2. Materials and methods
2.1. Soil samples
The experiments were carried out for two soil samples among a
series of 15 samples for which the origin of natural contents of
trace metals results from geological evolution. These soil samples
belong to different soil series developed in various parent materials
under similar climatic conditions. They were collected on 0.3 m2
areas with a spade from the 0 to 25 cm surface-ploughed layer in
fields at 15 sites across the southern part of the Yonne district, Burgundy,
France. Two non-calcareous samples were chosen to avoid
the co-extraction effect of calcium cations due to the non-selective
nature of EDTA (Manouchehri et al., 2006). The co-extraction of Ca
results in important variation of EDTA concentration with time
rendering complex the kinetic simulation (cf. Paragraph 3.2). Some
soil characteristics are briefly described in Supplementary data
(SD1).
2.2. Kinetic protocols
2.2.1. Soil/EDTA/Chelex mixture
The kinetic study of metal transfer in Soil/EDTA/Chelex mixtures
was made with an initial volume of 100 mL of 0.002 M EDTA
solutions (pH = 6.5) in contact with 3 g of resin and 10 g of soil
sample in a polyethylene flask. The mixture was stirred using a
rotatory stirrer during the reaction time (300 min). At selected
time intervals, an aliquot of 0.5 mL of the mixture was removed
via a syringe and immediately filtered through a Millipore syringe
filter membrane. The filtrates were kept in the polyethylene microtubes
at 4 C until analysis of elements.