Study of earthworm influence Lumbricus terrestris on soil solution complexation capacity

Four soil samples highly contaminated with metals of urban and mine origin (SE1, SE2, SM1, SM2) and having different physico-chemical proprieties were selected to study copper complexation capacity (LT) of soil solution The e ffect of Lumbricus terrestris on copper complexation capacity of soil solut ion was investigated on SE1 and SE2. The complexation capacity was estimate d by amperometric titration of soil solution by copper. Free hydrated catio n and labile complexes of copper were determined by DPASV. The results show that the copper complexation capacity variation depends on the physico-che mical caracteristics of soils, particulary pH. Thus, the values of copper c omplexation capacity are 0; 0.6x10(-7); 1.8x10(-7) and 5.5x10(-7) mol l(-1) respectively for SM2; SM1; SE1 and SE2 which are pH 5; 5.4; 6.5 and 7.4. B ased on these results, the bioavailability levels of heavy metals show the following pool ranking: ShM2 > SM1 > SE1 > SE2. The copper complexation cap acity of soil solution increases with the soil disturbance by Lumbricus ter restris. This is more obvious when the time of disturbance by lumbrics is l onger. Indeed, average values determined for 1 month and 3 months are 3.8x1 0(-7) and 7.8x10(-7) mol l(-1) for SE1; 7.7x10-7 and 15.2x10(-7)mol l(-1) f or SE2 respectively. It seems that the action of earthworm on soil can cont ribute to the decrease of bioavailability of heavy metals, particulary copp er.