KINETICS OF SELENOMETHIONINE DISAPPEARANCE FROM RECLAIMED COAL-MINE SOILS OF WYOMING, USA

Selenomethionine (SeM) is an organic toxicant that is present in selen iferous environments. No kinetic data is yet available regarding SeM r eactions in coal mine environments, where selenium (Se) toxicity is a potential concern. A kinetic study was conducted on two reclaimed coal mine soils (Typic Torriorthents) from Wyoming having sandy and clayey textures. Four levels of SeM treatments (0, 50, 100 mu M, and plant a mendment from the mine vegetation) were reacted with the soils for 4, 7, 14, 28, 42, 56, and 84 days to characterize the kinetic behavior of overall SeM disappearance from soil solutions. Detection of SeM in so il solutions at the control level (0 mu M SeM) indicated occurrence of indigenous SeM in the soils. In the plant-amended soil solutions, muc h greater concentrations of SeM were observed as compared with the soi l-only systems. This indicated the plant material was a more potential source of SeM than the mine soils. A time-dependent loss in solution SeM concentrations was observed for both soils under 0, 50, 100 mu M S eM treatments. For the soil-plant mixtures, the solution SeM concentra tion increased initially, reached a maximum after 14 days, and then de creased thereafter. In the plant-amended soil solutions, SeM concentra tions at all time intervals were higher for the sandy as compared to t he clayey soil. At 50 and 100 mu M Sem treatments, the solution pH was linearly related to the percentages of SeM disappeared from the solut ions; greater percentage of SeM was removed from solutions at comparat ively lower pH levels, which was greater than or equal to 90% at pH 7. 7 for both soils. Solution SeM concentrations decreased exponentially with time following first-order kinetic reactions. Under all applicati ons (except for the control), C-0 (SeM concentration at t=0) values fo r the sandy soil were greater than those determined for the clayey soi l, indicating higher solution SeM availability for the former and more SeM retention by the latter at t=0. Comparison of C-0 in controls (0 mu M SeM addition) suggested greater indigenous SeM in the clayey soil . For both soils, C-0 values under different treatments followed the o rder, (soil+100 mu M) > (soil+50 mu M) > (soil+0 mu M). The specific r eaction rate constants (K-r) of SeM for both soils were similar (0.031 and 0.029 day(-1) for sandy and clayey soils, respectively); low K-r values indicated that SeM loss from our reclaimed coal mine soil solut ions would follow rather slow kinetics. The half-life (t(0.5)) of SeM varied from 15 to 55 days depending on treatment level. The knowledge obtained from this study should contribute in developing time-based Se reclamation strategies in coal mine environments.