In this study, we report the formation and cancer risk estimation of trihalomethanes (THMs) emanating from ‘ex-situ’ chlorination of shallow hand-dug well water obtained from a peri-urban area of Mufulira District, Zambia. The aim of the study was to evaluate the potential cancer risks for people in this area where chlorine water disinfection at the household level is commonly practiced. Water samples from 13 randomly selected hand-dug wells (4–8 m deep) were collected and analyzed for pH, turbidity, and dissolved organic carbon before chlorination. Then another set of water samples from the same 13 wells was chlorinated using the methods commonly practiced in this area, consistent with WHO recommended doses. The chlorination degradation products, THMs, trichloromethane, bromodichloromethane (CHCl2Br), dibromochloromethane (CHClBr2), and tribromomethane, were determined at three different times of 60, 180, and 300 min after chlorination, while residual chlorine was determined immediately after chlorination and at 60 and 1,440 min after chlorination. THMs were determined using gas chromatography (GC), while residual chlorine was determined colorimetrically. Then cancer risk estimation from ingestion, inhalation, and dermal routes was carried out. All water samples from the 13 wells showed elevated amounts of THMs, which also increased with increasing contact time. For instance, the concentrations of THMs at 60 min after chlorination ranged from 24.3 ± 2.0 to 61.3 ± 1.0 μg/L, while at 180 and 300 min, ranged between 85.6 ± 4.3–146.9 ± 2.5 μg/L and 188.1 ± 7.1–250.1 ± 7.1 μg/L, respectively. It was observed that tribromomethane was not detected at all in all samples, while CHCl2Br and CHClBr2 were only detected at 180 and 300 min post chlorination. The lifetime cancer risk estimation results showed negligible risk at 60 min post chlorination. However, at 180 and 300 min post chlorination, the results were far above negligible, but within the regulatory US EPA limits. The overall risk, however, could not be ignored, given a multiplicity of exposure to various other contaminants, raising concerns over additivity and synergistic interactive effects, particularly for non-cancer hazard indices.

  • There was a high prevalence of trihalomethanes (THMs) in chlorinated water from shallow hand-dug wells in peri-urban settings of Mufulira, Zambia.

  • THMs concentrations increased with time post chlorination thereby increasing possible health risks.

  • Despite high levels of THMs, lifetime cancer risks were found to be within acceptable limits for the community of Mufulira, Zambia.

Graphical Abstract

Graphical Abstract
Graphical Abstract

Cholera is an acute intestinal diarrheal disease that is associated with poor water and sanitation infrastructure. It is caused by a bacterium, Vibrio cholera, an agent autochthonous to the aquatic environments (Choopun et al. 2002). Globally, there are 1.3–4.0 million reported cases of cholera per year, with the majority of these being in Sub-Saharan Africa (Ali et al. 2012). In Zambia, the cholera epidemic has become endemic since the 1990s, a testimony of the failure of socioeconomic infrastructure and difficulties by municipalities in implementing control measures. The first cases of cholera outbreak in Zambia were reported during the period 1977–1978, and of course, later on, there were other outbreaks that occurred in the 1983/1984 period (WHO 2011). From the 1990s to date (2021), the outbreaks of the cholera epidemic have become annual episodic events.

From Central Statistical Office projections (CSO 2010), Zambia has an estimated population of about 18 million, with approximately 60 and 40% living in rural and urban areas, respectively. According to NWASCO (2015), Commercial Water Utility Companies (CWUCs) that supply treated piped water in Zambia only manage to cover 47.9% of the country's population. Thus, more than half of the population relies on water sources whose safety cannot be guaranteed and therefore are at significant risk of diarrheal diseases, including the cholera epidemic. To make water safe for drinking at the household level, various water disinfection techniques are employed and one such technique is the addition of chlorine to the water, which may be done ‘ex-situ’.

It has been argued that in most poor communities, chlorination is the most common and economic method of water disinfection and can kill or deactivate microorganisms that cause waterborne diseases such as cholera, typhoid, and dysentery, among others (Garcia 2005; Siddique et al. 2015). However, chlorine can react with dissolved natural organic matter (NOM) in water, leading to the formation of trihalomethanes (THMs), the disinfection by-products (DBPs), which have been implicated in causing adverse health effects in humans (Nieuwenhuijsen et al. 2000; Bond et al. 2014) including various cancers (Siddique et al. 2015).

As observed elsewhere (Amjad et al. 2013), the public can be exposed to these THMs through various pathways/routes such as oral ingestion (drinking/food), inhalation during bathing/washing, and dermal absorption (bathing/washing). A review of literature has shown that elsewhere (Liu et al. 2006; Hrudey 2009; Bond et al. 2014), THMs are regulated and strictly monitored in public water supply systems. However, in Zambia, these compounds are not rigorously monitored, though the Zambia Bureau of Standards (ZABS), a statutory body responsible for standardization, standards formulation, quality control, etc., has set 30 μg/L as the maximum concentration permissible in drinking water. As expected, there is a paucity of data about their prevalence in public water supply systems, including in the ‘ex-situ’ chlorinated water from shallow hand-dug wells, which are prevalent in most peri-urban settings.

Mufulira is one of the districts on the Copperbelt Province, Zambia (see Figure 1), and it has an estimated population of more than 200,000 based on projections from the Central Statistical Office (CSO 2010). As a result of mining activities, a number of informal settlements (peri-urban settings) has mushroomed in Mufulira and one of these is Kawama East, with an estimated population of more than 12,000. Peri-urban settings in Zambia are usually characterized by overcrowding, non-existent safe water supply, and sanitation services. This area was selected for this study because it is a perfect example of peri-urban settings where residents’ source of water supply is from shallow hand-dug wells with close proximity to pit latrines. Our preliminary studies on the water from the shallow hand-dug wells in this and several other settlements in the Copperbelt Province showed high levels of NOM (averaging 17 ppm), which is one of the critical factors required for the formation of THMs (Wontae & Westerhoff 2009). Furthermore, people from peri-urban settings rely exclusively on the ‘ex-situ’ chlorination for water disinfection to make it safe for domestic use. Therefore, we argue that this area was a good case study for the investigation of the formation of THMs resulting from ex-situ chlorination of water. We opined that it was equally critical to estimate cancer risks, given that THMs have been previously implicated in causing various types of cancers (Siddique et al. 2015).

Figure 1

Location of study area, Kawama East, Mufulira District, Copperbelt Province, Zambia.

Figure 1

Location of study area, Kawama East, Mufulira District, Copperbelt Province, Zambia.

Close modal

According to the Ministry of Health National Cancer Control Strategic Plan 2016–2021 (National Cancer Control Strategic Plan 2016–2021 2016), the burden of cancers in Zambia was increasing with a significant impact on morbidity and mortality rates. A lot of cancers have been associated with lifestyles, such as unhealthy diets, physical inactivity, obesity, alcohol and substance abuse, and tobacco use (Jepson et al. 2010), though of course, some other cancers have an infectious etiology (Dalton-Griffin & Kellam 2009). In the case of the causes from diets, we argue that the increase in the concentration of xenobiotics in food and water would increase the probability of cancer occurrence and prevalence. It can also be argued that due to the paucity of data on the cancer disease segregation based particularly on age and socioeconomic status of the affected individuals, it was quite a challenge to assign the proportion of cases emanating from the poor communities of our society. However, what was certain was that the poor bear the brunt of the disease (cancer) burden due to their inability to access routine medical checkups and health care services. Since the extent of occurrence and prevalence of THMs in chlorinated water, especially from shallow wells from peri-urban settings in Zambian towns and cities was not known, the possible contribution of the cancer burden from this source remained uncertain.

The objectives of the current study were (1) to determine the formation and concentrations of THMs in chlorinated water from shallow hand-dug wells, (2) to estimate the potential lifetime cancer risks, and (3) to estimate the hazard indices, which would occur through oral, inhalation, and dermal routes. To the best of our knowledge, this is the first study to document the formation of THMs in chlorinated water from shallow hand-dug wells in Zambia.

