Economic and geographical isolation from the rest of the Iberian Peninsula has shielded Gibraltar from environmental pollution, according to research.
The first survey of soil geochemistry in the British independent territory revealed relatively low levels of toxins compared with similar sized settlements elsewhere, despite being one of the most densely populated areas in the world. Gibraltar has 33,000 permanent residents who are joined by 4 million tourists a year.
The research, led by Liesl Mesilio, a Gibraltarian PhD student at Imperial College London, gives Gibraltar a particularly clean bill of health in the year it celebrates 300 years of British rule.
"The fact that it was isolated for many years meant everything had to be brought to Gibraltar by sea, so we have not needed to develop any heavy industry that would increase elemental concentrations," she said.
She added that as there was no space to bury waste in landfill sites, it had been incinerated - though in recent years it had been shipped to Spain.
Ms Mesilio took 246 soil samples from across the 6.5km2 territory, from domestic back gardens to former Ministry of Defence sites and the surface of Gibraltar's famous limestone rock.
Each was studied at Imperial using spectroscopy to detect levels of 26 elements that could reveal patterns of contamination.
In addition, dust samples were collected from 83 households and further samples were taken from two species of plant growing throughout the territory.
The analysis revealed patterns of element distribution that were lower than other towns and cities investigated by the Imperial scientists. There were some signatures left by sand-blasting activities at the naval dockyard and from Gibraltar's waste incinerator, as well as a pattern of element distribution influenced by the underlying geology. But no hotspots of pollution emerged.
Iain Thornton, professor of environmental geochemistry at Imperial, said:
"Despite the fact that we have an enclosed environment, military occupation for many years and very high traffic density, we were pleased that there weren't concentrations of elements that were causes for concern for either the environment or the people."