|MadSci Network: General Biology|
Seawater contains 3.5% or 35,000ppm of dissolved salts, primarily Na+ and Cl- ions. To serve as drinking water, the salinity must be below 500ppm! The best explanation I can think of has to do with the effect drinking high salinity waters would have on your blood. If we ingest high amounts of salt, the ions pass through the stomach lining and into our blood stream. Once in our blood stream, our cells have mechanisms to keep the salts from entering the cells and disrupting the enzymes. However, part of this system involves sending water to the environment outside of the cell to balance the osmotic pressure. Thus, water is sent into the blood stream, and blood pressure rises. If the cells lose too much water or blood pressure is raised too high, this can be lethal. I am guessing that the dehydration is the typical cause of death when seawater is consumed for a long period. If you are shipwrecked, and you are so thirsty that you decide to drink saltwater, dehydration is amplified and death can result from a few cups of saltwater. If you want a more in depth explanation, forward this question to a physiologist. Cheers!
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