Exposure and Health https://doi.org/10.1007/s12403-017-0265-7

ORIGINAL PAPER

Major Chemical Carcinogens in Drinking Water Sources: Health Implications Due to Illegal Gold Mining Activities in Zamfara State‑Nigeria Raymond L. Njinga1,2   · Victor M. Tshivhase1 Received: 24 September 2017 / Revised: 22 November 2017 / Accepted: 24 November 2017 © Springer Science+Business Media B.V., part of Springer Nature 2017

Abstract The study aimed at quantifying the levels of three major chemical carcinogens (MCCs): Pb, Cd, and Cr in wells, boreholes, and river water sources using HRCS AAS of Bagega, Sunke, and Dareta villages of Zamfara State, Nigeria; estimating daily MCC intake; and determining the cancer and non-cancer risks associated with MCC exposure. In total, 202 water samples were collected from the three villages and their MCC contents measured. The levels of Pb in the three Wells in Sunke ranged between 21 ± 9.8 and 326 ± 13.1 mg/L. The highest concentrations of Cd and Cr of 15 ± 7.1 and 96 ± 9.7 mg/L, respectively, were obtained in the affected area in Sunke village. A high incremental lifetime cancer risk of 1.59 × 103 for children due to Cd was obtained in Bagega village. The computed average Chronic hazard index (CHI) values for adults and children were 2.81 × 106 and 2.32 × 106, respectively, in drinking water from the river in Bagega village followed by an average values of 1.62 × 106 and 1.35 × 106 in drinking water from boreholes in Sunke village. The target hazard quotients and the CHI values were far greater than 1 indicating a high risk of adverse health outcomes. Keywords  Chemical carcinogenic · Illegal gold mining activity · Water pollution · Chronic hazard index · Cancer risk

Introduction Chemical carcinogens are agents that are capable of inducing cancer in humans or animals (Tchounwou et al. 2014). Many chemicals when used properly can improve our quality of life, health, and well-being. Most chemical carcinogens have been recognized as a result of tests in rats or mice (Hague et al. 2008). WHO compiled a list of the 10 major chemicals of concern among which Pb, Cr, and Cd are considered highly hazardous human carcinogens (WHO 2007). Many lists of human carcinogens have been published, and differ widely according to the strength of the evidence that is accepted. Chemical carcinogenesis is a prolonged process with many stages, mostly very imperfectly understood, and a variety of other factors are known which potentiate * Raymond L. Njinga [email protected] 1

Center for Applied Radiation Science and Technology, North-West University, Mafikeng, South Africa



Department of Physics, Federal University Dutse, Dutse, Jigawa, Nigeria

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or inhibit the development of cancer (Järup 2003; Williams and Weisburger 1986). Some of these carcinogenic or toxic elements affecting the central nervous system, kidneys, or liver include Pb; and some affecting the skin, bones, or teeth include Cd and Cr which are generally present in the environment at low levels. The International Agency for Research on Cancer (IARC) classified Cr, Pb, and Cd as carcinogenic (Li and Zhang 2010). The potential exposure of these three major chemical carcinogens (MCCs) will be exploited based on two major pathways which include (1) direct ingestion of the water consumption and (2) dermal absorption of contaminants in water adhering to exposed skin. In these villages, the water sources are highly contaminated with lead from the ore processing that had previously taken place. The children bathe in the river as shown in Fig. 1 (Marcus 2011) This work was carried out based on the increase in the number of cases with gastrointestinal symptoms such as nausea, vomiting, abdominal pain, diarrhea, salivation, tenesmus, hemorrhagic gastroenteritis, hepatic necrosis, renal necrosis, and cardiomyopathy around these three villages (Sunke, Dareta, and Bagega) in Zamfara state, Nigeria (Derek Forseth 2014).

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R. L. Njinga, V. M. Tshivhase

Fig. 1  Dermal absorption of MCCs in water adhering to exposed skin in Bagega River (ZR1)

