A B S T R A C TEarthworms increase the availability of heavy metals in some situations and aid in maintaining the structure and quality of soil. The introduction of earthworms into metal-contaminated soils has been suggested as an aid for phytoremediation processes. In Wallonia, Belgium, a century of industrial metallurgic activities has led to the substantial pollution of soils by heavy metals, including copper (Cu), zinc (Zn), lead (Pb) and cadmium (Cd), due to atmospheric dusts. Two plant species, Vicia faba and Zea mays, and earthworms (Eisenia fetida) (Savigny, 1826) were exposed to different concentrations of longterm-contaminated soils for 42 days. The soil samples, which were collected from the land surrounding a former Zn-Pb ore-treatment plant, exhibited different levels of heavy metals. Our aim was to evaluate the role of earthworms E. fetida on the availability of metals in soils and their effects on metal uptake by V. faba and Z. mays plants at different soil concentrations.The results suggest that earthworms and plants modified the availability of metals in contaminated soils after 42 days of exposure. Earthworm life-cycle parameters were affected by metal contamination and/or the addition of plants; cocoon production and weight were more responsive to adverse conditions than earthworm survival or weight change. The concentrations of Pb and Cd in earthworm tissues decreased in the presence of plants. Results showed that metal accumulation in plants depended on the metal element considered and the presence of earthworms. However, the presence of earthworms did not change the concentrations of metals in plants, except for Cd. In the presence or absence of earthworms, V. faba accumulated higher concentrations of Cu and Zn compared with Z. mays, which accumulated higher concentrations of Cd. These findings have revealed that earthworm activities can modify the availability of heavy metals for uptake by plants in contaminated soils. Moreover, the study results show that the ecological context of phytoremediation should be broadened by considering earthworm-plant-soil interaction, which influence both the health of the plant and the uptake of heavy metals by plants.

Historical soil contamination within a 3 km radius of a former ore treatment plant was evaluated. A total of 247 topsoil samples were collected in a stratified random sampling design taking into account three factors: land use (LU), soil type (ST) and wind direction (WD). Concentrations of trace elements (Cd, Co, Cr, Cu, Ni, Pb and Zn) and major elements (Ca, Mg, K, Fe, Al, Mn) as well as various soil properties (pH water , pH KCl , TOC and N) were measured. Total Cd, Pb and Zn concentrations were higher than typical background values. Enrichment factors for these three metals were, respectively, 260, 77.4 and 35.5. Principal component analysis (PCA) and factor analysis segregated anthropogenic contamination as a premier factor in influencing concentrations, followed by a second lithogenic factor. The anthropogenic origin of substantial contamination was confirmed through mapping of sample locations relative to contaminant sources. Factor 1 (26.5% of the variance) impacts a large area around the contaminated site and is also indicative of WD influence. Factor 2 (23.9% of the variance) is naturally linked to the local lithology and geology. LU and soil fertility are, respectively, represented by factor 3 (16.5% of the variance), which is linked to pH, and factor 4 (9.3% of the variance), related to organic content. The significance of landscape factors in the spatial distribution of metallic trace elements (MTE) was assessed with an ANCOVA using "distance to the source" as a covariate. Results of the analysis support the hypothesis that Cd, Cu, Pb and Zn concentrations are mainly driven by anthropogenic factors, specifically historical industrial activity at the former ore treatment plant. The ANCOVA also provides a means to quantify the impact of LU and ST as well, particularly on MTE availability in soils. The presence of MTE in soil poses known, and potentially significant, risks to both human health and the environment.

No abstract