INTRODUCTION

As has already been mentioned the production of a synthetic or artificial substitute for seawater is not a new idea, but is of increasing importance for several reasons

(1) Ease of transportation to inland destinations.

(2) Stability of formulation, given adequate batch supervision of the salts used.

(3) The density of the final solution is controllable.

(4) The formula can be varied if required for specific uses.

(5) The sterility of the final solution can be assured.

 
Many
synthetic formulations demonstrated inadequacies in several respects when comparisons with their modern counterparts were made. Firstly, the statistics for natural waters from which they were compiled were not sufficiently accurate, especially with regard to their minor components, and, secondly, the purity of their component salts would not have been high enough. Today these problems still exist, but can be carefully controlled, and are ,for most purposes, well within acceptable limits. **

It is now relatively easy to produce a basic or standard water from which comparisons can be made,or variations for specific purposes can be derived. The first step in this process is to obtain an accurate analysis, or analyses, of the major compounds present in natural seawater. Such a breakdown is given in Table l, which gives figures for the major nine ions present. The nine ions shown in this table vary little throughout the oceans , a situation not found when the minor ions are considered later.


Given the information in Table 1 and knowing the exact chemical composition of the salts to be used the weights of such salts can be calculated. Two problems arise here and have to be considered before proceeding:

(1) THE PURITY OF THE SALTS PROPOSED FOR USE.

Most laboratory and analytical grade chemicals vary in purity between 90% and 99.9%.Technical grade salts are far less pure. Considering the accuracy required for the correct reproduction of certain of the minor constituents this purity is critical , endangering the final formulation unless the quantity   and quality of the impurities are known. To give an example of this point, if the Sodium chloride (common salt content of the final formulation is added using commercial grade or household salt the arsenic and barium levels (even though these are in minute quantities and can be measured in single figures, in parts per million) can present problems unless accounted for. In addition to these two, sodium chloride of this grade contains as many as twelve other elements in substantial enough quantities to give rise to doubt as to what their final concentrations would be

2 Allowance for the minor constituents

Of the minor constituents; many exist naturally in critical ratios, any variations of which are alien to marine life. Natural seawater probably contains all known elements and at least 78 of these have now been isolated (and accurately measured. A list of all recorded minor elements is given in Table 2 below. Of these minor elements some are far more important than others*** . It has been well known for many years that silicon, phosphorus, manganese, iron, copper and nitrogen are biologically significant  but many others have recently been identified as   having possible biological importance. A list of these 'latecomers', & their better recognised predecessors is given in Table 3,which also shows their minimum and maximum recorded concentrations for open ocean waters. (In waters near the coast in temperate & sub-tropical regions many of these greatly exceed this range.) Salts added to introduce minor elements also add major ions . If the above mentioned newly-acquired information is reliable and there is certainly no doubt on this score, It may answer at least in part a number of problems which are as yet unsolved Most synthetic seawaters have at some stage failed in certain respects, eg; in maintaining a specific organism, or in the breeding and rearing of the higher forms of marine life . Controversy over the relative merits of natural and synthetic waters has always been rife. More information and study of   synthetic substitutes in the light of recent research is badly needed

This introduction is but a simplified explanation of the facts that should be taken into account if an accurate synthetic seawater is to be produced and the natural ratios of component ions preserved . But do they ? Is what is required as exact a copy of the real thing possible using modern techniques and the most modern data ? Even now it is still not possible to produce a product TOTALLY indistinguishable from the real thing   The argument for its production is a natural one; we are trying   to study marine life,& as such should reproduce its natural environment as closely as possible to obtain valid answers. Arguments against seem to vary between 'if it cannot be done totally, then don't do it at all-try something else ' , and 'its uneconomic'
To a limited extent the latter has some validity - old formulae are still being used reasonably successfully, and solutions of salts not at all resembling seawater will support certain life.
forms for limited durations. A good formula would be expensive to produce. It is not within the scope of this report to favour either of these arguments.   `

For the purpose of comparison in the report proper we have formulated a Standard Synthetic Seawater based on the following criteria:
 


(1) The percentage composition of the major ions follows those quoted in Table l.

(2) The minor components of known or postulated biological importance are based on modern readings taken for open oceanic waters and follow closely the figures given in Table 3. All minor constituents are present in ratios calculated from Table 3.


(3) Atomic weights used are those published by IUPAC. 1973


(4) Chemicals used are the highest grade commercially sold by Messrs. B. D. H. Maximum limits of impurities are known and have been allowed for in the trace element entry.

(4) All calculations were computed to seven decimal places excluding; zeros. For convenience some have been reduced on the final print-out.

 

All salts quoted in the final formula are anhydrous ,(or dry forms) with the exception of strontium chloride.

(6) When dissolved in 95 litres of distilled water and topped up to 100 litres at 60 deg. F.the resultant solution has a salinity of 35 parts per thousand after aeration for 1 hr.

(7) After 1 hour of aeration the resultant solution should: (a) Have a carbon dioxide content in equilibrium with the atmosphere.

(b) Show no precipitation.


(c) Give a pH reading of 8.19 +/- 0.05


* Aeration of the distilled water prior to dissolving of the salts can be made in addition to that stated above.

All formulae examined later were tested as to their compliance with specifications (6) & (7) above in addition to other tests carried out.

It must be noted at this stage that this 'Standard   Synthetic Seawater' ,which for lack of a better epithet we shall from now on call the Calypso formula ,is ,in all practicality, exceedingly expensive to produce.


TABLE 2

 . RECORDED MINOR CONSTITUENTS
   
  Silicon
 
  Antimony
  Dysprosium
  Fluorine
 
  Beryllium
  Erbium
  Nitrogen(N03 )
 
  Bismuth
  Europaeum
  Lithium
 
  Cadmium
  Gadolineum
  Rubidium
 
  Caesium
  Hafnium
  Iodine
 
  Cerium
  Holmium
  Phosphorus(PO4)
   
  Chromium
  Lutetium
  Barium
 
  Gallium
  Neodymium
  Iron
 
  Germanium
  Praesodymium
  Molybdenum
 
  Indium
  Protoactinium
  Zinc
 
  Lanthanum
  Rhenium
  Selenium
 
  Krypton
  Samarium
  Manganese
 
  Lead
  Terbium
  Vanadium
 
  Mercury
  Tantalum
  Nickel
 
  Radium
  Ytterbium
  Uranium
 
  Ruthenium
 
  Aluminium
 
  Silver
 
  Arsenic
 
  Thallium
  Argon
  Copper
 
  Thorium
  Deuterium
  Cobalt
 
  Tin
  Helium
  Niobium
 
  Titanium
  Neon
  Yttrium
 
  Tungsten
  Radon
  B,12
 
  Zirconium
 
  Gold
   

   

Information from various international sources.

  **Data on regional variations would need to be consulted if total accuracy was required.For most purposes a good basic water is adequate.

*** The degree of importance is relative to the final use of the discussed water.

HomeHome Acknowledgements Contents List Preface Table 1 Major ions Introduction History Composition Basic Chemistry The Report Knowles Formulae Lyman & Fleming Wiedermann-Kramer Clark 'A' + Segedi-Kelley Clark-Jennings Properties Appendix Glossary Bibliography Conversion Factors Abridged guide Other researchers The Calypso Organization

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