Phytoavailability of antimony and heavy metals in arid regions: The case of the Wadley Sb district (San Luis, Potosí, Mexico)

Science of the Total Environment 427–428 (2012) 115–125

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Phytoavailability of antimony and heavy metals in arid regions: The case of the Wadley Sb district (San Luis, Potosí, Mexico) G. Levresse a,⁎, G. Lopez a, J. Tritlla a, E. Cardellach López b, A. Carrillo Chavez a, E. Mascuñano Salvador a, A. Soler d, M. Corbella b, L.G. Hernández Sandoval c, R. Corona-Esquivel e a

Geofluidos, Centro de Geociencias, Campus Juriquilla-UNAM, Blvd. Juriquilla 3000, 76230 Santiago de Querétaro, Querétaro, Mexico Departament de Geologia, Facultat de Ciències, Universitat Autònoma de Barcelona, Spain Facultad de Ciencias Naturales, Universidad Autonoma de Queretaro, Av. de las Ciencias s/n, Juriquilla, Delegación Santa Rosa Jáuregui, C.P. 76230 Querétaro, Qro, Mexico d Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain e Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria 04510, Coyoacán, México D.F., Mexico b c

a r t i c l e

i n f o

Article history: Received 3 October 2011 Received in revised form 2 February 2012 Accepted 7 April 2012 Available online 3 May 2012 Keywords: Antimony Heavy metals Phytoavailability Tailings Plants México

a b s t r a c t This paper presents original results on the Sb and heavy metals contents in sediments and waste tailings, plants and water from the giant Wadley antimony mine district (San Luis Potosí State, Mexico). The dominant antimony phases in mining wastes are stibiconite, montroydite and minor hermimorphite. The waste tailings contain high concentrations of metals and metalloids (antimony, iron, zinc, arsenic, copper, and mercury). Manganese, copper, zinc, and antimony contents exceed the quality guidelines values for groundwater, plants and for waste tailings. Results indicate that peak accumulation is seasonal due to the concentration by high metabolism plants as Solanaceae Nicotiana. The metal phytoavailability in waste tailings is highly dependant on the metal speciation, its capability to be transported in water and, more particularly, the plant metabolism efficiency. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Besides natural sources, mining and smelting activities are the two major anthropogenic sources of antimony in the environment (Adriano, 1986; Callender, 2004). Antimony is a metalloid of significant environmental concern because of its high toxicity (Gurnani et al., 1994). Antimony compounds are released into the atmosphere in the form of oxides during the incineration of waste, fossil fuel combustion and during the smelting of metals. Other sources of contamination include road traffic (dust from brake linings and tires), shooting ranges (antimony in ammunition), and older battery producing plants (Scheinost et al., 2006; Oorts et al., 2008). Historically, when mines were no longer economic, the mining sites were abandoned with little or no consideration for future environmental impact. In Mexico, where mining has been major economic activity for the past 400 years, the number of abandoned or inactive mining sites is estimated at more than 10,000, constituting a potential or even real environmental risk in some areas of the Republic. An example of this hazard is found in the Wadley area (San Luís Potosí state) where abandoned tailings and dumps from an older antimony mine are

⁎ Corresponding author. E-mail address: [email protected] (G. Levresse). 0048-9697/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2012.04.020

exposed to erosion and dispersion. Although in the Wadley area antimony is quantitatively the most abundant metal, other related elements in the deposit such as arsenic, mercury, copper, iron, lead and zinc may also constitute a potential danger for the vicinity communities. In non-contaminated soils, antimony occurs at very low concentrations (0.1 to 1.9 mg/kg; Shacklette and Boerngen 1984; Fowler and Goering, 1991; Callender, 2004; Murciego et al., 2007; Oorts et al., 2008) in the pentavalent (Sb(V)) and trivalent (Sb(III)) oxidation states. However, soil antimony concentrations up to 230 mg·kg− 1 have been found in mining areas (Filella et al., 2002, 2007; Casado et al., 2007). Sb(V) and Sb(III) are subjected to strong hydrolysis in aqueous solutions, by forming dominantly uncharged and negatively charged hydroxide and chloride species at pH above 2, and a range of positively charged and often polymeric species with poorly quantified stabilities and stoichiometries at extremely acid pH (Baes and Mesmer, 1976; Filella et al., 2002, 2007). This strong affinity of antimony in solution to OH− groups significantly limits antimony complexing with other inorganic and organic ligands. According to thermodynamic predictions, Sb(III) will normally exist in measurable concentrations in reducing and mildly reducing conditions (Pokrovski et al., 2006), whereas Sb(V) is the thermodynamically stable oxidation state in oxygenated waters and prevails in typically oxic environments like soils (Mitsunobu et al., 2006; Scheinost et al., 2006; Oorts et al., 2008). Nevertheless, Sb(III) has been detected in oxygenated lake pore waters (Deng et al., 2001;

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Chen et al., 2003). The trivalent Sb is the most toxic form, and seems to be sorbed quickly and non-reversibly onto soil minerals such as carbonates, in alkaline soils, or organic matter (ATS DR, 1992; Pilarski et al., 1995; Müller et al., 2009; Tella and Pokrovski, 2008). Direct human contact with contaminated soils has been the major exposure route considered in human health risk assessment of contaminated sites (Oorts et al., 2008). Evidences concerning the toxicity of antimony compounds to humans are available in the literature (Kuroda et al., 1991; Gebel et al., 1998; Denys et al., 2008). However, bioavailability of antimony to humans has not been taken into account to this date (Paustenbach, 2000; Kelley et al., 2002; Nathanail and Smith, 2007). Moreover, antimony bioavailability for micro-organisms or plants was shown to be very variable (Brooks, 1972; Bowen, 1979; Coughtrey et al., 1985, KabataPendias and Pendias, 1985; Ainsworth and Cooke, 1991, Jung et al., 2002; De Gregori et al., 2003; Flynn et al., 2003; Miravet et al., 2005; Tschan et al., 2008; Fu et al., 2011). Antimony is not an essential element to plants but it can be readily absorbed by their roots when available in soluble forms (Baroni et al., 2000). In contaminated areas, antimony may become ecologically toxic because of accumulation in plants although the toxicity and physiological behavior of Sb to plants has been considered as moderate (Casado et al., 2007). Phytotoxic levels of antimony have been given as 5–10 ppm in plant tissue (Kabata-Pendias and Pendias, 1985). The background antimony content in terrestrial vascular plants ranges from 0.2 to 50 ppm (Brooks, 1972; Bowen, 1979). However, in mining areas and around smelters, higher contents of antimony have been found in soil, vegetation, and herbivorous and insectivorous mammals (Ainsworth et al., 1991; Hammel, Debus, and Steubing 2000). Exceptional values (up to 1367 mg/kg) have been found in plants like Achillea ageratum, Plantago lanceolata, and Silene vulgaris (Baroni et al., 2000). In Mexico, the regulation on antimony concentration in the environment is limited to drinking and ground waters. As a member of the World Health Organization (WHO), Mexico applies the following guideline values for antimony and other metals present in the studied tailings: 6 ppb of antimony; 10 ppb of arsenic; 1.3 ppm of copper; 0.3 ppm of iron; 15 ppb of lead; 2 ppb of mercury; and 5 ppm of zinc. Antimony is present in food, including vegetables grown on antimony-contaminated soils, mostly in the low μg/kg of wet weight range or less. It is a nonessential element for humans. So far, no legacy exists to food exposure. Soil toxicity thresholds (EC50 values) identified in laboratory toxicity tests range from 0.5 to >8 mmol Sb kg− 1 depending on the endpoint, soil, and antimony form tested (Oorts et al., 2008). Present day concentrations of antimony in air are considered to be lower than in the past because industrial emissions have been significantly reduced by the introduction of dust filters. Exposure of urban population to air-transported antimony is estimated to be between 60 and 460 ng/day per person (Slooff, 1992). Daily oral uptake of antimony ranges from 10 to 70 μg and therefore it appears to be significantly higher than the uptake via inhalation. The main purpose of the present work is to study the distribution of antimony, arsenic, mercury, copper, iron, lead and zinc in sediments, mine tailings, groundwater and plants in the Wadley mining area (San Luis Potosí, México) in order to assess the potential threat of these elements to the environment. Questions such as the geochemical background, the possible natural and/or anthropogenic sources of the metals, and the geochemical process controlling their distribution are also discussed. 2. Materials and methods 2.1. Geographic and geological settings The study area, is located between 100°37′–101°00′W and 23°16′– 23°49′N, within the world class mining district of Real de Catorce, San Luis Potosi state, in the central part of Mexico and at 480 km north of

