This study investigates groundwater contamination by arsenic and iron and its health implications within the Sylhet district in Bangladesh. Utilizing geographic information system (GIS) and inverse distance weighting (IDW) methods, hazard maps have been developed to evaluate contamination risk across various upazilas. The findings show significant arsenic and iron pollution, particularly in the northwestern part of the district. In about 50% of the area, especially in Jaintiapur, Zakiganj, Companiganj, and Kanaighat where arsenic levels surpass 0.05 mg/L which is the standard limit of Bangladesh. Iron levels peak at 13.83 mg/L, severely impacting 45% of the region, especially in Gowainghat, northeastern Jaintiapur, Zakigonj, and Golabganj. The study employs USEPA health risk assessment methods to calculate the hazard quotient (HQ) and hazard index (HI) for both elements via oral and dermal exposure. Results indicate that children face greater noncarcinogenic and carcinogenic risks than adults, with oral HI showing significant risk in Balagonj and Bishwanath. Dermal adsorption pathways exhibit comparatively lower risks. Cancer risk assessments demonstrate high carcinogenic risks from oral arsenic intake in all areas. This comprehensive analysis highlights the urgent need for effective groundwater management and policy interventions in the Sylhet district to mitigate these health risks and ensure safe drinking water.

  • Arsenic levels exceed 0.05 mg/L in 50% of Sylhet, posing severe health risks.

  • 45% of the area suffers from iron contamination (1.01–13.83 mg/L).

  • Children in Balagonj and Bishwanath upazilas are exposed to high health risks.

  • Carcinogenic risks from arsenic are high, especially orally.

  • Combined arsenic and iron levels in some areas are 2.74–4.75 mg/L, indicating severe contamination.

Only 0.1% of the total water on our planet is pure drinking water (De Filippis et al. 2020). Most developing countries rely on groundwater as their principal supply of potable water, as well as water for agriculture and industry (Kadam et al. 2022). Despite meeting more than half of the world's drinking water requirement, rising population, growing urbanization, and mass industrialization have put a strain on groundwater resources (Amiri et al. 2021; Shukla & Saxena 2021). Additionally, depletion and deterioration of the available surface water supplies are also other contributing factors to increasing pressure on the groundwater (Singh et al. 2019). The chemical components of groundwater, which are primarily influenced by the underlying geological structures and activities caused by humans such as urbanization, wastewater discharges, and mining operations in the surrounding areas, determine its quality in most cases. Over the last few decades, growing anthropogenic interference has disrupted the chemical balance and resulted in a depletion of both the quality and quantity of groundwater (Devic et al. 2014; Selvakumar et al. 2017; Wang et al. 2020). In addition, the weathering and erosion of rocks, industrial discharges, agricultural practices, seepage of contaminated water, and the use of geothermal waters all contribute to the contamination of groundwater (Bodrud-Doza et al. 2020). When heavy metals are added to polluted groundwater, the contamination levels rise to even higher levels (Alsubih et al. 2021).

Heavy metals refer to both essential and non-essential trace metals, each of which can pose a risk to living things in varying degrees based on their properties, physical appearance, and concentration levels. These metals have a significant combined effect on the global water supplies (Marcovecchio et al. 2007). Because of their growing abundance in groundwater and risk to human health, arsenic and iron are among the most thoroughly investigated heavy metals by numerous experts worldwide, i.e., India (Ravindra & Mor 2019; Alsubih et al. 2021; Khan & Rai 2022; Sharma et al. 2022), China (Wu et al. 2009; Li et al. 2015; Liu & Ma 2020; Jiang et al. 2022), Thailand (Wongsasuluk et al. 2014), Italy (Sappa et al. 2014), Ghana (Asare-Donkor et al. 2016), and South Africa (Masok et al. 2017).

The presence of these metals in groundwater in colloidal, particle, or diluted phase forms, as well as their deposition in plants and animals, classifies them as components of the human food chain (Wcisło et al. 2002; Wongsasuluk et al. 2014). As far as groundwater contamination is concerned, Bangladesh has been facing a threat to arsenic and iron contamination. The Department of Public Health Engineering (DPHE) and the British Geological Survey (BGS) undertook a nationwide hydro-chemical survey and discovered that numerous drinking wells in Bangladesh exceeded arsenic and iron limits (Tonmoy et al. 2009).

