Emergy evaluation of human health losses for water environmental pollution

Water pollution in China has not only become one of the most vital factors impeding the social-economic development, but also threatening people’s health. In this study, Kaifeng was considered as an example, and the human health risk of drinking water pathway from 2010 to 2017 was evaluated on the basis of drinking water hygiene standards and the human health risk assessment model (HHRA). Besides, the human health loss caused by water pollution was quantitatively evaluated through emergy theory and analysis method. The results showed that the carcinogenic annual risk of carcinogenic pollutants ranged from 2.0 10 5 to 6.5 10 , and the average health risk of non-carcinogenic pollutants was about 1.5 10 , but the difference between different pollutants was obvious. Affected by water quality, social-economic development, Medicare, etc., the value of human health loss ranked at the top in 2016 with 8.73 10 sej, equivalent to 9.33 million RMB, while in other years, it was around 6 10 sej. It is indicated that among the factors, water quality is the direct inducement of healthy loss, the socio-economic development is the leading force effecting the value, and the Medicare is the final determinant of the public burden.

between water pollutants and the damage degree of human health, with risk degree as the index (Zhao et al., 2020). The common evaluation methods can be divided into many aspects, such as risk entropy, Monte Carlo simulation, loss of life expectancy, and health risk assessment four-step method (Zheng & Sun, 2017). After continuous improvement by the U.S. EPA and other agencies, the four-step evaluation method has developed into a human health risk assessment model (HHRA) (US National Research Council, 1983), which has been widely accepted. It has been used to evaluate the human health risks of drinking water (Pérez et al., 2019;Kujlu et al., 2020), surface water Zhu et al., 2015;Li et al., 2020), groundwater (Edokpayi et al., 2018;, and polluted water by a large number of researchers. Zhao et al. (2020) found that the human health risk through drinking water is two to three orders of magnitude greater than that of skin contact after the risk analysis of heavy metal pollution in the surface water of the Three Gorge Reservoir. , Akale et al. (2018), Huang et al. (2018), and Zhai et al. (2017) found that the order of health risk in various age groups is baby . child . adult female . adult male after evaluating the potential risk of nitrate concentration in groundwater to human health by the model. Gao et al. (2019), Ma et al. (2014), Khan et al. (2013), Holtby et al. (2014), and Pérez et al. (2019) evaluated the human health risks of drinking water environment by the model. Custodio et al. (2020), Genthe et al. (2018), and Neogi et al. (2018) evaluated the potential hazard risk of metals to human health in untreated coalfield mines and polluted river catchment water. Some scholars combined water environmental health risk assessment with mathematical analysis methods to make the results more authentic (Yang et al., 2011;Wongsasuluk et al., 2014;Sener et al., 2017;Ogbiye et al., 2018;Xu et al., 2018;Zhang et al., 2018;Vu et al., 2019). Although the mathematical methods were different, they all reflected the impact of different pollutants on human health and can judge what should be prioritized according to the risk, which plays a decisive role in the order of pollutant treatment.
HHRA can be used to calculate the impact on human health of each pollution indicator in water and to determine the pollutants that should be treated first, which enhance the possibility of protecting drinking water safety. However, it is only staying with health risk assessment analysis, without further quantifying the possible loss caused by the risk. The emergy theory connects economic society with the ecological environment system and realizes the unified measurement of material and emergy through solar emergy. It overcomes the shortcomings of traditional economics, which is based on monetary theory, and has been widely applied to assess the environmental resource value (Ling et al., 2018;Wu et al., 2018Wu et al., , 2019aWu et al., , 2019b. In order to evaluate the harm and loss of water pollution to human health and to arouse the great concern of government and the public, the human health risk of drinking water was evaluated by means of HHRA in this study, then the health loss was assessed combining with emergy theory. These efforts can be used to find the relationship between health loss and socio-economic development and to provide references for water pollution prevention and protection.

