The left-over filters of cigarettes (cigarette butts) are everywhere. We see them along street curbs, at the park, and even mixed in with sand and driftwood on the beach. Somehow it has become normal for people to toss them out of their car windows, or wherever they like. From a littering point of view this is terrible, but could cigarette butts do damage to the ecosystem by changing the water chemistry or the microbes living there?
Scientists in France and Tunisia wanted to know if either burned or unburned cigarette butts could change the water chemistry and microbes living on the beach near the sea. The scientists note that cigarette butts are made of a type of plastic called cellulose acetate, and that they are the most common form of plastic on marine coast. They also mention that one cigarette butt is estimated to have the potential to contaminate up to 1000 liters of water.
The researchers wanted to first know if smoked or unsmoked cigarette butts could change the amount of metals in the nearby beach sediment. They then wanted to know if the cigarette butts (smoked or unsmoked) could actually change the native microbes living in the beach sediments. Just like we could not live underwater without some type of support, some microbes cannot live under certain conditions like high levels of metals. To answer these questions, the scientists collected beach sediment and seawater just offshore from an urban beach along the Mediterranean. They then brought their samples back to the lab and started some experiments.
To provide some consistency for the age of each cigarette, the scientists immediately burned 12 fresh cigarettes for their filters. Another 12 filters were collected from unsmoked filters. They then placed one cigarette butt into a clear microbe-free tube and added beach sediment (which included beach microbes) and filtered seawater. Each tube sat outside for 4 days to mimic beach conditions. For comparison, a set of tubes with sediment and seawater, but without a cigarette, was also placed outside. After 4 days, they removed the cigarette filters, filtered the seawater, and measured the amount of metals in it using a version of a technique called inductively coupled plasma–mass spectrometry. DNA was then extracted from all the microbes living in the sediment to see which groups were there.
The scientists found that seawater in the tubes with smoked filters had higher levels of metals than the unsmoked filters. Regardless of burning, both filters did release iron, manganese, and zinc. However, in both filter types, cadmium, molybdenum, and vanadium decreased in concentration. The scientists proposed it was likely these metals were chemically attracted to the filters. It turns out that the microbes in the tubes with cigarette butts were very different from the microbes living without one. In the tubes with a smoked cigarette butt, the amount of microbe groups varied as there were less Cyanobacteria and Bacteroidetes, but more Gammaproteobacteria, Firmicutes, and Thermotogae. They also noted that the increased presence of Gammaproteobacteria, Firmicutes, and Thermotogae were related to groups adapted to extreme conditions, like high metal concentrations and high temperature.
This work is important, as it shows that cigarette butts are harmful in multiple ways. They not only litter a clean beach, but they can also introduce metals into an environment and change the local population of microbes, which are key to a healthy ecosystem. With this information, it is even more important that we keep our roads, sidewalks, and beaches clean.