I've read that seawater is chemically similar to blood -- is that true?

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I've read that seawater is chemically similar to blood -- is that true?

Actually, it is! It's even been used in transfusions in emergency situations when blood or plasma wasn't available and the patient needed to have his blood volume maintained.

Sea water is remarkably similar to blood in many ways. When comparing the concentrations of various elements in seawater and blood, we find that the two most common elements in each are Chlorine (Cl) and then Sodium (Na). Together they make Sodium Chloride (NaCl), or common table salt. The concentrations are higher in seawater than in blood, though. When it's been used for transfusions seawater needs to be diluted in fresh water first.

After Na and Cl, as you go to the lower-concentration elements the two liquids start to differ in their elemental concentrations as far as which is where on the list, but the next-most common elements or compounds in both are Sulfate, Magnesium, Calcium, and Potassium. So they actually are very similar.

The pH range (a measure of acidity or alkalinity) of seawater is normally 7.4 - 8.2, while in blood it's 7.38 - 7.44 (the body keeps this in a very tight range).

It's thought that seawater and blood used to be much closer in composition when organisms that eventually became land mammals developed in the oceans eons ago. Over time the oceans are believed to have risen in elemental concentrations (become more salty) as more elements dissolved and washed off of the land from the action of rainwater and into the sea.

When you look at the rarer elements in blood, you begin to find wider variations from what's in seawater. So it's certainly not identical to blood.

But it has been used in transfusions, both in emergencies and in medical experiments.

Experiments were run on dogs in the early 1900s to test diluted, filtered ocean water as a substitute transfusion liquid. An early experimenter named René Quinton and his team drained all of a dog's blood and replaced it with the seawater solution. The dog lived, and on the second day after the transfusion, half of its normal blood components had returned, regenerated by its body. By the fourth day its blood was back to virtually normal and the dog was active and full of energy and happy. The dog went on to live for many years afterward, with no visible problems as a result of the experiment.

[Website author's note: I'm not a doctor, but I would have thought that totally replacing an animal's blood with seawater wouldn't have worked at the start, because real blood uses hemoglobin to carry lots of oxygen to the tissues. Perhaps the seawater was highly oxygenated at the start, and the dog was breathing pure oxygen at the start also. I haven't read the details of the experiment so I really don't know.]

Not long after this surprising result was found the research was dropped, as World War I began and the researcher Quinton was drafted into the military. He later died in 1925. Similar tests were run by others who had read of his experiments, as late as 1969, with similar results.

As far as is known, no controlled experiments on humans have recently been attempted, as medical science has now developed safer, better-controlled alternatives. We now know that sea water contains many viruses, bacteria, and similar organisms that don't belong in a living organism's bloodstream unless there are no better options available.

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