The allowable concentration of arsenic for drinking water indicated by World Health Organization (WHO) is 0.01mg/L, while 0.05 mg/L is the standard limit in Bangladesh. Research has shown that 8.4% of tube wells in the country contain more than 0.3 mg/L arsenic (Smith et al. 2000; Hasan Shahriar & Jim 2019). According to the Bangladesh's Department of Environment (DoE), the acceptable limit for iron is 0.3–1 mg/L (Tonmoy et al. 2009; Hasan et al. 2019). Multiple researchers assessed the elevated arsenic and iron concentrations in Gopalgoanj (Rahman et al. 2018), Rangpur (Towfiqul Islam et al. 2017), Chapai-Nawabganj (Islam et al. 2017a), Patuakhali (Biswas et al. 2014) district and Central West part (Bodrud-Doza et al. 2019) of Bangladesh. These two elements are also found high in Sylhet district where groundwater is used for both drinking and residential purposes (Chowdhury et al. 2017; Ahmed et al. 2019a, 2019b; Begum et al. 2019). In 2020, Bodrud-Doza et al. identified a higher Fe concentration in Dhaka and demonstrated that the quality of subsurface water is influenced by anthropogenic activities, rock–water interaction, and ion exchange (Bodrud-Doza et al. 2020). Surma river basin in the Sylhet region witnesses a significant concentration of iron during the monsoon (Alam et al. 2007). A hydrogeochemical analysis done by Ahmed et al. revealed that silicate weathering, defined by an active cation exchange mechanism, and carbonate weathering increase element concentrations in the groundwater of Sylhet (Ahmed et al. 2019a, 2019b).

In addition to other factors, human activities have the greatest impact on the groundwater quality in this region (Islam et al. 2017a, 2017b; Ahmed et al. 2019a, 2019b). When this groundwater is used domestically, it can endanger people by exposing them to oral and dermal exposure pathways (Sappa et al. 2014; Khan & Rai 2022; Sharma et al. 2022). While many research studies have been done on the water quality of the drinking water along with its impurities and their effect on human consumptions, no thorough study of an overall hazard map of these metals and their risk for both oral and dermal ingestion has been carried out.

This research aims to find the arsenic and iron-contaminated aquifers in the Sylhet district through the development of a hazard map using geographic information system (GIS) and the IDW interpolation method. GIS serves as a powerful tool for managing and interpreting geographical information about water resources, offering efficient means to analyze pollution patterns and relationships (Selvam Manimaran & Sivasubramanian 2013). The resultant hazard map is critical for assessing groundwater contamination, which is vital for safe drinking water and agricultural use, as well as for mitigating serious environmental health issues. In addition, this study conducts a thorough risk evaluation of human health among the residents of Sylhet, including both adults and children. This assessment focuses on the noncarcinogenic hazard and cancer risk (CR) associated with the presence of arsenic and iron in groundwater. By doing so, it aims to provide a comprehensive understanding of the potential health impacts of these heavy metals in the region. This approach combines spatial analysis with health risk assessment, intending to offer a holistic view of the environmental challenges faced by the community in Sylhet, thereby guiding effective management and remediation strategies.

Study area

This study was conducted in Sylhet district, located in the northeastern edge of Bangladesh, between latitudes 24°35′ to 25°11′ N and longitudes 91°38′ to 92°29′ E, covering an area of 3,452.07 km2 (Chowdhury et al. 2017). The region, characterized by a subtropical monsoon climate with hot, wet summers and cooler winters (Akter et al. 2019), includes all upazilas (sub-districts) of Sylhet. Figure 1 illustrates the study area with sampling points.
Figure 1

Study area and sampling locations with both primary and secondary data.

Figure 1

Study area and sampling locations with both primary and secondary data.

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Data collection and laboratory analysis

Groundwater samples were collected from 12 upazilas in Sylhet from November 2018 to November 2019, in winter and summer to avoid monsoon dilution. Samples were randomly chosen across different administrative units, with primary data from five samples in each upazila and secondary data from DPHE. The sampling sites were geographically pinpointed using GPS, and the water was collected from deep tube wells, ranging in depth from 150 to 240 m. Samples of 500 mL were taken in pre-washed high-density polyethylene bottles and cleaned with HCl and NaOH. To ensure purity, the samples were filtered through the Whatman 42 filter paper. Acidification to pH <2 using 65% HNO3 was done to prevent precipitation and adsorption and were stored below 4 °C.

