The number of face masks ending up discarded as litter has been growing since their use has become largely optional, monitoring organisation Nederland Schoon has said.

The organisation analysed the data of last week’s annual litter clean up day and found the number of discarded face masks had ‘increased significantly’, spokesman Vincent Breedveld told Nu.nl.

Face masks now come in fourth place on the litter list, up from the seventh place last year. The complete list will be published shortly, the organisation said.

Most of the face masks were found in and around bus and train stations. They are no longer compulsive in public transport since Wednesday and, according to rail company NS, few people still wear them.

The relaxation of the rules has led to more face mask litter bugs, Breedveld said, although in many cases this is unintentional.

‘Most people want to take the trouble of throwing them in the bin but in and around stations people are always getting things out of their pockets or bags and the masks fall out,’ he said.

Masks tend to remain in the environment for a long time, Breedveld said ‘People are reluctant to pick them up. It’s not like a sweet wrapper. This is medical waste and people are wary of it. So we are calling on everyone to please leave them where they belong: in the bin.’