Heavy Metal Contamination of Soils and Water Resources Kettara Abandoned Mine

Problem statement: Metal mining; together with mineral smelting and pr ocessing, have contaminated the environment surrounding mine areas throughout the world exceeding natural background concentration. Approach: These processes introduce metal contaminants into t he environment through gaseous and particulate emissio n , waste liquids and solid wastes. The principal objective of this study was to investigate soil and water contamination in the vicinity of the kettara abandoned mine located in the South of Morocco. Results: High total concentrations of heavy metals were found in both tailings and soil samples. Furth ermore in the tailings the maximum concentrations of the mobile fraction of metals were 76, 80 and 79 mg kg of Cu, Pb and Zn, respectively, for the soil samples the maximum concentrations values were 68, 52 and 26 mg kg −1 of Cu, Pb and Zn, respectively. As a result of dispersion of the meta ls downstream and downslope, soils contained higher metal concentrations than those from nearby control sites (P<0.05). This may be due to surface runoff and strong wind action which caused the movement of mine waste material. The chemical properties of tailings were characterized by very low pH and h igh levels of EC. Furthermore, in the wet season the water from kettara mine contained elevated leve ls of Cu, Pb, Zn and SO 4 . Conclusion/Recommendations: According to this study, the agricultural activity n the vicinity of the kettara mine requires careful consideration. Recult ivation of the tailings and the remediation of surf ace water and soil are recommended.


INTRODUCTION
Mining is one of the most important sources of heavy metals in the environment. Mining and milling operation together with grinding, concentrating ores and disposal of tailings, along with mine and mill waste water, provides obvious sources of contamination. Heavy metal contamination has been one of the serious problems in the vicinity of abandoned mine sites. These heavy metals have a potential to contaminate soil and water. They can be dispersed and accumulated in plants and animals and taken in by human beings as a consumer. Human health risk assessment has been used to determine if exposure to a chemical, at any dose, could cause an increase in the incidence of adverse effects to human health (Fuge et al., 1989) Mining and milling/beneficiation processes (crushing, grinding, washing,) generate four major categories of waste, i.e. (i) Mine waste (low-grade ore, overburden and barren rocks), (ii) Tailings, (iii) Dump heap leach and (iv) Acid mine water. These wastes are disposed in surrounding land and water in more or less environmentally acceptable manner.
Therefore, large areas of agricultural land can be contaminated. Morocco, for example, has a long history of metalliferous mining and the most extensive activities occurred during the early twentieth century. As a result, over 1000 metalliferous mines were distributed along mineralized zones; most of the mines were abandoned mainly due to economic reasons. Upon closure of the mines, mine waste materials, including tailings with elevated levels of toxic elements including As, Cd, Cu, Pb and Zn, were left without full environmental treatment. Thus, soils, plants, waters and sediments in the vicinity of the mines have been contaminated by potentially toxic elements from tailings by clastic movement through wind and water. The principal objective of this study was to investigate soil and water contamination in the vicinity of the abandoned kettara mine located in the South of Morocco.

