Scientists are surprised by the radiation levels in a Spanish city.

After 15 years of monitoring, Melilla, a Spanish city on the coast of North Africa, was found to have lower levels of natural radiation than both the Spanish and global norms.

The city's danger map is redrawn as a result, with one volcanic corner serving as the exception that explains the entire situation. One pattern persisted in Melilla throughout 47 on-site dosage measurements and 27 soil samples.

Jesús García Rubiano, a physicist at the University of Las Palmas de Gran Canaria (ULPGC), used that evidence to track the calmest readings northward. More uranium, thorium, and potassium are naturally found in volcanic rocks near the airport and southwest boundary, where higher amounts are concentrated.

While highlighting the minor areas where additional testing is important, the north-south contrast kept the citywide average low.

Radiation in the soil of Melilla

The scientists measured radioisotopes, which are unstable atomic forms that emit radiation when they decay, in the soil itself. For every 2.2 pounds of soil, the average concentrations were 22, 24, and 305 decays per second.

The ground generally released less natural radiation than anticipated because these soil levels were below both Spanish averages and global medians. Nevertheless, the soil totals explain why Melilla's overall image remained remarkably calm, even though they do not eliminate local hot spots.

Why rocks are important

Stronger readings and quieter neighbourhoods were separated by two types of earth beneath Melilla. Because they contain fewer heavy elements that support natural decay cycles, carbonate and river-laid sediments typically hold lesser levels.

Values increased due to volcanic deposits in the southwest, particularly where potassium-rich volcanic rock grows close to the airport. The reason one end of the city has somewhat higher radiation readings than the other is due to geology, not an unnoticed coincidence.

Fallout traces

One of the most obvious hints came from cesium-137, a radioactive trace left by previous fallout, rather than from any local rock at all. It was more prevalent in northern forested land, probably because less erosion and digging allowed those particles to stay in place.

Lead-210, a second tracer, rose close to fuel depots and industrial regions and followed a similar trend. Fallout markings are more important as a fingerprint of how material is moved by wind, soil loss, and human activity than as a health warning.

Melilla beaches establish a baseline for radiation

Readings from cosmic rays decreased near the background around Melilla's beaches, providing researchers with a clear coastal baseline. Because diverse mineral mixtures might be carried by imported sand and leftover landfill material, certain constructed stretches are still different.

In a port city close to the Strait of Gibraltar, where high ship traffic and local industries complicate future contamination concerns, baseline work is crucial. Having a baseline allowed ULPGC researchers to identify subsequent spikes rather than including them into regular coastal variation.

Dose over a period of years

The team discovered a low average outdoor exposure even after converting soil data into gamma radiation, which are high-energy photons released during atomic decay. Volcanic spots increased to 172 nanograys per hour, although measurements at 47 sites yielded a mean terrestrial dose rate of 47.

Melilla's lifetime cancer risk remained below global averages, and the estimated yearly effective dose was 0.23 millisieverts. Because of these low averages, the survey reads more like a recommendation to where more thorough checks should be made than an alarm.

Radon trails the earth.

The more pressing issue indoors is radon, a radioactive gas that may build up inside structures after seeping upward from the soil. The indoor radon reference, according to a European directive, is 300 decays per second in around 35 cubic feet of air.

About 2,787 buildings in Melilla were in the monitoring zones, with 70.5 percent of the city falling into the lowest category. Although this divide indicates where testing should begin, it does not demonstrate significant indoor levels.

What's missing from the map

These kinds of maps are useful, but they don't measure the real amount of air that a single household breathes in a space. Even on the same street, indoor buildup can be increased or decreased by ventilation, cracked floors, construction design, and everyday activities.

Radon decay particles can harm DNA in airway cells when inhaled, which is why the gas is important for reasons other than geology. According to health officials, smokers are 25 times more likely to develop lung cancer due to radon exposure.

The significance of melilla radiation

A reliable radiation map is more than just a curiosity for a small community sandwiched between the sea, border crossings, and older buildings. Melilla had some of the lowest natural radiation levels in Spain, according to local reports years before this research was published.

Soil, air, and construction materials all contain natural radiation, which is a permanent background element of the environment. Inspectors, planners, and locals can now concentrate on the southwest with the use of a comprehensive map.

Melilla shows low average ambient radiation and sharply local geology-driven exceptions after 15 years of sampling. The next stage is straightforward: take measurements inside the hot regions in the southwest, update the beach baseline, and follow the ULPGC survey's recommendations.