Mexico City (Fig. 1). The area is characterized by an important altitude variation due to basin and range geometry. The Wadley antimony deposit cover an area of about ca. 35 km2 and is located at the eastern margin of the agricultural area of Real de Catorce and Cedral villages, where groundwater is the unique source of drinking and agricultural water (Figs. 1 and 2). The mine, operated from 1930 to 2002, produced around 300,000 t of ore with antimony average grades between 4 and 8%. Presently, a new Sb resource evaluation is underway. The geology of the area is characterized by the presence of sedimentary rocks (mainly carbonates) of Jurassic to Cretaceous ages, crosscut by plutonic intrusions of Eocene age (Barboza-Gudiño et al., 2004). The antimony deposits at Wadley are hosted within carbonates of Oxfordian age, locally named as the Zuluaga formation. Mineralization is stratabound and is distributed in seven mantos (0.5 to 3 m thick) that have a lateral continuity of several km. Stibnite and pyrite are the primary sulfides. Gangue is constituted almost exclusively by calcite, quartz and minor anhydrite and gypsum. Supergene alteration processes affected the hypogene mineralization, producing cervantite and stibiconite as the main supergene minerals concentrated in fractures and vugs, often pseudomorphing former stibnite crystals. Traces of supergene, powder-like cinnabar are frequently found mixed up with secondary Sb hydroxides (Tritlla et al., 2008; Mascuñano et al., 2011). 2.2. Hydrogeological setting The Wadley area is located in a semiarid region characterized by a highly irregular hydrological regime, with long periods of dryness and intermittent periods of rain, where precipitation volume in a few hours may be greater than the annual average precipitation. The mean precipitation is 200–300 mm/year with an evapotranspiration of 85–95% of the mean annual precipitation, which indicates that infiltration of rainwater into the soil can be low and that evapotranspiration may be very significant during certain periods of the year. A flotation and gravimetric separation plant was installed at the end of the Tierras Negras canyon, about 7 km E of Estacion Wadley and 600 m from San Juan de Concepcion village. During the rain periods, waters flowing down the hill slopes drain the mining sites and tailings (see Figs. 1 and 2). As a result of the mining and concentration operations, a minimum estimate of 1,210,520 m 3 of waste and tailings were produced since 1930, which are currently concentrated over an area of around 0.12 km 2 on the alluvial fan formed at the exit of the canyon. The sand-size particles from the tailings have been dispersed eolically and hydrodynamically all over the area during the last 80 years. Two types of aquifers are present in the study area: fractured carbonates in the ranges and in the basin area, and an unconfined aquifer related to the contact between the carbonates and the siliciclastic fans that fill up the basin. In both areas, rainfall is the unique source of recharge. 2.3. Sampling and analytical methods Stream sediments, tailings, waters and plants were sampled to analyze their metal content. The location of sampling spots is shown in Fig. 1 and a description of the sampling sites is shown in Fig. 2. Samples from stream sediments and tailings were collected using a stainless steel scoop and then packed into plastic bags. Sampling of stream sediments (AM-1 to 18) covered the area from the tailings to the town of Estación Wadley, following the main creek. Tailing samples (TM-10 to 45) were collected at 20 cm intervals from the surface down to 30 m along the vertical slopes of the creek created by runoff waters. In the laboratory, cores are cut in two parts along the longitudinal section with ceramic knife. Then, the core center part is removed with ceramic spoon for analysis. Samples were air-dried crushed and sieved through a 250 μm mesh before total acid digestion and analysis for antimony,

G. Levresse et al. / Science of the Total Environment 427–428 (2012) 115–125

117

10 km to Estación Catorce

101°00’

100°55’

110° W

0 280

U.S.A. 30° N

3000

2800

23°40’

Wadley late cp cifi Pa

Mexico city

2500

20° N

2700

2000

0

Gulf of Mexico

600 Km

El Mastranio

250 0

2300 2800

Vigas de Coronado 280

0

Estación Wadley 2300

Jose Coronado San Jose Coronado

AM18 AM15

28

00

AM11 AM8

AM5

MAP-1

AM1

MAP-2 Tierra Negras MAP-3

.

MAP-6

23°53’

MAP-4 MAP-5 1900

MAP-7

WASTE TAILING

12 km to Las Margaritas

Fig. 1. Location of the study area and sampling sites. Pink area: Mining area; red open stars (AM): stream sediments sample; red stars (MAP): plant from mining area; red open dots: groundwater samples.

chromium, cobalt, nickel, copper, zinc, arsenic, cadmium, mercury, iron and lead. The mineralogy of the waste tailings was studied by X-ray diffraction (XRD) and petrographic and electron microscope observations. XRD characteristics of minerals were determined using a Miniflex Rigaku diffractometer with Cu Kα radiation of 1.541874 Å. Samples for XRD were dried for 12 h at 50 °C and were prepared by hand crushing and sieving. Mineral identification was completed using an Olympus BH-55 polarizing microscope and a Hitachi TM1000 SEM-EDS system at the Centro de Geociencias, UNAM, Mexico. The relative mineral proportions in clay- and silt-size fractions were determined by sieving and, for the finest particles, using a Fritch laser photosedimentographer. Groundwater samples were taken from 3 wells that supply the town of Estación Wadley and nearby communities (Fig. 1). Temperature, pH,

electrical conductivity and dissolved oxygen were measured in situ with an electrochemical portable device. The water samples were filtered in the field (0.45 μm) and acidified (concentrated HNO3) to pH= 2 for anion and cation analysis. 22 plant species representative of the whole area were collected for heavy metal analysis. Sampling included seasonal and perennial plants around the mine workings, plants growing on and around the waste tailings and plants from areas situated in the valley at a distance from the tailings, close to Wadley village and apparently away from the influence of contaminants. Each part of the plant (roots, stem and leaves) was analyzed separately. The following plant species were collected: Buddlejaceae Buddleja, Ruscaeae Dasylirion, Asteraceae Gymnosperrna and PINACEAE Pinus in the mining sites (samples MAP-1 to 7); Asphodeloceae Asphodelus

SE

Mining Area (top of the mountains)

CWTP-2

flotation plant

Level 1(TM-10 to18) Level 2 (TM-20 to 27)

CWTP-1

WTP-8

Pre-erosi

Level 3 (TM-30 to 40)

on level 3

WTP-9

Level 4 (TM-41 to 45) WTP-11

Fig. 2. View looking northeast of a part of the Wadley. Location of the samples in the waste tailing.

