Phototransformation of 4-Chloro-2-Methylphenol in Water: Influence of Humic Substances on the Reactions.

Abstract

The phototransformation of 4-chloro-2-methylphenol was studied using distilled water, solutions of humic substances and natural waters. Samples were irradiated at 280 nm, with polychromatic lamps emitting within the wavelenght ranges 290-350 and 300-450 nm or exposed to sunlight. The photolysis of 4-chloro-2-methylphenol at 280 nm in pure aerated water leads to methylbenzoquinone as the main primary photoproduct; the quantum yield of the direct photolysis is equal to 0.66. When 4-chloro-2-methylphenol is irradiated alone by polychromatic light or exposed to solar-light, methylhydroquinone and methylhydroxybenzoquinone are found as main photoproducts because secondary photolysis of methylbenzoquinone occurs. Humic substances enhance the rate of photodegradation of 4-chloro-2-methylphenol at lambda > 300nm. In these conditions, 4-chloro-2-methylphenol is transformed into methylhydroquinone, methylhydroxybenzoquinone essentially via direct photolysis and into 3-chloro-trans-trans and cis-trans-1-methyl-1-one-2, 4-hexadienoic acids through photoinduced reactions. These four photoproducts are found when 4-chloro-2-methylphenol is irradiated in natural waters at lambda > 300 nm. The phototransformation of 4-chloro-2-methylphenol under environmental conditions occurs therefore through both direct and humic substances-photoinduced processes.JRC.(EI)-Environment Institut