Americans own around 90 million dogs. They provide companionship, reduce stress and help us stay active.

They also produce about 12.2 million tons of waste per year. Most of it ends up in landfills, where it generates planet-warming methane. And all those poop bags can shed microplastics into the environment.

Here’s how you can reduce that environmental poo-print.

Responsible disposal starts with picking up your dog’s poop. Bags are the most convenient way of doing that, but not all bags are created equal.

Whenever possible, you should avoid bags made from conventional, new plastic, which is derived from fossil fuels. One exception: bags that have already come into your home with things like takeout food and other deliveries. Since these bags are usually destined for a landfill anyway, reusing them to pick up dog poop is “a great option,” said Rebecca Ryals, an environmental scientist.

Bags made from recycled plastic are slightly better than conventional ones, but they still have a fairly large environmental footprint from production and transportation.

Then, there are bags that claim to be plant-based, biodegradable and compostable. “Plant-based” just means some of the stuff used to make the bag comes from plants rather than fossil fuels. WIt does not indicate whether the bag will leave harmful microplastics behind, said Ramani Narayan, a chemical engineer.

It’s the same for bags sold as biodegradable: There’s no guarantee that they’ll break down safely in nature or even in a compost bin. “To call it biodegradable is a purely misleading claim,” Narayan said.

Compostable bags, on the other hand, are specifically designed to biodegrade when the right conditions are met.

In some countries, they carry a certification confirming that they have passed tests in a simulated industrial composting facility. In the United States, though, no such seal of approval exists.

Americans who want to compost their bags should try to find ones that meet the D6400 standard of the American Society for Testing and Materials. That’s what the certifiers would be looking for. If a company that advertises these types of bags sells other products certified by the Biodegradable Products Institute, that’s a good sign, too.

Ideally, your dog waste should be composted. But in the United States, only a handful of places offer this service. It’s not for a lack of technology, Ryals said, but because of cultural aversion.

You can compost dog waste yourself, but you’ll have to take a few precautions.

The U.S. Department of Agriculture says dog-waste compost can be used as a soil additive for things like lawns, flower beds and potted plants, but not on anything grown for human consumption.

If composting is out of reach, then there’s one more possibility: the toilet. If you’re connected to a municipal sewage system, you should check with your local government to see if flushing is acceptable in your area.

If you have a septic tank, don’t flush. Doing so can cause problems, because dog feces don’t break down as easily as human waste.