Arsenic(V) and vanadium(V) fractionation after its incorporation into a sandy loam soil from Pampas region, Argentina

Arsenic is a well-known toxic substance, widely distributed, whereas vanadium is a pollutant of emerging interest. Both have been found to correlate positively in groundwaters, thus concern arises on the effect of these pollutants on crops, if such waters are used for irrigation. We conducted a study on the effect of aging with a typical crop soil mimicking soils initially irrigated with water containing As and V. Afterwards, the soil was subjected to wet/dry cycles. The fractionation of both elements at different times from the addition (onset of the experiment) was determined by a modified European Community Bureau of Reference (BCR) method. It is found that the greater part of V is located in the most stable fraction from the onset of the experiment. This is attributed to interaction with amorphous and clay minerals and the precipitation of Ca(VO₃)₂, which is predicted by speciation modeling. The remaining fractions show the expected behavior: the most labile fraction decreases over time, that associated to oxidizable increases with time, whereas the fraction associated to reducible components stays approximately constant. Arsenic shows a lower proportion in the most stable fraction compared with V, and a higher proportion in the most labile, but otherwise shows similar tendencies. The results suggest a low availability of V and a higher one of As. No competence was observed between As and V in the experimental conditions.