In March 2010, an unusually high number of deaths, primarily among children under the age of 5 years in Bukkuyum and Anka Local Government Areas (LGAs) of Zamfara State (Abatu 2014; Tirima et al. 2016), northern Nigeria, were reported by Médecins sans Frontières (MSF) Holland to state the health status (JEU 2010). Further study on blood samples taken by MSF revealed that the increased mortality was the result of acute Pb poisoning caused by massive environmental contamination from artisanal mining and processing of gold (JEU 2010). The grinding of the ore into fine particles may result in extensive dispersal of MCCs in the three villages of concerned. According to MSF, ingestion and inhalation of the fine Pb particles were determined to be the major reasons for high blood Pb levels in victims’ bodies. Blood lead levels (BLLs) were “unprecedented” for human beings, according to the US Centers for Disease Control (CDC) and Prevention (JEU 2010). From September 20 through October 7, 2010, the Joint UNEP/OCHA Environment Unit (JEU) investigated the emergence of Pb pollution in Zamfara State. This was done at the requests from the Federal Ministry of Health, Nigeria and the United Nation’s (UN) resident coordinator (JEU 2010). The investigation focused on the quantities of Pb in the ground and surface waters and was carried out to confirm the works conducted by CDC, World Health Organization (WHO), National Water Resources Institute of Nigeria (NWRI), and Terra Graphics Environmental Engineering and Blacksmith Institute. It was realized that drinking water from the wells did not meet WHO (0.01 mg/L) for Pb limits; three wells in at least one case were found to be exceeding this limit by more than tenfold (Tirima et al. 2016). In the five villages (Abare, Kirsa, Sunke, Bagega, and Dareta) visited, the soil was often highly polluted with Pb. Since young children readily ingest soil as part of normal hand-tomouth behavior, such high concentrations expose children to potentially harmful amounts of Pb (Bashir et al. 2014). International partners such as JEU, WHO, UN, NWRI, MSF,

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and CDC, in cooperation with the Zamfara state government, have treated 1,500 children and cleaned up seven villages contaminated with lead (UNICEF 2011). There are thousands of children who still need treatment and thousands more who continue to be at risk for acute lead poisoning because their villages remain contaminated (UNICEF 2011). In Bagega, the largest and most contaminated village, environmental remediation and the implementation of safer mining practices to prevent recontamination are urgently needed and must be put in place before comprehensive treatment can be provided for children. The Zamfara state government has started remediation in Bagega, but it lacks the resources necessary for an urgent comprehensive response (BLM 1998). Environmental pollution by MCCs is prominent in mining and old mine sites. Through mining activities, water bodies, mostly surface water, are most polluted (Garbarino et al. 1995), and when mined ores are dumped on the earth surfaces in manual dressing processes (Duruibe et al. 2007). Through rivers and streams, the MCCs are transported as either dissolved species in water or as an integral part of suspended matter causing the most deleterious effects on aquatic life (Duruibe et al. 2007). The type of water-source contamination produced by a mining operation depends to a large extent on the nature of the mineralization and on the processing chemicals used to extract or concentrate minerals from the host rock (Economopoulos 1993). As a result of the illegal gold mining activities within the three villages (Sunke, Dareta, and Bagega), the waste water generated may contain heavy metals that can spread into the water-source types (well, boreholes, and river) used for drinking by the community. Information about MCC concentrations in the water intake is very important for assessing their risk to human health. Levels of the MCC (WCRF/AICR 2007) in the water-source types have been quantified and the results extended to generate target hazard quotients (THQs) for individual and combinations of the concentrations (Hague et al. 2008). However, there are limited or no direct studies evaluating the MCCs in the three water-source types. Therefore, the objectives of this study were to (1) quantify levels of Pb, Cd, and Cr in the wells, boreholes, and river in the three villages (Sunke, Dareta, and Bagega) using the High-Resolution Continuum Source Atomic Absorption Spectrometry (HRCS AAS) in Zamfara State caused by massive environmental contamination from artisanal mining and processing of gold found in the lead-rich ore; (2) estimate daily MCC intake through consumption of these water-source types; (3) determine the cancer and non-cancer risks associated with the MCC intake using probabilistic risk-assessment models in the various drinking water sources in the three villages of Bukuyum Local Government area in Zamfara State of Nigeria.

Major Chemical Carcinogens in Drinking Water Sources: Health Implications Due to Illegal Gold…

The Study Area The field experiment was carried out at the three villages of Zamfara State (Fig. 2), Nigeria (11,86858 N to 11,89651 N and 5,91222 E to 5,99932 E). The villages being Bagega, Dareta, and Sunke are characterized typically of Sudan savannah vegetation having short stunted trees with communities of grasses. They all experience two distinct seasons; rainy, and dry seasons. The rainy season commences in April and end September, while dry seasons prevails from March to May. The peak of the rainfall is in July–August. The average temperature variation is between 30 and 35 °C (Hoffmann 2004). The coldest temperatures are experienced during the harmattan periods when the temperature drops to approximately 18 °C. During the harmattan periods, the winds are cold, dry, dusty, and strong. These villages are subjected to poor drainage system due to vast portions of clay terrain that makes up its landscape.

