The human health risk assessment and countermeasures study of groundwater quality

Due to various geological, hydrogeological conditions and human activities, groundwater of different regions has distinct hydrochemical characteristics. The harmful chemical components of groundwater affect human health, and thus, the groundwater quality health risk assessment (GQHR) is important to local residents. It is vital to select GQHR factors combined with hydrochemical features, and to explore their formation, concentration characteristics and the prominent controlling role of influencing risk distribution from natural and human reasons. The factors of NO3−, NO2−, NH4+ and F− were extracted as assessment factors to evaluate the GQHR. The factors NO3−, NO2− and NH4+ are derived by human activities and F− stems from irrigation of geogenic high-fluoride groundwater and fertilizer use. The results of GQHR showed the risk order as children > adult females > adult males. The low- and medium-risk regions correspond to high groundwater levels, which are mainly controlled by natural factors. The high-risk regions located in eastern part of the study area, which were affected by both natural and human reasons. The targeted measures to prevent the increase of groundwater health risk caused by different dominant controlling effects were put forward. The research provides a scientific basis for the safety of groundwater supply and environmental exposure in this area. The research ideas and methods can be a reference for similar studies.

, NO 2 − and NH 4 + are derived by human activities and F − stems from irrigation of geogenic high-fluoride groundwater and fertilizer use. The results of GQHR showed the risk order as children > adult females > adult males. The lowand medium-risk regions correspond to high groundwater levels, which are mainly controlled by natural factors. The high-risk regions located in eastern part of the study area, which were affected by both natural

Introduction
All over the world, more than 1.5 billion people depend on groundwater for drinking water supply (Alley et al., 2002). According to World Health Organization (WHO), 80% of human diseases are caused by poor water quality (Lyu et al., 2019;Zabala et al., 2016). In natural environment without human activities, along the flow path, groundwater maintains a stable exchange of material and energy with surrounding environment. According to the law of conservation of mass, the materials and energy in groundwater are exchanged with the surrounding environment and maintain a dynamic balance.
However, hydrochemical components in the natural groundwater are higher in some areas due to their geological conditions (Shen, 1993). For example, the geogenic high-arsenic groundwater has been found in the USA, Canada, Bangladesh, Vietnam and China (Erban et al., 2014;Wyllie, 1937;Zhang et al., 2015). With increasing human activities in the natural environment, such as rapid population growth, frequent agricultural activities, swift industrial development, the exchange balance between groundwater and stratigraphic media has been destroyed under natural conditions. Resulted in changes in the hydrochemical characteristics of groundwater in some areas (Glynn & Plummer, 2005;Goldberg, 2006;Qiu and Jane, 2010. In most cases, the evolution of hydrochemical composition in groundwater will have a deterioration effect on the groundwater environment and lead to groundwater pollution (Du et al., 2017;Li et al., 2018;Wu et al., 2015). For instance, excessive nitrogen fertilizer used during agricultural development resulted in groundwater pollution. Groundwater in the USA, some parts of Europe, Belgium, France, Spain, Portugal, Greece, and other countries is polluted by nitrate in different degrees (Canter, 1997;Costa et al., 2002;Hiscock et al., 1989;Luo & Jin, 2002).
Pollutants entering groundwater not only degrade groundwater quality but also pose varied degrees of hazard to human health (Li et al., 2018;Zhang et al., 2018). An extended period of time in drinking and contact with contaminated groundwater will have an irreversible impact on human health (Kuo et al., 2014;Li et al., 2016aLi et al., , 2016bSrivastava et al., 2015;Wu & Sun, 2016). For example, fluoride is one of the critical trace elements for human health, excessive or insufficient fluoride intakes will constitute a considerable t health risk to human body, with a high amount resulting in fluorosis and a low level will lead to dental caries Rao, 2017WHO, 2011.
To clarify the health hazards caused by contaminants in the environment and quantitatively calculate the potential health risk of pollutants to human health, the United States Environmental Protection Agency (USEPA) and China proposed a groundwater quality human health risk assessment (GQHR) model, respectively (Song and Wu, 2019;Su et al., 2013;Alam et al., 2016; Ministry of Environmental Protection of People's Republic of China, 2014USEPA 2015. And researchers used the GQHR model to assess human health risk in different regions in China (Chen et al., 2016;Li et al., 2016aLi et al., , 2016bWu & Sun, 2016).
It is vital to select factors of GQHR, the previous studies mostly considered pollution situation when they used the model (Teng et al., 2019;Zhai et al., 2017;Zhang et al., 2020Zhang et al., , 2022. They ignored the temporal and spatial variations in the causes of pollution situation, which affected by natural factors or human activities. In actually, due to the difference of natural environment and human activities in different regions, the crucial controlling factors of the origin and evolution of groundwater hydrochemical characteristics are various (Miao et al., 2020). In order to ensure the safety of groundwater supply, it is essential to clarify the hydrochemical characteristics of groundwater caused by different dominant factors (for instance water-rock interaction, precipitation, evaporation, sewage irrigation). Formation minerals determine the composition of substances in groundwater through water-rock interaction (Helgeson et al., 1970;Roy et al., 2020). Water-rock interaction is an important process of groundwater hydrochemical origin; thus, it is very important to define the type of groundwater. Geology and geomorphology control the distribution of hydrogeochemical types and total dissolved solids (TDS), as well as the migration of solids in groundwater. Climate can influence the precipitation and evaporation, results to the enrichment of different components of groundwater. And human activities can also change hydrochemical composition of groundwater (Jing et al., 2016;Li et al., 2020). Hence, the assessment model factors should be selected by the characteristic components combined with the actual situation influenced by natural factors and human activities.
Therefore, the objectives of this research are: (1) to select the GQHR assessment factors combined with hydrochemical characteristics and human activities; (2) to assess the GQHR and analyze the natural and human factors affecting the spatial distribution of GQHR; and (3) to put forward the targeted countermeasures to prevent the increase of GQHR in different level risk areas. The research results are of great significance to the safety of groundwater supply and the development of economic and social in this area.