Sample collection, preparation, and study site

The global positioning system (GPS) details for the selected sampling sites, the water-well depths, and the distances from the nearest pit latrines were compiled. The distances between the water wells and the pit latrines were measured and the nearest and furthest were found to be 7 and 26 m, respectively. The water-well depths ranged from 4 to 8 m and were all shallower than 13 m, consistent with studies reported by Liddle (2014) on water quality in hand-dug water wells in peri-urban areas of Ndola Town, Zambia. Three water samples in triplicates were collected from each shallow hand-dug well using clean glass containers. Figure 1 shows the location of the study area, Kawama East of Mufulira District in the Copperbelt Province of Zambia.

Chemicals and reagents

Certified THMs calibration mix standard (Supelco – USA – 4M8140-U) was obtained from Sigma Aldrich (Republic of South Africa). This calibration mix contained trichloromethane (CHCl3), bromodichloromethane (CHCl2Br), dibromochloromethane (CHClBr2), and bromoform (CHBr3); all at 2,000 ppm (2,000 mg/L). A series of calibration standard solutions were prepared in methanol purchased from Glass World Chemicals, (South Africa) and then extracted in n-hexane, purchased from Saarchem (South Africa). The calibration mix solutions and a series of standards and extracted samples were stored in the dark at 4 °C until required for the analysis.

Analysis of chemical parameters

The parameters that favor the formation of THMs were analyzed in water samples prior to chlorination. The pH was determined according to procedure described in ISO 10523 (ISO 2012) using the pH meters, Eutech Instruments PC 510 pH/mV/Conductivity/TDS. The water turbidity was determined using laMotte 2020we turbidimeter. The turbidity determination was performed according to the guidelines of EPA 180.1 of 1993 (La-Motte-Mannual). The dissolved organic carbon (DOC) was measured using a Shimadzu TOC-VCSH analyzer (high temperature combustion at 720 °C; non-dispersive infrared detection) with a TNM-1 TN unit (chemiluminescence detection) (Shimadzu, Japan) as described in Lee & Westerhoff (2009). The residual chlorine was determined immediately after chlorination and at 60 and 1,440 min after chlorination, using a Pocket Colorimeter II-HACH and Lovibond diethyl-paraphenylene-diamine No.1 (DPD1) tablet and the procedure used was as described by WHO (2005a, 2005b).

Domestic water chlorination

The procedure for domestic water chlorination was carried out as per daily practice of the resident of this peri-urban area. The practice is that 10 mL of 0.5% USP Sodium Hypochlorite (chlorine) solution is used for dosing 20 L of water. The samples for the analysis of THMs were taken at 60, 180, and 300 min after chlorination. The selection of sampling times was based on the average time it takes for an average family of eight people to use up the chlorinated water after chlorination. On average, it was found that chlorinated water would be consumed or used up within 5 h after chlorination. Once collected, the water samples were quenched immediately with ascorbic acid to eliminate any available free residual chlorine and stop further formation of THMs as described elsewhere (Basu et al. 2011; Kujlu et al. 2020) and were stored at 4 °C until required for the analysis. The THMs determined in this study were CHCl3, CHCl2Br, CHCl2Br, and CHBr3.

Sample extraction and GC-ECD analysis of THMs

The extraction of THMs was according to the modified EPA-Method 501 (EPA 1979) and some steps from the EPA-551 protocol were used as adopted by the University of Massachusetts (Reckhow 2012). Briefly, the samples were subjected to liquid–liquid extraction using n-hexane as a solvent. The vials were then shaken vigorously for 1 min and allowed to stand for 3 min to facilitate phase separation. The hexane phase was removed and placed in a clean dry vial and was ready for the analysis. The analysis of samples for THMs was carried out using a Perkin Elmer Clarus 500 gas chromatograph. Two Perkin Elmer columns were used for the analysis, Perkin Elmer Elite 1-N9316024 (30 m × 0.32 mm ID × 1.00 μm film) of dimethylpolysiloxane – 100% dimethyl and Perkin Elmer Elite 5-N9316086 (30 m × 0.25 mm ID × 1.00 μm film) of dimethylpolysiloxane – 5% diphenyl. The carrier gas used was nitrogen gas supplied by Afrox Gases Ltd (Ndola, Zambia). The flow rate employed was 0.45 mL/min. The volume of standards and samples that were manually injected was 5 μL using splitless injection mode. For both columns, the injection temperature was 200 °C and the detector temperature was set at 315 °C, and the 63Ni electron capture detector was used. Totalchrom Workstation, TcWSVer 6.2.1 was used for the analysis, generation, and processing of chromatograms.

Quality control and assurance

As a way of demonstrating that this analysis met the expected quality assurance requirements, four reagent blanks were each spiked with CHCl3, CHCl2Br, CHClBr2, and CHBr3 at 30 and 60 μg/L. The water from one of the shallow hand-dug wells was used for spiking the THMs (spiked blanks). The spiked blanks were done in triplicates and were subjected to liquid–liquid extraction using n-hexane as a solvent. The vials were then shaken vigorously for 1 min and allowed to stand for 3 min to facilitate phase separation and were analyzed as described under sample extraction and GC-ECD analysis of the THMs section. In all analyses, the GC syringe was rinsed five times with hexane after each injection. The recoveries obtained are shown in Table 1 below and are between 80 and 120%, all within the accepted range (Maria & Antonio 2003). The detection limits for CHCl3, CHCl2Br, CHClBr2, and CHBr3 were 0.08, 0.07, 0.08, and 0.3 μg/L, respectively.

Table 1

Recovery tests of THMs

THMsNominal (μg/L)Analyzed (μg/L)Recovery (%)Nominal (μg/L)Analyzed (μg/L)Recovery (%)
CF 30 29.5 98 60 65.2 109 
BDCM 30 32.2 107 60 58.3 97 
DBCM 30 26.9 90 60 54.6 91 
BF 30 33.2 111 60 63.5 106 
THMsNominal (μg/L)Analyzed (μg/L)Recovery (%)Nominal (μg/L)Analyzed (μg/L)Recovery (%)
CF 30 29.5 98 60 65.2 109 
BDCM 30 32.2 107 60 58.3 97 
DBCM 30 26.9 90 60 54.6 91 
BF 30 33.2 111 60 63.5 106 

CF, chloroform; BDCM, bromodichloromethane; DBCM, dibromochloromethane; BF, bromoform.

Cancer risk assessment

Estimation of cancer risk due to exposure to THMs through ingestion, inhalation, and dermal routes was carried out as described by Lee et al. (2004). In brief, the chronic daily intake (CDI) through oral or ingestion was calculated using the following equations:
formula
(1)
where PForal is the potential factor of a specific cancer substance.
formula
(2)
where CW is the chemical concentration in water, mg/L, IR is the ingestion rate, L/day, EF is the exposure frequency, days/year or events/year (days/year), ED is the exposure duration, year (62 years was assumed in this study), BW is the body weight, kg, and AT is the average time, days (62 years × 365 days/year).
formula
(3)
formula
(4)
where CW is the chemical concentration in water, mg/L, SA is the skin surface area available for contact, cm2, PC is the chemical-specific dermal permeability constant, cm/h (0.0020 m/h), ET is the exposure time, h/day or h/event (0.2 h/event), EF is the exposure frequency, days/year or events/year (1 event/day), ED is the exposure duration, years (365 days/year × 62 years), BW the body weight, kg (60 kg), AT the average time, days (62 years × 365 days/year).
Cancer risk for THMs through inhalation was calculated for CHCl3 only because, according to Lee et al. (2004), CHCl3 is the major compound to which people are exposed through inhalation due to its lower boiling point.
formula
(5)
where,
formula
(6)
where CA is the contaminant concentration in air, mg/m3, IR is the inhalation rate, m3/h (20 m3/day/24 h/day = 0.83333 m3/h), ET is the exposure time, h/day or h/event (0.2 h/event), EF is the exposure frequency, days/year or event/year (1 event/day), ED is the exposure duration, years (365 days/year × 62 years), BW is the body weight, kg (65 kg), and AT is the average time, days (62 years × 365 days/year).
Equation (6) was modified to an equation used by Semerjian & Denis (2007), to generally describe bathing and taking into account the volatilization factor (VF) for CHCl3 and was presented as follows:
formula
(7)
where Cw is concentration of CHCl3 in water and VF, 0.5 L/m3, is the VF, and AA is equivalent to IR = m3/h (20 m3/day/24 h/day = 0.83333 m3/h).
formula
(8)

In these estimations, some assumptions were made, for instance the average weight of Kawama residents was assumed to be 65 kg for both men and women, the water intake through drinking was assumed to be 1.5 L per capita and average life expectancy in Zambia was assumed to be 62 years (2020 average for Zambia).