Materials and Method Sample Collection and Preparation Techniques Each sampling point was marked using a global positioning system (GPS). In the first village Sunke, we identified three wells and three boreholes. From each of the wells (coded XW1-XW3) and boreholes (coded XB1–XB3), 17 water samples were collected from each sources as described in Tables 1 and 2 making a total of 102 samples collected

entirely. From the second village Dareta, only three wells were identified coded YB1–YB3, and 20 water samples were collected from each as described in Tables 1 and 2 making a total of 60 samples. Finally, from the third village Bagega, the river coded ZR1 was the major source of water used for consumption by the community. Forty (40) water samples were collected from this water source as described in Tables 1 and 2. The samples were transferred to the laboratory after they were labeled accordingly. The water samples were collected into 2.0-L plastic containers that were washed thoroughly and soaked in 10% H ­ NO3 overnight. There were rinsed several times with distilled water to prevent matrix contamination. The water samples were acidified with H ­ NO3 because they stayed for more than 24 h. This was to ensure that the elements present are in oxidation state and to set the pH values of both the samples and the standard to be equal. The water samples were then stored in a refrigerator at 4 °C (Haier Thermo cool) to slow down bacterial and chemical reaction rates.

Measurement of Pb, Cr, and Cd in Water The Pb, Cr, and Cd concentrations (MCCs) in the surface and underground water sources of Bagega, Dareta, and Sunke were determined by AAS standard procedures described by the American Public Health Association (APHA 1998). This was performed using the High Resolution Continuum Source Atomic Absorption Spectrometry (HRCS AAS) series ContrAA 700 manufactured by Analytik

Fig. 2  A map showing the studied villages in Zamfara State, Nigeria

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R. L. Njinga, V. M. Tshivhase

Table 1  Water sampling descriptions Village/location points

Number of samples

Methods of sampling collections

Sunke (XW1, XW2, XW3, XB1, XB2, and XB3)

From each of sampling points, 4 samples between January, and March From each of sampling points, 4 samples between April and June From each of sampling points, 4 samples between July, and September From each of sampling points, 5 samples between October and December

Once in January (morning period), twice in February (afternoon period) and once in March (evening period) Once in April (morning period), twice in May (afternoon period) and once in June (evening period) Once in July (morning period), twice in August (afternoon period) and once in September (evening period) Twice in October (morning period), Once in November (afternoon period) and twice in December (evening period) Twice in January (morning period), twice in February (afternoon period) and once in March (evening period) Once in April (morning period), twice in May (afternoon period) and Twice in June (evening period) Once in July (morning period), twice in August (afternoon period) and Twice in September (evening period) Twice in October (morning period), once in November (afternoon period) and twice in December (evening period) Four times in January (morning period), thrice in February (afternoon period) and thrice in March (evening period) Four times in April (morning period), thrice in May (afternoon period) and Thrice in June (evening period) Thrice in July (morning period), thrice in August (afternoon period) and Four times in September (evening period) Thrice in October (morning period), Thrice in November (afternoon period) and Four times in December (evening period)

Dareta From each of sampling points, 5 samples between Janu(YW1, YW2, and YW3) ary and March From each of sampling points, 5 samples between April and June From each of sampling points, 5 samples between July and September From each of sampling points, 5 samples between October and December Bagega (ZR1)

10 samples between January and March 10 samples between April and June 10 samples between July and September 10 samples between October and December

Table 2  Description of sampling sites and locations/ activities

Villages

Sampling location points

Number of samples collected

Description

Sunke

XW1

17

XW2 XW3 XB1 XB2 XB3 YW1 YW2 YW3 ZR1

17 17 17 17 17 20 20 20 40

A well around the problem area were mining activity is intensive A well within the mining site A well far from the mining site A borehole far from the mining site A borehole far from the mining site A borehole far from the mining site A well from the washing point A well from the washing point A well far from the washing point A river used by miners and the community for drinking and household

Dareta

Bagega

NB Sunke has only wells and boreholes, Dareta has only wells, and Bagega has only river for the community

Jena, Germany available in the National Research Institute for Chemical Technology (NARICT). This institute is a parastatal under Nigeria’s Federal Ministry of Science and Technology and is located in Basawa, Zaria, Kaduna State.

