Distribution and sources of arsenic contaminated groundwater in parts of Thatta district,Sindh

Problem of natural arsenic (as) in groundwater is of growing concern to the health of people worldwide because of its carcinogenic properties. arsenic contamination in groundwater affects the indus alluvial and deltaic plains in punjab and sindh including thatta district,where people are suffering from arsenic ingested diseases. groundwater samples were collected from deltaic areas of ghulamullah and gujjo in thatta district,where large section of population depends on groundwater for drinking and irrigation purpose. these water samples were analyzed to determine their arsenic contents,physicochemical and microbiological characteristics. arsenic concentrations in groundwaters of ghullamullah and gujjo are in the range of 10-200 μg/l and 10-20 μg/l respectively. most of as contaminated wells have also been found sewage impacted,which may be due to reducing conditions in the aquifers created by microbial degradation which favor as mobilization into groundwater. to determine the mobilization mechanism and source of arsenic,11 soil samples were also collected from near the well sites and analyzed for their mineralogical and elemental composition using xrd and aas techniques. average concentrations of as in the soil of ghulamullah and gujjo areas are 73 and 65 μg/kg respectively. higher as concentrations in ghulamullah groundwater are due to dominance of clayey soil and presence of arsenic rich minerals particularly muscovite and phloghopite than in gujjo area. the data reveal that the dominant hydrofacies in the study area are na-cl type indicating the impact of recent or ancient sea water intrusion. arsenic distribution in shallow aquifers of thatta district is patchy and seems to be controlled by degradation of organic matter by natural and anthropogenic sources. © 2014 national centre of excellence in geology. all rights reserved.