Materials
The International Agency for Research on Cancer (IARC) classifies the chemical pollutants in water into carcinogenic pollutants and non-carcinogenic pollutants. Among them, Cd, As, and Cr 6þ are carcinogenic pollutants; CN À , F À , phenol (Vp), NH 3 -N, Cu, Zn, Pb, Hg, Fe, and Mn are non-carcinogenic pollutants (U.S. EPA, 2005;IARC, 2016). Referring to the minimum detection limit and safety limit (Table 1) of the water quality index in Standards for drinking water quality (GB 5749-2006) and the environmental status of the selected study area, the major pollutant indicators were further selected. The water quality detection data of hydrological stations are the basis of subsequent calculation.

Methods
2.2.1. Human health risk assessment. According to HHRA, skin contact, direct drinking, and ingestion of food in water are the main ways for humans to come into contact with water pollutants. Among them, direct drinking is the most direct and main way to threaten the health of exposed population (Adimalla & Qian, 2019). In the study, the annual human health risk of drinking water sources was assessed using the HHRA based on the carcinogen and non-carcinogen health risk assessment methods , which was proposed by the U.S. EPA. The specific calculation steps are as follows: • Daily average exposure dose per quality of drinking water can be figured as: where i is the pollutant; D ig is the average daily exposure dose per unit body mass of chemical pollutant through drinking water, mg/(kg·d); C i is the concentration of pollutant in the water environment, mg/L; IR is daily water intake for exposed populations, with the data of 2 L/d (U.S. EPA, 2011); BW is the average body mass of exposed population, which is 66.2 kg (Ministry of Ecology and Environment, PRC, 2013b).
• The human health risk of chemical carcinogens can be computed as: where R C is the annual cancer risk per capita of exposed people through drinking water; R C ig is annual carcinogenic risk per capita of carcinogenic pollutant i through drinking water; q i is the carcinogenic intensity coefficient of carcinogenic pollutant i through drinking water, mg/(kg·d), and the value is • The human health risk of non-carcinogenic can be calculated as: where H N is the annual health risk per capita of exposed people through drinking water; H N ig is annual health risk per capita of non-carcinogenic pollutant i through drinking water; RfD ig is the exposure reference dose of non-carcinogenic pollutant i through drinking water, mg/(kg d), as shown in Table 2.

Emergy assessment of human health loss.
There is a large number of pollutants in the flying dust and sewage. After entering the water, some pollutants produce irritant gases, which enter the human body through the respiratory tract, causing various nervous system diseases and respiratory diseases; whereas the other part accumulates in the water and enters the human body through touching, drinking and so on, leading to the occurrence of various chronic diseases and cancers. For example, Pb poisoning affects the people's hemopoietic system and the nervous system, endangering the growth and intellectual development of infants; Cr and Hg have strong carcinogenic effects, but most of them are chronic. After human disease which need medical treatment, all kinds of medical resources are consumed in the process of treatment, which leads to the increase of nursing cost and medical measures, and affects resource investment. Besides, some patients lose their ability to work within a certain period of time, which leads to the decline of the labor force and affects the social output. Therefore, the damage process of water environmental pollution to human health can be summarized as two aspects: the increase of medical measures and the decrease of labor force.
Emergy theory and analysis method is a new environmental-economic axiology and system analysis method established in the 1980s by H.T. Odum, a famous American ecologist and pioneer of system emergy analysis. It has been widely used in the quantitative research on the relationship between human and nature, environmental resources, and social-economy (Lv, 2009). Emergy value theory can be used to analyze the transitions between emergy flow and material in the process of water pollution endangering human health from the source, and convert different kinds of non-comparable energy involved to the same standard emergy (solar) (Lan et al., 2002). The emergy system of water environmental pollution endangering human health is shown in Figure 1. The increased emergy value of medical measures was the value of using medical equipment and therapeutic drugs, which can be divided into seven parts: medicine, cure (including transfusion, nursing, oxygen delivery, etc.), examination (comprising clinical test and inspection), operation (including operation and anesthesia), bed, diagnosis and treatment, and others. Since it is difficult to objectively estimate the value of each operation in the medical process, it was replaced by the per capita treatment cost of cancer, whereas the medical value of other diseases was replaced by the per capita medical cost. Medical expenses involved were pure personal expenses after deducting the social financial reimbursement. The emergy of labor loss was expressed as the value that patients should create in the labor time delayed by treatment. Cancer patients basically lost their ability to work as they are weak during illness, and needed long-term treatment. Therefore, it was appropriated to take the annual delay time as half a year. While non-cancer patients were in poor condition before and after treatment, hence, 2.5 times of the average annual missed working time was desirable. Loss refers to the loss of a person or a thing as a result of an accident. Both losses in this research were considered as additional expenditures due to drinking contaminated water, which can be regarded as the loss of water pollution to human health. Therefore, the loss emergy of human health caused by water environment pollution can be quantified as: where EM S is the emergy of human health loss caused by water environment pollution, sej; EM Y is the emergy of healthcare capacity per capita for water pollution, sej/person; EM L is the per capita missed work emergy of water environment pollution, sej/person; EM 1 is the per capita healthcare emergy of cancer patients caused by carcinogenic pollutants, sej/person; EM 2 is per capita healthcare capacity of patients with other diseases caused by non-carcinogenic contaminants, sej/person; t L is the transformation ratio of solar emergy of human labor service (adult labor force aged 18-59) using 3.49 Â 10 15 sej/person/year (Lan et al., 2002); T Y is the average missed working time of cancer patients, a; T L is the average missed working time of patients with other diseases, a; and P is the total number of people in the study area, person.