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The instrument has a xenon short-arc lamp with UV arc in the hot-spot mode. The high-purity Ar 5.0 was used as inner gas for furnace AAS and acetylene 2.6 was used as fuel gas for the flame AAS. All samples were prepared in accordance

Major Chemical Carcinogens in Drinking Water Sources: Health Implications Due to Illegal Gold…

with the AAS standard procedures described by the American Public Health Association (APHA 1998) and measurements were carried out under optimized conditions with three replicates using an auto sampler Micropipettor unit MPE 60 for the sample solutions in flame AAS. The method was optimized for the atomic lines; Pb (283.306 nm), Cd (228.802 nm), and Cr (357.869 nm. A BT-214D electronic balance (Sartorius AG Weender Landstrasse, Goettingen, Germany) was used to weigh the samples.

Quality Control In order to perform quality control, an analytical blank and a sample with known heavy metal concentrations were prepared and analyzed using the same procedures and reagents. Based on the samples from three categories of water sources in this study (wells, borehole, and river), the standard reference material 1643e (NIST) was analyzed for trace elements, and the results obtained are shown in Table 3.

Estimating Water Ingestion Exposures Drinking the contaminated water from the three water sources in Sunke, Dareta, and Bagega villages by the inhabitant can lead to significant exposures to the MCCs. In order to estimate the exposure to these contaminants from drinking water, the amount of water the people drink must be determined. Ingestion of water includes straight water, water in coffee, tea, or other drinks made with the water types, and water in cooked food. Since we don’t have precise values for these communities, the standard values for the daily ingestion of water obtained from USEPA (2004, 2011a) will be used. To calculate the water ingestion dose, it is assumed that 100% of the contaminant is absorbed after ingestion. The amount of the MCC absorbed into the body through drinking water can be estimated with the following equation for both adult and children (Sadovska 2012):

C × IR × EFw EDW = BW

(1)

where

EDw = estimated dose from drinking water: The water ingestion dose is expressed as milligrams of the contaminant ingested, per kilogram of body weight per day (mg/kg/day). EFw = exposure frequency 365 day/year. BW = body weight of 15 kg for children and 70 kg for adults. IR = ingestion rate which is the amount of water a person drinks in a day, in liters (L/day). The amount of the MCC in the water-source types absorbed into the body through skin contact can be estimated with the equation (Health Canada 1994):

EDWS =

C × P × SA × ETws × EFws × 10−3 , BW × AT

where EDWS  = estimated dose through water on the skin expressed as milligrams absorbed through the skin per kilogram of body weight per day (mg/kg/day). C = concentration of the contaminant in the water in milligrams per liter of water (mg/L). ETws = exposure time which is the number of hours per day that the MCC in the water-source types is in contact with the skin, and we assumed a value of 0.25 h/day for adults and 0.1 h/day for children (Health Canada 1994). EFws = exposure factor which implies how often the individual has been exposed to the MCC in the water-source types over a lifetime (unitless). AT = average Time 25,550 days (Health Canada 1994). P = permeability constant which indicates the number of centimeters the chemical will travel through the skin in an hour and a cautious approach assumes a constant of 1.0 cm/h for both adults and children (USEPA 1990). SA = surface area of the skin that is exposed to the MCC in the water-source types, which is 16,200 cm2 for children (< 20 years) and 18,200 cm2 for adults (> 20 years).

Estimated Daily Intake (EDI) We are all exposed to a low level of contamination in the water we drink. The estimated daily intakes (EDI) for the MCCs represent the total exposure risk from all known or suspected exposure pathways for an average person. The EDI is evaluated using the equation below (Health Canada 1994):

EDI = EDW + EDWS Table 3  Three MCC validation in CRM 1643e (NIST) by HRCS AAS MCC

Reference values (μg/L)

Quality control results (μg/L)

Percentage confidence (%)

Cr Cd Pb

19.90 ± 0.23 6.408 ± 0.071 19.15 ± 0.2

18.9 ± 0.5 5.5 ± 0.4 18.60 ± 1.3

95 86 97

(2)

(3)

Risk‑Specific Dose It is desirable to reduce exposure risk to carcinogens to as low as possible, while recognizing that zero exposure is impossible. For MCC, a decision must be made on how large a risk of cancer can be accepted, in order to set acceptable intake levels for any given community (ATSDR 1992). There are various acceptable levels of risk currently being

