several variables; the chemical form of the element in solution, the 

 characteristics of the solid phase, and competing reactions for the 

 adsorption sites. An adsorption process may be distinguished as a 

 nonspecific physical type or as a stronger chemical interaction termed 

 chemisorption. The type of process will determine the subsequent 

 mobility of the minor element and the significance of competing reactions. 



Adsorption as a chemical process in the marine environment has not 

 received the intensive and definitive investigation it merits. Even through 

 it is widely acknowledged as a significant process, we do not know its 

 quantitative role in geochemical cycles nor the specific locations in 

 the marine environment where it is most important. Studies in regions 

 where rivers mix with seawater indicate that the greatest chemical 

 transformations occur at salinities of several parts per thousand rather 

 than gradually throughout the mixing range of salinities. Further knowl- 

 edge of this process is im.portant to evaluate the fate of both pollutants 

 and natural injections brought to the ocean by rivers. 



Several approaches can be suggested as possible ways to gain more 

 information on adsorption reactions. Basic knowledge can be obtained 

 through laboratory investigations of specific minor elements and specific 

 solid phases. Consideration should be given to the effects of the medium 

 on adsorption processes by duplicating as closely as possible the main 

 constituents of natural waters. For example, the presence of carbonate 

 ions may be important in the adsorption of those trace metals that form 

 carbonate complexes. The use of added minor element tracers is ham- 

 pered by the potential problems arising from the presence of nonequilib- 

 rium forms of the el'ement in natural systems. Variables in the solution 

 phase that should be considered for coastal adsorption reactions are 

 temperature, pH, ionic composition, and the potentially synergistic 

 efi'ects of adsorbable minor constituents. The solid phase should be 

 characterized in terms of its surface area, availability, and strength of 

 adsorption sites. Laboratory investigations of this type for selected 

 systems such as geochemically active metals (e.g., Al, Mn, Fe, Cu, Zn), 

 toxic technological metals (e.g., Cd, Hg, Pb), radioactive elements 

 (e.g., Cr, Co, Sr, Cs, Ra, Th, and especially Pu), and biologically im- 

 portant constituents (e.g., P, As, Se, Mo, I) will provide the information 

 required to assess some aspects of their behavior at continental bound- 

 aries of the ocean. These assessments would be substantiated or refined 

 by observations in the marine environment. 



In addition to the factors affecting adsorption processes in coastal 

 environments, the effects of pressure on the exchange of minor con- 

 stituents in the deep sea should be considered. This effect may be 

 significant for adsorption reactions on biogenic particles or within a 

 nepheloid layer. The study of adsorption processes should recognize 

 not only the equilibrium distribution of the minor element between the 



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