Applications of PB-210/RA-226 and PO-210/PB-210 disequilibria in the study of marine geochemical processes

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution November, 1975The distribution of Pb-210 and Po-210 in dissolved (0.4 micron) phases has been measured at ten stations in the tropical and eastern North Atlantic and at two stations in the Pacific. Both radionuclides occur principally in the dissolved phase. Unsupported Pb-210 activities, maintained by flux from the atmosphere, are present in the surface mixed layer and penetrate into the thermocline to depths of about 500 m. Dissolved Po-210 is ordinarily present in the mixed layer at less than equilibrium concentrations, suggesting rapid biological removal of this nuclide. Particulate matter is enriched in Po-210, with Po-210/Pb-210 activity ratios greater than 1.0, similar to those reported for phytoplankton. Box-model calculations yield a 2-y residence time for Pb-210 and a 0.6-y residence time for Po-210 in the mixed layer. These residence times are considerably longer than the time calculated for turnover of particles in the mixed layer (about 0.1 y). At depths of 100-300 m, Po-210 maxima occur and unsupported Po-210 is frequently present. Calculations indicate that at least 50% of the Po-210 removed from the mixed layer is recycled within the thermocline. Similar calculations for Pb-210 suggest much lower recycling efficiencies. Comparison of the Pb-210 distribution with the reported distribution of Ra-226 at nearby GEOSECS. stations has confirmed the widespread existence of a Pb-210/Ra-226 disequilibrium in the deep sea. Vertical profiles of particulate Pb-210 were used to test the hypothesis that Pb-210 is removed from deepwater by in situ scavenging. With the exception of one profile taken near the Mid-Atlantic Ridge, significant vertical gradients in particulate Pb-210 concentration were not observed, and it is necessary to invoke exceptionally high particle sinking velocities (>10 m/d) to account for the inferred Pb-210 flux. It is proposed that an additional sink for Pb-210 in the deep sea must be sought. Estimates of the dissolved Pb-210/Ra-226 activity ratio at depths greater than 1,000 m range from 0.2 to 0.8 and reveal a systematic increase, in both vertical and horizontal directions, with increasing distance from the sea floor. This observation implies rapid scavenging of Pb-210 at the sediment-water interface and is consistent with a horizontal eddy diffusivity of 3-6 x 107 cm2/s. The more reactive element Po, on the other hand, shows evidence of rapid in situ scavenging. In filtered sea water, Po-210 is deficient, on the average, by ca. 10% relative to Pb-210; a corresponding enrichment is found in the particulate phase. Total inventories of Pb-210 and Po-210 over the entire water column, however, show no significant departure from secular equilibrium, and reliable estimates of particle sinking rates cannot be made.Prepared under National Science Foundation Grant GA-41061 and U.S.A.E.C. Contract AT(11-1)

Bioturbation processes in continental slope and rise sediments delineated by Pb-210, microfossil and textural indicators

Measurements of Pb-210 activities, in conjunction with micropaleontological, geotechnical and sedimentological observations, on sediment cores have been used to characterize two distinctive bioturbation regimes on the continental slope and rise east of Newfoundland. On the rise (2600 m), excess Pb-210 is confined to the upper few centimeters of the coarser-grained sediments underlying the axis of the Western Boundary Undercurrent. The geological and geochemical evidence for a low rate of bioturbation in this high bottom current regime is consistent with a reduced population of deeper burrowing macrofauna, particularly the species Maldane sarsi. In contrast, a higher flux of organic-rich, fine-grained particulate material to the middle slope (1500 m water depth), and the comparatively stable sedimentological conditions that prevail in this low bottom current regime, have led to the active colonization of the sediment substrate by bioturbating organisms. Enhanced mixing of middle slope deposits is reflected by comparatively lower shear strengths within the upper 30 cm of the sediment column, and by the reduced variability of the sediment-depth distribution of the most abundant species of foraminifera. Excess Pb-210 has been transported downward from the sediment-water interface to depths greater than 12 cm. Some Pb-210 profiles from the middle slope can be interpreted in terms of a diffusion mixing model for which the biological mixing coefficients are of the order of 0.10 – 1.0 cm2 yr−1.Measurements of the two and three dimensional distribution of excess Pb-210 in one middle slope box core indicate that the mixing process in these sediments has a pronounced heterogeneous component on time scales of the same order as the half life of Pb-210 (22.3 yr). Spatial correlations between Pb-210 anomalies and artifacts of bioturbation observed in x-radiographs of the core suggest that Pb-210 maxima observed at depth may be the result of an inclined orientation of burrow structures which have introduced a significant lateral component to the downward transport of surficial sediments

The Aquatic Geochemistry of the Particle-Reactive Radionuclides PO-210, PB-210, and BE-7