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R. L. Njinga, V. M. Tshivhase

used around the world depending on specific circumstances. This level is one extra cancer death per ­106 people exposed to the MCC over their entire lifetime. Once an acceptable level of risk (ALR) has been established, it is divided by the cancer slope factor (CSF), which has been determined from the results of laboratory and epidemiological studies, to obtain a risk-specific dose (RsD). The RsD is the amount of MCC that people can be exposed to on a daily basis, over their entire lifetime that will not exceed the accepted level of risk of cancer expressed in mg/ kg/day and evaluated using the equation below:

RsD =

ALR , CSF

(4)

where ALR = accepted level of risk is one extra cancer death per year per ­106 people exposed. CSF = cancer slope factor (CSF) which is the risk produced by a lifetime average dose of 1 mg ­kg−1 BW ­day−1 and is contaminant specific (Pepper et al. 2012). Its value was worked out for Cd, Pb, and Cr using respective cancer slope factors of 6.3, 8.5 × ­10−3, and 0.5 (mg/kg/day)−1, respectively.

Cancer Risk Assessments Potential cancer risks associated with the exposure of the MCCs can be estimated using the incremental lifetime cancer risk (ILCR). This explained the incremental probability of an individual to develop any type of cancer over a lifetime due to a 24 h/day MCC exposure to a given daily dose for 70 years (Li and Zhang 2010). The ALR of one in a million (1 × ­10−6) cancer risk means that if a million people are exposed, one additional cancer case would be expected. The USEPA (2011b) cancer risk considered the ALR to be within the range of 1 × ­10−6–1 × ­10−4 for regulatory purposes (Li et al. 2013). Incremental lifetime cancer risk will be evaluated using the CSF as shown in Eq. 5 (Njinga et al. 2016):

ILCR = CDI × CSF (5) where CDI = chronic daily intake of chemical, mg ­kg−1 BW ­day−1 which represents the lifetime average daily dose of exposure to the MCC. The evaluation of the chronic daily intake of chemical was performed using Eq. 6: CDI =

EDI × EFw × EDRw AT

(6)

where EDI is the estimated daily intake of the MCC via consumption of the water-source types; E ­ Fw is exposure

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frequency (365 days/year); ­EDRw is the exposure duration 54.5 years, average lifetime for Nigerian (WHO 2015). It should be noted that cancer risk estimates for exposures ≤ 35 years introduce significant uncertainty.

Non‑Carcinogenic Risk Assessment Non-carcinogenic health hazards will be evaluated by the target hazard quotient (THQ) using Eq. 7:

THQ =

CDI RfD

(7)

where CDI is the exposure dose obtained from Eq. (6) and RfD is the oral reference dose of the contaminant. The RfD is an estimation of the maximum permissible risk on human population through daily exposure. The RfD values for Pb, Cd, and Cr are 4.0 × ­10−3, 1.0 × ­10−3, and 1.5 × ­100 (mg ­kg−1 ­day−1), respectively (Harmanescu et al. 2011, USEPA 2010).

Chronic Hazard Index Assessment Exposures to Pb, Cd, and Cr result in additive and or interactive effects. Hence, to estimate the potential risk to human health through more than one MCC, the chronic hazard index (CHI) is obtained as the sum of all hazard ratios (THQs) calculated for individual MCC for a particular exposure pathway WCRF/AICR (2007). The calculated CHI is compared to a benchmark; the community is assumed to be safe when CHI < 1 and is in a level of concern when 1 < CHI < 5 (WCRF/AICR 2007).

CHI =

n ∑ j=1

THQj =

n ( ) ∑ CDI j=1

RfD

j

(8)

where THQ, ­EDIL, and RfD are values of heavy jth metal.

Results and Discussion The analysis of three trace metals in the certified reference material (CRM) 1643e (NIST) with known concentration of respective reference values in μg/L evaluated by the high resolution continuum source atomic absorption spectrometry (HRCS AAS) for quality control are shown in Table 3. As shown in Table 3, the analysis of the certified reference material (CRM) 1643e (NIST) by the HRCS AAS leads to very good results for the three trace elements under validation. The percentage confidences (recovery) for the MCCs were 95% for Cr, 97% for Pb, and 86% for Cd. As demonstrated by this techniques (HRCS AAS), the three MCC were analyzed with good level of confidence. The

Major Chemical Carcinogens in Drinking Water Sources: Health Implications Due to Illegal Gold…

