Atmospheric dust deposition on soils around an

Environmental Research 158 (2017) 153–166

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Atmospheric dust deposition on soils around an abandoned fluorite mine (Hammam Zriba, NE Tunisia)

MARK

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Chaima Djebbia, , Fredj Chaabania, Oriol Fontb, Ignasi Queraltb, Xavier Querolb a b

Laboratoire des Ressources Minérales et Environnement. Département de Géologie, Faculté des Sciences de Tunis, Université Tunis-El Manar, 2092 Tunis, Tunisia Institute of Environmental Assessment and Water Research (IDAEA-CSIC), C/Jordi Girona 18, 08034 Barcelona, Spain

A R T I C L E I N F O

A B S T R A C T

Keywords: Dust deposition Mine wastes pollution Eolian dispersion Fluorine Barium

The present study focuses on the eolian dispersion and dust deposition, of major and trace elements in soils in a semi-arid climate, around an old fluorite (CaF2) and barite (BaSO4) mine, located in Hammam Zriba in Northern Tunisia. Ore deposits from this site contain a high amount of metal sulphides constituting heavy metal pollution in the surrounding environment. Samples of waste from the surface of mine tailings and agricultural topsoil samples in the vicinity of the mine were collected. The soil samples and a control sample from unpolluted area, were taken in the direction of prevailing northwest and west winds. Chemical analysis of these solids was performed using both X-ray fluorescence and X-ray diffraction. To determine the transfer from mine wastes to the soils, soluble fraction was performed by inductively coupled plasma and ionic chromatography. The fine grained size fraction of the un-restored tailings, still contained significant levels of barium, strontium, sulphur, fluorine, zinc and lead with mean percentages (wt%) of 30 (calculated as BaO), 13 (as SrO), 10 (as SO3), 4 (F), 2 (Zn) and 1.2 (Pb). Also, high concentrations of cadmium (Cd), arsenic (As) and mercury (Hg) were found with an averages of 36, 24 and 1.2 mg kg−1, respectively. As a result of the eolian erosion of the tailings and their subsequent wind transport, the concentrations of Ba, Sr, S, F, Zn and Pb were extremely high in the soils near to the tailings dumps, with 5%, 4%, 7%, 1%, 0.8% and 0.2%, respectively. Concentration of major pollutants decreases with distance, but they were high even in the farthest samples. Same spatial distribution was observed for Cd, As and Hg. While, the other elements follow different spatial patterns. The leaching test revealed that most elements in the mining wastes, except for the anions, had a low solubility despite their high bulk concentrations. According the 2003/33/CE Decision Threshold, some of these tailings samples were considered as hazardous. Furthermore, other waste samples, considered non hazardous, were not inert. In contrast, the SO42-, Ba, Pb and Sb leachable contents measured in most of the soil samples were relatively high, exceeding the inert threshold for landfill disposal of wastes.

1. Introduction With the growing global demand for raw materials and energy resources, heavy metal contamination due to mining activities are a major problem in many countries (Dudka and Adriano, 1997; Liu et al., 2005). Heavy metal contamination adversely affects the environment, particularly the agricultural soils which can often be treated with remediation (Lechner et al., 2016). Although numerous natural and anthropogenic activities can increase dust emissions, and consequently atmospheric pollution levels, the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions of mining operations is one of the most

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hazardous dust emission sources (Csavina et al., 2012). Heavy metals naturally occur in soil, but additional pollution come from anthropogenic activities such as agriculture, urbanisation, industrialisation, and mining (Facchinelli et al., 2001; Li et al., 2014). Numerous studies have shown that the primary source of heavy metal pollution in the environment is the result of these anthropogenic sources (Alloway, 1995; Wei and Yang, 2010; Li et al., 2014). Tailings of mine waste dumps are mixtures of crushed rock, solid residues from smelting/extraction procedures including processing fluids from mills, washeries, or concentrators that remain after the extraction of minerals, ore metals, fuels, or coal from a mine resource (Lottermoser, 2007; Kossoff et al., 2014). The wind resuspension of

Corresponding author. E-mail addresses: [email protected] (C. Djebbi), [email protected] (F. Chaabani), [email protected] (O. Font), [email protected] (I. Queralt), [email protected] (X. Querol). http://dx.doi.org/10.1016/j.envres.2017.05.032 Received 12 February 2017; Received in revised form 24 May 2017; Accepted 26 May 2017 0013-9351/ © 2017 Elsevier Inc. All rights reserved.

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The F-Ba-Pb-Zn ore deposits of Hammam Zriba are stratabound ore bodies controlled by a tectonic setting (Bouhlel, 1993). The mineral association of ore deposits of the Hammam Zriba mine includes, in order of abundance: barite-celestite series (with 40–45%); fluorite (15–35%); quartz (10–40%); sphalerite, galena and pyrite (5–15%) and calcite (2–10%) (Bouhlel, 1985). Hammam Zriba ore deposits, between 1970 and 1992, were exploited by flotation in a hydrometallurgical on-site plant with an estimated production of 732,000 tons of high-grade Fluorspar and 18,000 tons of barite (ONM, 2008). Since 1992, the production ceased and a volume of 260,374 m3 of waste is concentrated in three flat top tailings over 96,658 m2 (Mezned, 2010), with an average height between 2 and 14 m. The waste was left very near the ore treatment plants and surrounding olive tree groves, with no reclamation or protection against water and/or wind erosion. The tailings, from the youngest to the oldest mine waste material, were labeled TI, TII and TIII (Figs. 1 and 2). The tailings are trapezoidal in shape with strong slopes. Exposed to the climate conditions of the region, weathering crusts are present at the surface. Moreover on their sides, the tailings are affected by marked badlands and gullies, created by the superficial flow of water and by slop sliding on borders. Mine wastes were discharged using the subaerial technique by deposition of the slurry waste mixed with water at different points of discharge within the dumping site. The sedimented waste is heterogeneously distributed within the landfill and a natural segregation, depending on the particle size, occurs. Coarser particles settle near the pumping points, forming the periphery zone of tailings, and the finer fraction was performed closer to the center of tailings. This segregation was clearly observed at the surface of tailing TI; on the surfaces of oldest dumps TII and TIII, the particle size seems, by visual inspection, finer and more homogeneous than in TI. This discrepancy can be explained by the strong water erosion, the ravines and the partial ruin of the periphery zone characterised by coarser particles. The sliding is frequent in the slopes of the tailings dumps, allowing the wind and water dispersion of contaminants, specifically with rainy season runoff. The rain flow is collected in wadi Hammam and the sediments were transported and redeposited in the surrounding fields. These damp sites are located in a farming areas with olive trees for oil production and poultry farms for breeding chickens and turkeys, both located in the direction of the prevailing northwest wind. According to the Standard Soil Color Charts, the dumps are light gray (10YR 8/2 and 2.5Y 8/1). They are fine grained and non-stabilized. Spontaneous vegetation tends to partially cover the dumps. The most recent dump, scarcely vegetated TI, was deeply affected by wind erosion that in turn originated mobile dunes encroaching on the olive tree groves. A gravitational differentiation and accumulation of coarse particles near the dust fallout sources takes place during the wind generated suspension of dust particles by (Matějíček et al., 2008). Hammam Zriba is characterised by a semi-arid Mediterranean climate. The average annual rainfall may vary greatly with years, but also with a very irregular seasonal distribution. For instance, within the period 2005–2014, the annual rainfall was between 213 and 790 mm, with an average of 473 mm/year, primarily during the autumn and winter months. For the same period, the average monthly temperature fluctuated between 11 °C in February and 28 °C in August (INM, 2015). Moreover, the site is subject to northwestern prevailing winds during the winter and the spring, but southwestern winds during the summer (classical Sirocco winds of the region). The maximum altitude at Hammam Zriba is 350 m a.s.l. Nevertheless, the steep cliffs of Jebel (mountain) Zaghouan (1295 m a.s.l.), 8 km east of the village, characterise the landscape. The wadi Hammam, the main stream, flows very near to the mine waste landfill and ends in the El R’mel Dam. The wadi transports contaminated sediments from the dumps. The streamwater contains four times the natural concentrations of barium and fluorine (ANPE, 2002).

