Part 2: A Watery Grave

Fact: It’s better to drown in salt water than in fresh water.

Drowning is bad no matter which way you spin it, but you’re less likely to end up in Davy Jones’ locker if you get into trouble in the sea rather than in a freshwater source like a pool or river.

We always think of ‘drowning’ as dying due to a lack of oxygen, like suffocating underwater. In seawater, this is exactly what happens: you inhale salty water which fills your lungs, preventing you from breathing and eventually causing you to pass out due to a lack of oxygen to your brain. As we know, your brain can survive without oxygen for around 8 minutes, so that gives you some time to get rescued.

However, inhale fresh water and you’ll die much faster, and even if you’re rescued and start breathing again you could still be on death’s door. This is because the moment you inhale fresh water you’ll probably have a heart attack, drastically reducing your chances of survival even if you are rescued in that precious 8-minute window.

The reason behind this comes down to something called osmosis. Osmosis means the movement of water from a liquid with a low concentration of salt (e.g. freshwater) to a liquid with a high concentration of salt (e.g. seawater). Your blood has quite a high concentration of salt, so when you inhale seawater there isn’t much movement of water in or out of your blood.

However, fresh water has a much lower salt concentration than your blood, so when you inhale it loads of water moves into your bloodstream via osmosis. That water then moves into your red blood cells, causing them to swell up and eventually burst. Those cells contain lots of potassium (K+) ions, so bursting red blood cells causes the concentration of potassium ions in your blood to skyrocket, and as we learnt last week, high levels of potassium in your blood can quickly stop your heart.

Therefore even when you drag someone out of a pool and get them breathing again, the high levels of potassium in their blood could leave them at risk of a heart attack. It makes a good case for lounging on the beach instead of by the pool and besides, the sea is more fun to swim in anyway.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons License

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