Juni,
I think there is too much fear (concern) being generated over Polonium-210. It is an alpha emitter, which means that it cannot penetrate the skin. So, casual exposure on public trtansportation is not all that serious. However, if it gets airborne in any significant concentration, and ingested in the lungs, it can get nasty as we have seen. The people being asked to report to be checked out are not in any real danger, but their cloths and skin need to be checked to be sure that they are not still contaminated. Likely, their homes and personal effects that they have handled recently will have to be checked with a Geiger counter.
There are a number of myths and misinformed stories being generated ... and unfortunately, some stories are confusing Polonium-210 with Plutonium. The difficulty will be the long and tedious task of decontaminating all the places where it was found, such as restaurants and aircraft, or other public places. The quantity discovered in discrete locations (or "hot spots") will determine whether decontamination procedures are required.
Jim Whitney
PS: I worked in the nuclear power industry for 17-years of my 25-year engineering career. I conducted and analyzed a lot of research and destructive testing of components exposed to radioactive environments. Polonium-210 is a by-product that can appear in nuclear reactors, but is not used to power nuclear reactors. It used to be used to power sattelites in the 1950s and 1960s, but was stopped because of its short half-life of 140 days.