As and Fe levels were measured using a UV-spectrophotometer (DR 6000). For arsenic, a 35 mL sample was treated with hydrochloric acid, potassium iodide, and stannous chloride, reducing arsenic to its trivalent state. Lead acetate-treated glass wool was used in the scrubber, and the sample was treated with silver diethyldithiocarbamate (SDDC) solution and Zn dust. The resultant red complex indicated AsH3 presence, measured at 520/535 nm. For iron, 100 mL of the sample was mixed with HCl and potassium thiocyanide, and the absorbance was measured to determine concentration.

IDW interpolation method

Hazard maps for As and Fe were created using inverse distance weighted (IDW) interpolation in ArcMap (Version 10.5). This non-geostatistical tool averages values from neighboring areas, weighted by distance. The IDW power coefficient, a key accuracy factor, determines the influence of adjacent points (Li & Heap 2008). Equation (1) represents the IDW calculation. Other techniques like kriging were considered based on sample distribution and phenomena studied:
formula
(1)

Hazard map generation

Hazard maps were created using IDW interpolation. The Universal Transverse Mercator (UTM) projection system within zone 46 N-Datum Geodetic System (WGS) 1984 was used for spatial distribution maps, categorized into five classes (Mosaferi et al. 2014). A combined hazard map was created using an additive weight approach, assigning weights of 0.7 and 0.3 to iron and arsenic, respectively, based on Analytic Hierarchy Process (AHP) analysis considering their frequency, concentration, and impact (Do 2013).

Human health risk assessment

The health risk associated with such elevated levels of iron is a consequence of natural and human-induced factors, with ferric oxides and hydroxides being the primary natural contributors, while human impact stems from urban wastewater discharge and runoff from agricultural lands. It is suggested that geochemical interactions, particularly silicate and carbonate weathering through ion exchange, play a significant role in the escalation of iron content in the groundwater. The evaluation of health risks for each heavy metal is typically divided into carcinogenic and noncarcinogenic. There are two key toxicity variables to take into consideration when determining risk: cancer slope factor (CSF) for characterizing CR, and reference dose (RfD) for non-carcinogen risk (Wongsasuluk et al. 2014). For measuring the CR from carcinogenic pollutants, the carcinogenic approach is solely used, whereas for the noncarcinogenic risk effects, the hazard quotient (HQ) is used (Masok et al. 2017).

Exposure assessment

Trace metal-contaminated water can enter the body by inhalation, oral consumption, and skin absorption (Wu et al. 2010). However, ingestion and dermal absorption are the two most common water exposure methods. This study used USEPA guidelines for superfund health risk assessment to calculate the hazards of adults and children being exposed to contaminants in groundwater (Edokpayi et al. 2018; Li et al. 2018). The chronic daily intake (CDI) of pollutants by oral ingestion and skin absorption was determined using Equations (2)–(4) developed by the USEPA to quantify the ingestion and dermal absorption of pollutants in a human body via water consumption (USEPA 2004; Agyeman et al. 2021):
formula
(2)
formula
(3)
formula
(4)
where CDIing and CDIderm are the chronic daily intake (mg/kg-day) via ingestion as well as dermal.

The CDI, HQ, and hazard index (HI) are calculated in the current study using USEPA standards to measure the ingestion and dermal rate of pollutants. Tables 1 and 2 refer to the standard values and references used for the calculation of the metrics for human health.

