Fast abiotic sorption of selenates (SeO42-) in soils: pitfalls of batch sorption data acquired by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS)

Low selenium (Se) dietary intake has encouraged the development of fortification strategies such as SeO₄^2- application to arable land. Selenate is highly mobile in soil systems, but it is not known whether fast abiotic retention could reduce Se loss from topsoil after SeO₄^2- fertilisation. This work explicitly aims at fast abiotic SeO₄^2- sorption in three soils exposed to 20–1250 µg L^?1 Se in a 24-h batch experiment. This study demonstrated the susceptibility of Se sorption data to distortion when inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) measurements suffered from non-spectral interferences induced by concomitant elements in an aqueous soil-derived matrix. The distribution coefficient (K_d), not exceeding 2 L kg^?1 at any Se level, was shown to be a useful indicator for the extent of ion competition for sorption sites depending on the SeO₄^2- concentration employed. Sorption experiments conducted in the presence or absence of nitrate (10 mM), sulphate (0.52 mM) and phosphate (0.21 mM) allowed three phenomena explaining different SeO₄^2- retention behaviours found even between similar Cambisols to be proposed. Finally, we showed that the co-application of sulphate or phosphate with SeO₄^2- might decrease Se sorption from 150–170 µg kg^?1 to a net release from native Se pool.

Abbreviations: 1^st IP: first ionisation potential; RSD: relative standard deviation