Trillions of cigarette butts are littered every year, posing a risk to plant growth, research suggests.
The presence of cigarette butts in the soil reduces the germination success and shoot length of clover by 27% and 28% respectively, a study has found.
Published in the journal Ecotoxicology and Environmental Safety, the results also showed that the root weight was reduced by 57%.
For grass, germination success reduced by 10% and shoot length by 13%, say the team led by academics from Anglia Ruskin University (ARU).
Most cigarette butts contain a filter made of cellulose acetate fibre, a type of a bioplastic.
But filters from unsmoked cigarettes had almost the same effect on plant growth as used filters, indicating that the damage to plants is caused by the filter itself, even without the additional toxins released from the burning of the tobacco.
It is estimated that around 4.5 trillion cigarette butts are littered every year, making them the most pervasive form of plastic pollution on the planet.
As part of this study, the academics sampled locations around the city of Cambridge and found areas with as many as 128 discarded cigarette butts per square metre.
Control experiments contained pieces of wood of identical shape and size as the cigarette butts.
Lead author Dr Dannielle Green, senior lecturer in biology at ARU, said: “Despite being a common sight littering streets and parks worldwide, our study is the first to show the impact of cigarette butts on plants.
“We found they had a detrimental effect on the germination success and shoot length of both grass and clover, and reduced the root weight of clover by over half.
“Ryegrass and white clover, the two species we tested, are important forage crops for livestock as well as being commonly found in urban green spaces.
“These plants support a wealth of biodiversity, even in city parks, and white clover is ecologically important for pollinators and nitrogen fixation.”
She added that the filters can take years, if not decades to break down.
“Dropping cigarette butts seems to be a socially acceptable form of littering and we need to raise awareness that the filters do not disappear and instead can cause serious damage to the environment,” said Dr Green.
Co-author Dr Bas Boots, added: “Although further work is needed, we believe it is the chemical composition of the filter that is causing the damage to plants.
“Most are made from cellulose acetate fibres, and added chemicals which make the plastic more flexible, called plasticisers, may also be leaching out and adversely affecting the early stages of plant development.”