Ionising radiation can be used to destroy pollutants like polychlorinated biphenyles (PCBs) and heavy metals from water. The radiation treatment is being developed at the US government's National Institute of Standards and Technology in Gaithersburg, Maryland, and the University of Maryland in College Park. In the case of a PCB molecule, gamma radiation (provided by a passive source like an electron beam accelerator) shakes apart the chlorine atoms making the remaining molecule less toxic. The basic idea behind heavy metal removal is the splitting of the water molecule by the radiation releasing electrons. Some of the electrons released in the process collide with the heavy metal atom releasing metal ions, which are insoluble in water. These are later removed by settling or filtering ( New Scientist , Vol 150, No 2033).