Pollution that is easily perceptible in China's rivers and urban air has gotten a lot of attention in recent years.
Now a less obvious environmental concern with equally serious repercussions—soil contamination—is getting the attention it deserves thanks to a first-of-its-kind nationwide study that documents a heavy toll on China's farms, forests, and grasslands.
Eight years in the making, the Nationwide Soil Pollution Investigation Report released in April by the Ministry of Environmental Protection (MEP) and the Ministry of Land Resources (MLR) includes alarming statistics that underscore the damage done to cultivated and uncultivated land nationwide.
Some 16.1 percent of all soil samples collected in regions around the country were found to contain unacceptable levels of pollutants, the report said. The survey indicated that up to 19.4 percent of all cultivated land—an estimated 26 million of the 133 million hectares of arable land nationwide, based on government figures—has been contaminated.
The pollution rate for cultivated land has thus nearly doubled the previous oft-cited official figure which said that about 10 percent of the nation's arable land, or some 12 million hectares, had been spoiled by unacceptable levels of pollutants.
The latest report also looked at woodlands and grasslands across the country previously unchecked by environmental scientists. It drew a grim conclusion: Some 10 percent of the soil sampled in woodlands nationwide and 10.4 percent of all grassland samples showed high levels of contaminants.
Overall, the report said, the land in southern China was found to be more polluted than areas in northern provinces. Heavy-metal pollution, often associated with mining, is most serious in the southwest and south-central regions. And the most pervasive of all the toxic heavy metals detected by investigators is cadmium, the report said in a first-ever acknowledgment by government agencies of cadmium's poisonous legacy.
The report underscored the enormous price that the land underfoot is paying for China's economic development by offering firm figures to replace soil contamination estimates that had been used by scientists and officials since the early 1990s.
Don't Eat the Rice
One of the most serious threats posed by the soil contamination problem is that rice is being grown in cadmium-laced paddies, according to the report.
Since about 65 percent of China's population relies on rice as a dietary staple, the cadmium contamination issue is considered extremely serious. But officials have yet to map out a plan for addressing the problem.
One reason for a lack of action is that no one knows how much rice-growing farmland has been or is still at risk because of toxic quantities of cadmium. Neither is there a system for determining the full effects of soil pollution on any grain, rice, or otherwise raised on farms across the country.
The U.N. Environmental Program's website calls cadmium "a toxic element for humans, mainly affecting the kidneys and skeleton."
In 2007, a team of researchers led by Pan Genxing, a professor at the University of Nanjing's Institute of Resource, Ecosystem, and Environment of Agriculture, collected rice samples from farms across the country. The team concluded that 10 percent of the 91 samples examined had poisonous levels of cadmium.
The MEP-MLR report also cited the danger posed by soil contamination in urban and industrial areas.
"Soil pollution in residential, commercial and industrial areas can harm human health" by exposing a person "through the mouth, respiratory system, or contact with the skin," according to the report. "Developing and building on polluted areas that have not been cleaned up can lead to long-term harm to exposed groups of people."
Plants, insects, and animals are also threatened by soil pollution, the report said. The growth and reproductive abilities of plants, burrowing animals, earthworms, and micro-organisms are affected. Toxins upset ecological processes and the soil's natural functions, such as the ability to provide nutrients to plants.
Even rivers far away or groundwater far below polluted land can be damaged by contaminants, the report said. "Pollutants in the soil can seep into and change surface water (and) groundwater," the report said, "polluting sources of drinking water."
Based on the sampling, the report said cadmium levels have risen substantially since the late 1950s. Levels of this toxin alone have risen by more than 50 percent in the southwestern and coastal regions, and between 10 and 40 percent in northern and western areas.
What can be done? Not much, the report's authors lamented.
"Once soil has been polluted, it's very difficult to restore it by cutting off pollution sources alone," the report said. "Overall, the costs for cleaning up polluted soil are high. It takes a long time. And it's very difficult."
The report continued: "Because it's hard for heavy metals to degrade, it's impossible to completely remove heavy metals from the soil. Many organic pollutants in the soil need a long time to fully degrade."
On the other hand, some experts say steps can be taken to protect the public from rice grown in cadmium-laced soil. Ideas posed by Shang Qi, an environment and health researcher at the China Center for Disease Control and Prevention, include prohibiting all rice-growing in contaminated paddies and banning human consumption of any rice found to have been grown on polluted land.
