The association of arsenic exposure with mortality due to cancer, diabetes, Alzheimer's and congenital anomalies using Poisson regression

The present study aims to determine the relationship between the concentration of arsenic in the groundwater of Hamadan province and the mortality rate due to various types of malignancies, congenital anomalies, diabetes mellitus and Alzheimer's. Mortality data due to various causes of death in Hamadan province were collected for five years (2016–2020). Sampling of drinking water was determined in the reference laboratory using polarography method. Poisson regression was used to investigate the relationship between arsenic level and the death rate due to various types of disease, at a significant level (p value < 0.05). According to the results of Poisson regression, among the various causes of death (N = 8042), Alzheimer's 5.94 (3.67–9.61), diabetes mellitus 4.05 (3.5–5.37), congenital malformations 2.98 (1.88–4.72), breast cancer 2.72 (1.56–4.71), leukemia 1.90 (1.24–2.92), stomach cancer 1.64 (1.28–2.10), Liver cancer 1.58 (1.58–2.30), other digestive organs 5.86 (3.38–10.16), meninges and brain cancer 1.57 (1.02–2.41) showed the highest relationship with arsenic contamination. The results of this study could be evidence for a positive and significant relationship between arsenic concentrations and mortality rates due to cancers, diabetes mellitus, Alzheimer disease, and congenital malformations. Therefore, it's necessary to use appropriate water treatment methods to remove arsenic at the source in contaminated areas.

on human health have led to the classification of arsenic as a class I human carcinogen by the International Agency for Research on Cancer (IARC) 5 .The continuous use of groundwater contaminated with this element for drinking and irrigation has led to numerous health manifestations in the human body, which is generally called arsenicosis.These complications include intestinal, kidney, lung and bladder disorders, skin effects and cancer in different organs.Arsenic toxicity also causes neurological dysfunction, cardiovascular disease, and immunerelated disorders 6 .Arsenic consumption through water and food can cause reproductive problems in women and men, and it's also associated with childbirth issues such as stillbirth, abortion and premature birth.Reports show that children in areas with high arsenic contamination, have a higher risk of malnutrition, severe weight loss 7 .Based on the results of the analysis of water samples of Hamadan province, the groundwater of some areas, especially in Kabudarahang, is contaminated with arsenic.Considering the known effects of exposure to arsenic through drinking water, the present study aims to determine the relationship between the As concentration in the groundwater and the death rate due to malignancies, diabetes mellitus and congenital anomalies, Alzheimer's in the contaminated areas compared to other regions.

Results
The highest contamination of groundwater is reported in the rural areas of Kabudarahang with a maximum concentration of 190 µg per liter.In some areas of Malayer, Nahavand and Kabudahang, the concentration of arsenic was 2 to 18 times higher than the maximum residue limit (MRL).Table 1 and Fig. 1 give summary statistics and box plot for arsenic concentration in the nine areas, respectively.
Table 2 represents the death rate (per 100,000 people) due to various types of cancer, congenital anomalies, diabetes and Alzheimer's for each county during 2016 to 2020.According to the findings in the villages of Kabudarahang, the highest death rate during 2016-2020 related to diabetes mellitus, stomach cancer, bronchus and lung cancer, Alzheimer's, leukemia, brain and meninges cancer, and congenital anomalies, respectively.

