As a general characteristic, most of the eastern parts of Japan were effected by a total 137 Cs deposition of more than 1,000 MBq km−2 . Our estimates show that the area around NPP in Fukushima, secondarily effected areas (Miyagi and Ibaraki prefectures), and other effected areas (Iwate, Yamagata, Tochigi, and Chiba prefectures) had 137 Cs depositions of more than 100,000, 25,000, and 10,000 MBq km−2 , respectively. Airborne and ground-based survey measurements jointly carried out by MEXT and the US Department of Energy (DOE) (21) show high 137 Cs deposition amounts were observed northwestward and up to a distance of 80 km from Fukushima NPP. It was estimated from the first measurement that by April 29, more than 600,000 MBq km−2 had been deposited in the area, which is greater than our estimate of less than 500,000 MBq km−2 (Fig. 2A), yet well within the range of uncertainty of our method (Fig. S4).1,000 MBq (megabecquerels) per square kilometer is 1 kilobecquerel per square meter, so the three broad exposure estimates correspond to 100, 25, and 10 kBq m-2, with maximum treatments around 500-600 kBq m-2. To answer how worried we should be about this, we turn to Almond, Edlund, and Palme, 2009:
We use prenatal exposure to Chernobyl fallout in Sweden as a natural experiment inducing variation in cognitive ability. Students born in regions of Sweden with higher fallout performed worse in secondary school, in mathematics in particular. Damage is accentuated within families (i.e., siblings comparison) and among children born to parents with low education. In contrast, we detect no corresponding damage to health outcomes. To the extent that parents responded to the cognitive endowment, we infer that parental investments reinforced the initial Chernobyl damage. From a public health perspective, our ﬁndings suggest that cognitive ability is compromised at radiation doses currently considered harmless.The heaviest fallout in Sweden (also due to Cesium 137 contamination) was around 65 kBq m-2 (see figure 2 of the paper). Moreover Japan's population density is roughly an order of magnitude larger than Sweden's. Given this, it looks like the long term human costs of this disaster may be absolutely staggering.