Integrated monthly wet-only and bulk precipitation samples for Be-7 and Pb-210 analysis were collected from November 1982 through October 1983 at two sites in lower Chesapeake Bay. Atmospheric deposition fluxes for Be-7 in wet-only and bulk precipitation averaged 0.013 and 0.014 pCi/cm2/d, respectively, and for Pb-210 averaged 0.36 and 0.40 pCi/cm2/yr, respectively, suggesting that dry deposition makes only a minor contribution to the total fluxes. A seasonal trend was observed in the depositional flux of Be-7, with a pronounced maximum in the Spring. Approximately 40 percent of the annual Be-7 deposition occurred between February and April, with a maximum in March. This is consistent with the injection of Be-7 of statospheric origin into the tropopause during the vernal tropopause break. Pb-210 exhibited a slightly weaker seasonal trend, with ca. 35 percent delivered between February and April, which appears to be related to the rate at which its parent, Rn-222, emanates from the earth. The average deposition velocities for Be-7 and Pb-210 in bulk precipitation were 1.5 and 0.8 cm/s, respectively. The removal behaviors of two atmospherically-derived radionuclides, Pb-210 and Be-7, have been examined in real-time following their deposition to a shallow coastal bay by four precipitation events. In general, there was a marked elevation in the water column concentrations following a precipitation event and the concentrations decreased with time. The removal residence times of these radionuclides were on the order of several days. Po-210 exhibited similar behavior. Since the atmospheric flux of Po-210 is small, the elevated concentrations of Po-210 following a precipitation event may result from the mobilization of Po-210, in the dissolved form, from sediments. Vertical profiles of dissolved Po-210, Pb-210, and Ra-226 were obtained from the Orca Basin, an anoxic, hypersaline and yet non-sulfide bearing basin. At the seawater-brine interface at 2230 m, a sharp maximum was observed in the profiles of Po-210 and Pb-210, reaching concentrations of 56.0 and 28.3 dpm/l00 kg, respectively. These are some of the highest values reported for the open ocean. These sharp maxima may be caused by a combination of the dissolution of hydrous manganese oxides and the decomposition of biogenic particulate material. Below the interface, concentrations decreased to ca. 9 and 6 dpm/100 kg, respectively. These concentrations are much higher than those observed in sulfide-bearing anoxic basins. The residence time of Pb-210 in the brine is estimated to be ca. 1 year

Dating the Sea of Marmara sediments by a uniform mixing model

The sedimentation rates and Pb-210 fluxes on sediment surfaces were measured in the north, northwestern and southwestern parts of the Sea of Marmara. Each core had varying thickness of constant Pb-210 activity regions followed by a decreasing part with sediment depth. The sedimentation rates of the samples collected from the Bosporus and the Dardanelles could not be analysed due to the homogenization of activity in the strong currents of these straits. A uniform mixing model is proposed for the simultaneous analysis of sedimentation rates, Pb-210 fluxes and mixing depths from the experimental data. In this model, the parameters were obtained by minimizing the multi-dimensional parameter space using a grid search algorithm. The Pb-210 fluxes were found to be about 0.048 Bq cm(-2) year(-1) for all sampling sites. The mass sedimentation rates were 0.19 and 0.073 g cm(-2) year(-1) at the shelves of the Bosporus and the Dardanelles and 0.055 and 0.064 g cm(-2) year(-1) in the northwestern and middle northern basins, respectively, of the Sea of Marmara. Copyright (C) 1996 Elsevier Science Limite

Calibration of an HPGe detector and self-attenuation correction for Pb-210: Verification by alpha spectrometry of Po-210 in environmental samples

In this work the calibration of an HPGe detector for Pb-210 measurement is realised by a liquid standard source and the determination of this radionuclide in solid environmental samples by gamma spectrometry takes into account a correction factor for self-attenuation of its 46.5 keV line. Experimental, theoretical and Monte Carlo investigations are undertaken to evaluate self-attenuation for cylindrical sample geometry. To validate this correction factor (at equilibrium with Po-210 Pb-210) alpha spectrometry procedure using microwave acid digestion under pressure is developed and proposed. The different self-attenuation correction methods are in coherence, and corrected Pb-210 activities are in good agreement with the results of Po-210. Finally, self-attenuation corrections are proposed for environmental solid samples whose density ranges between 0.8 and 1.4 g/cm(3) and whose mass attenuation coefficient is around 0.4 cm(2)/g. (C) 2007 Elsevier B.V. All rights reserved

Polonium and Lung Cancer

The alpha-radioactive polonium 210 (Po-210) is one of the most powerful carcinogenic agents of tobacco smoke and is responsible for the histotype shift of lung cancer from squamous cell type to adenocarcinoma. According to several studies, the principal source of Po-210 is the fertilizers used in tobacco plants, which are rich in polyphosphates containing radio (Ra-226) and its decay products, lead 210 (Pb-210) and Po-210. Tobacco leaves accumulate Pb-210 and Po-210 through their trichomes, and Pb-210 decays into Po-210 over time. With the combustion of the cigarette smoke becomes radioactive and Pb-210 and Po-210 reach the bronchopulmonary apparatus, especially in bifurcations of segmental bronchi. In this place, combined with other agents, it will manifest its carcinogenic activity, especially in patients with compromised mucous-ciliary clearance. Various studies have confirmed that the radiological risk from Po-210 in a smoker of 20 cigarettes per day for a year is equivalent to the one deriving from 300 chest X-rays, with an autonomous oncogenic capability of 4 lung cancers per 10000 smokers. Po-210 can also be found in passive smoke, since part of Po-210 spreads in the surrounding environment during tobacco combustion. Tobacco manufacturers have been aware of the alpha-radioactivity presence in tobacco smoke since the sixties

