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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