BOGOTÁ —Colombians can add pollution caused by millions of cigarette butts to an already varied list of environmental calamities that include deforestation, forest fires and the pesticides and mercury dumped into their rivers.

It's the huge number of discarded cigarette butts that add gravity to what might seem an insignificant problem. In Bogotá alone, 95 million cigarette butts wind up on the pavement every year, and each cigarette end contains 4,000 chemical substances, 50 of which can cause cancer. Those that make their way into drains dissolve and pollute the country's waterways.

Universidad Piloto researchers William Lozano-Rivas, Rommel Bonilla and Alexandra Salinas compiled the stunning figures for a study published in the International Journal of Research Studies in Science, Engineering and Technology.

They found that the 95 million butts thrown to the ground constitute just 13% to 19% of all cigarettes smoked in Bogotá annually. Their weight, 16 tons, is but a fraction of the 6,500 tons of trash the capital generates daily and of the 10 million or more tons of trash produced every year nationwide.

Curiously, the study's social conclusion was that the government should amend its anti-smoking laws to keep cigarette butts from winding up into the drains. New laws had forced smokers outside of buildings and onto the pavement, but it seems nobody had thought to place ash disposals at building entrances.