Study area
Tongzhou District is located in the southeast of Beijing, China, covering an area of 907 km 2 (Fig. 1). It is situated on the axis of the Beijing-Tianjin Economic Belt. Due to its geographical advantages, Tongzhou has become the base of grain production, vegetable production, non-staple food supply, receiving the evacuated population, and industrial enterprises in Beijing. As one of the critical developing satellite cities of Beijing, groundwater in Tongzhou undertakes the task of water supply for residents. In recent years, groundwater in the study area has been strongly affected by human activities, because of the change of (1) Boundary of Beijing, (2) district boundary, (3) administrative district, (4) town boundary, (5) Chaobai river alluvial-pluvial fan, (6) Yongding river alluvial-pluvial fan, (7) groundwater samples, (8) section line land use type, the accelerated construction of public facilities, and the rapid growth of population.
The study area is a continental monsoon climate with an average temperature of 11.3 ℃. Average annual precipitation of 620 mm, 85% of which is concentrated from June to September. Groundwater flows from northwest to southeast.
The terrain in the study area is gentle and slopes from northwest to southeast. In terms of hydrogeological units, it is located at the fan margin of Chaobai River alluvial-pluvial fan and Yongding River alluvial-pluvial fan. The surface is covered by the Quaternary strata, and groundwater mainly exists in it. The aquifer of the Quaternary aquifer system in the study area is interbedded with sand layers and clay layers, and the multilayer arrangement involves thin sand layers divided by discontinuous heavy silt-andclay layers. The aquifer is mainly recharged by precipitation, river infiltration, groundwater lateral runoff, and irrigation return. The main discharge involves exploitation (for agricultural irrigation) and southeast lateral runoff. The object of this study is the shallow groundwater with a buried depth of 40 ~ 60 m.

