Hydrolysis and Chlorination of 2,6-Dichloro-1,4-benzoquinone under conditions typical of drinking water distribution systems

Halobenzoquinones (HBQs) are emerging disinfection by-products (DBPs) that are postulated drivers of bladder carcinogenicity. Prior assessments of 2,6-dichloro-1,4-benzoquinone (DCBQ) occurrence in drinking water distribution systems have revealed a gradual decline with increasing distance from points of entry. While this signals a degradation pathway, there is limited quantitative data on rate of that degradation. A systematic evaluation of DCBQ hydrolysis was performed, resulting in a rate law that is first order in both hydroxide [OH^-] and [DCBQ]. The impact of temperature on that rate was characterized according to the Arrhenius relationship. Under the conditions tested (pH~7.2, T = 20°C) chloramine did not significantly impact DCBQ concentrations. However, DCBQ was rapidly degraded in solutions containing free available chlorine (FAC). Kinetic analysis showed non-integer order with respect to FAC. Further investigation led to a model that invoked reaction with dichlorine monoxide (Cl₂O) as well as FAC.

The toxicity of 2,6-dichlorobenzoquinone on the early life stage of zebrafish: A survey on the endpoints at developmental toxicity, oxidative stress, genotoxicity and cytotoxicity

2,6-dichlorobenzoquinone (2,6-DCBQ), an emerging disinfection by-production, frequently occurs in reclaimed water and drinking water. However, limited information was available regarding its toxicity. To evaluate its impact, zebrafish at early life stage were exposed to 0, 10, 30, 60, 90, or 120 μg L^-1 2,6-BDCQ for 72 h. Our results indicated that 2,6-BDCQ decreased zebrafish's survival rate to 65% and 44% at 90 and 120 μg L^-1 treatments and increased its aberration rate to 11% and 26% at 90 μg L^-1 and 120 μg L^-1 treatments. Besides, 2,6-BDCQ had adverse effect on its oxidative stress (elevated superoxide dismutase activity), lipid peroxidation (increased malondialdehyde levels), DNA damage (increased 8-hydroxydeoxyguanosine contents) and apoptosis (increased caspase-3 activity). Although lower concentrations (≤60 μg L^-1) of 2,6-BDCQ didn't exhibit significant effect on its survival development or lipid peroxidation of zebrafish, they induced obvious DNA damage and apoptosis occurrence. These results revealed 2,6-BDCQ caused genotoxicity and cytotoxicity to zebrafish. This study provides novel insight into 2,6-DCBQ-induced toxicity in zebrafish.

Determination of dihalobenzoquinones in water using gas chromatography coupled with an electronic capture detector

Dihalobenzoquinones are a group of disinfection byproducts with high potential toxicity and thus currently receiving increased attention. A determination method of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ) was developed upon using liquid-liquid extraction and a gas chromatography with an electronic capture detector (LLE-GC-ECD). The optimized extraction condition was as the following: volume ratio of formic acid to water 0.005%, Na₂SO₄ dosage 200 g L^-1, methyl-tert-butyl ether (MtBE)/water volume ratio 1/10, and extraction with MtBE for once. With the dosed concentrations of 0.5-5.0 μg L^-1, the recovery rates of 2,6-DCBQ and 2,6-DBBQ were 81%-88% and 73%-96%. The limits of quantitation (LOQs) of the LLE-GC-ECD method were 2.4 and 2.7 ng L^-1 in 1-L water for 2,6-DCBQ and 2,6-DBBQ. In six local tap waters, 2,6-DCBQ was detected in the range of <LOQ-20.5 ng L^-1 and no 2,6-DBBQ was detected. The method is recommended for low-cost and rapid determination of 2,6-DCBQ and 2,6-DBBQ in water.

Formation of 2,6-dichloro-1,4-benzoquinone from aromatic compounds after chlorination

Halobenzoquinones are a group of disinfection byproducts formed by chlorination of certain substances in water. However, to date, the identities of halobenzoquinone precursors remain unknown. In this study, the formation of 2,6-dichloro-1,4-benzoquinone (DCBQ), a typical halobenzoquinone, from 31 aromatic compounds was investigated after 60 min of chlorination. DCBQ was formed from 21 compounds at molar formation yields ranging from 0.0008% to 4.9%. Phenol and chlorinated phenols served as DCBQ precursors, as reported previously. Notably, DCBQ was also formed from para-substituted phenolic compounds. Compounds with alkyl and carboxyl groups as para-substituents led to relatively higher molar formation yields of DCBQ. Moreover, p-quinone-4-chloroimide, 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), and para-substituted aromatic amines (e.g., aniline and N-methyl aniline) served as DCBQ precursors upon chlorination. It was deduced that DCBQ was formed from the para-substituted aromatic amines via 3,5-dichloroquinone-4-chloroimide, a structural isomer of 2,6-DCQC. These results suggested that DCBQ was formed by chlorination of natural organic matter containing para-substituted phenolic species and para-substituted aromatic amines, despite the absence of phenol in water.

Occurrence and formation of haloacetamides from chlorination at water purification plants across Japan

The occurrence of six haloacetamides (HAcAms), which are a group of emerging nitrogenous disinfection byproducts, was investigated in drinking water across Japan in September 2015 and February 2016. At least one of the six HAcAms were found in all of the drinking water samples and their total concentrations ranged from 0.3 to 3.8 μg/L. The detection frequencies and concentrations of 2,2-dichloroacetamide (DCAcAm) and 2-bromo-2-chloroacetamide (BCAcAm) were the largest among the targeted HAcAm species. The total HAcAm concentrations in the raw water after chlorination ranged from 0.8 to 11 μg/L. The bromine incorporation factors (BIFs) of the targeted dihalogenated HAcAms (di-HAcAms) (DCAcAm, BCAcAm, and 2,2-dibromoacetamide) in the drinking water samples correlated well with those in the raw water after chlorination. The total HAcAm concentrations and the BIF of the di-HAcAms in the raw water after chlorination correlated with trihalomethane concentrations. HAcAm concentrations after chlorination increased with chlorination time. While the formation of di-HAcAms after chlorination was higher at higher pH, that of 2,2,2-trichloroacetamide remained unaffected by pH.