Environmental groups are warning that discarded single-use face masks used to prevent the spread of coronavirus could harm the environment.

Single-use face masks are appearing on beaches and nature trails in Hong Kong after the semi-autonomous city’s 7.4 million people have been using them every day, Reuters reported.

Environmental groups have found the masks in the countryside or the sea, damaging the environment. Marine life in particular can suffer by mistaking the masks for food like they do with other trash. The masks, made of polypropylene, will not break down easily.

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These activists have said the masks have intensified the pollution problem occurring off mainland China.

Gary Stokes, the founder of the environmental group Oceans Asia, said he found 70 discarded masks within 100 meters of the beach and an additional 30 masks when he returned a week later, Reuters reported.

“We only have had masks for the last six to eight weeks, in a massive volume ... we are now seeing the effect on the environment,” he told the news outlet.

Experts also raised concerns about the hygienic issues surrounding the piles of masks, Laurence McCook, the head of the Oceans Conservation at the World Wildlife Fund in Hong Kong, said.

“Nobody wants to go to the forest and find masks littered everywhere or used masks on the beaches. It is unhygienic and dangerous,” he said, Reuters reported.

The city has already struggled with recycling with 70 percent of the city’s waste every year going to a landfill, according to Reuters.

Surgeon General Jerome Adams cautioned Americans to stop buying medical masks for protection earlier this month saying they are not effective and were needed by medical professionals in close contact with patients.