The discovery of dangerous levels of arsenic in large numbers of ground water tube wells in West Bengal, India during the early 1990’s, followed closely by even higher levels of arsenic in even greater numbers of wells in Bangladesh in the mid to late1990’s, has raised the specter of a potential environmental disaster in South Asia. The World Health Organization estimates that 40-60 million people are at risk from drinking arsenic-contaminated water in Bangladesh and West Bengal, and that this health risk also may extend into southern Nepal.

The first Nepalese studies on arsenic in groundwater were carried out in 1999 by the Department of Water Supply and Sewerage, and the World Health Organization, and in 2000 by the Nepal Red Cross Society and the Japanese Red Cross Society. Both studies provided evidence of arsenic contamination in Terai region of southern Nepal. Furthermore, an initial health survey in 2001-2002 found evidence of arsenic-related dermatosis and elevated amounts of arsenic in human hair and nail samples in four districts where tube well drinking water contained arsenic above 50 ppb (parts per billion). This initial evidence of arsenic contamination and associated health effects led to the creation of the National Arsenic Steering Committee (NASC) to help coordinate efforts by government and non-government agencies to address the potential problems of arsenic contamination in the rapidly growing region of southern Nepal.

Approximately 500,000 shallow tube wells provide water to about 11 million people, nearly half of the national population, in the agriculturally important Terai region. Ninety percent of the people in the Terai use groundwater as their primary source for drinking water. Providing clean drinking water and developing groundwater resources for agriculture are significant challenges for government and non-government organizations, and the issue of arsenic contamination must now be evaluated by all agencies and organizations that provide drinking water. Nearly all water organizations have been testing wells in their project areas since 2000 by various methods. Nearly 6% of these tube wells in the Terai have been recently tested for arsenic. This report integrates all qualified arsenic test results from these organizations, collected through the summer of 2003, into a national arsenic database, which is provided on the CD-ROM.

The national database in 2003 consists of 18,635 arsenic tested tube wells. Arsenic distribution and summary statistics for each district and VDC (village development committee) are shown on maps and tables, and are included on the CD-ROM. The majority of tube wells, 76.3%, are below the WHO Guideline of 10 ppb. Approximately 7.4% of all tube wells tested higher than the Nepal Interim Standard of 50 ppb of arsenic concentration and 16.3% of tube wells contained 11-50 ppb of arsenic concentration. Thus, 23.7% of tube wells in the Terai are above WHO Guideline. The percentage of wells contaminated above 50 ppb varies at district level from 0% in Dang, Chitwan, and Sunsari to 25.7% in Nawalparasi. Over half of the arsenic-tested tube wells in Rautahat and nearly half of those tested in Nawalparasi contain more than 10 ppb of arsenic. The highest concentrations of arsenic (up to 2,620 ppb) were measured in Devedaha VDC of Rupandehi district, near the border with Nawalparasi.

Most of the tube wells with high arsenic values are less than 50 m deep, and the majority of tube wells deeper than 50 m have arsenic values below 50 ppb. The highest percentage of contaminated wells is found from 11 to 30 m deep. In that depth range 11% of arsenic-tested tube wells were above Nepal Interim Standard; 32% of tube wells were above WHO Guideline; and 68% of the wells tested were below the WHO Guideline. A very low correlation was found between the level of arsenic of a well and the age of the well.

Classes of arsenic vulnerability are defined and presented on maps at the district level based on the percentage of arsenic tested tube wells exceeding the WHO Guideline. Four classes of vulnerability are defined. Low vulnerability to arsenic: VDCs where the percentage of tube wells above WHO guideline is zero (0). In these VDCs, all arsenic tested tube wells contain 0-10 ppb of arsenic. Moderate vulnerability to arsenic: VDCs where 1-25% of tested tube wells exceed the WHO Guideline for arsenic. Moderately high vulnerability to arsenic: VDCs where 26-50% of tested tube wells exceed the WHO Guideline. High vulnerability to arsenic: VDCs where over 50% of arsenic-tested tube wells exceed the WHO Guideline.

Among the 1,050 arsenic-tested VDCs, only 20 VDCs had more than 100 tube wells that were tested for arsenic by 2003. Moreover, there were only five VDCs, in Nawalparasi district, that contained more than 200 arsenic-tested tube wells. Although 60% of VDCs have low vulnerability, nearly 74% of those VDCs have a high uncertainty for that assigned vulnerability level, because of a very low number of wells that were tested in those VDCs. In order to account for VDCs with low levels of arsenic testing, a level of uncertainty was characterized to help describe the confidence that accompanies the level of vulnerability assigned to each VDC. The uncertainty is based on the proportion of household in a VDC that is using a tested tube well.

Among the 20 Terai districts only one district, Rautahat, is characterized with high vulnerability to arsenic. The uncertainty level is also low for this district. This indicates that more than 50% of arsenic tested tube wells were above the WHO Guideline, and that the percentage of households using arsenic tested tube wells is 26-50%. Two districts, Nawalparasi and Kailali, have been classified as having moderately high vulnerability to arsenic; however, their uncertainty levels are different. Nawalparasi has medium uncertainty, and Kailali has high uncertainty. Therefore, although both districts have moderately high vulnerability to arsenic, Nawalparasi district has more arsenic-exposed households than Kailali.

The majority of districts in the Terai have been classified as moderate vulnerability to arsenic. However, the level of uncertainty is different in these districts. Among 16 districts classified with moderate vulnerability to arsenic, 9 districts have high uncertainty, 4 districts have medium uncertainty and 3 districts have low uncertainty. There is only one district, Chitwan, with low vulnerability to arsenic. However, this classification has high uncertainty, because only 1% of total households of the district were using arsenic-tested tube wells.

In terms of population exposed to potential arsenic-related health risks, the 2003 arsenic database indicates that 69,126 people (5.4%) were drinking water above the Nepal Interim standard at the time of testing; 44% of those people live in Nawalparasi district, 21% in Rautahat, and the rest, or 34%, are distributed among the other districts. The population in the Terai estimated to be drinking water that exceeds the WHO Guideline is 272,626 (21.3%). These statistics will likely change in the future, because arsenic testing has not yet taken place in 345 VDCs - 25% of the total VDCs - in the Terai.

For more information, please contact ENPHO office