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Table 1 Average and predominant fraction of clay, silt or sand size material for all waste tailing samples (TM). Sample area

Predominant fraction (mm)

Average value (mm)

TM-10 Level-1 TM-12 Level-1 TM-15 Level-1 TM-18 Level-1 TM-20 Level-2 TM-22 Level-2 TM-27 Level-2 TM-30Level-3 TM-33 Level-3 TM-35 Level-3 TM-40 Level-3 TM-42 Level-4 TM-45 Level-4

0.023 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.125 0.125 0.0625 0.5 0.25

9.14366 69.45728 41.28974981 64.66761 46.51658 67.635505 33.73551 112.946195 73.1202 50.643115 18.05818 253.08361 92.254005

a closed pressurized digestion vessel, using a microwave digestion unit (MarsXpress, CEM Corporation, USA). After cooling in a fridge for 2 days the digested solution was filtered and eluate to a volume of 50 mL and analyzed. Water and acids used for cleaning, digestion and analysis, of all type of samples (solid wastes, waters and plants) were home-distilled to control their purity. All samples (solid waste, waters and plants) were analyzed by ICPMS using a VG Elemental model PQ3 instrument, calibrated with a multi-elemental standard solution (IV-71A; Inorganic Venture) for quality control. Matrix effects and instrumental drift were corrected using 115In (10 ppb) as an internal standard. The validity of the analytical procedure was assessed by accuracy and precision tests comparing measured and certified reference values (MAG-1). All element determinations had a precision better than 3%. Detection limits were less than 50 ppt. 3. Results and discussion

and Solanaceae Nicotiana (seasonal); Agavaceae Yucca, Anacardiaceae Schinus, Cupressaceae Juniperus and Myrtaceae Eucalyptus (perennial), from the tailings (samples WTP-1 to 11); Cactaceae Echinocactus, Cactaceae Opuntia, Berberidaceae Berberis, and Zygophyllaceae Larrea collected in the valley and in areas close to the tailings (samples CWTP-1 and CWTP-2), were collected from an area between the tailings and San Juan de Concepción village and samples VP-1 and 2 correspond to plants that grow in the valley, at 3.5 km from the waste and tailings (Fig. 1). Plant samples were thoroughly washed in tap water and then placed in an ultrasonic bath to remove soil particles. This was followed by repeated rinses with deionized water and a final rinse with double distilled water. Roots, stem and leaves were separated and dried at room temperature in the shade for 60 days and subsequently powdered. For plant digestion, 0.5 ± 0.05 g of ground plant sample was used. This was dissolved in 10 mL of nitric acid (65%) in

3.1. Mineralogy and heavy metal content in soils and waste tailings The mineralogy of the tailings is relatively simple and homogeneous and is constituted by carbonate (calcite; up to 90%), quartz, stibine (Sb2S3), stibiconite (Sb3O6(OH)), cervantita (Sb3O4), cinnabar (HgS), montroydite (HgO), and minor hemimorphite (Zn4Si2O7(OH)2·(H2O)). The grain size distribution within the tailings is heterogeneous and this could affect the analytical interpretation of the results. Then a granulometric study was carried out previous to their analysis for heavy metal content. Samples from the different horizons in the tailings have mixed grain sizes ranging from clay to sand fractions, where the 0.25 mm fraction reaches up to 40%. However, the granulometry (from 95 to b3 μm), determined through a particle-counter was found to be similar for all samples with a median at 48 μm. Table 1 shows the relative

Table 2 Geochemical characteristics of mine wastes tailing sediments (TM). Sample area

TM-10 TM-12 TM-15 TM-18 TM-20 TM-22 TM-27 TM-30 TM-33 TM-35 TM-40 TM-42 TM-45

Level-1 Level-1 Level-1 Level-1 Level-2 Level-2 Level-2 Level-3 Level-3 Level-3 Level-3 Level-4 Level-4

Sample area

TM-10 TM-12 TM-15 TM-18 TM-20 TM-22 TM-27 TM-30 TM-33 TM-35 TM-40 TM-42 TM-45

Level-1 Level-1 Level-1 Level-1 Level-2 Level-2 Level-2 Level-3 Level-3 Level-3 Level-3 Level-4 Level-4

Cr

Mn

Fe

Co

Ni

Cu

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

11.8 10.6 5.5 4.7 4.9 6.5 9.6 10.5 12 7.4 12.7 6.5 4.6

1.4 1.4 1.4 1.4 1.3 1.4 1.3 1.4 1.0 1.0 1.0 1.0 1.0

12.4 6.9 7 5 4.8 7.7 6.2 10.9 9.8 5.8 11.2 8.3 6.5

0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

3388 2713 1441 1041 996 1627 2303 2537 3799 2545 3327 2101 1341

33 33 34 35 34 35 33 34 31 33 33 34 36

4.3 8.1 6.6 10 10.2 15.4 9.2 6.9 7.9 6.4 17.5 10.2 9.4

0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.4 0.4 0.4 0.4 0.4

16.4 13.4 12.7 10.5 11.3 12.1 12.8 15.8 14.8 11.6 16.7 11.7 11.7

1.0 1.0 1.0 1.0 0.9 1.0 1.0 1.0 0.7 0.7 0.7 0.7 0.7

5.6 5.1 3.5 3.7 3.1 3.2 5.1 4.6 6.6 4.2 6.1 5.7 2.8

0.6 0.6 0.6 0.5 0.5 0.6 0.5 0.6 0.4 0.4 0.4 0.4 0.4

Zn

As

Mo

Sb

Hg

Pb

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

(ppm)

stdev

65.1 32 39.9 33 38.9 42 47.5 66.2 58.9 44.2 84.4 63.9 41.8

1.4 1.4 1.4 1.3 1.3 1.4 1.3 1.4 1.0 1.0 1.0 1.0 1.0

57.8 20.8 28.9 18.7 22.3 17.9 16.4 29.6 25.7 13.5 28.6 21.6 30.5

0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.2 0.2 0.2 0.2 0.2

12.4 6.9 7 5 4.8 7.7 6.2 10.9 9.8 5.8 11.2 8.3 6.5

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

13,743 6563 9749 6796 8608 8135 8541 13,626 8789 8707 13,198 12,786 9161

189 157 162 153 151 158 155 194 154 155 187 181 161

47.5 37.44 48.4 29.67 53.13 20.93 15.92 24.72 28.97 15.48 35.07 30.3 31.9

0.14 0.14 0.14 0.14 0.13 0.14 0.14 0.14 0.1 0.1 0.1 0.1 0.1

2.88 2.12 2.51 2.64 2.14 2.24 6.79 2.93 7.74 7.27 10 10.74 2.3

0.05 0.05 0.05 0.04 0.04 0.05 0.04 0.05 0.03 0.03 0.03 0.03 0.03

G. Levresse et al. / Science of the Total Environment 427–428 (2012) 115–125

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Table 3 Geochemical characteristics of stream sediments (AM) along the seasonal river from the waste tailing to the nearest town. Detection limit: Cr (35 ppm); Co (25 ppm); Ni (40 ppm); Hg (15 ppm). Sample

AM-1 AM-5 AM-8 AM-11 AM-15 AM-18

Cr

u.d.l. u.d.l. u.d.l. u.d.l. u.d.l. u.d.l.

Co (ppm) u.d.l. u.d.l. u.d.l. u.d.l. u.d.l. u.d.l.

