Content and distribution of arsenic in soils, sediments and groundwater environments of the southern Pampa region, Argentina.

The health of a large rural population in the southern Pampa (Argentina) is at risk owing to newly detected areas where As-groundwater exceeds 0.01 mg/L standard (WHO (1995) Guidelines for drinking water quality, 2nd edition. pp 43-45). Currently, devitrification of volcanic glass is invoked to interpret the origin of arsenic in the aquifers hosted in a sequence of pampean loess (Plio-Pleistocene) juxtaposed with postpampean loess (Holocene). Our data suggest that arsenic is not specifically associated with volcanic glass and that other minerals contribute to As-release into groundwater. The goals were (1) to understand As-groundwater spatial variability, (2) to explore soils/sediments/water relationships and to identify the probable As-provenance. Comparable As concentrations of the light and the heavy sand fractions suggest that though detrital glass is a major light constituent, other existing primary minerals are As-bearers that contribute to As-release into groundwater. Grouping of materials according to their As-content indicated spatial variability in the sedimentary distribution pattern leading to differences in the frequencies of occurrence of As-bearing minerals. Phreatic waters were Ca + Mg bicarbonate and devoid of As in the intake areas (Ventania System) and Na-carbonate but As-rich towards the discharge (Atlantic coast and local depressions). As-groundwater reflects a patchy distribution within the pampean landscape. A correspondence between As-high groundwater, EC >1 dSm, CO(3)H(-), alkaline pH and a longer water residence time do exist triggering As extraction from the loess sand fraction and desorption from charged fine particles which lead to As-toxicity towards groundwater discharge.

Mapping of arsenic content and distribution in groundwater in the southeast Pampa, Argentina.

The presence and spatial distribution of groundwater arsenic was evaluated in an area of approximately 6000 square kilometers that extends along the southeast border of the subhumid pampa plains of southeast Buenos Aires Province, Argentina. Groundwater constitutes the only easily exploitable source of water for the large rural and suburban population in the area, both for human consumption and for use in agricultural and livestock production. In the study area, 56.3 percent of water samples had seriously elevated arsenic levels (0.06 to 0.5 milligrams per liter [mg/L]), constituting a risk for human consumption and agricultural and livestock use. In 27.2 percent of the samples, arsenic content ranged from just below the World Health Organization-recommended maximum level of 0.01 mg/L to 0.05 mg/L. Only in 16.5 percent of the samples did the water contain no or very low concentrations. The contamination of domestic water supplies in the study area constitutes a serious water quality problem since this element has been identified as the cause of a number of health problems, including cancer.

Fluoride contamination of aquifers in the southeast subhumid pampa, Argentina.

A diagnostic survey was carried out of the groundwater in the southeast subhumid pampa of Argentina in order to determine the presence, spatial distribution, and concentration of fluoride. The area studied extends along the southeastern border of the pampa plains between latitude 38 degrees 18' and 38 degrees 58' S and longitude 60 degrees 43' and 61 degrees 43' W, covering an irregular surface area of approximately 6000 km2. The region has a large rural and suburban population that relies on this groundwater as its principal source of water for human consumption and for use in agricultural and livestock production. The variation in fluoride content in the groundwater is illustrated on maps of the area, showing that the whole region is affected by this ion contaminant. In 97.1% of the samples fluoride values exceeded the limits recommended by the Argentine Food Code for human consumption and indicated that the use of the water in livestock should be restricted. The quality of the water for irrigation purposes also was seriously affected. Critically affected zones were identified with a view to implementing public health measures to protect against this highly contaminated resource.