Additionally, non-cancer risks indices from the two exposure pathways of THMs were estimated as follows:
formula
(9)
formula
(10)
formula
(11)
where RfDTHMs is the reference dose for a specific THMs compound

Parameters that promote THMs formation

The formation of THMs in water is dependent on some factors such as pH, turbidity, dissolved organic matter, amount of chlorine, and the contact time (Hrudey 2009; Silva et al. 2012). To relate the formation and hence corroborate the THMs potential cancer risk to the community in this study, the results of the critical parameters in the formation of these disinfection degradation by-products are determined as shown in Table 2. The pH of the water samples prior to chlorination ranged from 5.69 to 6.56, while the concentration of natural dissolved organic matter determined as DOC, ranged from 5. 44 to 29.11 mg/L C. The turbidity of the water samples ranged from 2.46 to 12.09 FTU. The amount of residual chlorine remaining after water chlorination was determined at three different time spans. The first residual chlorine was determined immediately after chlorination, and thereafter the residual chlorine was determined at 60 and 1,440 min after chlorination. The reason for determining residual chlorine at the selected times was to know the amount of chlorine and consequently the extent to which THMs formation could persist post chlorination. According to literature (Anastasia et al. 2004), pH levels ranging from 4.0 upwards can promote the formation of THMs provided other factors, such as dissolved NOM and chlorine are at such levels that can lead to the formation of THMs. As can be observed in Table 2, the amount of dissolved NOM determined in this study was within the range that has been observed elsewhere to cause the formation of THMs (Chowdhury & Champagne 2008), and this was corroborated by the range of turbidity values observed (see Table 2) in this study, which were consistent with observations made elsewhere (Rizzo et al. 2005; Lantagne et al. 2010; AL-Fatlaw & Abd Al-Hussein 2014). It should, however, be noted that the high turbidity levels in this study may be more of a ‘correlational aspect’ than ‘cause and effect’ and therefore its corroboration in this case may need to be interpreted with caution, as high turbidity could have been due to other factors unrelated to dissolved organic matter.

Table 2

Parameters of some critical factors in the formations of THMs

Well IDpHTurbidity (FTU)DOC (mg/L)Residual chlorine (mg/L)
InitialAfter 60 minAfter 1,440 min
KE-01 6.56 ± 0.10 11.55 ± 0.07 9.02 ± 0.57 1.74 1.13 ± 0.04 0.17 ± 0.01 
KE-02 6.26 ± 0.28 4.30 ± 0.02 6.80 ± 0.25 1.68 1.50 ± 0.04 0.36 ± 0.01 
KE-03 6.18 ± 0.30 14.88 ± 0.20 19.4 ± 0.33 1.84 1.50 ± 0.03 0.59 ± 0.01 
KE-04 6.20 ± 0.27 9.40 ± 0.04 12.36 ± 0.25 2.08 1.79 ± 0.01 0.22 ± 0.03 
KE-05 6.03 ± 0.15 12.09 ± 0.07 29.11 ± 0.75 1.86 1.76 ± 0.01 0.25 ± 0.01 
KE-06 6.33 ± 0.30 10.64 ± 0.02 6.64 ± 0.19 1.84 1.72 ± 0.03 0.18 ± 0.01 
KE-07 5.90 ± 0.20 7.76 ± 0.04 6.66 ± 0.14 1.86 1.10 ± 0.03 0.19 ± 0.01 
KE-08 6.06 ± 0.20 5.25 ± 0.02 5.44 ± 0.21 1.88 1.29 ± 0.01 0.16 ± 0.00 
KE-09 6.21 ± 0.25 2.57 ± 0.08 5.73 ± 0.26 1.94 1.27 ± 0.04 0.11 ± 0.01 
KE-10 5.94 ± 0.28 2.46 ± 0.05 7.54 ± 0.37 1.78 1.31 ± 0.01 0.10 ± 0.00 
KE-11 5.69 ± 0.15 2.70 ± 0.11 5.65 ± 0.26 1.80 1.63 ± 0.04 0.07 ± 0.01 
KE-12 6.00 ± 0.16 3.41 ± 0.04 9.07 ± 0.07 1.84 1.57 ± 0.02 0.14 ± 0.01 
KE-13 6.06 ± 0.17 3.60 ± 0.08 8.86 ± 0.19 1.76 1.30 ± 0.03 0.24 ± 0.01 
Well IDpHTurbidity (FTU)DOC (mg/L)Residual chlorine (mg/L)
InitialAfter 60 minAfter 1,440 min
KE-01 6.56 ± 0.10 11.55 ± 0.07 9.02 ± 0.57 1.74 1.13 ± 0.04 0.17 ± 0.01 
KE-02 6.26 ± 0.28 4.30 ± 0.02 6.80 ± 0.25 1.68 1.50 ± 0.04 0.36 ± 0.01 
KE-03 6.18 ± 0.30 14.88 ± 0.20 19.4 ± 0.33 1.84 1.50 ± 0.03 0.59 ± 0.01 
KE-04 6.20 ± 0.27 9.40 ± 0.04 12.36 ± 0.25 2.08 1.79 ± 0.01 0.22 ± 0.03 
KE-05 6.03 ± 0.15 12.09 ± 0.07 29.11 ± 0.75 1.86 1.76 ± 0.01 0.25 ± 0.01 
KE-06 6.33 ± 0.30 10.64 ± 0.02 6.64 ± 0.19 1.84 1.72 ± 0.03 0.18 ± 0.01 
KE-07 5.90 ± 0.20 7.76 ± 0.04 6.66 ± 0.14 1.86 1.10 ± 0.03 0.19 ± 0.01 
KE-08 6.06 ± 0.20 5.25 ± 0.02 5.44 ± 0.21 1.88 1.29 ± 0.01 0.16 ± 0.00 
KE-09 6.21 ± 0.25 2.57 ± 0.08 5.73 ± 0.26 1.94 1.27 ± 0.04 0.11 ± 0.01 
KE-10 5.94 ± 0.28 2.46 ± 0.05 7.54 ± 0.37 1.78 1.31 ± 0.01 0.10 ± 0.00 
KE-11 5.69 ± 0.15 2.70 ± 0.11 5.65 ± 0.26 1.80 1.63 ± 0.04 0.07 ± 0.01 
KE-12 6.00 ± 0.16 3.41 ± 0.04 9.07 ± 0.07 1.84 1.57 ± 0.02 0.14 ± 0.01 
KE-13 6.06 ± 0.17 3.60 ± 0.08 8.86 ± 0.19 1.76 1.30 ± 0.03 0.24 ± 0.01 

As observed elsewhere (Godfrey & Reed 2011; Souaya et al. 2015), the amount of residual chlorine from 1.0 mg/L upwards was observed to lead to an increase in the formation of THMs as a function dose. Similarly, it was equally observed by Souaya et al. (2015) and Durmishi et al. (2016), that the amount of THMs formation was increasing with increasing time, post chlorination. Based on the fact that all the factors that are known to promote the formation of THMs in water were determined and confirmed to be present in this study, it was considered necessary to proceed and measure the formation and concentration of the chlorination degradation products as described and discussed in the next section.

THMs formation and concentration in the well water samples

The results of the THMs for chlorinated water from the thirteen wells are shown in Tables 35. The results indicated that in the first 60 min after chlorination, the THMs were 100% CHCl3 and the concentrations ranged from 24 to 61 μg/L. The observed 100% formation of CHCl3 in the first 60 min could probably be attributed to factors, such as much higher formation constant of CHCl3 than those of other THMs (Masoud et al. 2019) and low bromide ion concentration in raw water (Kumari & Gupta 2015), and hence such a lag time before other THMs could form. However, as contact time increased, not only did the concentrations of CHCl3 increase, but the formation and distribution of other THMs also increased. For instance, at 180 min after chlorination, the total THMs (TTHMs) ranged from 85 to 146.9 μg/L, CHCl3 ranged from 75 to 127 μg/L, CHCl2Br ranged from 4.2 to 14.7 μg/L, CHClBr2 ranged from 1.2 to 11.9 μg/L, while CHBr3 remained undetectable in all samples. Interestingly, at 300 min after chlorination, the TTHMs increased significantly and it ranged from 188 to 250 μg/L. Similarly, individual THMs also increased and ranged as follows: CHCl3 ranged from 155 to 219 μg/L, CHCl2Br ranged from 11 to 23 μg/L, CHClBr2 ranged from 8 to 24 μg/L, while CHBr3 was only detectable in two well samples, KE-05 and KE-09 with 1.4 and 1.6 μg/L, respectively.

