Ecotoxicology and Environmental Safety 116 (2015) 129–136
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Multipathways human health risk assessment of trihalomethane exposure through drinking water Azhar Siddique a,b,n, Sumayya Saied b, Majid Mumtaz b, Mirza M. Hussain c, Haider A. Khwaja c,d a
Unit for Ain Zubaida & Groundwater Research, King Abdulaziz University, Jeddah, Saudi Arabia Department of Chemistry, University of Karachi, Karachi, Pakistan c Wadsworth Center, New York State Department of Health, Albany, NY, USA d Department of Environmental Health Sciences, School of Public Health, University at Albany, Albany, NY, USA b
art ic l e i nf o
a b s t r a c t
Article history: Received 21 August 2014 Received in revised form 10 March 2015 Accepted 11 March 2015 Available online 20 March 2015
Life-time human health risk of cancer attributed to trihalomethanes in drinking water in an urbanindustrialized area of Karachi (Pakistan) was conducted through multiple pathways of exposure. The extent of cancer risk was compared with USEPA guidelines. Human health cancer risk for total trihalomethanes (TTHMs) through ingestion and dermal routes were estimated in “acceptable-low risk” ( Z1.0E 06; r5.10E 05), whereas through inhalation route it was estimated under “acceptable-high risk” (Z 5.10E 05; r1.0E 04) category. However, at some industrial–urban areas cancer risk for CHCl3 were estimated under “unacceptable risk” ( Z1.0E 04) through inhalation route. & 2015 Elsevier Inc. All rights reserved.
Keywords: Trihalomethanes Chloroform Risk assessment Disinfection byproducts Public health
1. Introduction The presence of microbiological organisms is the most common pollution culprit in the urban areas and microorganisms, such as bacteria, viruses, and protozoa can cause serious illnesses and deaths (Uyak et al., 2005). The most common and economic method of disinfection is chlorination (Yang et al., 1998; Hsu et al., 2001; Rodriguez and Serodes, 2001; Hamidin et al., 2008). Although chlorine disinfection reduces mortality and morbidity due to water-borne diseases (Calderon, 2000; Golfinopoulos and Nikolaou, 2005), chlorine can react with natural organic matter (NOM) and form various types of disinfection byproducts (DBPs), chiefly trihalomethanes (THMs). Epidemiological and clinical studies have revealed that several health effects are associated with the exposure to DBPs, such as elevated rates of bladder, colon– rectum and brain cancers (Cantor et al., 1998; McGeehin et al., 1993; Hildesheim et al., 1998; Cantor et al., 1999; Wilkins et al., 1979; Flaten, 1992; King et al., 2000a), cardiac anomalies, stillbirths, miscarriages, low birth weights and pre-term deliveries, and neural tube defects (Mills et al., 1998; Richardson., 2005; King et al., 2000b). Epidemiological data availability in Pakistan from n Corresponding author at: Unit for Ain Zubaida & Groundwater Research, King Abdulaziz University, Jeddah, Saudi Arabia. E-mail address: [email protected] (A. Siddique).
http://dx.doi.org/10.1016/j.ecoenv.2015.03.011 0147-6513/& 2015 Elsevier Inc. All rights reserved.
population-based registries is mostly unavailable, and institutional based registries seldom provide estimates of disease distribution. The only population-based cancer registry was established in Karachi, where statistics for 9 years (1995–2003) were published. The population-based cancer registry in Karachi has identified 8 major classes of cancers prevailing in males (lung (11%), oral cavity (13.1%), larynx (6.1%), urinary bladder (4.8%), prostate (4.1%), lymphoma (7%), pharynx (4.3%), colo-rectum (4.4%)) and females (breast (34.6%), oral cavity (8.9%), cervix (4.1%), esophagus (3.7%), ovary (4.2%), lymphoma (3.5%), gall bladder (2.6%), skin (2.6%)). The estimates show that the projected figures for Pakistan are double the estimates by the World Health Organization (WHO). Breast cancer rate among women is high in Karachi (34.6% rate of female cancer), the highest in Asia (Bhurgri, 2004). Exposures to DBPs can occur throughout a lifetime via multiple pathways, such as water ingestion by the oral route, inhalation through breathing and dermal contact through skin during regular indoor activities, such as showering, bathing and cooking. These chronic exposures to DBPs may pose risks to human health. Traditional risk assessment studies only considered the oral route of water to estimate the life time health risk. However, other routes of DBPs exposure for health risk assessment are now considered in scientific studies (Hsu et al., 2001; Mallika et al., 2008; Uyak, 2006; Lee et al., 2004; Weisel and Jo, 1996; Weisel et al., 1999). The study area, which encompasses the metropolitan area of
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Karachi along with its suburbs, is the world's second most populated city, (estimated at 20 million, http://www.karachicity.gov.pk/), spread over 3530 km2. Karachi is situated at (24°45′N–25°01′N and 66°55′E–67°15′E). The main source of water supply to the city of Karachi is from surface water (i.e., Indus River through Kenjhar and Haleji Lakes, and Hub dam built on Hub River). The present study was aimed at using a multi-pathway exposure model on the basis of our earlier studies (Siddique et al., 2012) for lifetime human health risk assessment to evaluate and quantify the adverse effect of trihalomethanes (THMs) in tap water.
