Wednesday, August 22, 2007

The Fightin' Eighty-Second

Over the last few weeks, the news has been inundated with reports of the largest toy recall in history. As millions upon millions of Mattel’s Chinese-made toys are being recalled because of lead-based paint, I thought I might say a few words on the vicious antagonist in this story.

As a geologist I am well aware of the eighty-second element on Mendeleev’s periodic table. It is a poisonous heavy metal, a most capable neurotoxin, and a substance that has had quite a long tenure under the EPA’s regulatory control. Many believe lead to have poisoned the Roman Empire, and thus in a manner of speaking, contributed to its eventual demise. In that time, lead was routinely added to wine in order to sweeten the taste. It could be found in make-up, pots and pans, water pipes, and in coined currency. Up until the late-seventies/early eighties, when the EPA stepped in, lead could be found in products like gasoline and paint. And as we have gathered from recent events, lead can still pop-up when we least expect it—in mass-produced sweatshop toys, in old houses, in our soil and water, and even in the air we breathe.

Although the old skull and crossbones pretty much sum up the lead lexicon these days, I would like to offer an alternative side to lead. Like for example, I bet few are aware that when allowed to form compounds, lead can contribute to some spectacular mineral specimens. Paired with sulfur, the two make galena, the metallic mineral that is the stuff of marine hydrothermal vents called black smokers, and also of ore deposits; with carbonate, comes cerussite—a mineral, which often forms beautiful cream-colored prismatic crystals; with vanadium, the uncommon mineral vanadinite springs to life, bringing with it vibrant hues of red and orange; and the list goes on. Lead’s isotopes (atoms of the same element that have a different number of neutrons) are important players in the field of geochronology (i.e. the dating of rocks, minerals, sediments, and fossils). The radioactive decay of various isotopes of uranium and thorium, produce the radiogenic lead isotopes—206Pb, 207Pb, 208Pb—which, consequently can be used in tandem with their respective parent isotopes, as well as the naturally occurring 204Pb, to act as geologic clocks to the specimen in question. The U-Pb geochronology method has been used to date meteorites and lunar rocks, as a proxy for the age of our own Earth. And it’s been used to date the earliest remnants of our Earth's crust, the 3.0-3.5 billion year old rocks of places like Wyoming, Canada, South Africa, and Western Australia.

Even though lead will most likely keep its current reputation as a deadly nuisance, we know that in the field of geology, lead will at least boast a few redeemable characteristics.

1 comment:

shashi said...

so, are some of the toys i played with when i was younger have lead in them? maybe that is my new blame for being sick all time instead of not eating my vitamins =)