Anomalous ratios of radioisotopes in PM as tracer of global fallout impact in the centre of Mexico.

The monitoring and evaluation of radioactive content in samples of PM aerosols have been investigated. The specific radioactivity concentrations (SRC) of U, U, U and Th were determined using inductively coupled plasma-sector field mass spectrometry in 13 samples collected in Mexico City and 8 samples collected in Cuernavaca in the centre of Mexico. The SRC of the radioisotopes analysed in PM were larger than those reported in PM. The enrichment factor was greater than 5, indicating anthropogenic influences in both sites. The activity ratios of these isotopes in the samples were determined. The U/U ratio showed variations with respect to the natural value, while the U/U and Th/U ratios did not show any secular equilibrium in all sites, corroborating that the increase of uranium is not influenced by natural sources. The annual dose results obtained have no impact on health.