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.