Benzo-Heterocyclic Compounds In Tap Water From China:Detection Methods And Distribution Characteristics

As two kinds of important benzo-heterocyclic compounds, benzotriazole(BTR) and benzothiazole(BTH) are largely synthesized and widely used in recent years in a variety of consumer products and industrial applications, due to their biological and chemical properties. BTR and BTH, as well as their derivatives are usually highly hydrophilic, and have been frequently detected in groundwater and surface-water environments. Although the acute toxicity of BTRs and BTHs for mammals was relatively low, adverse effects of these compounds have been observed in some in vitro and in vivo tests. At present, information on the occurrence and profile of BTRs and BTHs in tap water is still scarce. Study on the occurrence and profile of BTRs and BTHs in tap water is helpful to understand the pollution of water environments, and also useful in estimating the exposure risk of these chemicals in human.In this paper, solid-phase extraction method was established and ultra-performance liquid chromatography mass spectrometry detection method was used to detect 4 benzotriazoles(including BTR, 5-Me-BTR, 1-OH-BTR, 5-Cl-BTR) and 4 benzothiazoles(including BTH, 2-OH-BTH, 2-NH2-BTH, 2-Cl-BTH) in tap water as well as in surface water and sewage effluent. The recoveries of 73.7%~111.2% were obtained for the target analytes in different water matrices. The limit of detection of target substance was below 5 ng/L except for 2-chlorobenzothiazole.Using established method, benzo-heterocycle compounds were detected widely in 86 water samples from 51 main cities in China. ?BTRs concentrations were in the range of <LOQ-310 ng/L(with a median value of 15.6 ng/L), while ?BTHs concentration range from 40.1 to 1310 ng/L(with a median value of value of 406 ng/L). For the samples with detectable BTR, TTR, and 5-Cl-BTR, significant positive correlation between BTR and TTR, as well as between BTR and 5-Cl-BTR was observed. This suggests similar pollution source of BTR and TTR, while 5-Cl-BTR may be a by-products during the process of chlorine disinfection of tap water. In the water samples with detectable 2-OH-BTH, there was a significant positive correlation between BTH and 2-OH-BTH, which can be explained by the hydroxyl reaction of BTH. According to the concentration level of BTRs and BTHs in tap water and the reported urinary levels of these compounds, BTR exposure through tap water might contribute 12% of BTH daily exposed in human, while the contribution of tap water for BTR, TTR and 2-OH-BTH was less than 2%. Heating had a significant influence on BTH, in which case 90% BTH was removed after boiling for 10 min. However, for other substances(BTR, TTR and 2-OH-BTH), no obvious change of concentrations induced by heating was observed.According to the different water sources, i.e. from surface water or from groundwater, tap water samples were divided into two groups. BTRs' concentrations in group of “from surface water” is significantly higher than those in group of “from groundwater”. The geometric mean concentrations of two groups were calculated to be 21.6 ng/L and 4.3 ng/L, respectively. In tap water from the southern cities, the geometric mean concentration of BTRs reached 39.6 ng/L, which was significantly higher than that from the northern cities(10.9 ng/L). This can be explained by that most southern cities use surface water as tap water source. In tap water from different economic zones, i.e. eastern, central and western zone, highest BTRs level was detected in the samples collected from the eastern economic zone, with a geometric mean of 30.7 ng/L, which was much higher than of the central zone(16.5 ng/L) and the western zone(10.9 ng/L). Positive correlation between BTRs concentration and gross domestic product(GDP) of cities were found. Different to BTRs, no significant difference of BTHs concentration in tap water can be observed, when the water samples were divided according to different water sources, locations and economic zones.Concentrations and profiles of BTRs and BHRs in tap water were compared with that in surface water source and effluents of wastewater treatment plant(WWTP) of Tianjin. Similar compounds profile for BTRs in tap water and in surface water sources were observed, while the concentration of BTRs in tap water was lower than in water sources. Therefore, surface water source was speculated to be the main source of BTRs contamination in tap water. Differently, concentration level of BTHs in tap water of Tianjin was higher than that of the surface water and even the WWTP effluent. Water samples from a tap-water plantin Tianjin and 6 residential quarters which use water from this tap-water plant were further collected and measured for BTH. It is found that the average concentration of BTH in tap water of residential quarters(100.7 ng/L) was higher than in tap-water plant(53.8 ng/L). These results suggest contamination in distribution systems of tap water may played a major role for BTH contamination in tap water. In addition, it should be noted that, BTR might be hydroxylated and chlorinated in the water supply system, because the concentrations of BTR and TTR in the samples collected form tap-water plant were higher than those in tap water of the residential quarters, while the concentrations of 1-OH-BTR and 5-Cl-BTR in tap water of the residential quarters were higher than in water samples from tap-water plant.