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 (238)U and (232)Th was within typical values but that of (226)Ra exceeded the value of 60 Bq kg(-1) in both areas. In some places, the concentration of (40)K 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.