Arsenic Concentration in Groundwater of Meherpur District, Southwestern Bangladesh: Sources of Arsenic, Quality Evaluation for Irrigation and Health

In Bangladesh, groundwater arsenic poisoning has become one of the biggest concern because of its use for irrigation and domestic purposes. High arsenic concentration in groundwater, soil and crops around the study area are of the greatest environmental concern and a matter of interest about human health. Groundwater, soil and crops samples collected from Bholadanga, Meherpur district, southwestern Bangladesh to measure arsenic concentration and human health risk assessment. pH value of collected groundwater samples range from 7.17 to 8.09 which exhibit lightly acidic nature.The average abundance of major cations is Ca 2+ > Mg 2+ > Na + > K + and among major anions is HCO 3- >Cl - > NO 3- > SO 42- whereas Ca 2+ is the dominant cations and HCO 3- dominant anions. Arsenic as well as other cations and metal like Fe, Mn, Cr, Cd, Pb, Co, Ni and so on were determined for all sorts of samples in order to assess their concentration and possible health hazard with a different statistical approaches. Principal component and cluster analyses suggested significance metal concentration in samples. At the shallow aquifer (50 – 60 m of depth) concentration of arsenic in groundwater varies from 13.1 to 292 µg/L. In groundwater approximately all the trace metals concentration are within the WHO and DOE limit except Mn, As and Fe. So groundwater of the study area are contaminated with arsenic and which is not compatible for drinking as well as irrigation purposes. Piper Tri-linear, Durov and Schoeller Semi Logarithmic diagram have been prepared based on chemical analysis of major cations and anion data and these three diagrams express that groundwater of the study area is Ca-HCO 3 type, where Ca and HCO 3 is the principal cations and anion, respectively. Genetically groundwater collected from the study area is ‘normal chloride water’ based on chloride, ‘normal sulfate water’ based on sulfate and ‘elevated nitrate present’ based on nitrate concentration. Based on SAR, TH, SSP, KR, MH, TH, Na%, PI and PS values, it can be concluded that the groundwater collected from the investigated area is compatible for agricultural activities. Cancer risk, daily ingestion of metal, potential hazard quotient and carcinogenic risk are used to calculate possible health hazard in the study area. Average cancer risk value is 0.0057 from drinking water suggest that people of that area are at high cancer risk according to USEPA.


Introduction
Arsenic is known as one of the most common world environmental toxicants.
Groundwater arsenic poses a significant health anxiety in Asia. Today groundwater resources contaminated with arsenic have been invented in many place of Bangladesh, India, Pakistan, China, Myanmar, Mongolia, Cambodia, Nepal, Thailand, Viet Nam, Chile, Argentina, and USA (Reza et al., 2010;Ng et al., 2003;Smedley and Kinniburgh, 2002;Mandal and Suzuki, 2002). Arsenic contamination is considered a silent killer in all over the globe. The arsenic fatality of Bangladesh has been determined as the greatest inflammation in the history.
Currently, 59 district out of 64 across the country are stricken by arsenic contamination. According as, more than 80 million people are present at risk and 10 thousand people have already displayed the arsenicosis symptoms (Chowdhury, 2001). People exposed to arsenic mostly by drinking water contaminated by arsenic poisoning (Rabbani et al., 2002). The high levels of groundwater arsenic in the GMB (Ganges-Meghna-Brahmaputra) basin are of natural in origin. The two major principle on the fundamental processesare oxidation of arsenic bearing pyrite minerals and the reductive dissolution of iron oxyhydroxides (FeOOH) in together with discharge of As in our environment McArthur et al., 2004;Zheng et al., 2004;Smedley and Kinniburgh, 2002). More proof in favor of dissolution of FeOOH has been acquired in the last couples of years (Ravenscroft et al., 2001). Though oxidation of pyrite minerals due to a lowering groundwater table supposed to be cropped but there still is arguments whether or not groundwater expulsion for irrigation purposes influences arsenic behavior in the shallow aquifer. Organic matter entrance into the shallow aquifer causes dissolution of iron oxyhydroxides (FeOOH) (Harvey et al., 2002). Arsenic is entirely spread as trace elements in aquifer materials and soils in Meherpur district, southwestern Bangladesh.
Long-standing As contamination can cause dangerous health effects together with melanosis (dark and white spots), hyperkeratosis (obdurate skin), cancers, gangrene, lung enlargement, hypertension, Blackfoot disease, diabetes mellitus and ischemic heart disease (Rahman, 2002;Srivastava et al., 2001;Guha-Mazumder et al., 2000;Morales et al., 2000;Lin et al., 1998;Chen et al., 1995).The present research is guided to determine the groundwater quality for ascertaining its excellence for different uses. The main aim of this thesis work is to determine the groundwater quality for drinking, domestic and irrigation purposes and to assess health risk associated with arsenic contamination.

