Re: Drinking seawater

Greetings,
I was able to find several sites on the web that would be helpful in answering your question concerning drinking seawater. But first I would like to thank Ralph Logan an instructor in Chemistry from North Lake College .Visit his home page at: http://edie.cprost.sfu.ca/ ~rhlogan. Your question is answered by understanding the process of Osmosis. What follows is Ralph Logan's lecture on Osmosis, and lo and behold he explains the reason of why people get sick from drinking seawater.

                 Osmosis and Osmotic Pressure



Osmosis is the diffusion of small moleculaes through a semi-permeable membrane. 
Such a membrane is one in which small molecules such as water and small ion such 
as Sodium and Potassium ions may pass in either direction through the membrane. 
A example of osmosis is what happens when you place a membrane over the top of a 
thistle tube. Such a tube is a long capillary tube that is flared open at one 
end. The membrane is stretched over the top of the flared end. A solution of is 
placed inside the tube and it is immersed into a container of pure water. Such a 
solution could be anything but a sugar solution will serve as our example. If we
mark the level of the solution inside the thistle tube with a black marking pen 
and wait for several hours, we will discover that the liquid level inside the 
thistle tube has risen. After a certain amount of time the liquid level ceases 
to rise and levels off. What is happening here? From a macroscopic view the 
liquid inside the tube has increased and the resulting osmotic pressure has 
pushed the liquid farher up in the tube. However, why does the level suddenly 
level off? 

                  A Molecular View Of Osmosis

The solution is composed of sugar molecules, C12H22O11, which are relatively 
large when compared to the smaller water molecules, H2O. The water molecules can 
pass through the pores in the semi-permeable membrane, but the large sugar 
molecules cannot pass through. As a result water molecules pass in both 
directions. But why does the levels rise?  There is a higher population of water 
molecules in the pure water in the container than there is in the sugar 
solution. I draw an analogy of an elevator which has 5 people inside. As the 
elevator stops at a floor, were it not for the reasoned manners of the people on 
the outside of the elevator trying to get in, none of the people on the inside 
would be able to get off because there are many more tring to get inside the 
elevator. Water molecules cannot reason. They simply abide by the brute physical 
laws. More water molecules can get inside the tube then can get outside. The 
solution is diluted and the entropy (tendency toward equilibrium) is increased 
which is the natural order of things according to the second law of 
thermodynamics. The direction of osmosis is always from the more concentrated 
side to the more dilute side of the membrane. 

Water molecules will cause the liquid levels to rise, but why does the liquid 
level stabilize with time? As the sugar solution inside the tube becomes 
diluted, the water molecule population increases so that the osmosis toward the 
outside of the tube increases. Eventually just as many water molecules pass into 
the tube as pass out of it, and we have reached a state of dynamic equilibrium 
where the liquid level is in a steady state condition.

              Biological Applications Of Osmosis

Osmosis displays itself in most biological systems that are cellular. The cell 
wall is a semi-permeable membrane. So is the cell nuclear wall which keeps DNA 
molecules inside the nucleus while allowing the transfer RNA molecules to pass 
through in and out of the nucleus. Nutrients,oxygen, water, and waste gases can 
pass in or out of the cell through the semi-permeable cell membrane. Cells in 
which water passes out of the cell faster than can get in are said to shrink and 
undergo crenation. This happens when cells are placed in an extracellular fluid 
of more than .9% salt solution. The extracellular solution is concentrated 
enough to allow water molecules to osmotically pass to the outside of the cell 
faster than water can pass into the cell. As a result the cells dehydrate and 
shrink.  This is what happens if a person dying of thirst on a raft in the 
middle of the ocean decides to drink sea water. The sea water increases the 
salinity of the extracellular fluids, and a condition arises where more water 
osmotically leaves the cells than can get out. The cells dehydrate, and 
ironically, the person suffers from cellular dehydration which becomes more 
severe as the person takes in more sea water. Such an extracellular solution is 
called a hypertonic solution. 

On the other hand if cells are placed in a salt solution of less than .9% then 
the water on the outside of the cell in the extracellular fluid can pass into 
the cell faster than water can get out. The result is that the cells swell with 
the excess water and eventually burst open. When red blood cells do this it is 
referred to as hemolysis. The extracellular fluid itself is said to be 
hypotonic. A condition known as water intoxication results in too much water 
being ingested where the Sodium/Potassium ion pump can't control the water 
intake into the cells and the cells rupture due to this intoxication.

Pysiological saline (salt) solution is 0.9% and results in an equilibrium 
between osmosis into the cell and out of the cell. This kind of solution is the 
extracellular fluid that our cells respond most positively to. The solution is 
said to be isotonic. This intricate balance in osmosis in and out of the cells 
needs to be maintained at all times. The controller of this process is the 
kidneys themselves which filters out waste products and recycles needed 
nutrients while maintaining this isotonic condition in the extracellular fluids. 

Another example of osmosis is found in the plant kingdom. Plants through their 
leaves, stems, stalks and root systems take in needed CO2 and water during their 
photosynthetic process and takes in Oxygen during the respiration cycle of the 
plant. It is important that water be allowed to enter and leave in a balanced 
way just as in the animal kingdom. If the roots of plants are placed in soil 
that is too saline (salty), then a condition of hypertonicity occurs, and the 
cells in the roots will shrink and dehydrate.  That is why plants shrivel up and 
die in a soil that is too salty. Have you ever wondered how large tall trees can 
receive the necessary nutrients that only come from the soil? The total osmotic 
pressure of a large tree with an extensive network of roots can generate an 
osmotic pressure of several atmospheres enough to overcome the gravity pull 
downward. 

R. H. Logan, Instructor of Chemistry, Dallas County Community College
District, North Lake College.


                             Acknowledgements:

                            
Send Comments to R.H. Logan:

rhl7460@dcccd.edu

All textual content copyrighted (c) 1997
R.H. Logan, Instructor of Chemistry, DCCCD
All Rights reserved


Revised: 11/27/97 

There is also an experiment that was performed by a Dr. Bombard who also knew of the danger of drinking sea water but also that some countries especially Germany used sea water cures and that for many persons sea water was used as a remedy.

For this fascinating account go to:

http://www.zoomnet.net/ ~grsc/bible/sea1.html

I hope this answers your question on drinking seawater.

 
Sincerely,
  June Wingert
 Baylor College of Medicine
 Center for Comparative Pathology
 Houston, Texas

jwingert@bcm.tmc.edu
beachcomber@pdq.net