I like these studies how do they know it isn't the result of "Yes, the Fukushima Daiichi nuclear plant released significant amounts of cesium-137 (Cs-137) into the environment following the 2011 earthquake and tsunami, contaminating soils and the Pacific Ocean for decades. While much of this radioactive isotope dispersed, particularly in the ocean, it continues to be a concern due to its long 30-year half-life and potential to cause long-term environmental and health impacts on affected populations and migratory species. " so we could be lucky and be getting modern cesium - 137.

 

Possibly.

The details of this become obscured due to the odd units and the general lack of information. Both Cs137 and Sr90 were released in significant amounts.

However, the amount of fission products released during open air testing was quite large. So large that in 1961 the atmospheric concentration of C14 was twice baseline in the northern hemisphere.

Subsequently it decayed with an apparent half life of 11 years, almost entirely due to carbon entering and leaving the atmosphere.

As a side note, this is the clearest evidence that anthropogenic carbon is a small fraction of the carbon entering the atmosphere.

I suspect that the releases in the 50s and 60s of which about 25% remain, are the main source, especially in the US, as the concentration of CS137 fallout from (for example) Fukashima was mostly within a fairly short distance from the site.

I suppose the details could be ferreted out, but it would be unlikely to change the outcome.

Ionizing radiation is everywhere. In most places it is due to naturally occurring sources. I have a half kilo chunk of pitchblende which came from my wife's grandfather. I verified its composition by Archimedes' method. I am tempted to make a scintillation detector just to show my 14yo how. It should have a reasonable output of beta. I don't keep it under my pillow, of course. But it is likely harmless.

What I find interesting is how it is concentrated in nectar.

 

There is a possibility, although slim, that insecticides that effect the nerve firing effect the use of Sodium and Potassium.

From an AI search:

Neonicotinoids disrupt potassium usage by blocking the function of nicotinic acetylcholine receptors (nAChRs), which initially stimulates and then blocks the flow of potassium and sodium ions through these channels
. This action is central to their toxicity in insects but can also affect non-target species, including mammals and fish.

Cesium MAY be used by the cell in place of Potassium, being two elements directly below.????.

Psycho Roland