About 12 percent of plastic waste is burned globally, according to a landmark study based on data through 2015. Even when done in incinerators equipped with air scrubbers and filters, such burning is linked to higher rates of premature birth, congenital abnormalities including heart and neural tube defects, and may increase cancer risk for those living nearby, studies have found.

But when plastics—which a Nature study last year found can contain any of more than 16,000 different chemicals, a quarter of which may pose health concerns—are burned in low-tech furnaces lacking any pollution-reduction technology, the dangers are far greater.

That’s exactly what happens in Tropodo, a tofu production center where informal backyard factories use plastic as a fuel for making the soy-based staple.

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His parents were tofu-makers too, and when he was a boy, their factory burned rice husks. But they began using plastic in the 1980s, so when he started his own company, he did too. He later switched to wood, but when his wood supplier closed, he went back to plastic. “It’s good, and cheap,” he tells me. All Tropodo’s tofu factories burn plastic, he says, and he doesn’t see any problem with it.

Much of the plastic Gufron and factory owners like him use is waste from overseas—packaging tossed away in places such as the United States, Europe, South Korea, Japan, and Australia. He buys it from local sorters who purchase it from paper recycling companies. Plastic scrap is often mixed in with the bundles of waste paper those companies import, and they must remove it before processing the paper. Indonesian regulations limit such contamination to 2 percent of any shipment, and while the industry insists violations are rare, Daru Setyorini, the environmentalist and researcher who has accompanied me to Tropodo, says that in reality, the amount of plastic can far exceed that limit.

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An adult eating an egg like the one found in Tropodo would exceed Europe’s acceptable maximum intake of chlorinated dioxins—chemicals linked to cardiovascular disease, cancer, diabetes, and hormonal changes—by 70 times, the groups reported. The eggs also contained short-chain chlorinated paraffins and polybrominated diphenyl ethers, which are both used as flame retardants in plastic and are linked to hormonal disruption, developmental and neurological damage, and cancer.

Chickens wander everywhere in Indonesian villages, and Tropodo is far from the only place where they peck through toxic ash. Many rural areas lack garbage collection, so households there often burn their waste. The faint whiff of that smoke hangs everywhere, and I often see hens munching their way through the blackened remains of such fires.

The threat goes far beyond Indonesia, of course, to everywhere plastic is burned out in the open. In Accra, Ghana, for example, researchers testing eggs near one of the world’s largest electronic waste scrapyards, where workers burn plastic culled from discarded devices, found chlorinated dioxin levels more than three times Tropodo’s very dangerous levels.