166 PROVASOLI [chap. 8 



confirm Lucas's postulates. But all this, perhaps even for the algae, is only a 

 fraction of a bigger, more fascinating picture. 



B. Considerations on the Chemical Approach 



Extracting and identifying the organic compounds in sea-water is complex 

 because the dissolved organic C averages 2 mg/1. (maxima up to 20 mg/1.). 

 These minimal quantities have to be separated from the 35,000 mg of inorganic 

 salts in a liter of sea-water ; the salt content of fresh water varies from 50- 

 800 mg/1. In these few mg of organic matter we can expect to find any known 

 and a few unknown organic compounds ; some of them, like vitamins and other 

 biologically active substances, are present in 10~ 9 quantities or less. The main 

 obstacle is the separation of organic components from inorganic salts. This 

 necessary step for any detailed analysis is by no means simple even for fresh 

 waters. The extraction and identification of the microcomponents is further 

 complicated by the need to process very large quantities of water. Jeffrey and 

 Hood (1958) have reviewed and evaluated the various methods for isolation 

 of organic matter. 



To determine the effectiveness of various methods, they use a 14 C-labeled 

 test solution : a large sample of sea-water fertilized with N, P and labeled 

 bicarbonate was kept in light for 90 days to favor algal growth, then placed in 

 darkness for a long period to allow decay of the organic materials and filtered 

 through an HA millipore filter. The effectiveness of the various methods was 

 also tested on the recovery of biologically important compounds dissolved in 

 natural sea-water. 



Column absorption, electrodialysis and co -precipitation permit the isolation 

 of almost all the dissolved organic matter. Co-precipitation with FeCU or other 

 metals at alkaline pH values is the most promising method. The recovery is 

 close to 100% and the concentration factor is 10,000. However, the removal of 

 the co -precipitating ions without altering the organic materials offers some 

 problems ; further, it is not known whether the metal ions and alkali destroy 

 or change some of the organic compounds. Column absorption, especially with 

 pretreated activated carbon, is very effective, but recovery from the absorbent 

 is difficult and partial. Electrodialysis with cellulose membranes retains 97% 

 of the organic matter and is ideal for the separation of colloidal micellae and 

 large molecules, but inorganic sulfate is also retained and has to be eliminated 

 by electrochromatography, and large volumes of water must be evaporated at 

 low temperature. Electrodialysis with ion-exchange membranes employed for 

 industrial desalting of sea-water permits work with large volumes ; the recovery 

 of organics is equal to that with electrodialysis. Electrodialysis perhaps may be 

 improved by the use of several large cells separated by physical barriers of 

 membranes of increasingly fine porosity ; large sheets of the existing dialysing 

 membranes of very fine and graded porosity are produced for other uses. 



Ion-exchange and solvent extraction permit only a partial recovery of the 

 dissolved organic matter. Ion-exchange resins offer no advantages: impracti- 



