Equations are derived that describe the direct photolysis rates of pollutants in the aquatic environment. The equations translate readily obtainable laboratory data into "half-lives" for photolysis under sunlight. Photolysis half-lives are calculated as a function of season, latitude, time-of-day, depth in water bodies, and ozone layer thickness. Experimental verification of the computed half-lives is presented.

Acid degradation of malathion is too slow to be important under environmental reaction conditions. However, alkaline degradation is fast enough to be a competitive degradation pathway in the environment. The products of alkaline degradation are temperature dependent. Oxidation by molecular oxygen is too slow under acidic conditions to be a degradation pathway. Photolysis is slow in distilled water but may be important in natural waters.

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