The behavior of naproanilide [2-(2naphthyloxy)propionanilide] and its hydrolysis product NOP [2-(2-naphthyloxy) propionic acid] in water and soil in experimental plots treated with naproanilide bubbling tablets (NBTs) was examined in a greenhouse. NBTs containing sodium hydrogencarbonate and tartaric acid as a bubbling agent were prepared and treated at one end of the test plots (29cmx3.5m). Naproanilide diffused to within 1.5m of the application sites 0.5hr after application under both shallow

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... and deep water conditions. After bubbling stopped the compound gradually diffused in water even farther. The concentration of NOP, a hydrolysis product and the active form of naproanilide, was much higher than that of naproanilide in water. NOP was produced gradually and its concentration in water increased and was highest 48 hr after application. NOP seems to diffuse more extensively than naproanilide owing to its greater solubility. The concentrations of these two compounds on the soil surface decreased depending on distance from the site of application: they were higher in water 6 cm deep than in 2cm at areas distant from the point of application. This result indicates that these compounds diffuse more extensively in deep water than in shallow water. Examination of the relationship between herbicidal efficacy on Sagittaria pygmaea and concentration of naproanilide showed that the minimum lethal concentration of the compound in 2cm deep water was 0.35ppm and was 0.2ppm at 6cm.