Using Modified Tessier Scheme to Metal Speciation in a Former Sewage Farm and interpretation of the sequential extraction by FTIR

We present a study conducted on a former sewage farm near Berlin, where long term sewage disposal onto agricultural land resulted in a high accumulation of potentially toxic metals. Based on a previous study, 30 samples collected within an area of a former sedimentation basin were selected (at the depth of 15-20 cm and one borehole up to 100 cm deep). The modified Tessier sequential extraction was applied in order to determine the partitioning of particulate potentially toxic metals (Cr, Cu, Ni, Pb, and Zn) into following fractions: 1) Exchangeable, 2) Bound to carbonate, 3) Bound to Fe/Mn oxides, 4) Bound to organic matter, and 5) Residual fraction. As a complementary analysis, diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) technique was used for the interpretation purposes.

The obtained results demonstrated different metal speciation in the studied soil; Pb was mostly discovered in the residual fraction (77%) followed by Cr (53%), Cu (8%), and Zn (5%), while Ni was not extracted in this fraction. The organic matter-bound is the dominant species of Cu (77%). However, Zn and Ni exhibit the highest affinity for Fe/Mn oxides fraction (55% and 39%, respectively). The average mobility factor followed the order Ni > Zn > Cu whereas Cr and Pb were not found as exchangeable nor in carbonate forms. Study also revealed that DRIFTS is applicable to interpret the sequential metal extraction, especially for the carbonates-bound, organic matter-bound, and residual fractions. The spectral changes in organic and inorganic regions can indicate the soil components’ dissociation is proportional to the extraction.