2. Materials and methods Drinking water samples from various areas of the city (Fig. 1) were collected in headspace-free borosilicate amber glass bottles containing about 1.7 mL sodium thiosulfate (10%) quenching solution (APHA, 1992; Rodriguez and Serodes, 2001). Once collected, samples were stored in the dark at 4 °C and carried to the laboratory for analytical procedures. A modified EPA Method (EPA 551.1) was applied for the assessment of THMs (MTBE) (Nikolaou et al., 2002; Golfinopoulos et al., 2005). Two milliliter of MTBE extraction solvent were added to 35 mL of water sample in a 40 mL glass vial containing anhydrous sodium sulfate as drying agent. For phase separation, the vial was shaken for 1 min and left undisturbed for further 2–3 min. The upper 1 mL organic layer was injected into HP 5890 gas chromatograph (GC) equipped with DB5 chromatographic column and electron capture detector (ECD). Analysis conditions: injection on column volume 2 mL; oven temperature 30 °C for 10 min, 30–41 °C at 3 °C/min; hold at 41 °C for 6 min; 41–81 °C at 5 °C/min; 81–180 °C at 25 °C/min and hold at
Table 1 Average THMs level (mg/L) in water samples of different localities in Karachi. Locality
Hawk's bay SITE Orangi/Baldia Saddar Jamshaid Town Liaqutabad Mansoora Taimuria North Karachi DHA/Clifton Korangi/Landhi Shah Faisal/ Airport Gulshan e Iqbal Malir Ibrahim Hydri LITE/Cattle colony Port Qasim
n
Average THMs level (lg/L) CHCl3 SD
CHBrCl2 SD
CHBr2Cl SD
8 12 16 20 20 8 8 16 12 13 24 27
46.2 61.2 76.8 72.5 55.2 90.8 98.5 79.3 62.4 71.1 56.2 79.8
15.8 23.0 26.6 25.0 27.9 40.0 41.5 40.9 29.7 26.0 21.9 30.8
3.0 2.7 4.1 3.3 2.7 2.8 3.2 3.1 4.5 3.00 2.9 3.1
0.37 0.43 1.6 1.4 0.65 0.64 0.94 1.1 1.5 1.5 1.2 0.89
0.48 1.5 2.6 2.0 1.2 1.5 1.8 1.5 2.4 1.7 1.6 1.7
0.83 49.7 0.27 65.4 0.97 83.5 0.81 77.8 0.35 59.1 0.29 95.0 0.52 103.5 0.53 83.8 0.87 69.3 1.09 75.8 0.81 60.7 0.54 84.6
9 8 11 8
66.5 49.7 82.2 63.3
31.8 20.5 37.7 27.6
3.5 3.2 2.6 3.2
1.1 1.5 2.1 1.2
2.3 2.0 1.7 1.8
0.14 0.97 1.24 0.76
72.3 54.9 86.5 68.3
0.82 1.7
0.20
94.4
16 90.0
55.3 2.7
Total THMs
180 °C for 6 min; carrier gas Helium at a rate of 1.5 mL/min; detector temperature of 275 °C. A DB-1701 capillary column (30 m, 0.32 mm i.d., 0.25 mm film thickness) was used for the confirmation analysis. Stock THM standards were obtained from AccuStandard and were diluted to different concentration levels. The identification of individual THMs was based on the comparison of retention times of THMs in samples with those of THM standards.
Fig. 1. Map of the sampling locations.
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Table 2 Summary of seasonal variations in THMs (mg/L) in water samples. Winter
Min. Max. Mean SD
Summer
CHCl3
CHBrCl2
CHBr2Cl
Total THM
CHCl3
CHBrCl2
CHBr2Cl
Total THM
17.0 167.3 67.8 33.0
1.8 6.2 3.3 1.2
0.6 3.5 1.9 0.7
7.0 173.2 71.3 34.5
8.4 146.2 71.1 32.4
0.19 5.6 3.1 1.2
0.22 3.3 1.8 0.7
4.4 148.0 72.3 34.5
120
Table 4 Cancer risk estimates of THMs through ingestion, dermal and inhalation exposure routes.
100
Concentration [ug/L]
Exposure route WHO and USEPA limit
80
CHCl3
CHBrCl2
CHBr2Cl
TTHMs
Ingestion/oral
Mean 6.78E 06 3.04E 06 Min. 9.22E 07 1.85E 07 Max. 1.60E 05 6.05E 06 Median 6.23E 06 2.89E 06
Dermal/absorption
Mean 2.73E 05 1.22E 05 9.39E 06 4.42E 05 Min. 3.72E 06 7.45E 07 1.19E 06 8.89E 06 Max. 6.46E 05 2.44E 05 1.84E 05 8.62E 05 Median 2.51E 05 1.17E 05 8.91E 06 4.16E 05
60
40
2.33E 06 1.10E 05 2.95E 07 2.20E 06 4.56E 06 2.14E 05 2.21E 06 1.03E 05
20
Inhalation/breathing Mean 6.84E 05 1.28E 07 9.78E 08 6.68E 05 Min. 1.08E 07 7.77E 09 1.24E 08 2.03E 07 Max. 1.76E 04 2.54E 07 1.92E 07 1.76E 04 Median 6.20E 05 1.21E 07 9.28E 08 5.99E 05
0
Localities
Fig. 2. Distribution of TTHMs exceeding USEPA and WHO guidelines.
Table 3 Multipathways slope factor (SF) for THMs (mg/kg day) 1 and reference dose (RfD) values (mg/kg/day) (USEPA, 2009; Legay et al., 2011). THMs
Carcinogenicity
Ingestion/dermala
Inhalationb
RfD
CHCl3 CHBrCl2 CHBr2Cl CHBr3
B-2 B-2 C B-2
6.10E 03c 6.20E 02d,e 8.40E 02d,e 7.90E 03d,e
8.10E 02c 6.20E 02d 8.40E 02d 3.90E 03c
1.00E 02 2.00E 02 2.00E 02 2.00E 02
a Slope factors of oral route were used to calculate cancer risk of THMs through dermal contact. b Oral exposure slope factors of CHBrCl2 and CHBr2Cl were adopted for inhalation exposure. c RAIS (2009). d Lee et al. (2009). e IRIS (2009).