Fig. 3  Concentration of MCC concentrations in water from the three villages

Concentraon of MCC concentraons (mg/L) in water

results of the analyzed water sample for the three villages practicing “illegal” Gold mining in Zamfara State of Nigeria are presented in Fig. 3. From the analysis of the water samples, three major chemical carcinogens (MCC) were determined as shown in Fig. 3. Levels of Pb in the three Wells in Sunke illegal mine site XW1, XW2, and XW3 ranged between 21 ± 9.8 and 326 ± 13.1 mg/L. Permissible level of Pb in water is 0.01 mg/L (CAC 1995). The examined water samples therefore had Pb concentrations far greater than the limit. The maximum value of 326 ± 13.1 mg/L was observed in XW3 and is the nonaffected area. This high value could be due to the heavy metals associated with “illegal” gold mining dissolved in the soluble compounds or dispersed into surrounding streams which eventually are found in the Well water (Fernando et al. 2011). In terms of Cd, the highest value of 15 ± 7.1 mg/L was obtained in the affected area (XW2). The average value of Cd in the three wells studied was 15 ± 6.4 mg/L far greater than World Health Organization, Guidelines for Drinking Water Quality (2004, 2006, 2011a, b). High exposure to Pb and Cd may be a risk factor for the occurrence of iron deficiency anemia in humans. This suggests that well’s contribution to MCC exposure is a health hazard with respect to Pb and Cd particularly in children and regular consumers. Table 3 showed that the Boreholes waters from Sunke at the three locations XB1, XB2, and XB3 indicates that the average value of Pb obtained was 394 ± 10.6 mg/L and is far greater than the limit set by World Health Organization (2004, 2006, 2011a, b). The highest value of Pb was obtained in XB2 in the nonaffected area. The high value of Pb in the nonaffected area could be in the compound form which is soluble in water and could have dissolved into the surrounding streams and invariably ended up in borehole water. The average value of Cd was also found to be 12 ± 5.8 mg/L with maximum value obtained in the nonaffected area being 15 ± 6.6 mg/L against the permissible level

of 0.003 mg/L by World Health Organization, Guidelines for Drinking Water Quality (2004, 2006, 2011a, b). The results for Dareta village as shown in Fig. 3 revealed that the wells had all MCC concentration values being above the limit set by the World Health Organization, Guidelines for Drinking Water Quality (2004, 2006, 2011a, b). The value for Pb had a mean value of 257 ± 12.9 mg/L with the maximum value of 445 ± 14.6 mg/L being obtained in the off-washing point (YW3), while the lowest value of Pb (148 ± 10.6 mg/L) was obtained in the washing point (YW1). Cd had an average value of 16 ± 7.1 mg/L with the maximum value of 23 ± 9.2 mg/L being obtained in the offwashing point (YW3). In the case of the Bagega river (ZR1) which is used extensively by the miners, the Pb value was the highest (860 ± 16.8 mg/L) as shown in Fig. 3. This river (ZR1) is the only source of drinking water or for household work and is largely used for the “illegal” gold mining. The anomalously high value of Pb in this water sample (river water washing point) could be linked with the sedimentation of the washed gangues from the mine ore zone (Colin et al. 2010; Mohsen et al. 2011, Olatunde and Osibanjo 2012). The Cd concentration in this river also showed high value of 17 ± 4.6 mg/L far greater than the recommended values as shown in Fig. 3. As regards to other part of Nigeria, it was observed that the concentration of Pb obtained by Njar et al, (2012) was 0.01 mg/L in some boreholes in Calabar, South Local Government Area, Cross river State, Nigeria.

Estimated Daily Intake of MCC The World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR) recommend a tolerable daily intake of 3.57 × 1­ 0−3, 1.00 × 1­ 0−2, and 0.15 mg/kg/day of Pb, Cd, and Cr, respectively, in water intake in order to reduce the risk of contracting cancer (USEPA 2011a). The

1000 800

MCC (Cd)

MCC (Pb)

MCC (Cr)

600 400 200 0 XW1 -200

XW2

XW3

XB1

XB2

XB3

YW1

YW2

YW3

ZR1

WHO

Water sampling points

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R. L. Njinga, V. M. Tshivhase

computed EDI values in the three water-source types from the three villages are shown in Fig. 4. Pb contribution to the three MCC intakes from the watersource types was far greater than the TDI for both categories of consumers (adult and Children). Chronic exposure to Pb, even to small amounts, can be hazardous to children especially under 5 years of age because they absorb lead more rapidly than adults (Landrigan et al. 2002). As shown in Fig. 4, the exposure was thousandfold greater than the TDI in all the water-source types from the three villages. The EDIs for adult and children were far greater than the TDI for ZR1. The ZR1 is the river in Bagega where the mining materials are washed and is used widely in drinking and household activities since it is the only source for the community. This explains the high number deaths of > 400 children recorded in this village from 2010 through 2013 (Tirima et al. 2016).

