Evaluation of simultaneous reduction and transport of selenium in saturated soil columns

Speciation plays an important role in determining the overall leachability of selenium in soil. In this study we present a mathematical model and resu lts of miscible displacement experiments that were conducted to evaluate si multaneous reduction and transport of selenate in saturated soil columns. T he experiments were carried out in organic amended (compost manure or glute n) or unamended soil, with O-2-sparged or nonsparged influent solution. In all columns, reduction of selenate was fast enough to produce selenite flux in the effluent and elemental Se in the soil profile during a mean residen ce time of similar to 30 hours. Reduction was accelerated in the presence o f organic amendments and under low O-2 concentrations, resulting in an incr eased retardation of selenium transport as a whole. The results of our expe riments show that although selenate does not sorb to solid surfaces during transport, it reduces rapidly to forms that are strongly retarded. On the b asis of simulation with the consecutive reaction and transport model using parameters derived from this study, selenium is expected to be retained nea r the soil surface, even under extreme leaching conditions.