Understanding the transfer of radionuclides through the food chain leading to man and in particular, the uptake of transuranic nuclides by plankton, is basic to assess the potential radiological risk of the consumption of marine products by man. The main sources of transuranic elements in the Mediterranean Sea in the past were global fallout and the Palomares accident, although at present smaller amounts are released from nuclear establishments in the northwestern region. Plankton from the western Mediterranean Sea was collected and analyzed for plutonium and americium in order to study their biological uptake. The microplankton fractions accounted for approximately 50% of the total plutonium contents in particulate form. At Garrucha (Palomares area), microplankton showed much higher 239,240 Pu activity, indicating the contamination with plutonium from the bottom sediments. Concentration factors were within the range of the values recommended by the International Atomic Energy Agency. Continental shelf mesoplankton was observed to efficiently concentrate transuranics. In open seawaters, concentrations were much lower. We speculate that sediments might play a role in the transfer of transuranics to mesoplankton in coastal waters, although we cannot discard that the difference in species composition may also play a role. In Palomares, both 239,240 Pu and 241Am showed activities five times higher than the mean values observed in continental shelf mesoplankton. As the plutonium isotopic ratios in the contaminated sample were similar to those found in material related to the accident, the contamination was attributed to bomb debris from the Palomares accident. Concentration factors in mesoplankton were also in relatively good agreement with the ranges recommended by IAEA. In the Palomares station the highest concentration factor was observed in the sample that showed predominance of the dynoflagellate Ceratium spp. Mean values of the enrichment factors showed, on average, discrimination rather than enrichment in the primary producer trophic chain.

Radionuclides emitted from nuclear reactors, fuel reprocessing facilities and nuclear weapons tests are distributed widely in the atmosphere but have very low concentrations. As part of the Comprehensive Test Ban Treaty (CTBT), identification and verification of the emission of radionuclides from such sources are fundamental in maintaining nuclear security. To detect underground and underwater nuclear weapons tests, only the gaseous components need to be analyzed. Equipment has now been developed that can be used to collect large volumes of air, separate and concentrate the radioactive gas constituents, such as xenon and krypton, and measure them quantitatively. By measuring xenon isotopes with different half-lives, the time since the fission event can be determined. Developments in high-pressure (3500kPa) swing chromatography using molecular sieve adsorbents have provided the means to collect and purify trace quantities of the gases from large volumes of air automatically. New scintillation detectors, together with timing and pulse shaping electronics, have provided the low-background levels essential in identifying the gamma ray, X-ray, and electron energy spectra of specific radionuclides. System miniaturization and portability with remote control could be designed for a field-deployable production model.

Low levels of radioactive gases are released from nuclear electric power generation, nuclear fuel reprocessing plants, nuclear weapons tests and from diagnostic medical uses of radioactive gas tracers. A prototype model of an inorganic scintillator – Crystal Gas Electron Detector (CGED) – was built for measurements of xenon isotopes in-line by detecting the beta and internal conversion (IC) electrons present in atmospheric samples. The detection and quantification of the radionuclide spectra are accomplished, during air flow, without complete purification of the fission gases. Initial operational tests and calibrations made permit the integration of the CGED into a portable Gas Analysis, Separation and Purification (GASP) system 1, 2, 3. The CGED detector, Pulse Shaping and Timing (PSA) electronics, and mathematical treatment of the accumulated spectra are used to resolve the K and LMNO-IC electrons and beta continuum. These data are used, in-line, for dating the age of an air parcel containing fission gases released from nuclear reactors and/or from nuclear weapons tests, as part of the monitoring equipment required to enforce the Comprehensive Test Ban Treaty, CTBT. This report is one of a series of papers providing the design features, operational methods, calibration, and applications of radioactive gas analysis system to the International CTBT.

