KRAFT LIGNIN ADSORPTION OF METRIBUZIN AS A CONTROLLED-RELEASE FUNCTION EVALUATION

Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] adsorption by the nonsulfonated kraft lignins PC940A, PC940C, and Indulin AG was evaluated to determine if adsorption could explain the presence or absence of a controlled-release function. Indulin AG, a commercial grade lignin, adsorbed more than twice as much [C-14]Metribuzin in 6 h as did PC940C, an oxidized experimental lignin; however, by 24 h, PC940C had adsorbed approximately 80% as much [C-14]metribuzin as did Indulin AG. PC940A, an experimental chemically modified, high-surface-area lignin, adsorbed the, largest amount of [C-14]metribuzin and established equilibrium in 10 min. In view of an earlier study, which found PC940C to be 3 times more effective than PC940A in reducing the mobility of [C-14]metribuzin in soil and which found Indulin AG to have no effect, results of the adsorption study lead to two general conclusions. The first is that adsorption analysis should not be the sole criterion for selecting a kraft lignin as a potential controlled-release agent for a soil-applied pesticide. The second is that if a kraft lignin has been found to alter the soil mobility pattern of a pesticide, then adsorption analysis may prove useful in determining how the controlled-release function operates and may prove useful in maximizing the potential of a lignin as a controlled-release agent.