Utilisation intégrée des escargots pour la surveillance de la contamination métallique des sols

Abstract

During the last century, Algeria experienced a period of rapid demographic, industrial, and agricultural expansion involving the irrational exploitation of many of its natural resources, and thus causing soil contamination and dysfunction. Among these contaminants that affect the soil: metallic trace elements, which are, ubiquitous, persistent in the environment, and extremely toxic at high levels. In order to monitor the metallic contamination of soils, and to assess their quality, this study is led. It consists of a mixed approach using terrestrial pulmonate gastropods, i.e., snails for bioindication purposes. Thus, five zones located in North-East Algeria, and characterized by relatively important anthropic activities (urban, industrial, mining, sub-mountainous and mountainous zones) are investigated. The studied TEs are Cd, Cr, Cu, Pb and Zn. The bioindicator snail studied is Cornu aspersum, and the studied vegetation is Drimia maritima. Firstly, the biodiversity and density of terrestrial gastropods are studied in these areas. We reported 3269 individuals, belonging to 19 species harvested during the spring and summer seasons. The density is more important in spring and the diversity is higher in summer. Then, the typology and the contents of TEs in the soils (pseudo-total and bioavailable fractions) is investigated. TEs are also quantified in the vegetation and, in the various parts of the snail C. apsersum (feet, viscera and shells). The mean TES concentrations of studied soils are: 3,04 µg.g-1 for Cd, 56,65 µg.g-1 for Cr, 30,87 µg.g-1 for Cu, 185,03 µg.g-1 for Pb and, 312,90 µg.g-1 for Zn. The most affected areas being the mining, industrial and urban areas. Single and integrated metal contamination indexes: Igeo, Cf, EF, Cd, PLI, and PERI confirm the soil contamination, especially with Cd, Pb and Zn. Mostly; the concentrations of TEs in snails were higher in the viscera than in the feet or the shells. Vegetation TEs concentrations did not generally exceed regulatory backgrounds. Bioconcentration factors calculated for C. aspersum confirm the importance of the digestive tract in the gastropod contamination process. Finally, the bioassays carried out under controlled conditions and implying the contamination of the substrate and the food with Pb on the juveniles of the species C. aspersum, show that there is a dose-response relation, which conditions the weight growth, but growth in diameter is not affected.