Discussion
The results of arsenic concentration in the groundwater of the studied area.Based on the results, the highest level of arsenic contamination has been observed in the rural areas of Kabudarahang, which is located in the northwest of Hamadan province and adjacent to Kurdistan and Zanjan provinces.According to the studies, the origin of arsenic contamination in these areas is geological and geogenic activities.Chemical weathering of high altitudes such as volcanic and metamorphic rocks usually leads to the production of iron oxide.This weathering also causes the release of arsenic, which is absorbed on iron oxide or precipitates.An increase in pH in the area can cause the release of arsenic from iron oxide 8 .Arsenic competes with other ligands in groundwater for absorption on the surface of aquifer materials.Ligands that are usually found in high concentrations in groundwater (such as silicates, carbonates and organic acids) significantly reduce arsenic absorption 9 .In the studies conducted in the past on the groundwater of some regions of Iran, including the northwest of Iran (West Azerbaijan, East Azerbaijan, Kurdistan), the concentration of arsenic has been reported to exceed the standard limit 10,11 .In a study by Keshavarzi et al. 11 in Kurdistan province, the range of arsenic The relationship between mortality and arsenic concentration in groundwater.The findings of the present study showed that there is a positive and significant relationship between arsenic concentration and mortality due to cancers of the breast, meningeal and brain, stomach, liver, other digestive organ, and leukemia.In previous studies, there has been an association between arsenic in drinking water and mortality due to various cancers, which is consistent finding with the results of the present study.For example, in a meta-analysis study by Wang et al., a significant association between long-term exposure to arsenic and liver cancer mortality was observed (SMR, 1.84; 1.45-2.24).The final results of that study were obtained based on the analysis of 12 ecological and cohort articles conducted in Asia and South America 20 .A systematic review study by Khanjani et al., was conducted on the relationship between breast cancer and arsenic, in which seven studies were selected at the end, and a positive and significant association between arsenic and breast cancer was observed in four studies, while in the other three studies such a relationship was not seen.The reason for the difference in the results can be due to individual and regional differences 21 .The results of a study by Chen et al., in Taiwan showed a significant positive correlation between leukemia and arsenic in village well waters and arsenic concentration )SMR, 1.42; 1-1.84) 22 .A cross-sectional study in Bengal showed that long-term exposure to arsenic in people drinking contaminated water increased lymphocyte levels by 3.5 times compared to the control group of individuals 23 .On the other hand, in a study by Lin et al., a negative relationship was observed between the incidence of leukemia and arsenic levels in men and women 24 .In another study conducted in Chile, although a significant relationship was observed mortality due to liver cancer and arsenic, no significant relationship between was observed, no significant relationship was observed with arsenic level regarding mortality due to leukemia and brain cancer 25 .Compared to other cancers, fewer studies have investigated the relationship between arsenic and cancers of the stomach and other digestive organs have been investigated compared to other cancers.In a study conducted in southern Taiwan, the SMR for cancers of the stomach, colon, liver, bone, skin, and bladder was significantly higher in men and women who lived in the contaminated area than those in the non-contaminated area 26 .Vol:.( 1234567890) www.nature.com/scientificreports/ In the present study, a significant relationship was found between arsenic exposure and mortality due to Alzheimer's disease.Convincing evidence suggests that arsenic causes such as neurotoxicity and impairment of memory and cognition.In addition, arsenic can cause pathological processes including mitochondrial disorders, oxidative stress, inflammation, apoptosis, abnormal calcium signaling, and disruption of protein homeostasis.However, the hypothesis and molecular mechanisms of arsenic-related pathology in Alzheimer are still unclear 5 .In an ecological study by Li et al. 27 , the association between exposures to contaminated soil and the death rate due to Alzheimer was investigated, and the relative risk (RR) and Spearman's correlation coefficient were www.nature.com/scientificreports/calculated using based on10-year Alzheimer's mortality data.Based on the results, in the areas where the average concentrations of arsenic were 9.05, 10.4, and 13.1 μg/L, relative risks were calculated and found to be 4.3 (CI 4.3-4.39),6.1 (CI 6.04-6.17),and 9.1 (CI 9.03-9.2),respectively 27 .
In the present study, a significant relationship between arsenic and there was a significant relationship between arsenic exposure and mortality due to congenital anomalies.Previous reports have shown that long term exposure to arsenic through drinking water may cause reproductive problems in women and men and is associated with various issues related to childbirth, such as stillbirth, miscarriage, premature birth, and the congenital abnormalities 7 .In a study by Marie et al. in France, 5263 children who were exposed to high concentration of arsenic in drinking water were assessed, and a positive and significant association was found between exposures to As concentration greater than 10 μg/L and the risk of congenital malformation (OR 2.41; CI 1.36-4.14) 28.In another study, Ahmad et al. investigated the relationship between maternal exposure to arsenic through drinking water and the rate of miscarriage and as well as infant death.Based on the results, the risks of mortality as a combination of abortion and infant death for each unit of logarithmic increase of arsenic concentration equal corresponded to 1.35 (CI1.69,1.08) for weeks 25 to 28 and 0.81 (CI1.02,0.65) respectively, for weeks 9-12 29 .
