BEIJING—The Chinese government has lifted the veil just a bit on a nationwide soil survey that it had classified as a state secret. The environment ministry posted a bulletin to its website yesterday divulging that 16% of sites tested during the 5-year survey are polluted. The report concludes, dryly, that China’s “overall national soil environment” is “not optimistic.”

“Finally the public really knows the overall situation of the pollution under their feet, and the severe situation of food pollution,” says Chen Nengchang, a soil scientist at the Guangdong Institute of Eco-Environmental and Soil Sciences in Guangzhou. However, much of the data from the survey—which ran from 2005 to 2010—remains under lock and key. “The transparency is not enough,” says Chen Ruishan, a geologist at Hohai University in Nanjing.

Most worrying to researchers is that pollution is most widespread on agricultural lands, where 19% of sites are tainted. Major contaminants, the bulletin noted, are heavy metals such as cadmium, mercury, arsenic, and lead. The report blames mining and industrial waste for fouling croplands.

China’s State Council has ordered the environment ministry to formulate a plan for curtailing future soil pollution and for remediating contaminated land, the bulletin states. However, Chen Ruishan notes, “We need to know about the spatial distribution” of the soil pollution to devise a remediation strategy—and that kind of map has not been released to the public.