Comparing EDI with RsD Once the EDI has been calculated for the MCC (Cd, Pb, and Cr), it is then compared to the RsD depending on whether it is a non-carcinogen or a carcinogen. The computed RsD for Pd, Cd, and Cr were 1.18 × ­10−4, 1.59 × ­10−7, and 2.00 × ­10−6, respectively (USEPA 2010). As a general rule, if the RsD is exceeded, exposure to the MCC is a potential health concern. As observed in Fig. 4, the EDI were far greater than the RsD for the three MCC. In some cases, exposures below the RsD could be a health concern because of the interactions between the MCC or because certain individuals in the exposed population are more sensitive. Therefore, it should be recognized that the RsD are estimates of exposures at which adverse health effects are not expected to occur for the majority of the population. They do not describe a level at which we are

Incremental Lifetime Cancer Risk As shown in Table 4, the incremental lifetime cancer risks (ILCRs) were computed to be 1.59 × ­1 0 3 (highest) due to Cd in YW3 for children and the lowest in XW1 with a value of 1.64 × ­100 for adults. The YW3 is a well far from the washing point, while XW1 is a well around the problem area where mining activity is intensive. The highest value obtained in a well YW3 far from the mining site could be due to the type of activities around the well. The mineworkers crush rocks in a flour grinder around the well, and the dust which is highly toxic with the MCC comes to be settled in the well which is always open as shown in Fig. 5. These risk values indicate that the three waters consumption from the three villages would result in an excess of above 1­ 03 cancer cases for children in Dareta (YW3), Bagega (ZR1) and Sunke (XW2, XB1) due to Cd while consumption of water from all three villages would result into an excess of above 1­ 02 cancer cases for both adults and children due to Cd and Cr. The USEPA considers excess cancer risks above 1 in 10,000 (1 × 10−4) to be sufficiently large that some sort of remediation is desirable. An ILCR greater than one in ten thousand (ILCR > 10 −4) is benchmark for gathering additional information whereas 1/1000 or greater (ILCR > 10−3) is moderate increased risk and should be given high priority as a public health concern (Li and Zhang 2010). The results of this work as shown in Table 4 are far greater than the benchmark.

9.00E+03

Esmated daily intake of MCC

Fig. 4  Estimated daily intake (EDI) of MCCs for the population of the three villages through consumption of the water-source types (mg/kg/day)

absolutely certain that no risk to health will occur for every individual. However, in this study, a serious health concern is required.

8.00E+03 7.00E+03 6.00E+03 5.00E+03 4.00E+03 3.00E+03 2.00E+03 1.00E+03 0.00E+00 XW1

XW2

XW3

XB1

XB2

XB3

YW1

YW2

YW3

ZR1

Water types Pb

13

Pb

Cd

Cd

Cr

Cr

Major Chemical Carcinogens in Drinking Water Sources: Health Implications Due to Illegal Gold… Table 4  Incremental lifetime cancer risks for the adult and children population

Sample ID

XW1 XW2 XW3 XB1 XB2 XB3 YW1 YW2 YW3 ZR1

Pb

Cd

Cr

Adult

Children

Adult

Children

Adult

Children

1.64E+00 1.16E+01 2.55E+01 2.32E+01 4.29E+01 2.63E+01 1.16E+01 1.39E+01 3.48E+01 7.51E+01

1.96E+00 1.38E+01 3.05E+01 2.78E+01 5.13E+01 3.14E+01 1.38E+01 1.66E+01 4.16E+01 8.98E+01

6.96E+02 8.69E+02 6.38E+02 8.69E+02 7.53E+02 4.64E+02 6.38E+02 7.53E+02 1.33E+03 9.85E+02

8.32E+02 1.04E+03 7.62E+02 1.04E+03 9.01E+02 5.54E+02 7.62E+02 9.01E+02 1.59E+03 1.18E+03

1.15E+02 4.42E+02 1.84E+02 2.21E+02 1.84E+02 3.82E+02 1.75E+02 2.90E+02 1.75E+02 1.38E+01

1.38E+02 5.28E+02 2.20E+02 2.64E+02 2.20E+02 4.57E+02 2.09E+02 3.47E+02 2.09E+02 1.65E+01

Adult of 58.65 years of age; children of 5 years of age

Fig. 5  Example of how rocks are crushed in a flour grinder around the well

Non‑cancer Risk Non-cancer risk measured by target hazard quotients (THQ) was worked out for all the MCC in this study for both adults and children (Table 5). The THQ followed the decrescent order Pb > Cd > Cr in all the water-source types from all the three villages. Target hazard quotient Table 5  Target hazard quotients by MCC and sample types for adults and children

