The study was aimed at evaluation of environmental aspects on photooxidative treatment of phenolic compounds by UV/H2O2 process. Hydroxy- chloro-, nitro- and methyl-phenols substituted in ortho and para positions were used as model pollutants. The influence of pollutant chemical structure on variations of water quality during the photooxidative treatment was investigated. In that purpose, we monitored the changes of total organic carbon (TOC); chemical oxygen demand (COD); aromaticity, measured as absorbance at 280 (A(280)) and 254 nm (A(254)); biodegradability, estimated over ratio of biochemical and chemical oxygen demand (BOD5/COD); and toxicity, estimated on inhibition of Vibrio fischeri luminescence (TU). It was found that changes of monitored parameters are influenced by the type and position of substituent. Studied pollutants share sequence in degradation pathway and consequently some of the formed by-products are the same as well. However, their distribution and the formation of specific by-products with characteristic functional groups play significant role in observed variations of water quality, which was particularly reflected in biodegradability and toxicity. The cross-correlation between recorded sum-water parameters is assessed on the basis of calculated Spearman rank coefficients. (C) 2013 Elsevier B.V. All rights reserved.