atmospheric particulate matter (PM) and subsequent dry or wet deposition (Castillo et al., 2013; Querol et al., 2000) are primary pathways of atmospheric dispersion and transport of these pollutants which subsequently affect soil, biota, and water (Gonzalez-Fernandez et al., 2011a). Pollutants can also be transported with leaching by rainfall, stream and underground water. Wind, comparatively, transports atmospheric dust and contaminants rapidly over great distances. The main risk for atmospheric dust emission from abandoned mine areas is the presence of the unconfined tailings ponds with fine sized material containing a high metal load, which may be resuspended by wind or transported away by water runoff, or leached to groundwater; especially if confining layers are discontinuous (Martínez-Pagán et al., 2011; Gonzalez-Fernandez et al., 2011b). Few studies have evaluated the contribution of atmospheric dust emitted from mining wastes in the contamination of surroundings areas and estimate the flow of the metallic contaminants mobilised by the wind transfer to the soils of the mining site. In a Mediterranean climate and geography, with scant precipitation and poor soil cover, the dust resuspension from the tailings and the subsequent fallout can specifically affect nearby agricultural soil. The combination of wind and water causes weathering of the wastes and increases the dispersion of contaminants. In more humid regions, resuspension of anthropogenic dust is less relevant due to moisture and fast development of a soil cover. Therefore, characterising the atmospheric dispersion of pollutants resuspended from potential dust sources, such as abandoned mine sites without rehabilitation, is worthwhile (Kříbek et al., 2014; SanchezBisquert et al., 2017). Furthermore, the study of atmospheric PM (usually in the particle size range of 60 µm), including dust in the transport of pollutants, particularly those that have low volatility and low aqueous solubility and remain attached to soil particles (Rodriguez et al., 2009; Corriveau et al., 2011) is also consequential. Environmental studies in Tunisia have focused on the metal contamination of soils, plants, water, and sediments, specifically in lead (Pb)-zinc (Zn) mining areas, (Sebei et al., 2006; Boussen et al., 2010, 2013; Chakroun et al., 2013). The resuspension of metals is relevant when considering tailings from ore deposits made of complex mineral assemblages, such as the ones made of barite (BaSO4) – celestine (SrSO4) series, fluorite (CaF2), quartz (SiO2), calcite (CaCO3), galena (PbS), pyrite (FeS2) and sphalerite (ZnS) in Hammam Zriba, in Tunisia (Bouhlel, 1985). Yet, few studies focusing on metals/metalloids concentrations in atmospheric dust derived from mining operations have been performed in Tunisia (Ghorbel et al., 2010). For example, most of studies of barite mines have focused on the bioaccessibility of barium (Ba) from barite contaminated soils (Abbasi et al., 2016), its concentrations in the water (McGrath et al., 1989), and plants (He et al., 2012; Lamb et al., 2013). Therefore, the focus of the current research was: (a) to characterise the mineralogical and chemical composition of tailings of Hammam Zriba, an abandoned fluorite (CaF2) and barite mine area in Northeastern Tunisia; (b) to assess the contamination of the surroundings soils; and (c) to estimate the potential mobility of the metals and metalloids from the tailings redistributed in the area. 1.1. Study area The Hammam Zriba fluorite mine is located at the southern bank of wadi (an ephemeral water course usually dry and only during the rainy season contains water) Hammam, near Southern part of the Hammam Zriba (36°20′N 10°13.5′E, 9000 inhabitants) town, in northeastern Tunisia, 60 km south of Tunis (Fig. 1). This town is known for its thermal springs and its mining activities. The hydrothermal type ore (FBa-Pb-Zn) is hosted by the carbonate rocks from the Mesozoic-Paleogene era, and is located in the F-rich metallogenic district of North Tunisia. The Pb-Zn-Fe-Ba-Sr-F mineralisations in this region belong to the oriental continuity of the Pb-Zn Atlas belt, which continues west to Algeria and Morocco. 154

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Fig. 1. Location of the study area, tailings dumps and the soil sampling transects, and wind rose obtained during May and June 2013.

d Dunes

a

TI

Prevailing wind NW

Dunes

TI

TII

TIII

Wadi Hammem

b

c

Dust bearing wind

Fig. 2. a) Overview of the mining wastes dumps TI, TII and TIII, as well as of the dunes. b) and c) Dust resuspension and transport during 22 and 23/04/2013 (bottom). d) Eolian contamination of surrounding agricultural soils.

2. Materials and methods

quarters from the landfill areas samples, a representative homogenised bulk sample was prepared for each zone. In addition, 4 samples of sandy material from the dunes formed in front of dump TI were collected along a transect crossing the dunes from the dump.

2.1. Sampling 2.1.1. Tailing and dune sampling To characterise the source of contamination, in 2013, 13 composite tailings samples were collected from the surface of the three dumps. The sampling strategy considered the surface particle size. Mixing the

2.1.2. Soil sampling Soil samples were collected following the direction of the prevailing wind (northwest). The sampling was carried out along three transects 155

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the errors due to the physical-matrix effects, the surface of the sample should be perfectly flat; a 4 cm diameter pellet was then obtained by pressing the sample at 20 tonnes for 1 min, Due to the lack of an natural analogous reference materials and the difficulty to use Fundamental Parameter (FP) methods caused by the presence of light weight elements (such as fluorine, not accurately measured by EDXRF), synthetic standards were prepared to analyse the mining waste samples by an empirical calibration. The calibration was designed to cover the analytical range for all analytes of interest; both correction for matrix effects (variable alphas) and inter-element lines overlapping were applied. Determination of fluorine was performed following the method described by Sager (1987) and analysed by an F- sensitive electrode. The determination of trace elements content was performed by applying a prior acid digestion (HNO3, HF and HClO4, 1:3:1) followed by the analysis of the resulting solution by Inductively Coupled PlasmaAtomic Emission Spectroscopy (ICP – AES), (Thermo Scientific, iCAP 6000 Series Model) and the Inductively Coupled Plasma Mass Spectrometry (ICP – MS) (Thermo Electron Corporation, X-SeriesII Model), respectively. The analytical procedures were controlled using reagent blanks and standard reference materials. The used soil standards were SO-2 and SO-4, from the Canadian Certified Reference Materials Project, and a fly ash reference material (NIST-1633b). These were digested and analysed under the same conditions as all the samples. Moreover, blank values corresponding to acids (pro analysi) were subtracted from measured concentrations. Relative errors were for most elements < 5%, and < 10% for phosphorus (P). The content of mercury (Hg), after pyrolysis of each sample in combustion tube at 750 °C under an oxygen rich atmosphere, was determined directly on solid samples by a LECO AMA 254 Gold Amalgam Atomic spectrometer.

(T1, T2 and T3) following a hierarchical spatial design to evaluate possible spatial concentration gradients, the significance of the distance on the contamination and the eolian transfer of the contamination toward the agricultural soils. Using plastic spade and after the removal of pebbles, 19 topsoil samples (2 kg) were collected from the depth of 0–5 cm and stored in polyethylene bags. The sampling positions (see Fig. 1) were geo-referenced by a GPS (Global positioning system). To define the anomalies and/or contamination of soils from the dumps, we collected one sample (HZBt) to be used as a metal/metalloids concentration control of the local natural geochemical background. The reference soil sample (HZBt) is naturally protected from any influence of the windblown dust from the mine wastes. In fact, in Hammam Zriba, the air currents are influenced by a local wind corridor, bordered on the west by Jbel Boukrouf (350 m a.s.l) and Jbel Margib (270 m a.s.l). (This limit behaves as barrier limiting the spread of contamination toward the HZBt location Fig. 1). After air drying at laboratory, all samples were sieved through a 2 mm mesh. Subsequently, the sieved samples underwent a quartering to obtain representative quantities for analytical determinations. 2.2. Physical, chemical, and mineralogical characterisation 2.2.1. Density and mineralogy of mine waste and soil The density of mining waste samples was measured using a Helium Pycnometer. In addition, the cohesion tests for the mining waste samples were performed on-site, using a Geonor LG 1160 field vane shear tester with an accuracy of 1 kPa. To measure the loss of ignition (LOI), 1 g of each sample was oven dried overnight at 110 °C to remove moisture and retained water. Then, the sample was heated in a muffle furnace at 1000 °C for 4 h, cooled in a dessicator and then the calcined residue was weighed. The LOI was obtained by calculating the difference in weight before and after ignition. Mineralogical analysis was performed by X-Ray diffraction (XRD) analysis using a D8 Advance X-ray powder diffractometer (Bruker GmbH, Germany), with Cu-Kα1 radiation, Bragg-Brentano geometry, and a position sensitive LynxEyeXE detector. The diffractograms were obtained from 4º to 120º of 2 theta angles with a step of 0.015º, a counting time of 0.5 s, and sample rotation. To estimate mineral contents, the crystalline phase identification was performed using the software package linked to the instrumentation and the TOPAS software program (Bruker/AXS, 2000) with the fundamental parameter approach for a fitting profile and a Rietveld refinement (Young, 1993). In addition to XRD analysis, the content of calcium cabonates was determined by the volumetric method using a Bernard calcimeter. To investigate the metals/metalloids bearing particles, polished thin sections embedded in epoxy resin were prepared from the samples of the dump TI for Scanning Electron Microscopy (SEM) analysis. Specimens were studied using a Quanta MK2 200 SEM operated at 20 kV and equipped with an energy dispersive detection system (EDS).

2.2.4. Leaching tests Water soluble metals can be determined from a saturation paste extract of a soil or by extracting soil with deionised water at a certain soil–water ratio (Svete et al., 2000). To determine the soluble fraction of heavy metals and other potentially toxic elements in mining wastes and soil samples of Hammam Zriba, the leaching test, EN 12457 Part 2 procedure was performed. A sample suspension in water was prepared at solid-to-fluid ratio of 5:50 (g: mL). A mass of 5g of the fraction < 63 µm was placed in a polyethylene bottle and 50 mL of deionised water was added. After an agitation time of 24 h at the room temperature, the suspension was filtered through 0.45 µm cellulose nitrate filters and centrifuged. Blank values corresponding to deionised water treated with same conditions as the samples were subtracted from measured concentrations. Solutions were analysed for major, trace elements, and anions (NO2-, NO3-, SO42- and F-) by ICP – AES, ICP – MS and Ion Chromatography IC (Waters 1525 Binary HPLC Pump), respectively. The trace elements were expressed in mg·kg−1 and the major elements were expressed in wt% (percentage by dry weight of wastes and soils).

2.2.2. Grain size characterisation For the grain size analysis, samples were sieved through a 63 µm sieve and fractions smaller than 63 µm were analysed in ethanol suspension by the laser diffraction Mastersize 2000E particle size analyser (MALVERN, version 5.20).