Natural and anthropogenic influences on atmospheric Pb-210 deposition and activity in sediments : a review

The determination of the age of a sediment layer is invaluable for understanding geochemical processes and their time-scales. The application of Pb-210 as a radiometric chronometer has been extensively researched in recent years, being applied to a variety of freshwater, estuarine and marine environments worldwide. The estimation of sedimentation rate changes using Pb-210 dating can also provide valuable information on possible causes for variation in a water body’s physiochemical and biological characteristics; making the technique relevant to environmental remediation. However, to reliably draw conclusions based on Pb-210 dating; a comprehensive understanding of the influence that other natural and anthropogenic variables have on Pb-210 is essential. This literature review summarises the key factors which may influence both unsupported Pb-210 deposition from the atmosphere and the unsupported Pb-210 activity found in sediments. The deposition of unsupported Pb-210 is shown to be predominantly via the rain-out mechanism (within-cloud scavenging) as opposed to wash-out (below cloud), and the suppression or release of Rn-222 exhalation from sediments may also be controlled by surface air temperatures and pressures, which consequently will result in seasonal variations in atmospheric Pb-210 concentrations and Pb-210 deposition. Organic matter (OM), silt and clay content also have an influence on the sediment unsupported Pb-210 activity; thus leading to a general consensus of positive correlation between unsupported Pb-210 activity and the OM, silt or clay content as a result of greater adsorption affinity for Pb-210 and an enhanced specific surface area relative to sand and larger particles. Bioturbation will also impact the unsupported Pb-210 activity in sediments, however mathematical models used to estimate this influence still require further refinement to accurately represent activity variation associated with different species’ burrowing techniques and different soil porosities. Anthropogenic influences on sediment unsupported Pb-210 activity may also have been observed i.e. additional Pb-210 from the anthropogenic source, though research on these are limited and further research is advised in assessing the impact of anthropogenic activities such as farming, mining and fossil fuel combustion

PROGRAM JAMINAN KUALITAS PADA PENGUKURAN RADIONUKLIDA PEMANCAR GAMMA ENERGI RENDAH:RADIONUKLIDA Pb-210

Telah dilakukan kegiatan peningkatan kinerja terhadap pengukuran Pb-210 untuk program jaminan kualitas pengukuran radionuklida pemancar gamma energi rendah. Peningkatan kinerja tersebut,adalah kalibrasi dan pengukuran Certified Reference Material (CRM). Hasilkegiatan yang diperoleh berupa: (i) pengukuran Pb-210 menggunakanspektrometer gamma energi rendah; (ii) kalibrasi spektrometer gamma energi rendah; dan (iii) pengukuran Pb-210 pada CRM. Mengacu ke hasil kegiatan tersebut dapat disimpulkan, bahwa (i) pada sumber titik tidak dipengaruhi oleh fenomena self absorption; (ii) terdapat korelasi yang cukup besar antara nomor salur dan energi dan hasil pengukuran berada pada garis model pada kurva kalibrasi energi dan efesiensi; dan (iii) hasil pengukuran Pb-210 pada CRM mempunyai perbedaan 1,5% dari nilai yang tercantum di dalam sertifikat. The performance raising activity have been done against the Pb-210 measuring for the quality assurance program of the measuring onthe low energy gamma-ray (g-ray) radionuclide, the Pb-210 radionuclide.The raising of performance, namely calibration and meauring of the Certified Reference Material (CRM). The result of activity has gotten, namely (i) measuring of Pb-210 using the low energy gamma spectrometer, (ii) calibration of the low energy gamma spectrometer, and (iii) meassuring of PB-210 on CRM. Base on the result of activity can get the conclusion

Asian Influence Over the Western North Pacific during the Fall Season: Inferences from Lead 210, Soluble Ionic Species and Ozone

Aerosol samples collected over the western Pacific during the NASA/Global Tropospheric Experiment Pacific Exploratory Mission (PEM-West A) expedition (September - October 1991) revealed mean Pb-210 concentrations in the free troposphere in the 5-10 fCi m(exp -3) STP range. Most soluble ionic aerosol-associated species were near detection limits [much less than 40 parts per trillion by volume (pptv)] in these same samples. The altitude distribution of O3 near Asia closely resembled that of Pb-210, while no relationship was found between the concentrations of O3 and Be-7. Free tropospheric air over the western Pacific was depleted in soluble aerosol-associated species but enriched in Pb-210 and O3, indicative of deep wet convection over the Asian continent. The influence of Asian air on the composition of the free troposphere over the western Pacific was evident on most of the PEM-West A flights. However, evidence of continental influence was largely restricted to those species that are relatively insoluble (or have insoluble precursors), hence escape scavenging during vertical transport from the boundary layer into the free troposphere by wet convective activity