Derivative of 2,4-dichlorophenoxyacetic acid (2,4-D), type of bottom sorbent, and application concentration affected the rate and quantity of 2,4-D released into water from attapulgite granules. All three factors were temperature dependent. Temperature, granule size, and solution pH affected the rate during short exposure periods, but not the total quantity of release of herbicide during 256 hours. Generally, decrease in temperature was associated with a decrease in rate of release of 2,4-D. Decrease in granule size slightly increased the rate of release. Increased acidity reduced the rate of release of 2,4-D acid. Types of attapulgite granules were not significantly different.
Rates of subaqueous release of eleven granular herbicides were measured at concentrations of 10, 15, and 20 μg ai/ml. Compounds tested were 2,4-D and its butoxyethanol ester (BE), propylene glycol butyl ether ester (PGBE), and isooctyl ester (IOE) derivatives, tris-(2,4-dichlorophenoxyethyl)phosphite, the IOE of 2,4,5-trichlorophenoxyacetic acid, the BE, PGBE, and potassium salt of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), the sodium salt of 2,3,6-trichlorobenzoic acid, and 2,3,6-trichlorophenylacetic acid (fenac). The rate of release of herbicides from granules varied from complete release of silvex potassium salt in 4 hours to less than 10 per cent release of 2,4-D IOE in 256 hours.