GOLDBERG (34) stated that two general processes operate in the uptake of trace materials from the marine environment: (1) a direct transfer of ionic species and dissolved substances from the hydrosphere to the organism. and (2) the uptake of particulate matter, including adsorbed surface ions. LEHNINGER (16) discussed the physical bases of the specificity of metal ions in enzyme systemsin the light of ion structure and properties. Manyof these properties are also applicable to the study of the specificity of metal ions for proteins and other biological substrates, e. g. (1) mass, (2) ionic charge. (3) ionic radius, (4) oxidation-reduction potential, (5) the configuration and stability of the hydrates of the metallic ion in solution, and (6) the configuration and stability of coordination complexes of the metallic ion with substances other than water (i.e. organic detritus, bottom clays and muds). Manganese, iron, cobalt and nickel are closely related, since they are members of thefirst transition series of the periodical table; thus they differ little in atomic weight, ionic radius, oxidation-reduction potential or mobility, > 2 and are equal in charge. All are capable of forming coordination complexes with many organic functional groups, and may form either ionic or covalent linkages. It is probable that both Mn++ and Mg++ form aquocations of the type Mg(H,O0)++ as do Fet+, Ni++, and Cot++, and all may form coordination complexes with organic compounds. Mn++ and the other.transition metal ions would appear to be more versatile in this respect than Mg, since the unfilled 3-d electron orbitals allow formation of covalent as well as essentially ionic complexes. The type of electrostatic bonding (ionic bonding) of general importance in biological adsorption is the ion-dipole bond, which results from electrostatic attraction between the electrically-charged metal ion and a dipolar molecule. Many such complexes are known, ranging from the simple aquocations to very complex forms. Theability of metal ions to form such complexes generally increases with ionic potential, except for the ions of the transition series, which show ability to form complexes out of proportion to their ionic potentials. Ions of low ionic potential such as Cst+, Rbt+ and K* show the least tendency to hydrate or form complexes. Those of somewhat higher potential, such as Nat, Cat, Srt+t and Bat, show intermediate activity. _ The transition elements are far more active in forming coordination complexes. They differ in that they may form essentially covalent linkages between the metal and the complexing molecule as well as ionic complexes. This difference is due to the fact that the metals of the first transition series have a tendency to borrow electrons from other molecules to fill out their 3-d orbitals, thereby establishing essentially covalent linkages in which a pair of electrons is shared between the metal and the group bound. Thetransition elements may also form ionic complexes. However, many coordination complexes have properties which suggest that the bond must be regarded as a hybrid between the two extremes of both types (16). The relative interactions of the transition elements with any given biological substrate do not for the most part depend upon the chemical composition of the substrate. The stability usually occurs in the following order: Mntt+ < Fett <Cott <Nit+ <Cut+ >Zn*t, - SALTMAN (17) observed that the accumulation of the trace metal ions. iron, copper and zinc, by different cells was unique when compared with other 120 ‘ wf * yh‘ eo S \ i \ 4¥ wy et