An area of present cross-sectional research about investigating the concentration of Br-THMs in urine as a biomarker of exposure to drinking water disinfection by-products, in pregnant women was done in Isfahan, Iran, as the first study.
In the previous studies, the concentration of total trihalomethanes (TTHMs) has been identified in the water of Isfahan city (Mohammadi et al., 2016, Ali Dehnavi, 2018, Bijan Bina, 2012). In spite of this issue, TCM was not detected in the urine of pregnant women in this study, but DBCM, BDCM, TBM, and also brominated THMs were measurable. Researchers have attributed this, to the low volatility of Br-THMs (Gängler et al., 2017). Although the ingestion is the main route of exposure to DBPs (Liu, 2014) in a study by Gangler et al., the non-ingestion route, especially through the air, was more important in predicting TCM levels (Gängler et al., 2017).
The lifestyle habits of the participants in this study, such as using suitable ventilation or cool water during washing and bathing, have an effective role in limitation and its exit from the environment. Liu research revealed that hot water tanks are effective in degradation DBPs and have increased THMs (Liu, 2014).
According to Fig. 2, in addition to this study, the amount of Br-THMs in women's urine has been reported in three other countries. The urinary concentration levels of this group of contaminants in this study were dramatically different compared to Kuwait and Cyprus (Charisiadis et al., 2013, Gängler et al., 2017). This is due to personal habits and characteristics such as water consumption patterns and genetics and physiological features that have affected the metabolism of THMs(Rivera-Núñez et al., 2012). But, the same as Cyprus, mean urinary DBCM and BDCM were higher than compared to TBM; the reason is perhaps the increase in hydrophilicity of the compounds in the following order (TBM < DBCM < BDCM < TCM) (Rivera-Núñez et al., 2012). On the other hand, measurement in the blood compared to urine has been shown lower concentrations, which is in contrast to urine analysis. The amount of TBM was higher than DBCM and BDCM because of the lipophilicity of TBM compared to the other compounds (Rivera-Núñez et al., 2012).
Figure 2 Comparison of Br-THMs concentrations in global studies (Charisiadis et al., 2013, Zeng et al., 2016, Cao et al., 2016, Gängler et al., 2017, Wang et al., 2019, Chen et al., 2019, Sun et al., 2020, Liu et al., 2020).
In our study, according to statistical reports, the effective source of receiving Br-THMs in pregnant women in Isfahan was the use of a water storage tank (p < 0.05) (Tables 5). That showed a significant negative correlation with the concentration of urinary Br-THMs in the participants.
Using a tank is a common way for storage of water in the residential house. In this study, the use of water tanks, which are usually made of plastic, with a negative correlation, reduced the amount of DCBM, BDCM, and TBM. Scientific research by Cao et al. showed that the application of polyethylene pipes has been effective on water quality over time by sorption contaminants, especially THMs (Cao et al., 2020). Also, according to the study of Slavik et al., increasing the volume of the storage tank has reduced the amount of disinfection residual, thus affecting the formation of disinfection by-products (Slavik et al., 2020).
In Table 2, in addition to tap water, participants have used other sources, such as bottled water, for drinking; but most of them had a higher average consumption of tap water than other sources. According to the analysis of Charisiadis et al., the amount of THMs in water bottles against tap water was non-detectable (Charisiadis et al., 2013).
Although there was an excessive daily intake of drinking water with an average of 7.14 glasses per day, urinary levels of THMs were reduced because of dilution of the THMs mass (Charisiadis et al., 2013). As a result, according to Table 4, there is no significant relationship between the urinary concentration of these contaminants and water intake (p > 0.05).
Also, Table 4 revealed no significant relationship between other demographic and lifestyle parameters (age, education, weight, BMI, frequency, and time duration of washing dishes, clothes, as well as bathing and cleaning the house) with the concentrations of unadjusted urinary Br-THMs. Charisiadis et al. reported a significant relationship between the concentration of THMs in toilet cleaning and hand washing dishes (Charisiadis et al., 2013). In contrast, Chen et al., similar to the findings of this study, did not report a significant relationship between the concentrations of maternal blood THMs with the parameters of age, BMI, education, drinking water source, and showering (Chen et al., 2019).
In another evaluation, participants' tea consumption did not have a significant correlation with brominated THMs. According to Fakour et al., the use of boiling water and preserving the water temperature at 100°C for a long time, as well as more use of teapot instead of the flask as tea containers, reduces chlorine by 5–19% via better output evaporated volatile compounds into the atmosphere (Fakour and Lo, 2019). In Iran, based on the culture, tea is consumed as a common beverage during the day and for a long time, and also using teapot is usual but our data in this study did not agree with the findings of this researcher (25).
In Table 5, for other qualitative parameters, we did not observe a significant relationship between the concentration of Br-THMs and the use of household water purifiers, boiled water, dishwasher, gloves, and finally the type of detergent.
Carrasco-Turigas et al. stated that the use of household reverse osmosis filters affect the removal of THMs containing bromine as non-volatile compounds, moreover boiling through conventional heating such as electric kettles by creating big bubbles and equally energy had a significant influence on the chloroform removal (Carrasco-Turigas et al., 2013).
Study strengths and limitations
The strengths of this study include the population-based design, high-quality urinary Br-THMs assays.
One of the strong limitations of this study was the small statistical population. According to previous studies, despite long-term sampling, increased the identification of THMs compounds, especially chloroform, which has high volatility(Gängler et al., 2017), but the agreement of the participants to attend in this study depended on the short sampling time. In addition, the majority of participants have not much contribution in household tasks due to being in the third trimester of pregnancy.
The spot urine sampling may not be the best biomarker of maternal Br-THMs exposure and does not control the effect of other pollution during pregnancy.