Probabilistic Risk of Nitrates to Human Health Via Drinking Water: A Case Study of Water Supply for Dandan Station and its Quarters in Mosul, Iraq

Probabilistic risk of nitrates to human health via


Introduction
Freshwater resources, both surface and underground, are vital and indispensable for providing water for drinking, irrigation, and industrial purposes.They account for only 2.5% of the planet's surface water, with a significant portion existing in the form of ice and snow, making it less accessible for human use. 1 In recent decades, the world has witnessed the effects of climate change and declining rainfall, particularly in arid and semi-arid regions like Iraq. 2 Iraq faces a compounded issue as its surface water sources are limited, and the Tigris and Euphrates rivers, along with their tributaries, originate in neighboring countries that control the flow of these rivers.The construction of dams and water storage projects in Turkish territories has led to a significant reduction in the volume of water reaching Iraq, often disregarding international laws concerning shared international waters.In 2004, the combined discharge of the Euphrates and Tigris rivers amounted to 81.5 billion cubic meters, but this decreased to a 38.11 million cubic meters annually in 2005.][5] During dry seasons, the flow of the Tigris river within Iraq significantly decreases due to increased human activities.This surge in water consumption leads to a notable increase in the discharge of municipal, agricultural, and industrial wastewater into the river through numerous estuaries on both sides.This deterioration in water quality raises the likelihood of health risks for consumers who rely on the Tigris River as a source of raw water for water supply stations in Iraq, including Mosul.These risks encompass an elevated presence of bacteria, viruses, parasites, as well as toxic substances such as heavy metals, nitrate ions, Probabilistic risk of nitrates to human health fluorides, among others.
Hence, it is crucial to conduct regular studies and perform periodic checks on water sources and water supply stations to safeguard the health of consumers. 6,7f the most common methods of assessing drinking water in the world for hazardous substances are the approaches proposed by the US Environmental Protection Agency (EPA). 8They are the most important method for estimating the degrees of potential risks of drinking water pollutants such as nitrates and heavy metals.][11] Nitrate ions are naturally prevalent which can enter the human body.Approximately 85% of nitrate intake in humans is attributed to vegetables, while the remaining percentage is obtained from drinking water. 12The quantity of water consumed by individuals varies depending on factors such as age, environment, and seasons.In Mosul city, summer temperatures can increase above 45 °C, leading to increased daily consumption of drinking water.This, in turn, results in a higher intake of nitrates into the digestive system. 13The US EPA 14 has established maximum limits for nitrate levels in drinking water, with a standard of 10 ppm for NO3-N or 50 ppm of NO3.Hence, routine and systematic monitoring of public water supplies, including nitrate ions, is essential.Elevated nitrate levels pose a heightened risk of Blue Baby Syndrome, particularly for infants and the elderly. 15Researches indicate an association between long-term exposure of pregnant women to elevated nitrate concentrations and adverse impacts on both the fetus and newborns 16 , as well as hindering fetal development within the mother's womb and increasing the risk of miscarriage.8][19] Beyond its carcinogenic effects resulting from nitrate reduction when entering the mouth to form nitrite ions, nitrates can potentially interact with amines and amides in the digestive system, leading to the formation of N-nitrosamine compounds (NOCs), as illustrated in the equation 1 20 : most of which have carcinogenic and mutagenic properties, contributing to conditions such as leukemia, stomach, colon, rectal cancers, oral ulcers, and genital issues, as well as increased risks of sudden death, birth defects, and miscarriages in pregnant women. 21,22ortunately, the presence of ascorbic acid, polyphenols, and other compounds in high concentrations in most vegetables serves to inhibit the formation of NOC compounds, providing protection for human health against these serious diseases. 22,23Therefore, this study aimed to estimate both the nitrate ion concentrations and the associated health risks in the drinking water supply of the Dandan water station and its connected neighborhoods on the right side of Mosul city.

The Study Area
The study area is located to the west of Tigris River in the south of Mosul.The station was established in the mid-20th century to provide water to the neighborhoods of Al-Dandan, Jawsaq, Al-Dawas, Al-Nabi Sheet, Al-Sijin, Bab Al-Jadid, Bab Al-Beidh, Al-Akeedat, and others, with a daily production capacity of 45 000 cubic meters.The geology of the study area is characterized by the presence of the Al-Fatha formation containing gypsum (CaSO 4 •2H 2 O), anhydrite (CaSO 4 ), and dissolved evaporation salts in the water.This composition increases the likelihood of erosion and damage to the water supply network pipes, leading to potential contamination of drinking water.4][15][16][17][18][19][20][21][22][23][24] Figure 1 and Table 1 summarize the characteristics of the studied area.

