes a new methodology for assessing site-specific environmental impact of contaminants. The proposed method integrates traditional risk assessment approaches with real and variable environmental characteristics at a local scale. Environmental impact on selected receptors was classified for each environmental compartment into 5 categories derived from the whole (chronic and acute) risk assessment using 8 risk levels. Risk levels were established according to three hazard quotients (HQs) which represented the ratio of exposure to acute and chronic toxicity values. This tool allowed integrating in only one impact category all the elements involved in the standard risk assessment. The methodology was applied to an abandoned metal mine in Spain, where high levels of As, Cd, Zn and Cu were detected. Risk affecting potential receptors such as aquatic and soil organisms and terrestrial vertebrates were assessed. Whole results showed that impact to the ecosystem is likely high and further investigation or remedial actions are necessary. Some proposals to refine the risk assessment for a more realistic diagnostic are included.