Spatial trend and probabilistic health risk assessment of heavy metals, nitrate, and fluoride in groundwater resources, West Azerbaijan province, Iran

The quality of water resources used for drinking and their health effects is vitally important. The present study investigated the concentrations of F−, NO3−, and metal elements like Hg, Mn, As, and Pb in the groundwater resources and their health risk assessment on the west margin of Urmia Lake, Iran. Sampling points were selected and taken from 121 groundwater resources in the summer of 2014. Heavy metals (Pb, As, Mn, and Hg) were measured by ICP-OES (inductively coupled plasma optical emission spectrometer, model: Arcos, Germany), and some ions (Na+, NO3−, F−, and Cl−) by flame photometer and spectrophotometer according to the standard methods, respectively. The nitrate concentration range in groundwater samples measured from 1.7 to 137 mg/L and fluoride from 0.4 to 4.5 mg/L. The probabilistic method and Monte Carlo simulation were used to estimate carcinogenic and noncarcinogenic risks. The concentration of study elements in most samples was obtained in the WHO (World Health Organization) recommended range. The order of HM (heavy metal) concentration is based on the overall mean: Mn > As > Hg > Pb. The HI (hazard index ) level was found to be more than 1 for noncarcinogenic risk for As and NO3− and permissible risks for the other elements and fluoride. ELCR (excess lifetime cancer risk) levels of As were acceptable, except for some sampling points, the central region in the study area, near the seashore of Urmia Lake. Finally, it can be stated that the groundwater resources in the studied area are acceptable for drinking in most places. Still, due to the effects of As and NO3− contaminated water, the quality is unacceptable for drinking in some places. So, monitoring water quality is recommended by finding contamination sources to decrease the health risks of drinking consumption.