Sample collection and analysis
In June 2017, 20 groundwater samples were collected from wells at a depth of 80 m and used portable GPS to record the location (Fig. 1). Samples were collected and analyzed in accordance with the "Technical Specifications for Groundwater Environmental Monitoring" (HJ/T164-2004). pH was measured in the field by a portable water quality analyzer. K + , Na + , Ca 2+ , Mg 2+ , Cl − , SO 4 2− , HCO 3 − , CO 3 2− , F − , NO 3 − , NO 2 − , NH 4 + and TDS were analyzed in the laboratory (Table 1).

Groundwater quality human health risk assessment model
The drinking water source in the study area mainly depends on groundwater, and the most common exposure pathways are oral intake and dermal contact. In this study, quantified groundwater quality human health risk using (GQHR) assessment models proposed by the Ministry of Environmental Protection of the People's Republic of China from the above two pathways (Ministry of Environmental Protection of People's Republic of China, 2014). The models of oral intake and dermal contact are as follows.

Oral intake model
where Intake oral denotes the daily average exposure dosage through the oral pathway (drinking water intake) per unit weight (mg/(kg·d)). C indicates the concentration of the factors tested in the library in groundwater (mg/L). IR implies the ingestion rate of groundwater (L/d). EF and ED represent the exposure frequency (d/a) and exposure duration (a), respectively. BW and AT signify the average body weight (kg) and the mean exposure time (d), respectively. RfD oral denotes the reference dosage of factors (mg/(kg·d)). HQ oral characterizes the hazard quotient for pollutants through the oral exposure pathway. 2. Dermal contact model In these equations, Intake dermal represents the daily average exposure dosage through dermal intake per unit weight (mg/(kg · d)), EV is the daily exposure frequency of dermal contact, DA signifies the exposure dosage of every single event (mg/cm 2 ), SA indicates the skin surface area (cm 2 ), K denotes the coefficient of skin permeability, T implies the contact duration (h/d), CF is a conversion factor, H represents average resident height (cm), HQ dernal and RfD dermal represent the hazard quotient and the reference dosage (mg/ (kg·d)), respectively.

Total risk model
where HI i is the sum of the hazard index of contaminant i from oral intake and dermal contact, indicating the level of harm to the human body for contaminant i. And HI total is the total hazard index of all contaminants concerned. RfD dermal is derived from the RfD oral using Eq. (7), where ABS gi is the gastrointestinal absorption factor which equals 1. Thus, the values of RfDdermal and RfD oral are equal. As shown in Table 2

Results and discussion
Groundwater hydrogeochemical characteristics The groundwater hydrochemical types are classified according to the Shukarev classification method and showed in the zoning map (Fig. 2) and Piper diagrams (Fig. 3). Two pictures show that the hydrochemical type of groundwater at the edge of Chaobai River alluvial-pluvial fan is mainly HCO 3 -Ca·Mg (HCO 3 -Ca·Na) type, and HCO 3 -Na type water is distributed locally in upper. The groundwater hydrochemical type at the edge of Yongding River alluvialpluvial fan is mainly HCO 3 -Ca·Mg·Na type in upper and changes into HCO 3 ·Cl-Mg·Na (HCO 3 ·Cl-Na·Ca) type in lower; meanwhile, the cations change from Ca·Mg·Na (Mg·Ca, Ca·Mg) to Mg·Na (Ca·Na, Na·Ca).
The ranges of groundwater pH are from 6.97 to 7.84, presenting medium-weak alkaline. The total dissolved solids (TDS) increases with the direction of groundwater flow, which changes from < 0.5 in upper to 0.5 ~ 1 g/L in lower at the edge of Chaobai River alluvial-pluvial fan and changing from 0.5 ~ 1.0 in upper to > 1.0 g/L in lower at the edge of Yongding River alluvial-pluvial fan.
The results of counting the average content of ions in groundwater according to geomorphic units are shown in Table 3. (1) The content of each component at the edge of Chaobai River alluvial-pluvial fan is generally lower than that at the edge of Yongding River alluvial-pluvial fan. (2) In each geomorphic unit, the ion content generally increases from upper to lower. (3) The dominance of anions in groundwater is HCO 3 − > SO 4 2− > Cl − , and for cations is Ca 2+ > K + + Na + > Mg 2+ ( K + + Na + > Ca 2+ > Mg 2+ ) according to their mean values. In general, HCO 3 − and Ca 2+ are the dominant components, and K + + Na + is higher than Ca 2+ both in the upper of Chaobai River alluvial-pluvial fan and lower of Yongding River alluvial-pluvial fan. These changes indicate that the groundwater quality is getting worse along groundwater flow path.