Table 1

List of variables applied in the evaluation of human health risk

ParametersAbbreviationsGroup value
Unit
AdultChildren
Water ingestion rate IR 2.5 0.78 L/day 
Exposure frequency (oral) EF 365 365 Day/year 
Exposure frequency (dermal) EF 350 350 Day/year 
Exposure duration (oral) ED 70 10 Year 
Exposure duration (dermal) ED 30 Year 
Average body weight BW 80 15 kg 
Exposed skin area SA 19,652 6,365 cm2/day 
Exposure time ET 0.71 0.54 h/day 
Unit conversion factor CF 0.001 0.001 L/cm3 
Average time (oral) AT 25,550 (ED × EF) 3,650 (EF × ED) Day 
Average timing (dermal) AT ED × 365 = 10,950 6 × 365 = 2,190 Day 
ParametersAbbreviationsGroup value
Unit
AdultChildren
Water ingestion rate IR 2.5 0.78 L/day 
Exposure frequency (oral) EF 365 365 Day/year 
Exposure frequency (dermal) EF 350 350 Day/year 
Exposure duration (oral) ED 70 10 Year 
Exposure duration (dermal) ED 30 Year 
Average body weight BW 80 15 kg 
Exposed skin area SA 19,652 6,365 cm2/day 
Exposure time ET 0.71 0.54 h/day 
Unit conversion factor CF 0.001 0.001 L/cm3 
Average time (oral) AT 25,550 (ED × EF) 3,650 (EF × ED) Day 
Average timing (dermal) AT ED × 365 = 10,950 6 × 365 = 2,190 Day 
Table 2

Permeability coefficient (PC), reference dose (RfD), and slope factor (SF) for arsenic and iron

ElementAsFe
PC (cm/h11 × 10−3 1 × 10−3 
RfD(ing) (mg/kg/day) 3 × 10−4 3 × 10−1 
RfD(derm) (mg/kg/day) 1.23 × 10−4 1.40 × 10−1 
SFing (mg/kg/day)−1 1.50 n/a 
ElementAsFe
PC (cm/h11 × 10−3 1 × 10−3 
RfD(ing) (mg/kg/day) 3 × 10−4 3 × 10−1 
RfD(derm) (mg/kg/day) 1.23 × 10−4 1.40 × 10−1 
SFing (mg/kg/day)−1 1.50 n/a 

Noncarcinogenic risk assessment

The HQ was obtained by comparing the estimated pollutant intakes with the reference dose (RfD) using Equation (5) to evaluate possible noncarcinogenic effects induced by heavy metals (Khan et al. 2022):
formula
(5)
where RfDing/derm is the reference dose for ingestion/dermal toxicity (mg/kg/day). RfDing and RfDderm were acquired from Wu et al. (2009), and Masok et al. (2017). When HQ < 1, it is considered safe and acceptable (Alidadi et al. 2019), however when it exceeds one, there may be a substantial potential health hazard associated with human overexposure to pollutants (Wu et al. 2009; Masok et al. 2017; Ahmed et al. 2019a, 2019b).
HI is defined as the sum of all the HQ from various routes of exposure, such as oral, and dermal (Ravindra & Mor 2019). To estimate the overall noncarcinogenic effects that could be caused by more than one metal, the HQs for each metal were calculated and added together to obtain the HI using the following equation:
formula
(6)
where HIing/derm denotes the hazard index via ingestion or dermal contact (unitless) and HQing/derm denotes the hazard quotient via ingestion or dermal contact (unitless). If the value of HI > 1, the risk for harmful noncarcinogenic impacts on human health is considered unacceptable, but if HI < 1, it is acceptable or has little possibility of harmful health impacts (Wongsasuluk et al. 2014).

CR assessment

CRs are calculated as the incremental probability of an individual developing cancer because of exposure to the possible carcinogen throughout a lifetime. The slope factor (SF) is a toxicity parameter that describes the dose–response relationship quantitatively. The range for tolerable levels of CR as determined by the USEPA is 1 × 10−6 to 1 × 10−4 and considered unacceptable if the value of risks exceeds 1 × 10−4 (Hadzi et al. 2015; Saha et al. 2017; Alidadi et al. 2019). Equation (7) determines the CR due to ingestion in situations when chemical intakes may be high. Also, CDIing has been chosen according to USEPA guidelines and the SF value has been chosen from Table 2:
formula
(7)
where CRing is the cancer risk through ingestion pathway; CDI is the chronic daily intake averaged over 70 years (mg/kg-day); SF is the slope factor.

Hazard map of arsenic

Arsenic concentrations in the study area are categorized into five classes according to safety thresholds, as detailed in Table 3. The ‘Excellent’ category aligns with the WHO's recommended limit of 0.01 mg/L, while the ‘No risk’ category corresponds to the Bangladesh National Standard (<0.05 mg/L) (WHO 2008; Department of Environment 2023). The two categories encompass a combined area of 1,762 km2, or 51% of the study region. The remaining areas are classified into medium, high, or extremely high-risk zones, which constitute 29, 17, and 3% of the study area, respectively.