Site description
The study area is located in the Bholadanga village under Sholataka union of Gangni upazila, Meherpur, southwestern Bangladesh. It covers the portion of the southwestern part of Bangladesh and is located in the graphical co-ordinates between 23º51´00´´ to 23º51´15´´north latitudes and in between 88º51´35´´ to 88º51´50´´ east longitudes. It is bounded by Doulatpur upazila on the north, Mirpur upazila in the east, Alomdanga upazila in the south, and Meherpur sadar upazila on the west. This area covers 1.5 sq. km. which covers Bholadanga village area ( fig.   1).

Sampling
Groundwater samples were taken from hand and electric pumps at a depth ranges from 50 m to 70 m located in the Bholadanga village under Gangni upazila in Meherpur, southwestern Bangladesh in April, 2019. Before collecting groundwater samples all pumps and wells were being flushed for five minutes to geta new groundwater earlier to collect samples and stored in a new plastic bottle of 250 ml capacity. Groundwater samples (250 ml of each) were collected in triplicate in three separate plastic bottles consist of airtight caps. Ten samples were acidified with 2-3 drops of concentrated nitric acid (HNO 3 ) during collection for the measurement of trace elements to prevent any unexpected reaction causing precipitation and all the samples were marked and samples were concealed in insulated cooler bearing ice, transported to the laboratory and stored at 4º C. All essential water sampling guidelines were followed during collection of samples.
The physical parameters such as pH, EC, ORP, temperature and TDS were measured in the field. Major cations, anions and trace elements concentrations were measured at Institute of National Analytical Research and Service (INARS), BCSIR, Dhaka, Bangladesh.

Analytical Methods
The pH and Electrical Conductance (EC) of groundwater samples were measured in the field by using a portable pH (Model: pH211, Hanna instrument, Portugal) and EC (Model: Lutron CD-4301) meter. In laboratory TDS measured by portable HACH machine. Oxidation-reduction potential which were carried out using portable ORP meters (Toko Chemicals Laboratories Co. Ltd., Tokyo, Japan).

Quality Control
The analyses were carefully assured in all respects of the thesis work period beginning since samples collection to analyses in the laboratory. For sample preparation, analytical-grade reagents like HNO 3 , HClO 4, H 2 O 2 and deionized water (resistance 18.2 MΩ cm at 25 °C and electrical conductivity 0.2 μS cm -1 ) were used. All experimental glass wares like pipette, volumetric flask were well calibrated and cleaned with HNO 3 overnight and then rinsed with deionized water to reduce any sorts of anomaly during analyses. For samples weighing a calibrated digital electrical balance (GR-200, A&D CompanyLimited, Tokyo, Japan) was used. The instruments were calibrated with the certified reference materials (CRM) (Fluka Analytical, Sigma-Aldrich, Germany) of 1000 ± 4 mg/L stock solution as traceable to the National Institute of Standards and Technology (NIST), USA.
Accuracy and precision were checked with replicate analysis against NIST traceable CRM.

Statistical Analysis
For analytical calculation Microsoft Excel 2013, Aqua Chem and SPSS statistic software (version 20, IBM Corporation, Armonk, New York, USA) were used.

Sodium Adsorption Ratio (SAR)
Sodium adsorption ratio (SAR) is one of the most important factor for realizing suitability of water for agricultural activities. Higher the SAR value less the suitability. Irrigation with high SAR value cause soil degradation.

