Gas chromatographic analysis of benzene extracts was used to study the effects of temperature and relative humidity on the degradation and volatilization of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) in the soil. The relative humidity of a closed system had little effect on alachlor retention in air dry Sawyer fine sandy loam at 22 C, but had a pronounced effect when soil temperature was 38 C or higher. At 0% relative humidity (38 C or 46 C) alachlor was degraded to 2-chloro-2′,6′-diethylacetanilide. Decomposition, which also occurred in 5 N aqueous HCl, was attributed to acidic soil water film surfaces. As relative humidity within the system increased, the rate of degradation decreased, apparently because condensation of water vapor increased the thickness of the soil water film and decreased the surface acidity. At 38 C, minimum loss was noted at 31% relative humidity, and at 46 C, minimum loss was found at 79% relative humidity. The increased loss of alachlor at relative humidities above these critical points was attributed to volatility and not to chemical degradation.
