Groundwater_Arsenic_Contamination_in_Pakistan

Groundwater Arsenic contamination in Pakistan Hydrogeochemical studies and evaluation of field kit method for screening of arsenic in Southern Punjab Abstract Arsenic (As) has been recognized as a serious threat in many parts of south Asia, particularly in India, Bangladesh, Vietnam and China. In Pakistan, danger of As in groundwater has been recognized recently and since then, Pakistan Council of Research in Water Resources (PCRWR) and Pakistan Council of Scientific and Industrial Research (PCSIR) in collaboration with UNICEF launched different programs which include studies on overall groundwater quality and detection of As in groundwater. National Water Quality Monitoring Program (NWQMP) was launched in 2001 and Arsenic Mitigation Program was launched in 2002. The study deals with the critical analyses of the data obtained under As mitigation program to check the reliability of the field kits used for the screening of As in the districts of southern the data obtained under NWQMP and studies the groundwater quality of the two districts of southern Punjab viz. Bahawalpur and Multan. Three types of field kits were used for screening of As in the study area; Arsenic Quick, Wagtech and Merck fiel kit. Since field kit is the only tool which allows screening of As in groundwater while keeping within available financial resources and time period, therefore, reliability of the results obtained by the field kits must be checked comparing the results with laboratory analyses. Out of 2395 samples from the study area which were analyzed in the laboratory for cross validation, only 23% of the samples were detected correctly for As level above 50 μg/l (true positive results), however, on the other hand, 94% were detected correctly having As concentration level within the Pakistan drinking water standard level of 50 μg/l (true negative) which indicates good performance of field kits at this level and poses no threat from public health point of view. Results obtained against the threshold value setup by WHO (10 μg/l) revealed that almost 39% samples were detected correctly for As concentration greater than 10 μg/l and 86% samples were detected correctly for having As concentration within WHO guideline value. Considerable discrepancies were found in the determination of As at different As concentration categories, particularly, for the categories of 10-24 and 25-49 for As concentration level of 10 μg/l, results are misclassified and need to be rechecked. For 50 μg/l, As concentration categories of 50-99 and >100 are misclassified. The relative poor performance of the field kits even using the latest versions of the field kits could be due to the low prevalence of As i.e. 6% and 24% for 50 μg/l and 10 μg/l levels respectively. The risk of misclassification of As by the field kits can be reduced through proper training of field staff, proper usage of the field kits and using different other options to verify field kit results on site. Depth of samples ranges from 6.1m to 10.7m and 9.1m to 18.2m in Multan and Bahawalpur respectively which comes in the category of shallow groundwater. Reductive dissolution of ferric oxyhydroxides (FeOOH) could probably be the possible mechanism for As contamination in shallow groundwater of these cities as increase in the pollutant organics in urban areas promotes this mechanism and as a result As is sorbed into groundwater aquifers. However, in rural areas, which are not effected by such pollution, groundwaters have low levels of As as revealed by the data analyses of Arsenic Mitigation Program which shows that the prevalence of As above 50 μg/l is only 2.85% in rural areas as compared to that of 34% in urban areas. Key words: Arsenic, prevalence, groundwater, field test kit, National Water Quality Monitoring Program, Arsenic Mitigation Program, Pakistan