Sorption and degradation of tebutam in soil under controlled laboratory conditions

This study investigates tebutam (N-benzyl-N-isopropylpivalamide) sorption a nd degradation in the surface level (0-20 cm) of a brown silty clay soil. A ll the experiments were conducted under controlled laboratory conditions us ing C-14 uniformly ring labelled tebutam. The sorption process was evaluate d by adsorption kinetics, adsorption and desorption isotherms using a batch equilibration method. In our conditions, equilibration time for 95% of her bicide adsorbed was 0.21 h. This initial rapid sorption pattern, was follow ed by slower sorption continuing over 48 h. The adsorption isotherm was wel l described by the Freundlich equation with K-f = 1.48 and n(f) 0.95. This corresponds to a K-d of 1.48 l.k(g-)1 and a K-oc of 148 l.kg(-1), comparabl e to the coefficients measured for atrazine. Desorption of tebutam was easy and weakly hysteretic, particularly for large adsorbed amounts. For degrad ation, data showed that 50% of tebutam was degraded in 14 days (as a percen tage of extractable residues), and nearly 41% was mineralized in the same i nterval. Non-extractable residues reached 46% of initial applied amounts in 12 days. Their slow and gradual release determined after 12 days, appears to supply the mineralization process. Degradation products were formed from the fourth incubation day and three of them appeared to persist in soil me dia. They reached nearly 80% of extractable residual radioactivity at the e nd of incubation.