快猫短视频

BATTERIES, diesel, oil drums and dead dogs. These are just a few of the items that have been dumped in makeshift rubbish tips in Antarctica.

Decades of exploration and research have left more than 70 waste sites spread along the coast of the continent on ice-free rocky outcrops, which also happen to be home to most of Antarctica鈥檚 wildlife.

鈥淒ecades of exploration and research have left more than 70 waste sites in Antarctica鈥�

Under the 1991 Madrid protocol, the countries responsible for these waste sites must clean them up, yet progress has been painfully slow. This is largely down to the high cost of working in the inaccessible Antarctic, where removing just 1 tonne of contaminated ground costs $4000, compared with $400 in Alaska.

There are also serious technical difficulties. The waste is locked up in ice for much of the year, making it almost impossible to dig out. When the thaw does arrive, meltwater can carry pollution into lakes and the ocean just when animals in the region are beginning to reproduce. This makes digging up sites during the thaw risky, as disturbing the ground can cause even more pollution to be flushed into the ocean (快猫短视频, 6 October 2001, p 16). What鈥檚 more, traditional technologies used to prevent this run-off while the rubbish is removed 鈥� or render pollutants harmless so that they can be left in the ground 鈥� are rendered useless by the freezing conditions.

Cleaning up the continent could be about to get much easier, however, with the help of new techniques currently being tested in Antarctica and in laboratories elsewhere. For some sites with large amounts of solid waste such as fuel drums and batteries, removal is the only real option. Other sites, such as those contaminated with fuel or heavy metals, might be contained and treated on site at a fraction of the cost.

At Australia鈥檚 Casey research station on the east coast of Antarctica, for example, there has been a series of diesel spills, including an incident in 1999 when 5000 litres was discharged. That diesel is now seeping into a lake that empties into the ocean, so containing it is Australia鈥檚 highest remediation priority. A team led by Ian Snape of the Australian Government Antarctic Division in Kingston, Tasmania, is working on a new technique they hope could solve the problem. If successful, the team, which is collaborating with Geoff Stevens at the University of Melbourne and Damian Gore, a physical geographer at Macquarie University in Sydney, believe it will give a much needed boost to international clean-up efforts. 鈥淚f we can develop cheap, effective in situ techniques, it might encourage other countries to do more,鈥� Snape says.

In temperate climates, the most effective way to remove pollutants from groundwater is to use a permeable reactive membrane. These barriers contain materials that adsorb the pollutants or transform them into harmless substances. However, their absorbency means they generally hold a lot of water, and in Antarctic conditions that means they are likely to freeze solid. They then take longer than the surrounding soil to thaw in spring, rendering them useless just as the polluted meltwater begins to flow. 鈥淭hey effectively become a big plug, as water just flows around or over them,鈥� says Snape. To add to the problem, the fact that water expands as it forms ice crystals means the material is often left full of holes, Stevens says. 鈥淚t鈥檚 like someone comes along and drills a hole through your barrier.鈥�

To get around these problems, the team has been experimenting with barriers containing reactive granules of different sizes. One problem with conventional barriers is that granules less than 200 micrometres across can become clogged with 鈥渂iofilm鈥� created when bacteria form communities on the surface. This hinders water flow through the barrier, helping it to become waterlogged and freeze. The goal is to find a granule size small enough to retain a high surface area for adsorbing pollutants, but large enough to allow water to flow freely. The team is currently experimenting with granules ranging from 0.4 to 2 millimetres across.

Last December, the researchers installed a prototype barrier in the ground at Casey by digging a trench 5.5 metres long, 2 metres wide and 1 metre deep across the path of the polluted meltwater. They built wings on either side to funnel the water towards the trench, which was then filled with a barrier consisting of three layers of permeable, reactive materials.

The first layer uses zeolites to release nitrogen into the water. Zeolites are aluminosilicate compounds with a porous, honeycomb structure. Before installation, the zeolite is washed in a concentrated ammonium chloride solution to loosely bind positively charged ammonium ions to its porous surface. As the meltwater washes over the zeolite, native bacteria pick up the ammonium ions and use them to metabolise hydrocarbon pollutants. To trap the hydrocarbons long enough for bacteria to break them down, the second layer contains granules of activated carbon, a dry, porous material with a large surface area.

The final layer contains another zeolite, this time activated to take nutrients back out of the water by swapping its positively charged sodium ions for excess ammonium in the water. This prevents a plume of nitrogen-rich water moving downstream and causing an algal bloom that would kill fish and other aquatic life.

Last month a three-person team arrived at the site to begin analysing hydrocarbon levels in water that has passed through the barrier. The initial results are expected in the next few weeks, and if the barriers prove successful they could be used at four other Australian sites in the Antarctic.

This season, researchers will also collect soil samples from three waste sites for research into new ways to deal with heavy metal pollution caused by dumped batteries, construction waste and abandoned mechanical parts. Copper, lead, nickel, zinc and cadmium are the main culprits. In Australia, soil contaminated with heavy metals is churned with an orthophosphate solution, which immobilises metal in the soil and prevents it being leached out. The soil can then be safely buried in landfill. 鈥淲e want to know: would that work if we tried it in Antarctica?鈥� Snape says. 鈥淲ould the freeze-thaw process destabilise the binding? And could we find a way just to inject that orthophosphate solution, without having to dig the polluted soil up? That would be a huge cost saving.鈥�

It is not just Antarctica that could benefit from this research. The team hopes the methods could also be applied in the Arctic, particularly across the countries of the former Soviet Union, where Snape describes the amount of contamination as 鈥渟taggering鈥�. The size of the problem means low-cost remediation technologies are essential.

In North America, BP Exploration Alaska has agreed to provide funding for further development of the barrier concept, in the hope of using the technology to contain any spills from its petroleum exploration sites. Meanwhile in Canada, though the government committed CAN$3.5 billion (US$3 billion) in 2004 to the clean-up of federal contaminated land and innovative techniques for in situ stabilisation are being developed (see 鈥淪lammed in the cooler鈥�), there is also an urgent need for effective ways to clean up former mining areas.

In situ treatment is about being realistic, says Snape. 鈥淚n Antarctica, we鈥檇 all like to see it pristine again with no contamination, but for many sites that is just not going to be achievable. A far better thing is to manage these sites in a practical way. Let鈥檚 control it and make sure there are no further impacts, and let the environments recover. That鈥檚 our goal.鈥