Chemical quality assessment and health risk of heavy metals in groundwater sources around Saravan landfill, the northernmost province of Iran

ABSTRACT The penetration of landfill leachate into the subsoil contaminates soil and groundwater and has a negative effect on health. Therefore, the present study was conducted to investigate the quality and health risk of groundwater around Saravan landfill in Guilan province. To determine the effects of landfill on groundwater, leachate and water sampling of 5 wells around Landfill were performed according to standard procedures. The sampling was repeated 2 times and the samples were run through 0.45 Wattman filters to measure heavy metals. Then physico-chemical parameters were analysed and the results were compared with WHO standard and Environmental Protection Organization of Iran. Finally, the water quality index and potential health risks in children and adults were calculated. The results showed that the high pH of the leachate indicates the long life of the landfill. The concentrations of chromium, lead and manganese were higher than the allowed amount. The results of non-carcinogenic cumulative risk assessment in children and adults were 4.77 and 2.48 and the result of carcinogenic cumulative risk assessment in children and adults were 11 × 10 −3 and 23 × 10 −3, respectively Also, the health risk index of heavy metals for lead and manganese in gastrointestinal and cutaneous exposure in children was more than 1, respectively. Water quality index of 68.935 was obtained which was lower than recommended. According to the findings, the waste burial in Saravan landfill has led to a decrease in the quality of adjacent groundwater. The results of heavy metal concentrations and their health risk assessment showed the potential for pathogenic risk to the health of groundwater consumers in the study area. Therefore, due to the proximity of water wells to Saravan landfills and possible changes in the concentration of heavy metals, continuous monitoring is necessary.


Introduction
In developing countries, with the advancement of technology, population expansion, increase in human activities and urbanisation, waste production is increasing and its management is one of the most challenging measures [1,2].Despite the advanced waste management processes, still landfill method is the main waste disposal technology in developing countries due to the need for low capital, low operating costs and simple technique [3][4][5][6][7].Landfill waste is destroyed by physical, chemical and biological activities and leachate, which contains soluble organic materials, minerals, heavy metals, and pesticides, leaks into the subsoil [1,8,9].In general, factors such as hydrogeological conditions, waste composition, percipitation, landfill cover, geography of the area and time are effective in changing the characteristics of leachate [10][11][12][13].Leachate production in landfills has adverse and worrying effects on soil, plants, surface and groundwater, and health of human communities [14][15][16][17].Ya et al. in their research based on the DMFU model showed that the rate of leakage increases up to 10 times with increasing period.The harmful compounds in the leachate can turn the water quality and human health from a minor problem into a major challenge [4].Various studies have shown that the leakage of toxic organic and inorganic compounds in the leachate into the surface and groundwater (especially heavy metals that are formed as a result of natural and human activities in the environment and they take a long time to decompose) and due to their long shelf life, their consumption can have adverse health consequences [4,[18][19][20][21].As stated, 80% of diseases worldwide are caused by drinking low quality water [8,[22][23][24][25][26][27].Samadder et al., in their study of heavy metals in water and soil around an Indian landfill, found that the area's water was not drinkable.In addition, Tsarpali et al. in their research in Greece showed that the leachate compositions changes over the time.Therefore, as the groundwater is the most important source of drinking water supply for more than a third of the world's population [21] 52% for Iran [25], management of heavy metal contamination due to leachate leakage into groundwater aquifers is necessary [14].According (CERCLA) list in 2007, heavy metals were identified as the most dangerous pollutants [26].Although small amounts of some heavy metals are essential for the body [28], many studies have shown that chronic exposure to HMs, even at low concentrations, has significant negative effects on human health.Usually these compounds accumulate in adipose tissues, muscles, bones and then affect the function