Assessing the ability of soils and sediment to adsorb and retain cesium-137 in Puerto Rico.

摘要

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.