assessment was evaluated for multiple routes of exposure into consideration, such as oral, dermal (skin contact) and inhalation absorption (USEPA, 1989, 2005). Showering, bathing and oral consumption activities of water were mainly considered as dermal, inhalation and oral exposure (Williams et al., 2002; Lee et al., 2004, 2006; Viana et al., 2009; Uyak, 2006). The unit cancer risks were calculated through chronic daily intake (CDI) and corresponding slope factor (SF), whereas the hazardous development effect and indices were evaluated by calculating reference doses (RfDs) and reference concentrations. The CDI for each route of exposure i.e., oral, dermal and inhalation was calculated for each trihalomethane studied except for CHBr3 due to its low and sporadic occurrences in the study area as follows (USEPA, 2005; Lee et al., 2004; Legay et al., 2011):
CDI oral =
CW*IRw*EF*ED BW*AT
CDI dermal = Prior to each set of samples to be analyzed, the GC was calibrated with a series of standards. Then 6 point calibration was performed over the established concentration range. Linear regression of peak area versus concentration gave a good fit (r2 40.99). The THMs were quantified from peak areas obtained through automated integration and by comparison with known concentration of standards. 2.1. Exposure and risk assessment Human health risk assessment was estimated for the THMs occurrences in drinking water samples in Karachi, based on the US Environmental Protection Agency (USEPA) guideline (USEPA, 1999, 2002, 2005), Lee et al. (2004) and Legay et al. (2011). The risk
(1)
CW*SA*Kp*ET*EF*ED BW*AT
(2)
Ca*IRa*ET*EF*Ed BW*AT
(3)
CDI inhalation =
where CW is the concentration in water sample (mg/L), IRw the ingestion rate of drinking water (L/day), EF the exposure frequency (day/year), ED the exposure duration (years), SA skin surface area of human body (cm2), Kp the specific dermal permeability (cm/h), ET the exposure time (h/event), Ca the concentration of THM in the breathing air zone (mg/m3), IRa the inhalation rate (m3/h), BW is the body weight (kg) and average life time (days). Certain assumptions were made in addition to USEPA values to accommodate local factors. Since present study does not differentiate between male and female, average body weight of 65 kg (male
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Fig. 3. Cancer risk of THMs through oral, dermal and inhalation routes.
67.2 kg, female 63.9 kg), and adult exposure of 30 years average (male 64 years and female 66 years) (PAP, 2002; WHO, 2013) were adopted. The amount of water ingested (2.48 L/day) was considered on moderate consumption level for this study on the basis of study carried out in similar region (Choudhury et al., 2001), and skin surface area of 20,000 cm2 were used (USEPA, 1997). The concentrations of CHCl3 in air (Ca for CHCl3) were based on the Jo et al. (1990) study and statistical model by Kar (2000) as described by Legay et al. (2011). A volatilization factor of 5 10 4 1000 L/ m3 was used for the estimation of Ca for CHBrCl2 and CHBr2Cl (USEPA, 1991). Unit cancer risk through the multiple exposure routes for each chlorination byproduct species was calculated as follows (Eq. (4)) (USEPA 1989, 2005) and the total cancer risk (RT) for each location obtained by the summation of the individual risk estimate of CHCl3, CHBrCl2 and CHBr2Cl (Eq. (5)). Total risk (RT) is expressed as excess probability of contacting cancer over a lifetime period.
Rm =
∑ SFm*CDIm i
(4)
where Rm is the unit risk estimate of the mth compound (unitless of probability), i the exposure routes, SF the slope factor values (RAIS, 2009; IRIS, 2009; Lee et al., 2009; Legay et al., 2011), CDI the chronically daily intake and RT is the total cancer risk (unitless of probability).
3. Results and discussion The drinking water samples were collected from 18 localities in Karachi during the winter (October–February) and summer (May–
August) in year 2007 and 2008 and THMs analysis was performed. Average concentrations of THMs in water samples of selected localities are shown in Table 1 and seasonal variations are summarized in Table 2. Considerable variations of TTHMs levels (49.7– 103.5 mg/L) among selected localities were observed (Table 1). Comparatively, higher levels of THMs were found in central part of the city which is highly populated, served with drainage rivers of Lyari, and with poor infrastructure i.e., Liaqutabad, Mansoora, Orangi and Shah Faisal/Airport. CHCl3 is the largest contributor among the TTHMs in all the localities followed by CHBrCl2 and CH Br2Cl. Similar to earlier studies (Uyak, 2006; Toroz and Uyak, 2005; Uyak and Toroz, 2005; Lee et al., 2004; Hsu et al., 2001) concentrations of CHBr3 were detected in few samples and in low limits therefore it was not considered in the present study. Table 2 depicts the summarized seasonal difference among TTHMs. There were no significant difference among the winter and summer (post- and pre-monsoon) seasons was found. However, a wide range variations of TTHMs within the seasons of winter (7.0– 173.2 mg/L) and summer (4.4–148.0 mg/L) were observed and could result in a considerable range of cancer risk. Results were compared with USEPA regulation and WHO guidelines of 80 mg/L (USEPA, 2009) (Fig. 2) due to nonexistence of local legislation and guidelines for THMs. Compliance with WHO guideline and USEPA regulation was assessed using average concentrations of TTHMs in selected communities. Seven out of eighteen communities (Orangi/Baldia, Liaqutabad, Mansoora, Taimuria, Shah Faisal/Airport, Ibrahim Hydri, and Port Qasim) exceeded USEPA national primary drinking water regulation and WHO guideline of 80 mg/L and shows a greater tendency of THMs formation in the distribution network. Cancer risk assessment through ingestion, dermal and
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133
2.0E-04
19.2%
55.8%
25.0%
Health Risk
1.5E-04
1.0E-04
5.0E-05
0.0E+00
CHCl3
CHBrCl2
CHBr2Cl Slected communities
Fig. 5. Average cancer risk for THMs from different pathways in selected communities.
21.2%
1.4E-04 1.2E-04 1.0E-04
Cancer Risk
54.7% 24.1%
8.0E-05 6.0E-05 4.0E-05
CHCl3
CHBrCl2
CHBr2Cl
2.0E-05 0.0E+00 Oral
0.14%
Inhalation
Total
Health Risk Pathways
0.19%
Fig. 6. Average cancer risk through different pathways for Karachi population.
99.7%
CHCl3
Dermal
CHBrCl2
CHBr2Cl
Fig. 4. Contribution of THMs to average risk estimates for life time cancer through (A) ingestion/oral, (B) dermal/absorption and (C) inhalation/breathing routes.
