ak tat ali ant Pe ttle Cs 67° | | (13) 66°45' 66°30 66°15‘ oNOo 66° ‘ 65°45 1 ean! SAN JUAN 18°30 RINCON [ © MAYAGUEZ PUERTO RICO (12) LA PARGUERA ut 9) (wo) (9) (8) PONCE (7) 19° (6) (5) Fa a eed Km N !|OCU® Fic. 3.—Sampling locations for the collection of algae. (1) Guajataca: rocks and surf; (2) Fajardo, Bahia Yeguas; (3) Humacao, Cayo Santiago: rocks; (4) Guardarraya: rocks; (5) Aguirre: rocks, reef in front of Central Aguirre, (6) Cayo Cardona (12kmS.W. Playa de Ponce: rocks); (7} Cayo Don Luis, La Parguera; (8) Guayacon (~3 km W. Playa La Parguera); (9) Margarita (~12 km S.W. Playa La Parguera); (10) Cabo Rojo, La Playnela (Hast); (11) Cabo Rojo, Punta Aquila (West); (12) Punta Arenas; (13) Rincon: rocks, surf; (14) Culebra (not included on map). near Rincon on the northwest coast of Puerto Rico were then ground in a Wiley mill to a 20-mesh powder. land (Figure 3). These samples, together with several sites of collection are listed in Table 1. (For the coding of the sites of collection see Figure 3.) went critical, a series of samples of different species of marine algae were collected from sites around theisadditional collections made in 1967 and 1968, have been analyzed for (1) the naturally-oceurring alpha particle emitters, radium (??8Ra), thorium (#3°Th) and uranium (*8°U); (2) three components represen- tative of the total mass of the organism, total organic material, protein nitrogen, and ealeium; (3) trace ele- ments including cadmium, chromium, cobalt, copper, indium, gallium, iron, and arsenic; and (4) the gamma radioactivity from both naturally-occurring as well as fallout isotopes. In this paper we shall dis- cuss the relationships between the natural levels of radium, thorium, or uranium with protein nitrogen and calerum carbonate. METHODS Algae Samples Algal samples were colleeted from thirteen different locations around the coast of Puerto Rico and on the island of Culebra which is 38 km east of Fajardo (Figure 3). The algal samples were rinsed briefly in fresh water as soon as possible after collection, drained, and dried under forced draft at 100° C to constant weight. They The different species of algae collected and their Radium Radium was determined using the radon emanation method described by Lucas."*) Twenty-gram samples of the algae were suspended in dilute nitric acid to decompose any carbonates present and then digested with aliquot portions of concentrated nitric acid until the evolution of oxides of nitrogen ceased. A silicaceous residue was found after digestion of almost all of the samples. This residue was removed by fil- tration, dried, and weighed. The filtrate was diluted to approximately 200 mi with radium-free water and transferred to the emanation flask for radon anaylsis. The total radium concentration in these samples varied between 0.2 and 2 pCi (approximately 1-10 epm **"Rn). Thorium and Uranium Thorium, uranium, and other trace elements were determined by the neutron activation methods of Edgington and Lucas.© © QOne-gram samples of the algal powder were ashed by low temperature oxidaqe