Speciation and transformation pathways of chlorophenols formed from chlorination of phenol at trace level concentration

Abstract

Trace organic precursors remaining in water after primary treatment can originate a variety of toxic disinfection by-products during chlorination. Therefore, knowledge of conditions leading to their persistence or transformation in chlorinated media is crucial for human health protection. Using phenol as model compound at trace level (50 ppb), the short term formation and degradation of chlorophenols (CPs) in plain water and buffered water (pH 4.8, 7 and 9) treated with typical chlorine doses (1-5 ppm) was investigated. Total phenol consumption and quantitative degradation of formed CPs occurred in < or =5h with 5 ppm chlorine in plain water and alkaline buffer, and with 1 ppm chlorine in phosphate buffer of pH 7. The enhanced reactivity in this buffer was attributed to high ionic strength (0.18 M). On the contrary, phenol was only slowly transformed to monochlorophenols (MCPs) in acidic media. Analysis of phenol and CPs concentration profiles indicated the coexistence of two competing reaction pathways in neutral and alkaline conditions: 1) successive ortho-para chlorination of aromatic ring up to 2,4,6-trichlorophenol followed by ring cleavage, 2) direct oxidation of MCPs to rapidly degradable oxygenated aromatics (dihydroxybenzenes, benzoquinones). Ionic strength and pH had some influence on preferred pathway but chlorine dose was determinant.

Influence of Application Method on Disinfectant Byproduct Formation during Indoor Bleach Cleaning: A Case Study on Phenol Chlorination

“…This may be due to the larger forward reaction rate for DCP (∼1–2 orders of magnitude higher than TCP, Figure S2) leading to greater accumulation of TCP. These rates were previously investigated in the context of wastewater treatment and may differ relative to bleach cleaning, where a larger concentration of reactive chlorine is expected; rates have been observed to be first order relative to both reactive chlorine and phenol. ,, DCP and TCP also have similar Henry’s law solubilities, but partitioning between the gas and aqueous phases will also be influenced by droplet pH due to differing p K a values (Figure ). Bleach pH is likely in the range of 9.5 to 12, − but droplet pH is not easily estimated in the present work, in part because CO 2 dissolution and water evaporation may alter droplet pH .…”

“…Chlorophenolic DBPs have not been described in previous works examining gaseous emissions from bleach cleaning activities, ,,,− though phenol has been observed to partition to aqueous disinfectant solutions applied indoors . Previous studies on heterogeneous bleach chemistry observed a variety of volatile DBPs including chlorocarbons, chloroacids, chlorinated organic amines, and chlorinated terpenoids but did not report chlorophenols or similar DBPs. ,,,− Chlorophenolic DBPs have generally been studied in the context of wastewater treatment and form primarily through aqueous chlorine addition to the aromatic ring to produce 2,4,6-trichlorophenol (TCP) as the final phenolic product, ,,,− after which further chlorination forms a variety of nonaromatic products, including 2,6-dichlorobenzoquinone (DCBQ), 2,4,4,6-tetrachloro-2,5-cyclohexadienone (TCCHD), and small chlorocarbons. ,,,,− Chlorination of TCP has also been reported to form 2,3,4,6-tetrachlorophenol, but we suspect TCCHD is the primary tetrachloro species we observe. The dichloro (DCP) and trichlorophenol (TCP) molecules are detected as a protonated [M + H] + as well as an [M] + ion due to charge transfer (Figure S1), which is relatively efficient for aromatic molecules.…”

“…Microdroplet environments may lead to the formation of novel byproducts due to differences in solvation environment or pH compared to bulk solution. , Such reactions may occur between dissolved species already present in the disinfection solution or with ambient VOCs that can partition into microdroplets or collide with droplet surfaces. In this work, we discuss the aqueous reaction between reactive chlorine species and phenol. ,− We perform a series of experiments applying commercial bleach solutions within an environmental chamber using a commercial ultrasonic humidifier to inject and disperse bleach through microdroplets and analyze the emissions with a high-resolution Vocus proton transfer reaction mass spectrometer.…”

Desarrollo analítico de derivados del fenol en agua utilizando cromatografía de líquidos

“…Además, como este método se desarrolló para aplicarlo en muestras de agua residuales y superficiales, se pretendió que los tiempos de retención de los primeros solutos eluidos fueran relativamente grandes con el objeto de que todas las interferencias presentes en la matriz, no eliminadas durante los procesos de preconcentración y limpieza, y que generalmente eluyen a tiempos de retención muy cortos, pudieran interferir en el análisis y detección de los solutos de interés [6].…”

Study on oxidation of sodium chlorophenols by heterogeneous photo-fenton

“…Those kinds of compounds in the environment can stably exist a long-term, and can enter the body through the food chain. Till now, its extensive use has already caused serious human health threat [2]. Chlorophenols have a low solubility in water, often in the form of sodium or potassium salts dissolved in water.…”