Application and analysis
3.1. Overview of the research area 3.1.1. Current status of water pollution in Kaifeng City. Kaifeng is located in the eastern part of Henan Province, the southern part of downstream the Yellow River, with a total area of 6,444 km 2 . It is between 113°52 0 15 00 -115°15 0 42 00 E and 34°11 0 45 00 -35°0 0 20 00 N, which is 125 km from east to west and 87.5 km from north to south (Cabangon et al., 2003;Cao & Ding, 2005). Besides, there are many rivers in Kaifeng, which belong to the Yellow River basin and Huaihe River basin, respectively. The Yellow River basin occupies a small area, without any obvious sewage discharging into the river; Huaihe River basin is divided into three major water systems: Nansihu, Yinghe, and Wohe. Most rivers in Kaifeng can be categorized as the Wohe system; among them, Huijihe, the largest tributary of the Wohe system, originates in the suburb of Kaifeng and its main stream is 65.9 km in the city. It is an important river integrating flood discharge, urban drainage, irrigation, and other functions, and also the river with the largest pollution carrying capacity in Kaifeng (Zhang, 2012). With the socio-economic development, the water environment in the downstream of Huijihe is deteriorating; thus, the unsafe range of drinking water on both banks is also aggravating, which threatens people's health. It has been decided to comprehensively improve the environment of the Huiji River basin by the government of Henan Province since 2008, and the water quality is getting better recently.
3.1.2. Data source and processing. According to the geographical location and watershed area of the main tributaries of the Huiji River basin (Kaifeng Section), the monthly water quality concentration of five water-quality monitoring sections in the study area from 2010 to 2017 were collected. The data come from the Kaifeng Hydrology and Water Resources Survey Bureau (http://kf.hnssw.com.cn/). There are five water-quality monitoring sections in the Kaifeng development and utilization zone of Huijihe: Sunlitang, 150 m upstream of the pumping station, 1,000 m below Wangtun Bridge, Zhongzhuzhai Bridge, and Dawangmiao Hydrologic Station, the location is shown in Figure 2. According to the statistics of environmental status and water-quality monitoring data in the study area, Cr 6þ , Cd, As, Pb, Cu, Zn, CN À , NH 3 -N, Vp, and F À were selected as evaluation indexes. The annual average concentration was obtained from the average of the 12 monthly measurement data each year. In the case of the absence of measurement or interruption of current in some monthly measured data, the remaining monthly measured data in the year shall be used for calculation. In the process of processing original data from 2010 to 2017 of monitoring sections, ' , DL' was replaced by half of the lowest detection limit for this kind of substance, xx was a certain figure, and ', xx' was expressed as half of xx. If the concentration of pollutant index was not detected in some months, it would be supplemented with the minimum detection limit. The final water-quality monitoring data were sorted out as shown in Table 3.
In the original data, monitoring data of Hg, Cd, Cr 6þ , As, Pb, and Cu were below the minimum detection limit in most cases. The concentration of most pollutants would not cause harm to human health in a short time, which met the requirements of drinking water quality. However, due to the enrichment of food chain, the harm to people's health will show up after a relatively long time (Geng et al., 2016). The concentration of NH 3 -N and F À were higher than the safety limit of drinking water, which requires more attention. Besides, the measured values in several months were relatively high, which might bring harm. For example, the detected concentration of NH 3 -N was greater than 30 mg/L for 10 months and even reached 60 mg/L in January 2011, which may lead to the intestinal diseases as the proliferation of pathogenic microorganisms in the water (Yin et al., 2019;Gao et al., 2020). What's more, F À concentrations in water samples from January to May 2012 were all greater than 1 mg/L, exceeding the safe concentration in drinking water (0.5-1 mg/L), which would lead to the disorder metabolism of Ca and P, thus adversely affecting the skeletal development of teenagers (Fallahzadeh et al., 2017). The highest concentration of volatile phenol reached 0.09 mg/L. If it is relatively high in a short time, people may suffer from dizziness, nausea, anemia, and various neurological diseases. If people are exposed to it for a long time, it may stimulate the spinal cord and promote cancer.

