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 mu M. Sorption on organophilic O Cls, OCls with large quaternary alkylammonium groups, i.e. hexadecyl-trimet hylammonium (AHDT) and dioctadecyldimethylammonium (ADOD), were compared to that on sorptive OCls, which have large primary alkylammonium (octadecylam monium, AC18) and small quaternary alkylammonium (phenyltrimethylammonium, PTA) groups; The organophilic OCls showed much higher sorption (AHDT K-d = 652-1789; ADOD K-d = 838-1728) than the sorptive OCls (AC18 K-d = 38-40;PTA K-d = 0), suggesting hydrophobic bentazone-organocation interactions as th e main mechanism responsible for sorption. The incubation of the two organo philic OCls with soil contaminated with bentazone showed that availability of the herbicide decreased almost instantaneously from 124 mu g g(-1) to 1 mu g g(-1). Bentazone sorbed on the OCl, and thus immobilized, was partiall y extractable with CaCl2/methanol solution suggesting its potential bioavai lability. Two; OCls, with high and low sorptions, were assayed as herbicide carriers by preparing bentazone-OCl complexes and monitoring their herbici de release in water and soil-water suspensions, These bentazone-OCl complex es released 20-80% of their bentazone content, depending of the sorbent cap acity and the bentazone-OCl interaction. Results of this work show that by varying the sorptive properties of OCls, they can be used to immobilize pes ticide in a contaminated soil and to protect soil and water by using OCl as pesticide carriers in slow release formulations, (C) 2000 Elsevier Science B.V. All rights reserved.