Table 3

Average THMs concentrations in water samples at 60 min after chlorination (μg/L)

Well IDCHCl3CHCl2BrCHClBr2CHBr3TTHMs
KE-01 49.5 ± 0.1 ND ND ND 49.5 ± 0.1 
KE-02 37.4 ± 2.2 ND ND ND 37.4 ± 2.2 
KE-03 61.3 ± 1.0 ND ND ND 61.3 ± 1.0 
KE-04 46.8 ± 0.6 ND ND ND 46.8 ± 0.6 
KE-05 53.8 ± 0.4 ND ND ND 53.8 ± 0.4 
KE-06 47.8 ± 3.3 ND ND ND 47.8 ± 3.3 
KE-07 43.5 ± 2.8 ND ND ND 43.5 ± 2.8 
KE-08 41.5 ± 0.8 ND ND ND 41.5 ± 0.8 
KE-09 31.3 ± 1.7 ND ND ND 31.3 ± 1.7 
KE-10 24.3 ± 2.0 ND ND ND 24.3 ± 2.0 
KE-11 31.9 ± 0.4 ND ND ND 31.9 ± 0.4 
KE-12 35.4 ± 1.8 ND ND ND 35.4 ± 1.8 
KE-13 36.7 ± 0.2 ND ND ND 36.7 ± 0.2 
Well IDCHCl3CHCl2BrCHClBr2CHBr3TTHMs
KE-01 49.5 ± 0.1 ND ND ND 49.5 ± 0.1 
KE-02 37.4 ± 2.2 ND ND ND 37.4 ± 2.2 
KE-03 61.3 ± 1.0 ND ND ND 61.3 ± 1.0 
KE-04 46.8 ± 0.6 ND ND ND 46.8 ± 0.6 
KE-05 53.8 ± 0.4 ND ND ND 53.8 ± 0.4 
KE-06 47.8 ± 3.3 ND ND ND 47.8 ± 3.3 
KE-07 43.5 ± 2.8 ND ND ND 43.5 ± 2.8 
KE-08 41.5 ± 0.8 ND ND ND 41.5 ± 0.8 
KE-09 31.3 ± 1.7 ND ND ND 31.3 ± 1.7 
KE-10 24.3 ± 2.0 ND ND ND 24.3 ± 2.0 
KE-11 31.9 ± 0.4 ND ND ND 31.9 ± 0.4 
KE-12 35.4 ± 1.8 ND ND ND 35.4 ± 1.8 
KE-13 36.7 ± 0.2 ND ND ND 36.7 ± 0.2 

ND means non-detectable, mean ± standard deviation, n = 3.

Table 4

Average THMs concentrations in water samples at 180 min after chlorination (μg/L)

Well IDCHCl3CHCl2BrCHClBr2CHBr3TTHMs
KE-01 119.0 ± 5.6 8.5 ± 0.4 4.3 ± 1.6 ND 131.8 ± 5.8 
KE-02 99.6 ± 2.2 5.8 ± 0.3 2.6 ± 0.4 ND 108.0 ± 2.2 
KE-03 124.8 ± 2.1 4.2 ± 0.5 8.1 ± 0.1 ND 137.1 ± 2.1 
KE-04 102.9 ± 7.1 7.4 ± 0.3 5.7 ± 0.7 ND 116.0 ± 7.2 
KE-05 127.6 ± 1.8 14.7 ± 1.8 4.6 ± 0.1 ND 146.9 ± 2.5 
KE-06 115.2 ± 4.4 10.2 ± 0.9 11.9 ± 0.6 ND 137.3 ± 4.5 
KE-07 101.0 ± 1.8 8.4 ± 0.3 2.0 ± 0.4 ND 111.4 ± 1.9 
KE-08 100.0 ± 1.0 6.3 ± 0.3 5.2 ± 0.5 ND 111.5 ± 1.2 
KE-09 93.1 ± 6.1 6.2 ± 0.4 7.1 ± 0.3 ND 106.4 ± 6.1 
KE-10 75.8 ± 4.3 6.0 ± 0.3 3.8 ± 0.4 ND 85.6 ± 4.3 
KE-11 95.7 ± 3.8 6.9 ± 0.8 1.2 ± 0.1 ND 103.8 ± 3.9 
KE-12 97.1 ± 1.0 6.3 ± 0.5 2.4 ± 0.3 ND 105.8 ± 1.1 
KE-13 98.0 ± 1.7 5.6 ± 0.6 4.5 ± 0.9 ND 108.1 ± 2.0 
Well IDCHCl3CHCl2BrCHClBr2CHBr3TTHMs
KE-01 119.0 ± 5.6 8.5 ± 0.4 4.3 ± 1.6 ND 131.8 ± 5.8 
KE-02 99.6 ± 2.2 5.8 ± 0.3 2.6 ± 0.4 ND 108.0 ± 2.2 
KE-03 124.8 ± 2.1 4.2 ± 0.5 8.1 ± 0.1 ND 137.1 ± 2.1 
KE-04 102.9 ± 7.1 7.4 ± 0.3 5.7 ± 0.7 ND 116.0 ± 7.2 
KE-05 127.6 ± 1.8 14.7 ± 1.8 4.6 ± 0.1 ND 146.9 ± 2.5 
KE-06 115.2 ± 4.4 10.2 ± 0.9 11.9 ± 0.6 ND 137.3 ± 4.5 
KE-07 101.0 ± 1.8 8.4 ± 0.3 2.0 ± 0.4 ND 111.4 ± 1.9 
KE-08 100.0 ± 1.0 6.3 ± 0.3 5.2 ± 0.5 ND 111.5 ± 1.2 
KE-09 93.1 ± 6.1 6.2 ± 0.4 7.1 ± 0.3 ND 106.4 ± 6.1 
KE-10 75.8 ± 4.3 6.0 ± 0.3 3.8 ± 0.4 ND 85.6 ± 4.3 
KE-11 95.7 ± 3.8 6.9 ± 0.8 1.2 ± 0.1 ND 103.8 ± 3.9 
KE-12 97.1 ± 1.0 6.3 ± 0.5 2.4 ± 0.3 ND 105.8 ± 1.1 
KE-13 98.0 ± 1.7 5.6 ± 0.6 4.5 ± 0.9 ND 108.1 ± 2.0 

ND means non-detectable, mean ± standard deviation, n = 3.

Table 5

Average THMs concentrations in water samples at 300 min after chlorination (μg/L)

