Thrown out of windows or flicked on the ground and stamped underfoot like in the movies — cigarette butts are small, but they are still the most common form of litter, according to new research commissioned last year by the nonprofit Keep America Beautiful, and they are anything but benign.

Cigarette filters contain a cocktail of microplastics and toxicants, including heavy metals and carcinogens. Getting them off the streets is the mission of a group of volunteer New Yorkers who call themselves the No Butts Campaign.

On a cold Sunday afternoon last month, five members of the group fanned out across the streets of East Harlem where they used mechanical pinchers on long rods to collect cigarette butts along Madison Avenue.

When a passerby stopped and stared, campaign organizer Joyce Bialik seized the opportunity to educate a member of the public by asking if they or someone they knew smoked. The person said he didn’t, but still took a few free pocket ashtrays that the group distributes during events.

“They smell terrible, hard to pick up and they’re everywhere,” said Bialik, a petite redheaded senior citizen who usually dresses in a cigarette butt costume made of cardboard when she’s out collecting. But not on a cold winter day. It’s too difficult, she explained, to collect butts with a coat underneath it. She and other volunteers began grabbing at butts trapped inside gaps in the sidewalk, the first of thousands they collected over a five-block stretch in the proceeding hour.

Sharon Silbermann and Joyce Bialik (costumed) of the No Butts Campaign collect discarded cigarette butts from city streets.

According to Tobacco Atlas, a partnership between the American Cancer Society and Vital Strategies, 5.7 trillion cigarettes are sold annually worldwide. That’s more than 15 billion butts every day, 65% of which are intentionally littered, according to Keep America Beautiful.

These inch-long, non-biodegradable filters, along with a cigarette’s tobacco, contain more than 7,000 chemicals, according to the 2014 U.S. Surgeon General’s Report on Tobacco and Health. More than 50 of them are carcinogens. And a study by Imperial College London showed they contribute more than 1 million tons in microplastic waste every year. Research also shows those toxicants ultimately end up in our food and water supply, with negative impacts on human health and the environment.

Just having them on the ground is hazardous, according to Thomas Novotny, a medical epidemiologist and executive director of the Cigarette Butt Pollution Project.

“These filters act like a little teabag where chemicals ooze out,” Novotny said. “If they have the remnant tobacco on them, it’s even worse.”

When a cigarette butt leaches into the environment, it can kill. In a laboratory study, eight cigarette butts were soaked in approximately 8 ½ cups of water for 24 hours. Fish were placed in this leachate stock and by the fourth day, half of them had died.

On land, children and pets often pick up butts from the ground and ingest them. Poison Control received over 700 calls nationally involving cigarette butt ingestion over the last three years; nearly 90% of those incidents occurred in children less than 2 years old. Eating just one cigarette butt can be toxic to a child under 6 years old, according to Poison Control.

These chemicals can seep into the ground, and contaminate the soil and groundwater. Heavy metals such as cadmium are hazardous and cannot be destroyed, but are absorbed readily by plants such as root and leafy vegetables.

“It’s a vicious circle, what we are doing to our environment every day,” said Ana Navas-Acien, an environmental health sciences professor at Columbia University’s Mailman School of Public Health. “We are eating, breathing in and drinking toxic products, resulting in premature death and disease.”

The chemicals from cigarette butts can also accumulate in the bodies of animals, which means they can make their way through the entire food chain.

“Chemicals get leached out into an aquatic environment,” Novotny said. “Animals at the lower end of the food chain such as microorganisms are absorbed through filtration by a clam or an oyster. Then birds eat this, and it becomes food for some other animal, and maybe even us.”

Birds have been known to incorporate discarded filters in their nests. Novotny said this has two outcomes. One, the bird has fewer parasites or fleas because nicotine is a natural pesticide. Unfortunately, he said, the butts also cause DNA damage.

In East Harlem, as Bialik and other volunteers cleaned butts from the streets, they found a higher concentration of discarded filters around the perimeter of Mt. Sinai Hospital. Litter location surveys have found that medical facilities are hot spots for cigarette butts. Volunteers also reported high concentrations of cigarette butts at Carver Houses, a NYCHA complex across Madison Avenue. Americans living below the poverty level are much more likely to smoke than the rest of the country, according to the Centers for Disease Control, which said tobacco companies have historically targeted advertising toward low-income communities.

The No Butts Campaign is funded by the Manhattan Solid Waste Advisory Board, a citizen group dedicated to achieving zero waste by 2030. The campaign sends its findings to Terracycle, a company that recycles the plastics inside butts into park benches. Filters contain cellulose acetate, a non-biodegradable, synthetic compound that breaks down into a microplastic that can be found in storm-water runoff and all bodies of water in the United States — even our own bodies, according to Navas-Acien. One study found that humans ingest about a credit card or standard Lego brick worth of microplastic every week.

Approximately 2,700 cigarette butts is enough to make a park bench, according to Terracycle, which receives cigarette butts from community organizations across the country.

At the end of the collection event, Bialik sat on the floor in her apartment building’s hallway, surrounded by brown paper bags full of orange and white filters, wearing clear surgical gloves, counting each butt two at a time. The total: 1,631, or more than half a park bench. She documents exact counts in the hopes of persuading New York state lawmakers to pass the Tobacco Product Waste Reduction Act, a bill currently stalled in the senate that would ban the sale of tobacco products with single-use filters.

“There are just too many humans on this planet,” Bialik said. “If we each do whatever we want with our waste, in this case, cigarette butts, this is not going to be sustainable.”