This is very interesting, maybe we need to look into this. This could be great project for .Dr. Fields to look into

George

We test houses with houseplants that test over the action level frequently. If the plants do mitigate radon, it must not be very effective.

It’s my understanding that houseplants can reduce particulate. Radon doesn’t cause lung cancer - the decaying progeny solids do. Therefore, it seems plausible that house plants, by removing particulates with attached radon progeny)l could reduce the risks of radon caused lung cancer. How significantly, if true, would be very site specific. Note: removing radon progeny from the air would not reduce the radon level - just the risk.

Comments by Dawn and Donald above are essentially accurate. Radon gas itself does contribute a small (but non-zero) fraction of the alpha dose and hence lung cancer risk. Plants can collect from the air radon progeny that come in contact with them, and in proximity to them if there are favorable charge differentials.
I saw that there was at least one small study in this regard at https://www.sciencedirect.com/science/article/pii/S004896971732274X I hasten to point out that this study was made using a "Rn chamber." Of course, in real life, soil is gas is being introduced, and air in the building is being exchanged, on some kind of regular basis. The key to answering whether plants "work" lies in understanding two things:
1) how well plants themselves can "keep up" with the regular infusion of newly introduced radon and radon progeny into the air that passes around their leaves;
2) how well air in the building's breathing space has time to get into adequate proximity of the plants in order to have even a chance of being "cleaned" before that air is breathed.
Sure, certain plants can measurably reduce, to some extent, particulate concentrations in chambers, but I have yet to see a study that shows any level of significant effectiveness under typical circumstances in occupied buildings.
Simply, setting out a few candidate plants to solve a radon problem is likely to be akin to relying on magic.

So if i read this research paper correctly in a chamber over 72 hrs the plants reduced radon levels faster than test decay rates. i did not follow the math see by how much. i also did not see how they were measuring the radon levels based on gamma emmisions or alpha emmisions. Some adsorbtion into anything of volume in a chamber would reduce ability to measure the actual radon in the chamber by reducing the measurable alpha because alpha would not get out of plant or soil once it diffused in.
i am very suspect of this science could stand up to actual field testing. likely the belief that put forward by "plant lady" is just another well meaning non scientist spouting radon facts based on partial understanding of radiation science...... just like radon is a big heavy atom so it sinks to bottom of house claim i have heard over and over please if you are in the business squish this radon myth any time you can.

Did not review more than the abstract and a few thumbnails of figures, but noting use of chamber set-up was sufficient to raise some question for me about how this relates to real life. Full article doubtless has more details in answer to your questions, but I did not access it. Re: "i am very suspect of this science could stand up to actual field testing." Yes, that was my feeling as well. Note also that it's not the alphas that diffuse into or out of materials, but rather their source radionuclides that might become attached or otherwise incorporated therein. It strikes me that an interesting control object might be something else common in a house, such as a throw pillow; curious how that might do compared to this plant. :-)

Sorry i was unclear , the"it" was radon diffusing into the plants and soils........ What i was trying to say was the introduction of plants and soils into a volume of air that has a known activity (baseline). the plants offer now a smaller volume of air in the chamber when the radon adsorbs by diffusion into houseplants could change significantly the measurable alphas in the air from radon and daughter products until stable levels are achieved (the plants and soils now have a radon concentration of close to 5200 Bq/m3) . After stability is achieved it is also possible that the alphas created by radon and daughter products would not likely leave the plants and soils to be able to be measured, and what appears to be plants reducing radon could be pillows reducing radon.

The reduction could be simply achieved by the plate out factor, of a much larger surface area, created by the plants in the chamber. If one was only determining the levels in the chamber from alpha strikes, thereby inferring radon reduction but not really achieving it..... i still don't think this would stand up to field testing. i do hope someone got a PHD out of this, but i have trouble believing this. (that's Plumbing, Heating and Drains) which is the only one i have...........Bob the plumber

And what happens to the supposedly radioactive houseplants? Do they mutate like Little Shop of Horrors? Do they become radiation sources themselves? Enquiring minds want to know!

Radioactive mutations is likely how we got to be here! i like being at the apex of the food chain! thank you ancestors. :-)

If the radon removal was significant the plant would become radioactive. The theory could be tested this way.

Tobacco contains RDPs, of which polonium (half life = 138 days) is most important, since it is a high energy alpha emitter and volatile (vaporizes) at cigarette temperatures. Tobacco leaves are very sticky thus particulates (dust and RDPs) stick. So, plants can remove 'radon' but is it not significant compared to what's in the air.

The primary source of polonium in tobacco is radium in high-phosphate fertilizers that are used to grow tobacco.

This is interesting but I don't think it would be a valid mitigation method. I remember a few years ago someone gave a presentation on magnetic rods being placed into the basement slab or house slab and electrified them and that helped reduce radon. That did not prove to be effective either. The best method is to set up a negative pressure field under the foundation. This message is tried-and-true and most effective.