Tails of Woe

New Scientist 11 November 2000 Back to Main Page

MARVIC QUINDOZA lived his short life in one of the fishing villages on the north side of the island of Marinduque in the Philippines. Two years ago, at the age of 13, he died from heavy-metal poisoning. Two other local children died within months of Marvic, and dozens more suffered stomach aches, fever, brittle bones and other symptoms linked to heavy metal poisoning. Researchers investigating the deaths found dangerously high levels of lead and cyanide in the children's blood and in soil samples from the shores of Calancan Bay. The fishing communities of Marinduque blame wastes from a copper mine in the hills for the poisoning.

Imagine the load carried by a line of trucks parked bumper-to-bumper and stretching three times around the Earth. That is the volume of toxic, ground-up, waste rock piped into Calancan Bay between 1975 and 1991. An estimated 200 million tonnes of mine tailings have smothered coral reefs and sea grasses across 80 square kilometres of seabed, poisoned fish and created a causeway 7 kilometres long that is gradually being blown ashore by the wind. "The tailings in the bay are a continuing source of heavy metal contamination of the soil, air, biota and people of these fishing villages," says Catherine Cournans, an anthropologist who studied the incident.

And the villagers' problems don't end there. In 1991 the mine operator and largest shareholder, Canadian mining giant Placer Dome, began storing the waste in an abandoned pit. Five years later, a seal burst releasing more than a million cubic metres of thick sludge into the nearby Boac river. Following all the bad publicity, the mine was finally closed. But the river remains clogged with acid sludge and all the fish have died. In 1997, Placer Dome sold its stake in the Filipino holding company of the mine, Marcopper, but retains responsibility for cleaning up the mess. It wants to dredge 26 kilometres of the river channel and dump the tailings into the Tablas Strait on the island's west coast. The environment ministry has twice rejected the plan, but its decision is mired in legal disputes. Meanwhile, the islanders fear a new disaster and more dead children.




Mine tailings are a massive environmental problem, especially when they still contain traces of toxic metals. Modern mines often need to excavate 100 tonnes of ore to extract a tonne of metal. To make this pay, they operate on a huge scale and minimise the costs involved in disposing of tailings. The story of the Marinduque mine graphically illustrates the industry's problems and its attempts to find a solution. The pipeline into Calancan Bay was an anachronism for much of its life-an environmental travesty indulged by the then Philippines president Ferdinand Marcos, who owned a stake in the mine.

When the pipeline shut and disposal moved to land, the Marinduque mine was only catching up with a worldwide trend under way since the 1960s.

But land disposal, says Tom Pedersen, a mining consultant and geologist at the University of British Columbia in Vancouver, has often proved worse for the environment. This is because most mine tailings contain sulphides-notably iron sulphide or pyrites-which oxidise in air to produce sulphuric acid. The acid then dissolves toxic metals still in the tailings, allowing them to be washed into the wider environment-unless they are neutralised, sealed away or impounded behind dams. This oxidation can continue for centuries, creating a long term liability for companies that want to pack up and walk away when a mine closes. The dangers are greatest, says Pedersen, when heavy rainfall creates a risk of floods and if the threat of earthquakes hangs over tailings dams.

Peterson calls the tailings stored on land at hundreds of mines all over the world "disasters in waiting". Some have already happened. In 1996, a month after the plugs gave way on Marinduque, a burst tailings dam near Guadalquivir river in southern Spain covered thousands of hectares of farmland with an oozing mass of acid slurry laced with toxic metals, and seriously polluted the nearby Donana national park. This year, the collapse of another dam as a gold mine in Romania killed fish all down the Danube river system.

The solution, says a new generation of mining engineers and geologist, is to return to the ocean. But this time they want to dump waste at least 100 metres down. Below the surface layers, where the most mixing goes on, and away from upwelling currents, they say the tailings should flow down any slopes to the ocean floor at a depth of a kilometre or more. The most enthusiastic advocates of this approach are mine companies operating in mineral-rich South-East Asia, where high risks of floods and earthquakes make land disposal par-ticularly hazardous. Stuart Jones of NSR Environmental Consultants in Hawthorn East, Victoria, Australia, which advises many of them, sums up the case: "The environmental effects of deep-ocean disposal are temporary-and there is no need, or liability, for long-term maintenance."




Pedersen agrees that it is "the environmentally responsible option" because ocean waters solve the sulphide problem at a stroke. Oxygen is sparse in deep ocean waters, slowing the rate of oxidation of the tailings "by at least four orders of magnitude". Minimal oxidation means little or no acid formation, so the metals should stay put in the tailings and not wash out. Moreover, within a few years, the tailings will have been covered by other ocean debris, sealing them off from all oxygen so long as the seabed remains undisturbed. This "perpetual anoxia", says Pedersen, is "the ideal permanent storage setting".

But many marine biologists are suspicious. They point out that the environment will suffer and that little research has been done into the effects of metals and sulphide deposits on bottom-dwelling organisms. Ocean disposal "will save [mining companies a great deal of money that they would have to spend on tailings dams," says Rob McCandless of Environment Canada, the state environmental watchdog in a country that is the home base for many of the world's largest mining companies. He accuses the companies of exaggerating the hazards of keeping tailings on land and trying to per-suade Asian governments to allow ocean disposal-which is banned in Canada.

Despite the current stand-off between those pro and anti deep-sea disposal, the mining companies are forging ahead-and nowhere more so than in tropical Asia. This is the home of most of the 26 deep-ocean disposal projects that are up and running or at the planning stage. The first, begun in 1989, was at a huge gold and silver mine on the island of Misima, 200 kilometres east of the mainland of Papua New Guinea. This mine is owned, coincidentally, by Placer Dome. At Misima the company discharges up to 22,000 tonnes of tailings a day into the Solomon Sea at a depth of 112 metres. The tailings flow down a steep slope and come to rest more than a kilometre down.

