Aerodynamic size associations of 212Pb and 214Pb in ambient aerosols.

The aerodynamic size distributions of short-lived Rn daughters (reported as 214Pb and 212Pb) in ambient aerosol particles were measured using low-pressure as well as conventional low-volume and high-volume impactors. The activity distribution of 214Pb and 212Pb, measured by alpha spectroscopy, was largely associated with submicron aerosols in the accumulation mode (0.08 to 2 microns). The activity median aerodynamic diameter ranged from 0.09 to 0.37 micron (mean 0.16 micron) for 214Pb and from 0.07 to 0.25 micron (mean 0.13 micron) for 212Pb. The mean values of the geometric standard deviation (sigma g) were 2.97 and 2.86, respectively. By comparison, the median diameters of cosmogenic 7Be and ambient SO4(2-) were about 0.24 micron higher. In almost 70% of the low-pressure impactor measurements, the activity distribution of 214Pb showed a small shift to larger particle sizes relative to 212Pb. This shift probably results from alpha-recoil detachment of parent 218Po, which preferentially depletes 214Pb from smaller particles. The subsequent recondensation of 214Pb causes an enrichment of larger aerosols. Early morning and afternoon measurements indicated that similar size associations of 214Pb occur, despite humidity differences and the potential for fresh particle production in the afternoon. Health physics implications of the results are also discussed.

Field and greenhouse experiments on the fate of technetium in plants and soil.

The behavior of 95mTc in plants and in a Captina silt loam soil following a single application of the pertechnetate form of the radionuclide to bare soil was compared between field and greenhouse conditions. Over a period of approx. six months, the net uptake of 95mTc by plants from undisturbed, intact soil in the greenhouse was about a factor of 10 greater than that in the field. Sieving the soil through a 2-mm mesh screen before potting and then planting new grass further increased plant uptake of 95mTc by approx. a factor of 20 relative to the field. Uptake by new grass was increased even more by decreasing the pot size. Most of the 95mTc applied to soil in the field or the greenhouse remained in the top 4 cm of the profile. Soon following application to soil, pertechnetate was transformed, or otherwise immobilized, such that extractions with 0.01 M CaCl2 recovered only a portion of the 95mTc present in soil. The extractability of 95mTc from soil using CaCl2 decreased over time as did 95mTc concentrations in vegetation. The pertechnetate applied to soil appeared to be converted over time to a less soluble and therefore less bioavailable form.

Dissolution characteristics of Pu-contaminated soils and sediments in lung serum simulant solution.

Dissolution characteristics of Pu from contaminated Nevada Test Site (NTS) and Rocky Flats (RF) soils, and Mound Laboratory (ML) and Oak Ridge National Laboratory (ORNL) sediments in lung serum simulant solution at 37 degrees C were investigated. The dissolved Pu concentration had reached a maximum within a day of equilibration and the percent dissolved Pu at the maximum was 0.70 (RF), 0.43 (ML), 0.02 (ORNL), and 0.02 (NTS). The Pu concentrations of the RF, ML and ORNL samples in the successively extracted solutions decreased drastically but the concentration in the NTS soil extracts did not change significantly. The differences in Pu dissolution among the samples were caused by the differences in the total Pu concentration, particle size distribution, and chemical nature of Pu in contaminated soils and sediments. The higher solubility of the particulate Pu form in the RF soil relative to the ORNL sediment contaminated by dissolved Pu suggests that contamination source alone can not explain the observed differences. Variation of Pu solubility among the samples indicates that a single solubility class for dose assessment use may not be appropriate, particularly if one attempts to make comparative assessments among different sites.

Geologic migration potentials of technetium-99 and neptunium-237.

Relatively mobile TcO(+)(-) and NpO(2)(+) can be chemically reduced to less soluble oxidation states in the presence of igneous rocks, as predicted by oxidation-reduction measurements. Current risk assessments, which consider technetium and neptunium as potentially capable of migrating from high-level radioactive waste repositories, may be overestimating their potential hazard to the public since the Fe(II) content of many subsurface waters may maintain these elements in less soluble oxidation states.

Radioisotope techniques in delineation of the environmental behavior of cadmium.

Radioisotope techniques are being developed and utilized at Oak Ridge National Laboratory (ORNL) for evaluating the environmental behavior of toxic elements such as cadmium in aquatic and terrestrial ecosystems. Tracer techniques using 109Cd in microcosm, field plot, and stream systems are providing information on biogeochemical cycling and distribution of cadmium in the environment. Parameters being measured include adsorption capacity for cadmium in mineral soils and sediments; uptake rates of cadmium in various plant species from both soils and nutrient solutions as affected by pH, competing cations, and chemical form of cadmium; and distribution of cadmium in various components of both aquatic and terrestrial ecosystems following application of 109Cd to soil vegetation, or directly to streams. Food chain parameters being estimated with 109Cd include uptake, assimilation, and turnover by both aquatic and terrestrial organisms. Information obtained in these radiotracer studies is providing insight into the behavior of cadmium in aquatic and terrestrial ecosystems, especially transport rates of cadmium and potential biomagnification or dilution in food chains. The factors which influence the incorporation of cadmium into vegetative material as well as those affecting residence time in ecosystems have been identified. Use of 109Cd also has permitted evaluation of a cadmium specific electrode as a tool for rapid assay of free cadmium ions in soil solutions.