of the nervous system, endocrine system, immune system, cardiovascular, renal and cellular metabolism [27].On the other hand, the entry of these metals into plants, water, aquatic organisms and the human food can double its harms [10].According to the World Health Organization (WHO) standard, the maximum allowable concentration of Zn in surface and groundwater resource is 10 and 50 µg/dm 3 , respectively.Consumption of water containing zinc higher than the standard concentration of 3 mg/dm 3 can cause side effects such as dysfunction of the central nervous system, respiratory and endocrine systems, fever, vomiting, nausea, muscle cramps, stomach pain and diarrhoea [27,29].Zhang et al., showed that long-term exposure to Zn has negative effects on cholesterol balance and fertility.Permissible levels of Pb in drinking water according to the (WHO 2011) and (USEPA 2012) standards are 10 and 15 µg /l, respectively [30].Kaufmann et al., founded that Pb has negative effects on blood enzymes and central nervous system [31].It also accumulates in the grey matter of the brain, which can disrupt neurons and synapses and the transmission of nerve messages [23] Exposure to high concentrations of Pb can lead to impaired paediatric intelligence, hypertension in adults, kidney damage, miscarriage, and increased mortality in children [29].The permissible levels of chromium in drinking water stated by WHO and USEPA are 10 and 15 µg /l, respectively.Complications of long-term drinking of high-chromium-containing water, according to research by Loubieres et al., Knight et al., Include damage to the lungs, liver, kidneys, and nerve tissue [26,29].The standard limit for copper in drinking water is 2 mg/L according to WHO guidelines, which is highly toxic and can lead to vomiting, diarrhoea, impaired ability, and liver cirrhosis [26].Increased cadmium in the body can lead to kidney disorders, high blood pressure, lung problems and cancer [28] In a study conducted by Thomas Kwame Boateng et al., it was found that Leakage from the Oti landfill in Kumasi led to an increase in the average concentration of lead, cadmium, chromium and iron more than WHO limit in the groundwater around the landfill, which has adverse health effects [14].Ruchuwararak et al. reported heavy metals such as arsenic, lead, cadmium, and chromium in water, sediments, and edible plants near the Thai landfill [32].Dullius et al. also observed 10 metals including barium, zinc, copper, nickel, iron, manganese, titanium, calcium, and chlorine from landfill leachate in the Boipigua River, Brazil [16].Saravan is one of the most important and touristic cities in the north of the Iran due to favourable weather conditions and the existence of forest parks.This city with a population of 9750 people is located in 20 km south of Rasht (the capital of the Guilan province).Every year, unsanitary disposal of municipal and hospital waste in this place leads to water pollution in the surrounding area.Due to high humidity, heavy rain, sandy loam soil of the landfill, no treatment of leachate, lack of appropriate protection measures such as floor and wall insulation, flood and surface water management as well as continuous assessment measures, most of the resulting leachate, penetrates into soil layers and enters groundwater aquifers.Due to the lack of leachate management, leachate has entered the Chapli River and Gohar River directly and has turned these once fishing rivers into the most polluted rivers in the country.Since Saravan landfill is located in a rural area and most residents suffer from lack of surface water and water's low quality, their tendency to use well water for drinking and irrigating farms is very high.Contamination of these resources with heavy metals and ignorance of the villagers can be a serious threat to their health.To the best of our knowledge, no studies have been conducted on the impact of groundwater pollution on the health of people in this area.Therefore, planning to continuously monitor and measure the quality of groundwater resources in order to control measures and assess the health risk of these resources, as well as replacing drinking water resources, using dual systems and separating drinking water from other sanitary facilities, establishing treatment systems.Water before distribution and deployment of waste management systems is the most sensible way to ensure water safety and safe operation of groundwater.Considering the importance of the issue and the high groundwater level in the study area due to climatic conditions and the proximity of drinking wells to landfills, the purpose of this study was to analyse the quality of Saravan groundwater using metal pollution index and its health risk assessment.

