1This study was supported by grants from the National Science
Council, Republic of China (NSC-87-2815-C-038-014-B).
2To whom correspondence should be addressed. Fax:
886-2-2738-4831. E-mail: [email protected].
doi:10.1006/enrs.2000.4102, available online at http://www.idealibrary.com on
Estimation of Potential Lifetime Cancer Risks for Trihalomethanes from
Consuming Chlorinated Drinking Water in Taiwan
1Ching-Hung Hsu,* Woei-Lih Jeng,- Ruey-Mai Chang,? Ling-Chu Chien,* and Bor-Cheng Han*,2 *School of Public Health, Taipei Medical University, 250 Wu-Hsing Street, Taipei, Taiwan, Republic of China
-Institute of Oceanograghy, National Taiwan University, Taipei, Taiwan, Republic of China; and?Institute of Nuclear Science, National
Tsing Hua University, Hsin-Chu, Taiwan, Republic of China
Received December 16, 1999; published online November 30, 2000
Data on concentrations of trihalomethanes (THMs) in raw and chlorinated water collected from three water treatment plants in Taiwan and esti-mates of the lifetime cancer risk for THMs from drinking water, using age-adjusted factors and volatilization terms, are presented. Data on THM levels in drinking water were obtained from the annual reports of the Environmental Protection Ad-ministration (EPA) of Taiwan. The methodology for estimation of lifetime cancer risks was taken from the USEPA. Chloroform was the major species of THMs, especially in the water plant of south Taiwan. Chloroform contributed the majority of the lifetime cancer risks (range: 87.5}92.5%) of total
risks from the three water supply areas. All lifetime cancer risks for CHCl3, CHBrCl2, CHBr2Cl, and
CHBr3from consuming tap water in the three water
supply areas were higher than 10ⴚ6. The sum of lifetime cancer risks for CHCl3, CHBrCl2, CHBr2Cl,
and CHBr3 was highest (total risk for total
THMs:1.94;10ⴚ4) for tap water from south Taiwan.
2000 Academic Press
Key Words: trihalomethanes; exposure; cancer risks; Taiwan; drinking water.
INTRODUCTION
Water is required to sustain life, but has long been a source of much human illness. In Taiwan, water sources are mostly (59.3%) drawn directly from rivers; the rest comes from groundwater and reser-voirs, accounting for 21.7 and 19.0%, respectively.
Surface water and groundwater sources have be come increasingly contaminated due to increased industrial and agricultural activity. Nearly half of the rivers in Taiwan (48%) were found to be more or less polluted. In 1996, the water quality of most of the smaller tributaries, which are also tap water sources, was rather good (EPA, 1996).
Most of the potable water in Taiwan is tap water, supplying water to 84.2% of the population, or 17,312,204 persons. According to the Taiwan Water Works Corp., 77% of its tap water comes from sur-face water, 30% of which has been more or less polluted. It is known that when water sources are polluted, the costs of treatment (such as chlorine) will increase. When a water source is badly polluted, it can never be used for tap water. The Taiwan EPA reported that 30.01% and 4.81% of the tap water were unacceptable due to the excessive total bacteria and coliform bacteria contents, respectively (EPA, 1996).
Most sources of municipal water supplies are sur-face waters and are often treated with chlorine. The nonmunicipal sources are mainly privately owned wells (groundwater) and are often unchlorinated. Chlorination has been the major strategy for the disinfection of drinking water on Taiwan. It is cur-rently added to approximately 75.8% of the nation’s drinking water.
Chlorination of drinking water has been one of the most effective public health measures ever under-taken (Bull et al., 1995). In the 1970s it was found that chlorine reacted with natural organic matter present in surface water to produce disinfection by-products (DBPs). Special concerns are associated with the trihalomethanes (THMs) because they have been recognized as potentially hazardous and are the major by-products of chlorination (Bull et al., 1995). Chloroform is found in municipal water 77
0013-9351/00 $35.00 Copyright 2000 by Academic Press All rights of reproduction in any form reserved.
supplies that are disinfected by chlorination, the most common disinfection process in Taiwan (Yang
et al., 1998).
