Aquatic photochemistry of chlorinated triclosan derivatives: Potential source of polychlorodibenzo-P-dioxins

Abstract

Triclosan (TCS; 5-chloro-2-(2,4-dichlorophenoxy)phenol), a common antimicrobial agent, may react with residual chlorine in tap water during transport to wastewater treatment plants or during chlorine disinfection of wastewater, generating chlorinated TCS derivatives (CTDs): 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol (4-Cl-TCS), 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol (6-Cl-TCS), and 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol (4,6-Cl-TCS). The photochemistry of CTDs was investigated due to the potential formation of polychlorodibenzo-p-dioxin (PCDD) photoproducts. Photolysis rates were highly dependent upon CTD speciation, because the phenolate species degraded 44 to 586 times faster than the phenol forms. Photolysis quantum yield values for TCS, 4-Cl-TCS, 6-Cl-TCS, and 4,6-Cl-TCS of 0.39, 0.07, 0.29, and 0.05, respectively, were determined for the phenolate species. Photolyses performed in Mississippi River and Lake Josephine (USA) waters gave similar quantum yields as buffered, pure water at the same pH, indicating that indirect photolysis processes involving photosensitization of dissolved organic matter are not competitive with direct photolysis. The photochemical conversion of the three CTDs to PCDDs under solar irradiation was confirmed in natural and buffered, pure water at yields of 0.5 to 2.5%. The CTD-derived PCDDs possess higher toxicities than 2,8-dichlorodibenzo-p-dioxin, a previously identified photoproduct of TCS, due to their higher chlorine substitution in the lateral positions. The load of TCS- and CTD-derived PCDDs to United States surface waters is estimated to be between 46 and 92 g toxicity equivalent units per year. Other identified photoproducts of each CTD were 2,4-dichlorophenol and reductive dechlorination products.

Triclosan-Evoked Neurotoxicity Involves NMDAR Subunits with the Specific Role of GluN2A in Caspase-3-Dependent Apoptosis

“…In the environment, TCS is converted to dioxins such as 2,8-DCDD, 2,3,7-TCDD, 1,2,8-TriCDD and 1,2,3,8-TCDD [54,55]. Because of the structural similarity of TCS and dioxins, one may compare their effects with respect to the expression of NMDA receptor subunits in brain neurons.…”

Transformation Products and Human Metabolites of Triclocarban and Triclosan in Sewage Sludge Across the United States

“…17,31,32 TCS degrades into a range of carcinogenic and toxic chlorophenols 33,34 as well as dioxin-like compounds (and possibly traces of the toxic 2,3,7,8-tetrachlorodibenzo- p -dioxin). 18,35,36 Due to the higher relative toxicity of chloroanilines, chlorophenols, and dioxins compared to TCC and TCS, more controlled and efficient removal is warranted of these chlorinated antimicrobials prior to their environmental discharge via effluent and biosolids (i.e., treated sewage sludge fit for application on land, in accordance with regulatory requirements of the U.S. Environmental Protection Agency (EPA), 40 CFR Part 503).…”

Interactions between the antimicrobial agent triclosan and the bloom-forming cyanobacteria Microcystis aeruginosa

“…The estimated t 1/2 values vary from 2.59 to 67.96 h. The degradation of TCS was quickest in the extracellular secretions and raw M. aeruginosa reaction solution and was the slowest in DI water. TCS photodegradation varies with the pH of the solution, and the anionic form of TCS is more photo-reactive than the phenolic form (Buth et al, 2009). To eliminate the influence of pH, the pH values of all reaction solutions were close to 7 (Table 1).…”