Twenty species of marine algae were collected between 1961 and 1968 from coastal waters of Puerto Rico and analyzed chemically for total organic material, protein nitrogen, and calcium, and radiochemically for the naturally occurring alpha particle emitters 226Ra, 232Th, and 238U. Study of these data suggests that the concentration of radium, thorium, and uranium by tropical marine algae is controlled by two mechanisms: 1) ion‐exchange or coprecipitation of the ion with the calcium carbonate matrix, and 2) complex formation with either the protein nitrogen or some other component of the organic fraction. Radium (and possibly thorium) apparently is concentrated by both mechanisms, the dominant one depending on the phylum. For the Rhodophyta and the highly calcified Chlorophyta it is the former and for the Phaeophyta the latter. Uranium is concentrated by the first mechanism.
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Edgington et al. (1970) studied this question.