Soluble sodium percentage (SSP)
Low soluble sodium percentage is good for irrigation or agricultural production. Four classes of SSP (Todd 1980 andWilcox 1955) value were developed.

Magnesium adsorption ratio (MAR)
Magnesium adsorption ratio is believed that one of the most important essential parameter in classifying the irrigation water quality. High amounts of Mg in irrigation water affects soil physical properties. Negative effects on soils observe when Ca: Mg ratio decline below 50.

MH =
Magnesium hazard>50 is not suitable for agricultural activities (Khodapanah et al. 2009). Kelly (1940) and Paliwal (1967) developed another factor to evaluate quality and arrangement of groundwater for agricultural activitiesfounded on the amounts of Na + compared with Ca 2+ and Mg 2+ .

Kelley's Ratio (KR)
KR/KI > 1suggests a high amount of Na + in waters. When groundwater with a KI ≤ 1 has been suitable for agricultural practices, while groundwater contain KI ≥ 1 is not permissible for irrigation due to alkali hazards (Ramesh and Elango 2012;Karanth 1987).

Total Hardness (TH)
Total hardness is measured by the Ca 2+ and Mg 2+ content of water. Though Ca 2+ and Mg 2+ are essential plant nutrients, medium levels of hardness of 100 to 150 mg/L are recommended for plant growth.

Permeability index (PI)
Soil permeability is invaded by long-term irrigation with Na + , Ca 2+ , Mg 2+ and HCO 3contents of the soil. The PI values suggests the propriety of groundwater for irrigation. The values are expressed in meq/l and developed by Doneen (1964).

Potential salinity (PS)
Potential salinity is another irrigation water quality parameter-based index (Doneen 1964) for classified of water for agricultural purposes. Potential salinity is less than 3 meq/l is a sign of the excellence of water for irrigation.

Average Daily Dose (ADD)
To assess health risk, average daily dose (ADD) of arsenic because of the ingestion of arsenic contaminated drinking groundwater was estimated by the Equation

Cancer Risk (CR)
Cancer risk (CR) was calculated by using the formula: Where, CSF is the cancer slope factors (1.5 mg/kg/day) for arsenic in accordance with US-EPA (USEPA, 2005).

Field Measurements
The pH values of collected groundwater samples range from 7.17 to 8.09 (avg. 7.45) which is within permissible limit (6.5 to 8.5) suggested by WHO (1997)

Trace Metals Analyses
Trace metals analyses of groundwater samples shown in Table 2

Graphical Presentation of Analytical Cations and Anion data of Groundwater
Piper's Tri-linear and Durov diagram is a useful tool for arranging hydro-chemical analyses data for identifying the sources of the dissolved constituents in groundwater (Piper, 1953).

Genetic Classifications
Schoeller (1955), Madison and Brunett, (1994) classify water from various points of view like Cl -, SO 4 2-, and NO 3concentrations etc shown in Table 1. These are stated as below: Concentrations of Clin groundwater range from 0.04 to 1.77 meq/L (avg. 0.88 meq/L), which suggests the groundwater is normal chloride water. In the research area the concentrations of SO 4 2in groundwater range from 0.005 to 0.7 meq/L (avg. 0.18 meq/L), which reveal that the groundwater is normal sulfate water. In the study area concentrations of NO 3in groundwater range from 2.9 mg/l to 106.5 mg/l with an average value of 14.6 mg/l which indicates that concentration of nitrate is elevated related to the background value of 3 mg/l.

Assessment of Groundwater quality for drinking and Irrigation purposes
To determine the quality for drinking water and public health, the physical and chemical propertiesof the groundwater were likened with the standard pattern recommended by the World Health Organization (WHO 1997) and Environmental Quality Standard for Bangladesh in following Table 3. From this correlation Table   3, it can be summarized that pH, TDS, Na + , K + , Ca 2+ , Mg 2+ , Cl -,NO 3 2-, SO 4 2-(cations and anions) are within the standard limit which is permisible for domestic and drinking purposes and As, Fe, Mn (trace metals) values exceed the DOE and WHO standard are not suitable for human consumption.
To determine irrigation water quality several indices were calculated (Table 4), which are as follows;

Sodium Adsorption Ratio (SAR):
Sodium adsorption ratio is the measure the degree to which irrigation water tends to enter the cation exchange reaction in soil stated by US salinity laboratory. The SAR value of the research area ranges from 0.59 to 1.13 with an average of 0.87 which are ideal or excellent (SAR<10) in quality for irrigation purposes.