Sample ID

XW1 XW2 XW3 XB1 XB2 XB3 YW1 YW2 YW3 ZR1

was far greater than 1.0 in terms of MCC for both categories of consumers. The sequence was the same for both adults and children although the latter had THQ values of 1.2 times higher in all cases. Similar observations were reported by Sadovska (2012) as children are more susceptible to the impact of pollutants than adults. The non-cancer risks for each type of water sources were expressed as the cumulative chronic hazard index (CHI), which is the sum of the individual metal THQ. As shown in Fig. 6, the computed CHI values for adults and children were 2.83 × 1­ 06 and 2.35 × 1­ 06 for ZR1 followed by 1.65 × ­106 and 1.38 × ­106 for XB2. Like the THQ, a CHI > 1 represents a potential for adverse health outcomes. The contribution of individual MCC THQ values to the CHI was also evaluated be dominant contaminants that together contributed over 99.9% of the CHI through consumption of the water-source types. The potential health risk of Cr was minimal (0.1%) for both adults and children in comparison to Pb and Cd investigated, which is due to its high RfD (1.5 mg/kg/day). More attention should therefore be paid to Pb, Cd, and Cr pollution in the three villages.

Pb

Cd

Cr

Adult

Children

Adult

Children

Adult

Children

4.83E+04 3.40E+05 7.50E+05 6.83E+05 1.26E+06 7.73E+05 3.40E+05 4.09E+05 1.02E+06 2.21E+06

5.78E+04 4.07E+05 8.97E+05 8.17E+05 1.51E+06 9.24E+05 4.07E+05 4.90E+05 1.22E+06 2.64E+06

1.10E+05 1.38E+05 1.01E+05 1.38E+05 1.20E+05 7.36E+04 1.01E+05 1.20E+05 2.12E+05 1.56E+05

1.32E+05 1.65E+05 1.21E+05 1.65E+05 1.43E+05 8.80E+04 1.21E+05 1.43E+05 2.53E+05 1.87E+05

1.53E+02 5.89E+02 2.45E+02 2.94E+02 2.45E+02 5.09E+02 2.33E+02 3.86E+02 2.33E+02 1.84E+01

1.83E+02 7.04E+02 2.93E+02 3.52E+02 2.93E+02 6.09E+02 2.79E+02 4.62E+02 2.79E+02 2.20E+01

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R. L. Njinga, V. M. Tshivhase

Fig. 6  Chronic hazard index by MCC and three water-source types for adults and children

3.00E+06

Chronic hazard index

2.50E+06 2.00E+06 1.50E+06 1.00E+06 5.00E+05 0.00E+00 XW1

XW2

XW3

XB1

XB2

XB3

YW1

YW2

YW3

ZR1

Water types CHI (Adult)

CHI (Children)

Conclusion

References

This study aimed at quantifying the levels of MCC in three water-source types (well, borehole, and river) from Sunke, Dareta, and Bagega where illegal gold mining activities are carried out in Zamfara State, Nigeria; estimating daily MCC intake; and determining the cancer and non-cancer risks associated with the MCC exposure. The levels of the MCC (Cr, Pb, and Cd) were far greater than acceptable limits according to World Health Organization—Guidelines for Drinking Water Quality (2004, 2006, 2011a, b). The estimated daily intakes (EDIs) for Pb, Cd, and Cr from the three water-source types were far greater than the tolerable daily intake for this metal in both children and adults. The probabilities of an individual developing cancer over a lifetime as a result of exposure to MCC through consumption of the water-source types were higher than acceptable risk levels (ILCR > 10 −4). Values of THQ for the individual metals showed potential health risk for humans due to the intake of MCCs in the water-source types, and children were more susceptible for health risks compared to adults. In addition, hazard indices due to the combined non-cancer effects of MCC in this study were far > 1. Target hazard quotients (THQs) for children were higher than those for adults .

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Acknowledgements  We are grateful to the Centre for Energy Research and Training (CERT), ABU, Zaria, for their support and provision of their ancillary facilities used in the analytical part of this work. We are also grateful to the personnel of the CERT for the technical assistance received from them.

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