Results and discussion
3.2.1. Risk assessment of human health in Kaifeng City. The carcinogenic risk of pollutants in Kaifeng from 2010 to 2017 was evaluated based on HHRA, the results are shown in Table 4, and the trend is shown in Figure 3. From the table, there was no significant difference in the carcinogenic risk between As and Cr 6þ from 2010 to 2014. However, the cancer risk caused by these two elements had been changing rapidly since 2015, and the proportion of As had been increasing with years. According to the safety restrictions in drinking water, the minimum concentration requirement of As was lower than that of Cr 6þ , but quite to the contrary, the detection concentration of As was higher than that of Cr 6þ . Given that there was once a village in Kaifeng with a large number of cancer patients, it is necessary to strengthen water-quality monitoring to ensure the health and safety of drinking water, especially the control of As in water sources. However, it is shown that the annual risk of cancer from Cd did not change much, and the risk value was lower than that of the other two pollutants, which may be related to the underdeveloped manufacturing industry on both sides of the Huijihe. For one pollutant, when the risk of cancer is less than 1 Â 10 À6 , then the risk of cancer can be ignored, while the risk of cancer is more than 1 Â 10 À4 , it is considered as harmful and the risk of cancer is high (Mohammadi et al., 2019). The carcinogenic annual risk of Kaifeng was between 2.0 Â 10 À5 and 6.5 Â 10 À5 , far lower than the maximum acceptable risk level P (1 Â 10 À4 a À1 ) recommended by the U.S. EPA and ICRA, which was still within the acceptable range. It shows that a series of environmental protection policies in China have achieved remarkable results and water quality has significantly improved, especially the revision of The Law on Prevention and Control of Water Pollution and the implementation of Water pollution prevention and control plan for key river basins. However, the risk of carcinogens still exceeds the limit of 1.0 Â 10 À6 a À1 setting by the Chinese government (Gao et al., 2019). The population in Kaifeng is over a million and the incidence rate of cancer in China is around 3‰ , so it is estimated that there are about 1,500 cancer patients every year. According to the risk assessment, there are about 200 people who have cancer due to water quality per year. The number of cancerous people caused by water pollution accounts for 10-20%, which varies with water quality. Water environment is key consideration to people's health, so it is vital to take effective remedies for water pollution, thus ensuring the safety of the drinking water.
The average monthly concentration of non-carcinogenic pollutants in the monitoring section of Kaifeng development zone of Huijihe from 2010 to 2017 is calculated using Equation (4). Human health risks are shown in Table 5. The maximum and minimum per capita health risks of non-carcinogenic pollutants were in 2016 and 2010, respectively, and the ratio of the maximum to the minimum was  Figure 4 shows that the health risk of different pollutants was significantly different. For example, the health risk of Zn, CN À , and Vp was of the order of 10 À12 , accounting for a very small proportion. However, As, NH 3 -N, and F À have a risk magnitude of 10 À9 , with a contribution rate of more than 75% to the total health risk. Besides, the annual health risk of F À accounted for 41.2% of the total annual risk in 2016, which was the highest single contribution rate; the lowest single contribution rate occurred in 2015, which was the risk of NH 3 -N with a number of 17.6%. There are some reasons for this phenomenon: firstly, both sides of Huijihe are residential gathering places, and there is considerable ammonia nitrogen and fluoride in domestic sewage. Secondly, the centralized processing of domestic sewage in urban areas in China has not yet fully covered, the local residents' opinions varied for domestic sewage treatment, which have been significantly improved after 2016. In a word, non-carcinogenic pollutants may not cause serious diseases in a short time, but the harm they bring to human health still cannot be ignored. Moreover, the key pollutants of non-carcinogenic pollutants are obvious, which is easy to concentrate and should be given high priority to remedy. 