Water and oxygen, my favorite toxic chemicals
May24

Water and oxygen, my favorite toxic chemicals

(Russ’s post on osmium earlier this week and mine today are both for the “Our favorite toxic chemicals” carnival hosted by Sciencegeist. Go see the collected posts from Monday, Tuesday, and Wednesday. On Twitter, watch #ToxicCarnival.) In 2005, a California State University, Chico, student died after being forced to drink gallons of water during a fraternity hazing ritual. Four of his fraternity brothers pleaded guilty to charges ranging from involuntary manslaughter to hazing. In 2007, a woman participating in a radio contest to win a Nintendo Wii died after drinking nearly 2 gallons of water without urinating. A jury later awarded $16 million to her family. Water, H2O. Oxygen, O2. Without either one, we die. But also: With too much H2O, we die. With too much O2, we die.  The dose makes the poison. H2O is essentially the solvent in which all cellular substances are dissolved. Overall, the human body is about 60% H2O, although the amount varies depending on the body part: bone is 22%, brain is 70%, and blood is 83%. H2O is polar, with the oxygen carrying a slight negative and the hydrogens carrying a slight positive charge. That means that H2O tends to form strong interactions with other polar molecules but rebuff nonpolar ones, which is why dispersed oil droplets will gather together in a cup of H2O. At the cellular level, those polar and nonpolar interactions play an important role in things such as membrane formation, protein folding, and protein-protein or protein-substrate binding. But as the news reports above demonstrate, H2O can also kill, and not just by drowning. Drink more H2O than your kidneys can handle and the fluid builds up in your blood, diluting the sodium concentration–a condition called hyponatremia. H2O then moves into cells to equalize the sodium concentration between the two environments. The influx of H2O causes cells to swell. Some parts of your body have room for that, but your brain does not. “Rapid and severe hyponatremia causes entry of water into brain cells leading to brain swelling, which manifests as seizures, coma, respiratory arrest, brain stem herniation and death,” M. Amin Arnaout, chief of nephrology at Massachusetts General Hospital and Harvard Medical School, told Scientific American. For its part, O2 is a key player in cellular energy cycles. We breathe in O2, which red blood cells deliver throughout our bodies. Mitochondria in other cells turn that O2, sugar, and adenosine diphosphate into H2O, CO2, and adenosine triphosphate (ATP). ATP then serves as the energy source for a multitude of other cellular activities involved in being alive. One molecule of glucose produces 36-38 molecules of ATP. But human bodies evolved to breathe in O2 as about 20% of...

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My favorite toxic chemical is: Osmium (and its tetroxide)
May21

My favorite toxic chemical is: Osmium (and its tetroxide)

Osmium is the densest of all natural elements and certainly one of the rarest, with worldwide production of about 545 kilograms annually. It’s incredibly expensive stuff, and yet, look at all the varied uses!  Osmium is used by itself or as an alloy for fingerprint detection and in fountain pen tips, pacemakers, light filaments, and jewelry. And it’s reacted with oxygen to form osmium tetroxide. The word osmium actually comes from the Greek word “osme,” or odor, for the unique acrid odor given off by OsO4. Osmium tetroxide is incredibly toxic and has an OSHA permissible exposure limit (PEL) of 0.002 mg/m3. For comparison, elemental mercury vapor has a PEL of 0.1 mg/m3.  Osmium tetroxide might even be considered a perfect component of a terrorist “dirty bomb,” but it’s simply too expensive to buy enough to make that practical. A primary use for OsO4 is for tissue fixation in electron microscopy. Hundreds of hospitals use it in their clinical labs, and when the solution is spent, it needs to be disposed safely. My experience with OsO4 stems primarily from efforts to recycle the spent compound.  Ironically, despite its obvious toxicity, OsO4 isn’t regulated as hazardous waste. While it is certainly toxic to humans, it breaks down fairly readily in the environment, (apparently) isn’t toxic to aquatic or marine life, and isn’t mobile enough to be considered a threat to drinking water.  That means that theoretically one could take this non-regulated waste and sell it for a handsome sum to a refiner who could recover and resell the metal. However, here is a lesson in making sure you know the hazardous waste regulations thoroughly! It turns out that one of the several buffers that labs use with OsO4 is cacodylic acid, which has the formula (CH3)2As(O)OH. Therein lies the rub. While EPA decided that osmium isn’t hazardous to the environment, arsenic is. So, any refiner recovering osmium from the spent solution also containing that particular buffer must have a full-blown EPA hazardous waste treatment, storage, and disposal facility permit! Use a different buffer and you’re fine. It only took me stops at five hospitals to find out the popularity of the cacodylic acid buffer, thus ruining my plans for an early retirement. For more on osmium, check out this essay on the metal from C&EN’s 80th anniversary special issue on the periodic table and this video from the Periodic Table of...

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