Well IDCHCl3CHCl2BrCHClBr2CHBr3TTHMs
KE-01 203.1 ± 2.5 23.0 ± 1.6 16.5 ± 0.7 ND 242.6 ± 3.1 
KE-02 184.6 ± 2.1 11.3 ± 0.1 7.7 ± 0.6 ND 203.6 ± 2.2 
KE-03 219.5 ± 7.0 21.4 ± 1.0 9.2 ± 0.2 ND 250.1 ± 7.1 
KE-04 191.1 ± 3.8 24.9 ± 0.2 24.1 ± 1.1 ND 240.1 ± 3.9 
KE-05 205.6 ± 0.7 20.6 ± 0.5 8.4 ± 0.2 1.6 ± 0.1 231.2 ± 0.9 
KE-06 196.7 ± 7.3 22.5 ± 1.2 11.9 ± 1.2 ND 230.8 ± 7.5 
KE-07 187.8 ± 5.1 22.2 ± 1.0 15.9 ± 0.6 ND 225.9 ± 5.2 
KE-08 185.0 ± 1.7 22.5 ± 0.7 10.3 ± 1.3 ND 217.8 ± 2.3 
KE-09 159.8 ± 1.4 22.2 ± 0.4 14.4 ± 1.1 1.4 ± 0.1 197.8 ± 1.5 
KE-10 155.0 ± 7.1 19.2 ± 0.4 13.9 ± 0.9 ND 188.1 ± 7.1 
KE-11 176.3 ± 5.1 21.3 ± 1.4 17.1 ± 0.5 ND 217.7 ± 5.4 
KE-12 177.7 ± 4.3 18.8 ± 0.5 10.1 ± 0.5 ND 206.6 ± 4.4 
KE-13 182.0 ± 2.9 17.9 ± 0.4 9.5 ± 0.2 ND 209.4 ± 2.9 
Well IDCHCl3CHCl2BrCHClBr2CHBr3TTHMs
KE-01 203.1 ± 2.5 23.0 ± 1.6 16.5 ± 0.7 ND 242.6 ± 3.1 
KE-02 184.6 ± 2.1 11.3 ± 0.1 7.7 ± 0.6 ND 203.6 ± 2.2 
KE-03 219.5 ± 7.0 21.4 ± 1.0 9.2 ± 0.2 ND 250.1 ± 7.1 
KE-04 191.1 ± 3.8 24.9 ± 0.2 24.1 ± 1.1 ND 240.1 ± 3.9 
KE-05 205.6 ± 0.7 20.6 ± 0.5 8.4 ± 0.2 1.6 ± 0.1 231.2 ± 0.9 
KE-06 196.7 ± 7.3 22.5 ± 1.2 11.9 ± 1.2 ND 230.8 ± 7.5 
KE-07 187.8 ± 5.1 22.2 ± 1.0 15.9 ± 0.6 ND 225.9 ± 5.2 
KE-08 185.0 ± 1.7 22.5 ± 0.7 10.3 ± 1.3 ND 217.8 ± 2.3 
KE-09 159.8 ± 1.4 22.2 ± 0.4 14.4 ± 1.1 1.4 ± 0.1 197.8 ± 1.5 
KE-10 155.0 ± 7.1 19.2 ± 0.4 13.9 ± 0.9 ND 188.1 ± 7.1 
KE-11 176.3 ± 5.1 21.3 ± 1.4 17.1 ± 0.5 ND 217.7 ± 5.4 
KE-12 177.7 ± 4.3 18.8 ± 0.5 10.1 ± 0.5 ND 206.6 ± 4.4 
KE-13 182.0 ± 2.9 17.9 ± 0.4 9.5 ± 0.2 ND 209.4 ± 2.9 

ND means non-detectable, mean ± standard deviation, n = 3.

Examination of Tables 35 showed that the concentrations of TTHMs in all the samples at all the three times of 60, 180, and 300 (except for KE-10 at 60 min) after chlorination were greater than ZABS guidelines for drinking water of 30 μg/L (ZABS 2010). Further examination of these results showed that the minimum concentrations of TTHMs at 180 and 300 min after chlorination were all greater than the US EPA prescribed standard of 80 μg/L. The concentration of THMs above the 80 μg/L threshold has been implicated in causing damage to kidneys, liver, and central nervous system (Amjad et al. 2013). The increase in the concentration of the THMs with increase in the ‘contact time’ (increase in time after chlorination) observed in this study was consistent with observations made elsewhere (Souaya et al. 2015; Durmishi et al. 2016). Thus, the longer the chlorinated water was stored the more THMs were formed for as long as the concentrations of residual chlorine and dissolved NOM, and other factors necessary for THMs formation were still present in the water.

The results of this study equally showed that CHCl3 was the main component of the THMs group and could be used to predict the concentrations of THMs formation. This observation was consistent with observations made on similar studies elsewhere (Hrudey 2009; Aprea et al. 2010). Based on the significantly elevated concentrations of the THMs measured in the chlorinated water samples of shallow hand-dug wells, it was necessary to proceed with the process of estimating the potential lifetime cancer risks for the inhabitants of the Kawama East peri-urban community.

Estimation of cancer risk assessment

Arising from the elevated levels of the THMs from the chlorinated water samples obtained from the 13 shallow hand-dug wells, the estimation of the potential cancer risk was carried out as described by Lee et al. (2004) and Amjad et al. (2013). As described elsewhere (Hsu et al. 2001; Amjad et al. 2013), there are three possible exposure pathways, ingestion, inhalation, and dermal. Despite the mode of bathing used in the peri-urban areas of the study site, which involves the use of buckets or plastic basins in open air or roofless bathing rooms, exposure through inhalation was still considered significant as some THMs are quite volatile and can be breathed in during various water usages like bathing, showering, washing, and general water handling including cooking (Basu et al. 2011; Siddique et al. 2015). Therefore, all three exposure pathways, ingestion, inhalation, and dermal were considered for the estimation of lifetime cancer risks. However, cancer risk calculation through the inhalation route was only carried out for the CHCl3 as it is the only THMs with the lower boiling point as determined elsewhere (Ebrahim et al. 2016). Furthermore, because the cholera epidemic is prevalent during the rainy season and since this season lasts for about 6 months, the estimation of potential lifetime cancer risks was carried out covering a 6-month period per year. Critically important in these estimations were assumptions and generalizations that took into account local factors. For instance, the average weight for both males and females was assumed 65 kg. This was based on some preliminary study that revealed that women tended to be more obese than men, but their (women) average weight was about 5% more than that of men and was hovering around 69 kg. However, for purposes of this study, an average weight of 65 kg was deemed reasonable for both genders. The life expectancy for the Zambia, according the 2020 World Bank figures, was around 62 years. The other factors required for the estimation of cancer risks for the THMs were obtained from literature (Lee et al. 2004; Amjad et al. 2013) and US EPA values from the U.S. EPA database (RAIS US EPA 2009).

Ingestion route

For the ingestion route, 1.5 L per capital per day was deemed reasonable based on local culture and conditions. The results of the lifetime cancer risk estimates were shown in Tables 68 for both ingestion and dermal routes. These results were time adjusted, that is the lifetime cancer risk estimates were calculated for a 6-month period per year. This was because in Zambia, the use of chlorine as a water disinfectant in peri-urban settings occurs predominantly during rainy seasons (November–April), when cholera epidemic is prevalent. The CHCl3 lifetime cancer risk estimates ranged from 2.5 × 10−6 to 6.0 × 10−6, 0.77 × 10−5 to 1.30 × 10−5, and 1.58 × 10−5 to 2.23 × 10−5 for 60, 180, and 300 min post chlorination, respectively. These results at 180 and 300 min were all above the negligible risk level, but within the risk level acceptable as defined by the USEPA (Nsikak et al. 2017). At 60 min post chlorination, only the CHCl3 lifetime cancer risk estimates results were evaluated as the concentrations of other THMs such as CHCl2Br, CHClBr2, and CHBr3 were not detected (see Table 3). However, at higher times of 180 and 300 min post chlorination, the lifetime cancer risk estimates for CHCl2Br and CHClBr2 were calculated, though at 180 min post chlorination almost all the value estimates were within the regulatory limit as defined by the USEPA. Interestingly, even at 300 min, the life cancer risk estimates for CHCl2Br and CHClBr2 were all still within the regulatory limit as defined by US EPA. For CHBr3, the lifetime cancer risk estimates were not available as CHBr3 was not detected in this study. Critical examination of Tables 68 showed that the percentage contribution of average cancer risk through ingestion for CHCl3 to the total cancer risk had the highest percentage (100%) at 60 min post chlorination, but with increase in post chlorination time, this contribution decreased substantially.

