Origin of arsenic in the alluvial aquifer of the Region Lagunera, States of Coahuila and Durango, Mexico

Abstract

This thesis integrates work performed independently by previous investigators concerning the origin, mineralogy, occurrence, epidemiology, speciation and distribution of arsenic in the RegiOn Lagunera alluvial aquifer, northern Mexico. Geochemical modeling and literature data are used to evaluate its speciation, origin, transport, likely exposure pathways and the processes that may be affecting the arsenic species levels. The results show that arsenic is present primarily as arsenate, HAs04 2- . It was probably transported from the areas of volcanic activity located in the upper catchment regions of the rivers and within the Region Lagunera. Adsorptiondesorption of arsenic on ferric hydroxides and evaporation of the surface waters before infiltration are considered to be the main phenomena responsible for the elevated groundwater arsenic concentrations (range of 0.003-0.624 mg/1). Except for the possible dissolution of calcimagnesic arsenates, mineralogic controls appear to have no effect on arsenic solubility while hydrothermal processes may be occurring in isolated areas.