Factors affecting formation of deethyl and deisopropyl products from atrazine degradation in UV/H2O2 and UV/PDS

Abstract

In this study, the formation of deethyl products (DEPs) (i.e., atrazine amide (Atra-imine) and deethylatrazine (DEA)) and deisopropyl product (i.e., deisopropylatrazine (DIA)) from parent atrazine (ATZ) degraded in UV/H₂O₂ and UV/PDS processes under various conditions was monitored. It was found that SO₄˙⁻ displayed a more distinctive preference to the ethyl function group of ATZ than HO˙, leading to the higher ratio of DEPs/DIA in UV/PDS system than that in UV/H₂O₂ system in pure water. The effects of water matrices (i.e., natural organic matter (NOM), carbonate/bicarbonate (HCO₃⁻/CO₃²⁻), and chloride ions (Cl⁻)) on ATZ degradation as well as formation of DEPs and DIA were evaluated in detail. The degradation of ATZ by UV/PDS was significantly inhibited in the presence of NOM, HCO₃⁻/CO₃²⁻ or Cl⁻, because these components could competitively react with SO₄˙⁻ and/or HO˙ to generate lower reactive secondary radicals (i.e., organic radicals, carbonate radicals (CO₃˙⁻) or reactive chlorine radicals (RCs)). The yields of these DEPs and DIA products from ATZ degradation were not impacted by NOM or HCO₃⁻/CO₃²⁻, possibly due to the low reactivity of organic radicals and CO₃˙⁻ toward the side groups of ATZ. Howbeit, the increase of DIA yield companied with the decrease of DEPs yield was interestingly observed in the presence of Cl⁻, which was attributed to the promotion of Cl⁻ at moderate concentration (mM range) for the conversion of SO₄˙⁻ into HO˙. Comparatively, in the UV/H₂O₂ process, NOM and HCO₃⁻/CO₃²⁻ exhibited a similar inhibitory effect on ATZ degradation, while the influence of Cl⁻ was negligible. Differing from UV/PDS system, all these factors did not change DEPs and DIA yields in UV/H₂O₂ process. Moreover, it was confirmed that RCs had a greater selectivity but a lower reactivity on attacking the ethyl function group than that of SO₄˙⁻. These findings were also confirmed by monitoring the degradation of ATZ as well as the formation of DEPs and DIA in three natural waters.