Study area
Saravan Landfill is located in Saravan forest area of 18 hectares in Sangar city, 20 km away from Rasht (latitude 37°4´17.94"N, longitude 49°37´52:70″ E) and altitude of 200 metres above sea level.It is surrounded by agricultural fields and residential areas.This village is located in the lands between the mountains and the plains, with a humid and mild climate due to its proximity to the Sefidrood River.The average annual rainfall in Saravan is 1300 mm, it's temperature is 15.9°C, its relative humidity is 81.9% and the soil of the region is loamy.The geographical location of the landfill is shown in Figure 1.

Leachate sampling
In this study, leachate samples were collected in two stages and poured into a 50 cc polyethylene container.1.5 ml of concentrated nitric acid was added to each litre of sample to preserve heavy metals and it was immediately transferred to the laboratory at 4°C to reduce biological and chemical reactions.40 ml of the samples were poured into polytetrafluoroethylene tubes.Then 10 ml of 65% nitric acid was slowly added to the samples and then placed in a heater block for 1 hour at 50°C and 1 hour at 120°C for complete digestion.The samples were made up to 50 ml with twice distilled water.Finally, an atomic absorption device (Spector ARCOS, Germany) was used to determine the concentration of heavy metals (Cd,Cr,Pb,Zn,Fe,Mn,Cu,Ni).

