spain recently congratulated itself on saving Donana national park, one of the continent's most important wetlands, from a flood of toxic sludge from a mine. The celebrations, however, may be short-lived, for mining engineers and naturalists fear that land outside the park may have been contaminated with enough heavy metals to poison the entire region for years to come.
The disaster was caused by a breached dam at the huge open-pit mine at Los Frailes near Seville, owned by the Swedish-Canadian firm Boliden. In 1997, its first year of operation, the firm produced some 18,00,00 tonnes zinc, lead, copper and silver from four million tonnes of ore. The water, crushed ore and chemicals left behind after the metals have been removed are dumped in the settling pond of another mine that was abandoned in 1996 after 19 years of operation. An earth dam holds the effluent in the pond.
In May this year, a 50-metre-wide breach in the dam sent four million cubic metres of acidic water and silt down the Agrio River, heading straight for Donana. Frantic bulldozing diverted the flood wave into the Guadlaquivir river and into the Atlantic. A day after the incident Spain's Environment Minister Isabel Tocino announced: "Donana has been saved.'
However, the water still flooded around 2,000 hectares of land. Michael Priester of Projekt Konsult, a mining consultancy near Frankfurt, Germany, that is dealing with the aftermath of a similar accident in Bolivia in 1996, says the flood will have deposited most of its silt, and with it unknown quantities of cadmium, mercury, arsenic and other heavy metals, onto the land. "There is no way to get that material back,' Priester says. "The metals will be bound by soil particles, and then they will leak out slowly into the groundwater, at a rate depending on local acidity and rainfall.'
Run-off from the contaminated land could soon reach the Donana wetland downstream, he cautions, and once there the metals will enter the food chain after being taken up by swamp plants. "Swamps are actually used by mines to capture and concentrate heavy metals,' he adds.
Carlos Vallecillo of the Worldwide Fund for Nature in Madrid say the pollution could possible affect Donana's wildlife without reaching the wetland. The flood has critically damaged a protected region around the park. "Many of the birds that nest in the park fly to that area to feed,' he says. "We are already seeing dead storks there.' The flood could also hurt millions of migratory birds that pass through the area.
The disaster has enraged conservationists because in 1995, a local environmental group called cepa had launched a court case maintaining the dam holding back the pond was unsafe. That case, incidentally, is still pending.