In order to determine the effect of vegetation on soil contamination by fallout of heavy metals (lead (Pb), nickel (Ni) and zinc (Zn)), ten sites were randomly selected, within a wooded zone in the vicinity of an iron steel industrial plant (El Hadjar, Algeria). On each site, average samples of soils were taken, on two plots, under two Mediterranean tree species (olive tree (Olea europea) and mastic tree (Pistacia lentiscus)) and between those, under naked ground, at two depths. Leaves of the same trees were also the object of average sampling. Pb, Ni and Zn were measured, by a flame atomic absorption spectrophotometer, in washed and unwashed leaves, and in total and soluble extracts of soils, which were also the object of organic matter (OM), pH and cation exchange capacity (CEC) analysis. Significant differences were noted between Pb, Ni and Zn washed leaves contents, and those of unwashed leaves, suggesting an atmospheric contamination source, apparently industrial. Pearson correlation coefficients indicate that total Pb and total Zn soil contents are significantly and positively related to pH and to OM, and that soluble Ni is significantly and negatively related to pH. Analyses of variance (ANOVA) reveals: station effect, for all the variables, except for CEC; species effect, for pH, OM, total Pb, total Zn and soluble Ni; depth effect only for OM; and Interactions between stations and species only for OM, total Pb and soluble Ni. The classification of averages by Scheffé's test shows that the differences between the stations are important only for Ni and pH. This result indicates that the studied area presents little heterogeneity, from the point of view of the majority of the studied variables. Significant differences between soils under vegetation and those under naked grounds have been found for total Pb, total Zn, soluble Ni, OM contents and pH. The differences are more important between the olive tree and naked ground than between the mastic tree and naked ground, especially for pH, total Zn and soluble Ni. The results show that vegetation, by its protective effect on the soil and by the rates of OM, would support retention of metal elements in the soil, thus decreasing their mobility and then their biodisponibility and their migration towards deeper layers of the soils and the groundwater, or laterally towards other zones, in particular to the surface water. It thus reduces the risk of transfer of heavy metals toward the human being and therefore its toxification. So, the existence of a natural vegetable cover, in areas presenting an atmospheric source of contamination by heavy metals, would thus have, in an indirect way, a protective effect not only on the environment but also on population health and thus on quality of life (QoL). In that case, the olive tree seems more efficient than the mastic tree. Copyright © 2004 John Wiley & Sons, Ltd.

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   |texte=   Statistical analysis of vegetation incidence on contamination of soils by heavy metals (Pb, Ni and Zn) in the vicinity of an iron steel industrial plant in Algeria
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