Increased aquatic toxicity following photolytic conversion of an organochlorine pollutant

In studies of the photolytic degradation of chlorophenolic substances in aqueous media, 2,4,6-trichlorophenol was found to be converted into products with increased toxic effects on the Microtox® luminescence bioassay system. The chlorophenol was mainly photohydrolysed at the 2- or 6- positions and 3,5-dichlorocatechol was formed. The increased toxic effects were confined to this photolytic product. Although there were indications that the catechol was further modified, it accumulated in the aquatic medium at the test conditions, and most probably will appear in the aquatic environment upon illumination of the polluted parent compound. The 2,4,6-trichlorophenol/3,5-dichlorocatechol system here described therefore increases the environmental impact of an abiotic transformation of a polluted organic compound.