In the present study, deaths due to diabetes mellitus showed a significant relationship with high levels of arsenic in contaminated areas.Previous animal studies and human evidences support a potential role of early-life exposure to arsenic in the development of diabetes, possibly by increasing insulin resistance 30 .In an ecological study by Mahram et al., in Qazvin province, the prevalence of type 1 diabetes and hypertension were investigated in two cities with different arsenic concentrations, in the range of 20-30 µg/L and less than 5 µg/L.Based on the results, there was a significant correlation between arsenic concentration and prevalence of diabetes and hypertension (p < 0.001), and the average prevalence of hypertension in relatively high contaminated and areas with lower contamination was obtained as 7.09% and 3.73%, and for diabetes was 53.4% and 1.99%, respectively 31 .In a community-based study in Canada (where diabetes rates continue to climb), the incidence rate of type 1 diabetes in the age group (0-14) was 51.7 per 100,000 people, and a significant relationship was observed between the incidence of type 1 diabetes and concentration of arsenic and fluoride with the having correlation coefficient (β = 0.268, p < 0.013,) and (β = 0.202, p < 0.005) respectively 32 .In another study by Marie et al., in  France, the relationship between exposure to arsenic in drinking water and the risk of Gestational Diabetes was investigated in an ecological study, while the prevalence of gestational diabetes during the years 2003, 2006 and 2010 was analyzed using multivariate logistic regression.According to the findings, 5.7% of 5053 participants had gestational diabetes, and adjusted odds of developing gestational diabetes for women lived in the contaminated area (> 10 μg/L), were significantly higher than those who lived in the area with less than 10 μg/L (OR:1.62,CI 1.01-2.53) 33.
According to the results of Poisson Regression, the death rate due to most of the cancers (including oesophagus, breast, bronchus and lung, uteri, colon, gallbladder, kidney, myeloma, ovary, pancreas, prostate, small intestine, other digestive organs, bladder, leukemia, liver, lymphoma, brain), Alzheimer's Disease, diabetes mellitus 2, and congenital anomalies in urban regions were significantly higher than rural regions (p < 0.05).
Industrialization causes the transfer of the most important cause of death from infectious diseases and nutritional deficiency to chronic diseases (e.g., cancer and diabetes).According to the evidence, urbanization not only shows a direct effect on people's lifestyles and behavior but also affects the level of physical activity of people.Sedentary lifestyles and being inactive increase the risk of cancers, such as colon, breast, and prostate 34 .In addition, the highest smoking prevalence is among the socioeconomic groups and in urban areas that makes the higher lung cancer incidence in an urban population.Furthermore, air pollution is another factor in the development of lung cancer in urban areas 35 .On the other hand, based on the previous studies, there was a significant relationship between smoking, diabetes type2, obesity, over-weight and, physical inactivity, depression, hypercholesterolemia, hypertension and Alzheimer's disease 36 .
The current findings complement a study by Zahnd et al. 37 that showed combined cancers incidence rates were generally higher in urban populations.For individual cancers, urban regions had higher rates of prostate, breast (female), and thyroid cancers.However, cancer rates associated with modifiable risks-HPV, tobacco, and some preventive screening modalities (e.g., cervical cancers and colorectal) were higher in rural compared with urban populations 37 .
This study has two limitations; First, as mentioned earlier, there are several types of arsenic, including As5 + , As3 + , MMA, and DMA that adversely affects human health, however, in the present study, the concentration of different types of arsenic has not been determined separately.Second, some disruptive factors such as obesity, diet, physical activity, smoking, and genetic factors, which can contribute to disease risk, haven't been assessed in this study.Identifying cancer risk factors plays an important role in preventing and controlling them in each region.In this regard, it is suggested that further studies be designed to consider all confounding factors and assess health effects of the different type of arsenic species.
The results of this study could be evidence for a strong positive association of arsenic in drinking water and mortality rate due to cancers of the breast, liver, stomach, meninges and brain, congenital anomalies, diabetes and Alzheimer's disease.Considering various health complications resulting from the consumption of arseniccontaminated water, it's vital to determine the amount of arsenic in water sources before implementing any water supply program, and use appropriate water purification methods to remove arsenic of water resources, or use of alternative water sources.

