Natural radionuclides baseline in soil at unconventional oil fields in Mexico

Activity concentration of 238 U and 232Th and their decay products are assessed in soil at three hydrocarbon zones to determine the baseline before further fracking studies. The range of activity concentration for the three zones was 238U (from 9.2 ± 0.5 to 115.8 ± 7.5) Bq kg-1, 228Ra (from 8.3 ± 2.0 to 50.0 ± 4.4) Bq kg-1 and 226Ra (from 24.1 ± 2.3 to 86.8 ± 4.7) Bq kg-1; which are comparable to the global average values reported by UNSCEAR in soil. Similar activity-concentration patterns for 238U decay series and 232Th decay series for the three zones indicate no previous industrial action. This baseline is useful to assess a possible enrichment of Naturally Occurring Radioactive Materials if industrial activities take place in the future.