Percent sodium (%Na):
High level of Na + in irrigation water is not suitable for cultivation because Na + causes chemical reaction with soil to decrease water flowing capacity through soil (Ayers and Westcot 1985). The Na percentage

Permeability index (PI):
The permeability of soil is influenced by the regular use of water enriched with Na + , Ca 2+ , Mg 2+ and HCO 3 2ions, the soil is augmented by the utility of irrigation water (Chandu et al. 1995). The PI is a measure competent of water for cultivation. PI values of the research area ranges from 49.85 to 59.07 (avg. 54.64) which recommended suitable for irrigation purposes.

Potential salinity (PS):
Potential salinity is less than 3 meq/l is suitable for safe irrigation. The PS values of the study areas ranges from 0.18 to 1.81 (avg. 0.98) which suggest that PS value is safe for irrigation.

Graphical Representation of Concentrations of As, Fe and Mn with WHO and Bangladesh Domestic Water Quality Standard
In following figures 3, fig. 3(a) arsenic concentrations in all groundwater samples overstep the WHO Guideline for Drinking Water Quality (GDWQ) value (10 µg/L) and two samples out of 10 are within the Bangladesh domestic water quality standard value (50 µg/L). In fig. 3(b), iron concentrations in all groundwater samples exceed WHO (0.3 mg/L) and one sample is within DOE standard (0.3 to 1 mg/L). In fig. 3(c) Manganese concentrations show seven samples exceed the WHO value (0.5 mg/L) and nine samples exceed DOE values of (0.1 mg/L).

Correlation Analyses among Different Chemical Elements of the Groundwater Samples
In the following correlation (figure 4) it is noticed that arsenic is poorly correlated with Fe (R² = 0.0794), Mn (R² = 0.0121) and SO 4 (R² = 0.0401) in fig. 4(a), 4(b) and 4(c), respectively. Sulphate is poorly correlated with Fe (R² = 0.0067) and Mn Poorly to moderate correlations among soluble As, Fe and Mn concentration (As vs. Fe, R² = 0.0794); (As vs. Mn, R² = 0.0121) suggest that reductive dissolution of MnOOH and FeOOH where anaerobic bacteria represents a vital mechanism for arsenic discharge into the groundwater.
The weakly correlations among dissolved As, Fe and SO 4 concentration (As vs. SO 4 , R² = 0.0401); (Fe vs. SO 4 , R² = 0.0067) in groundwater suggest that oxidation of pyrite is not the principal process of arsenic release into groundwater.

Sources of Metals Concentration in Groundwater
Principal component analysis (PCA) was used for identification of contaminant source either of anthropogenic activities or geogenic in origin (Ahsan et al., 2019). which is mainly geogenic in origin. Again, cluster analyses (CA) was accomplished with Ward's methods to classify the metals into various groups and the results exhibitwith a dendrogram (Fig. 6). Four main clusters were identified for water sample with the phenon line set to a rescaled distance of about 10 to show statistical similarity. Cluster 1 for water sample included Mg, Ca, Na and K which showed positive accumulation on PCA-1 similarly cluster 2, cluster 3 and cluster 4 include Fe, Mn, Zn; Cd, Pb; and As which showed the similar positive loading on PCA-2, PCA-3 and PCA-4, respectively.

Human Health Hazard Assessment from Drinking Water
The human health hazard assessment model developed by United States Environmental Protection Agency (USEPA, 1998) was utilized to calculate the noxious impacts of arsenic contamination in drinking water on people. The average daily dose (ADD), hazard quotient (HQ) and cancer risk (CR) from arsenic exposure are considered for this purposes shown in table 6. The health hazard measurement was performed by calculating the possibility of individuals being exposed to contamination of arsenic from drinking water.

