Controlled release of aldicarb from carboxymethyl cellulose microspheres:: in vitro and field applications

Aldicarb is a carbamate pesticide that is widely used throughout the world in the protection Of crops (eg cotton, nuts, potatoes, onion, tobacco, sugar beet and sugar cane). In Turkey, especially in the Cukurova region, it is used for the control of the cotton white fly (Bemisia tabaci) which attacks cotton plants cultivated in this region. Aldicarb contamination in surface and ground water is a serious problem in several countries, partly due to its high water solubility. It is also highly toxic to mammals. In order to overcome these problems, microspheres of aldicarb were prepared using carboxymethyl cellulose (CMC) as the biodegradable support material cross-linked with aluminium chloride. A strong hysteresis behaviour was observed upon drying and reswelling. Encapsulation efficiency was in the range 12-23% and aldicarb contents of 5.7-10.3 mg per 100mg of microspheres was achieved. In vitro release was distinctly Fickian, and Higuchi constants were very close to 0.5. Release in pots revealed that only one sample had a release capability for more than four weeks. In the cotton plot much longer durations of release (more than seven weeks) were observed while a commercial granular formulation released its content immediately. It was thus possible to construct a controlled pesticide release system that prolonged the bioavailability to about eight weeks. (C) 1999 Society of Chemical Industry.