Effect of moisture and casein on demethylation of trimethylselenonium in soil

Trimethylselenonium ion TMSeq. is a major urinary selenium Se. metabolite of animals. The effect of soil moisture and casein on the demethylation of TMSeq were examined in three California soils wTulare Basin TL., Losthill LH. and Five Points FP. upland areasx treated with 20 mgrg TMSeq. Results showed that soil moisture positively affected the demethylation of TMSeq to volatile dimethylselenide DMSe.. In the non-saline TL and FP soils, the highest demethylation rates were 0.169]0.454, 0.646]2.71, and 3.15]6.01 mgrg per day from a 10, 20, and 100% moisture soil, respectively. During 51 days of the experiment, approximately 75.4]80.2% of added TMSeq was demethylated to volatile DMSe. In contrast, in a saline LH soil, the demethylation rate was -0.2 mgrg per day, and only 7% of the added TMSeq was demethylated to volatile DMSe. Addition of casein stimulated the demethylation of TMSeq in a 10% moisture TL soil. Dissolved DMSe, dimethylselenoxide DMSeO. and TMSeq, and adsorbed TMSeq were found in the three experimental soils. Concentrations of dissolved and adsorbed TMSeq were much higher in the LH soil than in the TL and FP soils. This study showed that demethylation of TMSeq dominates in the FP and TL soils, and adsorption of TMSeq is a more important process in the LH soil.