A wind tunnel for measuring selenium volatilization under field-like conditions

A wind tunnel was developed to measure the loss of volatile selenium (Se) from soil under field-like conditions. The wind tunnel consisted of a volatilization chamber made of Plexiglas (2.4 m long x 0.8 m wide x 1.2 m high), which was set above a stainless steel lysimeter (0.5 m(2) surface area x 0.8 m deep). High air exchange rates (arg. 700 air changes h(-1)) were used to simulate field-like environmental conditions inside the wind tunnel. To monitor the fate and transport of the Set radiolabeled Se-75 as sodium selenite ((Na2SeO3)-Se-75) was incorporated into the top 5 cm of soil. Volatile Se was trapped on activated carbon filters and measured directly using gamma counting. A 135-d bare-soil experiment was tarried out, during which 2.7% of the Se was released through volatilization without added C. The average flux rate of gaseous Se was 17 mg m(-2) h(-1), with a high of 72 mg m(-1) h(-1) occurring on Day 6. After 135 d, 59 and 34% of the Se-75 was located in the 0 to 5 and 5 to 10 cm soil layers, respectively. A total of 845% of all applied Se-75 was recovered. The purpose of this study was to improve estimates on Se volatilization from seleniferous soils and help close the gap between previous laboratory and field experiments.