Vol. 32 – 2006 - Ecologia Mediterranea

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BOUAMAR BAGHDAD, MUSTAPHA NAIMI, ABDELHAK BOUABDLI, PHILIPPE SONNET, STANLEY LUTTS Table 1 – Lead, zinc and copper concentrations (mg kg-1 dry wt.) and pH in soil, two plant species (Artemisia herba-alba asso. and Stipa tenacissima L.) and piles of tailing surrounding abandoned mine land of Zaida. Tableau 1 – Niveaux de concentration (mg/kg matière sèche) en plomb, zinc et cuivre dans Stipa tenacissima L. et Artemisia herba alba asso, leur sol ou leur rejet minier correspondants et le pH du sol dans la mine abandonnée de Zaida. 88 Trace element mg/kg Stipa tenacissima Artemisia herba-alba Soil Plant Soil Plant Tailings Root Shoot Root Shoot Lead Mean 18.2 338.6 84.7 21.2 253.8 129.0 1872.9 Minimum 3.0 6.4 2.8 8.8 3.4 3.9 224.2 Maximum 63.2 1214.3 193.2 63.2 704.0 660.0 2778.5 Zinc Mean 50.7 41.5 18.5 63.4 32.1 16.9 91.1 Minimum 34.7 13.4 10.6 34.7 5.4 5.3 84.7 Maximum 70.9 93.4 38.9 84.6 133.9 26.4 98.4 Copper Mean 25.6 23.2 9.3 28.2 18.0 9.3 47.7 Minimum 11.4 7.4 21.9 21.9 6.7 4.3 29.4 Maximum 41.8 58.4 41.8 41.8 56.2 15.3 56.2 pH Minimum 7.9 7.5 7.7 Maximum 8.6 8.7 8.0 In contrast to lead, concentration of zinc and copper was of the same order of magnitude in tailings on the one hand and at the sites where plants were harvested on the other hand. Zinc concentration in tailings was also more homogenous than lead since minimal and maximal values only differed by a factor of 10%. Both species accumulated zinc to a comparable extent and a similar trend was recorded for copper. It has been noticed that concentrations of heavy metals in the tissues of the studied species were high but that all harvested plants clearly remained alive at the time of harvest. All recorded pH values were close to 7.0 or even slightly alkaline. No significant difference was recorded among the soils colonized by A. herba-alba and by S. tenacissima. Table 2 – Lead, zinc and copper concentrations (mg/kg dry wt.) in Stipa and Artemisia roots and stems function of increased distance from the tailing in abandoned mine land of Zaida. Tableau 2 – Concentration en plomb, zinc et cuivre (mg/kg matière sèche) dans Stipa tenacissima (S1 à S3 ) et Artemisia herba alba (A1 à A4 ) (racine et tige) en fonction de leur éloignement des rejets miniers. Trace element (mg kg -1 dry weight) Cu Zn Pb Artemisia herba-alba Nearby the tailing (A 1 ) Root 15.6 22.0 87.7 Shoot 9.0 11.1 148.9 50 m away from the tailing (A 2 ) Root 14.9 23.4 508.8 Shoot 15.3 26.4 660.0 200 m away from the tailing and downstream of quarry (A 3 ) Root 56.2 133.9 704.7 Shoot 9.2 7.7 89.4 1000 m away from the tailing (A 4 ) Root 12.2 10.6 5.5 Shoot 6.1 5.3 3.9 Stipa tenacissima Near by the tailing (S 1 ) Root 10.9 13.4 124.9 Shoot 11.9 38.9 168.7 50 m away from the tailing (S 2 ) Root 58.4 93.4 1214.3 NB: Both species exist nearby and at 50 m away from the tailing. Beyond 50 m, only Artemisia dominates. ecologia mediterranea – Vol. 32 – 2006
A. herba-alba and S. tenacissima do not colonize the tailings themselves which remain thus as nude surfaces exposed to wind erosion despite the presence of a few individuals of Silybum marianum (L.) Gaertner. Concentrations of Cu, Zn and Pb in A. herba-alba and S. tenacissima roots and stems for four plant samples collected at these distances (50 m, 200 m and 1000 m) from the tailings are given in Table 2. It has to be mentioned that for both species and for the three considered elements, maximal concentration in the plant tissues were not recorded nearby the tailings but 50 to 200 m away from them. This is especially the case when considering the root concentration. No individual belonging to S. tenacissima was found 200 m away from the tailing and data are thus given for A. herba-alba only. When plant samples were collected 1 km away from those tailings, they contained only small amounts of heavy metals. Not only the absolute concentration, but also the shoot/root ratio of concentrations in studied plants strongly varied as a function of the distance to the tailings. This ratio remained very low when the plants exhibited the highest concentration (50 m from the tailings for S. tenacissima and 200 m away from the tailing for