Residents of Johannesburg and surrounding communities live among an estimated 600,000 metric tons of uranium buried in waste rock and covering an area four times the size of Manhattan, according to university researchers. Another undetermined amount lies below ground, where water has filled abandoned mines and leaks into the environment.
"There's nowhere in the world where you'll find so many people living alongside such a vast amount of ore-bearing uranium," said Carl Albrecht, head of research at the Cancer Association of South Africa, or Cansa. "There are 400,000 people in the area who are subjected to this environment and yet the government is unwilling to consider the health impact."
Government regulators and health advocates disagree over the public-health threat this poses. Albrecht and others point to U.S. Environmental Protection Agency data that says even low-level radiation exposure, if prolonged, can lead to an increased rate of cancers. Susan Shabangu, minister of South Africa's Department of Mineral Resources, said levels recorded in and around Johannesburg are "a cause for concern" but not yet a "level of danger."
One thing is indisputable: the amount of untreated waste material containing uranium is growing as a 28 percent plunge in the gold price last year has shuttered mines and increased the number of abandoned mine sites. The Blyvooruitzicht mine 50 miles (80 kilometers) southwest of Johannesburg -- near where the Bloomberg News soil sample was taken -- was closed in July, throwing 1,700 miners out of work.
The mine's last operator, Village Main Reef Ltd., isn't responsible for the environmental rehabilitation of the mine because it never took legal ownership of the operation, according to Chief Executive Officer Ferdi Dippenaar.
Village operated the 72-year-old mine for 18 months, he said.
"As far as I am aware, and based on tailings recoveries, the content of uranium during this time was definitely within limits," Dippenaar said. Tailings refers to waste material. Village has no plans to reopen the mine and it's currently being liquidated, he said.
Unmaintained, abandoned dumps lose their shape as their toxic material seeps into the surrounding area, said Anthony Turton, a professor at University of the Free State's Center for Environmental Management. When waste dumps, known as tailings dams, are abandoned "you get major erosion taking place and slides of toxic material into wetlands," he said.
While South Africa has required companies to set aside money for environmental mitigation since 1994, "the reality is the funds set aside for environmental liabilities are totally insufficient," Turton said.
South Africa will be forced to spend about $2.7 billion on cleaning up its nearly 6,000 abandoned mines, the World Wildlife Fund said in a 2012 report, citing the country's auditor general. Of the country's working mines, almost 40 percent don't have adequate funds available for rehabilitation, according to the Department of Mineral Resources' 2012-2013 annual report.
The effects of low-level, chronic exposure to radiation include cancer and changes to DNA, known as mutations, that can be passed onto offspring, according to the U.S. government. High uranium intake over time can also lead to increased cancer risk and liver damage, the agency said.
For every ton of ore mined, South African produces between 3 grams (0.1 ounce) and 15 grams of gold, meaning most rock removed from the earth is waste material, and contains toxic chemicals including uranium, mercury, radon, arsenic and sulfuric acid.
The upside of gold mining here is well known. The industry stretches back to 1886 and among its pioneers was German immigrant Ernest Oppenheimer, who founded Anglo American Plc and helped to turn Johannesburg into Africa's richest city. Mining helped make fortunes not just for the Oppenheimers but for Cecil John Rhodes, the first chairman of DeBeers, and current billionaire Patrice Motsepe, founder of African Rainbow Minerals Ltd.
That legacy's unsightly side is in plain view here. Waste rock from hundreds of mines that have been developed over the years has been deposited around Johannesburg in mounds that cover a combined area of 400,000 square kilometers and can be as many as 10 stories high. One such dump, which looks like a flat-topped sand mountain, sits next to the FNB Stadium, where the final of soccer's World Cup was played in 2010.
The tailings contain about 600,000 tons of uranium, three times the amount exported during the Cold War, according to Professor Frank Winde at South Africa's North-West University. It's getting into the water supply, according to Winde, a German-born scientist who has studied the effect of uranium on South Africa's environment for 30 years and overseen university testing for radiation levels.
This happens in a variety of ways, according to Winde. The radioactive metal dissolves in rainwater and runs off the dumps into rivers during storms or is carried into water sources when it seeps through porous rock as abandoned mines are flooded. It can also be spilled by companies that re-mine dumps for the metal. Dust clouds containing uranium form when high winds hit the dumps.
Soil taken by Bloomberg News from pumpkin roots about 100 meters away from Wonderfonteinspruit, a stream feeding the Vaal River and close to Blyvooruitzicht, was found to contain 10.4 milligrams of uranium per kilogram. That's five times higher than the 2 milligrams per kilogram average, according to the IAEA.
Shabangu, the mineral resources minister, says the levels aren't cause for alarm.
"Scientifically, it has been proven we're not at a level that poses a health threat to communities," she said in an interview.
Winde disagrees. "We have generally underestimated the presence of uranium in the water supply," he said. "If the government has a study saying it's safe then I would like to see it. As far as I'm aware, nobody has studied whether it has an impact on general health, on the likelihood of cancer, on hormonal functions, on DNA" in South Africa.
Two hours west of Johannesburg's business district of Sandton lies Khutsong, a township of 60,000 from which the soil sample was taken. Residents there struggle daily for water, electricity and work.
