Organosmectites as sorbent and carrier of the herbicide bentazone

Sorption isotherms of bentazone on diverse organoclays (OCls) were measured at aqueous concentrations from 25 to 1500 microM. Sorption on organophilic OCls, OCls with large quaternary alkylammonium groups, i.e. hexadecyltrimethylammonium (AHDT) and dioctadecyldimethylammonium (ADOD), were compared to that on sorptive OCls, which have large primary alkylammonium (octadecylammonium, AC18) and small quaternary alkylammonium (phenyltrimethylammonium, PTA) groups. The organophilic OCls showed much higher sorption (AHDT Kd = 682-1789; ADOD Kd = 838-1728) than the sorptive OCls (AC18 Kd = 38-40; PTA Kd = 0), suggesting hydrophobic bentazone-organocation interactions as the main mechanism responsible for sorption. The incubation of the two organophilic OCls with soil contaminated with bentazone showed that availability of the herbicide decreased almost instantaneously from 124 microg g(-1) to 1 microg g(-1). Bentazone sorbed on the OCl, and thus immobilized, was partially extractable with CaCl2/methanol solution suggesting its potential bioavailability. Two OCls, with high and low sorptions, were assayed as herbicide carriers by preparing bentazone-OCl complexes and monitoring their herbicide release in water and soil-water suspensions. These bentazone-OCl complexes released 20-80% of their bentazone content, depending of the sorbent capacity and the bentazone-OCl interaction. Results of this work show that by varying the sorptive properties of OCls, they can be used to immobilize pesticide in a contaminated soil and to protect soil and water by using OCl as pesticide carriers in slow release formulations.