Differences in arsenic, molybdenum, barium, and other physicochemical relationships in groundwater between sites with and without mining activities

Abstract

The characteristic relationships of trace metals and other water quality parameters in a specific region can be affected by anthropogenic activeties. Since the mid-18th century in the southwestern part of the Baja California Peninsula, intermittent gold mining activities have been developed. We analyzed 36 water quality parameters in accordance with the procedures suggested by international agencies to evaluate the impact of this activity and the time of year on the mobilization of trace element levels and their relationships in groundwater. Quantifiable levels of molybdenum help to establish the area influenced by ore deposits because it is one of the three elements in the paragenesis associated to gold. Arsenic in sites closer to ore burning areas was associated with cobalt, indicating the potential presence of a by-product generated from arsenolite; whereas in the non-mineralized area, it was associated with barium, forming a compound that tends to precipitate, thereby maintaining a natural geochemical control in this region. From the sites sampled, 45% exceeded the limit for arsenic (10 μg/l) established by international agencies. During area monitoring with annual precipitation of 207 mm, only seven of 36 parameters analyzed showed significant differences in relation to time of year.