Methodology
In this study, ten sites were chosen for water sample collection, encompassing both untreated raw water from the Tigris River (pre-treatment) and treated water (posttreatment).Additionally, samples were collected from the surrounding residential neighborhoods of the station.This data collection occurred over the period spanning from September 2021 to February 2022, with ten replicates taken at each site.The samples were collected using clean polyethylene bottles from the specified sites after opening the water tap for several minutes before filling the bottles.Then, the samples were placed in a cooler box and away from the light.
The concentration of nitrate ions was determined by ultraviolet spectroscopy method at wavelengths of 220 and 270 nm according to previous studies. 25,26

Calculate the Potential Risks of Nitrates to Human Health
The risks of drinking water were estimated by applying the model indicated by the US EPA.It serves as a valuable and effective tool for evaluating the health risks associated with nitrates for consumers of drinking water.8][29][30] It is as follows (equations 2 and 3): where CDI is chronic daily intake and HI nitrate is equal to HQ.Also, Ci is nitrate concentration for aqueous samples, IR is the daily rate of drinking water (l.day-1), EF is frequency of exposure to nitrates according to age (day and years), ED is nitrate exposure period (years), BW is body weight for each age group (kg), AT is mean time (day), and RfD is reference dose for Nitrate (1.6 mg/kg/d).
These factors are extracted based on previous evidence. 10,31,32

