Industrial cigarettes contain a filter made from cellulose acetate, which forms the "butt" once the cigarette has been smoked. This plastic is absolutely not biodegradable!
It is estimated that a cigarette butt takes up to 15 years to decompose under the action of sunlight.
The used filters also contain all the substances emitted when the tobacco burns. These include nicotine and numerous products that are toxic (arsenic, heavy metals, ethylphenol, etc.) and radioactive (polonium 210). When a cigarette butt ends up in the countryside, these substances are therefore going to contaminate the environment, particularly water, where their impact is seriously harmful to fauna and flora. A single cigarette butt can pollute up to 500 litres of water . Cigarette butts in the environment  are the most significant source of littering worldwide and are an environmental disaster, the effects of which are as yet unknown on biological and human health. So cigarettes butts should always end up in a bin.