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Increase in Rice Grain Arsenic for Regions of Bangladesh Irrigating Paddies with Elevated Arsenic in Groundwaters

P. N. WILLIAMS
School of Biological Sciences, University of Aberdeen.

M. R. ISLAM
Bangladesh Agricultural University.

E. E. ADOMAKO
School of Biological Sciences, University of Aberdeen.

A. RAAB
Department of Chemistry, University of Aberdeen.

S. A. HOSSAIN
University of Dhaka.

Y. G. ZHU
Chinese Academy of Sciences.

J. FELDMANN
Department of Chemistry, University of Aberdeen.

A. A. MEHARG
School of Biological Sciences, University of Aberdeen.

Abstract/ Executive Summary:

Concern has been raised by Bangladeshi and international scientists about elevated levels of arsenic in Bengali food, particularly in rice grain. This is the first inclusive food market-basket survey from Bangladesh, which addresses the speciation and concentration of arsenic in rice, vegetables, pulses, and spices. Three hundred thirty aman and boro rice, 94 vegetables, and 50 pulse and spice samples were analyzed for total arsenic, using inductivity coupled plasma mass spectrometry (ICP-MS). The districts with the highest mean arsenic rice grain levels were all from southwestern Bangladesh: Faridpur (boro) 0.51 > Satkhira (boro) 0.38 > Satkhira (aman) 0.36 > Chuadanga (boro) 0.32 > Meherpur (boro) 0.29 µg As g^-1. The vast majority of food ingested arsenic in Bangladesh diets was found to be inorganic; with the predominant species detected in Bangladesh rice being arsenite (AsIII) or arsenate (AsV) with dimethyl arsinic acid (DMAV) being a minor component. Vegetables, pulses, and spices are less important to total arsenic intake than water and rice. Predicted inorganic arsenic intake from rice is modeled with the equivalent intake from drinking water for a typical Bangladesh diet. Daily consumption of rice with a total arsenic level of 0.08 µg As g^-1 would be equivalent to a drinking water arsenic level of 10 µg L^-1.

Keywords: Rice Grain Arsenic, Bangladesh, Irrigating Paddies, Elevated Arsenic, Groundwaters

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Arsenic, Water pollution

Objectives:

This is the first inclusive food market-basket survey from Bangladesh that addresses the speciation and concentration of As in rice, vegetables (leafy, fruit, and tuberous), pulses (commonly consumed annual leguminous beans, rich in protein), and spices. What is unique about this rice survey is that samples were obtained from both predominantly contaminated and uncontaminated aquifer regions of Bangladesh, with different groundwater irrigation practices, allowing regional differences in wet (aman) and dry (boro) season rice production to be observed.

Methodology:

Survey. The extensive selection of rice collected included high yielding, locally improved, fine grained speciality, and deep-water varieties. Rice was obtained from both the aman and boro seasons. The survey encompassed regional areas with both high and low average arsenic tubewell waters. To reflect the way in which the Bangladeshi consumer obtains rice, grain was sourced from markets (local and wholesale) and directly from farmers. In each case details of variety and origin were recorded. Every sample collected was intended for direct human food use. Samples of market bought Chinese, Australian, Thai, Philippine, and Indian rice were obtained as a comparison to the Bangladesh samples. Vegetable samples were sourced from farmers’ fields from the districts of Satkhira, Rajshahi, and Comilla. Pulses and spices were collected from farmers’ homes in the Rangpur, Natore, Rajshahi, Pabna, and Mymensingh districts. Sample Preparation. Only the edible portion of the samples was subject to analysis. Rice and pulses, if raw, were dehusked, by hand or in ceramic grinders. The epidermal layer of root vegetables was discarded. Garlic, ginger, and turmeric skins were removed. Samples were washed with distilled water and weighed prior to drying. Vegetable, pulse, and spice samples for total analysis were oven dried at 65 °C for 48 h and then reweighed. Samples for speciation analysis were freeze-dried for 48 h. To assess the water content of the rice 0.5 g subsamples (n)34) chosen to reflect origin and varietal variation were oven dried for 48 h. The average water content of the rice was 10 ( 0.1% (n ) 35), in accord with previous studies (8, 7). All samples were ground using a MM2 ball mill (Retsch, Germany). Chemical Analysis. These were as for ref 8. Full details are given in the Supporting Information Statistics.All statistics were performed using general linear modeling (GLM) ort-tests and conducted using Minitab v.14 (State College, PA). Total As levels in rice data were ranked prior analysis to normalize distribution. Analytical Quality Control Data. Total Digest. The ICPMS detection limit for total As analysis was 0.36 µg As L^-1. Based on a sample weight of 0.1 g the detection limit equates to 0.036 µg As g^-1. The mean total recovery of As from NIST 1568a rice flour reference material was 98 (1.6% (n). Extraction.The ICP-MS detection limit for total As analysis precolumn was 0.009 µg As ^L-1. Postcolumn limits ranged from 0.27 to 0.33 µg As L^-1. The mean recovery of As from NIST 1568a rice flour reference material precolumn was 83 ( 2.4% (n ) 3), while postcolumn it was 82 ( 3.4% (n ) 6), i.e., quantitative chromatographic recovery. Presently no certified rice reference exists for As speciation. The As speciation of NIST 1568a rice flour reference material has been repeatedly characterized and was used to validate our arsenic speciation technique. Our results are in agreement with previously published data.

Source of Information: Environ. Sci. Technol. 2006, 40, 4903-4908

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Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In conclusion, the As detected in vegetables, pulses, and spices was found to be inorganic, contributing to As body burdens, but to a lesser extent than rice due to lower rates of consumption. There is clear evidence that in certain districts in Bangladesh rice is highly elevated in inorganic As, posing a real health risk. The low levels of inorganic As detected in Chinese rice could be important in breeding rice to reduce the dietary exposure associated with rice subsistence diets.

Knowledge Management: Journal