Water sampling
In this study, using regional water maps, groundwater resources of Saravan region were identified and 5 wells were selected which are shown in Figure 1.To measure the level of potentially toxic heavy metals Cd, Cr, Pb, Zn, Fe, Mn, Cu, Ni, water samples were collected according to the standard (APHA, 2005) in two stages with 2 repetitions in 2020-2021 from selected wells around Saravan Landfill.Sampling was performed in 3 to 5 minutes.50 cc polyethylene bottles were used to transfer water samples.The sampled plastic containers were washed with sulphuric acid to prevent the growth of bacteria.To protect water samples, 1.5 ml of concentrated nitric acid was added to each litre of sample to reduce the pH of the samples to less than 2. The samples were stored at room temperature for analysis and transferred to the laboratory.Water samples were passed through a 0.45 micron Watman filter for chemical analysis of heavy metals and measured by using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) model Perkin Elmer ELAN 9000 ICP-MS.obtained limits of determination (LOD) and quantification (LOQ) were 0.0005 mg/L and 0.0006 mg/L respectively.

Metal index (MI)
The metal index (MI) is calculated to determine the combined effects of a number of quality parameters that can have adverse effects on drinking water quality.Index values less than 1 indicate low pollution; index value of 1 indicates moderate pollution and index value greater than 3 indicate high pollution.MI is obtained using Equation (1): C i and S i are the concentrations of the measured metals (mg/l) and the standard for the evaluation of heavy metals (mg/l), respectively According to Lyulko et al.MI greater than 1 indicates the alert threshold.Lyulko metal index classification for drinking water and household use is given in Table 1.

Heavy metal pollution index (HPI)
HPI is a ranking method that is used to identify the effect of heavy metal pollution on groundwater and indicates the usability of that water.HPI was used to assess the potability of groundwater around the Saravan landfill.This index depends on several factors, including the weight of the metal unit (W i ) and the standard allowable limit (S i ) for each metal.In Equation ( 2) the weight index method was used [14].
W i is the weight of the heavy metal (in µg/l), Q i is the subindex of the element and n is the number of heavy metals being analysed.Equation ( 3) was used for evaluating W i .
K is a constant and S i is the standard limit set for each heavy metal (in mg/l).
W i , the weight ratio of each heavy metal is 0.0002 for zinc, 0.7 for lead, 0.3 for cadmium, 0.02 for chromium, 0.001 for copper, 0.02 for manganese, 0.005 for iron and 0.05 for nickel (in µg/l).
The Q i for each metal is obtained using equation ( 4): M i indicates the concentration of heavy metals in the environment.I i is the limit of heavy metals in drinking water in accordance with WHO standard.The higher the calculated HPI, the greater the ill effects of drinking contaminated water.An HPI above 100 is generally considered a critical HPI that has the potential to harm living organisms.If the value of this index is more than 100, water pollution with heavy metals is high.If it is equal to 100, heavy metal pollution is at risk, and if it is less than 100, water pollution of heavy metals is considered low.

Health risk assessment
The process of estimating the probability of occurrence and the degree of potential harmful effects of pollutants on health in a particular period is defined as health risk assessment, which includes four stages of dose: response, exposure assessment, identification and risk description [33].In the present study, the assessment of human health risk (carcinogenic and non-carcinogenic) due to consumption and skin adsorption of heavy metals in water wells in Saravan and its effects on the health of individuals was calculated using the criteria of the Environmental Protection Agency.The study groups in this study were children and adults.
Hazard Quotient Rate (HQ) for showing non-carcinogenic risk and Excess Lifetime Cancer risk (ELCR) indicates carcinogenic risk which was determined using the available information and parameters and EPA equations (5 to 10).
The average daily dose (ADD) of each heavy metal was calculated orally and by skin according to equations 5 and 6.
All the parameters used in formula (6,5) are given (in Table 2) assuming that all the people of Saravan use the water of wells and springs for drinking.
The maximum amount of metal that potentially has no chronic effects through direct drinking of water is defined as the RfD or reference dose of heavy metals (mg/kg/day).Oral reference doses (for each metal) are taken from the US Comprehensive Environmental Risk Management Information System.
Non-carcinogenic risk assessment of human health due to heavy metals in drinking water was calculated using ADD in the following formula: The reference dose (RfD) for each heavy metal according to the latest EPA 2018 edition is 0.0003 for arsenic, 0.3 for zinc, 0.0035 for lead, 0.0005 for cadmium, 0.003 for chromium, 0.04 for copper, 0.14 for manganese, 0.7 for iron and 0.02 for nickel.In this study, the HQ health risk index for children and adults was calculated separately.The total non- carcinogenic risk or total HI risk index, according to Equation ( 8), was obtained from the total HQ of various contaminants (heavy metals).
The risk is acceptable if it is HI ˂ 1 and the risk is unacceptable if it is HI ˃ 1 in terms of noncarcinogenic effects [39].Carcinogenic risk assessment: The probability of increasing the risk of cancer due to exposure to carcinogenic contaminants during life is calculated according to Equation (9).In this equation SF i carcinogenic slope factor (mg/kg/day) is 0.0085 for lead, 0.19 for chromium and 0.38 for cadmium.ADD i is the average daily dose of each metal through oral consumption, which was calculated based in Equation 7. Total carcinogenic risk (cumulative risk) is the result of the total carcinogenic risk assessment of various heavy metals, which was calculated in equation (10).
According to the EPA guidelines, there is no risk of cancer in humans if the risk level is < 10 −6 .If the risk level is > 10 −4 , there is risk of cancer in humans.And if the risk level is between 10 −6 and 10 −4 , it indicates an acceptable risk in humans [40].