Two-bedroom brick houses built by the local government are surrounded by improvised shacks with corrugated iron roofs. Jobs are scarce after gold mines, including Blyvooruitzicht, were closed.
While the government prohibits people from drinking, irrigating and washing in water taken directly from rivers, for thousands living in an area known as the West Rand there is no choice, said Sello Mokoena, 27, a worker on the vegetable patch in Khutsong.
"People tell us that the water is polluted from the mines but we have nothing else," said Mokoena, wearing a green sports shirt and orange trousers. He earns about 700 rand ($63) a month working on the vegetable patch and herding livestock, and uses it to support his mother, three brothers and a sister.
The Bloomberg soil sample was taken from an area suspected of containing mine waste and was not part of a scientific study. No vegetables picked from the patch by Bloomberg News were found to contain elevated levels of uranium.
Joe Maila, a spokesman for South African Health Minister Aaron Motsoaledi, referred questions to West Rand District Municipality. The municipality is "concerned with all activities which may have a negative impact on public health," Cheleng Khotle, a manager for municipal health, said in a statement. "The municipalities may currently not be able to provide funding" for further studies. "Continued technical monitoring is encouraged and would be supported by municipalities through participation."
Water samples from Wonderfonteinspruit show uranium levels on average 400 times background levels, and reaching as high as 4,000 times, according to Winde, who compiled a series of studies he and other scientists have done over the past 20 years.
Winde detected uranium levels of 53 micrograms per liter at the Boskop Dam, which supplies Potchefstroom, a town 75 miles west of Johannesburg and about 25 miles southwest of Blyvooruitzicht, in November 2012. That indicates 21 micrograms per liter of uranium in tap water sourced from that dam, 40 percent higher than the World Health Organization's safe level of 15 micrograms per liter, he said.
While that was a one-time test and exceeded usual tap-water readings of about 5 micrograms per liter in Potchefstroom, below the safe level, it shows that residents are sometimes exposed to dangerous water quality, said Winde, who lives in the town and doesn't drink the water.
Wonderfonteinspruit, Carletonville, and Potchefstroom are towns in the West Rand, downstream from Johannesburg and the mine-waste dumps. The metropolis's water supply isn't contaminated because it comes from the upper part of the Vaal River and from nearby Lesotho, a landlocked mountainous kingdom surrounded by South Africa.
Tap water in the West Rand including Potchefstroom is safe to drink, according to Marius Keet, senior manager at the Department of Water Affairs.
"At the moment there's no danger there," he said. "We're in contact with the scientists there and there are concerns -- not now, but in the future -- if there is a slow increase of uranium in the feed water."
People shouldn't drink water directly from rivers, such as Wonderfonteinspruit, dams or seasonal streams in the area, Keet said.
"You're not allowed to take water from any river in South Africa," he said. "For as much as uranium is a challenge, there's also the challenge of bacteria."
South Africa is unique among gold-mining countries because of the dense population that has grown up around its mines. That means exposure to low levels of uranium over a long period of time is unprecedented and should be investigated by the government, according to Cansa's Albrecht.
In 2011, Cansa found uranium levels in two Carletonville residents' teeth that were as many as 100 times higher than a 2007 study that took the same measurement from people living in a Brazilian mining area.
The Department of Water Affairs' Keet said he's in favor of studying the effect of low levels of uranium intake over long periods of time on people's health. The Department of Health should conduct such research, he said.
His major concern is uranium seeping from the mine dumps through dolomitic rock, which is porous, and into the water table. "That will have to be well monitored in the future," he said.
The government's long-term approach to remove uranium from mine dumps is to allow companies to re-mine them for gold, eliminating toxic wastes as they go. A number of companies are already doing that, among them AngloGold Ashanti Ltd., DRDGold Ltd. and Mintails Ltd.
DRDGold, which doesn't mine in the West Rand, said this process is "enormously" helpful because it removes waste and deposits it in modern tailings complexes under the scrutiny of regulators. Mintails is "proud to be playing a leading role" in removing hazardous materials from "potentially the most uranium contaminated landscape in the world," said Turton, who acts as an adviser to the company.
While re-mining can be part of a solution to uranium pollution, it's also part of the problem, according to Mariette Liefferink, CEO of the Federation for a Sustainable Environment.
"Cost-cutting and disregard for the environment mean there are radioactive spillages every few weeks in the West Rand," she said. "Unless these mining companies mine cleanly, they will only make the situation worse."
AngloGold was responsible for 10 environmental incidents it classified as "significant" in South Africa in 2012, according to the company's annual report. They involved toxic waste being spilled onto farmland and in rivers. Of the 10 incidents, seven were attributed to Mine Waste Solutions, which re-mines waste material and was bought for $335 million from First Uranium Corp. two years ago.
The company has spent about $90 million upgrading Mine Waste Solutions since the acquisition and has improved its water monitoring, pipeline maintenance as well as creating so-called containing areas for potential spills, CEO Srinivasan Venkatakrishnan said in an interview.
Winde, who is attempting to raise money for further research, says the companies and government aren't doing enough.
"We know there are elevated levels of uranium from years of gold mining all over the West Rand but what we don't know is how much worse it will get as mines close and what the health implications are," he said. "Given the magnitude of the problem, there's a complete lack of action to address it."