Distribution of arsenic in the Chaco salteño, Argentina

E. M. FARFÁN TORRES; PABLO M. NARANJO; I. LOMNICZI; A, BOEMO; L. LORENZO

Centro Atómico Constituyentes, Buenos Aires

Taller; Taller de distribución de As en Ibero-América; 2006

RED CYTED IBEROARSEN:

The wetlands region in the province of Salta, located in the northwest of Argentina, is composed by the AlbardonadaPlain and the Bajos Inundables lowland. Studies carried out in this area between 1980and 1995showed the presence of arsenic in groundwaterfrom shallow (dug, minimum depth of 12 m) to medium-depth (drilled, maximumdepth of 90 m) wells. The contents of arsenic determinedby these studies vary between 0.20 mg rl and 1.50mg rl (Rodríguezet al., 1993).The authors of these studies assessed and detected the presence of individuals showing RCEHA (Regional Chronic Endemic Hydroarsenicism)symptoms(Varillas et al., 1995; Rodríguezet al., 1993). et al., 1993).The authors of these studies assessed and detected the presence of individuals showing RCEHA (Regional Chronic Endemic Hydroarsenicism)symptoms(Varillas et al., 1995; Rodríguezet al., 1993). Thepurpose of this work is to update and extend existing data about the contents of arsenic in groundwater in the Bajos Inundables area of the Chaco Salteño, with particular emphasis on deep wells drilled during the last four years, all of them with depths between 190m and 220 m. Most of  these wells were drilled with the aim of alleviating the growing need for water in the region; they are located almost exclusively at schools, but they are also used as source of supply for nearby house holds. The results, obtained during the dry season in 2006, show that the concentration of arsenic is between0.13 and 0.27 mg r1 for all the sites studied, with the exception of three cases from a total of 24 sampled wells. These waters are also characterized for their alkalinity, with pH values between 8.1 and 9.1, and their high temperatures, between 28°C and 33°C. The analysis of major components shows a high content of Sulphate (concentrations ranging from 300 to 600 mg r1) and bicarbonate; (concentrations ranging from 21 to 140mg rl). However, these concentrations are remarkably lower than those observed in the northem region of the province of La Pampa, with similar geologic characteristics. In addition to these studies, the content of fluorine was also analyzed because it is usually associated with the presence of arsenic in alkaline waters with these hydrogeological characteristics and the inhabitants of the region have typical symptoms ofthe presence of fluorine. The contents found for fluorine vary between 6.6 and 7.0 g L-1.