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.)

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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 hyponatremiaH2O 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 air. Breathing higher concentrations can lead to hyperoxia, or higher-than-normal concentrations of oxygen in body tissues. Increasing the percentage of oxygen to about 50% can cause damage to the lungs and eyes. Increasing the pressure as well, such as in hyperbaric chambers, can be toxic to the central nervous system.

Water and oxygen. H2O and O2. Necessary for life. But there can, in fact, be too much of a good thing.

Author: Jyllian Kemsley

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  1. Toxic Carnival: Day Four | ScienceGeist - [...] The Safety Zone Jyllian treats us to some wonderful stories concerning water and oxygen. Obviously we need these molecules…