Radioactive gases are emitted into the atmosphere from nuclear electric power and nuclear fuel reprocessing plants, from hospitals discarding xenon used in diagnostic medicine, as well as from nuclear weapons tests. A high-pressure plastic scintillation detector was constructed to measure atmospheric levels of such radioactive gases by detecting the beta and internal conversion (IC) electron decays. Operational tests and calibrations were made that permit integration of the flow detectors into a portable Gas Analysis, Separation and Purification system (GASP). The equipment developed can be used for measuring fission gases released from nuclear reactor sources and/or as part of monitoring equipment for enforcing the Comprehensive Test Ban Treaty. The detector is being used routinely for in-line gas separation efficiency measurements, at the elevated operational pressures used for the high-pressure swing analysis system (2070kPa) and at flow rates of 5–15l/min 1, 2. This paper presents the design features, operational methods, calibration, and detector applications.

1Department of Physics and Center for Risk Analysis, Harvard University, Cambridge, MA 2Department of Environmental and Occupational Health, University of Pittsburgh, Pittsburgh, PA USA.

Atmospheric fallout of pollutant effluent from chemical industries, metal refining plants, coal and oil combustion sources and the nuclear industry are widely distributed in forests and wetland environments. These ecosystems are repositories which collect and store the waste products of man's industrial activities and provide a source of samples which may record the regional history of pollutant input to the ecosystem and to man. Measurements of such toxic elements must be accompanied by detailed quality control procedures for sampling and analysis in order to enable a critical evaluation of the results. In plant nutrition, the: local ecosystem is in general equilibrium with precipitation, nutrient and trace metal uptake from soil, and plant litter decomposition on an annual cycle. Distribution coefficients and soil-to-plant plant transfer factor measurements of elements provide equilibrium values but do not represent conditions where dynamic, long-term processes dominate. The fallout from nuclear weapons tests and the Chernobyl NPP reactor accident, however, provided tracers for identifying the kinetic processes which make up the total equilibrium of plant growth. In forests, the complications of long term-growth and nutrient availability can be separated into compartments representing deposition onto leaves, wash-off by precipitation, stem flow, understory and litter accumulation and, finally, infiltration into the root zone for plant uptake. Studies of cores collected from ombrotrophic bogs, forest floor and lake sediments have shown the rate of atmospheric deposition and transport of elements. The bog and wetland environments provide a highly organic medium where deposition and migration of elements can be studied without the complications of the forest roots. Models which provide insight into transport processes of elements have been made in order to evaluate and predict long term effects on ecosystems and to reconstruct the element dose to man from breathing the toxic metallic fumes from industrial sources.

Radionuclide pathways and relevant parameters can be quantified only when the processes controlling their transport and availability are known. Knowledge about processes of radionuclide transport and fate in natural and semi-natural ecosystems is limited due to their complexity and inherent variability. For many purposes, environmental transport parameters for a specific radionuclide can be derived by analogy with other radionuclides and/or other pollutants (such as heavy metals, etc.). Other parameters have nothing to do with a specific pollutant, but rather reflect time scales of biological and environmental processes inherent in ecosystems.We propose a unique model-directed approach for parameter quantification (Linkov, 1995, 1997, Schell et. al., 1996a). Initially, we review the fate and transport processes occurring in the ecosystem and formulate generic conceptual compartmental model. Then, we collect and review literature to identify environmental half-times in the model compartments. Finally, additional parameters most commonly used in available models are collected and evaluated. This approach does not bind the parameter search to a specific chemical agent or radionuclide, but rather is process-oriented.

As a result of the Chernobyl nuclear power plant accident in 1986, large forested areas in Europe were contaminated by radionuclides. Extensive societal pressure has been exerted to decrease the radiation dose to the population and to the environment. Thus, in making abatement and remediation policy decisions not only economic costs, but also human and environmental risk assessment are desired. Forest remediation by organic layer removal, one of the most promising cleanup policies, is considered in this paper. Ecological risk assessment requires evaluation of the radionuclide distribution in forests. The FORESTPATH model (1,2) is used for predicting the radionuclide fate in forest compartments after deposition as well as for evaluating the application of the remedial policy. Time of intervention and radionuclide deposition profile was predicted as being crucial for the remediation efficiency. Risk assessment conducted for a critical group of forest users in Belarus shows that consumption of forest products (berries and mushrooms) leads to about 0.004% risk of a fatal cancer. Cost‐benefit analysis for forest cleanup suggests that complete removal of organic layer is too expensive for application in Belarus.

