New Discoveries In The Fukushima “Black Stuff” Mystery

Marco Kaltofan announced last week some new understanding of the strange radioactive black sand being found in Japan. The substance has been found in parking lots and street gutters in some far flung areas including Minamisoma, Fukushima City, Tokyo and various locations in and around the evacuation zone. The substance has an intense radiation reading in all instances if its discovery but details of exactly what it is has been more elusive.

Marco was able to obtain a small sample from just outside the evacuation zone in Namie. The black sand like substance was tested using NaI-well gamma spectrometry. It was found to not contain any plant matter and was made up of mineral substances. Additional testing was done using “scanning electron microscopy with energy dispersive X-ray analysis.”.

The substance measured 1.5 MBq per kg (mega-becqurels). The following were found in the sample:
Cesium 134
Cesium 137
Cobalt 60
Radium 226
Rare earths

Some of the substances could be either natural or artificial in origin, others such as the cesiums and cobalt 60 would have had to come from an artificial source. More should be known soon after some additional testing is completed. Below is the complete communication as posted by Marco Kaltofan:


We recently received a sample of black street dust from Namie, Japan that tested usually high for radioactivity.   This small street dust sample weighed only 1/10th of a gram, but was found to measure at 153 Bq total of radioactive cesium and uranium daughter isotopes. (That’s equivalent to about 1500 Bq per gram or 1.5 MBq per kg.) Cobalt-60 was present at 0.3 Bq per gram.  The most concentrated uranium daughter isotope found was radium-226.
The dust sample had many particles containing mostly lead, yttrium, various rare earths, and thorium.  Some of these lead and rare earth particles were microscopic, measuring only 1 or 2 microns in size.  Under a digital optical microscope, no molds or plant materials were detected, just mineral particles.  Some of the microscopic lead particles found might have been paint, but others appeared to be metallic lead.
There is no sure way to know why a small street dust sample was so contaminated with radiation compared to its surroundings.  The dust was collected just a few hundred feet outside the 20 kilometer exclusion zone around Fukushima-Daiichi.  Occasionally observers have reported small deposits of windblown black sediment which measures higher than normal for radioactive forms of cesium and other radioisotopes.
This is the first time we have examined one of these black sand samples, and it had the highest radium-226 levels we’ve seen yet for dust or soil from Japan.  Normally the Cs-134 and Cs-137 levels are much higher than the uranium daughters.  A quick look at the gamma spectrum attached shows that Ra-226 and Cs-137 levels are similar in this dust.
The sample was measured by NaI-well gamma spectrometry.  I have attached the screen shot of the gamma spectrum.  Yttrium, lead, thorium, rare earths, and particle size were measured by scanning electron microscopy with energy dispersive X-ray analysis.


Marco Kaltofen, MS, PE, (Civil, Mass.)
Boston Chemical Data Corp.
2 Summer Street, Suite 14
Natick, MA 01760
Dept. of Civil and Environmental Engineering
Kaven Hall
Worcester Polytechnic Institute
Worcester, MA 01609

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