Geogenic Arsenic Contamination in Northwest of Iran; Role of Water Basin Hydrochemistry

Natural Contamination of surface and ground water with arsenic is a widespread problem around the world. The problem is of most concern where contaminated water is used for drinking purposes. Sahand is an important water reservoir in Northwest of Iran which supplies water for drinking and industrial purposes in addition to irrigation of 11000 hectares of agricultural lands.
The hydrochemistry status of Sahand dam basin and arsenic distribution were evaluated by analyzing 308 water samples from surface and ground water resources. Samples were collected based on the standard methods and some information about geological features of basin from site visiting, field investigations, and previous studies.
Elevated concentrations of arsenic (range=0-1440 ppb, mean=171.68 ppb) were detected in water basin and dam. According to the delineating evidences, regional geological background and volcanic activities can be considered to be the main sources of natural genesis of arsenic in water resources of the region.
A manifestation of arsenic sulfide was observed in seams, gaps, and fractures of limestone, marl, sandstone, and an ferruginous conglomerate. Concentrations of arsenic in Sahand reservoir varied seasonally; the maximum concentration of arsenic was observed in autumn and early winter (especially in December). Seasonal fluctuations can be attributed to changes in geochemical conditions of sediments at the bottom of reservoir which requires more studies.