Md. Nazmul Islam ¹, Basudev Kumar Das ¹, Md. Sultanul Islam ², Md. Entazul Huque ¹

Affiliations
1 Department of Chemistry, University of Rajshahi, BD
2 Department of Civil Engineering, Presidency University, Dhaka, BD

Abstract

Background/Objectives: The groundwater of 60 districts out of 64 in Bangladesh was contaminated with arsenic, whose irrigation usage is increasing over last two decades to raise food production. In this context, we studied the effects of pH and different oxidation states of arsenic (As³⁺ and As⁵⁺) in irrigation water and of both inorganic and organic fertilizers on arsenic-accumulation in vegetables. Method/Statistical Analysis: Five vegetable plants were grown with sandy clay loamy soil in pots under open field conditions and irrigated with model water of 10 mg As L-1. The pot experiments were well justified by field trails (n=80) that roughly showed 1:1 correlation. The samples were acid-digested and analyzed by GF-AAS for total concentration of arsenic. The regression equations of the fitted models were cross-checked by analyzing ANOVA, P value, r value and Durbin-Watson statistics. Findings: Prolonged use of irrigation water of pH range 5.00-11.00 for 90 days changed pH of surface soil of 0-3 cm depth from 6.22 to 8.93. The concentration of As in vegetables, [As]_veg, although varied irregularly, was comparatively higher at both lower pH (5.00) and higher pH (10.00) of irrigation water corresponding to soil pH of 6.22 and 8.34 respectively. Arsenic in +3 oxidation state accumulated more in vegetables than that in +5 oxidation state. Comparison showed that urea and TSP increased arsenic content in vegetables by 72.37% and 18.83% respectively, whereas potash and cattle manure decreased that by 14.76% and 51.16% respectively. The reduction of [As]_veg by the cattle manure is probably due to adsorption of As by cellulosic materials and microorganism induced methylation of As in soil, as we found 50.72% organic matter, 30.32% Organic C in cattle manure and about 106 Fecal Coliform bacteria per 100g of cattle manure amended soil. Novelty/Improvements: To our knowledge, this is the first paper that reports the effect of different oxidation states of arsenic (As³⁺ and As⁵⁺) of irrigation water towards arsenicaccumulation in vegetables. Our findings reveal that for As phytoremediation, soil pH should be around 6.80 and application of cattle manure should be highly encouraged, whereas uses of urea and TSP should be controlled. This study highlights the appropriate practices in cultivation process towards safety of human health.

Keywords

Arsenic, Effect, Fertilizer, Oxidation State, Vegetables, pH

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Md. Nazmul Islam ¹, Basudev Kumar Das ¹, Md. Entazul Huque ¹

Affiliations
1 Department of Chemistry, University of Rajshahi, Rajshahi − 6205, BD

Abstract

Background/Objectives: 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 Bangladeshis due to arsenic exposure from consumption of both aboveground and belowground vegetables. Method/Statistical Analysis: 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. We established linear regression equation of fitted model for water–vegetable as concentration (n=54, measured by GF-AAS) relationship. Statistical analyses with r value (0.767), P value (<0.05) of ANOVA table, Durbin-Watson Statistic and Lack-of-Fit test strongly validated the model. Merging British Geological Survey’s groundwater datasets (n=3,534) to the model led to estimation of as contents in vegetables district wise. We followed USEPA Guidelines for Exposure Assessment for evaluation of health risk. Risk, defined as ‘Hazard Quotient’ (HQ), was mapped for three vulnerable population sub-groups: Highly Exposed Child, Average Person and Senior. Findings: The average As concentrations in the vegetables 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. All the Highly Exposed 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. Generally the extent of such health risk is less in northern Bangladesh and more in southern Bangladesh. Application/Improvements: This study explored the extent of non-carcinogenic risk for Children (0-6 years), Adults and seniors of Bangladesh from consumption of both aboveground and belowground vegetables. Since the aquifer groundwater of Bangladesh (also contaminated with Co, Mn, Mo, Rb, Sr, U, etc.) is moving under hydraulic gradient, this study highlights the importance of sight-specific risk assessment considering more pollutant parameters.

Keywords

Arsenic, Bangladesh, Exposure, Groundwater, Risk Assessment, Vegetables

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