Introduction
Approximately one billion people in underdeveloping countries, particularly in rural societies, have limited access to treated and safe drinking water (WHO 2019).Therefore, people's public health as a standard of living can be at risk due to insufficient access to safe drinking water.Besides surface water, groundwater is an essential source for various consumption types, such as domestic cleaning and washing, drinking, and agricultural and industrial activities in all countries (Shakerkhatibi et al. 2019).
Currently, in many countries, such as South and Southeast Asian countries and the Middle East, groundwater is the primary water source for all consumption.Furthermore, reports state that nearly onethird of the population in the world uses groundwater for healthy consumption (Bacquart et al. 2015;Aghapour et al. 2016).Groundwater quality depends on natural or artificial parameters such as geological factors, urbanization, drought, population growth, and industrial and agricultural activities (Hajizadeh and Mohammadi 2017;Malakootian and Khashi 2014).Reducing the transmission of diseases and pathogenic agents through water is the advantage of using underground water instead of surface water (Katsanou and Karapanagioti 2019).
However, groundwater consumption for drinking has concerns due to exposure to possible contamination with toxic compounds, such as heavy metals, organic toxins, and disinfection byproducts (Mohammadi et al. 2022;Elehinafe et al. 2022).HMs are poisonous compounds that the US EPA (Environmental Protection Agency) and WHO continuously recommend controlling their permitted level in drinking water (Malakootian et al. 2016).HMs are the main factor for acute and chronic effects on water quality.Besides anthropogenic sources, these metals can naturally enter water sources through dissolution from the earth's crust, and long-term consumption of polluted water will adversely affect consumers' health.HMs cause reduced growth of organs, cancer, a disorder in the body's nervous system, a disorder in the body's defense system, and, in acute cases, it can bring the risk of death (Jafarzadeh et al. 2022;Khosravi et al. 2023).
Many studies reported the presence of HMs and toxic elements in water resources (Mohammadi et al. 2017;Marufi et al. 2022;Heydarirad et al. 2019).In the central area of Iran, significant values of As, Cr, Cd, Cu, Fe, Mn, Hg, Ni, Pb, and Zn were found in groundwater resources (Jafarzadeh et al. 2022;Shams et al. 2022).Human health risk assessment (HHRA) is a systematic method for defining the hazardous effects of exposure to hazardous chemicals (Ayejoto et al. 2022;Egbueri et al. 2023b).Human health risk evaluation (HHRE) is an advanced method in which the hazardous effects of pollutants, such as HMs in water, are evaluated for both intake and absorption (Ayejoto et al. 2022;Agbasi et al. 2023;Omeka and Egbueri 2023).In the center of Iran, lifetime cancer risks were reported as 1.09 × 10 −3 for the lead, 1.67 × 10 −1 , and 2 × 10 −1 for nickel in Ardakan, Meibod, and Bahabad city, respectively, which determined high carcinogenic risk (Fallahzadeh et al. 2017).In Pakistan, Ni, Pb, and Cd concentrations in the River Soan were higher than recommended for domestic water use or aquatic life (Nazeer et al. 2014).Kumar et al. investigated the values of As, Cd, Co, Cr, Cu, Mn, Ni, Zn, and Pb in drinking water in Bihar, India, in 2015. Groundwater (80%) samples exceeded the WHO guideline value (10 μg/L) of As, while Mn exceeded the WHO limit of 400 μg/L in 28% of samples (Kumar et al. 2016).
In West Azerbaijan, Iran, a high fluoride concentration ranging from 0.27 to 10.3 mg/L was reported in the groundwater of the northern villages of this region (Yousefi et al. 2018).In another study, contaminations of As in the groundwater of the Sahand area, East Azerbaijan, Iran, were found in a high unacceptable range (Feizi et al. 2008;Mosaferi et al. 2014).Also, HMs were measured in drinking water resources in southeast Iran (Malakootian et al. 2015;Malakootian and Khashi 2014;Malakootian et al. 2016).Increasing concentration of nitrates in drinking water causes nitrates to turn into other compounds, such as nitrites and nitrosamines, which are toxic, carcinogenic, harmful, and dangerous for the health of humans (Ayejoto and Egbueri 2023).Also, high nitrate levels in water can cause methemoglobinemia or blue baby syndrome in babies under 6 months old (Egbueri 2023).
Excessive fluoride consumption, especially in drinking water, increases the risk of dental and bone fluorosis, and lack of that causes tooth decay (Abba et al. 2023).So, nitrate and fluoride concentrations should be controlled in drinking water by the recommended levels (Egbueri et al. 2023a;Agbasi and Egbueri 2023;Abba et al. 2023).Also, due to the drought in Iran and the mean annual precipitation lower than 300 mm/year, water characteristics in different resources have to be controlled (Amiri et al. 2015).
Urmia Lake in northwest Iran is one of Asia's vast saltwater, having a 5000 km 2 area.In this decade, the decrease of water in drying lakes has been highly intensive, causing the accumulation of saltwater in the groundwater aquifer nearby of the lake.Also, industrial and agricultural activities indirectly dispose of heavy metals and nitrate into groundwater resources (Taghipour et al. 2013).Therefore, monitoring water quality for drinking purposes is essential, and assessing the human health risk of exposure to pollutants in drinking water for the study area is a novelty of this research.This study investigates F − , NO 3 − , and HM amounts in potable water sources and their probabilistic carcinogenic and noncarcinogenic on people in West Azerbaijan province, Iran.

Study area
This study was done in northwest Iran with longitude and latitude of 38° 44′-38° 45′ and 37° 45′-37° 46′.A total of 121 groundwater sources were selected for sampling points (Fig. 1).Based on the meteorological report, this area has been affected by the winds from the Atlantic Ocean and the Mediterranean Sea.Cold northern winds in winter caused heavy snow.The average temperature of this region is 13 °C, with a range of − 5 to 29 °C (Hosseinpoor et al. 2023;Iran 2017).The economy of this region is dependent on agricultural activities, which has caused the excessive withdrawal of water from the groundwater of this region and caused saltwater infiltration into the groundwater resources from Urmia Lake (Schmidt et al. 2021;Tussupova et al. 2020).

Sampling approach
In total, 121 water samples were collected from wells in the West Azerbaijan province.Wells were the primary potable water source in the study area.Samples were taken in 2 L polyethylene bottles, which were washed at least threefold with double-distilled water and one 1:1 ratio of HNO 3 (Merck, Darmstadt, Germany).In the first sampling, water streamed for a few minutes from a sampling tap.The bottles were filled within 1 to 2 in from the top.Samples were protected on the ice bag in the sample box at 4 °C and transported to the water lab.Four ions, including sodium (Na + ), nitrate ( NO 3 − ), fluoride (F − ), and chloride (Cl − ), were measured by ion chromatography (IC, Metrohm, Switzerland).Four HMs, including arsenic (As), manganese (Mn), lead (Pb), and mercury (Hg), were detected in the water laboratory by using an ICP-OES (Esmaeilzadeh et al. 2019).