Ni

Cu

(ppm)

(ppm)

stdev

Zn (ppm)

stdev

As (ppm)

stdev

(ppm)

stdev

u.d.l. u.d.l. u.d.l. u.d.l. u.d.l. u.d.l.

42 26 39 34 42 30

3 3 3 3 3 3

54 45 49 21 28 34

3 3 3 3 3 3

29 15 18 9 7 9

3 2 2 2 2 2

3773 2405 5771 168 175 1130

70 54 89 16 17 45

proportions of clay, silt and sand size fractions for all samples, resulting in an evolution line from sand to clay with minor (b20%) presence of silt size material. As expected, the heavy metal content in the waste tailings is high and reflects the mineralogy of the deposit. Results are reported in Table 2. Antimony (6563–13,743 ppm), iron (996–3799 ppm), zinc (32–84 ppm), arsenic (13–57 ppm), and mercury (15–53 ppm) are the most outstanding. The sampled tailings profile shows that minerals in the waste tailings are distributed homogeneously with depth, as shown in Table 3. Metal concentrations show a similar distribution in all sampling spots although some metals (zinc, mercury, and arsenic) seem to be preferentially concentrated in the clay fraction. Compared to waste tailings, stream samples show lower concentrations of all analyzed metals (Table 3) with the exception of copper (26 to 42 ppm) and lead (14 to 22 ppm). Lead, arsenic, zinc, and copper concentrations are homogeneous in all the stream samples, independently of the distance to the waste tailings, whereas the antimony content decreases by a 1-order magnitude from the tailings to the farthest sampling point. Antimony, arsenic and zinc concentrations show a

Sb

Hg (ppm)

Pb

u.d.l. u.d.l. u.d.l. u.d.l. u.d.l. u.d.l.

(ppm)

stdev

14 22 19 18 20 18

3 3 3 3 3 3

positive correlation (see Table 3), suggesting a common source related to the weathering of tailings.

3.2. Groundwater chemistry Three groundwater wells of the area (Estación Wadley, Estación Catorce, and Las Margaritas) and surface water from the waste tailings were sampled at the end of the wet season, in January 2007. The analyses of these samples are presented in Table 4. All groundwater samples resulted to be Ca-rich bicarbonate waters with low sulfate content. Most analyzed metals show concentrations below 10 ppb and only iron and zinc showed higher values (Fe: 300 to 900 ppb and Zn: 8.9 to 36.9 ppb). These figures are smaller than the standard for safe drinking water according to WHO. The surface water from the waste tailings composition is similar to the sampled groundwater, except that it contains more aluminum, arsenic, selenium, molybdenum, titanium and especially antimony (1645 ppb). The composition of this water was introduced into the geochemical code Medusa (Puigdomènech, 2002) in order to

Table 4 Geochemistry and isotopic analyses of groundwater from waste tailing and wells along the valley. Waste tailing superficial water is used in the study of speciation and aqueous mobility. Sample

Na

K

Ca

Mg

HCO3

Cl

NO3

SO4

F

meq/l

meq/l

meq/l

meq/l

meq/l

meq/l

meq/l

meq/l

meq/l

0.07 0.04 0.03 0.10

11.26 8.89 3.82 3.52

0.76 0.85 0.26 0.12

11.80 6.51 0.75 1.51

0.04 0.02 0.01 0.02

Li

Be

Al

Si

Ti

V

Cr

Mn

Fe

ppb

ppb

ppb

ppm

ppb

ppb

ppb

ppb

0.0 0.0 0.0 0.0

2.1 2.6 0.6 20.6

12.8 9.8 6.3 2.0

1.9 1.3 0.8 0.7

Co

Ni

Cu

Zn

As

Se

Sr

Mo

Cd

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

ppb

1.3 1.1 4.8 5.3

36.9 33.4 14.2 8.9

2.1 1.2 0.5 4.5

3.5 4.7 1.9 10.8

3798.8 1846.6 642.6 2244.6

2.0 0.6 1.6 13.8

0.0 0.0 0.0 0.0

C

O

Las Margaritas Est. Catorce Est. Wadley Waste tailing

2.02 1.63 0.34 0.06

Las Margaritas Est. Catorce Est. Wadley Waste tailing

31.4 10.3 5.1 3.5

Las Margaritas Est. Catorce Est. Wadley Waste tailing

Las Margaritas Est. Catorce Est. Wadley Waste tailing

0.3 0.3 0.1 0.2

8.1 6.6 2.8 5.4

Sb

Tl

Pb

ppb

ppb

ppb

2.2 0.7 1.2 1645.1

0.0 0.0 0.0 0.8

0.1 1.0 0.4 0.2

0.80 4.61 3.61 2.39

0.81 0.54 0.21 0.05

1.10 0.21 0.08 0.05

3.3 1.3 1.1 0.9

per mil

per mil

− 53.1 − 72.6 nd − 27.1

− 7.7 − 10.5 nd − 3.5

2.6 4.5 4.5 2.6

0.3 0.4 0.1 1.7

ppm 0.9 0.7 0.3 0.3

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determine the predominant antimony species in the contaminated water from the tailings. Two pH–Eh diagrams were constructed with this study data that show the most stable species at 25 °C and at atmospheric pressure. Carbon, sulfur and antimony species are included in Fig. 3A while Zn and Sb species are plotted in Fig. 3B The pH–Eh measured conditions ranges are indicated with a gray area in both figures. The main antimony phases of Wadley mine are stibnite and stibiconite. The grounded stibnite accumulated in the tailings under the oxidizing atmosphere was subsequently converted to valentinite, cervantite and other Sb-oxide. Part of the antimony minerals were also dissolved into the aqueous phase as antimonite (Sb(OH)6) according to Medusa database (Fig. 3A–B). At ambient neutral conditions, the minerals phases cervantite and stibiconite are stables which must limit the mobility of antimony. Sb(OH)6 is the only aqueous Sb species available to plants, which is in agreement with Denys et al. (2008) and Oorts et al. (2008) studies of antimony in sediment water with low dissolved organic carbon content. Hemimorphite, which was the Zn-mineral identified in the waste, is not visible in Fig. 3B as Si wasn't included in the geochemical model. Under ambient conditions hydrozincite is the unique stable Zn-phases in underground waters (Fig. 3B). Smithsonite can be stable in the aqueous phase during periods of slightly more acidic conditions (6.5b pH b 7). The pH–Eh diagrams point out the limited varieties of antimony and zinc complexes stable in the underground waters at atmospheric conditions. They illustrate that what drives the metal mobility in the aqueous

A

1.0

HSO4

ESHE / V

HCO3

CO3

2

SO42

H2CO3

0.5

0.0

C(c) Sb2S3(c) -0.5

CH4

H2S

HS

ESHE / V

Sb2O4(c) a Sb2O3(cr) 0.0

Sb(OH)6 ZnO(cr)

Zn2+

B Zn5(OH)6(CO3)2(c)

0.5

Sb2O5(c)

ZnCO3:H2O(c)

-1.0 1.0

Sb2S42

ZnS(cr)

-0.5

Sb(c)

-1.0

ZnSb(c)

Fig. 3. Diagrams constructed with MEDUSA geochemical package: A) Eh–pH diagram for the Sb–SO42 −–CO32 −–O2–H2O system. c Solid phase, E/V Eh (v); B) Eh–pH diagram for the SO42 −–CO32 −–O2–H2O–Sb–Zn system. c Solid phase, E/V Eh (v); C) Eh–pH diagram for the SO42 −–CO32 −–O2–H2O–Ni system. c Solid phase, E/V Eh (v).

phase, and bioavailable, is not directly related to their absolute concentration in sediments or wastes but the possible aqueous species stable in the pH–Eh measured conditions.