Table 6

Lifetime cancer risk estimates from THMs through ingestion and dermal exposure routes for water 60 min post chlorination

CHCl3 cancer risk (10−6)
CHCl2Br cancer risk (10−6)
CHClBr2 cancer risk (10−6)
TTHMs cancer risk (10−6)
Well IDIngInhalDerIngDerIngDerTotal
KE-01 5.0 1.1 0. 8 – – – – 6.9 
KE-02 3.8 0.8 0. 6 – – – – 5.2 
KE-03 6.2 1.3 1.0 – – – – 8.5 
KE-04 4.8 1.0 0.7 – – – – 6.5 
KE-05 5.5 1.1 0.8 – – – – 7.4 
KE-06 4.9 1.0 0.7 – – – – 6.6 
KE-07 4.4 0.9 0.7 – – – – 6.0 
KE-08 4.2 0.9 0.6 – – – – 5.7 
KE-09 3.2 0.7 0.5 – – – – 4.3 
KE-10 2.5 0.5 0.4 – – – – 3.4 
KE-11 3.2 0.7 0.5 – – – – 4.4 
KE-12 3.6 0.8 0.6 – – – – 4.9 
KE-13 3.7 0.8 0.6 – – – – 5.1 
CHCl3 cancer risk (10−6)
CHCl2Br cancer risk (10−6)
CHClBr2 cancer risk (10−6)
TTHMs cancer risk (10−6)
Well IDIngInhalDerIngDerIngDerTotal
KE-01 5.0 1.1 0. 8 – – – – 6.9 
KE-02 3.8 0.8 0. 6 – – – – 5.2 
KE-03 6.2 1.3 1.0 – – – – 8.5 
KE-04 4.8 1.0 0.7 – – – – 6.5 
KE-05 5.5 1.1 0.8 – – – – 7.4 
KE-06 4.9 1.0 0.7 – – – – 6.6 
KE-07 4.4 0.9 0.7 – – – – 6.0 
KE-08 4.2 0.9 0.6 – – – – 5.7 
KE-09 3.2 0.7 0.5 – – – – 4.3 
KE-10 2.5 0.5 0.4 – – – – 3.4 
KE-11 3.2 0.7 0.5 – – – – 4.4 
KE-12 3.6 0.8 0.6 – – – – 4.9 
KE-13 3.7 0.8 0.6 – – – – 5.1 

Ing, ingestion; Inhal, inhalation; Der, dermal; estimated for the actual exposure period of 6 months during the rainy season in Zambia (November–April each year).

Table 7

Lifetime cancer risk estimates from THMs through ingestion and dermal exposure routes for water 180 min post chlorination

CHCl3 cancer risk (10−5)
CHCl2Br cancer risk (10−5)
CHClBr2 cancer risk (10−5)
TTHMs cancer risk (10−5)
Well IDIngInhalDerIngDerIngDerTotal
KE-01 1.21 0.25 0.19 0.88 0.13 0.61 0.09 3.36 
KE-02 1.01 0.21 0.15 0.60 0.09 0.36 0.06 2.49 
KE-03 1.27 0.26 0.19 0.44 0.07 1.13 0.17 3.53 
KE-04 1.05 0.22 0.16 0.76 0.12 0.80 0.122 3.23 
KE-05 1.30 0.27 0.20 1.52 0.23 0.65 0.10 4.26 
KE-06 1.17 0.24 0.18 1.05 0.16 1.66 0.25 4.73 
KE-07 1.03 0.23 0.16 0.87 0.13 0.28 0.04 2.72 
KE-08 1.02 0.21 0.16 0.65 0.10 0.73 0.11 2.97 
KE-09 0.95 0.20 0.14 0.64 0.10 1.00 0.15 3.18 
KE-10 0.77 0.16 0.12 0.62 0.10 0.53 0.08 2.38 
KE-11 0.97 0.20 0.15 0.71 0.11 0.17 0.03 2.34 
KE-12 0.99 0.21 0.15 0.65 0.10 0.34 0.05 2.48 
KE-13 1.00 0.21 0.15 0.58 0.09 0.63 0.10 2.75 
CHCl3 cancer risk (10−5)
CHCl2Br cancer risk (10−5)
CHClBr2 cancer risk (10−5)
TTHMs cancer risk (10−5)
Well IDIngInhalDerIngDerIngDerTotal
KE-01 1.21 0.25 0.19 0.88 0.13 0.61 0.09 3.36 
KE-02 1.01 0.21 0.15 0.60 0.09 0.36 0.06 2.49 
KE-03 1.27 0.26 0.19 0.44 0.07 1.13 0.17 3.53 
KE-04 1.05 0.22 0.16 0.76 0.12 0.80 0.122 3.23 
KE-05 1.30 0.27 0.20 1.52 0.23 0.65 0.10 4.26 
KE-06 1.17 0.24 0.18 1.05 0.16 1.66 0.25 4.73 
KE-07 1.03 0.23 0.16 0.87 0.13 0.28 0.04 2.72 
KE-08 1.02 0.21 0.16 0.65 0.10 0.73 0.11 2.97 
KE-09 0.95 0.20 0.14 0.64 0.10 1.00 0.15 3.18 
KE-10 0.77 0.16 0.12 0.62 0.10 0.53 0.08 2.38 
KE-11 0.97 0.20 0.15 0.71 0.11 0.17 0.03 2.34 
KE-12 0.99 0.21 0.15 0.65 0.10 0.34 0.05 2.48 
KE-13 1.00 0.21 0.15 0.58 0.09 0.63 0.10 2.75 

Ing, ingestion; Inhal, inhalation; Der, dermal; estimated for the actual exposure period of 6 months during the rainy season in Zambia (November–April each year).

Table 8

Lifetime cancer risk estimates from THMs through ingestion and dermal exposure routes for water 300 min post chlorination

CHCl3 cancer risk (10−5)
CHCl2Br cancer risk (10−5)
CHClBr2 cancer risk (10−5)
TTHMs cancer risk (10−5)
Well IDIngInhalDerIngDerIngDerTotal
KE-01 2.06 0.43 0.316 2.38 0.36 2.31 0.35 8.22 
KE-02 1.88 0.39 0.287 1.17 0.18 1.07 0.16 5.14 
KE-03 2.23 0.46 0.341 2.21 0.34 1.29 0.20 7.07 
KE-04 1.94 0.40 0.297 2.58 0.39 3.37 0.52 9.51 
KE-05 2.09 0.43 0.320 2.13 0.33 1.18 0.18 6.65 
KE-06 2.00 0.42 0.306 2.33 0.36 1.66 0.25 7.32 
KE-07 1.91 0.40 0.292 2.29 0.35 2.22 0.34 7.80 
KE-08 1.88 0.39 0.288 2.33 0.36 1.45 0.22 6.91 
KE-09 1.62 0.34 0.249 2.30 0.35 2.02 0.31 7.19 
KE-10 1.58 0.33 0.241 1.99 0.30 1.95 0.30 6.69 
KE-11 1.79 0.37 0.274 2.20 0.34 2.39 0.37 7.73 
KE-12 1.81 0.38 0.277 1.94 0.30 1.42 0.22 6.34 
KE-13 1.85 0.39 0.283 1.85 0.28 1.33 0.20 6.18 
CHCl3 cancer risk (10−5)
CHCl2Br cancer risk (10−5)
CHClBr2 cancer risk (10−5)
TTHMs cancer risk (10−5)
Well IDIngInhalDerIngDerIngDerTotal
KE-01 2.06 0.43 0.316 2.38 0.36 2.31 0.35 8.22 
KE-02 1.88 0.39 0.287 1.17 0.18 1.07 0.16 5.14 
KE-03 2.23 0.46 0.341 2.21 0.34 1.29 0.20 7.07 
KE-04 1.94 0.40 0.297 2.58 0.39 3.37 0.52 9.51 
KE-05 2.09 0.43 0.320 2.13 0.33 1.18 0.18 6.65 
KE-06 2.00 0.42 0.306 2.33 0.36 1.66 0.25 7.32 
KE-07 1.91 0.40 0.292 2.29 0.35 2.22 0.34 7.80 
KE-08 1.88 0.39 0.288 2.33 0.36 1.45 0.22 6.91 
KE-09 1.62 0.34 0.249 2.30 0.35 2.02 0.31 7.19 
KE-10 1.58 0.33 0.241 1.99 0.30 1.95 0.30 6.69 
KE-11 1.79 0.37 0.274 2.20 0.34 2.39 0.37 7.73 
KE-12 1.81 0.38 0.277 1.94 0.30 1.42 0.22 6.34 
KE-13 1.85 0.39 0.283 1.85 0.28 1.33 0.20 6.18 

Ing, ingestion; Inhal, inhalation; Der, dermal; estimated for the actual exposure period of 6 months during the rainy season in Zambia (November–April each year).

