Graduation Year

2010

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Marine Science

Major Professor

Ashanti Johnson, Ph.D.

Co-Major Professor

Robert Byrne, Ph. D.

Committee Member

Kathleen Carvalho, Ph.D.

Committee Member

Brandon Jones, Ph.D.

Committee Member

Edward VanVleet, Ph.D.

Keywords

radionuclide, monitoring, soil, mineralogy, adsorption, desorption

Abstract

As part of the radioactive exercises taking place around the world anthropogenic

radionuclides were introduce to Puerto Rico’s terrestrial and aquatic environments

beginning in 1962. Two major projects took place in the island, the Rain Forest Project

and the construction of a Boiling Superheat Nuclear Power Plant (BONUS). While in

operation several accidental shutdowns occurred at the BONUS facility. One of these

accidental shutdowns released 582 MBq into the nearby environment. Vieques an island

located few miles east of the main island has received anthropogenic inputs of heavy

metals resulting from military practices conducted by the US Navy. Due to the potential

presence of Cs-137 in soils and sediments in Puerto Rico a radiological assessment was

performed.

Downcore soil and sediment analysis as well as surface samples analysis was

conduct in these three sites indicating the presence of Cs-137. Activity range varies

among site from below detection limit to 12 dpm/g at Vieques, 15 dpm/g at Espiritu

Santo Estuary and 12 dpm/g at the BONUS Facility. ICP-OES analysis indicates the

existence of an oxic environment at the sedimentary system of the island. Cs-137

retention is strongly influenced by particle grain size and at the study sites clay was

present in less than 20% for most sites. An X-ray diffraction analysis show that kaolinite

and smectite are present at all sampling sites and illite is absent.

To further analysis the ability of soil and sediments to retain adsorption and

desorption was conducted using clay reference material and samples from the island. All

samples, reference and natural, used in the study were placed in an aqueous solution that

contained MES buffer (5.0 micromol, pKa of 6.1), ammonium nitrate (0.010 M) and the

five metals (individual concentrations ranged from 0.48 micromol to 1.6 micromol).

Solution pH was adjusted by titration with acid or base, depending on the nature of the

sample. Results were quantified as distribution coefficients. These results indicate that

the absorption and retention of Cs-137 in the sediments in Puerto Rico is driven by the

mineralogy of the site.

Share

COinS