Abstract
This work presents an integral methodological approach to assess the environmental potential hazards posed by metals and metalloids hosted by spolic technosols derived from old tailings from a mining operation for galena (PbS, with high Ag contents)-sphalerite (ZnS, with a varied cohort of trace elements contents) in central Spain. We studied the total and soluble concentrations and spatial distribution of Pb, Zn, Cd, As, and Fe and the mineralogy of these soils, as well as an ecotoxicological evaluation by means of bioassays. The indices assessing soil contamination such as pollution load index (PI) and natural mobility index (NMI) have been calculated. Furthermore, the phytotoxic effect of the soil samples has been determined and a chronic sediment toxicity test using the benthic ostracod Heterocypris incongruens was applied. The geochemical study of 33 spolic technosols samples indicates large to extremely large metal and metalloid total contents: up to 48,600 mg kg−1 Pb, 34,000 mg kg−1 Zn, 500 mg kg−1 Cd, and 1000 mg kg−1 As. Given that sphalerite is usually the most important host mineral for cadmium in hydrothermal mineral deposits, there is a high correlation (R = 0.75) between this element and Zn. On the other hand, despite being two metallogenically intertwined elements in ore deposits, Pb and Zn show a less significant relationship, which can be attributed both to heterogeneities in the mineralogical composition of the veins, and to the complex history of the mineral concentration process: In the older process, the interest was only for Pb, meanwhile in the late period, the interest was focused in Zn. The Phytotoxkit® bioassay showed that soils with high PTEs presented very high toxicity, particularly the inhibition germination is related to Pb, As, and Cd content and root inhibition with Pb content. Both indexes were correlated with pH and electrical conductivity; samples with lower pH and higher soluble salt content are those with higher seed germination inhibition and root growth inhibition. On the other hand, the Ostracodtoxkit® bioassay showed very high sensitivity, with 100% mortality. The applied bioassays confirmed the soil toxicity and it is highly recommended to complement the results from environmental chemistry with results from bioassays, in order to provide a more complete and relevant information on the bioavailability of contaminants and to characterize the risk of contaminated areas.
Highlights
Sites where metal ores are mined or processed are potential sources of environmental pollution.In ancient mining districts, with long histories of mining and metallurgical activity, mine wastes represent one of the main sources of pollution for soils, water, air, and biota [1]
To assess the potential hazards derived from having metal and metalloid rich abandoned tailings deposits, we studied San Quintín West side of the old mineral recovery operations (Figure 2)
The Chung method is based on the determination of the reference intensity ratios (RIR) of the existing phases, which allows the intensity calculations to be normalized on the statement that the sum of all phases in the sample is equal to 100%
Summary
Sites where metal ores are mined or processed are potential sources of environmental pollution. Characterization of soil contamination by PTEs could be based on the determination of total contents, because it only provides limited information on the chemical behavior in terms of biological availability, potential toxicity, and mobility, but not in the possibility of affecting waters and biota. Good knowledge of the soil contamination and the assessment of the potential effect of soils polluted by PTEs require identification of the geochemical phases in which the elements are bound and the evaluation of metal retention and bioavailability [4]. The determination of the contaminants contents is not enough to fully evaluate the toxic effects or to characterize contaminated sites, because the ecotoxicological danger in the biota of the environment is not reflected, and no information is provided on the effects of the chemical compounds. Previous environmental studies in the area [9,10,11,12], mainly described the inorganic compartments of the local environment; the present study is the first including the biological effects of the soil pollution
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