Utilisation des gastéropodes pulmonés terrestres comme traceurs de la pollution métallique des sols dans le bassin du Kebir Rhumel

Abstract

The world is now witnessing the 6th massive biodiversity extinction crisis, which result for the first time from human activities and the pollution they generate. The state of the soils of the Kebir Rhumel basin (North-East of Algeria) and its diversity do not escape this reality, particularly considering the multiplication of anthropic activities there and the worrying levels of metallic pollutants that they generate. This study is conducted with the aim of evaluating the environmental quality of these soils. Thus in 30 sampled stations; an inventory was established based on 6105 collected individuals of terrestrial gastropods from the wadis’ edges of the said basin. The identification revealed the presence of: Tudorella sulcata; Rumina decollata; Rumina saharica; Ferussacia carnea; Ferussacia folliculum; Mauronapaeus terverii; Mastus pupa; Cantareus koraegaelius; Cornu aspersum; Cornus sp. ; Eobania constantina; Eobania vermiculata; Helix melanostoma; Massylaea massylaea; Cernuella virgata; Cochlicella acuta; Cochlicella barbara; Trochoidea pyramidata; Xerosecta cespitum; Xerosecta sp. ; Ganula flava; Sphincterochila candidissima; Sphincterochila otthiana; Sphincterochila sp. and Caracollina lenticula. These 25 species belong to 17 genera and 09 families. In addition, their morphological characterization, lifestyle, distributions, and abundance have been reported. This also allowed us to select the species Cornu aspersum as a biological model for the early detection of metalic contamination. The study also concerns the physico-chemical characterization of the soils by determining their pH, electrical conductivity, total limestone, CEC, total nitrogen, organic matter, C/N ratio, as well as clay, silt and sand rates. Subsequently, we undertook a passive biomonitoring of contamination by analyzing the pseudo-total levels of Cd, Cr, Cu, Pb and Zn in the soils, in the pedal and visceral mass of juveniles and adults of C. aspersum to trace their mobility. The ETM’s mean levels in soils being: Cd= 0.44µg/g ±0.51, Cr 44.56µg/g ±25.54, Cu15.69µg/g ±6.9, Pb 33.28 µg/g ±26.62 and Zn 90.82µg/g ±28.21. The calculation of the mono and pluri-elementary indices proves contamination in several stations especially in the vicinity of large agglomerations as Constantine city. The most worry elements remain Cd, Pb and Zn. The results from snail tissues showed a concentration of Cd, Cr, Pb, and Zn in the viscera, unlike Cu which is concentrated in the pedal mass. The contents of the majority of ETMs are higher in juveniles except for Cu and Pb. The BAFs calculated confirm the metal accumulating potential of C. aspersum: Which are Cd and Cu’ macroconcentrators, Cr and Pb’ deconcentrators, and Zn’ micro to macroconcentrators depending on the zinc level in the environments. Finally, to confirm the potential of C. aspersum indicated early contamination and to identify the rates at which Cr, Cu, and Zn affect living organisms, we exposed juvenile C. aspersum through substrate contamination via sub-chronic ecotoxical-assays. The monitoring of these bioassays conducted under controlled conditions which permit us to calculate the growth coefficient (kGC) and the inhibition of growth (Ic), and shows a dose-response relationship to the growth in biomass, in diameter and in height of the shells. . EC50s that affect biomass, diameter and height calculated from soil concentrations are higher than those calculated from internal concentrations; therefore they are better indicators of the toxicity of these three metals.