Chlorothalonil in a quartz sand soil: Wetting effects on sorption capacity and bound residue

Chlorothalonil has been found to persist but not leach in some quartz sandy soils. For this effect to be understood, it is necessary for the numbers of occupied and empty surface sorption sites to be known. This requires that the labile surface sorption capacity theta(C), which is the total number of sites, be measured. Wetting effects might however, affect theta(C). The measurement of theta(C) has been done only recently by very few laboratories, and the wetting effects have seldom been investigated. New analytical chemical methods are therefore required. On - line HPLC micro extraction has been used in the present work to develop a method for the titration of chlorothalonil onto the labile surface sorption sites. Two conclusions have been drawn from the measurements. The first is that theta(C) is one to 2 orders of magnitude greater than it is for the previously reported cases. Second, the effect of wetting on bound residue formation reported by Belliveau and Langford (g) has been confirmed. These effects help to explain the behavior of chlorothalonil in the quartz sandy soils.