Arsenic and Heavy Metal Pollution of Soil, Water and Sediments in a Semi-Arid Climate Mining Area in Mexico

The environmental impact of arsenic and heavy metals on a 105 km2 area of the historical and recent mining site of Villa de la Paz-Matehuala, San Luis Potosí (Mexico) was evaluated. Results of soil samples reported concentrations between 19–17 384 mg kg-1 As, 15–7200 mg kg-1 Cu, 31–3450 mg kg-1 Pb and 26–6270 mg kg-1 Zn, meanwhile, the concentrations in dry stream sediment samples were found to vary between 29–28 600 mg kg-1 As, 50–2160 mg kg-1 Pb, 71–2190 mg kg-1 Cu, and 98–5940 mg kg-1 Zn. The maximum arsenic concentration in pluvial water storage ponds (265 μg L-1), near the main potential sources of pollution, exceed by 5 times the Mexican drinking water quality guideline (50 μg L-1). The arsenic concentrations in water storage ponds and stream sediments decrease as distance from the potential sources increase. A special case is the `Cerrito Blanco' area located 5 km east of Matehuala, where the highest arsenic concentration in water was found (>5900 μg L-1), exceeding by 100 times the established guideline, thus representing a severe health risk. The results suggest that arsenic and heavy metal dispersion from their pollution sources (historical and active tailings impoundments, waste rock dumps and historical slag piles), is mainly associated in this site with: (1) fluvial transportation of mine waste through streams that cross the area in W–E direction; and (2) aeolian transportation of mineral particles in SW–NE direction. Finally, control measures for pollution routes and remediation measures of the site are proposed.