2.2.5. Data analysis The minimum, maximum, average, and median of content of the elements in the mine wastes and soils were calculated, as well as the matrix of the Pearson correlation coefficients among the elemental content of the samples. Enrichment factors (EFs) were calculated to determine the nature and extent of contamination in the area. Elemental EFs in the atmosphere, precipitation, or seawater are conventionally used to assess chemical modifications due to natural processes as well as anthropogenic induced chemical impacts (Goldberg, 1972; Zoller et al., 1974). The use of EFs has progressively been extended to the study of soils, lake sediments, peat, tailings and other environmental materials (Ragaini et al., 1977; Loska et al., 1997; Reimann and De Caritat, 2005). To quantify the contamination of soils, EFs for metals/metalloids

2.2.3. Bulk sample chemistry The estimation of major and minor elements content was made using an energy dispersive X-ray fluorescence (EDXRF) spectrometer (S2 Ranger, Bruker GmbH, Germany) with a Pd anode X-ray tube and a XFLASH Silicon Drift Detector (SDD) with an energy resolution of 129 eV at Mn-Kα line. Sample preparation was made following the recommendations and procedures detailed in Margui et al. (2016); 10 g of finely ground powder of each sample mixed with 1 g of Hoeschst Wax-C micropowder were homogenised in an agate mortar. To avoid 156

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northwest wind and a relevant proportion of the finer fraction has been already mobilised by eolian transport. Samples of Hammam Zriba (HZ) mine tailings show a bimodal and lognormal grain size distribution with a prevailing coarser mode around 10 – 40 µm and a finer mode less than 0.6 µm (Table 2). The grain size of the TI, TII and TIII Hammam Ziba mine tailings show slight differences, with median (P50) ranging from 9 to 26 µm, 16–32 µm, and from 16 to 27 µm, respectively (Table 2). The < 2.5 µm fraction in the HZ tailings is in the 7 – 21% range. The highest < 2.5 µm fraction was attained in sample ZIGr2, from the most recent tailing (TI). The opposite trend of the < 63 and < 2.5 µm fractions, with higher proportion in the old and in the recent tailings dumps may be due to: i) The mode of deposition of wastes ii) the degree of exposure of the inner parts of the dump; due to hydric erosion and collapse, these being more intense in the older ones. The windblown material collected as a movable dune at the foot of TI in the direction of the prevailing wind is relatively coarse, with low proportion of the < 63 µm fraction (0.1% and 4.6%). During the suspension of dust particles from tailings by wind, a gravitational differentiation occurs, with the accumulation of coarse particles near the sources (Matějíček et al., 2008). The depletion of the finer fraction in the dunes and tailings is due to the wind transport of the finer particles further away, while the coarser (up to sand size) grains are accumulated in the dunes near the tailings. Our results show that dune material does not contain < 2.5 µm, < 5 µm and < 10 µm fractions, with the exception of the nearest sample to the dump (DATA), which contains 2.7%, 3.8% and 7.0% respectively, with the median (P50) size of the < 63 µm reaching 59–62 µm (Table 2). According XRD results, the (Sr-rich) barite and (Ba-rich) celestine are the major mineral components of the tailings. The percentages of barite-celestine mineral series in the three tailings reached 38 – 65%, 52 – 65% and 23 – 41%, respectively for TI, TII and TIII. A high content of fluorite was also determined, particularly in the oldest tailing TIII (12 – 35%). However, in the most recent tailing TI, the content of fluorite was much reduced (5–18%). The calcite content in the tailings ranged 8–32% according calcimetry, and 10–34% according XRD analysis, so calcite is a major mineral in the tailings. Quartz contents reached 3 – 9% in the tailings from the three dumps. Furthermore, the hemimorphite [Zn4Si2O7 (OH)2·(H2O)] and the strontianite (SrCO3) with contents lower than 4% and 8%, respectively, are present in all the samples. Gypsum (CaSO4·2H2O) with contents reaching up to 7% was detected in some samples. Galena, the only sulfide detected by XRD in our research, was present in only two samples (ZIGr1 and ZIIGr1) of the recent dump TI with (2% and 3%, respectively). The windblown material collected as the mobile dune at the foot of TI and in the direction of the prevailing northwest wind, had the same mineral association than the dumps. Galena is detected in all dunes samples with a content of 1 – 2%. The distribution of major minerals (especially fluorite) among the three dumps were slightly different. This difference could be explained by a lack of efficiency of the ore beneficiation methods in the beginning of the exploitation, but also possible by variations in the ore mineralogy along the life of the mine and the exploitation of economic interests.

Table 1 Classification of soil pollution according geochemical indicators: Enrichment Factor (EF, Han et al., 2006; Khalil et al., 2013) and Combined Pollution Index (CPI, Abrahim and Parker, 2008). Soil indicator

Class

Degree of contamination

EF

EF < 2 2≤EF < 5 5≤EF < 20 20≤EF≤40 EF > 40

States deficiency to minimal enrichment Moderate enrichment Significant enrichment Very high enrichment Extremely high enrichment

CPI

< 1.5 2–4 4–8 8 – 16 16 – 32 > 32

Nil to very low Moderate High Very high Extremely high Ultra high

were calculated by dividing the concentration of a given element versus the one of aluminum (Al) as a reference element and normalised by the same rate using the reference soil background sample according the following formula:

EF = [Me /Al] sample / [Me / Al]

(1)

background

where [ Me/Al] sample is the concentration ratio of a given metal to Al in each sample and [Me/Al] background is the average ratio of the same metal to Al in the reference soil background sample (Table 1). Moreover, the Combined Pollution Index (CPI), also referred to as the Coefficient of Industrial Pollution (CIP), was calculated as the sum of EFs for a given pollutants divided by the number (n) of elemental EFs included in the calculation (Abrahim and Parker, 2008; Mileusnić et al., 2014) using the following equation: i=n

CPI =

∑ ([Me/Al] sample/[Me/Al] background)/n

(2)

i=1

3. Results and discussion 3.1. Mining wastes characterisation 3.1.1. Physical and mineralogical patterns The mining wastes of Hammam Zriba consist of more than a quarter of million of cubic meters (ONM, 2008) disposed in tailings composed of residues from mineral flotation procedures, with an average of density of 3.6 g/cm3. Moreover, its cohesion is weak and is between 36 and 50 kPa. Wastes with a grain size less than 125 µm are most susceptible to resuspension by dust blow; but these particles, depending on the mineralogy, also tend to form stable aggregates (Xenidis et al., 2003). The Hammam Zriba tailings contain a major fraction finer than 63 µm, higher in the old tailings (TIII, 86.4%) than in the recent one (TI, 2.7 – 76.5%). This particle size fraction is prone to wind transfer. Clearly, the recent dump, TI, is prone to the erosive action of the prevailing

Table 2 Grain size of mining wastes and dune materials samples: Mass percentage below 2.5, 5 and 10 µm and size (in μm) for the percentiles 10, 50 and 90. Tailing TI

< 2.5 µm < 5 µm < 10 µm P10 P50 P90

Tailing TII

Tailing TIII

Dunes materials

ZIGr1

ZIGr2

ZIIGr1

ZIIGr2

ZIIGr3

TII1

TII2

TII3

TIII1

TIII2

TIII3

TIII4

TIII5

DATA

DATB

DATC

DATD

3.8 5.3 8.8 13.5 50.4 94.8

21.2 38.6 55.3 1.2 9.5 41.4

2.8 3.7 6.4 20.9 55.4 100.4

8.6 14.9 23.8 3.5 25.5 69.2

11 20 32 2.5 19.8 61.1

7.2 12.7 18.9 4.5 32.3 75.5

6.8 12.8 22.2 4.8 25 58.9

12.3 23.9 37.2 2.2 16.5 43.8

10.9 20.3 31.2 2.5 21.8 62.9

7.8 15.1 23.4 3.8 24 54.8

12.1 24.3 37.1 2.3 17.6 53.9

10 17.5 24.9 2.8 27.4 66.1

14 26.3 40.2 1.9 15.6 51.8

2.7 3.77 6.95 18.32 59.25 109.9

0 0 0 43.52 62.35 101

0 0 0 37.33 61.93 101.9

0 0 0 36.39 61.86 103.4

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Fig. 3. SEM micrographs in Back-Scattered Electrons (BSE) of metals/metalloids bearing particles from the dump TI of Hammam Zriba: (a) quartz (Qtz), calcite (Cal) and hemimorphite (Hmm); (b): barite, (Sr rich) (Bar, Sr rich) and celestite (Ba rich) (Cel, Ba rich); (c) celestite (Ba rich) (Cel, Ba rich) and fluorite (Flu); (d) galena (Gal) with alteration rims in cerussite (Cer); (f) galena (Gal), quartz (Qtz) and cerussite (Cer); (g) oxidized galena (Gal) and cerussite (Cer); (h) galena (Gal), barite (Sr rich) (Bar, Sr rich) and pyrite (Pyr).

3.1.2. Geochemical characterisation The concentrations of major elements in tailings and dune materials are shown in Table 3. Results showed that the mining wastes have the same complex mineralogy as the ore and the gangue, and probably because changes in the ore composition, differences between the three dumps were evident. Thus, the chemical composition of recent and old tailings varied significantly. Tailings and dunes still had elevated contents of Ba, Sr and S, with concentrations ranging between 23.0 – 45.0, 9.4 – 19.3% and 5.7 – 21.6%, determined by stoichiometry as BaO, SrO and SO3 respectively. In addition, Ca (calculated as CaO) was present in the mine wastes in the range of 7.0% and 30.5%. The old tailings TII and TIII are enriched with F (4.8 – 5.2%) compared

SEM-EDS analysis of the tailing TI showed various metals/metalloids bearing minerals in the form of sulphate, carbonate, silicate, fluorite and sulfide species (Fig. 3). The Sr-rich barite and the Ba-rich celestite are the main mineral components, but fluorite was also found in noticeable quantities. Lead was present in carbonate and sulfide forms as cerussite and galena, respectively. Zinc was present as hemimorphite and was associated with cerussite, fluorite, barite and strontianite as a secondary element in this assemblages. Moreover, iron was present as pyrite in smaller proportion and was associated with hemimorphite and Sr-rich barite. Arsenic occurred in both galena and barite and copper was only determined in some barite grains. Due to their very low concentrations and the lack of sensitivity, Cd and Hg were not detected by SEM-EDS.