MATERIALS AND METHODS
Description of the area: The studied mine are located 30km northwest of Marrakech in the core of the central Jebilet Mountains (Southern Morocco) Fig. 1 Hakkou et al., 2008). The Kettara mine produced more than 5.2 Million tons (Mt) of pyrrhotite from 1964-1981and was closed in 1982(Hakkou et al., 2008. During the exploitation, more than 3 Mt of mine wastes were stockpiled over an area of 16ha without concern for environmental issues. The ore contains minerals such as pyrrhotite, sphalerite, galena, chalcopyrite, pyrite, arsenopyrite and glaucodot. The mine was exploited for Cu, Fe and S. The large quantities of waste materials, including tailings, have been left untreated. Thus; these materials have been dispersed downslope both by surface erosion and wind action and by effluent draining the wastes into lower lying land used for growth of paddy rice and household garden crops. Soils and tailings analysis: The samples of soil were taken from the upper 20 cm after removing the first layer of surface soil 2 cm within an area of 100 cm 2 per sample. Additionally 3 representative background samples, namely T1-T3, were collected 1 km far away from the mining site Fig. 2. Each soil sample comprised a composite of 9 subsamples. 4 Tailing samples were also collected as undisturbed core, by using a specially designed cylindrical stainless steel corer. Soon after collection, the soil and tailing samples were carefully transferred to clean and dry self-sealing polyethylene bags for transport to laboratory. After being air-dried in paper lined propylene trays at room temperature and disaggregated with a wooden roller, all samples were sieved through 2 mm sieve. The tailing samples were thoroughly mixed and homogenized by coning and quartering, finally the soil and tailing samples were stored in tightly sealed polyethylene bags until further analysis. The Physicochemical significant parameters of the soil and the Tailing samples such as pH values, Electrical Conductivity values (EC), Organic Matter (OM) and carbonate content were determined following the standard analytical methods (Aubert, 1978). Total heavy metal concentration in soil and tailing samples was determined after digestion of the samples with microwave assistance. 0.5 g dry sample (100 mesh) was weighted in a PTFE digestion vessel and 3 mL HNO3 (70%), 6 mL HCL (37%) and 3 mL HF (48%) were added. The digestion vessel was placed in the chamber of the microwave system (CEM MARS 5, Matthews, USA). After digestion, the sample solution was allowed to aircool and then diluted with deionized water to 50 mL.
Mobility assays were performed by applying the established methodology (Perez et al., 2008) consisting on sample extraction with HCl 0, 5 M at 1:5 ratio during 1h under magnetic stirring. After each extraction, the suspension was centrifuged and the supernatant was separated by filtering with 0.22 µm filter (Millex GS, Millipore and Ireland). The concentrations of Zn, Cu and Pb after total acid digestion and the resultant solutions of Mobility assays were determined by an Inductively Coupled Plasma Mass Spectrometer (Thermo Scientific XSERIES 2 ICP-MS). The isotopes 65 Cu, 66 Zn, 111 Cd and the sum of 206 Pb+ 207 Pb+ 208 Pb were selected for the Determination of the elements of interest. 72 Ge, 115 In and 209 Bi (each 100 µGL −1 ) were added to both the calibrated and sample solutions as internal standards to monitor and compensate for possible instrumental drift and matrix effects. Each experiment was conducted in triplicate and the results reported were the average values.
Waters analysis: Water samples were taken in and around the mine both in (dry and wet season) Fig. 2. The samples were filtered through 0.45 mm Millipre membrane filter .The pH; Total Dissolved Solid (TDS), Electric Conductivity (EC) and temperature of the samples were measured using a portable pH-TDS-EC meter. After acidification with concentrated nitric acid, the samples were stored in a cool box before chemical analysis. For anion determination, the filtered waters were directly stored in a cool box without acidification. Cu, Pb and Zn concentrations in acidified waters were determined by ICP-MS and the concentrations of HCO3 -, NO3and SO4 2in non-acidified waters were measured by Ion Chromatography (IC).