inhalation exposure was carried out in the Karachi distribution system. Table 3 shows the slope factor or potency factors for THMs that are associated with lifetime cancer risk to the exposed population. Results of 95th percentile values of cancer risk through ingestion or oral exposure are summarized in Table 4 and spatial variability is depicted in Fig. 3. Average life time cancer risk for THMs in drinking water samples was found to be higher than the negligible cancer risk of 10E 06 through all the routes and the contribution of risk was observed in the following order:
CHCl3 4CHBrCl2 4CHBr2Cl. Maximum unit cancer risk of 2.57E 04 for CHCl3 was observed in the industrial areas of Port Qasim and 3.07E 05 and 2.32E 05 for CHBrCl2 and CHBr2Cl was found in Saddar, the downtown area. Submersion in industrial and domestic effluents due to old and poor infrastructure may expose areas’ populations to multiple toxicants of varying nature, which may result in additive effects and could increase the health deterioration (Hsu et al., 2001). The median lifetime cancer risk of 1.03E 05 was estimated for TTHMs (CHCl3, CHBrCl2 and CHBr2Cl) through ingestion/oral route higher than USEPA's negligible risk of 1.0E 06. The highest TTHMs lifetime cancer risk through oral route was found in Port Qasim, Saddar and SITE localities. CHCl3 made the highest percentage contribution to the average lifetime cancer risk (55.8%), followed by CHBrCl2 and CHBr2Cl with 25.0% and 19.2%, respectively (Fig. 4). A similar trend of higher CHCl3 percent contribution to the average lifetime cancer risk through ingestion has been observed in previous studies (Hsu et al., 2001; Lahey and Connor, 1983), whereas Uyak (2006) and Lee et al. (2004) reported CHBr2Cl and CHBrCl2, respectively, to be the highest contributor to the average lifetime cancer risk. Lifetime cancer risk through dermal absorption of THMs upon showering and bathing were estimated in water. Slope factor (SF) of ingestion/oral route is used for the dermal/absorption route and ingestion/oral slope factor of CHBrCl2 and CHBr2Cl were adopted for inhalation exposure similar to earlier studies (Lee et al., 2009,
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Fig. 7. Distribution of probabilistic risk zones for human health in Karachi.
2004; Uyak, 2006). A skin surface area of 2.0E þ04 cm2 has been used for the risk estimation though several studies have calculated risk separately for males and females due to the difference in skin surface area in male and females (Uyak, 2006; Lee et al., 2004, 2009). Table 4 shows the 95th percentile lifetime cancer risk through dermal absorption and Fig. 3 shows the spatial distribution among the communities. Average and median cancer risk estimates through dermal absorption were higher than USEPA negligible human health risk. Localities of Port Qasim and Saddar downtown areas showed relatively higher risk estimates. The highest values of risk for CHCl3 were estimated in the Port Qasim industrial area located on the shore line of Arabian Sea. The highest risk of TTHMs through dermal/absorption route was found at Port Qasim (8.62E 05) industrial area and Saddar (8.58E 05) downtown area. The TTHMs cancer risk through dermal absorption route ranges between 8.89E 06 and 8.62E 05 (Table 4). The percentage contribution of each THM to the dermal cancer risk estimates followed the pattern of the ingestion route i.e., CHCl3 (54.7%), CHBrCl2 (24.1%), CHBr2Cl (21.2%) (Fig. 4). The inhalation exposure through CHCl3 is assumed to be the major contributor to lifetime cancer risk. Since CHCl3 has a lower boiling point than other THMs, it is assumed to be the major contributor through inhalation route and several studies have directly estimate the cancer risk of CHCl3 from concentration in water through its volatilization factor (Wang et al., 2007; Uyak, 2006; Lee et al., 2004). In the present study, the CHCl3 in air through bathing and showering was estimated by the statistical model used previously by Legay et al. (2011), Kar (2000), Nazir and Khan (2006). The major contributor through inhalation was CHCl3 (99.7%) (Fig. 4). As evident from Table 4, mean (6.68E 05) and median (5.99E 05) cancer risk of CHCl3 inhalation route are well above the USEPA 1.0E 06 negligible risk. The average distribution of inhalation risk can be viewed spatially in Fig. 3. The total lifetime cancer risk (CR) as RT was estimated in each
sampling location by adding the studied THMs cancer risk through multiple pathways exposure under study
RT =
∑ Rm
(5)
The total cancer risk (RT) for THMs through oral, dermal and inhalation for each of the locality are described in Fig. 5. It shows that inhabitants at a higher risk if all the conditions of THM precursors, disinfection technology practices, temperature etc. remained in similar fashion. CHCl3 is the major contributor among the risk factor through all the exposure routes. Fig. 6 depicts the overall contribution of higher CHCl3 and respective THMs (CHBrCl2, CHBr2Cl) in the average cancer risks through exposure routes and for total cancer risk. The distribution probabilities of cancer risk were estimated by the ordinary kriging in ArcGISs and distributed into four categories according to their nature and extent of cancer risk based on the USEPA guidelines for human health risk (Hammonds et al., 1994; USEPA, 2001). These four categories are divided into negligible (RT o1.0E 06), acceptable low (1.0E 06 rRT o5.10E 05), acceptable high (5.10E 05rRT o1.0E 04) and unacceptable (RT Z1.0E 04) risk zones (Legay et al., 2011). The estimated probabilistic distribution of the lifetime cancer risk approximations in the drinking water samples are presented in Fig. 7. Probabilities of occurring cancer risk are illustrated with the recommendation of the zone where no action, low and high priority of monitoring and immediate action is required. High risk zones are characterized by localities surrounded by industrial areas and streams of Lyari and Malir River (Fig. 7) containing untreated wastes from industry and domestic sources. The impact of poor infrastructure in old populous areas of the city and thickly populated areas around industrial zones could also be an important factor in providing precursor organic compounds to generate toxicological levels of disinfection byproducts in addition to excess chlorination practices by the local authorities. It is evident from
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the probability distribution of life time cancer risks that careful monitoring of disinfection dosage (chlorination) is very important for the city water distribution and dosage should be monitored for optimum disinfection. Introduction of technological advancement of alternate options, properly maintained monitoring network and skilled human resource could help city and public health mangers to reduce the chances of consumer exposure to potent toxicological impacts of chlorine disinfection by products.
4. Conclusions In conclusion, the present study provides a primary human health risk categorization for disinfection by-products in drinking water of the industrial–urban city of Karachi. Our results show that the city water supply has a great potential for generating chlorination by products i.e., trihalomethanes, which potentially may exert a burden of health risk to its inhabitants. Therefore, we recommend a carefully monitored program of chlorination doses, otherwise, alternate disinfection technologies are warranted.
Acknowledgments The authors gratefully acknowledge the funding support of Higher Education Commission of Pakistan (Grant No. 20-613/ R&D/ 06/755). Authors are also thankful to the Wadsworth Center, New York State Department of Health, Albany, NY and King Abdulaziz University management for the facilitation of resources for this study.