3.3. Heavy metals in plants Antimony tends to be present in sediments as low-solubility sulfides (Hammel et al., 2000), bound to immobile iron and aluminum oxides or associated with organic matter (Lintschinger et al., 1998; Tighe et al., 2005). The presence of relatively insoluble species or low contents of mobile fractions results in a low phytoavailability and uptake into biological systems, resulting in a low phytoaccumulation in food chains (Ainsworth et al., 1991; Flynn et al., 2003; Hammel et al., 2000). Results of the analyzed metal concentrations in plants from the waste tailings are presented in Table 5. All the plants present similar metal concentration profiles whatever the species or the part of plant analyzed (stem, root and leaf). However, metal concentrations are generally higher in seasonal than in perennial plants. In seasonal plants, the highest concentrations correspond to iron (116 to 618 ppm), antimony (1 to 447 ppm), zinc (15.5 to 350 ppm), manganese (8 to 218 ppm), copper (1.5 to 56 ppm) and nickel (0.5 to 43.5 ppm). In perennial plants, the highest metal concentrations correspond to iron (86 to 589 ppm), manganese (4 to 54 ppm), zinc (4 to 113 ppm), antimony (1 to 20 ppm) and copper (1 to 13 ppm). Perennial plants growing around the waste tailings and in the mining area show Fe contents one order of magnitude higher than manganese, zinc and antimony. Metal concentrations in plants growing around the waste tailings are presented in Table 5. The Cactaceae were collected at the margins of the waste tailings whereas the other species were collected ca. 3.5 km east from the tailings. All sampled plants show a similar metal content profile whatever the species or the part of the plant (stem, roots and leaf). The metals with the highest concentration are iron (892 to 62 ppm), manganese (34 to 21 ppm), zinc (68 to 7 ppm), antimony (13 to 1 ppm) and copper (12 to 0.5 ppm). The analyzed plants from the waste tailings show higher contents in antimony, copper and nickel, compared to plants from the mining area and from around the waste tailings which have similar metal contents. Bioremediation is gaining a lot of importance in recent times as an alternate technology for removal of elemental pollutants in soil and water, which require effective methods of decontamination (Eapen and D'Souza, 2005). Phytoremediation may offer an effective, environmentally nondestructive, clean and cheap remediation method (Witters et al., 2012). Examples where phytoremediation has been used successfully include the restoration of abandoned lead, nickel, arsenic, cadmium, gold, mercury and uranium mine workings, reducing the impact of pollution (Anderson et al., 1999; Azizur and Hasegawa, 2011; Ye et al., 2011; Sorkhoh et al., 2010; Lim et al., 2004; Chen et al., 2008). However, one major disadvantage of phytoremediation is that it requires a long-term commitment, as the process is dependent on plant growth, tolerance to toxicity, and bioaccumulation capacity. As well, phytoremediation is limited to the surface area available and the roots depth. To make the phytoremediation more attractive is important mention the possibilities to evolve to a profit making operation as phytomining and the potential CO2 abatement that accompanies this production (Witters et al., 2012). Phytoavailability is the capacity of a plant for the sorption of components from the sediments and varies with factors such as plant species, metal concentrations in sediments, metal oxidation grade, adsorption and desorption from mineral surfaces, precipitation, release through the dissolution of minerals, and interactions with sediments, plants and microbes (Adriano, 1986; O'Neill, 1990; Li and Thornton, 1993; Jung et al., 2002). The phytoavailability grade is determined from the ratio between the metal concentration in the plant and the metal concentration in the substrate. Phytoavailability grades are given in Table 6.

G. Levresse et al. / Science of the Total Environment 427–428 (2012) 115–125

121

Table 5 Geochemical characteristics of plants from waste tailing (WTP), mining area (MAP) and valley (VP). Mining area Plant name

Plant part

Sample no.

Bubblejaceae Buddleja

Leaf Stem Leaf Stem Leaf Stem Leaf Stem Root Leaf Stem Root Leaf Stem

MAP-1L MAP-1S MAP-2L MAP-2S MAP-3L MAP-3S MAP-4L MAP-4S MAP-4R MAP-5L MAP-5S MAP-6R MAP-7L MAP-7S

Plant part

Sample no.

Li ppm

Bubblejaceae Buddleja Ruscaeae Dasylinin Asteraceae Gymnosperna

Pinaceae Pinus Pinaceae Pinus Pinaceae Pinus

Plant name

Bubblejaceae Buddleja Bubblejaceae Buddleja Ruscaeae Dasylinin Asteraceae Gymnosperna

Pinaceae Pinus Pinaceae Pinus Pinaceae Pinus

Leaf Stem Leaf Stem Leaf Stem Leaf Stem Root Leaf Stem Root Leaf Stem

MAP-1L MAP-1S MAP-2L MAP-2S MAP-3L MAP-3S MAP-4L MAP-4S MAP-4R MAP-5L MAP-5S MAP-6R MAP-7L MAP-7S

Plant part

Sample no.

0.09 1.23 0.64 1.34 u.d.l. 0.18 0.26 0.04 0.04 0.04 0.38 0.14 0.25 0.21

V

Cr

ppm

ppm

1.03 0.45 0.94 1.75 2.91 0.74 2.66 0.54 1.57 0.60 1.48 0.96 0.94 1.19

1.54 1.08 1.46 1.60 3.09 1.11 0.81 1.35 1.68 1.32 1.65 1.26 1.52 1.40

Mn

Fe

Co

Ni

Cu

ppm

ppm

ppm

ppm

ppm

46.51 43.53 54.81 38.93 34.23 26.56 31.26 11.76 27.11 16.55 38.56 4.67 104.79 43.69

122.07 591.62 161.10 440.08 88.91 190.97 199.09 165.13 117.27 102.41 343.35 141.84 202.54 199.37

0.03 0.19 0.09 0.40 u.d.l. 0.01 0.01 0.01 0.03 u.d.l. 0.22 u.d.l. 0.16 0.25

1.11 2.12 2.02 1.41 3.12 0.42 0.67 0.51 0.75 0.26 1.00 0.42 0.54 0.96

13.50 0.90 8.35 7.70 2.00 5.32 9.51 1.49 7.34 3.84 10.61 1.76 2.25 6.13

Zn

As

Se

Cd

Sb

Hg

Pb

U

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

18.04 4.49 24.17 37.15 12.76 103.25 114.00 20.80 70.67 57.22 24.35 9.68 25.28 21.72

0.45 0.09 0.59 0.63 0.36 0.35 0.50 0.24 0.43 0.11 0.60 0.13 0.30 0.41

0.64 0.30 0.42 0.18 − 0.01 0.10 − 0.06 0.20 0.22 0.02 0.32 − 0.01 0.64 0.22

u.d.l. 0.35 u.d.l. u.d.l. u.d.l. 0.00 u.d.l. u.d.l. 0.00 u.d.l. u.d.l. u.d.l. u.d.l. u.d.l.

