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[en] Traces of particulate radioactive iodine (I-131) were detected in the European atmosphere in January/February 2017. Concentrations of this nuclear fission product were very low, ranging 0.1 to 10 mu Bq m(-3) except at one location in western Russia where they reached up to several mBq m(-3). Detections have been reported continuously over an 8-week period by about 30 monitoring stations. We examine possible emission source apportionments and rank them considering their expected contribution in terms of orders of magnitude from typical routine releases: radiopharmaceutical production units > sewage sludge incinerators > nuclear power plants > spontaneous fission of uranium in soil. Inverse modeling simulations indicate that the widespread detections of I-131 resulted from the combination of multiple source releases. Among them, those from radiopharmaceutical production units remain the most likely. One of them is located in Western Russia and its estimated source term complies with authorized limits. Other existing sources related to I-131 use (medical purposes or sewage sludge incineration) can explain detections on a rather local scale. As an enhancing factor, the prevailing wintertime meteorological situations marked by strong temperature inversions led to poor dispersion conditions that resulted in higher concentrations exceeding usual detection limits in use within the informal Ring of Five (Ro5) monitoring network.

[en] As a consequence of therapeutic and diagnostic treatment of patients with thyroid diseases, ¹³¹I is introduced into the sewage system on a regular basis. This presents an opportunity to use the ¹³¹I as a tracer to study its partitioning and transport within a wastewater treatment plant (WWTP). In the case of nuclear accidents where ¹³¹I is one of the most prominent nuclides, an understanding of iodine partitioning and transport will be valuable for developing models that may prognosticate the activity concentrations in sludge and outflow, especially after an accidental input. In this study, samples from various locations inside a municipal WWTP were taken and for each sample, three different fractions were separated by a chemical extraction process. These fractions were analysed for their ¹³¹I activity concentrations by gamma-ray spectroscopy. While about 30% of the radioiodine activity in the inflow is associated with organic molecules, this amounts to about 90% after biological treatment. This is caused by the accumulation of ¹³¹I bound to organic matter in the return sludge and by a transfer of ¹³¹I from the inorganic to the organic fractions, most likely mediated by microbial action. In the outflow, inorganic and low-molecular ¹³¹I is dominant, but the overall activity concentration is reduced to about 50–75%. - Highlights: • The partitioning of medical ¹³¹I changes on its way through a municipal wastewater treatment plant. • The organically bound fraction amounts to ∼90% after biological treatment compared to ∼30% in the inflow. • Apart from accumulation of organic material, this is caused by transformation of inorganic ¹³¹I to organic ¹³¹I. • In the effluent, the activity concentration is reduced to about 50%–75%.

[en] In this study it is shown how radionuclide distributions in agricultural soils and their dependence on soil parameters can be quantitatively estimated. The most important sorption and speciation processes have been implemented into a numerical model using the geochemical code PHREEQC that is able to include specific soil and soil solution compositions. Using this model, distribution coefficients (K_d values) for the elements Cs, Ni, U and Se have been calculated for two different soil types. Furthermore, the dependencies of these K_d values on various soil parameters (e.g. pH value or organic matter content) have been evaluated. It is shown that for each element, an individual set of soil parameters is relevant for its solid–liquid distribution. The model may be used for the calculation of input parameters used by reference biosphere models (e.g. used for the risk assessment of nuclear waste repositories). -- Highlights: • We present a geochemical model for radionuclide distribution in agricultural soils. • The model has been validated by using experimental studies from the literature. • The model works well for Cs, Ni, U and Se. • The dependencies of nuclide distribution on soil parameters have been evaluated

