1. (1) G. R. Choppin and P. J. Unrein, Transplutonium Elements, eds. W. Muller and R. Lindner, North Holland, Amsterdam (1976).
2. (2) G. R. Choppin, J. Chem. Edu. 71, 826 (1994).
3. (3) R. L. Ryan, Inorganic Chemistry: Lanthanides and Actinides, ed. K. W. Bagnall, Buterworths, London (1972).
4. (4) J. W. Morse and G. R. Choppin, Reviews in Aquatic Science 4, 1 (1991).
5. (5) W. L. Keeney-Kennicutt and J. W. Morse, Marine Chemistry 15, 133 (1984).