Statistical analysis
IBM Statistical Package for the Social Sciences (SPSS) 20.0 was used for the statistical analysis.Basic statistical parameters including max, min, mean, and standard deviation were analysed.

Leachate characterisation
Leachate is a highly toxic landfill by-product that can contaminate soils and groundwater not only around it but also over long distances, causing harmful damage to the environment and human health.These problems are exacerbated when the landfill is uncontrolled, illegal, and leachate is not properly treated.Various studies have generally found that leachate is toxic, mutagenic, and genotoxic [41].Factors such as climate, geological and hydrogeological conditions, temperature, pH, precipitation, landfill cover, age and composition of waste, geography and time play an important role in changing leachate compositions.The average physicochemical properties and heavy metals of Saravan landfill leachate are shown in Table 3.The average pH of the leachate in this study was 8.61 ± 0.716199 and it was found that according to the report of Zakaria et al., the landfill leachate was an old one.Zakaria et al.Showed in their research that Alor Pongsu Malaysian landfill leachate is young and old with a pH of 5-6.5, 7.8-8.64,respectively.A study by Kumar et al. on the Uttarakhand river in India proved that landfill leachate could potentially raise the pH of drinking water around it, posing a risk of elevated trihalomethanes and a serious health threat [17].COD was 5479 ± 465.6913 mg L −1 , which was higher than the standard.Therefore, according to Arij, leachate with COD 3000-15,000 mg L −1 is in the middle category and contains volatile fatty acids and less folic and humic acids.Kaur et al., Rana et al. found that increasing the concentration of COD in leachate leads to changes in physicochemical properties and an increase in groundwater organic pollutants [17].The BOD in this study was 1300 ± 220.0282 mg L −1 .In the study by Pang et al., the BOD content in young leachate varied between 4,000-13,000 mg L −1 and increased to 81,000 mg L −1 .El-Gohary et al in their study at Borg Al Arab Landfill reported BOD from 4820 to 6600 mg L −1 .BOD/COD ratio is used as an indicator of age and the presence of organic pollution in landfills.The BOD/COD ratio for Saravan landfill was 0.237.In stabilised leachate, the BOD/ COD ratio is below 0.1, but in young leachate it reaches 0.7 due to the acidic phase in new landfills [17].Kamaruddin et al. in their report stated that Kulim landfill leachate has a high degradability due to the BOD/COD ratio of about 0.2.The BOD/COD ratio at the Virginia (USA) landfill was 0.19 in the study by Iskander et al., and the leachate had low biodegradability.In general, the BOD/COD ratio in stable leachate is less than 0.1.Ghani et al. stated that if this ratio is reduced to 0.5-0.1, the landfill will be in the middle phase.Middle phase leachate often contains heavy metals and low organic compounds with moderate pH and NH4 + -N [17].With the above interpretations, the leachate is in the middle phase.The concentration of Cl − 3403 ± 381.0744 mg L −1 was estimated to be higher than that of Alexandre et al. staudy, maybe because of the alloys and industrial waste salts dumped in the landfill.In our study, the mean amount of Zn 2+ was 2.12 ± 1.311855 mg L −1 , Cu 2 + , 0.355 ± 0.139111 mg L −1 and Cd 2 + was 1.02 ± 0.715338 mg L −1 .In a study conducted by Panahifard et al. at Qazvin landfill, the mean values of Zn 2 + was 2 mg L −1 , Cu 2+ , 0.1 mg L −1 and Pb 2+ was 1.33 mg L −1 .The amount of iron in the leachate was 37.73 ± 27.26288 mg/l.In the study of Boatng et al. in Kumasi, Ghana, the amount of iron was 25.612 ± 2.855.We suspect that the high rate of disposal of iron and steel scrap similar to the study is one of the reasons for its increase in the landfill [14].Abdul et al. in their study stated that factors such as used batteries, lead-based paints, industrial effluents, plastics and pipes have the greatest impact on the amount of heavy metals in the leachate.In their study in Punjab (India), Tiwari et al. stated that the existence of several industrial plants near drinking water sources and industrial wastewater from them is the main reason for the increase in heavy metals in these waters [42].T.coli and F.coli were found to be approximately 11,000 per 100 ml, which was higher than expected.Sodium and potassium concentrations were 1752.836± 272.5098 and 1293.743± 200.058 mg/l, respectively.The presence of these ions in the leachate is probably the result of the decomposition of the remaining fruits and vegetables [15].As shown in Figure 1, the potential for landfill contamination depends on the geographical conditions of the area.Saravan landfill has the potential to contaminate groundwater because it is located in a rainy area and has sandy loam soil, level surface and shallow aquifer.Therefore, it is necessary to prepare corrective measures to control water, soil and land pollution.One of the best ways to reduce the volume of leachate is to spread the leachate to reduce evaporation and transpiration.Evapotranspiration can be increased by planting vegetation [17].