Table 3 Chemical composition (in wt%) of mining wastes and dune materials. wt%

LOI

SiO2

Al2O3

Fe2O3

K2 O

MgO

SO3

BaO

SrO

CaO

F

Zn

Na2O

Pb

TiO2

P2O5

Sum

TI

ZIGr1 ZIGr2 ZIIGr1 ZIIGr2 ZIIGr3

6.63 10.32 8.96 12.20 11.00

6.53 7.10 2.58 5.86 6.90

0.20 1.36 0.20 0.67 1.03

0.49 1.00 0.47 0.72 0.79

< 0.06 0.27 < 0.06 0.10 0.15

0.05 0.19 0.05 0.13 0.16

21.63 9.08 13.97 7.86 9.04

33.87 30.02 31.25 28.68 29.91

15.17 12.35 19.26 11.87 11.64

14.25 21.67 9.52 21.98 22.08

1.40 0.20 2.34 5.81 6.43

1.99 1.37 1.88 1.92 1.63

0.15 0.91 0.17 0.17 1.08

2.26 1.22 1.93 0.92 1.05

< 0.01 0.07 < 0.01 0.03 0.04

0.09 0.34 0.09 0.18 0.22

104.63 97.49 92.74 99.09 103.14

TII

TII 1 TII 2 TII 3

4.57 9.62 7.52

7.88 6.59 7.16

0.61 0.86 0.87

0.85 0.68 0.82

< 0.06 0.17 0.15

0.07 0.34 0.10

12.92 10.88 10.55

43.64 29.02 34.71

14.86 12.39 13.63

6.99 21.41 18.06

1.68 6.56 6.27

1.78 1.42 1.60

0.15 3.30 0.19

0.89 0.82 0.82

0.02 0.04 0.04

0.21 0.51 0.60

97.18 104.60 103.10

TIII

TIII 1 TIII 2 TIII 3 TIII 4 TIII 5 Min Max Median Average

12.47 11.99 12.59 12.02 13.66 4.57 13.66 11.00 10.27

8.27 4.40 5.50 6.03 10.02 2.58 10.02 6.59 6.52

1.44 0.77 1.08 1.00 1.56 0.20 1.56 0.87 0.90

0.96 0.65 0.76 0.99 1.32 0.47 1.32 0.79 0.81

0.23 0.12 0.17 0.16 0.29 < 0.06 0.29 0.15 0.15

0.19 0.14 0.17 0.18 0.58 0.05 0.58 0.16 0.18

7.86 5.66 6.65 8.68 7.26 5.66 21.63 9.04 10.16

25.33 22.99 24.44 31.47 23.44 22.99 43.64 29.91 29.91

12.11 9.37 10.14 11.29 10.51 9.37 19.26 12.11 12.66

20.63 30.52 25.50 20.98 21.60 6.99 30.52 21.41 19.63

4.08 5.50 4.10 5.88 6.58 0.20 6.58 5.50 4.37

2.31 1.40 2.02 1.99 1.72 1.37 2.31 1.78 1.77

0.23 0.18 0.42 0.55 1.71 0.15 3.30 0.23 0.71

1.13 1.36 1.25 1.11 1.30 0.82 2.26 1.13 1.24

0.06 0.04 0.04 0.04 0.08 < 0.01 0.08 0.04 0.04

0.27 0.23 0.25 0.32 0.68 0.09 0.68 0.25 0.31

97.58 95.31 95.08 102.68 102.30 – – 100.96 99.62

Dunes

DATA DATB DATC DATD Average

7.23 6.40 13.84 10.93 9.60

2.65 2.24 6.24 3.84 3.74

0.21 0.16 0.26 0.25 0.22

0.47 0.40 0.55 0.50 0.48

< 0.06 < 0.06 < 0.06 < 0.06 < 0.06

0.07 0.05 0.10 0.09 0.08

13.43 13.57 10.93 11.44 12.34

40.18 44.53 33.04 34.49 38.06

17.10 19.11 14.74 15.52 16.62

11.74 8.45 15.57 13.78 12.39

1.75 1.98 1.17 1.37 1.57

2.07 1.70 2.45 2.46 2.17

0.15 0.14 0.15 0.14 0.15

1.27 2.38 1.03 1.03 1.43

< 0.01 < 0.01 < 0.01 < 0.01 < 0.01

0.11 0.08 0.13 0.14 0.12

98.50 101.25 100.25 96.04 99.02

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Table 4 Trace elements concentrations (mg kg−1) in tailings and dune materials of Hammam Zriba. mg kg

-1

Li

Ga

Rb

Cs

La

Ce

V

Cr

Mn

Co

Ni

Cu

Ge

As

Mo

Cd

Sb

Hg

TI

ZIGr1 ZIGr2 ZIIGr1 ZIIGr2 ZIIGr3

5 7 4 10 10

0.3 4.1 0.3 1.5 2.1

0.3 7.2 0.3 2.5 3.9

0.3 1.2 0.3 0.3 0.3

0.3 3.6 0.3 1.9 2.3

0.3 3.4 0.3 1.9 2.5

2 15 1.8 6 8

18 211 44 91 108

16 43 17 43 49

< 0.1 2.3 < 0.1 1.6 1.9

2 10 3 5 6

37 56 33 33 35

5 7 4 4 5

15 32 16 17 20

< 0.1 0.4 < 0.1 < 0.1 < 0.1

29 34 29 33 30

16 32 10 9 18

0.8 2.0 1.1 0.6 0.6

TII

TII 1 TII 2 TII 3

11 8 7

1.8 3.0 3.6

1.6 4.5 4.2

0.3 0.3 0.3

1.0 2.2 1.9

1.2 2.1 1.8

3 9 8

112 250 196

46 49 22

1.3 1.7 1.2

5 6 5

33 42 51

5 5 7

16 19 25

< 0.1 0.2 < 0.1

42 35 47

14 10 19

0.6 1.0 1.5

TIII

TIII TIII TIII TIII TIII

11 5 10 7 13

3.1 2.5 2.7 2.4 3.8

6.2 3.4 4.3 4.0 7.2

0.3 0.3 0.3 0.3 1.1

3.1 2.3 2.3 2.5 3.8

3.4 2.5 2.2 2.3 4.4

13 8 10 10 15

293 86 179 209 246

52 43 48 43 70

2 1.5 1.7 2.0 2.3

8 6 6 7 7

50 33 40 36 106

7 5 6 5 7

21 15 22 24 69

< 0.1 < 0.1 < 0.1 < 0.1 < 0.1

43 38 38 32 41

16 13 13 15 38

0.7 0.6 0.8 1.1 4.0

TI-TIII

Min Max Median Average

4.3 13.0 8.0 8.2

0.3 4.1 2.5 2.4

0.3 7.2 4.0 3.8

0.3 1.2 0.3 0.5

0.3 3.8 2.3 2.1

0.3 4.4 2.2 2.2

1.8 15.0 8.0 8.4

18 293 179 157

16 70 43 42

1.2 2.3 1.7 1.8

2.0 10.0 6.0 5.8

33 106 37 45

3.9 7.3 5.1 5.6

15 69 20 24

0.2 0.4 0.3 0.3

29 47 35 36

9.0 38.0 15.0 17.2

0.6 4.0 0.8 1.2

Dunes

DATA DATB DATC DATD Average

5 3 12 12 8

< 0.1 < 0.1 1.0 1.0 1

< 0.1 < 0.1 < 0.1 < 0.1 -

< 0.1 < 0.1 < 0.1 < 0.1 -

< 0.1 < 0.1 < 0.1 < 0.1 -

< 0.1 < 0.1 < 0.1 < 0.1 -

2.1 1.3 3 2.4 2

16 9 15 15 14

23 15 32 30 25

< 0.1 < 0.1 1.0 < 0.1 1

3 2 3 3 3

29 28 29 29 29

4 3 3 4 3

17 14 16 18 16

< 0.1 < 0.1 < 0.1 < 0.1 -

29 27 37 35 32

8 9 10 9 9

0.9 1.1 0.9 0.7 1

1 2 3 4 5

and Hg), as well as S and F, mainly in the form of sulphate, fluoride and sulfide species, as the mineralogical analysis evidenced. Fig. 2b, c and d show how agricultural soils are polluted by the eolian transport of anthropogenic dust. These soils are frequently ploughed and as a consequence, the dust is transeferred to deeper layers of the soil.

to the recent dump TI (3.2%). Meanwhile, the dune materials contain lower F content (1.6%) than the tailings. These major and trace elements are continuously dispersed from the tailings mainly by wind. The materials from the dunes contain more Fe2O3, BaO, SrO, SO3, Zn and Pb, and less F and CaO, than the tailings. However, the concentrations of Al2O3, K2O, MgO, Na2O and TiO2 did not vary significantly in the three dumps and dunes. The concentrations of trace elements in tailings and dunes are shown in Table 3. Elevated levels of Zn and Pb were detected in the tailings and these reached mean of 1.8 and 1.2% respectively. Mean concentrations of Cd, Cu, Cr, As and Hg in the tailings reached 36, 45, 157, 24 and 1.2 mg kg−1, respectively. In comparison with the tailings, the materials from the dunes on the foot of the TI dump contain, less Mn, Co, Cu, As, Cd, Hg, and (as stated above) more Zn and Pb (with mean concentrations of 2.2% and 1.4%, respectively). These results are also reflected by the XRD analysis showing that the dune materials contain more galena than the tailings. This may be due to its enrichment by the preferential deposition of the resuspended dust.The surfaces of tailings dumps and dunes are the main sources of the metals/metalloids bearing dust in the surroundings of the mining area, especially under prevailing strong northwest and west winds. As shown in Tables 3, 4, the tailings and associated dune material from Hammam Zriba contain high contents of different metals/ metalloids (Ba, Sr, Fe, Pb, Zn, and in a minor degree Cr, Cu, Cd, As, Sb

