Scientists in Sweden have discovered a moss that purifies water contaminated with poisonous arsenic so successfully that it becomes safe to drink.

Researchers at Stockholm University say the aquatic moss, warnstofia fluitans, which flourishes in northern Sweden, can rapidly absorb arsenic, removing as much as 82 per cent of the toxins within one hour in some tests.

Due to mining operations in this part of Sweden, wetlands and water sources used for drinking and for growing crops are often contaminated with arsenic.

The research team said the discovery could provide an environmentally friendly way to purify the water.

One possible scenario is to grow the moss in streams and other watercourses with high levels of arsenic, they said.

"We hope that the plant-based wetland system that we are developing will solve the arsenic problem in Sweden's northern mining areas," said Maria Greger, associate professor at the Department of Ecology, Environment and Plant Sciences at Stockholm University and leader of the research group.

Arsenic is a metalloid element common in many minerals, and is a common waste product from mining. Mine tailings are a major environmental issue as they can often be highly toxic. It is difficult to successfully isolate large deposits of waste, and as a result, concentrations of toxins can end up in water sources.

In Sweden the bedrock contains high levels of arsenic, which has been brought to the surface by mining.

The arsenic enters water courses, and then raises levels of arsenic in crops. In Sweden, this applies to wheat, root vegetables and leafy greens, the researchers said.

A small amount of arsenic in some foods is not abnormal. In other countries, there are high levels of arsenic in rice, for example.

“How much arsenic we consume ultimately depends on how much of these foods we eat, as well as how and where they were grown,” said Professor Greger.

“Our aim is that the plant-based wetland system we are developing will filter out the arsenic before the water becomes drinking water and irrigation water. That way, the arsenic will not make it into our food," she added.

The research, published in the journal Environmental Pollution, centres around the ability of the moss to perform a process called phytofiltration, in which waste products such as heavy metals like arsenic are largely absorbed.

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