I found this when I searched Tulsi Basil which is reputed to have beneficial health effects.

Tulsi leaves contain a high amount of mercury and iron

Is it possible for a plant to produce these things if the soil doesn't contain any? I can't see how potting mix would have mercury in it but I don't know.
The only caution re: tulsi, is that it might discolour teeth if chewed raw...... so, not a huge deal.
Just wondering.

I dont see how a plant can produce it's own elements.
Iron from soil yes but mercury.
Really who wants mercury in the soil much less our food.
Tuna and other fish contain too much as it is.

If it's grown in mercury-contaminated soil or water, then it could contain mercury. But only then would it have mercury in it.

I think that statement should be "tulsi leaves may contain high amounts of mercury and iron", if grown in soil with high amounts of those elements.

There used to be a database at GRIN of the constituents of plants - this also showed metal contents that were certainly related to the soil contamination level, and it seemed to be a pool of data where some results could just be a single test (without a who or where). So although useful, this kind of data always has to be tempered by how much we know about the sample.
There are certain plants and fungi that accumulate specific metals if present in the environment, while others don't. A lot of work was done on remediation after Chernobyl, for example, you could actually remove certain elements from the landscape if you knew which plants to pick and take away. OTOH they'd be the worst thing to pick for a salad.

In the case of the tulsi basil, we don't know where the sample was grown, that produced these results. All you can say is, it could accumulate these elements if sources are present. Just another reason to grow your own and keep it clean.

I believe pretty much all soil has mercury in it; it's just a matter of how much.

While I don't think any plant is known to synthesize mercury, they can accumulate it from the soil. I believe sunflowers are supposed to be good at accumulating it. Trees tend to have some mercury in their wood. I believe fruits like tomatoes tend to have less mercury than vegetation, in high mercury soil.

Rice is good at accumulating mercury, if it's high in the soil. A lot of the Asian rice tested at one point was high in mercury. Hopefully that has changed by now.

Most Mercury is in the form of inorganic salts in the soil, water and rock. Bacteria in the soil convert some of salts those into methylmercury. Methylmercury then gets distributed through various means.Mercury comes from wildfires, coal fired power plants,volcanoes, old mining activity, and other human activity. It’s inescapable and worldwide. Everyone on earth has detectable amounts of Mercury in their tissues. Eating fish is the most common way to get elevated Mercury levels in the body. Interestingly, saltwater fish tends to also have selenium in it and that is protective towards Mercury toxicity in humans. Freshwater fish rarely has the selenium, but can have high levels of Mercury.

https://www.epa.gov/international-coope ... text#types