Epidemiological studies examining the health ef-fects of chlorinated water have found that popula-tions exposed to chlorination by-products have elevated rates of bladder (Cantor et al., 1998; McGeehin et al., 1993), colon}rectum (Hildesheim
et al., 1998), and brain (Cantor et al., 1999; Wilikins et al., 1979; Lawrence et al., 1984; Flaten, 1992)
cancers. Animal studies have demonstrated that liver, kidney, and intestinal tumorigeneses are asso-ciated with chronic ingestion of trihalomethanes (Dunnick and Melnick, 1993; Doyle et al., 1997). As summarized in a recent meta-analysis by Morris
et al. (1992), higher exposure to chlorination
by-products in drinking water may be related to an approximately 10 to 40% excess risk of cancers of the bladder and colon}rectum. It has also been sugges-ted that there is an association between exposure to chlorination by-products in water and adverse repro-ductive outcomes (Kramer et al., 1992; Bove et al., 1995). THMs in drinking water have been related to spontaneous abortion (Waller et al., 1998). In Taiwan, Yang et al. (1996) indicated that there was a signi7cant association between municipal (chlorin-ated) drinking water in Taiwan and mortality from certain cancers. On the other hand, the results of that study suggest a positive association between consumption of chlorinated drinking water and can-cer of the rectum, lung, bladder, and kidney because chlorination of water is so widely practiced in Taiwan.
Individuals are exposed to volatile compounds present in tap water by ingestion, inhalation, and dermal absorption. Traditional risk assessments for water often consider only ingestion exposure to toxic chemicals, even though showering has been shown to increase the body burden of certain chemicals due to inhalation exposure and dermal absorption. Accordingly, it has been proposed that inhalation and dermal absorption need to be considered in the analysis of total human exposure to volatile contaminants in tap water (Jo et al., 1990; Maxwell et al., 1991;Weisel and Jo, 1996; Weisel et al., 1999; Lin and Hoang, 2000).
This study presents the concentrations of THMs in raw and chlorinated water collected from three different water treatment plants in Taiwan. Furthermore, the data were used to estimate the lifetime cancer risk for THMs from drinking water, using age-adjusted factors and volatilization terms.
MATERIALS AND METHODS
Data on THM levels in drinking water throughout Taiwan were obtained from the annual reports of the Environmental Protection Administration (EPA) of Taiwan. Both raw water and chlorinated drinking water samples were collected from three regional water treatment plants in Taiwan from 1994 to 1997. The raw water and treated water were col-lected once every month from the three water treat-ment plants. The raw water at these waterworks was pretreated and disinfected with chlorine (10:20 mg/L). Water samples were analyzed for THMs by purge and trap followed by GC/MS or GC/electron capture detection (ECD) (Chang et al., 1996). THMs considered in this study are chloroform (USEPA Group B2), bromodichloromethane (USEPA Group B2), chlorodibromomethane (USEPA Group B2), and bromoform (USEPA Group C) (US EPA, 1999).
Smith (1996) has summarized the USEPA methods for cancer risk assessment, which calcu-lates a slope factor (upper-bound lifetime cancer risk per mg< kg!1< day!1
) for many substances. That work combines some ‘‘toxicological constants’’ with predetermined risk levels (a 10!6 cancer risk) and protective human exposure assumption (e.g., 70 kg body mass, 30 year exposure, 2 L/day drinking water ingestion, etc.) to produce risk-based concentrations for contaminants in air, drinking water, edible7sh, and soil. We used this information to calculate life-time cancer risks for THMs and compared the mea-sured environmental levels with EPA’s acceptable concentrations. These risks serve as a surrogate for potential health impacts and can be used to priori-tize problems for attention in Taiwan. The lifetime average daily doses and incremental cancer risk esti-mates corresponding to 30-year residential expo-sures were calculated using the measurements in this study and published exposure guidelines.
