Spatial, temporal variability and carcinogenic health risk assessment of nitrosamines in a drinking water system in China

Highlights

• NDMA, NDEA and NPIP in this drinking water system were frequently detected.

• Nitrosamine concentrations decreased from influent water to finished water to tap water.

• Nitrosamine occurrence in tap water varied temporally but not significantly spatially.

• Exposure to drinking water nitrosamines posed higher cancer risk for children than for adults.

Abstract

Nitrosamines, as a class of emerging frequently detected nitrogenous disinfection byproducts (N-DBPs) in drinking water, have gained increasing attention due to their potentially high health risk. Few studies focus on the occurrence variation and carcinogenic health risk of nitrosamines in drinking water systems. Our study aimed to investigate the spatial and temporal variability of nitrosamines in a drinking water system and to conduct a carcinogenic health risk assessment. Three types of water samples, including influent water, treated water and tap water, were collected monthly during an entire year in a drinking water system utilizing a combination of chlorine dioxide and chlorine in central China, and 9 nitrosamines were measured. The nitrosamine formation potentials (FPs) in influent water were also determined. N-nitrosodimethylamine (NDMA) was the most prevalent compound and was dominant in the water samples with average concentrations ranging from 2.5 to 67.4 ng/L, followed by N-nitrosodiethylamine (NDEA) and N-nitrosopiperidine (NPIP). Nitrosamine occurrence varied monthly, and significant seasonal differences were observed in tap water (p < .05). There were decreasing mean NDMA, NDEA and NPIP concentrations from influent water to treated water to tap water, but no significant spatial variability was observed within the water distribution system (p > .05). The average and 95th percentile total lifetime cancer risks for the three main nitrosamines were 4.83 × 10⁻⁵ and 4.48 × 10⁻⁴, respectively, exceeding the negligible risk level (10⁻⁶) proposed by the USEPA. Exposure to nitrosamines in drinking water posed a higher cancer risk for children than for adults, and children aged 0.75 to 1 years suffered the highest cancer risk. These results suggest that nitrosamine occurrence in tap water varied temporally but not spatially. Exposure to drinking water nitrosamines may pose a carcinogenic risk to human health, especially to children.

Introduction

Nitrosamines, as a class of emerging nitrogenous disinfection byproducts (N-DBPs), have aroused increasing concern due to their frequent occurrence and potentially high health risk (Diana et al., 2019; Nawrocki and Andrzejewski, 2011; Song et al., 2015; Ward et al., 2018). The formation of nitrosamines can occur during drinking water treatment involving disinfection with chloramination, ozonation and chlorine dioxide (Bond et al., 2011; Richardson et al., 2007; Zhao et al., 2008). To date, multiple nitrosamines, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosomethylethylamine (NMEA), N-nitrosodi-n-butylamine (NDBA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), N-nitrosodiphenylamine (NDPhA) and N-nitrosopiperidine (NPIP), have been detected in treated water or/and tap water at various levels in different countries, including America (Uzun et al., 2015; Woods et al., 2015; Zeng et al., 2016), Spain (Jurado-Sánchez et al., 2012), Canada (Brisson et al., 2013; Russell et al., 2012), Scotland (Goslan et al., 2009), Australia (Kristiana et al., 2013), Japan (Asami et al., 2009), and China (Bei et al., 2016; Fan and Lin, 2018; Li et al., 2015; Luo et al., 2012; Wang et al., 2016a; Zhao et al., 2019). The United States Environmental Protection Agency (USEPA) has estimated that NDMA has a 10⁻⁶ cancer risk level when its concentration in drinking water is 0.7 ng/L (Integrated Risk Information System (IRIS), 2011), and the World Health Organization (WHO) has set a guideline value of 100 ng/L (World Health Organization (WHO), 2013).

The species and levels of nitrosamines in drinking water systems are influenced by many factors, including weather events (e.g., temperature), source water (e.g., organic precursors), water treatment processes (e.g., types of disinfectants) and distribution system materials (e.g., rubber gaskets) (Bond et al., 2011; Krasner et al., 2013; Kristiana et al., 2013; Uzun et al., 2015; Zhao et al., 2008). As a result, the occurrence of nitrosamines across drinking water systems varies spatially and temporally. A long-term study in the USA has provided evidence that seasons have an influence on the formation of NDMA (Woods et al., 2015), but several other studies have failed to find a temporal trend (Brisson et al., 2013; Li et al., 2015; Woods and Dickenson, 2015). Data on the spatial variation of nitrosamines within drinking water distribution systems are still limited, and there is only evidence that the concentration of NDMA increases with increasing pipe length or residence time (Brisson et al., 2013; Jurado-Sánchez et al., 2012; Woods et al., 2015). Therefore, the characteristics of the spatial and temporal variability of nitrosamines in drinking water systems remain to be elucidated.

The occurrence of nitrosamines in drinking water systems may pose a high health risk to humans. Accumulating animal studies have shown that nitrosamines have mutagenic, teratogenic, and carcinogenic potential (Althoff et al., 1977; Anderson et al., 1979; Mestankova et al., 2014; Sheweita et al., 2017; Wang et al., 2017; Zheng et al., 2018). Some epidemiological studies have also suggested that exposure to nitrosamines is associated with an increased risk of bladder cancer (Diana et al., 2019), esophageal cancer (Totsuka et al., 2019; Zhao et al., 2019), colorectal cancer (Knekt et al., 1999; Zhu et al., 2014), pancreatic cancer (Zheng et al., 2019), liver cancer (Mitacek et al., 1999) and birth defects (Brender et al., 2013). NDMA, NDEA, NMEA, NDPA, NDBA, NPYR and NDPhA have been categorized as class B2 carcinogens (probable human carcinogens) by the USEPA; NDMA and NDEA have been classified as class 2A carcinogens (probably carcinogenic to humans) by the International Agency for Research on Cancer (IARC), and the remaining 6 except NDPhA are class 2B carcinogens (possibly carcinogenic to humans). Nevertheless, only a few studies, mainly focusing on adults, have been performed to assess the human health risk of exposure to nitrosamines in drinking water (Chen et al., 2019b; Fan and Lin, 2018; Ma et al., 2012; Wang et al., 2016b; Yin et al., 2019). There are still data gaps on the health risk with respect to early-life and childhood exposure, and children are generally more vulnerable to hazardous chemicals than adults (Ginsberg, 2003). Moreover, given the spatial and temporal variability of nitrosamine concentrations in drinking water systems, incorporation of such data into human risk assessment may provide more accurate prediction information.

In the present study, we conducted a year-long surveillance of 9 nitrosamines in a drinking water system utilizing a combination of chlorine dioxide and chlorine in a city in central China. We evaluated the occurrence of nitrosamines in different types of water samples (influent water, treated water and tap water) and characterized their spatial and temporal variability. Based on the monitoring data, we further calculated the carcinogenic risks of exposure to nitrosamines in drinking water for adults and children via multiple routes in this city.