Disposable face masks could be releasing chemical pollutants and nano-plastics into the environment, researchers have warned.
Scientists said there needed to be better regulation and more research carried out.
The Swansea University team found heavy metals and plastic fibres were released when throw-away masks were submerged in water.
The researchers said the public health impact needed more investigation.
"Before the pandemic, we were looking at reducing the use of plastic straws, reducing packaging, but now we are looking at hundreds and thousands of these masks being disposed," said the project leader, Dr Sarper Sarp, of the university's College of Engineering.
"We need to sort our priorities - first of all we need to get over the pandemic and protect each other and the public health. Then, in the meantime, we need to take steps to protect the environment."
Back in November last year, the researchers were only originally interested in the plastic waste impact on our environment.
But as they tested more and more masks, they uncovered more chemicals.
The pollutants were often linked to dyes used in producing the masks, mostly made in southern Asia, and China in particular.
The team found traces of lead, antimony and cadmium - all heavy metals which can be toxic in low doses.
They said the levels found were in the range of parts per million or parts per billion.
"On an environmental scale with the amount of production of these things - it all accumulates," warned Dr Geraint Sullivan, technology transfer fellow at the university.
He said the heavy metals found were also "bio-accumulative", which means they are not removed from aquatic systems and they build up over time.
Every mask tested leached chemicals when submerged.
"That's what's quite shocking really - even though they are at such trace levels, the amount of material being produced out there is going to have an effect on the wider environment," added Dr Sullivan.
Project leader Dr Sarp, who is also a member of the Welsh government's Covid technical advisory group of scientists, said there was much more work to be done on the face masks.
"It might not be a big issue now but accumulation is a problem we will face in the future," he said.
"The benefits of wearing the masks are huge, so we need to keep wearing them, but we need to be looking at different regulations and standardisation of the masks and the quality of the materials we use.
"We need to look at how they are produced, how we can test these, and how to standardise their quality."
Dr Sarp said with that information, they would be able to educate and inform the public about the masks, and ensure they are safer for individuals and the environment.