Table 3

Range of arsenic concentration and covered area for each range

ItemArsenic concentration interpolated map
Range of concentration (ppm) 0–0.01 0.02–0.05 0.06–0.07 0.08–0.09 0.1–0.15 
Reclassified range Excellent No risk Medium risk High risk Very high risk 
Area (km21,041 721 988 578 92 
Percentage (%) of area 30 21 29 17 
ItemArsenic concentration interpolated map
Range of concentration (ppm) 0–0.01 0.02–0.05 0.06–0.07 0.08–0.09 0.1–0.15 
Reclassified range Excellent No risk Medium risk High risk Very high risk 
Area (km21,041 721 988 578 92 
Percentage (%) of area 30 21 29 17 

Figure 2 reveals the spatial variations in groundwater arsenic content across 12 regions of Sylhet. It indicates that Jaintiapur, Zakiganj, Companiganj, Gowainghat, and Kanaighat exhibit arsenic levels ranging from 0.1 to 0.15 mg/L, signifying a substantial risk. Additionally, the northwestern and northeastern regions display arsenic levels between 0.06 and 0.09 mg/L. In contrast, central Sylhet's arsenic levels are within the safe range of 0–0.05 mg/L.
Figure 2

Hazard map for arsenic (As) within the study area.

Figure 2

Hazard map for arsenic (As) within the study area.

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Hazard map for iron

Groundwater iron concentrations have been classified into five risk categories according to established safety thresholds, as shown in Table 4. Approximately 53% of the area falls within the safe zone, with iron concentrations ranging from 0.2 to 1.0 mg/L, considered excellent to no risk. However, the remaining 47% are categorized from medium to high risk.

Table 4

Range of iron concentration and covered area for each range

ItemIron concentration interpolated map
Range of concentration (ppm) 0.20–0.30 0.31–1.0 1.01–5.17 5.18–9.67 9.68–13.83 
Reclassified range Excellent No risk Medium risk High risk Very high risk 
Area in km2 838 1,016 908 520 137 
Percentage (%) of area 24 29 26 15 
ItemIron concentration interpolated map
Range of concentration (ppm) 0.20–0.30 0.31–1.0 1.01–5.17 5.18–9.67 9.68–13.83 
Reclassified range Excellent No risk Medium risk High risk Very high risk 
Area in km2 838 1,016 908 520 137 
Percentage (%) of area 24 29 26 15 

The spatial visualization of the varying concentration is presented in the iron hazard map in Figure 3. The figure illustrates areas like Gowainghat, Zakigonj, and parts of Golabganj and Jaintapur, where concentrations soar to 9.68–13.83 mg/L, exceeding both Bangladesh and WHO guidelines. Sylhet Sadar, Fenchuganj, southwestern parts of Golabganj, and the northeastern part of Balaganj and Kanaighat are safe from iron contamination since in these areas the concentration of iron is between 0.20 and 0.30 mg/L. The elevated Fe concentrations in the study area might be attributed to high loads of urban wastewater and agricultural runoff. The research area is located inside the notable Sylhet Limestone Formation, which is one of the Bangladesh's richest mineral deposit locations (Ahmed et al. 2019a, 2019b).
Figure 3

Hazard map for iron (Fe) within the study area.

Figure 3

Hazard map for iron (Fe) within the study area.

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Combined hazard map of arsenic and iron

The composite map in Figure 4 suggests that the northwest part of the Sylhet district is heavily contaminated with arsenic and iron, while the southwest remains comparatively less affected. The primary hotspots for these metals include the majority of Gowainghat Upazila, the southeastern part of Companiganj, the northwestern section of Jaintiapur, and the eastern region of Zakiganj. Furthermore, most of the areas in Companiganj, Gowainghat, and Jaintiapur, along with the southwestern parts of Kanaighat, the northern regions of Golabganj, Beanibazar, and Zakiganj, exhibit total concentrations of both arsenic and iron ranging from 2.74 to 4.75 mg/L. Conversely, Sylhet Sadar, Fenchuganj, the northeastern section of Kanaighat and Balaganj Upazila, and the western part of Dakshin Surma are considered safe, with lower combined concentrations (0.14–1.83 mg/L) of arsenic and iron. The northeastern part of Companiganj, southwestern Kanaighat, and certain sections of Beanibazar, Dakshin Surma, Balaganj, and Bishwanath fall within the medium to high-risk zone, spanning a total of 1,438 km2.
Figure 4

Composite hazard map for arsenic (As) and iron (Fe) concentrations.

