Effect of incubation time of three single extraction procedures on trace element extraction from sediment and soil.

Abstract

The use of standard single-extraction procedures to evaluate the mobility and availability of trace elements is a common practice in most laboratories dealing with soil or sediment analysis. Most standard single-extraction procedures describe incubations last for 2h. However, these were tested and validated for soil analysis. Applying them for sediment analysis without further investigation might be misleading and should be reviewed with care. This paper investigates the effect of incubation time on the extraction efficiency of three standard single-extracting reagents (0.01M CaCl2, 1M NH4NO3, and 0.05M EDTA). Incubation experiments with sediment and soil samples lasting for 2h, 10h, and 10 d were performed. The results indicated that 2h appears sufficient to reach equilibrium using CaCl2 or NH4NO3 for soil analysis; but when analyzing sediments, incubation for 10 d resulted in higher concentrations. Incubation experiments with 0.05M EDTA showed that incubation for 2h was enough to extract Cd from the soil sample, Mn and to a lesser extent Cd from the sediment samples; while for the other elements, incubation for 10 d yielded higher concentrations for both sample types compared to that obtained after 2h and 10h separately. Relative to the pseudo-total metal contents, more than 55% of all studied elements were extracted by using 0.05M EDTA, indicating high bioavailable metal fraction.