Mobility and bioaccessibility of trace metals in soils assessed by conventional extraction procedures and passive diffusive samplers

Our objective was to verify the use of the diffusive gradient in thin films technique (DGT) for assessment of metal mobility and bioaccessibility in soil and to compare the results with classical extraction procedures. Non-contaminated natural grassland and arable land soil samples from the South Moravian district, Czech Republic, both homogenised and undisturbed, were studied. DGT applied to soil cores gave information about the vicinity of the sampling probe related predominantly to the local structure and heterogeneity of the soil. However, measurement of mobile and kinetically labile metal species in the soil slurry could provide an approximation of the average information on plant accessible metals pools in soils, that was several orders of magnitude lower in comparison with results obtained by extraction procedures. Most DGT measured metals occurred in low molecular labile forms as demonstrated by using the diffusive gels with different pore size. Concentration of metals measured in soil solution was used for R-value (c(DGT)/c(sol)) calculation. The R-values (0.6-1.1) indicated high lability of Cd species at both sampling sites. In contrast to Cu and Ni (R=0.11-0.15), Pb was relatively labile in nature grassland near the highway with heavy traffic density (R= 0.45-0.75) in agreement with results obtained by extraction procedures.