Field of Science

Eating periodically: is there thallium in your wasabi?

Wasabi, Iwasaki Kanen 1828
via Wikimedia Commons 

Could your wasabi peas be poisoning you?  Short answer. Maybe.

Delish recently posted an article on thallium — a highly toxic metal — in kale, the quintessential healthy green.  The Internet relished the irony of finding toxic metals in the highly touted greens. The piece points to an article in Craftsmanship magazine, which attempts to make a link between consumption of kale and thallium levels.  This is not new news.  There are dozens of reports, going back two decades, in the scientific literature of thallium in cruciferous vegetables, such as kale and brussell sprouts — and wasabi.

Thallium is definitely a nasty element, and has an infamous history of use as a poison in fact and fiction, starting with Ngaio Marsh's Final Curtain.  Read Deborah Blum's hair-raisingly fascinating Poisoner's Handbook (or her short article at Wired about a recent murder case in Princeton).  But as with everything, dose makes the poison, and the amounts of thallium in plants vary widely depending on the concentrations in the soil.  In highly contaminated soils, plants can contain enough thallium to be hazardous.  But if such highly contaminated soils were widespread, we'd have seen the effects already. (See this paper for some background.) (Also, you can leverage this ability and use it to clear out the thallium from a contaminated area.)

So how does thallium get into the plants? There is some evidence that thallium ions travel the same pathways as potassium ions (which play key roles in plant metabolism), and so might find their way into plants (and animals) though similar processes.

Thallium is also in the same column as boron, and elements in the same column of the periodic table often have similar behaviors, because their electrons are arranged in similar patterns.  For example, strontium, which is underneath calcium, sneaks into the body by way of the same processes calcium does. Boron is found in plants (coffee is a good source, and plants in the same family as kale are also heavy absorbers of boron); it is believed to be critical to cell wall formation.

And if there is boron and thallium, indium - in the same column is another likely companion. And yes, indium has been detected in plants in the cabbage family.  

As always, eating a wide variety of things is good advice, and it's key to remember that "natural" is not the same as "safe."

First woman in 'space'

I keep checking to see how far away New Horizons is from Pluto (459,770 km at 0235 GMT) even though I know there's nothing to see at the moment, but I am a space junkie.

The first space launch I can remember seeing is the last of the Mercury missions, launched in May of 1963.  I was 5 and I was hooked on space.  In retrospect, I suspect my hours watching rockets erect on their launch pads, the vapor streaming off the only sign this was live TV,  fed my desire to do science as much as the biography of Marie Curie I chewed through while ill one summer or my parents' careers.

I'd be glued to the TV for every launch I could for the next decade, and I confess I can still be found streaming a launch in the corner of my screen while grading.  I'm still hooked on space.

S o I was delighted to discover the first woman to leave the atmosphere — at least the breathable part of it — was both a chemist and an alum of the college where I teach.  In October of 1934, Jeannette Ridlon Piccard, a licensed balloon pilot, flew a balloon with her husband on board to an altitude of 17.5 km, well into the stratosphere.  Her altitude record (for women) would not be broken until Russian astronaut Valentina Tereshkova's flight in June 1963.  You can watch the Piccards take off in this video and see the wreckage of the gondola after they crash landed.  Her first person account of the trip was published in the New York Times the next day, including her chagrin at such an inelegant landing.

Ridlon's entry in Bryn Mawr's Undergraduate Catalog of 1916, she
would concentrate on chemistry and physics over the next 2 years. 
Piccard was a Bryn Mawr College graduate, class of 1918, taking course work in chemistry and physics, as well as psychology and philosophy.  She went on to get her master's degree in chemistry from the University of Chicago and later a Ph.D. in education from the University of Minnesota.  All wonderful preparation for being an...executive secretary (those were not the days), pilot and stratospheric explorer.  Piccard's papers are the Library of Congress and I'd love to go read the experimental notes from that epic flight.

Piccard's grand-nephew Bertrand Piccard is one of the pilots on the Solar Impulse, a solar powered plane attempting to circumnavigate the globe.

My thanks to Bryn Mawr College's registrar, Kirsten O'Beirne, for figuring out how "majors" worked in the early 20th century.

Sequencing data

The New York Times recently posted a piece on problem solving which asked readers to first solve a problem:

"We’ve chosen a rule that some sequences of three numbers obey — and some do not. Your job is to guess what the rule is. We’ll start by telling you that the sequence 2, 4, 8 obeys the rule."

You can test your hypotheses by typing sequences into three boxes to see if they follow the unstated rule.  Once you think you know, you type in a description.  Most people it turns out, suggest an answer without ever trying a sequence that returns a firm "NO."  Psychologists interpret this as being evidence of confirmation bias: once we get a "yes" for our theory - we don't poke around trying to find a "no."

When I teach chemical kinetics, I point out to students that few experiments can prove a reaction goes in a particular sequence, only that the data is consistent with a proposed mechanism.  No answers can be as or more critical to problem solving as yes.

I failed to 'correctly' solve the puzzle, [SPOILER ALERT] though I did get several no answers.  One rule I tried was an: 21, 22, 23 = 2, 4, 8.  The sequence 1, 1, 1 follows that rule (11, 12, 13 are all one), but yielded a no.  The rule an = 2 x an-1: 2, 2x2=4, 2x4 worked for every sequence I tried, but is not 'the 'answer.  The answer is that correct sequences have each number larger than the last.

The study suggests I failed not only because of confirmation bias, but because I complicated the problem, assuming that there was some sort of trick to the rule. Actually, I assumed the technical mathematical meaning of sequence held, in that there was a rule that uniquely specified each number in the sequence given the starting value(s). An ordered list of numbers, each of which is larger than the previous value is not a sequence in the mathematical sense.

In retrospect, I should have tried the sequence 0, 0, 0. It follows the rule I proposed (an = 2 x an-1) as the correct one, but returns a "no." It would have ruled out my proposed rule, a useful "no".  (I might also have tried non-integer numbers.)  I failed in part because I didn't understand the question they were asking, we didn't have the same definition of "sequence."  In some sense I fell prey to the "when all you have is a hammer, everything looks like a nail" scheme.

There are more than 2500 rules that would give you the mathematical sequence 2, 4, 8.  See Sloane's encyclopedia of integer sequences.  My first proposed sequence is A000079 in the collection.

For more about sequences and Sloane's encyclopedia, read this article at AT&T.