DISCARDED CIGARETTE butts are highly toxic and harmful to marine and freshwater fish.
Just a single butt in one litre of water is enough to kill half of any fish present, according to research published this morning.
Cigarette ends are the most common form of litter.
Every year, 5.6 trillion of them are discarded worldwide, according to research published in Tobacco Control, a publication owned by the British Medical Journal group.
Many are disposed of in landfill, but a large number are simply flicked away, representing a significant litter burden on the environment.
Cigarette waste represents almost a third of the total amount of litter found on US shorelines, according to the authors of the report, Toxicity of Cigarette Butts and their Chemical Components to Marine and Freshwater Fish.
The San Diego State University researchers soaked cigarette butts in fresh and sea water for 24 hours, creating a “stock” that was diluted to six different strengths. Fish were then dropped into this brew and left for four days.
Toxicity is assessed by “LC50” – the lethal concentration needed to kill 50 per cent of a sample of living organisms.
The researchers found that a smoked filter plus tobacco remnant was the most toxic to fish, with just one butt in a litre of water enough to reach the LC50.
A smoked filter with no tobacco attached was also highly toxic, with between two and four butts in a litre enough to kill half the fish trapped in it.
Surprisingly, an unsmoked filter with no tobacco was also bad for fish – with five filters a litre enough to kill half the marine fish and just over 13 butts enough to kill the freshwater fish.
Other tests have shown that cigarette butt leachate can harm other aquatic species including invertebrate organisms, which form an important part of the overall food chain, and marine bacteria.