RESULTS AND DISCUSSION
Physical-Chemical properties of the soil and the Tailings samples: The results obtained for pH, Electrical Conductivity (EC), Carbonate Content (CaCo3), organic matter and total metal concentration for the soil and Tailings Samples are summarized in Table 1.
The results obtained revealed that, in general, all samples of tailings have a very acidic pH ranged from 1.9-2.8 this low pH may be due to the weathering of sulfide minerals (pyrite (FeS2) and pyrrhotite (FeS) which join other metal sulfides: chalcopyrite (CuFeS2), glaucodot), galena and sphalerite have been observed but in very small proportions; a high electrical conductivity from 3000-3700 which means a high salt content, Organic matter content was mainly lower than 0.7% and a low concentration of carbonates (lower than 0.8%,) indicating that the nature of these tailings is not calcareous Table 1. In general, the 30 soil samples featured widely different soil properties. The Organic matter content was mainly lower than 3 % and ranged from 0.60 to 2.90%. The presence of a vegetation cover in some parts of the mining area, could explain the high values of OM content in some samples of soil.
The pH values showed a very broad interval, from alkaline soils to soils close to strong acidity: points located near the both tailing reservoirs R1 and R2 present a very acidic pH (2.30-5.10) compared to the reference samples with basic pH (pH = 8.12), the others sampling points have a basic pH very close to the reference sample .
The acidic pH is related to the phenomenon of oxidation of metal sulphides and iron sulphides such as pyrite and pyrrhotite in the tailings , Metal sulfides, especially Pyrites, can be oxidized easily under natural weathering conditions, resulting in large quantities of AMD generated and transferred into the surrounding environment through atmospheric dispersion and through the flow of water and release of metals from the ore and tailings because of the low acidity and high salinity of percolating solutions. This was one of the most important sources of heavy metals in the environment surrounding the mine.
The study area Promoted by a topography which causes a flow from north to south of the mine, the alkaline pH of soils in northern part (Tailing 3) of the mine can be explained by the intervention of topographical factors, because the Tailings reservoir is located at a higher level compared with samples of soils, which meant that theses soils does not undergo the same changes on the pH. The majority of samples taken around the tailing 1 and tailing 2 (tailing reservoir R1 and R2) present a high electric conductivity in comparison to the reference samples (60 µs cm −1 ). The electric conductivity in the nearest sites of R1 and R2 is ranged between 670-2370 µs cm −1 Table 1. For the northern part (around the tailing reservoir R3) the electric conductivity is ranged between 520-1700 µs cm −1 . It is observed to have a decreasing salinity gradient from the mining site to the far away points (S8, S16, S17, S19, S24, S25, S26, S27, S28, S29 and S30). The carbonate content mean Range is between 0.60-2.9%, the majority of the samples have carbonate content similar to those found in reference samples (2.80%).
Total metal concentrations were classified based on the background levels for sandy soils (Kabata-Pendias and Pendias, 2001) and the upper values established by European Directive 86/278/EEC (86/278/EEC, 1986) for the addition of sludge as amendment to agricultural soils, the maximum allowable concentrations of heavy metals Cu, Zn and for agricultural soils is 140,300 and300 mg.kg −1 respectively. The Tailings contained mostly Cu, Zn and Pb Table 1, the mean concentrations of Cu, Zn and Pb in tailing 1 (n = 4) were 1518, 610 and 530 mg.kg _1 , in tailings 2 (n = 4) 1248, 510 and 400 mg.kg _1 and in tailings 3 (n = 4) 780, 330 and 100 mg.kg −1 respectively. The metal concentrations in the tailings exceeded the European standards (Usero et al., 2000;Hakkou et al., 2006) for Cu, Zn and Pb in the tailing 1, in the tailing 2 and for Cu, Zn in the tailing 3.
According to the European standards (Kabata-Pendias and Pendias, 2001;86/278/EEC, 1986) the majority of the soil samples located at the far away points of each reservoir of tailings (R, R2 and R3) showing values considered as background or tolerable levels for Cu, Zn and Pb. The soil samples taken around the area covered by mine tailing1 and tailings2 (S1, S2, S3, S5, S6, S7, S9, S10, S11, S13, S14 and S15) showed the highest values for all the metals, the maximum concentrations of heavy metals in soils around the tailing 2 were 1347, 406 and 349 mg kg −1 of Cu, Zn and Pb, respectively, around the tailing 1 the maximum values of heavy metals were 772, 328 and 310 mg kg _1 of Cu, Zn and Pb, respectively Table 1.
According to the European standards (Kabata-Pendias and Pendias, 2001;86/278/EEC, 1986) the majority of the soil samples located around the tailing 1 and tailing 2 were classified into much polluted levels and exceed the maximum allowable concentrations of heavy metals Cu, Zn and Pb for agricultural soils.

Contamination Factor (CF):
The CF is the ratio obtained by dividing the concentration of each metal in the soil by the baseline or background value (Eq. 1) (concentration in unpolluted soil) The contamination levels may be classified based on their intensities on a scale ranging from 1-6 (0 = none, 1 = none to medium, 2 = moderate, 3 = moderately to strong, 4 = strongly polluted, 5 = strong to very strong, 6 = very strong) (Muller, 1969).

Pollution Load Index (PLI):
For the entire sampling site, PLI has been determined by the calculation of the product of the n CF (Eq. 2) (Usero et al., 2000) where, n is the number of metals (n = 3 in this study) index provides a simple, comparative means for assessing the level of heavy metal pollution.
The Pollution Load Index (PLI) calculated from CF shows that the soils are moderately to heavily contaminate by investigated heavy metals Table 2.
The sampling Sites located around the tailings (S14, S9, S3, S5, S15, S1and S2), shows the highest PLI more than 7 within the sampling Sites S4,S6, S7, S16, S12, S20 and S23) and the rest of the area is low to moderately polluted. Statistical analysis of the total metal concentrations showed a high significant correlation between metals in all the sampling points (P<0.05). This fact suggests the common origin of all the metals analyzed and, therefore, the mining activity can be pointed out as the source for the metal pollution of the studied area The agricultural soils that are irrigated by mine drainage water contain very high levels of potentially toxic trace elements, although the total contents vary considerably depending on the location of the samples Table 1.
Two reasons may be suggested to explain the scattering of the metals from the mine area. Firstly, the physicochemical properties of the Kettara mine tailings Table 1, i.e., high heavy metal concentrations, low pH, low carbonates content, nature of the deposit: mine tailings contain sulfides which react with oxygen, generating a stream of acid water that also contains dissolved heavy metals and other minerals that can be transported to the mine surroundings by means of acidic drainage, aided by a topography which causes a flow from north to South of the mine. Secondly, wind transport of dust may be another important factor influencing the spreading of pollution. Previous study in the same site (Hakkou et al., 2006) showed that runoff have an acidic pH (<3). This acidity favors the attack of the mineral content in discharges and release of contaminants in solution. According to these authors, this runoff is highly sulfated and has a very high salinity, resulting in a very high conductivity (Hakkou et al., 2006) Production of Acid Mine Drainage (AMD) in addition to decreasing pH, inevitably the leaching of various metals and high concentrations of sulfates (Hakkou et al., 2006). In the reference area, however, the average concentrations of the metals are close to the world average of 30, 35 and 90 mg kg −1 of Cu, Pb and Zn, respectively, reported by (Bowen, 1979). There is a statistically significant difference between metal concentrations in the contaminated and reference soils (P<0.05).