Figure 4

Composite hazard map for arsenic (As) and iron (Fe) concentrations.

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The very high-risk zone, which includes Gowainghat Upazila, the southeastern part of Companiganj, and the eastern part of Zakiganj, occupies an area of approximately 140 km2, accounting for about 4% of the total district. On the other hand, the groundwater in Sylhet Sadar and Fenchuganj, which covers an area of 831 km2, is deemed perfectly safe for consumption. The threshold used to define the categories in the composite map has been shown in Table 5.

Table 5

Range of combined spatial distribution map and covered area for each range

ItemCombined concentration interpolated map
Range of concentration (ppm) 0.14–1.83 1.84–2.73 2.74–3.62 3.63–4.75 4.76–9.69 
Reclassified range Excellent No risk Medium High Very high 
Area in km2 831 1,010 916 522 140 
Percentage (%) of area 24 29 27 15 
ItemCombined concentration interpolated map
Range of concentration (ppm) 0.14–1.83 1.84–2.73 2.74–3.62 3.63–4.75 4.76–9.69 
Reclassified range Excellent No risk Medium High Very high 
Area in km2 831 1,010 916 522 140 
Percentage (%) of area 24 29 27 15 

Calculation of CDI of arsenic and iron

The potential health risks from consuming and encountering these elements through the skin have been carefully evaluated using CDI metrics (see Supplementary Tables A1 and A2). Figures 5 and 6 illustrate the comparative analysis for the exposure of arsenic and iron ingestion across adult and child demographics, respectively. The data reveal that all the upazila show a higher CDI value except Dakkhin Surma, Fenchugonj, and Sylhet Sadar upazilas for both adults and children. These high values indicate potential health risks linked to groundwater contamination. For children, even with a lower water ingestion rate, the CDI value is higher compared to the adults. This higher CDI reflects the greater impact of the same level of a substance on a smaller body. It underscores the importance of ensuring lower levels of exposure of these heavy metals to the children as they are more vulnerable to the effects of toxins due to their smaller size and developing bodies.
Figure 5

Comparative analysis of arsenic intake across adult and child demographics.

Figure 5

Comparative analysis of arsenic intake across adult and child demographics.

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Figure 6

Comparative analysis of iron intake across adult and child demographics.

Figure 6

Comparative analysis of iron intake across adult and child demographics.

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Noncarcinogenic risk assessment

The estimated HQ values for ingestion of As and Fe polluted drinking water for oral and cutaneous absorption pathways of exposure are shown in Table 6. The noncarcinogenic risk assessment reveals that arsenic poses a greater risk than iron through oral consumption, particularly for children. The HQ values for arsenic are notably higher than those for iron, showing a more significant health concern. This disparity is further emphasized by the finding that certain regions show extremely high HQ values for arsenic, due to increased groundwater contamination from urbanization and agricultural activities.

Table 6

Hazard quotient of arsenic and iron through oral and dermal pathways for adult and child

