Anomalous ratios of radioisotopes in PM₁₀ as tracer of global fallout impact in the centre of Mexico

ABSTRACT

The monitoring and evaluation of radioactive content in samples of PM₁₀ aerosols have been investigated. The specific radioactivity concentrations (SRC) of ²³⁴U, ²³⁵U, ²³⁸U and ²³²Th 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 PM₁₀ were larger than those reported in PM_2.5. 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 ²³⁵U/²³⁸U ratio showed variations with respect to the natural value, while the ²³⁴U/²³⁸U and ²³²Th/²³⁸U 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.

KEYWORDS:

• Aerosols
• dose
• enrichment factor
• ICP-SFMS
• Mexico City
• radioactive nuclides
• radio ecology
• uranium isotope ratio

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors are grateful to the CONACYT-2014, Modality A. Establishment of National Laboratory. Project No. 232762 National Laboratory of Nuclear Forensic Investigations (LANAFONU for its acronym in Spanish), Project ININ/CB-417: CB-417: Development of New Analytical Methods of Forensic Investigation and Nuclear and Project ININ/QU-001: Development and optimization of analytical methods to measure actinides by mass spectrometry and radiometric techniques for financial support. The research was partially funded by grants CONACYT 205317, 232718 and project code IG100313LEMA from the National Autonomous University of Mexico.