Selected GQHR factors
According to the second detailed land use survey data of Tongzhou by the Ministry of Land and Resources (October 31, 2001), the land use types in study area mainly include cultivated and agricultural land (48.19%) (Lan et al., 2018). Related to the extensive use of nitrogen fertilizer in cultivated land, nitrogen built up in the environment. Besides, long-term surface water sewage irrigation and geogenic high-fluoride groundwater, resulted in excessive fluoride in groundwater (Liu, 2008;Zeng, 1997).
On the basis of the China Drinking Water Standards (GB5749-2006) and concentration isogram distribution maps of nitrate nitrogen (NO 3 -N), nitrite nitrogen (NO 2 -N), ammonia nitrogen (NH 4 -N) and fluorine (F − ) (Fig. 4). The concentration of NO 3 -N in groundwater ≤ 20 mg/L in most areas and exceeds the standard only in Majuqiao and Yongledian (92.27 and 175.12 mg/L, respectively). The concentration of NO 2 -N in Tongzhou is all ≤ 1.00 mg/L. The concentration of NH 4 -N ≤ 0.5 mg/L in most areas, and exceeded standard areas in Lucheng, Huoxian, and Yongledian southern region, among them, the highest concentration of NH 4 -N was 3.60 mg/L, which was 7.2 times of the standard concentration. F − ups to standard in most areas, excessive points (> 1.0 mg/L) are mainly distributed at the edge of Chaobai River alluvial-pluvial fan, Due to the hydrochemical characteristics of groundwater and considering that Tongzhou is a significant agricultural area accompanied by a large amount of use of nitrogen fertilizer and surface water sewage irrigation, the GQHR factors in this study are selected as NO 3 -N, NO 2 -N, NH 4 -N, and F.

Groundwater quality health risks
Groundwater quality human health risks are related to GQHR factors, this study assessed the risk on human health from exposure to NO 3 -N, NO 2 -N,   Figure 5 shows the health risks to adult males, adult females, and children when they are exposed through oral intake and dermal contact. For adult males, HQ oral ranges from 0.01 to 5.39, with a mean value of 0.93, and 75% of the samples have an HQ oral less than 1. Similarly, for adult females and children, the HQ oral values are 0.01-6.37 and 0.01-15.93, with mean values of 1.37 and 3.44, respectively. Besides, 40% of the samples have an HQ oral over than 1 for adult females, and 35% less than 1 for children. And HQ oral < 1 indicates that 35% of the groundwater is in a relatively safe condition by the exposure pathway of drinking groundwater in the study area.
HI total is basically the same as HQ oral (mean values are 1.16, 1.37 and 3.44, respectively), indicating that the risk of dermal contact to human health is negligible compared with the risk of oral intake. Still, the values of HQ oral , HQ dernal and HI total show the same trend in the same species, all follow the order: males < females < children. That is, the influence order is males < females < children through contaminated groundwater on both exposure pathways and human health risks in the study area, denoting that children face higher risks than females, which are higher than males, because children have the lowest average weight and males have the highest average weight.
Groundwater quality human health assessment factors contribute differently to GQHR. As shown in Fig. 5d, F − contributes the most to the health risk (60.15%), followed by NO 3 − (34.97%). NO 2 − and NH 4 + are all less than 3% (2.00% and 2.88%, respectively), which means F − and NO 3 − are the main factors affecting human health. The abnormal values in Fig. 5a, Fig. 5b and Fig. 5c are caused by the fact that F − and NO 3 − in groundwater samples S5 and S18 are significantly higher than other ions, which is consistent with the conclusion obtained in Fig. 5d.
Similar human health risk assessments were attempted in various of the China, viz. agricultural area in northeast China (Su et al., 2013), Chinese Loess Plateau , and Jiaokou irrigation district (Zhang et al., 2021). They have also pointed out that compared to adults, children are under more risk for same contaminants, and oral intaking is the major source of infection related to Fig. 5 Boxplots showing the results of groundwater quality human health risks assessment. a Oral intake, b dermal contact, c total risk, d contributive ratios of factors to health risks. S5 and S18 are the groundwater samples dermal contact (Teng et al., 2019;Zhai et al., 2017;Zhang et al., 2020).

