My guess is it'll eventually be traced back to improperly disposed of Cs-137 source. This wouldn't be the first time [1] [2].

There was also a famous case in the 80s where a scrapyard in Mexico sent some steel contaminated with Cobalt-60 to a foundry where it was melted down into rebar. It was detected when a truck transporting rebar to a construction site took a wrong turn and ended up at Los Alamos National Laboratory, where it triggered contamination alarms. By that point, the rebar had been used in a whole bunch of construction that had to get torn down.

[1] https://en.wikipedia.org/wiki/Goi%C3%A2nia_accident

[2] https://en.wikipedia.org/wiki/Acerinox_accident

[3] https://en.wikipedia.org/wiki/Ciudad_Ju%C3%A1rez_cobalt-60_c...

> Officials from Indonesia’s nuclear energy regulatory agency have traced the source of contamination to a steel manufacturer in the Cikande industrial area known as Peter Metal Technology, or PMT. Some of the highest levels of contamination detected in the area were reportedly found in the company’s furnace, which is about 1.5 miles southwest of the BMS Foods facility where the shrimp was processed.

> It’s unclear how it may have become contaminated with cesium-137. Biegalski, whose area of expertise includes nuclear forensics, told CR that the “easiest explanation” is that a medical or industrial device containing cesium-137 was inadvertently reprocessed as scrap metal. The radioactive material could have become gaseous after entering the PMT furnace and then been released from the facility’s smokestack, he said.

For intensely radioactive materials used in medical equipment and elsewhere, can we require the equivalent of a bottle deposit, where buyers pay a large sum up front when their device is installed and then, when the device reaches the end of its life, the manufacturer or government pays them to get it back and properly disposes of it? I'm guessing that nearly all instances of this sort of thing happening are because of attempts to dodge the - likely large - cost of proper disposal. Make it profitable to do the right thing and organizations will.

I found this article a bit better than Reuters one;

https://www.consumerreports.org/health/food-safety/radioacti...

There is something so horrifying about basic nuclear physics.

Weird. Cesium 137 is only produced in spend nuclear fuel as far as I know. Was someone trying to get rid of nuke waste contaminated scrap metal? Soviet maybe?