Evaluation et comportement des métaux lourds(Cd-Cr-Cu-Ni-Pb-Zn- et Mn) dans les sols à vocation agricole et à végétation naturelle soumis à une pollution atmosphérique.(El-Hadjar-Annaba-Est algerien).Influence de la végétation sur la dynamique de ces MÉTAUX

Abstract

The objective of this survey consists of assessing the impairment due to the atmospheric dismissals loaded with heavy metals coming from El-Hadjar (Annaba- East of Algeria) metallurgical complex, either on soils aimed at agriculture or on natural vegetation. To set off the metals content into the soil and vegetation, and thus to prove the obvious existence of a qualitative impairment of the soil, we have opted the method of chemical extraction of the heavy metals. Four extractions have been used:  An extraction with pure water (extract 1/5, soluble contents);  An extraction with a neutral salt, NaNO3 0.1M (exchangeable contents);  An extraction with HNO3.2M (total contents);  An extraction with H2SO4-HNO3-H2O2 (heavy metal in vegetation). The Cd, Cr, Cu, Ni, Pb, Zn and Mn are the seven metals selected in this survey and measured out of atomic absorption spectrometry (SAAF-100A) provided with a BGCD2 correction in the soils of six parcels on two levels: on the surface (0-5 and 0-20cm) and in depth (5-10 and 20-40cm) and in six plants species: meadow grss, mastic tree (Pistacia lentiscus); olive tree (Olea europea) and tomato (Lycopersicum esculatum) situated north of factory; broad bean (Viciafaba Minor); melon (cucumis melo) and wheat (Triticum durum), situated south of the factory. Beside an analysis of the heavy metals, a physico chemical characterization of the soils of the six parcels has also been done, which concerned: the pH, the contents in organic matter, in limestone, in clay, sand and silt and in the CEC. The gotten results showed that the parcels in the north area are characterized by a sandy texture (Mastic tree- olive tree) to a limono-sandy (meadow) and silty- clayey (Tomato) from slightly acidic pH to neuter, a relatively low to average CEC and an absence of total limestone (except for tomato vegetation in depth). The parcels in the south area are characterized by a clayey texture (Melon and broad bean parcels) too very clayey texture (Wheat parcel) from neutral pH to slightly alkaly, a high CEC and presence of low contents in total limestone. Has for contents made of heavy metals in soils: Cd and total and exchangeable Cr have not been detected. It is the same for the exchangeable contents in Cu and Pb. Concerning total contents, the recorded values taken into consideration, except for lead, where this standard has been exceeded in some parts of the ‘’Meadow- Tomato and Melon’’ parcels. As for the exchangeable contents, only Ni and Zn have been detected in all the parcels. The recorded values are truly superior to the norms, and thus, generating an established contamination. The exchangeable Pb has been detected only in a part of the ‘’Meadow’’ parcel. These results have been also the subject of a statistical treatment. The analysis proved the evidence of a strong variability of the total and exchangeable contents on a same parcel and among the parcels, dragging a dissymmetry made of heavy metals contents in the plants. Four elements have been detected on the whole of the analyzed plants (Cu, Ni, Pb and Zn), the recorded values (excepted Zn) are truly superior to the norms, especially at the level of the ‘’Broad bean’’ and the ‘’Meadow’’ (two plants aimed at feeding animals). On the environmental side, the danger doesn’t seem very high as regard to the total contents. However the exchangeable contents attest of a proved contamination of soils and plants. If the risk of pollution appears negligeable or rather unrecognized (for us) concerning the investigation by the livestock (a veterinary control is imperative), the major risk concerns the pollution of the underground waters and the waterways exposed to the streaming down from the northern parcels, characterized by light, filter-ring and little evolved soils and exposed also to the washing and lixiviation of metals by specific nature of the ‘’Vertisols’’ characterizing the cultivated parcels of the south area.