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

The state of Zacatecas (Mexico) is one of the places most affected by pollution from the mining industry. A total of 21 samples from two areas were collected (6 samples from zone A and 15 samples from zone B) to evaluate the level of radioactivity and the degree of contamination with heavy metals. The activity concentration for ²³⁸U and ²³²Th was within typical values but that of ²²⁶Ra exceeded the value of 60 Bq kg^-1 in both areas. In some places, the concentration of ⁴⁰K was higher than the world average according to UNSCEAR. The radium equivalent activity Ra_eq and outdoor gamma exposure dose (D) indicated that some sites presented a radiological risk for the population. The excess lifetime cancer risk (ELCR) presented a higher risk than the world average in both sampled areas. Other parameters, such as the radiation index R_i, the external risk index H_ex, and the internal risk index H_in, also indicated that there was a greater risk due to radiation exposure in these areas. In the case of heavy metals, some parameters, such as the EF, the I_geo, and the CF, showed that some places in zone A and zone B were contaminated with As and Pb. However, the concentration of selenium obtained by ICP-MS in the sampled soil was higher than the average in the Earth's crust, both in mine waste dumps and in unaltered soil, which indicated that the background concentration for selenium in these places is higher than the world average.