Targeted countermeasures coping with GQHR
Based on HI total , the groundwater quality human health risk distribution map is shown (Fig. 6). It can be seen that the groundwater quality health risk increases from northwest to southeast. Low and medium risk regions are located in the west and middle of the study area, while high-risk regions are mainly located in the east. The highest risk regions are Lucheng (S5) and Yongledian (S18), which are consistent with the polluted distribution of F − 、NO 3 − 、NO 2 − and NH 4 + . Previous studies (Lan et al., 2018;Miao et al., 2020) showed that the sources of groundwater pollutants (including health risk assessment factors) were mainly affected by human factors, but their distributions were controlled by natural factors (water-rock interaction, precipitation infiltration and dilution, evaporation and concentration, etc.). The government should propose appropriate policies and local incentives to ensure sustainable production and consumption of groundwater. Based on our results, efficient countermeasures should be implemented in accordance with the formation of groundwater pollutants influenced by human and natural reasons. Ignoring the influenced reasons of formation would ultimately impact managers' decision-making process (Su et al., 2013;Yang et al., 2010).
First, the low-and medium-risk regions are located in upper groundwater, and the pollutant load is the lowest in the study area (Lan et al., 2018;Miao et al., 2020), indicating that human factors play a small role and natural factors play a leading role. According to the hydrogeological and hydrochemical profile (Fig. 7), the groundwater depth in the north is deep (5-10 m), the hydraulic slope is about 2‰, and the aquifer is dominated by medium-coarse sand and fine sand, which is mainly recharged by meteoric precipitation in flood season. When the recharged groundwater passes through the aquifer, the water-rock interaction mainly occurs by leaching. From the north to the south, the particle size becomes finer, the evaporation and concentration effect is enhanced. The main performance is that the hydraulic slope becomes slower (average value is 1.2‰), the groundwater depth is less than 6 m, the material accumulation in groundwater, and the TDS increases (0.5-1 g /L). In the south, the groundwater depth becomes shallow (0 ~ 5 m), the hydraulic slope becomes slow (1‰), and with the combination of evaporation-concentration and human activities, the ionic components continue to accumulate. This region is characterized by natural factors, in the subsequent groundwater management for these regions, the monitoring of pollution sources should be strengthened, such as surface pollution monitoring and river drain contamination management, to prevent river pollution then pollute groundwater. Legitimately regulate the use of groundwater resources, improve people's awareness of resource protection and pollution prevention and control. And controlling individuals to exploit and use groundwater resources in large quantities without permission, so that avoid the increase of runoff and discharge intensity caused by changes in hydrological cycle conditions. Further, the high-risk regions are mainly located in the eastern part of the groundwater discharge area, which is affected by both natural and human factors. Tongzhou, as an agricultural irrigated area, is principally affected by the use of chemical fertilizers (mainly nitrogen fertilizer), and chemical Fig. 6 Groundwater quality human health risks distribution map fertilizers are an important source of health risk assessment factors F − , NO 3 − , NO 2 − and NH 4 + . About 48.05% of the land is used for agriculture, and the average fertilizer application rate is 1172.8 kg/hm 2 . In addition, there is primary highfluoride water in the North China Plain, and the use of high-fluoride water irrigation is another important source of fluoride in groundwater. The annual average evaporation is about 3 times the precipitation in the study area, and the groundwater flow rate is slow, reflecting that the hydrochemical changes of groundwater caused by evaporation exceed the dilution effect of rainfall. So, the groundwater depth plays a decisive role in evaporation. The highrisk regions are located in the discharge area, the groundwater depth changes from 5 ~ 10 to 0 ~ 5 m, evaporation and concentration enhance, so the concentration of F − , NO 3 − , NO 2 − and NH 4 + increases. As major agricultural irrigation regions, long-term use of sewage irrigation and chemical fertilizers. Lucheng (S5) and Yongledian (S18) are the areas with the highest risk and located in the discharge area of groundwater. Both human and natural factors lead to high concentrations of F − and NO 3 − in the chemical indicators of S5 and S18.
In the regions where natural and human factors work together, the use of chemical fertilizers should be controlled, replacing traditional agriculture with organic agriculture and farmers' awareness of environmental protection. It is forbidden to irrigate with sewage and prevent surface soil pollution. We should arrange agricultural irrigation scientifically and reasonably, reduce flood irrigation and promote agricultural pure water sprinkler irrigation. The groundwater pollution caused by human activities should be reduced, and the monitoring of groundwater exploitation should be strengthened to prevent pollutants from infiltrating into groundwater through the surface.

