Soaring numbers of tourists and expanding research projects are increasingly polluting Antarctica, scientists warned Wednesday, a fresh blow for one of Earth's most pristine environments already threatened by human-driven climate change.

In Antarctic areas where humans have been active, the concentration of fine particles containing heavy metals is 10 times higher than it was 40 years ago, the international team of researchers said in a new study.

That change has come as the number of annual tourists visiting the white continent has risen from 20,000 to 120,000 over the last two decades, according to the International Association of Antarctica Tour Operators.

"The increasing human presence in Antarctica raises concerns about pollutants from fossil fuel combustion, including those from s

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