Heavy metal pollution makes no distinction between how crops are grown. Irrespective of whether farming practices are organic or conventional practices are used, if the likes of cadmium, arsenic, lead, nickel and mercury are in the soil, water or air they can contaminate food and poison the people who consume it. With enough exposure, heavy metals can build up in the body, causing chronic problems in the skin, intestine, nervous system, kidneys, liver, and brain. Some heavy metals occur naturally in soil, but rarely at toxic levels, while human activities like mining, manufacturing and the use of synthetic materials like paint, and even some agricultural chemicals, can release heavy metals into the air and water, and from there they find their way to the soil. And once in the soil, heavy metals are virtually impossible to remove.

China acknowledged last April that a staggering one-fifth of its arable land is seriously polluted with heavy metals, thanks to decades of aggressive industrial development. China’s Environmental Protection Ministry looked at data sampled between 2006 and 2013 and described the situation as “not optimistic.” The most commonly found heavy metals were cadmium, nickel and arsenic. The revelation came after months of speculation about the report, which at one point was not going to be released as the results were considered to be a “State Secret.”

Cadmium, one of the metals found in high concentrations in Chinese soil, is one of the most toxic heavy metal pollutants. It moves through soil layers with ease, and is taken up by a variety of plants, including leafy vegetables, root crops, cereals and grains. Last year it was discovered that nearly half of the rice for sale in the southern China city of Guangzhou was tainted with cadmium, which caused a major uproar.

Nickel and arsenic, the other two pollutants found in greatest amounts, aren’t so great either.

In the U.S., arsenic in apple juice has been on the popular radar since September 2011, when Mehmet Oz reported high arsenic levels in multiple samples of apple juice that were independently tested for his television show. More than half of the apple juice consumed in the U.S. comes from China.

Oz was taken to the woodshed for being alarmist by a number of experts and authorities, including the FDA, which disputed the results with its own data. ABC News’ senior health medical editor, Richard Besser, called Oz’s claims “extremely irresponsible,” comparing it to yelling fire in a crowded theater.

A few weeks later, FDA admitted it had withheld many test results which did, in fact, support Oz’s claim. Besser apologized to Oz on national television, and soon after the FDA collected about 90 retail samples of apple juice for a new round of analysis. According to FDA documents now available, the levels reported by Oz are in fact consistent with those detected by the agency in samples from China and Turkey.

Last year the agency set a limit, also known as an “action level,” on arsenic in juice, at 10 parts per billion, the same level that’s enforced in drinking water. Currently, FDA has import alerts set for four firms, two each in China and Turkey. The products of these companies, while regularly tested for arsenic because of previous violations of the action level, continue to be imported.

While China is not the only polluted region from which we import food, with a combination of aggressive industrial development and legendarily lax enforcement, it’s become a poster child for scary food imports. But any region with rapid industrial development and suspect environmental regulations could be a candidate for producing food contaminated with heavy metals.

While we don’t import a huge amount of food from China overall, we do consume large amounts of certain things in addition to apple juice, like garlic and farmed seafood—including 80 percent of the tilapia we eat. Much of China’s surface water, including water used for aquaculture, is polluted, not only with industrial toxins but also with agricultural fertilizers, which fuel the growth of algae. Algae can accumulate heavy metals, as will the fish that eat it.

“Foods offered for import into the U.S. are required to meet the same U.S. food safety standards as domestic products,” explained FDA spokesperson Lauren Sucher, via email. “If the FDA encounters information that indicates that a particular product could pose a public health concern, the FDA can target that product for increased testing.”

When asked if the revelation that 20 percent of China’s farmland is polluted with heavy metals would spur increased testing on Chinese imports, Sucher replied, “The FDA doesn't announce its actions in advance. If our surveillance sampling indicated a problem with a particular commodity, the agency would take steps to protect the public.”

Wary consumers who aren’t interested in waiting for FDA to ramp up its testing of Chinese food imports can take their own measures to minimize the possibility of contamination. Local, as in American-grown produce, will trump labels such as “organic,” if the food in question was grown in a potentially polluted place.

In fact, if it’s grown in a polluted place, organic produce could contain more heavy metals than conventionally grown food. Organic agriculture practices include the use of manure, which could add heavy metals to the soil if the cattle were eating contaminated feed, such as hay grown in a contaminated field, according to Michael Schmitt, a soil scientist at the University of Minnesota. “Once you put metals in a field,” he said, “they don’t go away.”

Thus, organic food from a polluted area of China could carry significantly more heavy metals than nonorganic food from the U.S. This puts a new spin on the idea of eating locally. In this case it could mean from anywhere in this vast continent—Canada and Mexico don’t seem to have heavy metal problems. But in a way, the reasons are similar to why many people prefer buying from the local farm stand: you have more information about how something is grown.

Not all food is required by law to be labeled with a country of origin. Foods purchased abroad and processed in the U.S., for example, are exempt, as are foods containing multiple ingredients. The safest way to confirm a food item didn’t come from China is to look for labels that announce where it is from. If no information is given, avoid it.

Dietary supplements can pose even more of a risk of heavy metal contamination than food because they are so highly concentrated. If the materials from which they are made are contaminated, the contaminants will be concentrated. In 2010 the New York Times reported that many supplement manufacturers have set up shop in China in recent years, and that Chinese supplement factories are notoriously under-regulated.

FDA does not test supplements. Rather, it sets up guidelines and leaves the testing to the manufacturers. This self-policing is notoriously inadequate. According to testimony given to a congressional committee by Tod Cooperman, president of ConsumerLab.com, about one in four supplements his lab tested had issues. The two most common problems were lack of the appropriate quantities of the ingredients indicated on the label, and presence of excessive heavy metals.

Michael Pollan and others have advised keeping your diet simple, using locally grown, minimally processed food, and getting most of your nutrition from whole plants rather than supplements. Pollan may not have been thinking about heavy metals when he penned that guidance, but given what we are learning today, it makes his advice all the more worth following.