Utilisation des arbres et des sols des bords de routes comme indicateurs de la pollution métallique

Abstract

The assessment of pollution intensity, through passive biomonitoring processes is a very efficient nvironmental technique used for several decades. Indeed, the use of organisms makes it possible to overcome encountered the difficulties during direct physico-chemical measurements, which are often very complex and expensive. In the region of Constantine, it is easy to see that we have a real pollution problem, on the one hand because of the existence of a large car fleet compared to the distances traveled and on the other hand certain climatic and topographical characteristics which create a favorable climate to the development of pollution. In this context, this study focused on the use interest of soils and trees (leaves and bark) as metal pollution indicators in urban areas. The concerned area is the national road N ° 03 linking the Constantine city center to Hamma Bouziane commune, in addition to a control zone which is remoted from any anthropogenic disturbance source (Arboretum of Draa Naga). In order to understand the objectives, three main axes were developed, namely: a pseudo-total and sequential contents quantification in metallic trace elements (HMS) in soils (0-20 cm and 20-40 cm), an abiotic or metallic stress evaluation via the assay of biochemical and HMS markers in 12 ligneous species leaves and bark that found, and also, the lead ecotoxicity assessment in some species via ecotoxicity tests. Our investigations related to the contamination level assessment by HMS were: cadmium (Cd), copper (Cu), manganese (Mn), lead (Pb) and zinc (Zn). Pseudo-total contents in HMS soils in both profiles record the following abundance order : Mn > Pb > Zn > Cu > Cd. Otherwise, the sequential contents study in soils allowed us to evaluate the HMS distribution in the different fractions and thus to highlight the anthropic contribution. Regarding to the revealing markers results of abiotic stress, it appears that the urban area trees have low chlorophyll levels, and high proline and soluble sugars levels compared to those in the control zone. The HMS quantification in leaves and bark recorded the following order of abundance: Mn > Zn > Pb > Cu > Cd. Trees turned out to be good metallic air pollution. The bioconcentration factor and the metal accumulation index confirmed the usefulness and effectiveness of these species in bioindication and / or phytoremediation For the ecotoxicity tests, the concentration that inhibits the 50% of seeds germination is 64.97 μg.L-1 for C. sempervirens and 110.43 μg.L-1 for P. halepensis. Lead seems to have a much greater toxic effect on seed germination of C. sempervirens than on P. halepensis.