Biokinetics distribution of radionuclides in fish and shellfish and risk assessment for consumers in Sweden
Food habits including seafood results in a 4.5 higher ingestion dose from 210Po than for example ovo-lacto vegetarian diet. In addition, if we consider population groups with high consumption of fish and shellfish, the ingestion dose levels could increase as far as three times more than common diet. Thus, the current project aims to study the biokinetic distribution of NORM and 137Cs in fish and shellfish to better understand the biodistribution and the radiological impact of radionuclides in fish and shellfish. Gamma spectrometry and alpha spectrometry are used to carry out the radiological determination of 137Cs and NORM radionuclides.
Project financing: Swedish Radiation Safety Authority (SSM2020-642). Stiftelsen Wilhelm och Martina Lundgrens Vetenskapsfond (2021-3730).
The mining industry has been important for Sweden's economy for a long time due to the mineral rich bedrock. Only a few mines are active today, however, the remains of Sweden's mining history can still be seen through the many mining pits located across the country. Following mine closure, if the pit reaches below the groundwater level, it will be filled with groundwater up to the same level which creates a so-called pit lake.
Since both uranium and thorium and other naturally occurring radionuclides are present in the bedrock, they will be present in all stages of the mining process. The levels of naturally occurring radionuclides in and around the mining lakes are in most cases unknown. Furthermore, there is a lack of knowledge regarding how these radionuclides and various elements are distributed in mining lakes in different parts of the country, as well as the radiation exposure received when visiting these sites. These questions have been dealt with at our unit and a summary can be read in the PhD-thesis by Rimon Thomas (Primordial radionuclides in pit lakes in Sweden).
Project financing: Swedish Radiation Safety Authority
Wildfires are a recurring natural phenomenon during the dry periods of summer where soil and vegetation are one of several factors that determines the risk of the fire outbreaks. Bogs have a high amount of carbon stored in the soil and as long as the soil is moist, it forms a natural barrier that prevents wildfires from spreading across the bog. In extreme drought however, the bog itself will pose a fire hazard due to the high proportion of carbon in the soil, if a fire breaks out, large parts can therefore burn for a long time.
A radioactive isotope of cesium is found in large parts of the world in varying amounts due to previous atmospheric nuclear weapon testing and nuclear accidents such as the Chernobyl accident. Cesium is an element that is chemically similar to potassium, which is an important nutrient for plants. The plants cannot distinguish between these two elements, thus, radioactive cesium is also taken up by the vegetation. In the event of a wildfire in the bog, radioactive cesium present in the vegetation will therefore become volatile. An ongoing project is therefore looking at the relative amount of radioactive isotopes that become volatile after a wildfire by studying soil cores taken from bogs. An estimate of volatility is made by analyzing earth cores from bogs that have burned where earth cores inside and outside the burnt area are studied.
Optimization of radiochemical methods
At our unit, we are working with method optimization of the chemical separations used in the analysis of radionuclides via alpha spectrometry. Most of the available methods today require evaporation of acids to go from one type of acid to another. This is something we strive to minimize as much as possible and to minimize the volume required to perform the separations. Recent tests have shown that neutralizing an acid with a base such as NaOH, and then adding the desired acid works well in many cases. Furthermore, we have seen an increased chemical yield for water samples as we have minimized the volume of acids and reagents, however, the chemical yield and energy dissolution decrease for other types of samples that contain a higher content of interfering elements such as calcium.
Naturally occurring radioactive elements at the Kvarntorp pile
The Kvarntorp pile, consisting mainly of shale ash, and nearby pit lakes are the remains of a former oil shales industry. The aim of this project is to perform a radiological hazard assessment by measuring naturally occurring radioactive elements, such as 238U, 235U, 234U and 210Po in soil, water and plants. The analyses have shown that the external dose rate are elevated at sites with exposed alum shale walls and on shale ash at the pile. The radiological risk to biota cannot be regarded as being of negligible concern and this work is thus ongoing. For humans, however, the effective dose to members of the public is only slightly elevated compared to the natural background radiation.
Transfer of radioactive elements in the marine environment
Bioaccumulation of radioactive elements in animals and plants will determine the radiological consequences for humans and biota following a release of radioactive elements to the environment. We are engaged in studies on transfer in the marine environment by theoretical modelling and experiments. For example, kinetic modelling of the bioaccumulation processes, measurements of concentration ratios in laboratory experiments and analyses of radioactive elements in seals.
Radiation doses and risk
In cooperation with researchers from Lund and Uppsala University, we have developed a model that sums up the contributions from external and internal exposure, likely to be incurred under various scenarios following a nuclear power plant accident. By combining this model with the lifetime attributable risk (LAR) concept, the effect of age and sex in risk estimates can be studied. The model is also applied to studies on decontamination of areas affected by fallout from a nuclear power plant release of radioactive elements.
Radioactive elements in the human body
In case of accidents or contamination at workplaces, radioactive elements can end up in the human body where they give rise to a radiation dose over time. To assess this radiation dose, it is essential to be able to measure the content of radioactive elements in the body. This is traditionally made by so called whole body counting in which specially designed detector systems are used. The access to dedicated whole body counters are, however, limited and we are therefore studying to what extent gamma cameras (used in nuclear medicine) can be used as a complement. This work includes theoretical modelling of the gamma camera response to various photon energies and geometries, as well as experimental work. The aim is to determine generic calibration factors and to increase the efficiency of the gamma camera for radioactive elements encountered in emergency situations.