3.2.2. Quantitative analysis of health loss of water environmental in Kaifeng City. The health loss caused by water environmental pollution in Kaifeng City from 2010 to 2017 was evaluated using emergy theory and methods, and the results are shown in Table 6. From the table, the annual change of per capita medical emergy value of cancer was not significant and declines generally, with a significant decrease of 24.38% in 2016-2017. While the trend of medical emergy per capita of patients with other diseases was the opposite, increasing year by year. The annual change trend of per capita nursing emergy value was consistent with and greatly affected by that of cancer, while the per-capita cure emergy for other diseases was almost negligible due to its risk order of magnitude. Figure 5 shows that the health risk of carcinogenic pollutants was not completely correlated with the per capita nursing emergy of cancer, the same to the health risks of non-carcinogenic pollutants and the medical nursing emergy of other diseases, influenced by many factors. But medical care emergy and labor losses with same rise and fall in a great measure. As the cure emergy was mainly reflected from the treatment cost, when the emergy monetary ratio was gradually reduced, the emergy had a small change, which indicated the superiority of China's medical security system. As for the basic medical insurance system in urban and rural areas (Liu et al., 2020), it focuses on making overall plans for major diseases and settling indisposition claims, which has been gradually well-developed since was basically achieved in 2010. The government took a series of measures such as lowering the line of deductible, improving the policy of serious illness insurance, increasing the proportion of financial reimbursement, and narrowing the gap of reimbursement ratio between policy and actual. These efforts have greatly reduced the medical burden of urban and rural residents and also avoided the poverty and returning to poverty caused by illness to some extent. The per capita emergy of missed work is related to two factors: health risk and lost time. When the absenteeism time of cancer patients was 0.5 year and other patients' absenteeism time did not change much, water quality plays a leading role, and the trends were consistent with changes in health risks. The ratio of emergy absenteeism emergy value to medical emergy per capita increased from 0.05 to 0.10, which reflected China's efforts in remedying water pollution and bringing down the medicine price. The inter-annual change of human health loss caused by water environment pollution was not large, EDR: the emergy currency ratio of Kaifeng City, which can be calculated in this study; EM 1 : the treatment cost, which can be obtained from different references (Dong et al., 2015;Hung et al., 2016;Bai et al., 2019;Wan, 2019;Yuan et al., 2019); EM 2 : the per capita health cost, which can be obtained from the national statistical yearbook; T L : the average treatment day, which was obtained from the statistical data of various hospitals in the National Statistical Yearbook.
as the maximum value of 8.73 Â 10 18 appeared in 2016, which was 1.86 times of the minimum year in 2010. This may be due to insufficient monitor data, because there were only monitoring data from January to May 2016, during which, there were small surface basic flow, low temperature and selfpurification capacity, resulting from little change in coastal discharge capacity. Therefore, the annual average pollutant concentration and annual health risk were high in 2016, as a result, the other data in 2016 were also large. Combined with the emergy currency ratio, the human health loss of water pollution was about 2.5 million to 9.33 million RMB, which was still a large number. It reminded us that water pollution does great harm to human health, which needs to be pay long-term attention. There is still a long way to go to control water pollution in our country. The overall loss of human increased firstly and then decreased due to the national efforts to protect water resources and the development of Medicare. In general, the value of human health loss is affected by water quality, socio-economic status, Medicare, etc. Among them, the water quality is the inducing factor. In addition, the governance policy was affected by social-economic status, and the public burden and loss value were determined based on the level of medical security.