Quality assurance and quality control (QA/QC)
The water lab, trip, blanks, and spike samples were analyzed with real samples for each type of test to check the accuracy

Legend
Sampling points West Azerbaijan p. Urmia Lake

IR. IRAN
and precision.All the chemical compounds were supplied from Merck Company products, and all tests were repeated threefold according to the standard methods.Standard solutions and controls were examined after every ten samples to obtain accuracy and precision of detection.In the next step, continuing calibration verification (CCV) standards were drawn, and a linear regression coefficient (r 2 ) in calibration curves higher than 0.99 was accepted.The limit of detection (LOD) was noticed to be three-fold the standard deviation of the measurements in the blank solutions.The analytical method for the recovery test was similar to the local samples (Malakootian et al. 2020).

Health risk assessment
The pathway entrance of heavy metals, NO 3 − , and F − from water in the human body is the ingestion and skin (for arsenic).The average daily dose (ADD) exposure pathways (mg/ kg.day) were computed from the USEPA recommendation as follows (USEPA 2001a): These parameters are defined as the below equations (USEPA 2001a), where The hazard quotient (HQ) was used to estimate noncarcinogenic risk for each element, and the total HQ was known as the hazard index (HI), which the whole exposure routes HI and HQ were estimated as follows: Here, the RfD was known as the reference dose (mg/ kg.day), which was separate for each toxic element, and each exposure route was taken from the USEPA Integrated Risk Information System (IRIS) (Malakootian et al. 2020).Having HQ or HI more than number 1 was estimated as the probability of noncarcinogenic effects due to exposure to toxic elements.Also, HI less than number 1 was shown The cancer risk was extracted using ELCR.The ELCR for two skin and digestion route was computed following below formulas: ELCR was known as the unitless, SF (slope factor) was the cancer slope factor (USEPA 2001a), and its value for As is 1.5 (mg/kg-day) −1 (Malakootian et al. 2020).An ELCR within the range of 10 −6 -10 −4 , less than 10 −6 , and higher than 10 −4 were classified as an acceptable or tolerable, negligible, and significant cancer risk for humans, respectively ((USEPA), U. E. P. A. Guidelines for carcinogen risk assessment 2005; Praveena et al. 2018;Qing et al. 2015).

Monte Carlo simulation
Crystal Ball software (Version 11.1.2.4,Oracle, Inc., USA) was used for the Monte Carlo simulation with 1000 iterations to calculate sensitivity analysis.This technique enables researchers to decrease the estimated risk uncertainty compared to competing approaches like the deterministic method with single-point variables.We used sensitivity analysis to calculate the impact of factors on the risk amount separately.The high value shows the important effect of each factor on the risk factor (USEPA 2001b).

Statistical analysis
The elements' values in the water were measured.Then, data were analyzed, and the spatial analysis of the metals and ions was mapped and highlighted using ArcGIS 10.1.The Kriging method was used to interpolate and produce independent raster layers for metals and ions.