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Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv
Multipathways human health risk assessment of trihalomethane exposure through drinking water Azhar Siddique a,b,n, Sumayya Saied b, Majid Mumtaz b, Mirza M. Hussain c, Haider A. Khwaja c,d a
Unit for Ain Zubaida & Groundwater Research, King Abdulaziz University, Jeddah, Saudi Arabia Department of Chemistry, University of Karachi, Karachi, Pakistan c Wadsworth Center, New York State Department of Health, Albany, NY, USA d Department of Environmental Health Sciences, School of Public Health, University at Albany, Albany, NY, USA b
art ic l e i nf o
a b s t r a c t
Article history: Received 21 August 2014 Received in revised form 10 March 2015 Accepted 11 March 2015 Available online 20 March 2015
Life-time human health risk of cancer attributed to trihalomethanes in drinking water in an urbanindustrialized area of Karachi (Pakistan) was conducted through multiple pathways of exposure. The extent of cancer risk was compared with USEPA guidelines. Human health cancer risk for total trihalomethanes (TTHMs) through ingestion and dermal routes were estimated in “acceptable-low risk” ( Z1.0E 06; r5.10E 05), whereas through inhalation route it was estimated under “acceptable-high risk” (Z 5.10E 05; r1.0E 04) category. However, at some industrial–urban areas cancer risk for CHCl3 were estimated under “unacceptable risk” ( Z1.0E 04) through inhalation route. & 2015 Elsevier Inc. All rights reserved.
Keywords: Trihalomethanes Chloroform Risk assessment Disinfection byproducts Public health
1. Introduction The presence of microbiological organisms is the most common pollution culprit in the urban areas and microorganisms, such as bacteria, viruses, and protozoa can cause serious illnesses and deaths (Uyak et al., 2005). The most common and economic method of disinfection is chlorination (Yang et al., 1998; Hsu et al., 2001; Rodriguez and Serodes, 2001; Hamidin et al., 2008). Although chlorine disinfection reduces mortality and morbidity due to water-borne diseases (Calderon, 2000; Golfinopoulos and Nikolaou, 2005), chlorine can react with natural organic matter (NOM) and form various types of disinfection byproducts (DBPs), chiefly trihalomethanes (THMs). Epidemiological and clinical studies have revealed that several health effects are associated with the exposure to DBPs, such as elevated rates of bladder, colon– rectum and brain cancers (Cantor et al., 1998; McGeehin et al., 1993; Hildesheim et al., 1998; Cantor et al., 1999; Wilkins et al., 1979; Flaten, 1992; King et al., 2000a), cardiac anomalies, stillbirths, miscarriages, low birth weights and pre-term deliveries, and neural tube defects (Mills et al., 1998; Richardson., 2005; King et al., 2000b). Epidemiological data availability in Pakistan from n Corresponding author at: Unit for Ain Zubaida & Groundwater Research, King Abdulaziz University, Jeddah, Saudi Arabia. E-mail address: [email protected] (A. Siddique).
http://dx.doi.org/10.1016/j.ecoenv.2015.03.011 0147-6513/& 2015 Elsevier Inc. All rights reserved.
population-based registries is mostly unavailable, and institutional based registries seldom provide estimates of disease distribution. The only population-based cancer registry was established in Karachi, where statistics for 9 years (1995–2003) were published. The population-based cancer registry in Karachi has identified 8 major classes of cancers prevailing in males (lung (11%), oral cavity (13.1%), larynx (6.1%), urinary bladder (4.8%), prostate (4.1%), lymphoma (7%), pharynx (4.3%), colo-rectum (4.4%)) and females (breast (34.6%), oral cavity (8.9%), cervix (4.1%), esophagus (3.7%), ovary (4.2%), lymphoma (3.5%), gall bladder (2.6%), skin (2.6%)). The estimates show that the projected figures for Pakistan are double the estimates by the World Health Organization (WHO). Breast cancer rate among women is high in Karachi (34.6% rate of female cancer), the highest in Asia (Bhurgri, 2004). Exposures to DBPs can occur throughout a lifetime via multiple pathways, such as water ingestion by the oral route, inhalation through breathing and dermal contact through skin during regular indoor activities, such as showering, bathing and cooking. These chronic exposures to DBPs may pose risks to human health. Traditional risk assessment studies only considered the oral route of water to estimate the life time health risk. However, other routes of DBPs exposure for health risk assessment are now considered in scientific studies (Hsu et al., 2001; Mallika et al., 2008; Uyak, 2006; Lee et al., 2004; Weisel and Jo, 1996; Weisel et al., 1999). The study area, which encompasses the metropolitan area of
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Karachi along with its suburbs, is the world's second most populated city, (estimated at 20 million, http://www.karachicity.gov.pk/), spread over 3530 km2. Karachi is situated at (24°45′N–25°01′N and 66°55′E–67°15′E). The main source of water supply to the city of Karachi is from surface water (i.e., Indus River through Kenjhar and Haleji Lakes, and Hub dam built on Hub River). The present study was aimed at using a multi-pathway exposure model on the basis of our earlier studies (Siddique et al., 2012) for lifetime human health risk assessment to evaluate and quantify the adverse effect of trihalomethanes (THMs) in tap water.