LocationsAs (Adult)
As (Child)
Fe (Adult)
Fe (Child)
HQ(ing)HQ(derm)HQ(ing)HQ(derm)HQ(ing)HQ(derm)HQ(ing)HQ(derm)
Balagonj 5.508 0.072 9.166 0.095 0.346 0.004 0.056 0.005 
Beanibazar 3.020 0.039 5.026 0.052 0.483 0.006 0.080 0.007 
Bishwanath 5.347 0.070 8.897 0.092 0.375 0.004 0.062 0.006 
Companiganj 3.281 0.043 5.460 0.056 0.690 0.008 0.114 0.001 
Dakkin Surma 0.886 0.012 1.477 0.015 0.345 0.004 0.057 0.005 
Fenchugonj 1.122 0.015 1.868 0.019 0.179 0.002 0.029 0.003 
Guwainghat 4.104 0.054 6.829 0.070 0.605 0.007 0.100 0.009 
Gulapgonj 1.945 0.025 3.237 0.033 0.488 0.006 0.081 0.007 
Jaintapur 3.967 0.052 6.601 0.068 0.506 0.006 0.084 0.008 
Kanaighat 3.825 0.050 6.364 0.066 0.303 0.003 0.050 0.000 
Sadar 2.125 0.028 3.536 0.036 0.206 0.000 0.034 0.003 
Zakigonj 3.667 0.048 6.101 0.063 0.493 0.006 0.082 0.007 
LocationsAs (Adult)
As (Child)
Fe (Adult)
Fe (Child)
HQ(ing)HQ(derm)HQ(ing)HQ(derm)HQ(ing)HQ(derm)HQ(ing)HQ(derm)
Balagonj 5.508 0.072 9.166 0.095 0.346 0.004 0.056 0.005 
Beanibazar 3.020 0.039 5.026 0.052 0.483 0.006 0.080 0.007 
Bishwanath 5.347 0.070 8.897 0.092 0.375 0.004 0.062 0.006 
Companiganj 3.281 0.043 5.460 0.056 0.690 0.008 0.114 0.001 
Dakkin Surma 0.886 0.012 1.477 0.015 0.345 0.004 0.057 0.005 
Fenchugonj 1.122 0.015 1.868 0.019 0.179 0.002 0.029 0.003 
Guwainghat 4.104 0.054 6.829 0.070 0.605 0.007 0.100 0.009 
Gulapgonj 1.945 0.025 3.237 0.033 0.488 0.006 0.081 0.007 
Jaintapur 3.967 0.052 6.601 0.068 0.506 0.006 0.084 0.008 
Kanaighat 3.825 0.050 6.364 0.066 0.303 0.003 0.050 0.000 
Sadar 2.125 0.028 3.536 0.036 0.206 0.000 0.034 0.003 
Zakigonj 3.667 0.048 6.101 0.063 0.493 0.006 0.082 0.007 

The total HI values, illustrated in Figure 7, suggest a more pronounced sensitivity in children to arsenic in drinking water. Notably, the majority of the regions show HI values exceeding the threshold of one, indicating serious health implications. However, from Figure 8, the dermal exposure to these metals appears to pose minimal risk, with HI values remaining below 1 across all regions.
Figure 7

Hazard index through oral intake for arsenic.

Figure 7

Hazard index through oral intake for arsenic.

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Figure 8

Hazard index due to dermal intake for arsenic.

Figure 8

Hazard index due to dermal intake for arsenic.

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Iron is crucial for public health, serving vital roles in oxygen transport, DNA synthesis, and electron transport, yet its bioavailability is often limited due to its tendency to form insoluble oxides (Abbaspour et al. 2014). This poses a significant nutritional challenge, particularly affecting children, adolescents, and women of reproductive age, leading to potential impacts on cognitive development, immune function, and pregnancy outcomes (Abbaspour et al. 2014). The fraction of iron absorbed from the amount ingested is typically low but may range from 5 to 35% depending on circumstances and the type of iron (McDowell 1992). Iron absorption occurs by the enterocytes by divalent metal transporter 1, a member of the solute carrier group of membrane transport proteins which takes place predominantly in the duodenum and upper jejunum (Muir & Hopfer 1985). Generally, drinking water is not considered a significant source of iron compared to other dietary sources as the permissible iron content in water according to the WHO guidelines is very low (<0.3 mg/L). Also, the water with more than the permissible amount of iron can cause distaste, staining, and other esthetic problems. Considering that an adult might drink about 2 L of water per day, the contribution of iron from water would typically be much less than 1 mg/day, making it a small fraction of the overall daily requirement. The dietary needs for iron vary among individuals, especially between adults and children, and between males and females. The average adult stores about 1–3 g of iron in his or her body (Abbaspour et al. 2014). About 1 mg of iron is lost each day through the sloughing of cells from skin and mucosal surfaces, including the lining of the gastrointestinal tract (Abbaspour et al. 2014). Menstruation increases the average daily iron loss to about 2 mg/day in premenopausal female adults (Abbaspour et al. 2014).