Physiochemical characteristics of groundwater
In developing countries, highly toxic and polluted leachate from non-engineered landfills usually enters the surrounding soils and waters, which can cause serious damage to the natural ecosystem and human health.Risk assessment guidelines state that swallowing is the main route of exposure to elements present in water and soil (USEPA, 1989; Health Canada, 2010, 2012, 2017) [41].Nagarajan et al, Mor et al, Longe and Enekwechi found that groundwater pollution from landfill leachate is one of the most dangerous environmental problems.To prevent adverse effects, it is necessary to estimate the amount of metals and raise public awareness about the dangers of drinking such waters [43].
The results of physicochemical characteristics of groundwater and their comparison with the WHO (2011) and environmental standards of Iran are shown in Table 4.

pH
The pH of groundwater in the study area was between 7.13 and 8.1 with an average of 7.56 ± 0.29152, which may be due to proximity to the uncontrolled burial site.Low pH helps with chlorination, while high pH helps control corrosion of water pipelines [44].In 2017, Samadder et al. stated that the pH of groundwater around India Landfill varies from 6.14 to 8.1.Also, Abd El-Salam and Abu-Zuid in their study reported the pH of the groundwater in the landfill of Alexandria, Egypt, between 7.4 and 8.8 [45].

Electrical conductivity
EC indicates the amount of inorganic pollution in the water.Its high value indicates the high concentration of soluble solids, which is used as a primary method to evaluate the suitability of water for various applications or may be due to the high concentration of inorganic ions from leachate in groundwater [46].EC values were obtained from 1253 to 1527 with an average of 1376.6 ± 91.79392 µS/cm which was higher than the standard.This could be due to e-waste in landfills and agricultural activities.Similar to the result of the study conducted by Vahabian et al. showed the EC level of groundwater in Hamedan from 1080.18 to 10,875.43 µS/cm, which indicates the salinity of water because of the proximity to the landfill [45].The EC of two controlled wells near the landfill of Alexandria, Egypt was also examined by Abd El-Salam and Abu-Zuid, ranging from 10,354 to 12,745 µS/cm [45].High EC makes the taste of water unpleasant, which may cause gastrointestinal problems when swallowing [44].

Total dissolved solids
One of the physical and chemical parameters for evaluating the quality of drinking water is TDS, which represents cations and anions.Since this parameter may have serious health effects, its high amount usually leads to consumer dissatisfaction.Groundwater TDS was calculated between 752 and 917 mg/L with a mean of 821.4 ± 51.0296 mg/L.Contrary to our conclusion, Samadder et al. showed that the TDS concentration of groundwater near the study site ranged from 2400 to 7000 mg/L, which was significantly higher.Abd El-Salam and Abu-Zuid also reported TDS from 2855 to 16,276 mg/L [45].In another study, Ravindra et al. reported a maximum TDS of 1540 mg/L in the groundwater of Daddhu Majra village, near the burial site [44].Inadequate landfill is therefore expected to increase the TDS of groundwater around it.

Chlorides
Chloride is considered by researchers as an important element for analysing groundwater pollution [45].Its concentration in this study was from 118.15 to 196.4 mg/l with an average of 159.04 ± 26.72939 mg/l which was lower than the WHO (2011) standard.
Although the permissible level of chloride can help maintain the health of the kidneys and nervous system (CantorHoover et al), concentrations above its standard level can react with sodium ions in the human body and lead to heart attacks [44].In Malaysia, Bahaa-Eldin et al reported a groundwater chloride concentration of 355.48 mg/L, indicating that groundwater quality was severely affected by landfill leachate [45].