The methodology for estimation of target cancer risks (TR) used was provided in USEPA, region III risk-based concentration table (USEPA, 1999). For carcinogenic effects (THMs), risk is expressed as ex-cess probability of contacting cancer over a lifetime (70 years). Because contact rates with tap water for children and adults are different, carcinogenic risks during the7rst 30 years of life were calculated using age-adjusted factors. The models for estimating tar-get cancer risks (lifetime cancer risks) are
TR"CC< EFr < [(K < IFAadj < CPSi)#(IFWadj < CPSo)] ATc< 1000 lg
TABLE 1
Geometric Mean Trihalomethanes (THMs) Concentration (lg/L) in Raw and Chlorinated Water Collected from Different Water Supply Plants and Water Sources of Taiwan (1994:1997)
North Taiwan Central Taiwan South Taiwan South Taiwan*
Raw Chlorinated Raw Chlorinated Raw Chlorinated Raw Chlorinated
Chemical water water water water water water water
Chloroform (CHCl3) 2.05 14.2 2.30 14.4 1.50 27.6 1.68 4.19 Bromodichloromethane (CHCl2Br) 0.32 5.12 0.27 3.24 0.06 6.35 ND 0.11 Chlorodibromomethane (CHClBr2) 0.15 4.19 0.11 0.63 0.08 3.92 ND 0.31 Bromoform (CHBr3) ND 0.21 0.08 0.08 0.03 0.68 ND ND Total THM 2.52 23.8 2.76 18.4 1.67 38.5 1.68 4.31
Note. ND, bromodibromomethane (0.03, chlorodibromomethane (0.03, bromofrom (0.02lg/L, respectively. *Well water. and IFWadj L< year Kg< day" EDc< IRWc BWc #(EDtot!EDc)< IRWa BWa ,
where CC is contaminants in water (lg/L), TR is target cancer risk, CPSo is carcinogenic potency slope oral (risk per mg/kg/day), CPSi is carcinogenic potency slope inhaled (risk per mg/kg/day), BWa is body weight, adult (70 kg), BWc is body weight, age 1}6 years (15 kg), ATc is averaging time carcinogens (25,550 days), IFAadj is inhalation factor, age-ad-justed (11.66 m3
-years/kg-days), IRWa is tap water ingestion, adult (2 L/day), IRWc is tap water inges-tion, age 1}6 years (1 L/day), IFWadj is tap water ingestion factor, age-adjusted (1.09 L-years/kg-days), EFr is exposure frequency (350 days/year),
EDtot is exposure duration, total (30 years), EDc is
exposure duration, age 1}6 years (6 years), and K is volatilization factor (0.5 L/m3
).
RESULTS AND DISCUSSION
Concentrations of THMs in Raw and Chlorinated Water
Table 1 shows the geometric mean THMs concen-tration (lg/L) in raw and chlorinated water collected from three different water supply plants and one well water source in Taiwan (1994:1997). THM con-centrations (geometric means) in chlorinated water have the following ranges: chloroform (CHCl3), 4.2:27.6 lg/L; bromodichloromethane (CHCl2Br), 3.24:6.35 lg/L; chlorodibromomethane (CHClBr2), 0.63:4.19 lg/L; and bromoform (CHBr3),
0.08:0.68 lg/L. Chloroform was the major species of THMs, especially in the water plant of south Taiwan. Similar results were also observed in Korea (Shin et al., 1999). The bromo-THMs, including CHBr3, CHBr2Cl, and CHBrCl2, were present in lower concentrations than CHCl3. In most studies, concentrations of CHBr3are nondetectable, whereas those of CHBr2Cl are very low and do not vary with time (Chang et al., 1996). In addition, the lowest THM (18.4lg/L) concentration was observed in cen-tral Taiwan, which also had the lowest TOC concen-tration. Chang et al. (1996) reported that chemical oxygen demand (COD) had a strong positive correla-tion with chlorine demand, which suggests that COD could be regarded as a surrogate parameter for water quality concerns.
THMs in drinking water are regulated at a max-imum contaminant level (MCL) of 100lg/L for the sum of the four THMs in Taiwan. However, it is probable that MCL will soon be lowered to 10:25 lg/L, because total trihalomethane levels 9100 ppb reduced birth weight among term births (Bove et al., 1995). From the risk-based concentra-tion (RBC) table of the USEPA it is found that the total risk-based concentration (TRBC) for THMs is 2.85lg/L (sum of RBC for CHCl3, CHBrCl2, CHBr2Cl, and CHBr3) (USEPA, 1999; Smith, 1996). Figure 1 shows the GM concentration of THMs in raw water from various water sources generally less than TRBC (2.85lg/L) of the USEPA. The concen-trations of THMs in chlorinated water are much higher than those in raw water by about 9.44, 6.67, and 23.1 times for north, central, and south Taiwan, respectively. As shown in Fig. 2, chloroform concen-trations of both surface and ground water are much higher than the RBC for chloroform of the USEPA by
FIG. 1. Total THMs in raw and chlorinated water of different areas of Taiwan compared to the total risk-based concentration (TRBC) of USEPA.
FIG. 2. Chloroform concentrations in drinking water after being chlorinated from different water sources of south Taiwan compared to the risk-based concentration (RBC) for chloroform of USEPA.
FIG. 3. Total THMs in raw and chlorinated water of Taiwan compared to the total risk-based concentration (TRBC) of USEPA.
about 184 and 27.9 times, respectively. Higher chloroform concentrations are observed in surface water than in groundwater. Higher chloroform con-centrations in surface water could be attributed to
total dissolved organic matter concentrations. Chang et al. (1996) found the highest concentration of TOC (23 mg/L) in raw water collected from water supplies of south Taiwan. After chlorination, the concentration of THMs in chlorinated surface water is much higher than that of RBC of the USEPA. THMs in chlorinated ground water are slightly high-er than that of TRBC for THMs of the USEPA (Fig. 3). A similar analysis of volatile organic compound con-centrations in Taiwan’s drinking water has been reported (Kuo et al., 1997).
