CONTROLLED-RELEASE OF PESTICIDES INTO WATER FROM CLAY-POLYMER FORMULATIONS

The release of alachlor and atrazine into aqueous solution from contro lled-release formulations (CRFs) prepared from alginate and pectin, wi th and without the addition of clay minerals, was studied. The rate of release of the incorporated herbicides was a function of both the pro perties of the herbicide and the composition of the CRF. The rate of r elease of herbicides was related their aqueous solubility; the greater the solubility of a compound, the more rapid its release from a CRF. The rate of release of the chemicals from pectin-based CRFs was genera lly greater than from alginate-based CRFs. This seems to be related to the relatively large number of methoxy groups in the pectin, which hi nders the gelation process and results in a more porous matrix than in the case of alginate. The addition of sodium montmorillonite to these CRFs was found to have a profound inhibitory effect on the release of alachlor. This was attributed to the sorption of the herbicide to the clay mineral. Other clays generally had little or no effect on the ra te of release of the active ingredient. Bead radius was observed to ha ve a profound effect on release rates; the smaller the radius, the gre ater the release rate. Release rates conformed to the Higuchi equation for a diffusion controlled release mechanism from a porous polymer in which the active ingredient is present in excess of its solubility.