A. herba-alba). We were thus unable to establish a clear correlation between heavy metal concentrations in roots and stems because of a high variability. Discussion The levels of contamination around the mining site of Zaida appeared heterogeneous, although the importance of heterogeneity depends on the type of considered heavy metal: maximal values for lead, zinc and copper (Table 2) were recorded for the tailings. Values recorded for Pb clearly exceeded the threshold level of 400 mg Kg-1 considered as the maximal values in soils; in most of the European legislation, agronomic soils should not contain more than 70 mg Kg-1 of total lead (Treme-Schaub & Feix 2006). To be able to interpret these higher contents of MTE in soils, it’s important to distinguish between potential contaminations and natural weathering (Baize 1997). The fact that total heavy metal concentration at the tailing level ecologia mediterranea – Vol. 32 – 2006 Heavy Metals in Tailings,Soils and Vegetation of an Abandoned Lead Mine Land in Morocco was high does not imply that all the quantified metal is available for plant absorption. This is especially the case for lead, which is commonly considered as an element exhibiting a low bioavailability (Alloway 1990). Soil acidity may strongly increase lead availability in contaminated areas: in general terms, heavy metals are available to plants in small amounts when the environmental conditions are alkaline (Hesse 1971). In the present case, however, soil remains neutral or slightly alkaline (7.5 to 8.7) and acidity therefore should not be a major problem increasing lead availability. On the other hand, soil consists in a sandy substrate typical of semi-arid steppe and thus exhibits a very low level of organic matter susceptible to retain lead. In the present study, very high levels of Pb, Zn and Cu have been observed in both tested tissues. The data appeared quite surprising for lead: although those plants were never reported as lead hyperaccumulators, it is noteworthy that the analyzed plants always accumulated this element to higher concentration than the surrounding substrate (Table 1). Only few plants were reported to be able to accumulate lead (Reeves & Baker 2000). Since the presence of lead constitutes a characteristic of numerous mining areas throughout the world, the opportunity to use these two plant species to help in soil decontamination should be considered in the future. Lead contents of A. herba-alba and S. tenacissima colonizing areas near the tailings were higher than normal (Kabata & Pendias 1992). This might suggest some kind of tolerance mechanism of plants as they grow normally and survive in spite of higher lead concentrations in soils (Steinborn & Breen 1999). Copper concentrations levels in plants were also higher as compared to soils and tailings. This implies that both species display unusual abilities to extract, accumulate and tolerate these heavy metals, even if the registered concentration remains lower than in classical hyperaccumulating plants (Fleming & Parle 1977; Türkan et al. 1995). It is also noteworthy that the highest heavy metal concentration was found in plants growing at 50-200 m of the tailings and not nearby the tailings. It may be hypothesized that hot spots of contaminations were also present, not only on the tailing themselves, but also in the surrounding area. Wind erosion may have occurred and transport contaminated particle over a given distance: nevertheless, the fact 89
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ecologia mediterranea Revue interna
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Pr Thierry DUTOIT Éditeur en chef
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AMAR MADOUI, JEAN-MARIE GEHU, DJAME
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Écologie trophique de la Cigogne b
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zones of the steppe range play a pi
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10%); and (iii) barren steppe (B-st
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occur from small subpopulations rat
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Page 94 and 95: Résumés de thèses Catherine BRET
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