Résumé:
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.