2. Materials and methods Drinking water samples from various areas of the city (Fig. 1) were collected in headspace-free borosilicate amber glass bottles containing about 1.7 mL sodium thiosulfate (10%) quenching solution (APHA, 1992; Rodriguez and Serodes, 2001). Once collected, samples were stored in the dark at 4 °C and carried to the laboratory for analytical procedures. A modified EPA Method (EPA 551.1) was applied for the assessment of THMs (MTBE) (Nikolaou et al., 2002; Golfinopoulos et al., 2005). Two milliliter of MTBE extraction solvent were added to 35 mL of water sample in a 40 mL glass vial containing anhydrous sodium sulfate as drying agent. For phase separation, the vial was shaken for 1 min and left undisturbed for further 2–3 min. The upper 1 mL organic layer was injected into HP 5890 gas chromatograph (GC) equipped with DB5 chromatographic column and electron capture detector (ECD). Analysis conditions: injection on column volume 2 mL; oven temperature 30 °C for 10 min, 30–41 °C at 3 °C/min; hold at 41 °C for 6 min; 41–81 °C at 5 °C/min; 81–180 °C at 25 °C/min and hold at
Table 1 Average THMs level (mg/L) in water samples of different localities in Karachi. Locality
Hawk's bay SITE Orangi/Baldia Saddar Jamshaid Town Liaqutabad Mansoora Taimuria North Karachi DHA/Clifton Korangi/Landhi Shah Faisal/ Airport Gulshan e Iqbal Malir Ibrahim Hydri LITE/Cattle colony Port Qasim
n
Average THMs level (lg/L) CHCl3 SD
CHBrCl2 SD
CHBr2Cl SD
8 12 16 20 20 8 8 16 12 13 24 27
46.2 61.2 76.8 72.5 55.2 90.8 98.5 79.3 62.4 71.1 56.2 79.8
15.8 23.0 26.6 25.0 27.9 40.0 41.5 40.9 29.7 26.0 21.9 30.8
3.0 2.7 4.1 3.3 2.7 2.8 3.2 3.1 4.5 3.00 2.9 3.1
0.37 0.43 1.6 1.4 0.65 0.64 0.94 1.1 1.5 1.5 1.2 0.89
0.48 1.5 2.6 2.0 1.2 1.5 1.8 1.5 2.4 1.7 1.6 1.7
0.83 49.7 0.27 65.4 0.97 83.5 0.81 77.8 0.35 59.1 0.29 95.0 0.52 103.5 0.53 83.8 0.87 69.3 1.09 75.8 0.81 60.7 0.54 84.6
9 8 11 8
66.5 49.7 82.2 63.3
31.8 20.5 37.7 27.6
3.5 3.2 2.6 3.2
1.1 1.5 2.1 1.2
2.3 2.0 1.7 1.8
0.14 0.97 1.24 0.76
72.3 54.9 86.5 68.3
0.82 1.7
0.20
94.4
16 90.0
55.3 2.7
Total THMs
180 °C for 6 min; carrier gas Helium at a rate of 1.5 mL/min; detector temperature of 275 °C. A DB-1701 capillary column (30 m, 0.32 mm i.d., 0.25 mm film thickness) was used for the confirmation analysis. Stock THM standards were obtained from AccuStandard and were diluted to different concentration levels. The identification of individual THMs was based on the comparison of retention times of THMs in samples with those of THM standards.
Fig. 1. Map of the sampling locations.
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Table 2 Summary of seasonal variations in THMs (mg/L) in water samples. Winter
Min. Max. Mean SD
Summer
CHCl3
CHBrCl2
CHBr2Cl
Total THM
CHCl3
CHBrCl2
CHBr2Cl
Total THM
17.0 167.3 67.8 33.0
1.8 6.2 3.3 1.2
0.6 3.5 1.9 0.7
7.0 173.2 71.3 34.5
8.4 146.2 71.1 32.4
0.19 5.6 3.1 1.2
0.22 3.3 1.8 0.7
4.4 148.0 72.3 34.5
120
Table 4 Cancer risk estimates of THMs through ingestion, dermal and inhalation exposure routes.
100
Concentration [ug/L]
Exposure route WHO and USEPA limit
80
CHCl3
CHBrCl2
CHBr2Cl
TTHMs
Ingestion/oral
Mean 6.78E 06 3.04E 06 Min. 9.22E 07 1.85E 07 Max. 1.60E 05 6.05E 06 Median 6.23E 06 2.89E 06
Dermal/absorption
Mean 2.73E 05 1.22E 05 9.39E 06 4.42E 05 Min. 3.72E 06 7.45E 07 1.19E 06 8.89E 06 Max. 6.46E 05 2.44E 05 1.84E 05 8.62E 05 Median 2.51E 05 1.17E 05 8.91E 06 4.16E 05
60
40
2.33E 06 1.10E 05 2.95E 07 2.20E 06 4.56E 06 2.14E 05 2.21E 06 1.03E 05
20
Inhalation/breathing Mean 6.84E 05 1.28E 07 9.78E 08 6.68E 05 Min. 1.08E 07 7.77E 09 1.24E 08 2.03E 07 Max. 1.76E 04 2.54E 07 1.92E 07 1.76E 04 Median 6.20E 05 1.21E 07 9.28E 08 5.99E 05
0
Localities
Fig. 2. Distribution of TTHMs exceeding USEPA and WHO guidelines.
Table 3 Multipathways slope factor (SF) for THMs (mg/kg day) 1 and reference dose (RfD) values (mg/kg/day) (USEPA, 2009; Legay et al., 2011). THMs
Carcinogenicity
Ingestion/dermala
Inhalationb
RfD
CHCl3 CHBrCl2 CHBr2Cl CHBr3
B-2 B-2 C B-2
6.10E 03c 6.20E 02d,e 8.40E 02d,e 7.90E 03d,e
8.10E 02c 6.20E 02d 8.40E 02d 3.90E 03c
1.00E 02 2.00E 02 2.00E 02 2.00E 02
a Slope factors of oral route were used to calculate cancer risk of THMs through dermal contact. b Oral exposure slope factors of CHBrCl2 and CHBr2Cl were adopted for inhalation exposure. c RAIS (2009). d Lee et al. (2009). e IRIS (2009).
