Updated

Nearly one-fifth of China's farmland is polluted, mostly from yearslong accumulations of toxins from factories, mining and agriculture, the government said, raising sharp concerns about the country's food safety after years of unbridled industrialization.

Results of a nationwide survey of soil samples taken from 2005 through last year, and announced late Thursday, showed contamination in 16.1 percent of the country's soil overall and 19.4 percent of its arable land.

More than 80 percent of the pollution is the result of inorganic toxins, with the top three contaminants identified as cadmium, nickel and arsenic, according results of the investigation jointly announced by China's Environmental Protection Ministry and its Land and Resources Ministry.

"The overall condition of the Chinese soil allows no optimism," said the report, posted on the environment ministry website. "Some regions suffer serious soil pollution underscored by worrying farm land quality and prominent problems with deserted industrial and mining land."

The report confirms widespread concerns about the safety of China's soil following decades of explosive growth in the country's industry, the overuse of farm chemicals and lax environmental enforcement which have left vast swaths of the countryside tainted.

The worst pollution centers around the country's most industrialized regions, the Yangtse and Pearl River deltas in southern China and heavily industrial portions of the northeast, the report said.

China's leaders have expressed resolve in tackling the country's pollution problem, although the threat to the country's food-producing soil has so far been overshadowed by public alarm at smog and water contamination.

However, recent scandals of tainted rice and crops have begun to shift attention to soil.

A key concern among scientists is cadmium, a carcinogenic metal that can cause kidney damage and other health problems and is absorbed by rice, the country's staple grain. Last May, authorities launched an investigation of rice mills in southern China after tests found almost half of the supplies sold in Guangzhou, a major city, were contaminated with cadmium.

In early 2013, the newspaper Nanfang Daily reported that tens of thousands of tons of cadmium-tainted rice had been sold to noodle makers in southern China since 2009. It said government inspectors declared it fit only for production of non-food goods such as industrial alcohol but a trader sold most of the rice to food processors anyway.