Exposure to mercury in the mine of Almaden

To describe the process for obtaining mercury and the historical exposure of Almadén miners to mercury.

Information on every workplace and historical data on production, technological changes in the productive process and biological and environmental values of mercury was collected. A job-exposure matrix was built with these values and the exposure to inorganic mercury was estimated quantitatively as mug/l of urine mercury. A cumulative exposure index was calculated for every worker by adding the estimates for every year in the different workplaces.

In the mine, the highest exposures occurred during drilling, with values up to 2.26 mg/m3 in air, 2194 microg/l in urine and 374 microg/l in blood. Furnace operation and cleaning were the tasks with the highest values in metallurgy, peaking up to 3.37 mg/m3. The filling of bottles with mercury by free fall gave values within a range of 1.13-2.43 mg/m3 in air; these values dropped to 0.32-0.83 mg/m3 after introducing a new ventilation system. The toxicity effects of high doses of inorganic mercury on the central nervous and urinary systems have been known for decades.

The exposure of the workers in Almadén mines to mercury has been very high. The extremely high content cinnabar ore of the mine explains the increased concentrations of mercury in air at the work places. This, together with inadequate working conditions, explains the high mercury levels found in blood and urine during the study period.