Health Risk Assessment for Bangladeshis due to Arsenic Exposure from Consumption of Vegetables Grown with Natural Arsenic Contaminated Groundwater

In the context of increasing uses of Arsenic contaminated groundwater for irrigation in Bangladesh and observed health related problems, we evaluated potential health risk for Bangladesh is due to As exposure from consumption of vegetables. Eight vegetable plants (Amaranth, Arum, Carrot, Eggplant, Indian Spinach, Okra, Potato and Radish) were grown in open field and irrigated with natural As contaminated water (0.005-0.903 mg L-1) for 80-90 days. The average As concentrations in the vegetables, measured by GF-AAS, were 0.431, 0.719, 0.928, 1.574 and 2.287 mg kg-1 (ww.) corresponding to irrigation water As concentrations of 0.005 (control), 0.044, 0.103, 0.507 and 0.903 mg L-1 respectively. We established linear regression equation of fitted model for water-vegetable As concentration (n=54) relationship (r=0.767 and P<0.05). Statistical analyses with r value, P value of ANOVA table, Durbin-Watson Statistic and Lack-of-Fit test strongly validated the model. Merging British Geological Survey’s (BGS) groundwater datasets (n=3534) for Bangladesh to the model led to estimation of As concentrations in vegetables district-wise. We followed USEPA Guidelines for Exposure Assessment for evaluation of human health risk. Risk, defined as ‘Hazard Quotient’ (HQ), was mapped for three vulnerable population sub-groups: Highly Exposed Child, Average Person and Senior. The results showed that all the children (0-6 years) were at health risk, whereas 98% of seniors and 76% of average persons (i.e., adults) were safe in consuming vegetables. The eight administrative division-wise HQ values for average persons were as follows: Rangpur (0.760)<Rajshahi (0.775)<Mymensingh (0.805)<Barisal (0.815)<Sylhet (0.820)<Khulna (0.990)<Dhaka (0.996)<Chittagong (1.147). The worst affected district was Chandpur. The findings explored the extent of As health risk for children (0-6 years), adults and seniors of Bangladesh precisely from vegetable consumption. This study highlights the importance of sight-specific risk assessment considering more pollutant parameters.

flask. After adding 10 mL of 69% HNO 3 , the flask was swirled to moisten the entire mass of the tissue and was placed on a steam plate for 30 minutes. It was then placed on the electric hot plate at 180 0 C. The suspension was boiled nearly to dryness. This pre-digestion with HNO 3 required about 45 minutes.
The digestion flask and the contents were cooled slightly. Then 10 mL of the ternary acid mixture (prepared by mixing 69% HNO 3 , 98% H 2 SO 4 and 60% HClO 4 in the volume ratio of 10 : 1: 4) was added. The digestion was carried out on the electric hot plate at 220 0 C until dense white fumes of H 2 SO 4 and HClO 4 were vigorously evolved. The digestion was stopped when the residues in the flask were clear and white and only slightly moist with H 2 SO 4 . The HClO 4 , at that point, had been largely removed. This digestion with ternary acid mixture required about 2 hours.
The digestion flask and the contents were cooled and 10 mL of 82% HCl was added. The flask was swirled and the digestate was collected in a 100-mL measuring flask. After rinsing the flask with small amounts of 6N HCl, it was washed twice with distilled, deionized water and diluted to make a final volume of 100 mL.

C. Digestion of Soil Samples:
Digestion of soil samples were carried out by modified method of Small and McCants with oxidizing acids such as the H 2 SO 4 -HClO 4 acid mixture [2][3]5].
Accurately 0.5 ± 0.005 g of the soil sample was heated in a 250-mL Erlenmeyer flask until fuming with 2 mL of 98% H 2 SO 4 . When the organic matter had been destroyed and the soil assumed a gray color, the flask was cooled and 3 mL of 70% HClO 4 were added with a few boiling chips. The mixture was boiled on an electric hot plate at 220 O C for about 2 hours. Heating was discontinued when the soil was near to dryness.
The digestion flask and the contents were cooled and 10 mL of 82% HCl was added. The flask was swirled and the digestate was collected in a 100-mL measuring flask. After rinsing the flask with small amounts of 6N HCl, it was washed twice with distilled, deionized water and diluted to make a final volume of 100 mL.  The temperature programs of GF-AAS for analysis of concentrations of arsenic are tabulated in the following Table (S2).

Element
Step

Analyses of Groundwater Samples:
The physical and chemical properties of the five natural groundwater used for irrigation purpose are mentioned in the following Table. The distribution of the eight metals concentrations in five groundwater samples that were employed for irrigation purposes is presented in the following Box-and-Whisker plots. Since Ca 2+ and Mg 2+ ions are the two principal contributor of water hardness, their higher values roughly indicate that the groundwater used in our study are hard.
The elevated level of Fe and Mn concentrations is a consequence of predominance of reducing conditions in the aquifers, that facilitates reductive dissolution of both iron and manganese oxides. All the wells except for one have As T concentrations exceeding the WHO limit recommended for drinking. The higher concentration of arsenic is probably due to the development of strongly-reducing conditions of aquifer, which is supported by our observed low values of redox potential.

Analyses of Cultivated Soil:
The studied soil of the field was under an agro-ecological zone of the Ganges Fluvial