An investigation on Norfolk beaches found seal pups lying next to potentially toxic microplastics known as nurdles.
More than 3,000 seal pups were born at Blakeney National Nature Reserve this winter and at nearby Horsey a record 2,000 pups were born.
But a field trip last month by staff from conservation organisation, Fauna & Flora International (FFI) revealed hundreds of nurdles littering beaches near some of the pups' favourite spots.
Blakeney and the Horsey Dunes are listed as Special Areas of Conservation under the European Habitats Directive but this protected status has failed to keep them safe from plastic pollution.
Nurdles are tiny plastic pellets that are produced and melted together by the plastics industry to create new plastic products. Spilt and discarded by companies in their billions, about 53 billion nurdles end up in the oceans every year.
Seals are known to ingest microplastics, most likely by eating prey that has itself consumed microplastics. Scientific studies also suggest that nurdles may transport chemical contaminants into the bodies of marine animals that eat them.
Dilyana Mihaylova, marine plastics projects manager at Fauna & Flora International, said: 'All companies that make, use and transport nurdles must take action to stop these microplastics polluting Britain's beaches and damaging critical habitats for our iconic seal colonies. The plastics industry needs to implement robust measures across its entire supply chain to stop nurdle pollution.'
The findings come ahead of the Great Global Nurdle Hunt which starts on Friday, February 8 and is organised by environmental charity Fidra, one of FFI's partners in Scotland. The nine day event sees volunteers scour beaches around the world for nurdles. Last year a search of 279 sites in the UK found nurdles on 73pc of them.
Jasper Hamlet, project officer at Fidra, said: 'This February (8 to 17) we are inviting people to take part, collect essential data on pellet pollution worldwide and put pressure on the global plastic industry to ensure pellets are handled responsibly throughout the supply chain. It is easy and fun for people to take part in, but provides valuable information to help create positive change.'
Victoria Egan, general manager for the National Trust on the North Norfolk coast, said: 'Thankfully our grey seal population at Blakeney appears to be thriving with record numbers of seal pups this year.
'Our ranger teams and volunteers keep a close eye on rubbish on our beaches, and on the seals themselves, and we do what we can to rid our beaches of rubbish through regular beach cleans, as well as part of our everyday work on the coast.
'We recognise that the small plastic nurdles are a real threat to all marine life, not just seals, and we are supportive of anything that can be done to lessen their usage; providing they aren't replaced by anything more harmful to marine life; and of any actions to remove these from our seas and oceans in an environmentally friendly manner.'
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