Comparison and analysis
Human Capital Approach and Medical Expenditure Approach were usually applied to assess the impact of the water environment on human health. Medical cost and emergy theory were combined to obtain the human health loss based on health risk in this study, and human capital was used for comparative analysis. Water pollution has reduced the supply quality of waterworks, which can be improved by a large number of medicament and purification facilities and technology; all are belong to production cost. On the contrary, health level of human beings would be greatly reduced without those costs. To ensure the comparability of results, the loss of human health can be expressed as the volume of water intake and production cost. 1 As shown in Figure 6, the gap of human health loss calculated by the shadow price method and emergy theory was narrowing with years, but the results were still quite different. The former was based on market demand and price changes, with single influencing factors and small inter-annual variation, which cannot truly reflect the impact of water pollution on human health. The latter was based on the current situation of water quality and the degree of social development, and fully considered the possible impact of different pollution levels. Although the result was small, it was more scientific and objective.

Conclusions
It is feasible to further quantify the risk of water environment health risk based on emergy theory and obtain the health loss of urban residents caused by water environment pollution, which is more scientific than the results calculated by economic methods directly. The human health risk of drinking water in Kaifeng from 2010 to 2017 was evaluated with HHRA in this study, and the human health loss 1 According to Notice on adjustment of water supply price in Kaifeng City published by the Development and Reform Commission of Henan Province, the water price in Kaifeng City has been adjusted from 1.10 to 1.50 ¥/m 3 since February 1, 2010, and then adjusted to 1.75 ¥/m 3 after trialing 1 year. Water resources fee of 0.2 ¥/m 3 was added on December 1, 2015. caused by water environmental pollution was quantitatively estimated with the emergy theory. The results showed that the carcinogenic annual risk of carcinogenic pollutants ranged from 2.0 Â 10 À5 to 6.5 Â 10 À5 , without a significant difference; the average health risk of non-carcinogenic pollutants was about 1.5 Â 10 À8 , but the difference between different pollutants was obvious. It is also indicated that the human health loss value of water environmental pollution in Kaifeng City is affected by water quality, social-economic status, Medicare, etc. Among them, the water quality is the direct inducement, socio-economic status is the leading factor, and the public burden is determined by the Medicare, which is the final determinant. Except for the obvious change of the loss in individual years, the overall loss of value has not changed much. The case in point is the value of human health loss ranked at the top in 2016 with 8.73 Â 10 18 sej, equivalent to 9.33 million RMB, while in other years, it was around 6 Â 10 18 sej, which was smaller than the result calculate by shadow pricing. Combining the economy, society, and environment, the impact of water environmental pollution on cities was analyzed from the perspective of human beings with the emergy theory. Through the specific loss of value, the result is more intuitive. It reflects the practical significance of the government to ensure residents' drinking water safety and to improve the Medicare to some extent, which is a bold attempt. Last but not least, it is an arduous task to implement water resources protection and pollution prevention to ensure the safety of drinking water. It requires not only the efforts of the government but also the strength of the public's awareness of water conservation and environment protection, which need to be put into action for a long time.
However, there are still some deficiencies due to data limitations, which can through assessing the emergy value of each medical measure into its input and output after in-depth researches to make the results more reliable. It is desirable and essential to add the risk evaluation of skin contact pathway and food intake pathway to realize the all-around value of water environmental pollution loss in the future.

Funding
This research was funded by the Key Project of the National Natural Science Foundation of China (51739009).

Data availability statement
All data generated or analyzed during this study are included in this published article. All relevant data are included in the paper or its Supplementary Information.