Materials and methods
The places in the study include; Asadabad, Bahar, Famenin, Hamadan, Malayer, Nahavand, Razan, Tuyserkan, and Kabudarahang, which are nine parts of Hamadan province.Hamadan Province, situated between latitudes 33º59′ N and 35º48′ N and longitudes 47º34′ E and 49º36′ E, covering an area of approximately 19,546 km 2 (as shown in Fig. 2), and its population is around 1,738,234 population 38 .The climate of Hamadan is typically arid or semi-arid and characterized by long, cold winters and mild summers.The average temperatures in the hottest month (July) and the coldest month (January) are 25 °C and − 2 °C, respectively.The average annual precipitation is 360.3 mm, and its wettest month is April (with 47.9 mm).More than 90 percent of the water in this area is used for agricultural purpose.Farming is the basic occupation of the rural regions, with major crops, including cereals, fodder crops, potatoes and sugar beets.The socio-demographic information of study population (N = 8042) is shown in Table 5.In this study, the data include two datasets: 1. the data of death rate due to various types of malignancies (based on ICD Codes), diabetes mellitus, Alzheimer's and congenital anomalies, 2. The data of arsenic concentration.All data and information were obtained from Vice-chancellor for Health of Hamadan University of Medical Sciences over a period of five years (2016-2020).
The analysis of arsenic concentration in water samples was carried out by the experts of the Vice-chancellor for Health as follows: The water samples were collected in clean polyethylene bottles, and labelled for easy identification.The samples were filtered through a 0.45 µm membrane filter immediately after collection.Then, they were transferred to the reference laboratory at the shortest possible time, under cold chain conditions.The samples were refrigerated and stored at 4 °C until the measurement was taken.The pH of the samples was stabilized in the range of 0.2 ± 0.2 by nitric acid 39 .The analysis of the samples was performed using a Metrohm 797 VA Computrace Voltammograph (Metrohm, Switzerland) equipped with a voltammetric cell 40 .
All data were collected and cleanup in an Excel form.The data was determined using Stata software, and appropriate analytical statistical methods.Poisson regression was used to investigate the relationship between arsenic level and the death rate (per 100,000 population) due to various types of disease in Kabudarahang compared to the other cities of the Hamadan province.Using goodness of fit tests, the best model was selected for estimating the arsenic effect.All the tests were performed at the 95% confidence level.

Figure 1 .
Figure 1.Box plots of arsenic concentration in the nine areas of Hamadan province.

Table 1 .
Summary statistics of concentration of arsenic for each county.

Table 2 .
The death rate (per 100,000 people) due to various types of disease for each county during 2016 to 2020.

Table 3 .
Evaluation of relation between concentration of arsenic and death rate due to various disease using Poisson regression.*Incidence rate ratio, computed for Kabudarahang in comparison of the other eight cities.

Table 4 .
Comparison of death rate due to various disease in rural and urban using Poisson regression.*Incidence rate ratio, computed for rural in comparison of urban.