Space-time variation of arsenic and fluoride in groundwater in the city of Durango, Mexico

In the present study, the spatial and temporal behavior of the levels of arsenic (As) and fluoride (F) in the groundwater of the city of Durango was determined. To do this, a database was integrated, which was analyzed by non-parametric statistical tests and represented by geographic information systems. The database included 455 measurements of As and 473 of F, obtained from annual monitoring results from 2012 to 2016, in 97 wells and 7 tanks that supply water to the city. The analysis of the results shows that the concentrations of As and F exceed the reference values of the maximum limits recommended by the World Health Organization (WHO). 88% of the As determinations are in the range of 20 to 35 mu g/l and 84% of the F measurements are in the range of 3 to 6 mg/l. The analysis of the period 2012-2016, presents an increase in the concentration of As and a statistically significant decrease (p-value < 0.01) in the concentrations of F. The highest concentrations of As and F occurred in the areas: Northeast, southeast and northwest of the city. While the southeast area presented the lowest values of As and F. The temporal and spatial study suggests that the alluvial deposits and the volcanic rocks of the basement as tobas and riolites present in the areas with the highest concentrations of As and F condition the distribution of the levels of these elements in the groundwater. However, local factors such as extraction and evaporation, influence the observed inter annual spatial-temporal variations.