Assessment of environmental radioactivity in the City of Melilla

There is a significant scarcity of environmental radiological data from the 19 Spanish territories in the North Africa and along the southern Alboran Sea coast. This paper presents the results of environmental radioactivity campaigns conducted between 2010 and 2025 in Melilla to produce a terrestrial gamma radiation map and analyse the distribution of natural radioisotopes (226Ra, 232Th and 40K) and 137Cs in soils. Mean activity concentrations are 22 Bq kg⁻¹ for 226Ra, 24 Bq kg⁻¹ for 232Th, and 305 Bq kg⁻¹ for 40K, all below global medians and Spanish averages. Using these data, a dose model was applied to generate a dose map of the territory. The estimated annual effective dose of 0.23 mSv y⁻¹ is also below the global average, indicating no radiological concern for the population. Due to Melilla’s border location and proximity to the Strait of Gibraltar, a characterization of its beaches was performed to establish a baseline for potential external contamination. Several indices established by international regulatory agencies were calculated to quantify radiological risk in outdoor and indoor environments. Finally, a radon potential exposure map was developed to identify areas where buildings could exceed the 300 Bq m⁻³ reference level set by the Building Technical Code in accordance with Council Directive 2013/59/Euratom