Doing nothing about cadmium-laced rice, Shang said, in effect condemns the people who eat it.
"Once cadmium is in the soil, it's difficult to remove," Shang said. "Once it's in the human body, it cannot be eliminated in a short time.
"What we can do is—what's most urgent—is to implement effective measures to limit exposure to cadmium in polluted regions."
Shang's ideas already have been endorsed by the State Council. In January 2013, the cabinet's General Office confirmed that the government would work toward limiting cadmium exposure to rice and rice-eating. The office released a document that spelled out measures to be taken.
For starters, the State Council ordered local governments to map out all farm areas with contaminated soil and ban those areas from agricultural production.
The job of demarcating contaminated rice paddies is still incomplete, though, so the State Council's order to stop growing rice on cadmium-laced land has yet to be heeded.
Statistical Gymnastics
Researchers working on the eight-year report tested for 10 types of pollutants. Of the samples that tested positive, 13.7 percent were found to be lightly polluted, 2.8 percent mildly polluted, 1.8 percent moderately polluted, and 1.1 percent heavily polluted.
Samples with "light" pollution exceeded acceptable levels of a toxic substance such as cadmium by one to two times. Soil samples with up to 0.6 milligrams per kilogram of cadmium were considered lightly polluted.
Samples rated with "mild" contamination had two to three times acceptable levels, while "moderate" meant three to five times, and any samples with more than five times acceptable levels were labeled "heavily" polluted.
Not all experts agree that the survey can be used to conclude that 19 percent of all farmland has been tainted.
For example, Chinese Academy of Sciences specialist Chen Tongbin said it would be unscientific to extrapolate from the sample-collection effort exactly how much arable land has been polluted, since the survey involved limited sampling. Chen is Director of the Academy's Environmental Restoration Center at the Institute of Geographic Sciences and Natural Resources Research.
An official representing the ministries that prepared the report said even though samples were taken from around the country, no one knows exactly how much land has been polluted.
In fact, said the official, the report was aimed at providing a general assessment of the soil's condition and the status of the environment in China.
Nevertheless, based on the finding that 16.1 percent of sampled soil was tainted, Chen admitted the report highlighted the seriousness of the soil pollution problem.
The fact that pollution was found in soil samples taken from woods and uncultivated grasslands opened an especially worrisome window to the extent of the problem.
The MLR's most recent national land-use report said China had 250 million hectares of forests and about 220 million hectares of grassland, in addition to 133 million hectares of arable land, as of December 2012.
MLR also estimated China has about 180 million hectares of idled land. Of the samples taken from these areas, 11.4 percent were found to be contaminated.
In addition to cadmium, samples were found to have various amounts of mercury, arsenic, copper, lead, chromium, zinc, and nickel. Cadmium was the most prevalent toxin, found in 7 percent of all samples. Nickel, the second-most common pollutant, was detected in 4.8 percent of the samples. Arsenic was third, found in 2.7 percent of the soil plugs studied.
Some toxins in China's soil, the report said, fell to earth after being pumped into the sky with smokestack emissions. Other poisons got into the soil via factory or urban wastewater, or from mining waste such as tailings.
Auto emissions have also been cited as a major contributor to heavy metal pollution. Tailpipes are sources of lead, zinc, and polycyclic aromatic hydrocarbons, for example.
Farming is the second-most common source of soil pollution, the report said. "Polluted water used for irrigation, unreasonable amounts of chemical fertilizers, pesticides, plastic sheeting and other agricultural inputs, as well as livestock raising, have all led to soil pollution on cultivated land," the report said.
In Hunan province, said environmental researcher Tong Qianmin, phosphate fertilizers are the single biggest source of soil pollution. Tong studied six areas around the central province's Dongting Lake and found high levels of cadmium left behind after farmers applied phosphate fertilizers.
The report said pollution is most serious in the Yangtze River Delta, Pearl River Delta, and the country's northeast, while heavy-metal pollution damage is concentrated in the southwest and south-central regions.
MEP and MLR officials said they plan to broaden their investigations of the soil pollution problem. The report didn't answer every question about the contamination problem. But at least, said one official, "we now have an initial, overall implementation plan" that can lead to further study.