Abstract
The presence of high level of heavy metals involves a human healthy risk that could induce chronic diseases. This work reports on the metal contamination due to heaps of steel-slag accumulated during more than 40 years in allotments and industrial areas in the southern part of Madrid (Spain). Several slag and soil samples were collected in an area of 10 km(2) and characterized by different conventional (XRD and XRF) and no so common methods (ESEM, thermoluminescence and EDS-WDS). The analysis reveal the presence of: (i) important amounts of Fe (43%), Mg (26%), Cr (1.1%), Mn (4.6%), S (6.5%) in the form of Fe-rich slag phases (wustite, magnetite...), Si and Ca-rich phases (larnite, ghelenite...), Cr (chromite), Mn (bustamite) and graphite, (ii) traces of some other contaminants such as Cr (7700 ppm), Zn (3500 ppm), Ba (3000 ppm), Pb (700 ppm) or Cu (500 ppm) on pathway soil samples that come from the steel slag, and (iii) Co (13 ppm), Pb (78 ppm) and V (54 ppm) in farmland soil samples. Although the existing heavy metals content is not appropriate for the current use, the extremely high metal contamination of the surrounding areas is more worrying. The properties of the soil farmlands (pH circa 7, 13% of clay, mainly illite, and 1-4% of organic matter content) show suitable conditions for the retention of cationic metals, but further studies on the movilization of these elements have to be performed to determine the possibility of severe human health risks. This sort of study can provide useful information for the politicians regarding the appropriate use of the territory to prevent possible health hazard for the population.
Highlights
The production of iron and steel yields important amounts of slag as by-products, which is one of the main sources of metal environmental pollution
In addition to the conventional methods commonly employed for sample characterization (X-ray diffraction, XRD, scanning electron microscope, SEM, Inductively Coupled Plasma Mass Spectrometry, ICPMS, or X-ray fluorescence, XRF), there are some others techniques that could contribute especially to singleparticle characterization, namely: environmental scanning electron microscope (ESEM), thermoluminescence (TL) or energy-dispersion, and wavelength-dispersive spectrometry (EDS-WDS), depending on the nature of different soil constituents
This study, in which several pathways and farmlands soil samples from the southern part of Madrid (Spain) have been investigated, demonstrates the presence of a high concentration of metal contaminants coming from heaps of steel slag
Summary
The production of iron and steel yields important amounts of slag as by-products, which is one of the main sources of metal environmental pollution. Based partially on the CLEA (Contaminate Land Exposure Assessment) model employed in England and Wales (Environment Agency 2002), the local authorities in Madrid (Spain) standardized the levels of soil contaminants assuming three different scenes depending on the land use: industrial, urban and others (e.g. agricultural crops) (Comunidad de Madrid 2006). One of the main challenges required from the local authorities or policy makers concerning the metal contamination is to define new methodologies that are faster, simpler, more reliable and cheaper, which look for different and sensitive analytical techniques to discriminate, among others, (i) geogenic and anthropogenic origin of metal concentration, (ii) biological interactions including oxidation-reduction processes, (iii) phase complexation, (iv) precipitation, (v) dissolution, etc. All of them show pros and cons, but all together offer an excellent sample characterization since the deficiency of one technique can be covered by some of the others (Gunst et al 2000)
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