Inhalation route

Inhalation exposure occurs when the air breathed contains compounds volatilized during water usage, such as bathing/showering, laundering, and cooking (Kujlu et al. 2020). It has been reported however, that bathing/showering is a much more prominent contributor to volatile compounds through inhalation exposure (Lee et al. 2004), particularly for CHCl3, which has a lower boiling point than other THMs (Siddique et al. 2015). Ebrahim et al. (2016) tabulated the boiling points of the THMs as 61.2, 90, 120, and 149 °C for CHCl3, CHCl2Br, CHClBr2, and CHBr3, respectively. The preliminary investigations that were undertaken in this study area revealed that people heated/warmed their chlorinated water before bathing. Therefore, the lower boiling point for CHCl3 justifies its exclusive use for estimation of cancer risks for the inhalation route. Interestingly, the levels of CHCl3 in this study were observed to be significantly higher than those of other THMs, even at 300 min post chlorination as shown in Tables 35.

To explain and justify the inhalation route for CHCl3, the VF of 0.5 L/m3 as suggested by Semerjian & Denis (2007) was used. All other factors required for the estimation of cancer risks for the inhalation route were obtained from literature (Lee et al. 2004; Amjad et al. 2013) and US EPA values from the U.S. EPA database (RAIS US EPA 2009).

The results of the CHCl3 lifetime cancer risk estimates for inhalation route were shown in Tables 68. Similarly, as earlier stated under the ingestion route, these results were time adjusted, to account for the actual time of exposure, of 6-month period per year. The CHCl3 lifetime cancer risk estimates for inhalation ranged from 0.5 × 10−6 to 1.5 × 10−6, 0.16 × 10−5 to 0.27 × 10−5, and 0.33 × 10−5 to 0.46 × 10−5 for 60, 180, and 300 min post chlorination, respectively. Interestingly, these results at 180 and 300 min were all above the negligible risk level, but within the risk level acceptable as defined by the US EPA.

Dermal route

As described elsewhere (Arman et al. 2016), dermal exposure to THMs may occur through several ways that involve water handling activities such as washing, cooking, bathing, and showering. For purposes of simplifying the study, several assumptions were made and these included the average skin surface area for males and females was assumed to be approximately equal and was assigned a value of 1.6 m2, though researchers elsewhere (Kujlu et al. 2020) used 1.7 and 1.53 m2, males and females, respectively. The other factors required for the estimation of cancer risks for the THMs were obtained from literature (Lee et al. 2004; Amjad et al. 2013) and US EPA values from the U.S. EPA website. Generally, the lifetime cancer risk estimates for all THMs through dermal route were substantially lower values in comparison to those from the ingestion route. As was observed for ingestion, at 60 min post chlorination, only the cancer risk estimates for CHCl3 were evaluated, as the concentrations of the other THMs were not detected. However, as would be expected, at 180 and 300 min post chlorination, the lifetime cancer risk estimates through dermal route were evaluated for CHCl2Br and CHClBr2, as their concentrations in the water samples were well above detection levels (see Tables 4 and 5). The estimated risk values were all within the negligible risk level as defined by the USEPA.

Total cancer risk

The examination of Tables 68 showed that TTHMs lifetime cancer risk average estimates were predominantly arising from the contribution through the ingestion route. For instance, a quick calculation would show that the ingestion route contributed more than 85% of all detected THMs in the chlorinated water samples. For the 180 and 300 min post chlorination, the lifetime cancer estimates were observed to be within the regulatory limit defined by US EPA (10−6–10−4) (Nsikak et al. 2017). The results of this study were within the range of results observed elsewhere (Kumari & Gupta 2018). For instance, at 300 min post chlorination, the lifetime cancer risk estimates for the TTHMs through ingestion, inhalation, and dermal routes ranged from 5.14 × 10−5 to 9.51 × 10−5. Although the results of this study were similar and within the range of results observed elsewhere as earlier noted, the implications present an interesting and uniquely different scenario given that the study area is at the epicenter of mining part of Zambia, the Copperbelt Province, as shown in Figure 1. Mufulira town in the Copperbelt Province of Zambia is one of the most polluted mining towns, where people may be exposed to a large number of diverse contaminants (Mwaanga et al. 2019). Thus, despite the lifetime cancer risk estimates being within the regulatory limits, the implications for the people in this community may still present dire consequences, given that exposure to multiple toxicants may result in additive and synergistic interactive effects. As earlier indicated, this community gets its water from shallow hand-dug wells, where elevated concentrations of heavy metals in water were not uncommon. Previous studies in this and several other settlements, in the mining towns of Zambia, have shown that the concentrations of heavy metals such as copper, cobalt, arsenic cadmium, zinc, and manganese are well above tolerable levels (Nachiyunde et al. 2013). Furthermore, other studies conducted elsewhere (Kim et al. 2015; Romaniuk et al. 2017) have implicated heavy metals in causing certain types of cancers. Thus, based on the lifetime cancer estimation results from this study, there was still significant likelihood that people consuming ex-situ chlorinated water from shallow hand-dug wells could be at risk of developing cancers. This could be particularly true for older age (>60), who may be more vulnerable to developing cancer due to chronic exposure (Kumari & Gupta 2018), coupled with increased duration of exposure owing to age and age-related immuno-deficiencies (Aiello et al. 2019; Bajaj et al. 2021).

Estimation of non-cancer/hazard quotients

The non-cancer indices or hazards that can be induced by exposure to THMs include effects such as birth defects, miscarriages, reproductive abnormalities, immuno-suppression, liver and kidney damage, cardiac, and neural defects as described elsewhere (Villanueva et al. 2015). According to WHO (2005a, 2005b), most of these effects have been demonstrated in animal models, though for humans, more epidemiological studies are required to add weight of evidence in view of some insufficient evidence (Nieuwenhuijsen et al. 2009) and sometimes contradicting results as observed elsewhere (Mohamadshafiee & Taghavi 2012). The results of non-cancer or hazard quotients (HQs) for this study are calculated and are shown in Tables 911. The non-cancer hazards targeted in Tables 911 include the liver and kidney damage and neural defects. The kidneys and liver are highly susceptible due to their inherent biotransformative attributes as elucidated elsewhere (OEHHA 2020). For 60 min post chlorination, only CHCl3 HQs were determined as other THMs concentrations were below detection. At 180 and 300 min post chlorination, HQs for CHCl2Br and CHClBr2, in addition to that of CHCl3 were determined. The HQs were also calculated for a period of 6 months per year, for reasons as already explained above. The total HQs for the TTHMs for ingestion, inhalation, and dermal routes ranged from 0.055 to 0.139, 0.155 to 0.264, and 0.384 to 0.527 for 60, 180, and 300 min post chlorination, respectively. Similar such results were reported elsewhere (Kumari et al. 2015; Mosaferi et al. 2020). As observed, the values obtained were less than the US EPA prescribed risk level of greater than 1 (HQ < 1). Thus, in an environment where there were no other contaminants other than THMs, such results would be assumed not to possess any significant non-cancer effects on human health. However, as already indicated above, possible concern exists on to human health due to multiplicity of exposure to other contaminants that were ubiquitous in the study area (Nachiyunde et al. 2013; Mwaanga et al. 2019). Thus, the presence of other contaminants may exacerbate the non-cancer effects predominantly through additivity and synergistic interaction.