Mobility of Cu, Pb and Zn in soil:
Once detected the most polluted samples of soil, a real evaluation of their potential risk can be obtained from the results of metals mobility, by using the single extraction procedure, the concentrations of heavy metals in soils extracted by the HCl 0, 5 M solution are shown in Table 3.    Type  Total  Mobile Total Mobile Total Mobile  Tailing1  1518  76  610  49  530  80  Tailing 2  1248  62  510  41  400  60  Tailing3  780  39  230  18  100  15  S 1  355  18  168  13  130  20  S2  567  28  125  10  146  The maximum concentrations of the metals were found in the tailings sites (R1-R3) Fig. 2 with up to 76-soil samples the maximum concentrations of mobile fraction were found in the soil around the tailings (R1-R3) with were 68-32 and 52 mg kg −1 of Cu, Pb and Zn, respectively, this Mobility assays indicates also that the mobile fraction present about 15% of Zn, 10% of Pb and 5% of Cu in the soil samples; this indicated that the mobility Zn and Pb was high than that of Cu and we know that the bioavailability and eco-toxicity of metals mainly depends on their speciation in soil.
However, were relatively low in a nearby control area with, the results indicate that there is a statistical difference between average metal concentrations in the contaminated and reference soils (P<0.05).
In general Heavy metals in soil are distributed in 4 fractions: the mobile fraction, the reducible fraction, the oxidizable fraction and the residual fraction, the mobile fraction and the reducible fraction are readily to be absorbed in plants or in water system causing pollution. So, these fractions should be identified as direct effect fraction. Because the all the soil samples analyzed for Mobility assays are acidic and located in AMD area, the soil has highly oxidizing property.
The oxidizable fraction in this oxidizing condition is easily mobilized and transformed into mobile fraction or reducible fraction, potential of that eco-toxicity should not be ignored. So, the oxidizable fraction can be identified as potential effect fraction.
The heavy metal bound to residual fraction is often considered "unreactive" and not affected by environment changes, is identified as stable fraction. Therefore, it could be inferred that the potential environmental impact of heavy metals in soils was related not only to their total concentrations and chemical forms, but also could increase with time depending of pH, EC and the content of organic matter.

The chemical properties and concentrations of Cu, Pb and Zn in water samples:
The chemical properties and the concentrations of Cu, Pb and Zn in water waters are shown in Table 4. The pH values was found being lower in mine waters (W1-W3) located nearest the tailings (R1-R3) the pH values were ranged from 2.60-5 for waters taken in dry season and from 2.20-4.10 in wet season, the pH in waters samples (W4-W6), located to the far away points of the tailings was higher than 7.12.
The relatively low water pH of mine waters may be due to the dissolution and decomposition of sulfide minerals including pyrite in mine waste dumps tailings. Total Dissolved Solid (TDS) give information on the total cations and anions in waters. Because effluent draining the mine wastes contained elevated levels of those ions, the maximum TDS of water samples in the effluent was 980 m L −1 sampled in the dry season and 1185 m L −1 sampled in the wet season, Electric Conductivity (EC) is positively correlated with TDS. The highest EC was found in effluent draining from the mine wastes with 2700 µS cm −1 sampled in dry season and 3280 µS cm −1 sampled in wet season. TDS, EC and concentrations of metals in waters decreased with distance from the tailings.
In general, metal concentrations in natural waters are very low due to their low solubility in the aquatic environment. According to (Bowen, 1979), fresh water contains 3.0, 3.0 and 15 m/L of Cu, Pb and Zn, respectively. However, tens to hundreds of times these concentrations of the metals can be found in waters contaminated by various sources (Fergusson, 1990). The concentrations of Cu, Pb and Zn in water samples are also shown in Table 3. High concentrations of heavy metals were found in mine waters taken in the wet season, with maximum contents of 1.90, 4.15 and 33.00 m L −1 of Cu, Pb and Zn, respectively. These concentrations may be derived from interaction of rain with tailings containing elevated levels of these metals. Heavy metals from acidic tailings with sulfide minerals can be extracted by large amounts of rain, especially in the wet season.
Thus, they can be continuously discharged downstream and decreased exponentially with distance from the mine.
The dispersion patterns of these metals varied depending upon their solubility and mobility in the aquatic environment. In general, Zn with higher mobility can be widely dispersed downstream and Cu and Pb with lower solubility can be dispersed only to the area adjacent to the tailings.