Radionuclides emitted from nuclear reactors, fuel reprocessing facilities and nuclear weapons tests are distributed widely in the atmosphere but have very low concentrations. As part of the Comprehensive Test Ban Treaty, identification and verification of the emission of radionuclides from such sources are fundamental in maintaining global nuclear security [1]. To detect underground and underwater nuclear weapons tests, only the gaseous components need to be analyzed. Equipment has now been developed which can be used to collect large volumes of air, separate and concentrate the radioactive xenon, and measure it quantitatively. By measuring xenon isotopes with different decay half-lives, the time when fission occurred can be determined. Developments in high pressure (3500 kPa) swing chromatography using molecular sieve adsorbents have provided the means to collect and purify trace quantities of the gases from large volumes of air automatically. New measurement detectors together with timing and pulse shaping electronics have provided the low background levels essential in identifying the X-, gamma-ray and electron energy spectra of specific radionuclides.

A comparative study has been made of the history of lead and other trace metals that have been deposited on wetlands. A series of sediment cores from the USA, Ireland and the Czech Republic were measured for 210Pb, Pb, other trace metals and the radionuclides 137Cs, 90Sr and 239,240Pu. The 210Pb chronology of the core profiles was established using the CRS method of Appleby and Oldfield and the minimum variance method of Tobin and Schell, i.e., the CRS-MV method. Using the minimum variance of the least-squares fit of the line representing the total core data and propagating the errors, the apparent time error ranges from 2 to 10 years. Cores were taken from Hudson River wetlands, a mountain top bog in the USA, blanket bogs in western and eastern Ireland, and bogs in a highly polluted and a "pristine" zone in the Czech Republic and provided profiles. At the most westward European station in Ireland, the Pb deposition history appears to exceed background levels at dates similar to those in eastern USA, whereas the profiles near Dublin exceed background values at approximately the same date but have maximum deposition values significantly later. Such initiation of the Pb deposition in Ireland could be due to long-range transport across the Atlantic Ocean. In the Czech Republic, the initiation of metal deposition occurs before that in Ireland and the USA, reflecting the earlier development of industrialization and release of metals.

The ability to quickly detect and assess the magnitude of releases of fission-produced radioactive material is of significant importance for ongoing operations of any conventional nuclear power plant or other activities with a potential for fission product release. In most instances, the control limits for the release of airborne radioactivity are low enough to preclude direct air sampling as a means of detection, especially for fission gases that decay by beta or electron emission. It is, therefore, customary to concentrate the major gaseous fission products (krypton, xenon and iodine) by cryogenic adsorption for subsequent separation and measurement. This study summarizes our initial efforts to develop an automated portable system for on-line separation and concentration with the potential for measuring environmental levels of radioactive gases, including 85Kr, 131,133,135Xe, 14C, 3H, 35S, 125,131I, etc., without using cryogenic fluids. Bench top and prototype models were constructed using the principle of heatless fractionation of the gases in a pressure swing system. This method removes the requirement for cryogenic fluids to concentrate gases and, with suitable electron and gamma ray detectors, provides for remote use under automatic computer control. Early results using 133Xe tracer show that kinetic chromatography, i.e., high pressure adsorption of xenon and low pressure desorption of air, using specific types of molecular sieves, permits the separation and quantification of xenon isotopes from large volume air samples. We are now developing the ability to measure the presence and amounts of fission-produced xenon isotopes that decay by internal conversion electrons and beta radiation with short half-lives, namely 131mXe, 11.8 d, 133mXe, 2.2 d, 133Xe, 5.2 d and 135Xe, 9.1 h. The ratio of the isotopic concentrations measured can be used to determine unequivocally the amount of fission gas and time of release of an air parcel many kilometers downwind from a nuclear activity where the fission products were discharged.