HMs, NO 3 − , F − concentrations, and spatial distribution
The descriptive statistics of HMs, NO 3 − , and F − in the study area are shown in Table 1.The mean values of As, Hg, Mn, Pb, NO 3 − , and F − were in order 4 (ppb), 2 (ppb), 20 (ppb), 0.3 (ppb), 0.7 (ppm), and 29 (ppm).The ranking of HMs values based on the overall mean from the more to the low range was Mn > As > Hg > Pb.HM concentrations were less than the amounts recommended for drinking water by the EPA and WHO (USEPA 2012; WHO 2011).However, maximum As and Hg concentrations were higher than the US EPA standards.
(8) ELCR = ADD × SF Figure 2 illustrates the spatial trend and scattering of the study elements in the northwest area of Iran.Spatial analysis of environmental pollutants is used as an attention graphic pattern to highlight the probably polluted source and hotspot area with the highest concentration of contaminants (Zhao et al. 2014;Sun et al. 2010).
Arsenic is one crucial element found in many environments (e.g., soil, air, and water resources) in northwest Iran due to geogenic sources, industrial and agricultural activities, and air pollution with anthropogenic and natural phenomena, like particular dust storms from the dried bed of Urmia lake (Soleimani et al. 2022;Ravan et al. 2022;Mosaferi et al. 2017;Malakootian et al. 2020;Parsinejad et al. 2022).In 5% of sampling points, the measurement of As is more than WHO and EPA permitted levels.In some sources, the As amounts were an extra tenfold from the drinking water standard level.According to Fig. 2, the As concentration hotspot is located in the center and southwest of the Urmia Lake area.Several previous studies mentioned this area's high As in soil and air pollution; unfortunately, water resources had a similar problem (Malakootian et al. 2020;Soleimani et al. 2022).
In the present research main finding belongs to mercury amounts in the study area, which in 56 sampling sources detected more than the EPA standard.However, Hg amounts agreed with the WHO recommended level, but according to the EPA permitted level, it has health concerns.According to the distribution map of Hg in Fig 2, north and central areas have highlighted points that need more investigation because mercury has severe chronic and acute health effects.In research conducted in the city of Ilam, located in the west of Iran, the mercury amount was 0.9 ppb, and in another study done in the Aras Dam lake, situated in the northwest of Iran, the mercury amount measured between 20 and 70 ppb (Fakhri et al. 2018;Farsani et al. 2019).
The fluoride concentration range in the study area measured from 0.4 to 4.5 mg/L with a mean of 0.7 mg/L.Fluoride concentration at 3 points was more than the WHO recommended guidelines, which is between 0.5 and 1.5 mg/L; and at 13 sampling points, it was less than the recommended level.Previous studies reported fluoride concentrations in 28 villages of Poldasht in west Azerbaijan were in the range of 0.27 to 10.3 mg/L (Yousefi et al. 2018).In the study in Maku city near Poldasht, the concentration of F − in 65 villages was reported from 0.29 to 6.68 mg/L in winter (30% of sampling points higher than the permitted level) and 0.1 to 11.4 mg/L in summer (48% of sampling points higher than the permitted level), respectively (Yousefi et al. 2019a).In another study in Showt's villages near Poldasht and Maku, the concentration of F − measured in a wide range of 0.0-5.5 mg/L (Nabizadehb et al. 2019).
The primary sources of water in the study area were wells and springs.These results are shown in Fig. 2. Flouride concentration in the north area was higher than in the other areas.The main reason for F − contamination in this area is related to georgic sources.Thus, extra fluoride is a known natural health problem in water sources used to drink in the northern part of West Azerbaijan (Amouei et al. 2012;Yousefi et al. 2019b).
The nitrate concentration range in groundwater samples measured from 1.7 to 137 mg/L with a mean of 28.65 mg/L.The nitrate concentration in 19 samples detected was more than the WHO guideline that is lower than 50 mg/L (as NO 3 − ).In Fig. 2, nitrate distribution is shown in the study area.The hotspot for nitrate concentration is located in the seashore of Urmia Lake and the center part of the province.West Azerbaijan province and Urmia tertiary are important agrarian hubs.So, the origin of nitrate is biological pollution and chemical fertilizer, which are these two sources due to the disposal of untreated wastewater and agricultural activity.
In several studies, including around Urmia Lake water sources, industrial park, and Urmia City, nitrate values were reported to be 5-30 mg/L, which were lower than our  findings in some areas (Malakootian et al. 2020;Nanbakhsh et al. 2010;Nanbakhsh 2006).The nitrate concentration in many drinking water sources in Iran was recorded in the range of unpermitted levels for drinking usage.For example, Azadshahr, Bandar-Gaz, the central zone of Shiraz, Esfahan, Gonabad, Bajestan, Hashtgerd, Kerman, Qom, and Ghorveh Dehgelan all recorded unpermitted levels of nitrate in water sources to drink (Marhamati et al. 2021;Golaki et al. 2022;Nasseri Maleki et al. 2021).
Finally, the statistical correlation test did not show a significant correlation between measured elements and the ions, and the reason is possibly related to the difference between each origin.
Distribution map analysis disclosed the non-alike distribution patterns for all elements with non-alike levels except Na + and Cl − .These two elements originated from Urmia Lake, which is drying and each year affects groundwater quality; searchers found boron pollution and increasing salinity near the seashore lake northwest of Urmia Lake (Mosaferi et al. 2020).A similar trend for the other elements is possible due to their uniform sources.