[en] ¹³¹I is a radionuclide that may be introduced into natural and urban environments via several pathways. As a result of nuclear accidents it may be washed out from air or settle onto the ground by dry deposition. In urban landscapes this is again washed out by rain, partly introduced into the sewer system and thus transported to the next wastewater plant where it may accumulate in certain compartments. In rural landscapes it may penetrate the soil and be more or less available to plant uptake depending on chemical and physical conditions. On a regular basis, ¹³¹I is released into the urban sewer system in the course of therapeutic and diagnostic treatment of patients with thyroid diseases. The speciation of iodine in the environment is complex. Depending on redox state and biological activity, it may appear as I^-, IO₃^-, I₂ or bound to organic molecules (e.g. humic acids). Moreover, some of these species are bound to surfaces of particles suspended in water or present in soil, e.g. hydrous ferric oxides (HFO). It is to be expected that speciation and solid-liquid distribution of iodine strongly depends on environmental conditions. In this study, the speciation and solid-liquid distribution of iodine in environmental samples such as waste water, sewage sludge and soil are estimated with the help of the geochemical code PHREEQC. The calculations are carried out using chemical equilibrium and sorption data from the literature and chemical analyses of the media. We present the results of these calculations and compare them with experimental results of medical ¹³¹I in waste water and sewage sludge. The output of this study will be used in future work where transport and distribution of iodine in wastewater treatment plants and in irrigated agricultural soils will be modeled. (authors)

[en] The OSPAR agreement obligates the German government to determine and report the annual I-131 insertion from German rivers into the Northern Atlantic Ocean. In the frame of a research program the I-131 concentrations were determined in the rivers Elbe, Weser, Ems and Rhein that allowed the evaluation of the contamination load into the Northern Sea using a balance model.

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[en] City sewer systems have to reliably carry residential and industrial wastewater to treatment plants, often mixed with rainwater. Transport in the sewer system is regularly modelled in order to predict sewerage levels, transport velocities and volume discharges. Radioisotopes would be interesting tracers, as they can be detected quickly and without the need of applying wet chemistry. Medical isotopes are released in large quantities (many MBq) by excretion from patients either at the location of administration or from elsewhere, most probably the patient's home. Depending on diagnostic or treatment modality, isotopes of different physical characteristics are used, often bound to compounds of specific metabolic behaviour. Routine environmental surveillance regularly detects the most common diagnostic (^99mTc) and therapeutic (¹³¹I) isotopes in city wastewater samples. Except for ¹³¹I in the case of a nuclear emergency, no contributions from sources other than medical are expected. Medical isotopes therefore might be used for tracing purposes, provided individual inputs can be identified and separated. A field experiment has been designed involving ¹³¹I releases from a single patient who had undergone radioiodine thyroid ablation therapy. This modality is applied after thyroid cancer surgery in order to destroy residual thyroid tissue. Activities up to 5 GBq of ¹³¹I are used which are excreted within few days, as no iodine-retaining thyroid tissue remains. In Germany, about 20,000 of these treatments are performed yearly. For a sewer system of 500,000 inhabitants, about 150 cases would be expected per year, making it quite improbable to have interference between individual patient releases in the same region of the city sewer system. Practically, the radiometric laboratory was informed of the expected release of an (anonymous) patient from the collaborating radiotherapy unit several days in advance, plus the approximate location of the patient's home. Together with the sewage system authority, automated sampling (mostly in 6 h intervals) over one week at four locations between the patient's home quarter and the sewage plant inlet was planned and successfully conducted, delivering a total of 84 samples. Sampling started before the assumed arrival of the patient at his home, to account for 'background' signal due to releases from other patients. The samples were investigated for ¹³¹I by high resolution gamma spectroscopy, with a detection threshold of down to ca. 0.1 Bq/l, depending on the allocated measurement time. Data time series plots show clearly distinguishable peaks in ¹³¹I activity, with peak amplitude decreasing from over 1 kBq/l to below 1 Bq/l with distance from the patient's home quarter (due to dilution) and peak time being retarded (due to transport time). At the two most distant sampling points, the peak appears on a variable background, attributed to ¹³¹I releases of other patients. Modelling with specific sewer system software is still under way, but the data already show that under suitable conditions medical isotopes can successfully be used as sewage tracers. (authors)