China’s air pollution is infamous. The haze from belching factories and clogged highways can make it impossible to see buildings across the street. It forces schools to close. Face masks are commonplace.

But China has another pollution problem – soil pollution.

Until recently, the country called its soil contamination a “state secret.”

In April, however, the environmental ministry released data showing that at least one-fifth of all arable land is polluted with chemicals such as lead, cadmium and arsenic. Chinese officials say an area the size of Maryland is so polluted that farming shouldn’t be allowed there at all.

Hunan province is the country’s top producer of rice. It’s also China’s top producer of heavy metals and the home of major mining operations. Factories ring farmlands.

Wastewater containing mining sludge, toxic solvents and metals seeps into the soil and irrigation systems.

Heavy metals contaminate at least 12 million tons of Chinese grain each year, say official estimates. This admission comes even though Chinese leaders hesitate to discuss industrial pollution at any level. (It wasn’t until last year, for example, that the Chinese government was forced to recognize the existence of “cancer villages” despite more than a decade of reports that clusters of people in towns near factories had been dying of different cancers.)

Hunan rice caused a major scandal last year. In Guangzhou, a city of 12 million near Hunan, almost half the rice tested was found to be tainted with cadmium.

Cadmium can cause kidney failure and cancer. Misuse of pesticides and fertilizers also contribute to the soil pollution. Farmers plant their crops in contaminated soil. They water those crops with contaminated water. Naturally, the crops absorb the pollutants as they grow. Now, China’s food supply is at risk for dangerous levels of metal contamination, according to Yale Environment 360 and Chinadialogue.

Halting agricultural production in many of the worst-hit areas simply isn’t an option.

It would put people’s livelihoods at risk and could result in food shortages.

The government has promised an “action plan.” But soil cleanup is a long and expensive process that doesn’t have a lot of momentum in government right now.

Part of the problem is that no one knows who’s really responsible. The government, which owns all the land? The company doing the polluting? One new law in the making will allow the government to decide who is responsible for the contamination. It also will figure out a way to help pay for the cleanup.

It’s a problem that affects everybody. Farmers working the soil are exposed. People eating the crops are exposed. Plus, former industrial sites are often reclassified as residential –that means construction workers building apartments and tenants in those new apartments also are exposed to polluted soil.

The national government hasn’t completed a first draft of its promised law, and experts quoted in state media say it likely won’t be finished until 2017. Even with commitment, soil pollution takes decades to overcome. In the meantime, farming polluted land continues, though China’s Greenpeace says the government is working harder to ensure contaminated crops don’t enter the market.

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Rachael Bale is a reporter and researcher for The Center for Investigative Reporting. Previously, she worked at KQED in San Francisco and The Center for Public Integrity, an investigative journalism nonprofit in Washington, D.C., where she covered campaign finance in the 2012 election. A California native, she has a bachelor's degree in political science from Reed College and a master's degree in journalism from American University.