3.67 0.97 7.31 6.93 14.64 11.95 11.65 10.87 20.42 2.55 8.36 14.83 15.61 11.02

0.11 0.13 0.12 0.11 0.10 0.29 0.24 0.27 0.13 0.08 0.22 0.11 0.20 0.19

0.58 0.21 0.49 1.30 0.12 0.70 0.82 0.22 0.78 0.07 1.07 0.15 0.31 0.29

0.10 0.09 0.10 0.13 0.10 0.12 0.12 0.10 0.14 0.09 0.12 0.12 0.12 0.11

Waste tailing Plant name

Asphodelaceae Asphodelus

Asphodelaceae Asphodelus

Asphodelaceae Asphodelus

Agavaceae Yucca Anarcardiaceae Schinus Cupressaceae Junipesus Cupressaceae Junipesus Myrthaceae Eucalyptus Myrthaceae Eucalyptus Solanaceae Nicotiana

Solanaceae Nicotiana

Plant name

Asphodelaceae Asphodelus

Leaf Stem Root Leaf Stem Root Leaf Stem Root Leaf Leaf Stem Leaf Stem Leaf Stem Leaf Stem Leaf Stem Leaf Stem Root Leaf Stem Root

WTP-1L WTP-1R WTP-1S WTP-2L WTP-2R WTP-2S WTP-3L WTP-3S WTP-3R WTP-4L WTP-5L WTP-5S WTP-6L WTP-6S WTP-7L WTP-7S WTP-8L WTP-8S WTP-9L WTP-9S WTP-10L WTP-10S WTP-10R WTP-11L WTP-11S WTP-11R

Plant part

Sample no.

Leaf Stem Root

WTP-1L WTP-1R WTP-1S

Li

V

Cr

Mn

Fe

Co

Ni

Cu

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

18.51 4.54 13.32 23.72 9.66 26.28 59.85 29.21 10.50 4.18 24.44 30.63 21.32 17.18 12.38 7.61 210.25 219.02 60.50 55.05 11.65 6.51 5.04 40.62 10.27 12.84

137.94 77.62 163.21 223.36 218.90 174.78 188.17 199.03 314.72 212.67 148.41 232.40 193.46 621.44 159.85 202.83 264.02 544.11 163.68 384.53 408.81 199.20 126.28 331.95 119.36 330.53

u.d.l. u.d.l. 0.02 0.00 0.08 u.d.l. u.d.l. 0.01 0.10 0.01 u.d.l. 4.00 0.02 0.20 0.03 0.69 0.05 0.21 0.02 0.11 0.12 0.10 0.06 0.14 0.09 0.12

2.23 0.62 2.12 1.70 2.90 0.49 2.17 2.53 3.51 1.51 3.71 6.39 1.41 3.97 2.25 4.98 37.97 43.65 14.21 28.06 3.60 1.85 2.51 17.96 12.67 7.80

6.67 2.29 9.45 11.08 8.35 8.38 4.84 7.37 4.76 2.03 12.08 25.09 1.62 3.96 2.13 5.82 47.85 11.06 18.81 25.35 47.11 13.51 14.35 56.42 7.42 13.73

0.54 0.52 0.66 0.43 0.47 3.07 0.50 0.36 1.22 0.93 5.57 2.71 0.19 0.97 0.51 1.20 5.47 0.72 8.55 1.14 0.74 0.01 0.82 0.80 0.09 7.41

0.95 0.67 0.88 0.82 0.91 0.96 1.13 0.64 1.69 1.42 1.12 0.80 1.13 1.91 1.00 0.62 1.91 0.60 0.46 0.53 0.71 0.45 1.38 1.35 0.96 1.62

1.41 1.77 1.40 1.31 2.14 1.37 1.52 1.08 1.11 1.70 1.43 2.45 1.88 2.27 1.26 1.87 1.87 1.93 1.37 1.62 1.40 0.84 0.74 1.58 1.43 2.32

Zn

As

Se

Cd

Sb

Hg

Pb

U

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

u.d.l. u.d.l. u.d.l.

24.62 22.06 142.17

0.15 0.10 0.40

82.89 64.88 66.03

0.33 0.26 0.58

2.98 1.93 2.04

0.18 0.15 0.39

0.10 0.10 0.14

(continued on next page)

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G. Levresse et al. / Science of the Total Environment 427–428 (2012) 115–125

Table 5 (continued) Waste Miningtailing area Plant name

Plant part

Sample no.

Asphodelaceae Asphodelus

Leaf Stem Root Leaf Stem Root Leaf Leaf Stem Leaf Stem Leaf Stem Leaf Stem Leaf Stem Leaf Stem Root Leaf Stem Root

WTP-2L WTP-2R WTP-2S WTP-3L WTP-3S WTP-3R WTP-4L WTP-5L WTP-5S WTP-6L WTP-6S WTP-7L WTP-7S WTP-8L WTP-8S WTP-9L WTP-9S WTP-10L WTP-10S WTP-10R WTP-11L WTP-11S WTP-11R

Plant part

Sample no.

Asphodelaceae Asphodelus

Agavaceae Yucca Anarcardiaceae Schinus Cupressaceae Junipesus Cupressaceae Junipesus Myrthaceae Eucalyptus Myrthaceae Eucalyptus Solanaceae Nicotiana

Solanaceae Nicotiana

Zn Li

As V

Se Cr

Cd Mn

Sb Fe

Hg Co

Pb Ni

U Cu

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

131.31 108.74 31.59 162.53 120.61 29.53 22.45 28.94 60.62 15.48 48.42 18.08 27.34 65.60 71.33 60.82 64.15 350.88 143.23 54.95 191.41 161.88 64.42

0.30 0.33 0.25 0.45 0.22 1.94 0.42 0.37 0.35 0.57 1.16 0.48 0.41 0.58 0.32 0.36 0.33 0.26 0.10 0.46 0.66 0.38 2.66

u.d.l. 0.04 0.00 0.04 u.d.l. u.d.l. u.d.l. u.d.l. 0.05 u.d.l. 0.01 0.03 0.00 u.d.l. 0.04 u.d.l. u.d.l. 0.12 u.d.l. u.d.l. 0.25 0.10 0.02

34.37 10.39 0.78 18.30 11.12 447.52 43.20 57.71 9.88 122.46 128.18 87.59 48.87 58.50 13.07 27.75 8.76 168.02 23.30 4.72 155.88 37.89 286.24

0.24 0.10 0.07 0.24 0.14 2.56 0.15 0.23 0.18 0.30 1.03 0.34 0.76 0.26 0.19 0.17 0.13 0.25 0.10 0.05 0.43 0.12 1.66

0.11 0.76 0.29 0.10 0.29 0.25 0.08 0.13 0.65 0.36 1.20 0.56 0.43 47.28 0.57 0.30 0.35 0.15 0.02 0.44 0.07 0.03 0.44

2.00 8.87 0.83 8.30 3.93 6.26 0.50 8.58 8.49 2.10 1.29 1.06 0.46 2.57 2.23 2.75 5.46 55.94 21.23 6.16 14.40 5.19 1.84

0.10 0.14 0.10 0.10 0.10 0.33 0.11 0.13 0.11 0.12 0.17 0.11 0.13 0.14 0.20 0.13 0.11 0.11 0.09 0.17 0.11 0.10 0.43

Around the waste tailing Plant name

Cactaceae Echinocactus Berberidaceae Berberis

Plant Leaf Stem

CWTP-1P CWTP-2L CWTP-2S

Plant name

Plant part

Sample no.

Cactaceae Echinocactus Berberidaceae Berberis

Plant Leaf Stem

CWTP-1P CWTP-2L CWTP-2S

Plant part

Sample no.

