The distribution of chlorothalonil among the dissolved, labile sorbed, and
bound residue states was monitored during an 18 day period in an aqueous sl
urry of an analyzed quartz sand soil from Simcoe, ON, Canada. The Simcoe so
il is 90.-95.% quartz sand. The online HPLC microextraction method was used
for this purpose, because it is the only available technique that can reso
lve the total amount of a pesticide in a soil into its dissolved, labile so
rbed, and bound residue components. The processes for which the molecular l
evel kinetics were determined included labile surface sorption and desorpti
on and bound residue formation. At a reaction time of 14 days, the solution
concentration of 0.75 x 10(-6) M was 43.3% of the total chlorothalonil, 26
.2% was in the labile sorbed state, and 30.5% was a bound residue. There we
re no chemical reactions and no biodegradation during the 18 day period. Th
e kinetics of mass transfer among the three states were determined and are
consistent with intraparticle diffusion. Although the amounts are small, it
is suspected that the 5. - 10.% nonquartz materials in the Simcoe soil con
tribute most of the sorption and bound residue effects.