How can I measure mercury in my tomatoes?

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Andy Allen

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How can I measure mercury in my tomatoes?
« on: 06/09/2009 19:30:02 »
Andy Allen  asked the Naked Scientists:
   
Hi Chris,

I love your podcast.  I live in Chicago, Illinois, near a coal-burning power plant which spews forth a certain amount of mercury. I have heard that vegetables can absorb lead from polluted soil.  Is the same true for mercury?  If so, is there a way I can do a reasonably accurate yet inexpensive mercury test on my tomatoes?

Thanks,

Andy Allen

What do you think?

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Offline Jeff Corkern

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How can I measure mercury in my tomatoes?
« Reply #1 on: 20/09/2009 22:21:36 »
Andy Allen  asked the Naked Scientists:
   
Hi Chris,

newbielink:http://www.thenakedscientists.com/HTML/podcasts/ [nonactive].  I live in Chicago, Illinois, near a coal-burning power plant which spews forth a certain amount of mercury. I have heard that vegetables can absorb lead from polluted soil.  Is the same true for mercury?  If so, is there a way I can do a reasonably accurate yet inexpensive mercury test on my tomatoes?

Thanks,

Andy Allen


What do you think?

Hey, Andy. I am an analytical environmental chemist and am qualified to answer this question.

Yeah, it's at least theoretically possible for mercury to be in your tomatoes. Fortunately it's possible to do a reasonably cheap test for it.

It just so happens to be relatively easy to test for mercury, because mercury possesses the unique property (for a metal) of being easily volatilized. What you do is:

---suspend a very small amount (around 0.2 gram) of tomato in water.

--- smash all the organics down to nothing with potassium permanganate, which will also take all the mercury to Hg+2

---remove the excess permanganate with thiosulfate.

---add tin chloride, which will reduce the Hg+2 to Hg0, Hg metal.

---bubble argon through the solution. The Hg metal will be blown out into the argon stream.

---measure the absorbance of the argon stream at 253.7 nm. Mercury is VERY absorptive at this wavelength, so the resulting sensitivity is EXTREMELY high. Routine Minimum Detection Limits in water are around .002 ppb.

Most environmental labs are capable of carrying out this test. Look a few up in your neighborhood, call them up and ask them what they charge for doing Method 7471A on a small piece of tomato. There are special mercury machines for doing this test. I don't expect the cost to be all that much. I would recommend telling the lab to spike the sample with a 20 ppb spike to have a better idea how good the final results are.

Here's a link to the method I am talking about:

newbielink:http://www.cornerstonelab.com/SW-Methods/PDFS/7471A.PDF [nonactive]
Jeff Corkern

"Either war goes away, or the human race goes away."---^NMG^Dark_Hunter

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Offline techmind

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How can I measure mercury in my tomatoes?
« Reply #2 on: 20/09/2009 22:50:59 »
Jeff, if the test is that sensitive, what would you consider to be an acceptable harmless / background level for mercury?

And if the level in the tomatoes did turn out to be concerning (hopefully not) would the tomatoes actually be the least of the worries - because it would indicate a high level of mercury inthe soil/air around the house?
"It has been said that the primary function of schools is to impart enough facts to make children stop asking questions. Some, with whom the schools do not succeed, become scientists." - Schmidt-Nielsen "Memoirs of a curious scientist"