Carcinogenic effects
The mean ELCR concentration of As is located in the negligible class (i.e., < 10 −6 ) shown in Table 2.But in 4 sampling points, ELCR extracted 10 −4 to 10 −5 .These points are located southwest of Urmia Lake.The ion and HM exposures have additive, synergistic, or antagonistic unhealthy effects on the human body (Anyanwu et al. 2018).The calculation of ELCR in the present study, except for the highlighted area for As in Fig. 2, was significantly lower than in previous studies with different exposure pathways; the reason could be the low value of HMs in our samples (Liu et al. 2013;Kamani et al. 2014;Fallahzadeh et al. 2018;Malakootian et al. 2020).However, due to the possible outbreak of lung cancer, chronic bronchitis, emphysema, and asthma from exposure to arsenic, we need to continue monitoring (Zhao et al. 2012;Malakootian et al. 2020).
The value of HI is given in Table 2.The most value of HI values was obtained for As and NO 3 − with noncarcinogenic risk.Our findings were none like the results of previous research (Kamani et al. 2014;Chen et al. 2015;Zhao et al. 2014).In the present study, HI for the other elements was at an acceptable level (HI less than 1) for elements and ions through exposure routes.The spatial trend of As and NO 3 − in the sampling points (Fig. 2), given the center area of the study area, had high HI values.Our results indicated that these areas' agricultural and industrial activities and the droughty beds of Urmia Lake lead to higher HI.Many previous types of research also recorded the pollution of this area in the soil, water, and air quality (Mohammadi et al. 2018;Mosaferi et al. 2020;Ravan et al. 2022;Soleimani et al. 2022;Mohammadi et al. 2020b).

Sensitivity analysis
In addition to the point investigation, the Monte Carlo method by 1000 bootstraps was applied to find the parameters in the ADD using a probabilistic technique.Uncertainties were computed to forecast ADD some descriptive statistics, e.g., standard deviation, median, 95, and 5 percentile, respectively.Sensitivity analysis found the main factors associated with cancer risk.Also, sensitivity analysis was used to highlight the main influential factor in the HQ due to exposure to toxic elements of high value (Fig. 4).This study illustrated that the exposure duration (ED) for As, Mn, and Pb; ingestion rate of water (IR) for NO 3 − and F − ; and Hg concentration (C) for Hg had the highest impact on average daily dose (ADD) value-related ELCR and HI.Also, a reverse correlation was found for average time (AT) and body weight (BW) for As, Hg, F, NO 3 − , Pb, and Mn.Thus, health effects of exposure to HMs and ions seem to be acceptable, and its significance were uncertainties caused by detection, human exposure factors, and day-to-day or areato-area changes in risk factors (Mohammadi et al. 2020a;Mohammadi et al. 2020c).

Conclusion
The present study investigated heavy metal (Pb, As, Mn, and Hg) and ion (Na + , NO 3 − , F − , and Cl − ) levels in drinking water resources and health risks.The mean concentration of study elements was obtained in the World Health Organization (WHO) recommended range.But in 5% of sampling points, the measurement of As was more than WHO and EPA permitted levels.The As concentration hotspot was located in the center and southwest of the Urmia Lake area.
In the present research main finding belongs to mercury amounts in the study area, which in 56 sampling sources detected more than the EPA standard.The north and central areas have highlighted points that need more study because mercury has severe chronic and acute health effects.Nitrate at 19 points was detected in the unacceptable ranges and more than WHO-recommended guidelines, which is carcinogenic.The hotspot for nitrate concentration is seen in the Urmia Lake seashore and the province's center part.That is the main origin to be guessed to belong to biological pollution and chemical fertilizer.Fluoride at 13 points less than WHOrecommended guidelines can cause tooth decay, and at 3 points more, it can cause dental and skeletal fluorosis.The extra fluoride was found in the northern part of West Azerbaijan.
The order of heavy metal and ion noncancerous risks based on the overall mean extracted as As (32%) > Hg (20%) > (1%) Mn, Pb, and NO 3 − (43%) > F − (3%), respectively.According to the risk assessment analysis, arsenic and nitrate in some sampling points could have noncarcinogenic effects on the human body.Furthermore, arsenic had unacceptable carcinogenic risks in some water samples.So, further studies are recommended to monitor water quality to find probable contamination sources due to decreased health risks.

Fig. 1
Fig. 1 Map of the study area and sampling points

Fig. 3
Fig. 3 Percentage contribution of mean noncancer risks

Fig. 4
Fig. 4 Sensitivity analyses of excess lifetime cancer risk of exposure to As, Hg, Mn, Pb, NO 3 − , and F ▸

Table 2
Values of health risk of heavy metals for different groups of people in groundwater