Results and Discussion
The results revealed that the hazard quotient values of the Dandan station are higher in infants compared to other age groups.The values ranged between 0.08561 and 0.10694, as illustrated in Table 2.The increase in the values is due to the high values of CDI, which ranged between (0.13698 -0.17110 mg/kg/d).These values are notably lower than the values reported in a prior study 22 concerning the human health risks associated with nitrates in the water sources of Al-Manara village, located to the north of Mosul city.In that study, the HI and CDI values for infants ranged between 0.4942 to 0.5432 and 0.7907 to 0.8691 mg/kg/d, respectively.However, our findings were relatively similar to those found in another study 15 which investigated the sources of drinking water in the village of Abu Wajna, located to the west of Mosul city.In that study, the values ranged between 0.0466 to 0.1125 for HI and 0.0746 to 0.1800 mg/kg/d for CDI.Similarly, in the age group of > 21 years, there is higher values of CDI among females compared to males.These CDI values for females ranged between 0.07413 to 0.13288 mg/kg/d, resulting in a HQ value of 0.08305.In contrast, the CDI values for males did not surpass 0.05299 in this age group.
In regard to the remaining age groups examined, the HI values ranged from 0.0226 to 0.07180.Notably, the age group (16 to 18) exhibited comparatively lower susceptibility to nitrate-related risks in comparison to other age groups, with the CDI and HI values fluctuating within the range of 0.05245 to 0.09253 mg/kg/d and 0.03278 to 0.05783, respectively.This finding is supported by Al-Bhar and Al-Saffawi's study, 22 which also identified the age group (16-18) years as the least affected by nitrate exposure.In general, the risk quotient values for the age groups were as follows: Infant > )6 to 11( > ( > 21-Females) > (18 to 21) > ( > 21-Males) > (11 to 16) > (16 to18).
Limited research has been conducted in Iraq.Some studies have been conducted by the University of Mosul.Our study's findings show similar results to those reported in previous studies 33 involving water supply stations in the old Al-Yasir, Al-Zohour, Al-Saheroon, and the residential neighborhoods on the left side of Mosul.In this context, the values did not exceed risk quotient values (0.0480, 0.0256, 0.0307) and the CDI of nitrates (0.0768, 0.0441, 0.0492 mg/kg/d).The age group (16 to 18 years) exhibited lower susceptibility to nitrate-related risks compared to the other studied age groups, with consecutive risk quotient  Probabilistic risk of nitrates to human health (HI) values not exceeding (0.0221, 0.0126, 0.0141).
Our findings were similar to the found health risks associated with nitrates in the water sources of Abu Wajna village, located to the northwest of Mosul city, where they reported a range of HI values from 0.125 to 0.0147. 15hese values were notably lower than those reported in Al-Manara village, located to the northeast of Mosul city, in which the risk quotient value was as high as 0.5432. 22verall, the risk quotient values for all studied age groups remained within safe limits as recommended by the US Environmental Protection Agency (HI = HQ ≥ 1.0). 8,15xceeding these recommended limits can lead to severe health implications for consumers. 34,35Research has shown that nitrite and nitrate compounds have the potential to cross the placental barrier within the pregnant mother's womb, affecting fetal health.Furthermore, a strong correlation has been established between elevated nitrate concentrations ( ≥ 10 mg/L) and the risk of premature birth, birth defects, and spontaneous abortion. 16,36Additionally, research has highlighted a significant association between high nitrate levels and certain types of cancer, such as breast cancer in women, as well as cancer of the rectum, bladder, and pancreas, particularly in individuals with diets rich in amines and those who smoke.However, the consumption of fruits and vegetables rich in antioxidants has been found to inhibit the formation of nitrosamine compounds, thereby offering protection against various health risks.The decrease in the values of the CDI of nitrates and the risk quotient (HI) are mainly due to the decrease in the concentration of nitrate ions as shown in Table 3 and Figure 2, which did not exceed the permissible limits for drinking according to international standards. 37he raw water values at Site 1, sourced from the waters of the Tigris River, ranged from 0.696 to 3.601 mg/L, with an average of 2.072 ± 0.887 mg/L.
The increase in concentrations can be attributed to the unprocessed discharge of sewage water from Mosul through numerous estuaries on both sides of the river.These estuaries contain organic materials, which undergo a transformation where microorganisms convert amino acids into ammonium ions through the action of the deaminase enzyme.Subsequently, these ammonium ions are oxidized aerobically to nitrate by Nitrosomonas bacteria in a process known as nitrification, as demonstrated by the equations 4 and 5 38,39 : R -NH 2 Organic matter → NH 4 + + OH - Table 3 and Figure 2 also highlight the notably high nitrate concentrations, particularly at sites (4, 5, 6, 10).This elevation in nitrate levels may be attributed to the contamination of the drinking water supply with sewage and septic tank effluents, potentially resulting from the direct connection of water pumps to the network pipes.Such connections increase the risk of contamination in the event of pipe breaks at connection sites, with concentrations reaching as high as 3.614 mg/L and an average of 2.402 mg/L.A decrease in the pH of the aquatic environment can slow down the nitrification process due to reduced growth and activity of nitrifying bacteria.Because the ideal pH for Nitrosomonas and Enterobacteriaceae ranges from 7.5 to 8.5, most nitrification processes may stop when the pH falls below 6.0.The speed of these reactions is influenced by water temperature, with slower rates observed when the temperature falls below 20 °C or rises above 40 °C.Regarding the studied water temperature displayed in Figure 3, it fluctuated between 15.8 and 16.6 °C, which directly affected the growth and activity of nitrifying bacteria.Additionally, the pH levels remained close to the relatively ideal state. 33hese findings were similar to the study by Al-Hamadany et al, 24 which investigated the water quality of the old Al-Yaser station and its associated neighborhoods, yielding a nitrate concentration of 3.16 mg/L.Additionally, our results are consistent with the nitrate concentration reported by Al-Dulaimi and Younes 40 for the Tigris River, which amounted to 2.78 mg/L.When comparing the nitrate ion concentrations in our study with other regions around the world, it becomes evident that certain water resources exhibit significantly higher concentrations.For example, in the Guanzhong Basin and Xinzhou Basin of China, as well as in the provinces of Mahbubnagar and Nalgonda, nitrate concentrations have been reported to reach as high as 90, 44, 504, 880 mg/L, respectively. 10,29,33enerally, the consumption of nitrates at low concentrations, whether through drinking water or nitrate-rich vegetables, triggers the activation of nitrate ions, converting them into nitrites and subsequently into nitrogen oxide.This process plays a crucial role in the regulation and reduction of systolic blood pressure, contributing to the prevention of various cardiovascular diseases. 41,42nclusions and Recommendations This is one of the few rare studies in Iraq that has examined the potential health risks associated with nitrates.Our findings revealed that the nitrate level in the drinking water supplied to Dandan station was significantly below the global permissible limits.The risk quotient values for nitrates were low for all age groups and below the dangerous levels to human health.We found that the infant group was the most who affected by nitrate, followed by children aged 6-11, while the youth group (18 to 21years) was less affected by the nitrate.As a result, this study recommends the use of the examined water for drinking purposes due to its healthy and safe nitrate ion concentrations.No potential health risks, whether related to cancer or non-cancerous conditions, have been identified.It is further suggested to continue conducting periodic assessments of drinking water supply stations to ensure the ongoing safety of consumers.

Figure 1 .
Figure 1.Satellite Image of the Dandan Water Plant and Residential Quarters (the right side of the Tigris River, south of Mosul city)

Table 1 .
Characteristics of Dandan Water Supply Plant and the Residential Quarters on the Right Side of Mosul City

Table 2 .
Results of chronic daily intake (mg/kg/d) and risk quotient (HI) values of nitrates in drinking water

Table 3 .
The Concentration of Nitrate Ions in the Water Supply of Dandan Station and its Neighborhoods (mg/L) Average Concentration of Nitrate Ions in Water Supply of Dandan Station and its Neighborhoods (mg/L) Figure 3. Water Temperature and pH Values for the Water Supply of Dandan Station and its Neighborhoods