Linking Triclosan’s Structural Features to Its Environmental Fate and Photoproducts

Abstract

Triclosan is a high-production volume chemical, which has become widely detected in environmental systems because of its widespread usage. Photodegradation has been identified as a major degradation pathway, but the identified photoproducts are also chemicals of concern. In this study, lower chlorinated derivatives of triclosan were synthesized to investigate the impact the chlorine substituents have on the photodegradation rate and the photoproducts produced. In addition, the photodegradation of two classes of photoproducts dibenzo-p-dioxins (DDs) and 2,2′-dihydroxylated biphenylswas also investigated. Degradation of triclosan in near-surface sunlit waters was relatively fast (t 1/2 < 5 h). Calculated degradation rates were slower for DDs and faster for dihydroxylated biphenyls in comparison to that for triclosan. In addition, the 2′-Cl substituent was critical for the high quantum yield measured for triclosan and necessary for the photodegradation mechanism that forms DDs and dihydroxylated biphenyls. The 4-Cl substituent was responsible for higher rates of light absorption and the environmentally relevant pK a . Without either of these substituents, the environmental fate of triclosan would be markedly different.

Enhanced UV Direct Photolysis and UV/H2O2 for Oxidation of Triclosan and Ibuprofen in Synthetic Effluent: an Experimental Study

“…The low mineralization data point to byproduct formation from the oxidation of TCS and IBU by both the direct photolysis system and the UV/H 2 O 2 system. TCS has been known for its high rate of byproduct formation by phototransformation (Apell et al, 2020 ). Huang et al ( 2018 ) draw attention to non-removal of byproduct cytotoxins by the UV and UV/H 2 O 2 processes applied in the oxidation of TCS, even when reduction of the target contaminant concentration occurs, and increased UV fluence is required.…”

“…7 . For TCS, some byproducts formed are 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) arising from the skeletal rearrangement of the molecule, 2,4-dichlorophenol (DCP) formed from the cleavage of the ether (R-O-R), and 4 ′ -chlorophenoxyphenol (4 ′ -ClPP) from hydrodechlorination (Apell et al, 2020 ; Kliegman et al, 2013 ), where due to the use of MeOH as a cosolvent, the formation of 2-phenoxyphenol (PP) is facilitated (Apell et al, 2020 ). For IBU, it has been widely reported that decarboxylation occurs (Luo et al, 2018 ; Szabó et al, 2011 ).…”

Enhanced UV Direct Photolysis And UV/H2O2 For Oxidation of Triclosan And Ibuprofen In Synthetic Effluent: An Experimental Study

“…The low mineralization data point to byproduct formation from the oxidation of TCS and IBU by both the direct photolysis system and the UV/H2O2 system. TCS has been known for its high rate of byproduct formation by phototransformation (Apell et al 2020). Huang et al (2018) draw attention to non-removal of byproduct cytotoxins by the UV and UV/H2O2 processes applied in the oxidation of TCS, even when reduction of the target contaminant concentration occurs, and increased UV fluence is required.…”

“…7. For TCS, some byproducts formed are 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) arising from the skeletal rearrangement of the molecule, 2,4-dichlorophenol (DCP) formed from the cleavage of the ether (R-O-R), and 4'chlorophenoxyphenol (4'-ClPP) from hydrodechlorination (Kliegman et al 2013;Apell et al 2020), where due to the use of MeOH as a cosolvent, the formation of 2-phenoxyphenol (PP) is facilitated (Apell et al 2020). For IBU, it has been widely reported that decarboxylation occurs (Szabó et al 2011;Luo et al 2018).…”

“…Some byproducts are 1-ethyl-4-(2-methylpropyl)-benzene, 1-(4-isobutylphenyl)ethanol, and 4-isobutylacetophenone (Szabó et al 2011;Wang et al 2021). (Kliegman et al 2013;Apell et al 2020) and (b) IBU (Szabó et al 2011;Wang et al 2021).…”