Aquatic degradation of triclosan and formation of toxic chlorophenols in presence of low concentrations of free chlorine

Abstract

The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products (2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when products containing triclosan are mixed with chlorinated tap water.

Triclosan breakdown by Fenton-like oxidation

“…The former gives rise to the formation of highly toxic byproducts like chlorinated phenoxy-phenols, chlorinated phenols, tetraclosan, pentaclosan and trihalomethanes [7,16,17]. Ozonation suffers from the potential generation of carcinogenic byproducts [18] as well as from corrosion problems.…”

Transformation Products of Emerging Contaminants upon Reaction with Conventional Water Disinfection Oxidants

“…Following this scheme, they obtained the first evidence of the existence of chlorinated forms of methyl and propyl parabens in urban sewage water, a fact which was further confirmed with pure standards and HR-MS [17]. A similar sample preparation strategy has been considered in GC-MS chlorination studies dealing with medium and low polarity UV filters, such as benzophenone-3 (BP-3) and 2-ethylhexyl-pamino benzoate (EHPABA) [18,19], lipid regulators [11] and bactericides [7,20]. Most of the analytes involved in the above studies contain polar functionalities, such as phenolic or carboxylic groups; thus, to improve their detectability, different derivatization reactions, based on the use of silylation or pentafluorobenzylation agents, have been introduced in the sample preparation scheme, Table 4.1.…”

Pharmaceuticals, Personal Care Products and Endocrine Disrupting Agents in the Environment – A Review

“…Identification of triclosan by-products is necessary not only because bio-methylation or photolysis results in the formation of lipophilic, stable and bioaccumulative by-products but also for the reason that sometimes these may be more toxic than the parent compound. Thus, the coexistence of triclosan and chlorophenols in non treated wastewater contributes to the introduction of 2,4 DCP (dichlorophenol) and 2,4,6, TCP (trichlorophenol) in the environment [59]. The investigation of the photochemical transformation of the natural estrogenic steroids E2 and EE2 have shown that this process is slow, occurring with a quantum yield of 0.06 both by monochromatic (254 nm) and polychromatic (A290 nm) irradiation; values similar to that determined for phenols [60].…”