Analytical and Toxicity Characterization of Halo-hydroxyl-benzoquinones as Stable Halobenzoquinone Disinfection Byproducts in Treated Water

Abstract

Exposure to chlorination disinfection byproducts (DBPs) is potentially associated with an increased risk of bladder cancer. Four halobenzoquinones (HBQs) have been detected in treated drinking water and have shown potency in producing reactive oxygen species and inducing damage to cellular DNA and proteins. These HBQs are unstable in drinking water. The fate and behavior of these HBQs in drinking water distribution systems is unclear. Here we report the high-resolution mass spectrometry identification of the transformation products of HBQs as halo-hydroxyl-benzoquinones (OH-HBQs) in water under realistic conditions. To further examine the kinetics of transformation, we developed a solid-phase extraction with ultrahigh-performance liquid chromatography tandem mass spectrometry (SPE-UHPLC-MS/MS) method to determine both the HBQs and OH-HBQs. The method provides reproducible retention times (SD < 0.05 min), limits of detection (LODs) at subnanogram per liter levels, and recoveries of 68%-96%. Using this method, we confirmed that decrease of HBQs correlated with increase of OH-HBQs in both the laboratory experiments and several distribution systems, supporting that OH-HBQs were more stable forms of HBQ DBPs. To understand the toxicological relevance of the OH-HBQs, we studied the in vitro toxicity with CHO-K1 cells and determined the IC50 of HBQs and OH-HBQs ranging from 15.9 to 72.9 μM. While HBQs are 2-fold more toxic than OH-HBQs, both HBQs and OH-HBQs are substantially more toxic than the regulated DBPs.

Precursors of Halobenzoquinones and Their Removal During Drinking Water Treatment Processes

“…The wide occurrence of DCBQ precursors detected here is consistent with the prevalence of DCBQ in DWTP effluents. 8,9 TCBQ precursors were also present in all nine influents, but at much lower concentrations (3.6−48 ng/L) compared to those of DCBQ. This may be because TCBQ may largely share the same precursors with DCBQ, where DCBQ may act as the intermediate for TCBQ formation.…”

“…The concentrations of HBQs were all lower than the detection limits in the plant influents from the nine DWTPs, which is consistent with the previous studies that suggested that HBQs were formed by chlorination. 8,9 To evaluate the concentration of HBQ precursors in the plant influents, we performed FP tests on the nine plant influents and measured the formation of the four HBQs. Table 1 presents the results of HBQ FP testing in the nine plant influents.…”

“…These results agree with the previous findings that DCBQ was the most frequently detected HBQ in low-bromide DWTP effluents and in swimming pool water. 8,9,35 DBBQ was detected in the FP samples of only five plant influents where bromide was present ( Table 1). Formation of DCMBQ was limited by its precursor concentration, whereas DBBQ was limited by the bromide content (DBBQ should have the same organic precursors as DCBQ).…”

“…6,7 Recent studies have identified four HBQs, 2,6-dichloro-1,4-benzoquinone (DCBQ), 2,6-dichloro-3-methyl-1,4-benzoquinone (DCMBQ), 2,3,6-trichloro-1,4-benzoquinone (TCBQ), and 2,6-dibromo-1,4-benzoquinone (DBBQ), and these HBQs occurred commonly in drinking water treatment plant effluents at nanogram per liter levels. 8,9 DCBQ was detected most frequently and was the most abundant (up to 275 ng/L) in low-bromide waters among the four HBQs. 8,9 The predicted chronic lowest adverse effect levels (LOAELs) for HBQs were 10000 times lower (i.e., more toxic) than those of the regulated DBPs, such as trihalomethanes (THMs) and haloacetic acids (HAAs).…”

“…8,9 DCBQ was detected most frequently and was the most abundant (up to 275 ng/L) in low-bromide waters among the four HBQs. 8,9 The predicted chronic lowest adverse effect levels (LOAELs) for HBQs were 10000 times lower (i.e., more toxic) than those of the regulated DBPs, such as trihalomethanes (THMs) and haloacetic acids (HAAs). 7 The chronic cytotoxicity (IC 50 at 72 h) of HBQs on Chinese hamster ovary (CHO) cells was significantly higher than those of the regulated DBPs.…”