Results of ADD, HQ and CR from Drinking Water
Here we considered the maximum, minimum and average concentration of arsenic for groundwater. Water arsenic concentration in the study area shows normal value of average daily dose in accordance with FAO and WHO acceptable daily dose of arsenic is 100 µg/L. But HQ value greater than 1 indicate that people of the study area were at highly carcinogenic hazard. The enumerated cancer risk (CR) values were greater than that of the United States Environmental Protection Agency (USEPA) limit (10 -6 ) which revealing that the people in vicinity of the area were at high carcinogenic hazard. So that, the regular monitoring of arsenic level in groundwater is necessary in order to measure if any potential health hazard from consumptions of arsenic rich water exist, thereby protecting every single person from drinking of arsenic contaminated water that might be poisonous to their health.

Conclusion
The pH value of the groundwater samples collected from Bholadanga, Meherpur, southwestern Bangladesh is 7.17 to 8.09 which suggests normal fresh to minor alkaline water. Electrical conductance of groundwater sample range from 571 to 1056 µS/cm which are excellent for irrigation purposes and classified as non-saline in taste. Average temperature ranges from 24.3 to 25.1 º C. TDS value ranges from 283 to 519 mg/L indicate palatability of water is good and which is safe for drinking purposes.The cations analysis (Na, K, Ca, Mg) of the groundwater sample collected from the study area revealed that values of those elements are normal in ranges and safe for drinking and as well as domestic purposes. Anions analysis (Cl,NO 3 and SO 4 ) show that all the sample from within the permissible limit except one sample which exceeds World Health Organization (WHO) and Department of Environment (DoE) standard for Nitrate.Groundwater quality of the study area by comparison with WHO and DoE standards shows that the trace element Fe,As and Mn exceed the WHO and DoE standard. It strongly indicate that groundwater sample from Bholadanga village area is affected by arsenic contamination and which is not suitable not only for drinking purposes but also irrigation and other domestic uses.All of these three diagram Piper Tri-linear, Durov and Schoeller Semi Logarithmic express that groundwater of the study area is Ca-HCO 3 type, where Ca and HCO 3 is the dominant cations and anion, respectively. Genetically groundwater collected from Bholadanga, Meherpur, Southwestern Bangladesh area is 'normal chloride water' based on chloride, 'normal sulfate water' based on sulfate and 'elevated nitrate present' based on nitrate concentration. Arsenic concentration in groundwater in shallow aquifer (50 to 60 m depth) range from 13.1 to 292 µg/L in Bholadanga, Meherpur, southwestern Bangladesh showed that groundwater of the research area is highly toxic to human health. Poorly to moderately correlations among dissolved As, Fe and Mn concentration (As vs. Fe, R² = 0.0794); (As vs. Mn, R² = 0.0121) suggest that reductive dissolution of MnOOH and FeOOH where anaerobic bacteria represents a vital mechanism for arsenic releasing into the groundwater. The poor correlations among dissolved As, Fe and SO 4 concentration (As vs. SO 4 , R² = 0.0401); (Fe vs. SO 4 , R² = 0.0067) in groundwater indicate that sulfide/pyrite is not the principal process of arsenic release into groundwater. Principal component and cluster analysis indicate that arsenic in groundwater source are of geogenic in origin.Based on pH, TDS, Ca 2+ , Mg 2+ , Na + , K + , Cl -, NO 3 2-, SO 4 2-(cations and anions) are within the standard limit which is suitable for domestic and drinking purposes and As, Fe, Mn (trace metal) values exceed the DOE and WHO standard are not suitable for human consumption. After calculate total hardness, SAR, SSP, KR, MH, TH, Na%, PI and PS values, it can be concluded that the groundwater of the research area is good for irrigation purpose. The maximum (0.0105) and minimum (0.00047) cancer risk value got over the United States Environmental Protection Agency (USEPA) limit of 10 -6 which strongly indicate that the people in the Bholadanga village were at extremely carcinogenic risk. Figure 1 Location map of the study area Piper diagram 2(a), Durov diagram 2(b) and Schoeller Semi Logarithmic diagram 2(c) of groundwater samples Figure 3 Contamination levels in the groundwater samples, 5 (a) As, 5 (b) Fe and 5 (c) Mn collected from the study area.