Évaluation du risque de contamination des sédiments de l'oued Boumerzoug par les éléments traces métalliques sur la faune macroinvertébrée benthique et via la pertinence des bioindicateurs Spinacia oleracea (L.) et Physa acuta (D.).

Abstract

Our study is part of the deepening of our knowledge of a lotic ecosystem, the Boumerzeug wadi and its tributaries, which has been the subject of various complementary approaches to characterize its physico-chemical and biological quality The objective of this work is to assess the level of contamination of contamination of the abiotic and biotic compartments of the ecosystem by trace metals (TM) whose anthropogenic origin is added to the natural background levels. The samples were collected from 20 sites on five occasions spread over 15 months. Among the elements determined, some are essential to the physiological functions of organisms such as Cu, Cr, Ni, Ni, Zn, others are toxic such as Cd and Pb and finally Mn is a natural element without consequences on living beings. The TM measured in surface sediments follow the following sequence: MnZn > > Cu > Pb Ni>Co> Cd. The study of benthic macroinvertebrate fauna compartments highlights a faunal impoverishment following the disappearance of species sensitive to organic and/or metallic pollution, the method does not allow the nature of stress to be identified. The hydrobiological quality of the watercourse, expressed by the biotic index, reflects a situation of significant disturbance illustrated by the drop in values from upstream to downstream. The transfers of TM to the different parts, roots, leaves of Spinacia oleracea revealed that the chenopodiaceae concentrates and sequesters in its roots all TM except zinc, which has a higher content in the leaves. Thus, the roots seem to constitute a barrier that reduces the transfer of metal elements to the aerial part, while zinc, an essential metal, is translocated to the leaves. The hierarchy of average TM contents in spinach is as follows: Zn > Mn > Cu > Pb > Cr > Ni> Co>Cd. The transfer of TM to Physa or Physelle acuta lung gastropods in the various specimens, soft tissues and shells of P. acuta adults/juveniles) reflects the bioavailability of the element. The spatio-temporal data of TM contents in Physa acuta record the following order of abundance: MnZn > Cr> Cu > Ni>Pb > Co > Cd. All detected heavy metal concentrations were higher in soft tissue than in shell for adults and juveniles. There was a significant effect of the age (p < 0,001) on the concentrations of the eight metals, the adults of P. acut showing higher concentrations than juvenile. The biota-sediment accumulation factor (BSAF) of Cd in soft tissue was higher than 1, hence the usage of this species as a bio indicator for Cd pollution The present study provides data and information on the concentrations of 8 TM (Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn) in the sediments of the Boumerzoug wadi and its tributaries and their transfer to plant and animal. It will provide a database and knowledge base that could provide new information for any future biomonitoring study of freshwater aquatic ecosystems.