Figures 9 and 10 illustrate that the total HI for iron, derived from both oral and dermal exposure, remains below 1 across all regions for both adults and children. This suggests that iron is not a significant risk factor for causing adverse health effects. The bar graphs reveal a similar pattern of sensitivity to dermal exposure to iron in contaminated water. However, adults exhibit greater sensitivity to oral exposure compared to children, possibly due to a higher volume of water consumption. Despite this, the noncarcinogenic effects of iron, including mild toxicity, astringency, and bitterness render the water sources unsuitable for consumption (Alsubih et al. 2021).
Figure 9

Hazard index through oral intake for iron.

Figure 9

Hazard index through oral intake for iron.

Close modal
Figure 10

Hazard index due to dermal intake for iron.

Figure 10

Hazard index due to dermal intake for iron.

Close modal

CR assessment

The CR assessment focuses primarily on arsenic due to its classification as a Category 1 carcinogen by the WHO. Our comprehensive analysis indicates that the cancer risks associated with arsenic in contaminated groundwater are alarmingly high, significantly surpassing the established safe threshold in certain areas. The study identifies Balaganj as the most vulnerable location with respect to arsenic-related cancer risks, while Fenchuganj and Dakkin Surma exhibit lower risks (as shown in Figure 11). This disparity highlights the geographical variability in arsenic contamination and its associated health impacts. Another striking aspect of our findings is the higher potential danger posed to children compared to adults. The CR values for children range from 4.11 × 10−3 to 6.64 × 10−4, substantially exceeding the adult range of 2.48 × 10−3 to 3.99 × 10−4.
Figure 11

Carcinogenic risk for adult and child.

Figure 11

Carcinogenic risk for adult and child.

Close modal

The comprehensive study conducted in the Sylhet district of Bangladesh provides an insightful analysis of groundwater contamination by arsenic and iron, highlighting critical areas of concern and their associated health risks, especially among adults and children. By constructing hazard maps for arsenic and iron contamination, the research identifies the most polluted regions – Gowainghat, Companyganj, Jaintiapur, the eastern part of Zakiganj, and the southern part of Balaganj – as exceeding both national and WHO guidelines for safe drinking water. Conversely, areas such as Golabganj, Dakkin Surma, and Fenchuganj are recommended for their low risk of arsenic contamination, with certain locations like Sylhet Sadar and Kanaighat Upazilla also being iron-free. The detailed risk analysis reveals the highest hazards in Balaganj and Bishwanath, based on HIoral values for adults and children, whereas the lowest risks are observed in Dakkin Surma and Fenchuganj, with dermal hazard indices suggesting minimal risk to residents.

Crucially, the study underscores the arsenic noncarcinogenic effects of both iron and arsenic as well as the carcinogenic potential of arsenic across the areas, emphasizing heightened vulnerability of the children. This alarming revelation demands urgent attention toward mitigating these risks through effective groundwater management and the development of public health policies that ensure the provision of safe drinking water, thereby aligning with the sustainable development goal (SDG) 6 aimed at securing clean water and sanitation for all. Furthermore, the spatial analysis not only delineates the zones of significant contamination but also serves as a vital tool for legislative authorities and policymakers in strategizing tube well placements and enacting legislation to combat groundwater pollution. The acknowledgement of arsenic and iron as prevalent contaminants sets a precedent for future research to explore other heavy metals present in the groundwater of Sylhet, aiming to devise comprehensive mitigation strategies against the adverse health effects posed by these pollutants.

In conclusion, this study effectively maps out the hazardous landscapes of arsenic and iron contamination within the Sylhet district, offering a foundational understanding of the health risks involved and proposing a pathway for enhancing water quality management and public health initiatives. By doing so, it not only contributes to the immediate need for safe drinking water but also emboldens the broader objective of sustaining environmental health and well-being, encapsulating a vital step forward in the global endeavor to mitigate water-related diseases and ensure environmental sustainability.

The authors thank the Department of Civil and Environmental Engineering at Shahjalal University of Science and Technology, Sylhet, DPHE and Sylhet City Corporation for their resources and support in data gathering and insights into groundwater issues. Special appreciation is extended to the participants and local communities in the Sylhet district for their cooperation during sample collection.

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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