3.2. Soil characterisation 3.2.1. Physical and mineralogical patterns Brown calcareous soils and lithosols (according to the FAO soil classification) are the most widespread soils in the study area. The soils are calcareous with calcite contents ranging from 2.6 (HZBt) to 46.4% (HZBII). The results of grain size distribution showed that the < 63 µm fraction in soils is between 5.7% and 34.4%. In addition, the Hammam Zriba soils show a unimodal grain size distribution with a prevailing coarser mode around 10 – 40 µm, a median ranging from 34 to 49 µm, a < 2.5 µm fraction in the range of 2.7 – 6.8%, with the highest values attained in HZBII sample (Table 5). Furthermore, the < 10 µm fraction ranged from 6.6% to 16.5%. The XRD analysis showed that the reference soil HZBt contains quartz as the major mineral component (73%), with much less calcite (4%), kaolinite (Al2Si2O5(OH)4, 6%), illite-muscovite (KAl2(AlSi3O10) (F,OH)2, 8%), microcline (KAlSi3O8, 4%), albite (NaAlSi3O8, 4%), anatase (TiO2, 1%) and traces of hematite (Fe2O3). The mineralogical

Table 5 Grain size of soils samples: Mass percentage below 2.5, 5 and 10 µm and size (in µm) for the percentiles 10, 50 and 90. Ref. soil

Transect T1

Transect T2

HZBt

HZBa

HZBb

HZBc

HZBd

< 2.5 µm < 5 µm < 10 µm

4.3 7.1 11.7

4 6.5 9.9

3.3 4.9 7.8

6.1 10 15

P10 P50 P90

9.5 42.1 88

11.4 46.9 87.9

15.8 48.2 88.1

6.4 38.5 76.9

Transect T3

HZBe

HZBf

HZBg

HZBj

HZBh

HZBo

HZBi

HZBn

4.9 8 12.6

3.3 5.3 8.9

3.7 6.2 10.6

3.1 4.8 8

3.6 5.6 9.2

3.3 5.3 8.3

4.6 7.6 12.2

3.8 6.2 10.1

4.9 8.4 13.6

8.4 43.8 85

12.9 45.3 87.8

10.6 43.8 90.4

14.4 46.9 89.2

12.5 46.1 91.1

14.3 44.9 83.1

8.9 40.7 80.5

11.1 43.9 84.8

7.8 40.8 83.7

159

HZBI

HZBII

HZBIII

HZBIV

HZBV

HZBVI

2.9 4.2 6.5

6.8 10.8 16.2

5.1 8.6 14.3

5.9 10.6 16.5

5.5 9.4 15.4

2.7 4 6.6

18.1 47.6 87.2

5.6 37.6 78.8

7.6 34.5 71.1

5.9 39.4 79.2

6.9 40.2 82.1

18.4 48.9 88.4

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Table 6 Chemical composition (in wt%) of soil samples and recommended maximum soil concentrations from the Canadian Environmental Quality Guidelines CEQG (CCME, 2011). wt%

LOI

SiO2

Al2O3

Fe2O3

K2O

MgO

SO3

BaO

SrO

CaO

F

Zn

Na2O

Pb

TiO2

P2O5

Sum

Transect T1

HZBa HZBb HZBc HZBd HZBe HZBf HZBg

20.4 17.9 23.9 19.7 12.6 13.1 13.6

20.3 37.4 23.4 30.6 51.5 49.0 49.8

4.68 8.95 5.63 7.02 11.60 12.80 8.97

1.54 3.66 2.83 2.94 5.61 7.82 5.14

0.87 1.32 1.04 1.38 2.05 1.92 1.24

1.14 1.86 1.24 1.53 2.01 2.35 1.49

7.23 1.84 0.83 1.20 1.06 0.27 0.28

5.44 1.71 0.85 1.15 0.90 0.26 0.22

4.14 1.27 0.56 0.77 0.63 0.18 0.13

32.00 21.90 38.30 32.00 10.30 9.97 18.20

1.04 0.27 0.11 0.07 0.15 0.10 0.05

0.81 0.20 0.07 0.10 0.08 0.03 0.02

0.53 0.23 0.14 0.22 0.02 0.24 0.07

0.158 0.073 0.027 0.039 0.030 0.008 0.006

0.20 0.34 0.23 0.30 0.71 1.03 0.59

0.27 0.19 0.04 0.10 0.15 0.12 0.02

100.7 99.1 99.2 99.1 99.4 99.2 99.8

Transect T2

HZBj HZBh HZBo HZBi HZBn

12.8 16.7 18.2 7.6 15.4

49.8 40.2 38.2 63.3 37.6

8.97 9.94 9.48 9.91 7.22

5.14 3.89 5.04 4.51 3.46

1.24 1.50 1.89 1.81 1.30

1.49 2.13 1.88 1.64 1.41

0.28 2.37 0.58 0.55 0.21

0.22 2.10 0.54 0.32 0.09

0.13 1.70 0.35 0.18 0.06

18.20 17.10 21.60 9.18 31.30

0.34 0.21 0.08 0.05 0.03

0.29 0.17 0.01 0.02 0.04

0.07 0.18 0.27 0.02 0.18

0.096 0.065 0.002 0.008 0.017

0.59 0.42 0.63 0.60 0.46

0.02 0.18 0.08 0.09 0.02

99.7 98.9 98.8 99.8 98.8

Transect T3

HZBI HZBII HZBIII HZBIV HZBV HZBVI

8.1 26.4 24.2 25.8 21.7 14.9

62.6 27.6 33.3 27.4 31.8 45.5

7.56 7.45 8.63 6.91 7.62 10.70

2.91 4.22 4.02 3.67 4.72 6.22

1.06 1.35 1.91 1.20 1.11 1.67

1.19 1.71 1.85 1.52 1.53 2.19

1.52 0.24 0.42 0.22 0.12 0.27

1.01 0.30 0.28 0.24 0.12 0.19

0.62 0.19 0.18 0.13 0.10 0.16

11.50 28.80 23.20 31.20 30.10 15.90

0.13 0.30 0.11 0.08 0.07 0.07

0.06 0.03 0.03 0.02 0.01 0.02

0.02 0.16 0.27 0.17 0.08 0.24

0.027 0.010 0.013 0.007 0.004 0.006

0.25 0.48 0.51 0.43 0.56 0.79

0.16 0.08 0.24 0.04 0.02 0.06

98.7 99.3 99.2 99.0 99.7 98.9

T1 to T3

Min Max Median Average

7.6 26.4 17.3 17.3

20.3 63.3 37.9 39.9

4.68 12.80 8.79 8.56

1.54 7.82 4.12 4.30

0.87 2.05 1.34 1.44

1.14 2.35 1.59 1.68

0.12 7.23 0.49 1.08

0.09 5.44 0.31 0.89

0.06 4.14 0.19 0.64

9.18 38.30 21.75 22.26

0.03 1.04 0.11 0.18

0.01 0.81 0.04 0.11

0.02 0.53 0.18 0.17

0.002 0.158 0.015 0.033

0.20 1.03 0.50 0.51

0.02 0.27 0.09 0.10

– – 94.7 99.3

HZBt

9.30

58.70

13.60

7.65

2.13

2.14

0.13

0.08 0.02

0.02

4.70

0.02 0.04

0.02 0.01

0.18

0.007 0.002

1.24

0.07

99.9

CEQG Ref. soil

*Ref.soil: reference soil.

from the first transect T1 to the tailings. Sr-rich barite was detected in the nearest samples of the three transects (18%, 6% and 1%) and decrease as function of the distance from the dumps. The same areal distribution was observed for the fluorite (6%, 2% and 1%). Strontianite and galena were not detected in the soils.

composition of surrounding soils of Hammam Zriba mine dumps varies from that described for the reference soil and change with the distance from the tailings dumps. Indeed, calcite and quartz are the main minerals in these soils (with 4–54% and 22–82% respectively). Kaolinite (2 – 8%), microcline (0–6%), albite (0–6%), illite-muscovite (1 – 3%), and anatase (0 – 1%) were detected in most samples; and hemimorphite (1%), gypsum (4%) and hematite (1%) in some samples. Additionally, Ba-rich celestite was also detected (2%) in HZBa, the nearest sample

3.2.2. Soil geochemistry The results of chemical analysis of soils are summarised in Tables 6, 7.

Table 7 Trace elements concentrations (mg kg−1) in soils of Hammam Zriba and recommended maximum soil concentrations from the Canadian Environmental Quality Guidelines CEQG (CCME, 2011). mg kg−1

