The remarkable metal binding properties of the dried biomass of the water fern Azolla are exploited to purify various contaminated liquids. One aspect of the invention relates to a method for the ultrapurification of an aqueous solution from a heavy metal ion comprising passing the solution through a dried biomass of the water fern Azolla. Further aspects relate to the reclamation of potable water from contaminated water and the purification of radioactivity contaminated liquid waste. Also disclosed is a sampler for determining the presence of a heavy metal ion in an aqueous solution comprising a receptacle containing a dried biomass of the water fern Azolla.
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