I'm not sure to get. They say took decades for this particular pollution to reach the Philippines via ocean circulation systems but the images suggest it's coming from rivers. Is it possible that china is hiding something?
You'd see other isotopes if it was something recent. It's hard to hide things like this, see the Ruthenium plume that was detected over Europe in 2017 [0]. Radiation instruments are very sensitive!
By publishing recent studies showing a smoking gun?
UP MSI said the results were consistent with recent Chinese studies linking iodine-129 in the Yellow Sea to decades-old nuclear weapons tests and nuclear fuel reprocessing facilities in Europe, ...
China has a great many reactors, nuclear warheads, acres of low level waste from rare earth processing .. they have as much to hide as the US does, that said there's not a lot to gain here by pretending they don't have potential sources - but isotope fingerprints can be verified and all the byproducts from > 2,000 test explosions and the creation of 10,000+ warheads globally do get mapped and tracked.
[0] https://cen.acs.org/safety/industrial-safety/caused-plume-ra...