What happens to a cigarette butt after 10 years?

We all know that abandoning a cigarette butt on the street or in the ground is an environmentally harmful act. However, until recently, relatively little was known about what really happens to this small waste in the long run. New research coordinated by Professor Giuliano Bonanomi‘s group in the Department of Agriculture has finally provided a scientific answer to this question.

The study represents the first ten-year-scale empirical analysis ever conducted on this topic. For ten years, the researchers monitored the chemical, microbiological and toxicological transformations of cigarette butts in soil, observing step by step how this waste behaves over time. The results, published in the international scientific journal Environmental Pollution, offer elements of great interest in better understanding the environmental impact of one of the world’s most common wastes.

One of the most significant findings concerns the persistence of filters. Many people think that, over the years, butts degrade completely in the soil. In fact, the study shows that this is not the case. Cigarette filters are composed mainly of cellulose acetate, a plastic material that does not readily biodegrade. Even after ten years, the researchers observed that the filter does not disappear, but gradually fragments. The fibers turn into tiny spheroidal particles invisible to the naked eye, microplastics that remain in the soil for very long times and have the potential to enter the food chain.

Another aspect that emerged concerns the behavior of soil microorganisms. To degrade the filter residue, bacteria and fungi try to use the material as a carbon source. However, cellulose acetate is low in essential nutrients, particularly nitrogen. To succeed in breaking down the butts, microorganisms are therefore forced to draw nitrogen from the surrounding soil, creating competition with plants and other organisms. This process can lead to a temporary depletion of the soil, altering the nutritional balance of the ecosystem.

Research has also identified a surprising phenomenon in the dynamics of toxicity over time. There is a tendency to think that a butt is more dangerous as soon as it is extinguished, when it releases nicotine and other chemicals. Instead, the study showed a second peak in toxicity after about five years. At this stage, when the filter begins to physically break down and fragment, there is a new release of harmful substances accumulated in the fibers. This is a veritable “second wave” of pollution that affects soil organisms years after the butt is abandoned, a particularly important finding for ecological risk assessment.

During the 10-year monitoring, researchers also observed significant changes in the soil microbial community. The presence of butts acts as a kind of ecological filter: many species of bacteria and fungi tend to gradually disappear, while only a few specialized microorganisms survive and proliferate, capable of tolerating or exploiting the substances in the filter. The result is a reduction in soil biodiversity, with possible consequences for the functioning of terrestrial ecosystems.

Overall, the results of the study clearly show that cigarette butt is not a biodegradable waste but a persistent pollutant. Over the years it changes shape, fragments into microplastics, alters soil chemistry and continues to release toxic substances.