Li

Ga

Rb

Cs

La

Ce

Th

U

V

Cr

Mn

Co

Ni

Cu

Ge

As

Mo

Cd

Sb

Sn

Hg

Transect T1

HZBa HZBb HZBc HZBd HZBe HZBf HZBg

12 22 13 14 23 36 18

3 8 5 6 11 15 7

10 28 18 23 46 46 26

0.8 2.1 1.2 1.5 2.8 3.0 1.6

7 20 14 16 27 33 16

14 41 27 31 56 69 34

2 5 4 4 8 9 4

< 0.1 1.2 0.1 0.9 1.4 1.9 1.0

22 59 38 43 68 98 46

43 55 29 37 57 78 35

94 196 125 164 371 281 146

3 6 5 6 10 11 5

9 16 13 14 21 23 13

23 22 12 16 22 16 9

3.6 1.8 1.0 1.2 1.5 1.5 1.1

15 11 7 8 12 8 5

< 0.1 0.8 0.1 0.3 0.3 < 0.1 < 0.1

18 5 1.9 2.4 2.0 0.2 0.2

8 2.4 1.1 1.5 1.6 0.8 0.2

0.2 0.9 0.2 0.6 1.6 1.7 0.6

0.34 0.08 0.04 0.07 0.06 0.02 0.01

Transect T2

HZBj HZBh HZBo HZBi HZBn

23 21 20 16 13

9 9 9 7 5

34 36 37 27 19

2.4 2.4 2.4 1.6 1.2

23 22 22 17 12

45 45 46 35 26

6 6 6 4 3

1.4 1.2 1.2 1.0 < 0.1

63 60 35 44 61

64 54 26 35 48

256 288 125 183 285

7 8 5 5 9

18 20 11 12 20

24 24 6 11 16

2.2 1.8 1.2 1.2 0.8

11 10 4 5 9

< 0.1 < 0.1 < 0.1 < 0.1 < 0.1

6.9 4.2 0.2 0.2 1.3

3.3 2.3 1.0 0.8 0.2

1.0 1.0 1.0 0.5 0.4

0.21 0.13 0.02 0.02 0.06

Transect T3

HZBI HZBII HZBIII HZBIV HZBV HZBVI

12 26 22 21 22 29

5 10 10 8 8 11

18 34 42 28 33 41

1.1 2.4 2.5 2.0 4.8 3.0

14 24 26 22 22 27

29 48 52 44 45 57

4 6 7 5 6 7

0.8 1.4 1.5 1.2 1.2 1.5

34 78 69 63 56 74

27 61 55 45 45 60

190 202 353 230 165 284

4 8 10 7 6 9

9 20 23 17 15 21

10 14 23 11 10 14

1.2 1.1 1.2 1.0 1.0 1.4

5 8 11 8 6 7

< 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1

1.5 1.1 1.1 0.2 0.2 0.2

0.9 1.0 1.5 0.2 0.2 0.2

0.5 1.0 1.4 0.9 0.7 1.2

0.04 0.03 0.04 0.02 0.02 0.02

T1 to T3

Min Max Median Average

12 36 21 20

3 15 8 8

10 46 31 30

0.8 4.8 2.2 2.2

7 33 22 20

14 69 44 41

2 9 6 5

< 0.1 1.9 1.2 1.1

22 98 59 56

26 78 46 47

94 371 199 219

3 11 7 7

9 23 16 16

6 24 15 16

0.8 3.6 1.2 1.4

4 15 8 8

< 0.1 0.8 < 0.1 0.2

0.2 18 1.2 2.6

0.2 8.2 1.0 1.5

0.2 1.7 0.9 0.9

0.01 0.34 0.04 0.07

HZBt

31

14

48

2.8

34

71

10

23 1.8

130 93

64 74

272

40 10

50 22

63 14

1.5

12 7

3.3

1.4 0.2

0.2

5 1.6

0.02

CEQG Ref. soil

160

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concentrations: Sr, S, Zn, Sb, Cd, F, Pb, Ge and Hg (r = 1.0-0.8); and P, Na, As and Cu, Cl (r = 0.7-0.5). Elements supplied to the soils by their natural aluminum-silicate fractions (mostly clay, feldspars, and quartz) and other soil components (nitrate): These include elements highly correlated with Al contents: Fe, Ti, Hf, Mg, REE, Zr, Rb, Ga, K, Th, Sc, Y, Nb, U, Sn, V, Li, Ta, W, Ni, Mn, Si and Cr (r = 0.9-0.7); and Cs, NO2-, NO3- (r = 0.5-0.4). Ca-carbonate fraction: Ca is anticorrelated with the Al group, (r = −0.5 to −0.9), and poorly correlated with the Ba-group of elements (r = 0.1-0.2). The content of Ca in soils probably reflects the natural soil variations of CaCO3 contents, with a light influence of tailings dust.

As described above, all samples, except HZBt (reference soil), were collected according to three transects, T1, T2 and T3, in the direction of prevailing northwest wind (Fig. 1). Not surprisingly, the concentrations of BaO, SrO, SO3 and F were very high in the closest samples to the tailings dumps (5.4%, 4.1%, 7.2% and 1.0%, respectively). From the HZBa sampling point, concentrations decrease with distance from the dumps, although evidence (high major and trace elements contents) of northwest wind transport of pollutants were found further away (0.2%, 0.1%, 0.3% and 0.05%, respectively, in the farthest sample HZBg). Also the highest concentrations of Zn, Pb and Cd were registered in the samples taken in the proximity of the tailings (Table 7), with 0.8%, 0.2% and 18 mg kg−1, respectively in the HZBa sample. The same spatial distribution was observed for As and Hg. Comparing tailings and soil composition, the concentrations of Fe2O3 in topsoils were higher (and lower than in the reference soil), indicating a higher content of Fe-bearing minerals in soils, and were spatially distributed differently from the previous mining pollutants. Thus, non-affected soils in the surveyed area are naturally or anthropogenically iron enriched, but from sources other than the mining wastes dumps (mostly present in hematite and illite-muskovite), as also deduced for CaO, P2O5, Na2O, SiO2, MgO, TiO2, K2O, Li, Ga, Rb, Cs, La, Ce, Th, U, V, Cr, Mn, Co, Ni, and Sn. The concentration of these elements were relatively homogeneously distributed across the study area, without a major enrichment in the most contaminated soils in Ba, Sr, Zn, Pb, S and F. Thus, the origin of these pollutants in the soils was different to the mining activity. Cross-correlation analysis of the geochemical data might yield relevant information about the origin or mode of occurrence of the elements and minerals. Much attention has been paid to factors that control the bonds of metals and metalloids in soils contaminated by dust fallout (Li and Thornton, 2001; Luo et al., 2006; Ettler et al., 2011; Kříbek et al., 2014). Factor analysis (FA) statistics might also yield relevant information on these issues, although interpretations would also require subjective evaluations to identify metal and metalloid origins (Glavin and Hooda, 2005; Lima, 2008; Kříbek et al., 2010). The number of samples used for this study was insufficient to provide an appropriate data matrix for such analysis. The cross-correlation analysis allowed grouping elements into the following 3 major geochemical assemblages as a function of Pearson correlation coefficients (r) (Fig. 4):

Transect T1 had higher levels of pollutants, an affect of the prevailing wind direction (Tables 6, 7); Whereas, transect T3 was protected by a green wind barrier (Cupressus sempervirens) planted as shelterbelts. Shelterbelts can lower the wind speed across the field, thus reducing the resuspension and transport risks, and consequently the dust deposition. The bulk concentrations of pollutants in the soils were compared with the Canadian Environmental Quality Guidelines CEQG (CCME, 2011) (Tables 6, 7, bottom). The concentrations of V, Co, Ni and Cu in our soil samples do not exceed their corresponding CEQG guideline values for soils. However, the concentrations of Ba and F in all samples greatly exceeded the recommended concentrations levels for soils by 5 fold (10 fold when the average values of our samples are compared to guidelines, and near all samples exceeded the guidelines, Table 6). On the other hand, average soil concentrations of Pb and Zn exceed by 5 fold the thresholds recommended for soils (Table 6). These are exceeded in 68% of the samples; particularly those closer to the dumps. Average concentrations of Cd in our soils also exceed by 1.8 fold the CEQG threshold; and those of As and Cr were exceeded in a significant proportion of our soil samples, including the control soil in the case of Cr (Table 7). The extent of pollution caused by the mining and beneficiation activities might also be evaluated by calculating EF and CPI values, in the reference to soil samples. The calculated EFs yield to the following classification of elements (Table 1):

• Elements supplied to the soils by contamination from the mining

• Ba and Sr: extremely high enrichment and significant to extremely

•

•

high enrichment, with EFs ranging from 44 – 3162 and 9 – 567. The

dust: These include all elements with a high correlation to Ba

Sr S 1.0

Zn F Sb

0.8

Pb Cd Hg

Ge

Mining wastes-related elements AsP

Na

0.6

Cu

r with Ba

Cl 0.4 Ca 0.2

0.0 -1.0 -0.2

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4 NO3-

Soil ferlizers

NO2-

-0.4

Soil elements -0.6

0.6

0.8

Cr Sn Mg Mn Co Ni Li U K Zr Th Si Ti Ga V Fe La Rb Sc Ti

-0.8

r with Al 161

1.0

Fig. 4. Scatter plot of the Pearson’s correlation coefficients (r) obtained for the elemental and anion concentrations with Ba and Al contents in soils of the study area.

