The city still runs on Dunkin’, just a little bit differently now. Dunkin’ Donuts is debuting an eco-friendly coffee cup in New York that will keep their steamy java hot, but won’t violate the Styrofoam ban that took effect on July 1. The new cup is made of polypropylene and is slowly being rolled out in the city’s more than 500 stores. It features a slimmer-looking design and — unlike the old containers — can be recycled in the city’s system with plastics.

New York City is joining a growing group of cities (Washington, DC, Minneapolis, San Francisco, Oakland,Portland, Albany and Seattle) in banning Expandable Polystyrene Foam (EPS). Starting July 1, single-use EPS products including cups, bowls, plates, takeout containers and trays and packing peanuts are not allowed to be possessed, sold, or offered in New York City. Companies have six months to comply or face a fine.

Marketed in the US under the name Styrofoam, EPS was invented by Dow Chemical scientist Otis Ray McIntire in 1941. To make it, small beads of the polymer polystyrene are steamed with chemicals until they expanded to 50 times their original volume. After cooling and settling, the pre-expanded beads are then blown into a mould – such as that of a drink cup or cooler – and steamed again, expanding further, until the mould is completely filled and all of the beads have fused together. The finished product is a lightweight, inexpensive material that is about 95% air. The insulating properties and cheap manufacturing costs of EPS have made it a popular choice for businesses.

It is estimated that Americans alone throw away 25 billion polystyrene coffee cups a year – a lot, but not compared to the 100 billion plastic bags used annually by Americans. And in 2006, for instance, 135 tons of polystyrene waste was dumped into Hong Kong landfills. Still, that only accounted for a small fraction of Hong Kong’s plastic waste – less than 5%.

But environmentalists say that EPS waste causes outsized trouble when it leaks into marine environments and contaminates water. According to Douglas McCauley, a marine biology professor at the University of California, Santa Barbara, there are two main issues that polystyrene causes for marine animals – mechanical and chemical.

“The [mechanical root] is very straight-forward,” said McCauley, “Oftentimes, we find polystyrene foam lodged in the intestines that causes blockages that can be lethal. If you think about how we worry about a mild blockage from eating the wrong thing, imagine eating a ball of Styrofoam. That’s what some of these animals are doing.”

Chemically, absorbent properties make EPS even more dangerous. “Polystyrene foams essentially act like little pollutant sponges, picking up and concentrating some of the nastiest contaminants in the ocean,” McCauley says. “Then something like a sea turtle comes along and eats this thinking it is a jellyfish.”

That’s not just bad for the fish and the oceans. It could be bad for humans.

Read more on why EPS cannot be recycled and what are the alternatives here.