Assessment of the ecological risk and mobility of arsenic and heavy metals in soils and mine tailings from the Carmina mine site (Asturias, NW Spain)

Abstract

An evaluation of the pollution, distribution, and mobility of arsenic and heavy metals in spoil heaps and soils surrounding the abandoned Carmina lead-zinc mine (Asturias, northern Spain) was carried out. Fractionation of arsenic was performed by an arsenic-specific sequential extraction method; while, heavy metal fractionations was carried out using the protocol of the Bureau Community of Reference (BCR) (now renamed Standards, Measurements and Testing Programme). Arsenic appeared predominantly associated with amorphous iron oxyhydroxides. Among the heavy metals, lead and zinc showed high availability since significant amounts were extracted in the nonresidual fractions; whereas, chromium, copper and nickel showed very low availability, indicating their lithogenic origins. The results showed that the extractability of heavy metals in soils is influenced mainly by the presence of iron and manganese oxides as well as by pH and Eh. Multiple pollution indices, including the enrichment factor (EF), geoaccumulation index (Igeo), ecological risk index (Er) and potential ecological risk index (PERI), were used to assess the degree of soil pollution in the mine area. All results showed that lead was the key factor causing the pollution and ecological risk in the studied area, and copper, zinc and arsenic also had significant contributions. Notably, the sites at higher risk coincided with those with high availability of arsenic and heavy metals. This study provides an integrative approach that serves as a powerful tool to evaluate the metal pollution status and potential threats to the local environment of abandoned mining areas, and the results are useful for making management decisions in these areas.

Keywords: Abandoned mines; Arsenic; Ecological risk assessment; Fractionation; Heavy metals; Mobility.

Fig. 1

Some galleries and the hosting quartzites above the spoil heaps of the Carmina mine (A); Details of the spoil heaps (B)

Fig. 2

Soil sampling points location

Fig. 3

Mineral constituents of the mine wastes. A Galena inclusions in sphalerite denoting an early formation of Pb-sulfide. B Galena (ga) and sphalerite (sph) cementing silicates of the host rock. C Arsenopyrite (apy) and chalcopyrite (cpy), closely associated, accompanied by sphalerite. D Galena partially replaced by anglesite (ang) with well-preserved sphalerite and quartz (qtz). The images in Figures A–C were taken by optical microscopy in reflection mode. Figure D is a backscattered electron image obtained with the SEM. The horizontal framing is 0.65 mm for Figure (A) and 1 mm for Figures (B and C)

Fig. 4

Arsenic distribution in different supporting phases in the sampled soils

Fig. 5

Distribution of Cr, Cu, Ni, Pb and Zn in different supporting phases of the soil samples

Fig. 6

Scanning electron microscope-backscattered electrons (SEM-BCE) images. A Appearance of mineral particles in soil samples: angular silicates (dark tones, area analyzed and spectra indicated by a red point) and very fine particles of Fe oxides with significant amounts of Pb (6.01%) and minor quantities of As (0.15%, light-colored particles, yellow circle). B crystalline particle with a composition close to that of plumbojarosite (2.24% Cu, 1.29% Cu and 0.31% As, orange point). C crystalline Fe oxide with particulate mineral matter finely dispersed over its surface; arsenic was not detected in the supporting grain (white point), but 0.23% As and 5.85% Pb were measured over the top coating (also a Fe oxide, green point). Horizontal axis units in all spectra are keV

Fig. 7

TEM images. Mapping results for Fe–Si–Pb–As in two soil particles of alkali silicates and Fe oxides. Above: Distribution of Si, Fe and Pb. Below: Distribution of Si, Fe and As. Fe oxides are indicated in red contour in the last column; the rest of the particles are silicates

Fig. 8

Dendrogram corresponding to statistical clustering analysis of total elemental concentrations, pH, Eh and TOC using the Ward method

Fig. 9

Graph of rotated components (PCA, Varimax rotation)

Fig. 10

Ecological risk (Er) for each metal(loid) (bars) and integrated potential ecological risk (PERI) (black line) in the studied soils