Table 9

Hazard index from THMs through ingestion and dermal exposure routes for water 60 min post chlorination

CHCl3
CHCl2Br
CHClBr2
TTHMs
Well IDIngInhalDerIngDerIngDerTotal
KE-01 0.083 0.017 0.013 – – – – 0.112 
KE-02 0.062 0.013 0.010 – – – – 0.085 
KE-03 0.102 0.021 0.016 – – – – 0.139 
KE-04 0.078 0.016 0.012 – – – – 0.106 
KE-05 0.090 0.019 0.014 – – – – 0.122 
KE-06 0.080 0.017 0.012 – – – – 0.108 
KE-07 0.073 0.015 0.011 – – – – 0.099 
KE-08 0.069 0.014 0.011 – – – – 0.094 
KE-09 0.052 0.011 0.008 – – – – 0.071 
KE-10 0.041 0.008 0.006 – – – – 0.055 
KE-11 0.053 0.011 0.008 – – – – 0.072 
KE-12 0.059 0.012 0.009 – – – – 0.080 
KE-13 0.061 0.013 0.009 – – – – 0.083 
CHCl3
CHCl2Br
CHClBr2
TTHMs
Well IDIngInhalDerIngDerIngDerTotal
KE-01 0.083 0.017 0.013 – – – – 0.112 
KE-02 0.062 0.013 0.010 – – – – 0.085 
KE-03 0.102 0.021 0.016 – – – – 0.139 
KE-04 0.078 0.016 0.012 – – – – 0.106 
KE-05 0.090 0.019 0.014 – – – – 0.122 
KE-06 0.080 0.017 0.012 – – – – 0.108 
KE-07 0.073 0.015 0.011 – – – – 0.099 
KE-08 0.069 0.014 0.011 – – – – 0.094 
KE-09 0.052 0.011 0.008 – – – – 0.071 
KE-10 0.041 0.008 0.006 – – – – 0.055 
KE-11 0.053 0.011 0.008 – – – – 0.072 
KE-12 0.059 0.012 0.009 – – – – 0.080 
KE-13 0.061 0.013 0.009 – – – – 0.083 

Ing, ingestion; Inhal, inhalation; Der, dermal; estimated for the actual exposure period of 6 months during the rainy season in Zambia (November–April each year).

Table 10

Hazard index from THMs through ingestion and dermal exposure routes for water 180 min post chlorination

CHCl3
CHCl2Br
CHClBr2
TTHMs
Well IDIngInhalDerIngDerIngDerTotal
KE-01 0.198 0.041 0.030 0.007 0.001 0.004 0.0006 0.241 
KE-02 0.166 0.035 0.025 0.005 0.001 0.002 0.0003 0.199 
KE-03 0.208 0.043 0.032 0.004 0.001 0.007 0.0010 0.252 
KE-04 0.172 0.036 0.026 0.006 0.001 0.005 0.0007 0.210 
KE-05 0.213 0.044 0.033 0.012 0.002 0.004 0.0006 0.264 
KE-06 0.192 0.040 0.029 0.009 0.001 0.010 0.0015 0.243 
KE-07 0.168 0.035 0.026 0.007 0.001 0.002 0.0003 0.204 
KE-08 0.167 0.035 0.026 0.005 0.001 0.004 0.0007 0.203 
KE-09 0.155 0.032 0.024 0.005 0.001 0.006 0.0009 0.192 
KE-10 0.126 0.026 0.019 0.005 0.001 0.003 0.0005 0.155 
KE-11 0.160 0.033 0.024 0.006 0.001 0.001 0.0002 0.192 
KE-12 0.162 0.034 0.025 0.005 0.001 0.002 0.0003 0.195 
KE-13 0.163 0.034 0.025 0.005 0.001 0.004 0.0006 0.198 
CHCl3
CHCl2Br
CHClBr2
TTHMs
Well IDIngInhalDerIngDerIngDerTotal
KE-01 0.198 0.041 0.030 0.007 0.001 0.004 0.0006 0.241 
KE-02 0.166 0.035 0.025 0.005 0.001 0.002 0.0003 0.199 
KE-03 0.208 0.043 0.032 0.004 0.001 0.007 0.0010 0.252 
KE-04 0.172 0.036 0.026 0.006 0.001 0.005 0.0007 0.210 
KE-05 0.213 0.044 0.033 0.012 0.002 0.004 0.0006 0.264 
KE-06 0.192 0.040 0.029 0.009 0.001 0.010 0.0015 0.243 
KE-07 0.168 0.035 0.026 0.007 0.001 0.002 0.0003 0.204 
KE-08 0.167 0.035 0.026 0.005 0.001 0.004 0.0007 0.203 
KE-09 0.155 0.032 0.024 0.005 0.001 0.006 0.0009 0.192 
KE-10 0.126 0.026 0.019 0.005 0.001 0.003 0.0005 0.155 
KE-11 0.160 0.033 0.024 0.006 0.001 0.001 0.0002 0.192 
KE-12 0.162 0.034 0.025 0.005 0.001 0.002 0.0003 0.195 
KE-13 0.163 0.034 0.025 0.005 0.001 0.004 0.0006 0.198 

Ing, ingestion; Der, dermal; estimated for the actual exposure period of 6 months during the rainy season in Zambia (November–April each year).

Table 11

Hazard index from THMs through ingestion and dermal exposure routes for water 300 min post chlorination

CHCl3
CHCl2Br
CHClBr2
TTHMs
Well IDIngInhalDerIngDerIngDerTotal
KE-01 0.338 0.071 0.052 0.019 0.003 0.014 0.002 0.499 
KE-02 0.308 0.064 0.047 0.009 0.001 0.006 0.001 0.437 
KE-03 0.365 0.076 0.056 0.018 0.003 0.008 0.001 0.527 
KE-04 0.318 0.066 0.049 0.021 0.003 0.020 0.003 0.481 
KE-05 0.343 0.071 0.052 0.017 0.003 0.007 0.001 0.494 
KE-06 0.328 0.068 0.050 0.019 0.003 0.010 0.002 0.479 
KE-07 0.313 0.065 0.048 0.018 0.003 0.013 0.002 0.463 
KE-08 0.308 0.064 0.047 0.019 0.003 0.009 0.001 0.451 
KE-09 0.266 0.055 0.041 0.019 0.003 0.012 0.002 0.398 
KE-10 0.258 0.054 0.040 0.016 0.002 0.012 0.002 0.384 
KE-11 0.294 0.061 0.045 0.018 0.003 0.014 0.002 0.437 
KE-12 0.296 0.062 0.045 0.016 0.002 0.008 0.001 0.431 
KE-13 0.303 0.063 0.046 0.015 0.002 0.008 0.001 0.439 
CHCl3
CHCl2Br
CHClBr2
TTHMs
Well IDIngInhalDerIngDerIngDerTotal
KE-01 0.338 0.071 0.052 0.019 0.003 0.014 0.002 0.499 
KE-02 0.308 0.064 0.047 0.009 0.001 0.006 0.001 0.437 
KE-03 0.365 0.076 0.056 0.018 0.003 0.008 0.001 0.527 
KE-04 0.318 0.066 0.049 0.021 0.003 0.020 0.003 0.481 
KE-05 0.343 0.071 0.052 0.017 0.003 0.007 0.001 0.494 
KE-06 0.328 0.068 0.050 0.019 0.003 0.010 0.002 0.479 
KE-07 0.313 0.065 0.048 0.018 0.003 0.013 0.002 0.463 
KE-08 0.308 0.064 0.047 0.019 0.003 0.009 0.001 0.451 
KE-09 0.266 0.055 0.041 0.019 0.003 0.012 0.002 0.398 
KE-10 0.258 0.054 0.040 0.016 0.002 0.012 0.002 0.384 
KE-11 0.294 0.061 0.045 0.018 0.003 0.014 0.002 0.437 
KE-12 0.296 0.062 0.045 0.016 0.002 0.008 0.001 0.431 
KE-13 0.303 0.063 0.046 0.015 0.002 0.008 0.001 0.439 

Ing, ingestion; Inhal, inhalation; Der, dermal; estimated for the actual exposure period of 6 months during the rainy season in Zambia (November–April each year).

This study has shown that the presence of organic matter emanating from pit latrines, in water from shallow wells, once chlorinated can lead to the formation of THMs. In particular, this study showed thatCHCl3, CHCl2Br, CHClBr2, and CHBr3 were formed. It was further shown that as long as residual chlorine remains in the water, there will be continued formation of these compounds, and hence it was observed that there was an increase in the concentration of THMs with time, post chlorination. The lifetime cancer risk estimation however, showed that the risks were within the US EPA regulatory limit. Thus, based on the results of this study, there was no significant cancer risk for the community in this peri-urban setting. However, it was argued that given that other contaminants such as heavy metals are ubiquitous in these areas, multiplicity of exposure was highly likely, raising concerns about the possible occurrence of interactive effects of chemicals, such as additivity and synergistic effects, and hence cancer risks could not be ruled out. Similarly, the non-cancer HQs were observed to be less than unity, but significant risks, arising from chronic effects could not be ruled out, for the same reasons as those given under the cancer risks, particularly for the elderly members of the community whose immuno-deficiencies could be accelerated by the ageing process.

Data cannot be made publicly available; readers should contact the corresponding author for details.

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