Li

V

Cr

Mn

Fe

Co

Ni

Cu

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

0.88 0.02 0.37

0.45 0.44 2.02

1.14 1.53 1.15

21.82 21.02 28.01

421.39 64.66 303.24

0.11 u.d.l. 0.10

1.80 0.60 1.00

0.74 2.66 5.71

Zn

As

Se

Cd

Sb

Hg

Pb

U

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

0.12 0.14 0.46

0.19 0.10 u.d.l.

0.13 − 0.05 − 0.02

7.42 15.11 32.40

4.72 6.93 7.03

0.05 0.11 0.15

0.34 0.14 0.94

0.09 0.09 0.11

Valley Plant name

Zygophyllaceae Larrea Cactaceae Opuntia

Plant name

Zygophyllaceae Larrea Cactaceae Opuntia

Leaf Stem Leaf Stem

VP-1L VP-1S VP-2L VP-2S

Plant part

Sample no.

Leaf Stem Leaf Stem

VP-1L VP-1S VP-2L VP-2S

Li

V

Cr

Mn

Fe

Co

Ni

Cu

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

211.48 228.89 387.25 348.10

0.07 0.06 0.14 0.08

0.20 0.12 0.42 0.70

1.45 1.38 1.30 0.46

1.56 1.15 2.70 1.55

33.68 34.72 22.90 23.71

2.28 2.54 1.21 2.09

8.50 12.17 6.37 3.45

Zn

As

Se

Cd

Sb

Hg

Pb

U

ppm

ppm

ppm

ppm

ppm

ppm

ppm

ppm

17.42 22.57 68.31 16.32

Plants in the waste tailing area show similar or higher manganese, copper, and zinc concentrations than the substrate (R ≥ 1), indicating that these metals were phytoavailable and incorporated in plant tissues. On the contrary, chromo, iron, cobalt, arsenic, antimony, mercury, lead show low phytoavailability ratios (R b 1) suggesting that these metals, although present in sediments and tailings in high concentrations, were not absorbed by plants. The phytoavailability ratios for copper and zinc are higher for seasonal plants than perennial plants (see Table 6). The phytoavailability ratio for manganese is high for both seasonal and perennial plants. But some perennial plants (Myrthaceae Eucalyptus) present the higher values. On the other hand, Asphodelaceae Asphodelus, which grows in all the waste tailing area, is an example of humidity and plant

0.38 0.47 0.24 0.07

1.16 0.39 0.07 0.45

0.00 0.12 u.d.l. 0.17

2.87 3.71 2.75 0.87

0.08 0.17 0.16 0.04

0.31 0.23 0.68 0.23

0.11 0.10 0.11 0.09

metabolism rate influence, because its phytoavailability capacity is higher when growing in wet zones. Antimony is present in high concentrations in mine tailings, stream sediments and plants, but the phytoavailability ratio indicates a very low bioavailability. These data are in agreement with the study of Casado et al. (2007) of antimony and arsenic uptake by plants in an abandoned mining area in the NW Spain, which concluded that these metals have a low bioavailability in mine sediments. The soluble forms of antimony, Sb(V), may absorb onto mineral surfaces and are favored by acidic and oxidizing conditions (Fig. 3 and Casado et al., 2007), but these are not the usual conditions found in the waste tailings, which must be more basic due to the high carbonate content, thus explaining the low phytoavailability of antimony in Wadley.

G. Levresse et al. / Science of the Total Environment 427–428 (2012) 115–125

123

Table 6 Accumulation rate for all the analyzed plants from the waste tailing area (nd: no data; bold: accumulation in plant; underline: similar concentration; non: non phytodisponibility). Waste tailing Plant name

Plant part

Sample no.

Cr

Mn

Fe

Co

Ni

Cu

Zn

As

Sb

Hg

Pb

Asphodelaceae Asphodelus

Leaf Stem Root Leaf Stem Root Leaf Stem Root Leaf Stem Root Leaf Stem Root Leaf Stem Leaf Leaf Stem Leaf Stem Leaf Stem Leaf Stem

WTP-1L WTP-1R WTP-1S WTP-2L WTP-2R WTP-2S WTP-3L WTP-3S WTP-3R WTP-10L WTP-10S WTP-10R WTP-11L WTP-11S WTP-11R WTP-5L WTP-5S WTP-4L WTP-6L WTP-6S WTP-7L WTP-7S WTP-8L WTP-8S WTP-9L WTP-9S

0.17 0.21 0.17 0.16 0.26 0.17 0.18 0.13 0.13 0.17 0.10 0.09 0.19 0.17 0.28 0.17 0.30 0.21 0.23 0.27 0.15 0.23 0.23 0.23 0.17 0.20

2.35 0.58 1.69 3.01 1.22 3.33 7.59 3.70 1.33 1.48 0.83 0.64 5.15 1.30 1.63 3.10 3.88 0.53 2.70 2.18 1.57 0.97 26.67 27.78 7.67 6.98

0.06 0.03 0.07 0.10 0.10 0.08 0.08 0.09 0.14 0.18 0.09 0.06 0.15 0.05 0.15 0.07 0.10 0.09 0.09 0.28 0.07 0.09 0.12 0.24 0.07 0.17

nd nd 0.00 0.00 0.01 nd nd 0.00 0.01 0.01 0.01 0.01 0.02 0.01 0.01 nd 0.43 0.00 0.00 0.02 0.00 0.07 0.00 0.02 0.00 0.01

0.17 0.05 0.16 0.13 0.22 0.04 0.16 0.19 0.27 0.27 10.33 0.14 0.19 1.36 0.96 0.59 0.28 0.48 0.11 0.11 0.30 0.17 0.38 2.88 3.31 1.08 2.13

1.46 0.50 2.07 2.43 1.83 1.84 1.06 1.62 1.04 6.93 2.96 3.15 12.37 1.63 3.01 2.65 5.50 0.45 0.36 0.87 0.47 1.28 10.49 2.43 4.12 5.56

1.64 1.28 1.30 2.60 2.15 0.62 3.21 2.38 0.58 0.01 2.83 1.09 3.78 3.20 1.27 0.57 1.20 0.44 0.31 0.96 0.36 0.54 1.30 1.41 1.20 1.27

0.01 0.01 0.02 0.01 0.01 0.01 0.02 0.01 0.08 0.00 0.00 0.02 0.03 0.01 0.10 0.01 0.01 0.02 0.02 0.05 0.02 0.02 0.02 0.01 0.01 0.01

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.01 0.00 0.01 0.00 0.02 0.01 0.00 0.01 0.01 0.02 0.00 0.01 0.00 0.00 0.01 0.00 0.02 0.00 0.01 0.04 0.02 0.01 1.47 0.02 0.01 0.01

0.02 0.02 0.03 0.02 0.03 0.02 0.02 0.02 0.07

Cu

Asphodelaceae Asphodelus

Asphodelaceae Asphodelus

Solanaceae Nicotiana

Solanaceae Nicotiana

Anarcardiaceae Schinus Agavaceae Yucca Cupressaceae Junipesus Cupressaceae Junipesus Myrthaceae Eucalyptus Myrthaceae Eucalyptus

0.02 0.04 0.02 0.02 0.09 0.03 0.02 0.02 0.03 0.04 0.02 0.03 0.03 0.04 0.03 0.02

Valley Plant name

Plant part

Sample no.

