Radioactivity Levels and Heavy Metal Concentration in Mining Areas of the State of Zacatecas, Mexico

The State of Zacatecas (Mexico) is one of the places most affected by pollution from the mining industry. 21 samples from two areas have been collected (6 samples from zone A and 15 samples from zone B) to evaluate the level of radioactivity and the degree of contamination by heavy metals. The activity concentration for 238U and 232Th is within typical values, but 226Ra exceeds the value of 60 Bq kg-1 in both areas. In some places, the concentration of 40K is higher than the world average, according to UNSCEAR. The radium equivalent activity Raeq and outdoor gamma exposure dose (D) indicate that some sites present a radiological risk for the population. Excess lifetime cancer risk (ELCR) presents a higher risk than the world average in both sampled areas. Other parameters, such as the radiation index Ri, the external risk index Hex, and the internal risk index Hin, also indicate that there is a greater risk due to radiation exposure in these areas. In the case of heavy metals, some parameters, such as the enrichment factor (EF), the geoaccumulation index (Igeo), and the contamination factor (CF), show that some places in zone A and zone B are contaminated with As and Pb. However, the concentration of selenium obtained by ICP-MS in the sampled soil is higher than the average in the Earth's crust, both in mine waste dumps and in unaltered soil, which indicates that the background concentration for selenium in these places is higher than the world average.