Nitrates
As nitrates (NO 3 − ) dissolve well in water, they can penetrate the soil with rainwater and contaminate groundwater [44].In this study, its value was obtained from 0 to 3.9 with an average of 1.21 ± 1.148595 21 mg/l.Since Gilan province is the centre of rice production and agricultural activities in the country, the use of fertilisers to accelerate crop growth and preventing the growth of weeds is the main reason for the presence of nitrate in groundwater.Similar to the present study, Bahaa-Eldin et al. reported a concentration of NO 3 − in groundwater around the Malaysian landfill 10.40 mg/L, which was below the standard [45].Ravindra et al. at C2 and C1 sampling sites (Chandigarh India) cited the main cause of nitrate contamination as agricultural activities and dumping of industrial waste along with municipal waste and the resulting leachate, respectively [44].Research has shown that although nitrate is a nutrient for microorganisms, its high amount affects water quality and leads to problems for the consumer [15].The human body can easily absorb and excrete low levels of nitrate, but excessive levels of groundwater orally in infants can lead to blue baby syndrome [44].According to research (Sadeq et al), excessive increase in the amount of nitrogen in the blood leads to a decrease in the oxygen binding capacity of haemoglobin and eventually methemoglobinemia [15].

Sodium and potassium
Sodium and potassium are important minerals in nature.Because they are not affected by microbiological activities at landfills, they enter groundwater and they are considered as an indicator of water pollution [15].Sodium and potassium ions are essential elements for the human body and their regular consumption helps maintain salt in the blood and thus regulate water balance in the human body.The results of groundwater analysis showed that the concentration of Na + was obtained from 38.26 to 162 mg/l with an average concentration of 90.22 ± 37.81317 mg/l.K + was measured in the range of 2.13 to 5.14 mg/l with an average concentration of 3.68 ± 0.903738 mg/l.

Heavy metals
The results of heavy metal analysis of samples collected from groundwater around Saravan Landfill, using Arc GIS software version 10.4.1 are shown in Figure 2. The presence of heavy metals in groundwater can be related to factors such as the type of rock, soils around the landfill, human activities, especially the wastes of Pars Khazar and Pars Shahab factories.The mean concentrations of metals were Mn > Fe > Zn > Cr > Pb > Ni > Cu> Cd, respectively.The soil of the area is sandy loam and leachate from it has penetrate groundwater and exposed them to a serious threat of chromium, manganese, iron and lead, which has led to unhealthy drinking water and if they aren't filtrated properly, their accumulation poses serious risks to the health of consumers.Cadmium levels were measured between 0.0007 to 0.0024 mg/L with an average of 0.0011 ± 0.000543 mg/L lower than the WHO standard (2011).Cadmium is used as a widely used chemical in industrial activities such as battery manufacturing, plating and galvanising processes [21].
The low concentration of cadmium may be due to the lack of industries related to plating and galvanising activities in the study area.Contrary to our findings, Edokpayi et al. reported cadmium levels in the groundwater of Muledane South Africa 0.003-0.24mg/l [26].Also, in Mirzabeygi study in groundwater of Sistan and Baluchestan, the maximum concentration of cadmium was 20 mg /l, which was higher than the standard [47].The use of galvanised pipes for water supply may be effective in increasing its cadmium level [21].
Frickel and Elliott and Mann stated in their research, respectively that the main reason for the high level of cadmium in the region's water is industrial waste from paint and human waste [14].Consumption of cadmium-contaminated water can cause serious problems such as kidney clogging, bronchitis, nausea, diarrhoea and vomiting [14,21].In this study, the concentration of zinc which was from 0.11 to 0.495 mg/l with an average of 0.31 ± 0.121666 mg/l was lower than the WHO (2011) standard.Concentrations of cadmium and zinc in groundwater were lower than the allowable level, which may be due to the uptake of metal by soil organic matter, which is consistent with the study (Nagarajan et al) [15].Contrary to our study, Ravindra & Mor in their study reported the high use of fertilisers on farms due to the high concentration of zinc in the groundwater of Chandigarh, India [21].Also Lawerence et al .;Ipeaiyeda & Dawodu stated that because zinc is used as an additive in fossil fuels in vehicle engines, the leakage of exhaust pipes may be one of the reasons for the increase of this metal in water [21].Lead levels ranged from 0.056 to 0.28 mg/l.In a similar study, Kubare et al. reported that the average lead content in wells around Richmond was 0.21 ppm [43].Tiwari et al. also found in their study in Punjab, India that 32.8% of groundwater samples had a lead content above the WHO (2011) limit of 10 µg/L [42].Reasons for high levels of lead in the samples include the disposal of lead batteries, pipes and paints in landfills [14].Neurological disorders and kidney and brain damage, fatigue, anaemia, behavioural changes, hypertension can be mentioned from the ill effects of drinking water containing lead and cadmium [14,21,43,48].Concentrations of manganese in groundwater from 0.24 to 4.2 mg/l with an average of 1.501 ± 1.312237 mg/l and chromium from 0.06 to 0.51 mg/l with an average of 0.14 ± 0.124133 mg/l, which was higher than the standard.In his study, Mirzabeygi reported a maximum concentration of chromium of 79.3 µg/l [47].We suspect that similar to a study conducted in Neishabour, the high infiltration of landfill leachate due to heavy rainfall is the main reason for the increase in chromium concentration in the groundwater of the study area [49].Singh et al. cited the use of chromium in plating and wood preservation processes as the reason for its increase in drinking water in the Ghaziabad region of Uttar Pradesh [42].Tiwari et al. in their study in India showed that one of the reasons for the increase in chromium in groundwater could be the leather and tanning industry [42].Nickel concentration was obtained from 0 to 0.02 mg/l with an average of 0.006 ± 0.004951 mg/l which was lower than the standard.A study in Mysore, India, reported nickel concentrations ranging from 39 to 129 mg/l [21].Tiwari et al. in their study stated that a large part of Ni and Cr in the Punjab waters of India is related to human and industrial activities [42].Conjunctivitis, eosinophilic pneumonia, asthma, cancer, and foetal toxicity are some of the side effects of drinking nickel-contaminated water.Iron is one of the essential elements in the body, which is essential in the daily diet, but high levels of it in groundwater can cause problems.Consumption of water contaminated with iron and ferric salts is oxidised by contact with barley and converted to ferric hydroxide, which can affect the quality of clothing and utensils.Also, using such water for cooking may change the taste of the food [21].Iron levels ranged from 0.159 to 0.81 mg/l with an average of 0.48 ± 0.216393 mg/l above the WHO standard (2011).Edokpayi et al reported the concentration of iron in the groundwater of Muledane South Africa from 0.15 to 1.86 mg/l [50].We believe that the dissolution of iron due to oxidation and the presence of nitrate may be the reasons for its high concentration in groundwater.Iron overload, according to the Toxic Disease Agency (ATSDR 2012) and according to the studies conducted by Hime et al., Isley et al., Sagbara et al., can lead to severe fatigue, weight loss, joint pain, heart and liver failure [51].Hopps stated that consumption of water with high concentrations of iron leads to haemochromatosis [14].Iron, chromium and lead from solid and industrial wastes can cause problems such as respiratory damage (cough, asthma, shortness of breath), sperm damage, cancer, brain damage, cardiovascular disease and genetic mutations [51].Copper with 0 to 0.01 mg/l with an average of 0.0058 ± 0.003842 mg/l was obtained.We found that the dumping of metal, electronic and industrial waste could be one of the main reasons for the presence of these metals in the groundwater of Saravan region.

