Release of Fenamiphos, Atrazine, and Alachlor into Flowing Water from Granules and Spray Deposits of Conventional and Controlled-Release Formulations

The release into water of active ingredients from spray deposits or granules of fenamiphos, atrazine, and alachlor was measured for commercial and experimental controlled-release formulations. Granules or spray mixtures of the pesticides were mixed with coarse sand and dried if necessary, and the mixture was placed in 5 mm × 35 mm stainless steel cylinders through which distilled water was then pumped for 24 h. Pesticide concentrations in the eluate were determined by HPLC analysis. The conventional formulations (emulsifiable concentrates, granulars, and dispersible granules) gave total release in 5−24 h and in some cases appeared to release particles into contacting water. Controlled-release starch-encapsulated formulations gave between 5% and 94% release in 24 h. Clay/alginate and clay/alginate/linseed oil formulations gave 0.3−100% release in 24 h, depending mainly on the aqueous solubility and lipophilicity of the pesticide. This simple technique provides comparative insights into the amounts and rates of release of pesticide active ingredients (and/or other chemicals such as oxidative degradates) when these formulations are contacted by flowing water. Initial results indicate that formulation can affect the potential of these pesticides to be water pollutants under severe rainfall conditions. Keywords: Atrazine; alachlor; fenamiphos; formulation; controlled release; spray deposit; water quality; runoff; leaching; granules