Cr

Mn

Fe

Co

Ni

Zygophyllaceae Larrea

Leaf Stem Leaf Stem

VP-1L VP-1S VP-2L VP-2S

– – – –

– – – –

– – – –

– – – –

– – – –

Cactaceae Opuntia

Manganese, copper and zinc show similar phytoavailability as antimony, suggesting that these elements follow an analogous cycle from the polluting source to the plant. Manganese, zinc and copper are natural micronutrients for plants and are used in fertilization processes (Ziaeian and Malakouti, 2001; Curtin et al., 2008). It is commonly believed that copper has little mobility in plants, so once it is taken up, it tends to accumulate in the roots, while manganese and zinc are easily transported up to the leafs (Kabata-Pendias and Pendias, 1992; Andrew and Thorne, 1962). However, in some plants like colza (Brassica napus) the concentration of copper in the leaf tissue may exceed the root content (Planquart et al., 1999) similarly to what we found in our analyzed plant species. The capability of the studied plants for fixing metals in similar amounts does not depend on the type of plant (trees vs. herbs), species, or the perennial vs. seasonal characteristics, as shown when comparing a tree as Myrthaceae Eucalyptus and a seasonal ground plant (Solanaceae Nicotiana). However, the phytoavailability ratio of some species, as Asphodelaceae Asphodelus, increases significantly with the humidity of the sediments where the plant grows. On the other hand, the plant metabolism seems to be an important factor controlling the phytoavailability. Thus, Agaveceae Yucca, characterized by a low metabolism shows low phytoavailability ratio compared with high metabolism plants as Myrthacea Eucalyptus, which present the highest phytoavailability ratio. Despite the homogenous chemical characteristics of the waste tailing, the studied plants show a different heavy metal concentration behavior following their taxonomy and metabolism. The presence of water in sediments (humidity) and fast metabolism seem to have a major effect on the metal concentration ratios, suggesting that the most important control of the sediments/plant system is not directly the metal concentration, but the metal solubility in soil, the ligand potential in the water phase and the transport to the plant.

0.24 0.34 0.18 0.10

Zn

As

Sb

Hg

Pb

0.63 0.82 0.47 0.59

0.05 0.06 0.03 0.01

0.01 0.01 0.01 0.00

– – – –

0.02 0.01 0.04 0.01

The importance of metal speciation is supported by the observation that the lowest phyto-accessibility rate was found in a sample having the highest antimony content (waste tailings). This low phytoaccessibility can be explained by the association of antimony to stable phases, as iron oxides and sulfide minerals (Tighe et al., 2005; Gal et al., 2007; Denys et al., 2008), a presence confirmed by DRX and petrographic analysis. The apparent low bioavailability of antimony in the studied case makes the environmental concern for the people living close to the Wadley mining district to be limited. Furthermore, Solanaceae Nicotiana is not part of the local sheep and goats' diet, which limits the metal accumulation in food chains. However, it is important to emphasize that the affinity of some metals (zinc, mercury, and arsenic) for the clay fraction and the semiarid environment of the district favors the dissemination of these metals eolically and should be taken into account in future studies. So harvesting at the end of each season must be performed with some precautions to limit the potential eolical dispersion. As observed for groundwater and plants outside the waste tailing samples, antimony, iron and zinc concentration in the geochemical background are high. 4. Conclusions This study presents original results in the giant Wadley antimony mine district regarding the antimony and heavy metals contents in soil, water and plants. It should be highlighted that this is the first study concerning the contents and behavior of antimony in soil, water and plants in Mexico reported in scientific papers. The results show that the dominant antimony phases in mining wastes are stibiconite and stibine. Groundwater and plants samples recollected in the waste tailing contain elevated antimony concentrations

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and are also contaminated with other metals, especially manganese, iron and zinc. These plants show significant lower contents in antimony, copper and nickel compared to the plants growing on the mine tailings. These metals main source is the regional Sb mineralization of The Sierra de Catorce, and have probably a common cycle between the polluting source, soil and plant. Metal concentrations were compared with quality guidelines values and they were exceeded sometimes for groundwater and plants and frequently for waste tailing. Eolic dissemination/contamination of finest particles seems to be the most challenging problems in the semi desert area (Castro-Larragoitia et al., 1997). Speciation analysis of water was performed providing information of phytoavailability of metal. Manganese, antimony, iron, zinc, and copper were found the most phytoavailable metals. The effect of this potential pollution was studied by evaluating the metal contents in 14 species of endemic plants in the mine tailing area (Bubblejacea Buddleja, Ruscaeae Dasylinin, Asteraceae Compositae Gymnosperna, Pinaceae Pinus, Asphodelaceae Asphodelus, Agaveceae Yucca, Anarcardiaceae Schinus, Solanaceae Nicotiana, Cupressaceae Junipesus, Myrthaceae Eucalyptus, Cactaceae Echinocactus, and Berberidaceae Berberis) in separated root, stem and leafs aliquots. High concentration of iron, zinc, manganese and antimony were found in all plants. High metals phytoavailability ratio in all type of plants i were determined only for Mn, Cu and Zn. Results indicate highest accumulation in seasonal and high metabolism plants recollected in wet soil. The metal phytoavailability in contaminated soils is highly dependent on the metal speciation in soil, its capacity to be transported in water, and more particularly the plant metabolism efficiency. Solanaceae Nicotiana seems the most effective plant to limit metal contamination. These plants combine a high metal accumulation ratio, with a fast growing and high grade of land cover. So, they not only fix the metals from the mine tailings but also limit the particles eolic dissemination. Acknowledgments Our deep thanks to Lic. José Cerrillo Chowell, General Director of Negociación Minera Santa María de La Paz y Anexas, S.A. de C.V. for the support received for the fulfilment of the present study, and for allowing its publication. This study has been supported by projects PAPIIT IN100707, IN114106, Conacyt 49234-F and 81584, and AECI (Agencia Española de Cooperación Internacional) A/4727/06. We greatly appreciate the comments and suggestions made anonymous reviewers that considerably helped to improve an earlier version. References Adriano DC. Trace elements in the terrestrial environment. New York: Springer; 1986. Ainsworth N, Cooke JA. Distribution of antimony in contaminated grass- land: 1- vegetation and soils. Environ Poll 1991;65:65–77. Ainsworth N, Cooke JA, Johnson MS. Distribution of antimony in contaminated grass land: 1. Vegetation and soils. Environ Pollut 1991;65:65–77. Anderson CWN, Brooks RR, Chiarucci A, LaCoste CJ, Leblanc M, Robinson BH, Simcock R, Stewart RB. Phytomining for nickel, thallium and gold. J Geochem Explor 1999;67: 407–15. Andrew CD, Thorne PM. Comparative responses to copper of some tropical and temperate legumes. Aust J Agr Res 1962;13:821–35. ATS DR (Agency for Toxic Substances, Diseases Registry). Toxicological profile for antimony and compounds. US Department of Health and Human Services; 1992. p. 1-36. Azizur Rahman M, Hasegawa H. Aquatic arsenic: phytoremediation using floating macrophytes. Chemosphere 2011;83(5):633–46. Baes CF, Mesmer RE. The Hydrolysis of Cations. 1976; Wiley. Barboza-Gudiño JR, Hoppe M, Gómez-Anguiano M, Martínez-Macías PR. Aportaciones para la interpretación estratigráfica y estructural de la porción noroccidental de la Sierra de Catorce, San Luis Potosí. Méx Rev Mex Cienc Geol 2004;21:299–319. Baroni F, Boscagli A, Protano G, Riccobono F. Antimony accumulation in Achillea ageratum, Plantago lanceolata and Silene vulgaris growing in an old Sb-mining area. Environ Pollut 2000;109:347–52. Bowen HJM. Environmental chemistry of the elements. Londres: Academic Press; 1979. 333 pp.

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