It’s not only radioactive debris but also daily garbage from your house that emits radiation when it’s burnt.
This is the comparison of the cesium contained in incinerated ash in Tokyo and Osaka.
The data of Osaka is in early September, which is more likely to be contaminated. (“不検出”=ND)
It means the daily garbage from kitchen, living room, garage, and the garden contains more cesium in Tokyo.
(Source) OsakaIori Mochizuki