ZIGr1

8.0 2.5 285 1 3 2 664 13 4 53 0.42 < 0.01 < 0.01 0.05 0.6 < 0.01 < 0.01 259 < 0.01 < 0.01 0.08 0.3

mg Kg−1

pH Ba Ca K Mg Na SO42ClNO3FCr Mn Ni Cu Zn As Se Sr Mo Cd Sb Pb

TI

7.3 0.2 993 33 53 498 2832 542 175 42 0.09 0.04 < 0.01 0.08 1.3 < 0.01 < 0.01 234 < 0.01 0.04 0.03 0.8

ZIGr2

8.0 3.6 151 2 3 6 456 23 8 27 0.25 < 0.01 < 0.01 0.06 0.4 < 0.01 < 0.01 298 < 0.01 < 0.01 0.11 0.1

ZIIGr1

8.0 1.0 385 47 11 24 922 58 5 63 0.29 0.03 < 0.01 0.26 0.8 0.02 < 0.01 410 0.02 < 0.01 0.14 0.2

ZIIGr2 7.5 0.1 1482 39 61 683 4017 840 339 54 0.02 0.03 0.02 0.30 1.5 < 0.01 < 0.01 203 < 0.01 0.05 0.03 0.9

ZIIGr3 7.7 0.9 614 25 6 14 1459 38 11 42 0.08 0.09 0.03 0.41 7.8 0.02 < 0.01 252 < 0.01 0.36 0.03 1.0

TII 1

TII

7.4 0.1 4558 82 907 2362 17,026 1671 752 298 0.02 0.04 0.05 0.05 2.4 < 0.01 < 0.01 140 0.02 0.19 0.03 1.1

TII 2 7.6 0.5 333 2 7 10 869 25 24 76 0.30 < 0.01 < 0.01 0.04 2.3 < 0.01 < 0.01 422 < 0.01 0.11 0.02 0.2

TII 3 7.5 0.6 558 32 14 18 1293 33 146 51 0.36 0.04 0.02 0.14 0.9 < 0.01 < 0.01 293 < 0.01 0.06 0.02 1.0

TIII 1

TIII

8.1 9.8 284 35 11 22 622 45 2 53 0.06 0.06 < 0.01 1.02 3.1 0.04 < 0.01 271 < 0.01 0.03 0.03 2.1

TIII 2 8.0 0.4 424 2 62 180 1480 74 3 83 0.05 < 0.01 < 0.01 0.02 0.6 < 0.01 < 0.01 299 0.03 < 0.01 0.03 0.6

TIII 3 7.7 0.1 1662 64 116 278 4626 346 87 224 0.06 0.02 0.02 0.03 1.2 < 0.01 < 0.01 212 < 0.01 0.03 < 0.01 0.8

TIII 4 7.6 0.1 1862 88 397 1169 6796 1000 750 192 0.11 < 0.01 0.02 0.04 0.9 0.02 0.02 166 0.02 0.04 0.03 0.9

TIII 5 8.2 2.6 281 1 2 3 622 13 1 49 0.21 0.02 < 0.01 0.05 0.6 < 0.01 < 0.01 226 < 0.01 < 0.01 0.07 0.4

DATA

Dunes

8.5 4.0 197 1 1 4 455 14 4 44 0.19 < 0.01 < 0.01 0.04 0.3 < 0.01 < 0.01 244 < 0.01 < 0.01 0.07 0.1

DATB

8.2 3.9 206 10 3 5 475 19 4 50 0.18 < 0.01 < 0.01 0.04 0.4 < 0.01 < 0.01 257 < 0.01 < 0.01 0.07 0.1

DATC

8.1 4.0 204 1 3 6 450 14 1 51 0.18 < 0.01 0.02 0.06 1.3 < 0.01 < 0.01 263 < 0.01 0.02 0.07 0.5

DATD

pH Ba Ca K Mg Na SO42ClNO3FCr Mn Ni Cu Zn As Se Sr Mo Cd Sb Pb

mg/kg

6 100

20,000 15,000 150 10 10 50 50 2 0.5 10 1.00 0.70 10

1000 800 10 0.5 0.4 2 4 0.5 0.1 0.3 0.04 0.06 0.5

N-H 6 20

Inert

2003/33/EC thresholds

162

30 5.00 5.00 50

40 100 200 25 7

500 70

50,000 25,000

6 300

H

Table 8 Leachable concentrations of major, trace elements and anions (mg kg−1) in tailings and dune materials from Hammam Zriba and reference values for disposal of wastes in landfills (2003/33/CE). Bold and underlined numbers indicate samples that exceed the non-hazardous (N-H) and hazardous (H) thresholds.

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• • • • • •

large number of samples, with maximum values of 422, 10, 8, 2, and 0.4 mg kg−1. In absolute leachable concentration levels, those measured for SO42-, Cl-, NO3- and F- attained high values (450 – 17026, 13 – 1671, 2 – 752 and 27 – 298 mg kg−1, respectively), while NO2- was below the detection limit in all samples. The highest leachable concentrations for these two groups of leachable elements were found in the Tailing TII, particularly the TII2 sample. The high leachable SO42concentration may be explained by the presence of soluble sulphates in mining wastes such as gypsum. Whereas, those of Cl- and NO3- may be related to the procedures and products used for the beneficiation of minerals. Despite the high bulk Ba and Sr concentrations, leachable contents were low, probably due to low solubility of barite and celestite. The percentages of leachable fractions of most metals were relatively low, as were the range of variation among samples: Zn (0.06%), Pb (0.08%), Mn (0.2%), As (0.3%), Cd (0.9%); Ni (1.0%); Cr (2.3%); Cu (3.1%). Therefore, if we compare them with the high bulk concentrations determined for a number of elements and species, most elements showed relatively low leachable fraction in the Hammam Zriba samples. With the exception of Cr, leachable levels were surprisingly higher in the dune materials than in the mining wastes. With F- leachable concentrations exceeding the 2003/33/EC Decision threshold for non-hazardous/hazardous wastes (298, 224 and 192 mg kg−1, and values from 150 to 500 mg kg−1 indicating hazardous materials), three tailings samples (TII2, TIII4 and TIII5) could be considered hazardous (Table 8). All the other samples can be considered as non-hazardous, but not inert wastes, given that these exceed (by 3–8 fold) the 10 mg kg−1 F- threshold, the maximum leachable concentration for a waste to be considered inert. Furthermore in TI, TII and TIII, 61% of the waste samples also exceed the threshold for inert wastes by 1.3 – 17 fold, and 3 samples exceed the same threshold for Cl-. For metals, a large proportion of tailings samples cannot be considered as inert wastes because these exceed the Pb threshold, some samples also exceed the respective Cd and Sb thresholds for inert wastes, and one of them for Zn, Cd and Pb. All dune material samples exceed the inert thresholds for Sb. The most problematic samples were found in the TII and TIII dumps. Thus, according the F- leachable content the TII2, TIII4 and TIII5 samples can be considered as hazardous wastes, and these also exceed the inert waste thresholds for Cl-, SO42-, Pb (plus Cd in TII2). All samples of TII, and 1 of TI and one from TIII exceed the inert threshold for Cd.

highest values of each transect are those samples closest to the dumps. Pb, F, SO3: moderate to extremely high enrichment, with EFs ranging from 4 – 259, 2 – 74 and 2 – 168, respectively. Cd, Zn, Sb and Hg: minimal to extremely high enrichment, with values ranging from 1 – 255, 1 – 223, 1 – 119 and 1 – 49, respectively and identical spatial distribution to the above elements. Ca, P and Na: moderate to very high enrichment and minimal enrichment to significant enrichment, with EFs ranging from 2 – 20, 0.1 – 11, and 0.4 – 9, but without relation to the distance from the source point. Ge, As and Cu: minimal to significant enrichment, with EFs ranging from 1 – 7, 1 – 6 and 1 – 5. Si, Mg, Fe, Ti, K, Li, Ga, Rb, Cs, La, Ce, Th, U, V, Cr, Mn, Co, Ni and Sn: deficiency to minimal enrichment in our soil samples, with EFs lower than 2, and in most cases close to 1. Mo was clearly depleted in our samples, with EFs lower than 0.1, in most cases.

For transects T1, T2 and T3, the soil samples yielded CPI values ranging from 7 – 376, 7 – 24 and 6 – 39, respectively, for Ba > Sr > Pb > Cd > Zn > SO3 > Sb > F > Hg > Ge > As > Cu (in order of enrichment), pointing to high to ultra high contamination (Table 1) due to the pollution derived from the mining activities and beneficiation wastes (the EFs and CPI decrease as we increase the distance from tailings dumps). Cr levels were higher than the CEQG value, but the enrichment was probably not due to the mining activities. As previously stated, after a strong wind episodes, the soils were covered with dust fallout from mine tailings (Fig. 2) and we sampled only topsoils, the continuous tillage of soils by farmers might yield contamination to deeper soil layers. Pollutants are partitioned into the soils as a consequence of their high surface area to volume ratio and their heightened capacity to absorb contaminants (Dennis et al., 2003). Therefore, soils can be a second source of releasing contaminants after water or/and wind transport. 3.3. Leaching patterns of mining wastes and soils The leachability of a given inorganic pollutant from solid samples is affected by several factors, including solubility of the involved species, clay mineral content, salinity of solutions, pH, and Eh (De Matos et al., 2001). Toxic elements can be leached from mine wastes and transported to soils and groundwater, or also leached from soils. Tables 8, 9 show the leachable concentrations of elements and species in the our mining wastes and soil samples and the comparison with the respective regulatory leaching limit values established by 2003/33/EC Decision for classification of wastes for landfill disposal (CEC, 2003). The content of a given element in strongly bound compounds was determined as the difference between the total amount of metals in soils and their weakly bound compound forms (Motuzova et al., 2014). In our samples, the distribution between the leachable and the nonleachable fractions showed that the latter is the predominant fraction with values between 100% and 99.31% of the bulk concentration in the studied samples. Thus, the occurrence of low soluble pollutant-bearing species in the waste samples and soils might account for a diminished leaching yields obtained for a number of potentially toxic elements in mining wastes and soils from the Hammam Zriba area.