A carpet of tailings up to 75 metres thick already covers 20 square kilometres of seabed, obliterating all life. Some organisms will eventually return but, as Jones con-cedes, they will inhabit a much poorer ecosystem in which "hard-bottom" habitats are gone for good. Even so, for mining engineers this is a small price to pay. They see Misirna as a success story. Jones claims that no tailings have resurfaced and nearby coral reefs are undamaged. Local deepwater fish do contain enough heavy metals to make their sale illegal, but the metals are of natural origin and their levels have not increased since the mine opened, he says.

Not good enough, say the marine biologists. They point out that even this model project has had its problems. In 1997, a submarine landslide broke the discharge pipe. Fortunately, the breakage occurred far enough down the pipe for the tailings to continue falling to the ocean floor until repairs could be made. But it underlined the risks. And, say the critics, Misima is the exception in an industry still plagued by slack technical standards, wishful environmental thinking and a cavalier disregard for local communities.

Mega-mines across the region are already adding prodigious volumes of ground-up rock to the bays off some South-East Asian islands. The biggest and newest, the Batu Hijau copper and gold mine, opened last year on the island of Sumbawa in Indonesia. It will discharge more than a billion tonnes over the next decade or so into the local bay. No mine has ever dumped so much over so wide an area, says McCandless.




Can such volumes really be safely buried at sea? Pedersen thinks so. "The main challenge is to ensure no upward pluming," he says. The ideal is to discharge more than 250 metres down into a submarine canyon which naturally channels sediment into deep waters. But he admits that in the real world things can be less than ideal.

Take the Minahasa mine on the Indonesian island of Sulawesi. It discharges tailings into Buyat Bay just 80 metres down. Since it opened in 1996, people living around the bay have complained about mud and dead fish being washed up along the shoreline, empty fishing nets, and skin rashes among people exposed to the seawater. Toxicologist Rizal Rompas of Sam Ratulangi University in Manacle, Sulawesi, last year found heavy-metal contamination in fish and plankton. He blamed the mine discharges and warned that, contrary to the mine operator's claims, toxic tailings were returning to the surface.




Mining watchdogs fear a repetition at the planned Ramu nickel mine in Papua New Guinea. It will pour 60 million tonnes of tailings a year into Astrolabe Bay at a depth of around 150 metres. Jones, who helped prepare the plan, says the tailings will come to rest a kilometre or more down. But a study by Australia's Mineral Policy Institute in Bondi junction, New South Wales, says it is "highly likely" the slope is too shallow and the flow will stop short, causing surface pollution during storms and monsoons. Jones, however, insists that even at 150 metres down the tailings would be safe.

But tailings bobbing to the surface are not the only issue. Critics of deep-ocean disposal say new research shows that, even when they stay down, tailings disperse much farther than previously thought. Particles in tailings range in size from fine clay to grains of sand. The big stuff usually sinks quickly, but the fine fractions get trapped in narrow layers of water that, because of their different temperatures and densities, tend not to mix together. These layers can break away and spread for tens, even hundreds of kilometres in what McCandless calls "the marine equivalent of a dust storm".

Does this matter? Jones suggests not. The plumes, he says, are small compared with the natural clouds of sediment entering the ocean from rivers. McCandless, however, thinks even the thinnest fog of tailings could be disastrous in some cir-cumstances. His biggest fear is that they could effectively blind the many creatures that manufacture their own light to look for everything from food to a mate. "We know very little about what goes on down there, and how the biota manufacture and use their own light sources. We certainly cannot predict the effect of a cloud of sediment that might be measured in cubic kilometres." Peter Herring, a bioluminescence expert from the Southampton Oceanography Centre says: "Any event or process that disrupts the range at which light communication can occur in the sea could have profound consequences."

Jones says this is alarmist. But he admits that the subject of bioluminescence "has never come up in any of the 24 deep submarine placement projects we have worked on to date". I know of no research into this issue," says Pedersen. Perhaps no effects have been seen because nobody has looked.

In this scientific fog, does it really make sense to begin the excavation of whole mountainsides and dump their ground-up remains on the floor of pristine, coral-fringed tropical bays? McCandless thinks not. The answer to the problem of acid tailings is to improve engineering on land to prevent the oxidation of stored sulphide tailings, he says. "We need simple, good engineering of safe structures."

Pedersen profoundly disagrees. Land disposal is almost always misguided, he says. 1n fact 1 think that it is irresponsible to put sulphide-rich tailings in conventional ponds in seismically active, high-rainfall areas with the expectation that they will remain in a safe state in perpetuity." But tailings put beneath the waves, "if disposed of properly are essentially chemically inert in perpetuity".

So is this the answer for Marinduque: take the spilled tailings that still pollute the Boac river and deposit them on the seabed? Placer Dome believes it is. "The deep-sea environment has the natural capacity," it told the Philippines government. But, when pressed on this point, even the pro-ocean disposal experts get coy. "Not all tailings are suitable for submarine disposal," says Pedersen. "Careful study would be needed prior to making a decision on sea dumping."

Joe Mifsud, an environmental specialist at Placer Dome, claims that the amount of oxidation in the tailings would be "very small", because it is mostly buried in piles along the river channel. But a new survey by the US Geological Survey, published this autumn, reveals that the tailings are heavily oxidised, and that acid and metals are leaching out. It warned against submarine disposal, saying its tests revealed "considerable potential that a highly acidic, metalenriched and environmentally detrimental plume would develop in the ocean around the tailings discharge point".

It sounds as though the people of Marinduque may be right to fear the worst.