A baseline of natural radionuclides in water and sediment of a pristine coastal ecosystem: The Xcalak and Mahahual coral reef lagoons in the western Caribbean

In ecosystems, natural radionuclides are present in the environment and living organisms. The 238U natural decay chain produces multiple radioactive elements, such as 234U, 226Ra, 210Pb, and 210Po. These radionuclides can be found in air, water, rocks, soil, and other biotic and abiotic components, mainly derived from minerals, such as zircon and apatite. In this study, we determined the activity concentration of radionuclides from the 238U decay chain in the sediment of a coastal ecosystem on the southern Mexican coast in the western Caribbean, an ecosystem minimally affected by industrial activities. Methods included high-resolution gamma-ray spectrometry and alpha-particle spectrometry. Results showed that the sediment samples had an activity concentration range of 18.2–36.6 Bq/kg for 238U, 25.0–41.4 Bq/kg for 234U, 10.1–37.3 Bq/kg for 210Pb, and 29.9–46.0 Bq/kg for 210Po. Water samples ranged between 17.9 and 36.3 mBq/L and 27.9–66.0 mBq/L for 238U and 234U, respectively. The activity concentration of these radionuclides in the sediment and water of this area is compared with that of other coral reefs worldwide, providing a radiometric baseline for comparison purposes. [Display omitted] •Radiometric baseline of 238U natural decay chain in a pristine coastal ecosystem.•18.2–36.6 Bq/kg in coral reef sediment and 17.9–36.3 mBq/L in water for 238U.•Non-secular equilibrium in all 238U decay chain; absence of radium.