3.3.2. Soils The pH of soils is alkaline and ranges between 7.8 and 8.1. Soil pH is in agreement with the mineralogical analysis that indicate the presence of carbonates (Table 9). Leachable levels in soils for P, Be, Sc, Ga, Ge, Se, Y, Zr, Nb, Mo, Cd, Sn. Cs, REEs, Ta, W, Tl, Th and U were mainly below the detection limits. Conversely, the highest leachable concentrations were obtained for Ca, SO42-, K, NO3-, Cl-, Na, Si, Mg, NO2-, Sr, F- and Ba (460, 272, 165, 137, 90, 71, 83, 36, 35, 45, 7 and 6 mg kg−1, respectively) (Table 9). From the environmental point of view, the relatively high SO42- and Ba (much lower in the reference soil) leachable concentrations measured in most soil samples, as well as the relatively high leachable contents of Pb and Sb (even exceeding the inert threshold for landfill disposal of wastes) in some samples of the transect T1 (Table 9) are notable. The high pH values of natural soils favour metal precipitation, and decreased their mobility in most cases; and this is relatively frequent in semi-arid areas of the circum-Mediterranean regions (Yaalon, 1997; Martínez-Martínez et al., 2013).

3.3.1. Mining waste samples and dune materials Table 8 showed that the pH of leachates from tailings and dune material is slightly alkaline (7.3 – 8.5). Leachable concentrations of Al, Fe, P, Li, Be, B, Sc, Ti, V, Co, Ni, Ga, Ge, As, Se, Rb, Y, Zr, Nb, Mo, Sn, Cs, REEs, Hf, W, Tl, Ta, Th, U, are below the detection limits for all samples. Leachable concentrations for Sr, Ba, Zn, Pb and Cd were evident in a

4. Conclusions This study has shown that the tailings wastes and the associated dune materials of Hammam Zriba contain much environmentally 163

pH Al Ca Fe K Mg Na P Si SO42ClNO3FNO2Cr Mn Co Ni Cu Zn As Sr Mo Cd Sb Ba Pb

mg kg

−1

8.0 0.2 331 0.1 56 32 71 0.2 60 70 90 58 7 33 < 0.01 < 0.01 < 0.01 0.02 0.02 < 0.01 < 0.01 2 0.04 < 0.01 < 0.01 0.3 < 0.01

HZBt

Reference

7.8 5.4 258 3.2 36 13 17 0.2 23 202 18 24 7 3 0.04 < 0.01 < 0.01 < 0.01 0.06 1.25 < 0.01 45 < 0.01 < 0.01 0.04 6 0.67

HZBa

T1

8.0 0.2 417 0.5 60 35 56 2.3 50 135 76 2 4 3 0.02 < 0.01 0.04 0.05 0.06 0.41 0.02 32 < 0.01 < 0.01 0.02 2 0.09

HZBb 8.0 0.2 287 0.4 24 15 39 0.2 28 156 64 16 3 3 0.05 < 0.01 < 0.01 < 0.01 0.02 0.13 < 0.01 24 < 0.01 < 0.01 < 0.01 4 0.03

HZBc 7.9 1.5 270 0.7 33 16 55 0.2 38 153 73 2 3 3 0.03 < 0.01 0.05 0.06 0.05 0.25 < 0.01 22 < 0.01 < 0.01 < 0.01 3 0.03

HZBd 8.1 0.2 325 0.3 34 22 34 0.2 52 131 25 2 3 3 0.03 < 0.01 0.04 0.06 0.05 0.14 < 0.01 18 < 0.01 < 0.01 < 0.01 2 < 0.01

HZBe 7.9 1.0 326 0.3 90 34 42 1.0 50 105 55 137 3 15 < 0.01 < 0.01 < 0.01 0.02 0.03 < 0.01 < 0.01 11 < 0.01 < 0.01 < 0.01 2 < 0.01

HZBf 7.9 1.3 246 0.7 26 11 27 1.0 38 93 24 2 4 3 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 9 < 0.01 < 0.01 < 0.01 2 < 0.01

HZBg 8.0 0.2 275 0.3 62 22 26 0.2 46 272 6 55 6 3 0.04 < 0.01 < 0.01 < 0.01 0.06 0.25 < 0.01 28 < 0.01 < 0.01 0.02 3 0.05

HZBj

T2

8.0 0.2 353 0.5 37 21 29 0.2 47 110 42 2 3 13 0.02 < 0.01 < 0.01 0.02 0.04 0.27 < 0.01 25 < 0.01 < 0.01 < 0.01 3 0.04

HZBh 8.0 0.2 460 0.3 42 28 38 0.2 62 66 44 42 1 22 0.02 < 0.01 0.02 0.02 0.04 0.08 < 0.01 21 < 0.01 < 0.01 < 0.01 3 < 0.01

HZBo 8.1 1.4 398 0.8 129 23 34 0.2 83 57 15 12 2 14 < 0.01 < 0.01 0.16 0.08 0.04 0.04 < 0.01 14 < 0.01 < 0.01 < 0.01 3 < 0.01

HZBi 8.1 1.4 272 0.6 18 12 32 0.2 35 89 32 28 1 3 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 8 < 0.01 < 0.01 < 0.01 2 < 0.01

HZBn

Table 9 Leachable concentrations of major, trace elements and anions (mg kg−1) in soils from Hammam Zriba. Underlined and bold numbers indicate high leachable fractions.

8.0 2.2 289 1.1 28 15 29 0.2 36 12 8 10 1 3 0.02 0.02 < 0.01 < 0.01 < 0.01 0.13 < 0.01 18 < 0.01 < 0.01 < 0.01 3 0.04

HZBI

T3

7.9 1.0 353 0.4 26 21 27 1.0 48 82 21 18 2 15 0.02 < 0.01 < 0.01 < 0.01 0.02 < 0.01 < 0.01 17 < 0.01 < 0.01 < 0.01 3 < 0.01

HZBII

8.1 0.2 428 0.4 165 36 40 6.4 74 33 41 49 1 35 < 0.01 < 0.01 0.02 0.05 0.07 0.11 0.03 9 < 0.01 < 0.01 < 0.01 1 < 0.01

HZBIII

8.1 1.5 257 1.5 19 10 15 0.2 47 59 9 19 2 10 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 < 0.01 8 < 0.01 < 0.01 < 0.01 2 < 0.01

HZBIV

8.0 1.8 266 1.3 33 17 21 0.2 42 96 18 15 3 3 < 0.01 < 0.01 0.07 0.03 < 0.01 < 0.01 < 0.01 11 < 0.01 < 0.01 < 0.01 3 < 0.01

HZBV

8.0 1.0 342 0.3 42 19 27 1.0 65 6 6 6 1 1 < 0.01 < 0.01 < 0.01 < 0.01 0.03 < 0.01 < 0.01 12 < 0.01 < 0.01 < 0.01 2 < 0.01

HZBVI

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References

hazardous major and trace elements/species (Ba, SO3, F, Zn and Pb) and Sr, mainly in the form of sulphates, fluorides, carbonates, silicates and sulphides. We also evidenced that the dry surfaces of tailings dumps and dunes are the main sources of these particulate pollutants in the surroundings of the mining area affected by the prevailing northwest and west winds. The pollutants are continuously emitted and deposited at various distances, with the consequent soil pollution. Analyses revealed very high levels of pollutant elements correlated with Ba concentrations, supplied to the soils by contamination from the mining dust, which exceed the established geochemical background and the maximum admissible concentrations by the Canadian Environmental Quality Guideline. In contrast, calculations of soil enrichment factors (EFs) reveal an enrichment to extremely high enrichment for Ba, Sr, SO3, F, Pb, Zn, Cd and Hg. Other analysed elements were found without enrichment. Moreover, the Combined Pollution Index (CPIs) values reveal moderate to ultra high contamination in the mine area. The above soil indexes revealed that the emission of these pollutants affects soil chemistry up to 2 km downstream from the mining wastes. However, elements correlated with Al contents are relatively homogenously distributed across the study area and they are below the environmental threshold levels, with the exception of Fe and Cr, indicating a geogenic origin or another anthropogenic source apart from the mining wastes. Consequently, it is plausible that the eolian transport by wind borne dust is the main cause of the soil contamination in Hammam Zriba. We also concluded that, in spite of the high bulk concentrations of a number of elements in the mining wastes, most of them (excluding anions) have a relatively low leaching potential. Eventhough, a number of tailings wastes samples (the TII2, TIII4 and TIII5) qualify as hazardous material according the F- guidelines of the 2003/33/EC Decision for Land Filling. Other samples qualify as non-hazardous, but not inert materials, according the same guidelines. Furthermore, SO42-, Ba, Pb and Sb leachable contents measured in most soil samples are relatively high and exceed the inert threshold for landfill disposal of wastes. Thus, the polluted soil samples qualify as non-hazardous but not inert materials. We evidenced in addition that the leaching of contaminants might have already partially occurred before our sampling due to the age of the waste dumps and the weathering processes. In any case, the occurrence of low leachable pollutant-bearing species in wastes and soils favours the decrease of the environmental mobility of a number of potentially toxic elements. This low leaching pattern is then attributed to both i) the high pH values reached as a result of abundance of carbonates in soils, and ii) the relatively low solubility of major ore minerals. Accordingly, the comparison with regulatory limits indicates a low risk mobility for a number of harmful elements. Our results emphasize the effect of the eolian dispersal of polluting dust and its deposition on surrounding soils of Hammam Zriba mining area.

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Funding sources This research did not receive any specific grant from funding agencies in the public, commercial, or non-profit sectors. Acknowledgements This study was supported by the Institute of Environmental Assessment and Water Research (IDAEA-CSIC) in which the majority of analysis were conducted. The authors aknowledge Ms. Mercè Cabañas, Mr. Rafael Bartroli, Ms. Silvia de los Angeles Martinez and Dr. Natàlia Moreno for their support in laboratory activities. We also thank Dr. Fulvio Amato for his help with the statistical analysis and Ms. Garay Sosa for her valuable help. The authors aknowledge the constructive comments of the three anonymous reviewers. 165

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