assessment was evaluated for multiple routes of exposure into consideration, such as oral, dermal (skin contact) and inhalation absorption (USEPA, 1989, 2005). Showering, bathing and oral consumption activities of water were mainly considered as dermal, inhalation and oral exposure (Williams et al., 2002; Lee et al., 2004, 2006; Viana et al., 2009; Uyak, 2006). The unit cancer risks were calculated through chronic daily intake (CDI) and corresponding slope factor (SF), whereas the hazardous development effect and indices were evaluated by calculating reference doses (RfDs) and reference concentrations. The CDI for each route of exposure i.e., oral, dermal and inhalation was calculated for each trihalomethane studied except for CHBr3 due to its low and sporadic occurrences in the study area as follows (USEPA, 2005; Lee et al., 2004; Legay et al., 2011):
CDI oral =
CW*IRw*EF*ED BW*AT
CDI dermal = Prior to each set of samples to be analyzed, the GC was calibrated with a series of standards. Then 6 point calibration was performed over the established concentration range. Linear regression of peak area versus concentration gave a good fit (r2 40.99). The THMs were quantified from peak areas obtained through automated integration and by comparison with known concentration of standards. 2.1. Exposure and risk assessment Human health risk assessment was estimated for the THMs occurrences in drinking water samples in Karachi, based on the US Environmental Protection Agency (USEPA) guideline (USEPA, 1999, 2002, 2005), Lee et al. (2004) and Legay et al. (2011). The risk
(1)
CW*SA*Kp*ET*EF*ED BW*AT
(2)
Ca*IRa*ET*EF*Ed BW*AT
(3)
CDI inhalation =
where CW is the concentration in water sample (mg/L), IRw the ingestion rate of drinking water (L/day), EF the exposure frequency (day/year), ED the exposure duration (years), SA skin surface area of human body (cm2), Kp the specific dermal permeability (cm/h), ET the exposure time (h/event), Ca the concentration of THM in the breathing air zone (mg/m3), IRa the inhalation rate (m3/h), BW is the body weight (kg) and average life time (days). Certain assumptions were made in addition to USEPA values to accommodate local factors. Since present study does not differentiate between male and female, average body weight of 65 kg (male
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Fig. 3. Cancer risk of THMs through oral, dermal and inhalation routes.
67.2 kg, female 63.9 kg), and adult exposure of 30 years average (male 64 years and female 66 years) (PAP, 2002; WHO, 2013) were adopted. The amount of water ingested (2.48 L/day) was considered on moderate consumption level for this study on the basis of study carried out in similar region (Choudhury et al., 2001), and skin surface area of 20,000 cm2 were used (USEPA, 1997). The concentrations of CHCl3 in air (Ca for CHCl3) were based on the Jo et al. (1990) study and statistical model by Kar (2000) as described by Legay et al. (2011). A volatilization factor of 5 10 4 1000 L/ m3 was used for the estimation of Ca for CHBrCl2 and CHBr2Cl (USEPA, 1991). Unit cancer risk through the multiple exposure routes for each chlorination byproduct species was calculated as follows (Eq. (4)) (USEPA 1989, 2005) and the total cancer risk (RT) for each location obtained by the summation of the individual risk estimate of CHCl3, CHBrCl2 and CHBr2Cl (Eq. (5)). Total risk (RT) is expressed as excess probability of contacting cancer over a lifetime period.
Rm =
∑ SFm*CDIm i
(4)
where Rm is the unit risk estimate of the mth compound (unitless of probability), i the exposure routes, SF the slope factor values (RAIS, 2009; IRIS, 2009; Lee et al., 2009; Legay et al., 2011), CDI the chronically daily intake and RT is the total cancer risk (unitless of probability).
3. Results and discussion The drinking water samples were collected from 18 localities in Karachi during the winter (October–February) and summer (May–
August) in year 2007 and 2008 and THMs analysis was performed. Average concentrations of THMs in water samples of selected localities are shown in Table 1 and seasonal variations are summarized in Table 2. Considerable variations of TTHMs levels (49.7– 103.5 mg/L) among selected localities were observed (Table 1). Comparatively, higher levels of THMs were found in central part of the city which is highly populated, served with drainage rivers of Lyari, and with poor infrastructure i.e., Liaqutabad, Mansoora, Orangi and Shah Faisal/Airport. CHCl3 is the largest contributor among the TTHMs in all the localities followed by CHBrCl2 and CH Br2Cl. Similar to earlier studies (Uyak, 2006; Toroz and Uyak, 2005; Uyak and Toroz, 2005; Lee et al., 2004; Hsu et al., 2001) concentrations of CHBr3 were detected in few samples and in low limits therefore it was not considered in the present study. Table 2 depicts the summarized seasonal difference among TTHMs. There were no significant difference among the winter and summer (post- and pre-monsoon) seasons was found. However, a wide range variations of TTHMs within the seasons of winter (7.0– 173.2 mg/L) and summer (4.4–148.0 mg/L) were observed and could result in a considerable range of cancer risk. Results were compared with USEPA regulation and WHO guidelines of 80 mg/L (USEPA, 2009) (Fig. 2) due to nonexistence of local legislation and guidelines for THMs. Compliance with WHO guideline and USEPA regulation was assessed using average concentrations of TTHMs in selected communities. Seven out of eighteen communities (Orangi/Baldia, Liaqutabad, Mansoora, Taimuria, Shah Faisal/Airport, Ibrahim Hydri, and Port Qasim) exceeded USEPA national primary drinking water regulation and WHO guideline of 80 mg/L and shows a greater tendency of THMs formation in the distribution network. Cancer risk assessment through ingestion, dermal and
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133
2.0E-04
19.2%
55.8%
25.0%
Health Risk
1.5E-04
1.0E-04
5.0E-05
0.0E+00
CHCl3
CHBrCl2
CHBr2Cl Slected communities
Fig. 5. Average cancer risk for THMs from different pathways in selected communities.
21.2%
1.4E-04 1.2E-04 1.0E-04
Cancer Risk
54.7% 24.1%
8.0E-05 6.0E-05 4.0E-05
CHCl3
CHBrCl2
CHBr2Cl
2.0E-05 0.0E+00 Oral
0.14%
Inhalation
Total
Health Risk Pathways
0.19%
Fig. 6. Average cancer risk through different pathways for Karachi population.
99.7%
CHCl3
Dermal
CHBrCl2
CHBr2Cl
Fig. 4. Contribution of THMs to average risk estimates for life time cancer through (A) ingestion/oral, (B) dermal/absorption and (C) inhalation/breathing routes.
