Bentonite and humic acid as modifying agents in controlled release formulations of diuron and atrazine

The herbicides diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and atrazin e [6-chloro-N-2-ethyl-N-4-isopropyl-1,3,5-triazine-2,4-diamine] were incorp orated in alginate-based granules to obtain controlled release (CR) propert ies. The basic formulation [sodium alginate (14.0 g kg(-1))-herbicide(6.0 g kg(-1))-water] was modified by addition of sorbents. The effect on diuron and atrazine release rate, caused by incorporation of natural bentonite and humic acid in the alginate Formulation, was studied bg immersion of the gr annies in water under static conditions. The release of the active ingredie nt from alginate-based CR grannies in water was affected by the addition of natural bentonite, and to a greater extent, by the addition of the humic a cid, The water uptake, permeability, and the time taken for 50% of active i ngredient to be released into water, T-50, were calculated for the comparis on of the preparations. Addition of both bentonite and humic acid samples t o the basic alginate-based Formulation produced the higher T-50 values (43. 11 and 50.49 d for diuron and atrazine formulations, respectively), indicat ing a slower release of herbicide. Based on parameters of an empirical equa tion used to fit the herbicide release data, it appears that the release of diuron and atrazine from the various formulations into water is controlled by a diffusion mechanism. Sorption rapacity of the sorbent and the permeab ility of the formulations (ranging from 3.77 to 20.83 mg d(-1) mm(-1)) were the most influential Factors affecting herbicide release.