Anion concentrations in waters samples:
The concentrations of HCO3 -, NO3and SO4 2in water samples are shown in Table 5: All the samples contained less than 45 mg l of bicarbonates, High concentrations of SO4 2-, over 1000 mg/L, were also found in the waters sampled in both the dry and wet seasons (waters around the tailings). These levels are likely to be due to the oxidation and dissolution of sulfide minerals in tailings. However, the concentrations of NO3 in all the water samples were relatively low.

CONCLUSION
The principal objective of this study was to investigate soil and water contamination in the vicinity of the abandoned kettara mine located in the South of Morocco. This investigation was based firstly on the determination of total concentration of several heavy metals (Pb, Zn, Cu) in both soil and water (dry season and wet season) by ICP-MS, secondly on the determination Mobility of Pb, Zn and Cu in the most polluted soil and tailings samples by using the single extraction procedure with solution of HCl 0, 5 M), finally on the determination of some anions (HCO3-, NO3-, SO4 2 -) in water taken in and around the mine both in dry season and wet season by Ion Chromatography (IC). In this study of an area around the abandoned kettara mine, soils and waters have been contaminated by past mining activity. High concentrations of heavy metals extracted by acid digestion were found in tailings with maximum values Cu (1500 mg.kg −1 ), Pb (510 mg.kg −1 ) and Zn (650 mg.kg −1 ). A high total concentration of heavy metals was also found in soil samples with maximum values, Cu (1347 mg.kg −1 ), Pb (349 mg.kg −1 ) and Zn (406 mg.kg −1 ).
Furthermore in the tailings the maximum concentrations of the mobile fraction of metals determined by extraction in 0.5N HCl were 76 , 80 and 79 mg.kg −1 of Cu, Pb and Zn, respectively, for the soil samples the maximum concentrations values were 68, 52 and 26 mg.kg −1 of Cu, Pb and Zn, respectively, this Mobility assays indicates also that the mobile fraction present about 15% of Zn, 10% of Pb and 5% of Cu in the soil samples; this indicated that the mobility Zn and Pb was high than that of Cu .
Pollution Load Indices (PLIs) derived from contamination factors show that all sampling points around the tailings reservoir area exceed unity and may be considered as highly polluted sites. Lower values for pH and higher levels of TDS and EC are found in waters sampled immediately downstream of effluents passing through tailings. Furthermore, high levels of heavy metals are found in the water. Thus, it can be understood that the main source of heavy metals in waters is the tailings containing elevated levels of the metals. In addition, over 1000 mg L −1 of SO4 2is also found in the effluents, mainly due to leaching and oxidizing of sulfide minerals including pyrite, arsenopyrite, galena and sphalerite in tailings. Like dispersion patterns of soils, heavy metal concentrations in waters exponentially decreased with increasing distance from the tailings and they reach background levels at 1 km downstream. Tailing dumps have mainly a local impact and it is most likely that the activity of wind does not contribute significantly to contamination of surroundings. The higher heavy metal content in close proximity to the tailings is likely due to leaching and surface runoff.
The latter is a consequence of an inadequate deposition of the waste material .Shows the fate and impact of the tailing dump. The leachate of the tailing dump may contaminate the soil and groundwater. Surface runoff increases the heavy metal content of top soil, surface water and indirectly, the tissues of plants.
All these elements are receiving environment surrounding the mine abandoned Kettara, an area with a high risk of metal pollution that can affect water, soil, fauna, flora and undoubtedly human health of the area nearest and around the mine of kettara. Hence the importance of providing substantial efforts to develop methods of restoration and remediation cost-effective.