inhalation exposure was carried out in the Karachi distribution system. Table 3 shows the slope factor or potency factors for THMs that are associated with lifetime cancer risk to the exposed population. Results of 95th percentile values of cancer risk through ingestion or oral exposure are summarized in Table 4 and spatial variability is depicted in Fig. 3. Average life time cancer risk for THMs in drinking water samples was found to be higher than the negligible cancer risk of 10E 06 through all the routes and the contribution of risk was observed in the following order:
CHCl3 4CHBrCl2 4CHBr2Cl. Maximum unit cancer risk of 2.57E 04 for CHCl3 was observed in the industrial areas of Port Qasim and 3.07E 05 and 2.32E 05 for CHBrCl2 and CHBr2Cl was found in Saddar, the downtown area. Submersion in industrial and domestic effluents due to old and poor infrastructure may expose areas’ populations to multiple toxicants of varying nature, which may result in additive effects and could increase the health deterioration (Hsu et al., 2001). The median lifetime cancer risk of 1.03E 05 was estimated for TTHMs (CHCl3, CHBrCl2 and CHBr2Cl) through ingestion/oral route higher than USEPA's negligible risk of 1.0E 06. The highest TTHMs lifetime cancer risk through oral route was found in Port Qasim, Saddar and SITE localities. CHCl3 made the highest percentage contribution to the average lifetime cancer risk (55.8%), followed by CHBrCl2 and CHBr2Cl with 25.0% and 19.2%, respectively (Fig. 4). A similar trend of higher CHCl3 percent contribution to the average lifetime cancer risk through ingestion has been observed in previous studies (Hsu et al., 2001; Lahey and Connor, 1983), whereas Uyak (2006) and Lee et al. (2004) reported CHBr2Cl and CHBrCl2, respectively, to be the highest contributor to the average lifetime cancer risk. Lifetime cancer risk through dermal absorption of THMs upon showering and bathing were estimated in water. Slope factor (SF) of ingestion/oral route is used for the dermal/absorption route and ingestion/oral slope factor of CHBrCl2 and CHBr2Cl were adopted for inhalation exposure similar to earlier studies (Lee et al., 2009,
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Fig. 7. Distribution of probabilistic risk zones for human health in Karachi.
2004; Uyak, 2006). A skin surface area of 2.0E þ04 cm2 has been used for the risk estimation though several studies have calculated risk separately for males and females due to the difference in skin surface area in male and females (Uyak, 2006; Lee et al., 2004, 2009). Table 4 shows the 95th percentile lifetime cancer risk through dermal absorption and Fig. 3 shows the spatial distribution among the communities. Average and median cancer risk estimates through dermal absorption were higher than USEPA negligible human health risk. Localities of Port Qasim and Saddar downtown areas showed relatively higher risk estimates. The highest values of risk for CHCl3 were estimated in the Port Qasim industrial area located on the shore line of Arabian Sea. The highest risk of TTHMs through dermal/absorption route was found at Port Qasim (8.62E 05) industrial area and Saddar (8.58E 05) downtown area. The TTHMs cancer risk through dermal absorption route ranges between 8.89E 06 and 8.62E 05 (Table 4). The percentage contribution of each THM to the dermal cancer risk estimates followed the pattern of the ingestion route i.e., CHCl3 (54.7%), CHBrCl2 (24.1%), CHBr2Cl (21.2%) (Fig. 4). The inhalation exposure through CHCl3 is assumed to be the major contributor to lifetime cancer risk. Since CHCl3 has a lower boiling point than other THMs, it is assumed to be the major contributor through inhalation route and several studies have directly estimate the cancer risk of CHCl3 from concentration in water through its volatilization factor (Wang et al., 2007; Uyak, 2006; Lee et al., 2004). In the present study, the CHCl3 in air through bathing and showering was estimated by the statistical model used previously by Legay et al. (2011), Kar (2000), Nazir and Khan (2006). The major contributor through inhalation was CHCl3 (99.7%) (Fig. 4). As evident from Table 4, mean (6.68E 05) and median (5.99E 05) cancer risk of CHCl3 inhalation route are well above the USEPA 1.0E 06 negligible risk. The average distribution of inhalation risk can be viewed spatially in Fig. 3. The total lifetime cancer risk (CR) as RT was estimated in each
sampling location by adding the studied THMs cancer risk through multiple pathways exposure under study
RT =
∑ Rm
(5)
The total cancer risk (RT) for THMs through oral, dermal and inhalation for each of the locality are described in Fig. 5. It shows that inhabitants at a higher risk if all the conditions of THM precursors, disinfection technology practices, temperature etc. remained in similar fashion. CHCl3 is the major contributor among the risk factor through all the exposure routes. Fig. 6 depicts the overall contribution of higher CHCl3 and respective THMs (CHBrCl2, CHBr2Cl) in the average cancer risks through exposure routes and for total cancer risk. The distribution probabilities of cancer risk were estimated by the ordinary kriging in ArcGISs and distributed into four categories according to their nature and extent of cancer risk based on the USEPA guidelines for human health risk (Hammonds et al., 1994; USEPA, 2001). These four categories are divided into negligible (RT o1.0E 06), acceptable low (1.0E 06 rRT o5.10E 05), acceptable high (5.10E 05rRT o1.0E 04) and unacceptable (RT Z1.0E 04) risk zones (Legay et al., 2011). The estimated probabilistic distribution of the lifetime cancer risk approximations in the drinking water samples are presented in Fig. 7. Probabilities of occurring cancer risk are illustrated with the recommendation of the zone where no action, low and high priority of monitoring and immediate action is required. High risk zones are characterized by localities surrounded by industrial areas and streams of Lyari and Malir River (Fig. 7) containing untreated wastes from industry and domestic sources. The impact of poor infrastructure in old populous areas of the city and thickly populated areas around industrial zones could also be an important factor in providing precursor organic compounds to generate toxicological levels of disinfection byproducts in addition to excess chlorination practices by the local authorities. It is evident from
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the probability distribution of life time cancer risks that careful monitoring of disinfection dosage (chlorination) is very important for the city water distribution and dosage should be monitored for optimum disinfection. Introduction of technological advancement of alternate options, properly maintained monitoring network and skilled human resource could help city and public health mangers to reduce the chances of consumer exposure to potent toxicological impacts of chlorine disinfection by products.
4. Conclusions In conclusion, the present study provides a primary human health risk categorization for disinfection by-products in drinking water of the industrial–urban city of Karachi. Our results show that the city water supply has a great potential for generating chlorination by products i.e., trihalomethanes, which potentially may exert a burden of health risk to its inhabitants. Therefore, we recommend a carefully monitored program of chlorination doses, otherwise, alternate disinfection technologies are warranted.
Acknowledgments The authors gratefully acknowledge the funding support of Higher Education Commission of Pakistan (Grant No. 20-613/ R&D/ 06/755). Authors are also thankful to the Wadsworth Center, New York State Department of Health, Albany, NY and King Abdulaziz University management for the facilitation of resources for this study.
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