Interesting video here, nut I don't know geographiacally where from?
The main interest of this video is that it shows clearly a phenomenon that has to be understood by anybody who wants to (try to) link measurements and risks for human health. It shows that in the very same area, measurements in microSv/h can HUGELY vary depending on how and where the measurement is done (and this is very often the origins of disputes between associations and autorities: meaning of measurements depending on how the measurement is done).
Which means that any measurement disclosed (also for the global measurements in the areas in the 20 or 30 kms areas) has to be taken as an indication but not a true picture of reality when trying to assess the mid or long term risks for human health (especially when trying to compare those to "thresholds" or "limits" or whatever).
A good part of contamination is related to dust particles carrying contamination, which will concentrate in geographical areas (leopards spots) and in one of such areas, there will be also a huge variability in places where particles will concentrate. The video shows for example that at the output of draining pipes from roofs, where particulates deposited with rain for example, the contamination concentrates. In a few meters distance, the levels can vary from one or several orders of magnitude.
The problem is that if you measure it at a level of let say 1-1,5m (your hands level) you'll get a measure very different than if you measure it at ground level, and at ground level, this measure will also widely vary depending on the spots. Everything that can move the particles is of factor of variation or concentration, and this can of course evolve with time: wind can relocate particles that were on the ground (so people can inhalate them), water will concentrate the dust all along its paths, etc.
The real exposition of a person living at a certain place for a given time will depend more on what he will do, breath, drink and eat, than on a global measured (but measured how?) value then extrapolated for a year, because this doesn't take into account the complexity of the processes involved.
In classical studies done for ongoing chemical pollutions out of many factories in their "normal" activities, the calculations done to assess the excess risks of cancers for example into one exposed population take into account a huge number of parameters, such as what people will eat and so on. And these will only give you a rough idea of some average exposition (that's why safety coefficient are put into place, to try to take into account the fact that measurements and dispersions are complex matters).
It is known for example that in the case of children, a major path for contamination to enter their body is through "ingestion of soil". This looks always surprising but not so much when you consider what they do during the day and also the fact that their mouth is not at the same level than ours as adults!
This info illustrates very well the point: http://www3.nhk.or.jp/daily/english/26_19.html
(even if this is maybe a "good" decision, it seems more a psychological related one than an effective one... because who can think of dust particles not moving from around with the wind and rain and redepositing?
This remembers me a lot of silly stuff done at Tchernobyl to try to fix contamination. Environment and contamination processes are somewhat different in essence than just the basic housekeeping cleanliness psychology: "this is dirty, this is clean"!
Ok, doing something is sometimes the only thing to do, so...
Hope this video and these explanations will help to understand the difficulty for REALLY assessing exposition risks for various people in a given area. Reality is always more complex than models and comparison of a number to an other number!
