It is widely accepted that ingestion of arsenic-contaminated groundwater is the major cause of arsenic poisoning in arsenic-affected areas of the world, including West Bengal in India and Bangladesh. Contamination of groundwater by arsenic in the Deltaic region, particularly in the Gangetic alluvium of Bangladesh and part of West Bengal, has become one of the world's most important natural calamities. The Department of Public Health Engineering first identified arsenic in well-water in Bangladesh in 1993 (1). According to Karim (2), groundwater in the majority of wells in 60 of the 64 districts, covering approximately 118,000 sq km (nearly 80% of the country), has concentrations of arsenic exceeding the World Health Organization's limit of 10 pg/L (3), and only 30% of groundwater contains arsenic at levels below 50 pg/L, the Bangladesh drinking-water standard. Concentrations of arsenic exceeding 1,000 pg/L in shallow tubewells were reported from 17 districts in Bangladesh (4). High levels of arsenic in groundwater occur in the districts of Chandpur, Comilla, Noakhali, Munshiganj, Brahmanbaria, Faridpur, Madaripur, Gopalganj, Shariatpur, and Satkhira. High levels of arsenic have also been found in isolated 'hot-spots' in the southwestern, northwestern, northeastern, and north-central regions of the country (5). The reported number of people exposed to arsenic-contaminated drinking-water, exceeding 50 [micro]g/L, varies significantly. Literature shows that the figures range from 29 million (6) to about 40 million people (7). About 7,500 patients with arsenicosis have been identified in 37 districts (8).
Efforts are being directed towards ensuring safe drinking-water either through mitigation techniques or through finding alternative sources of water. Even if supply of an arsenic-free drinking-water is ensured, arsenic-contaminated groundwater will continue to be used for irrigation purposes, posing a significant risk of this toxic element accumulating in the soil and, consequently, entering into the food-chain through plant uptake and consumption by animals and humans. Thirty to forty percent net cultivable land is under irrigation, and more than 60% of this irrigation is met from groundwater (9); thus, the risk of arsenic-contaminated water being used is high.
During the past 10 years, researchers have mainly focused on ingestion of arsenic through contaminated drinking-water, but the incidence of arsenicosis in the population is not consistent with the concentration of arsenic in drinking-water obtained from groundwater. This inconsistency has raised questions on potential pathways of ingestion of arsenic (10). According to Ahmed (3), while there is a very weak relationship between the number of patients and the average arsenic content in drinking-water at a local level, there is a stronger relationship at the regional level. These findings are consistent with observations of many researchers that people using water from the same source are not equally affected and that people from the same household ingesting water from a common tubewell may not be equally affected (11).
The observed clinical symptoms of arsenic toxicity vary greatly, which poses a considerable challenge in relating the potential pathways of transfer of arsenic from groundwater to human metabolic system through food-chain. Although there may be several other factors involved in the relationship between ingestion of arsenic and epidemiology of arsenicosis, the significance of groundwater-arsenic ingested through the food route is not known. Along with intake of food, it is also possible that incidental ingestion and inhalation of dust containing arsenic may be a significant pathway of exposure (10).
This paper concentrates on arsenic contamination in food-chain through water-soil-crop route. The dietary habit of an individual, especially the nature and the amount of food eaten, might play some role in the arsenic dilemma. The extent of the role of arsenic in food-chain necessitates an in-depth study of bio-magnification of arsenic toxicity through the food-chain. The paper provides data on the contamination of soil through arsenic-contaminated irrigation-water and the subsequent transfer of arsenic via water/soil to crops. The findings are likely to help plan remedial measures to combat arsenic contamination in the food-chain through water-soil-crop transfer.
MATERIALS AND METHODS
For the study, information about contamination of arsenic was obtained from secondary sources (1). Based on the information gathered, selected areas were identified as control (wherein arsenic contamination in groundwater was below the Bangladesh water-quality guideline of 50 [micro]g/L), and as less-affected, moderately-affected, and severely-affected. Water, soil and vegetable/crop samples from 160 sites representing 15 districts were collected (fig. 1 and Table 1).
Water samples (100 mL) from hand-tubewells or irrigation-pumps were collected from mid-stream by initially pumping water for five minutes. Immediately after sampling, one mL of concentrated HCl was added to the 100 mL vials containing water and transported to laboratory for …