Conclusions
Ensured the hydrochemical characteristics of the study area by analyzing components in groundwater, and the distribution of groundwater chemical composition is mainly controlled by natural conditions like geology, topography, and hydrogeological conditions, at the same time influenced by human activities.
With the intensification of human activities, nitrogen and fluorine in groundwater have increased. The chemical type of groundwater in the study area gradually changed from HCO 3 -Ca·Mg (HCO 3 -Ca·Na/HCO 3 -Ca·Mg·Na) to HCO 3 ·Cl-Mg·Na (HCO 3 ·Cl-Na·Ca). These changes of contaminants in groundwater indicate that the groundwater quality is getting worse along the direction of groundwater flow. When selected the factors to evaluate the health risk of groundwater, compared to previous studies only consider contamination status or the pollutants in study areas, our study provides a useful method to select the indexes of GQHR assessment model with the characteristics and evolution of groundwater hydrochemistry, meanwhile considering the study area influenced by human activities.
In terms of the calculated results of GQHR, distributed degrees of GQHR and identified the dominant control factors. According to various degrees of risk caused by different natural factors and human factors, the targeted countermeasures of reducing the GQHR increase were proposed. The low and medium risk regions are mainly characterized by natural factors (groundwater depth, aquifer medium, hydraulic slope, etc.). Therefore, targeted countermeasures, including monitoring of pollution sources, legitimately regulate the use of groundwater resources, and avoiding the increase of runoff and discharge intensity caused by changes in hydrological cycle conditions. The highrisk regions are mainly affected by both natural and human factors. The targeted countermeasures include controlling the use of chemical fertilizers, forbidding the sewage irrigation and surface soil pollution. The point is to raise people's awareness of environmental protection.
The research results provide a scientific basis for the safety of groundwater supply and environmental protection in Tongzhou and provide a reference for the same kind of research.
Author's contributions The content of the manuscript was drafted by T L and revised by Y C, S B and F W. J M, Y B and S J provided the basic data of this paper. All authors provided written feedback and edits on the manuscript and agreed with its content.
Funding This work has been funded by the Graduate Innovation Fund of Jilin University (No. 101832020CX236) and geological survey project of China Geological Survey (No. DD20160229).

Conflict of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data are available in this manuscript. The research does not involve human or animal research; hence, there is nothing about consent to participate and publish.