Heavy metal pollution index and metal index
The HPI index, as a reference method, estimates water quality in terms of heavy metals, and MI is used to predict drinking water quality [14].The results of MI and HPI analysis are given in Table 5.In this study, the mean values of MI and HPI in two stages of sampling were −2.[14].Yankey et al, after examining the HPI of Ghana's Tarkwa Groundwater, stated that activities such as mining are among the causes of their severe pollution [21].Based on the MI index, it was determined that the groundwater around Saravan Landfill is of good quality.

Carcinogenic and non-carcinogenic health risk assessment
One of the convenient methods for determining the potential risk of exposure to heavy metals in humans is health risk assessment.In this study, non-carcinogenic risk assessment for all metals and carcinogenic risk assessment was performed for lead, cadmium, chromium and nickel according to guidelines EPA 34.Assessment of non-carcinogenic and carcinogenic risk of heavy metals in groundwater around Landfill Saravan from oral and dermal route in children and adults are shown in tables S1 and Table S2, respectively.In the present study, the non-carcinogenic HQ of oral and dermal cadmium in children and adults was 0.4 and 0.19, respectively, which was lower than the standard.Contrary to the present study, Guleria & Chakma in their study reported that the amount of HQ cadmium through oral and skin exposure in children is more than safe level and is dangerous for their health [53].For manganese metal from oral and dermal route in children and adults, HQ values were estimated to be 1.97 and 0.95, respectively, which was higher than the permissible level in children through dermal route.As in our study, Guleria & Chakma in their study found that the average amount of manganese HQ in children and adults orally was less than 1, indicating that a non-carcinogenic risk was permissible.Oral and dermal HQ levels of nickel, copper and zinc in children and adults were estimated to be 0.02, 0.01 and 0.02, 0.01 and 0.13, 0.06, respectively.Negi et al. reported that the mean HQ of copper and manganese in children and adults through oral consumption at the Chandigarh, Mohali and Panchkula burial sites was less than 1, which was similar to this study [53].In a similar study, Ghosh et al. reported that the mean HQ of manganese, copper, and nickel from the oral route in the Okhla landfill was much lower than allowed; therefore, the consumption of this water has no side effects on the health of children and adults [53].As in the present study, during the study by Neogi et al., dissolved concentrations of chromium, copper, and zinc did not exceed the standard, and the level of risk was safe for the people living around the North Karanpura India coal mine.In this study, the non-carcinogenic HQ levels of iron and lead from the oral and dermal pathways in children and adults were lower and higher than safe, respectively.The highest and lowest possible non-carcinogenic risk factors (HQ) from the oral route, in both adult and paediatric groups were for lead and chromium respectively and from the dermal route, in both adult and paediatric groups were for manganese and nickel.The highest levels of potential carcinogenic risk of oral and dermal exposure were for lead and the lowest for nickel.The total non-carcinogenic and carcinogenic HQ of all the studied metals from the oral and dermal pathways in children and adults were 4.77, 2.48 and 2.3 × 10 −2 , 1.1 × 10 −2 , respectively, which was higher than the standard and one of the possible causes was adjacency to landfill.In Sakizadeh & Mirzaer study, which was conducted to assess the risk of iron, manganese, copper and chromium metals in the groundwater of Shousha and Andimeshk, Iran, it was found that the HQ of all metals except iron was higher than standard [54].Similar to the present study, the HQ levels of heavy metals As, Cd, Co, Cu, Ni, Pb, Zn in the Ravindra & Mor orthopaedic study were higher than 1, which is a noncarcinogenic threat to the health of people living in Chandigarh villages [53].The mean HQ of all metals studied in the Guleria & Chakma study was obtained from the oral and dermal pathways around the Bhalswa landfill for children and adults to a safe level, which was inconsistent with our results [53].The Guleria & Chakma study in India also showed that 95% of the population of Ariyamangalam and Tiruchirappalli were not exposed to any non-carcinogenic risk from consuming cadmium-contaminated water orally [53].Heavy metal risk assessment analysis indicates that the general groundwater situation around Saravan Landfill is at low to moderate risk level.

Conclusion
Analysing uncontrolled landfill leachate factors, especially its alkaline pH, indicates the long life of the landfill.In this study, the contamination of groundwater around landfill with heavy metals, especially chromium, lead, iron and manganese in 60% of cases were more than the allowable level.Therefore, continuous monitoring, risk assessment and intervention measures are necessary.The results of the assessment of carcinogenic risk of heavy metals in the water of wells around Saravan landfill were in the range of low to medium risk and the health risk index (HQ) of heavy metals for lead metals in gastrointestinal exposure and manganese in skin exposure in children was estimated more than 1.Another result of this research was the permissibility of water quality index.High levels of pH, electrical conductivity, chromium, lead, iron and manganese above the standard limit require purification interventions before consuming this water.Since groundwater is the main source of drinking and irrigation of farms of residents around Saravan landfill, the results of risk assessment of heavy metals in this water can play a positive role in managing intervention decisions by responsible organisations for providing water with optimal quality.

Table 1 .
Classification of water quality based on the metal index.

Table 2 .
Input parameters to characterise the average daily dose value.

Table 4 .
Physico-chemical and heavy metal analysis of groundwater samples.Therefore, it may have adverse effect on health and agricultural use.According to research (Muhammad et al), pH can change the reaction mechanism of different ions in groundwater and its slight changes lead to significant changes in reactions.
[21]−2.18 and 69.19, 68.68, respectively, and the HPI index in all samples was less than 100, which indicates the low level of heavy metals in the water of the region.Similar to the results of our study, we can refer to the study ofGhaderpoori et al.in Khorramabad, where the HPI value in all samples was estimated to be less than 100, which confirms the optimal quality of drinking water in terms of heavy metals[52].Kwame Boateng et al. also found that the HPI in the Kumasi wells ranged from 9.48 to 37.68, which was below the standard, indicating that the water under study was suitable for drinking[14].Contrary to our research, the study by Kaur et al. reported that the reason of high levels of heavy metal contamination of water around Chandigarh burial sites was proximity to landfills, industrial plants and agricultural activities.Other studies that contradict our results include the studies of Mor et al, Negi et al, and Ravindra et al[21].which considered the disposal of municipal waste in marginal and low-lying areas as the reason for the low quality of groundwater under their study.Ojekunle et al., and Bhuiyan et al. in their research had HPI values of 518.55 and 250.77, respectively, which were higher than the results of the present study

Table 5 .
Results of the calculation of water quality pollution indexes.