Estimation of Lifetime Cancer Risks for THMs
Potential human health risks associated with THM uptake for tap water and well water were evaluated. Carcinogenic risks were estimated by multiplying the exposure estimate by the carcino-genic slope factor for consuming four THM com-pounds, 6.10;10!3 , 6.20;10!2 , 8.40;10!2 , and 7.90;10!3 (mg/kg/day)!1 for CHCl3, CHBrCl2, CHBr2Cl, and CHBr3, respectively (USEPA, 1999).
Table 2 shows the various estimated lifetime can-cer risks for four THM compounds associated with different chlorinated water at various consumption rates. These risks varied with different water sour-ces, water supply areas, and consumption rates. For example, based on a consumption rate of 1:3 liter/day, all lifetime cancer risks for CHCl3,
TABLE 2
Estimated Lifetime Cancer Risks for THMs from Ingested Different Water at Various Ingestion Rates (1}3 liter) Tap water
*Well water
North area Central area South area South area
Chemical (;10!6) 1 L 2 L 3 L 1 L 2 L 3 L 1 L 2 L 3 L 1 L 2 L 3 L Chloroform (CHCl3) 91.6 92.3 92.5 93.1 93.2 93.9 178 179 180 27.0 27.2 27.3 Bromodichloromethane (CHCl2Br) 3.22 4.74 6.22 2.03 2.99 3.93 3.99 5.87 7.70 0.069 0.101 0.133 Chlorodibromomethane (CHClBr2) 1.78 2.63 3.45 0.536 0.792 1.04 3.33 4.91 6.46 0.263 0.388 0.509 Bromoform (CHBr3) 0.081 0.089 0.097 0.031 0.034 0.037 0.261 0.287 0.312 ;? ;? ;? Total THM 97.0 99.8 102 95.7 97.1 98.9 186 190 194 27.4 27.6 27.7 ?Not determined.
FIG. 4. The percentage contribution of total risks for various THMs from three water treatment plants of Taiwan.
CHBrCl2, CHBr2Cl, and CHBr3from consuming tap water of three water supply areas were higher than 10!6, the lower end of the range of acceptable risk by the USEPA. The highest lifetime cancer risk of 1.80;10!4 (based on 3 liter water/day) was for chloroform in tap water from water supply plants of south Taiwan, and this was higher than the risks from well water (2.73;10!5).
A risk additivity hypothesis was assumed for four THMs. Table 2 shows the risk values for the popula-tions in several areas calculated for each substance and the additive risks to take all THMs into consid-eration. Exposure to multiple toxicants may result in additive and/or interactive effects. Interactive ef-fects may be synergistic or antagonistic. The USEPA sets exposure standards using an additive model (Hallenbeck, 1993). Accordingly, the sum of lifetime cancer risks for CHCl3, CHBrCl2, CHBr2Cl, and CHBr3 was highest (total risk for total THMs" 1.94;10!4) from consuming tap water from south Taiwan. All additive lifetime cancer risks for THMs from consuming tap water and well water were high-er than 10!5
(Table 2). Based on consumption of 2 liter/day, the lifetime cancer risks for THMs of consuming tap water and groundwater from the four different water supply areas were higher than the EPA acceptable risk (10!6
) by about 99.8, 97.1, 190, and 27.6 times, respectively (Table 2). Figure 4 shows the percentage contribution of total risks for various THM compounds in tap water collected from three water supply areas in Taiwan. The lifetime cancer risks for chloroform made the highest per-centage contribution (range from 87.5 to 92.5%) to total risks. Lahey and Connor (1983) calculated that the risk from drinking water is about 3.4;10!5, with more than half of the risks coming from
chloro-form contamination. Our 7ndings are in no way intended to suggest that the disinfection of drinking water with chlorine should be abandoned. However, it should not be forgotten.
In the United States many drinking water regula-tions for organic chemicals are based on the goal of minimizing the risk of developing cancer. The level of acceptable risk in the United States is currently considered to be between one-in-ten-thousand and one-in-a-million. In the underdeveloped world, how-ever, millions of children under the age of 5 years die each year due to waterborne infectious diseases. Thus, the goal of the water supply engineering in this situation is signi7cantly different. When com-paring the risk of death from microbiological patho-gens in drinking water with the risk of cancer from disinfection by-products, the risk of illness and death from those pathogens is 100 to 1000 times greater than the risk of cancer.
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