Spatial datasets of radionuclide contamination in the Ukrainian Chernobyl Exclusion Zone

The dataset “Spatial datasets of radionuclide contamination in the Ukrainian Chernobyl Exclusion Zone” was developed to enable data collected between May 1986 (immediately after Chernobyl) and 2014 by the Ukrainian Institute of Agricultural Radiology (UIAR) after the Chernobyl accident to be made publicly available. The dataset includes results from comprehensive soil sampling across the Chernobyl Exclusion Zone (CEZ). Analyses include radiocaesium (134Cs and 134Cs) 90Sr, 154Eu and soil property data; plutonium isotope activity concentrations in soil (including distribution in the soil profile); analyses of “hot” (or fuel) particles from the CEZ (data from Poland and across Europe are also included); and results of monitoring in the Ivankov district, a region adjacent to the exclusion zone. The purpose of this paper is to describe the available data and methodology used to obtain them. The data will be valuable to those conducting studies within the CEZ in a number of ways, for instance (i) for helping to perform robust exposure estimates to wildlife, (ii) for predicting comparative activity concentrations of different key radionuclides, (iii) for providing a baseline against which future surveys in the CEZ can be compared, (iv) as a source of information on the behaviour of fuel particles (FPs), (v) for performing retrospective dose assessments and (vi) for assessing natural background dose rates in the CEZ. The CEZ has been proposed as a “radioecological observatory” (i.e. a radioactively contaminated site that will provide a focus for long-term, radioecological collaborative international research). Key to the future success of this concept is open access to data for the CEZ. The data presented here are a first step in this process. The data and supporting documentation are freely available from the Environmental Information Data Centre (EIDC) under the terms and conditions of the Open Government Licence: https://doi.org/10.5285/782ec845-2135-4698-8881-b38823e533bf

The Relative Importance of Different Trophic Pathways for Secondary Exposure to Anticoagulant Rodenticides

Secondary exposure of predators to anticoagulant rodenticides, and in particular second generation anticoagulant rodenticides (SGARs), is a global phenomenon. The widespread and large-scale nature of this exposure has attracted considerable concern, although the consequences in terms of likelihood of poisoning of individuals and resultant impacts on populations are not well characterised. Secondary exposure of predators may as rise from once or more of: (i) eating contaminated commensal rodents subject to control (target species are typically rats and house mice); (ii) consumption of contaminated non-target small mammals (such as Peromyscus, Microtus, and Apodemus species) that encounter and feed on what are rodent-attractive baits; (iii) consumption of non-rodent vertebrate and invertebrate prey that may also incidentally encounter and eat baits. We hypothesised that predators feeding primarily on target species may be most at risk of exposure to SGARs while those predominantly taking non-mammalian prey may be at least risk. We tested this hypothesis by comparing exposure, determined from the presence and magnitude of SGAR liver residues, in red kites (Milvus milvus), which feeds extensively on rats, in barn owls (Tyto alba), kestrels (Falco tinnunculus), and tawny owls (Strix aluco) that feed widely on non-target small mammals, and in sparrowhawks (Accipiter nisus) that feed predominantly on small birds. We found that the scale and magnitude of exposure was broadly consistent with our hypothesis, and that controlling for age in the analysis could be important as older birds can accumulate residues with age. However, exposure in kestrels was typically greater than that in barn owls and tawny owls, despite what is thought to be a general similarity among the species in their diets. We discuss the relative importance of trophic pathways relative to other factors that may drive secondary exposure in predators, and confirm that species that feed on rats or other target species may be at most risk of exposure and poisoning

CONFIDENCE overview of improvements in radioecological human food chain models and future needs

Radioecological models used to make predictions of the radionuclide activity concentrations in human foodstuffs must be sufficiently robust and fit for purpose with uncertainties reduced where practicable. The CONFIDENCE project had a work package with the objective to improve the capabilities of radioecological models and this paper presents the key findings of this work. Recommendations for future radioecological studies/model developments are made based on the findings of the work conducted and consultations with end-users

A simple approach to better estimates of Sr-90 concentrations in crops

To predict radionuclide concentrations in crops most predictive models use equilibrium concentration ratios (the dry mass activity concentration in plant relative to the dry mass activity concentration in soil). However, for a given radionuclide-crop type combination, concentration ratios can be highly variable (variation over three orders of magnitude is common). A considerable proportion of this variation is due to soil properties. In the 1990’s/2000’s ‘process-based’ models using relatively readily available soil parameters (e.g. percentage clay, exchangeable potassium content) were developed to make predictions of radiocaesium concentrations in crops. Such models offer an approach which give predictions appropriate to site characteristics and can also be applied spatially to identify ‘at risk’ areas in the event of a nuclear accident. They can also be used to predict the effect of some countermeasures (i.e. K-fertiliser application). Whilst these models were developed for radiocaesium and have received recent renewed attention prompted by the Fukushima accident, there has been no development and testing of a similar approach for the other likely long-term contaminant following a nuclear accident, Sr-90. In this presentation, we will report on our recent studies to develop process-based modelling approaches to predict Sr-90 activity concentrations in crops. We have successfully developed two approaches to predicting Sr concentrations in crops using soil parameters. The first of these used model reduction to adapt an existing, well established, chemical speciation model. Whilst we will give an overview of this work, the focus of the paper will be on a simpler approach, which only requires information on soil and crop calcium concentrations. To test the developed models we conducted greenhouse studies growing crops in six soil types from the United Kingdom and Spain. The crops grown were grass, lettuce, courgette, potato, chard, radish and strawberry. As already noted, the simpler of the two approaches developed requires soil and plant calcium concentrations. If we assume that either soil calcium concentrations will be available from measurements at a given site or national soil databases then we only need to estimate calcium concentrations in crops of interest. To enable this we have compiled a database of approximately 1000 values collated from various worldwide databases. Strontium concentrations in the crops grown in the greenhouse study are relatively poorly predicted using published concentration ratio values (International Atomic Energy Agency Technical Report Series 472) (R2=0.01). Predictions are considerably better using the simple approach we have developed (R2>0.5). In addition to the soil-plant model development and testing, we will also present a summary of our recent evaluation of the ability of suggested ‘phylogenetic models’ to predict Sr (and Cs) concentrations in crops. There is scope to use phylogenetic and process-based models in combination. Acknowledgements: We thank other staff at UK CEH Lancaster who have contributed to this work. The studies discussed here were conducted as part of the CONFIDENCE project, which is part of the CONCERT EJP funded by the European Union's Horizon 2020 research and innovation programme (grant agreement No 662287)

The comparative toxicity to soil invertebrates of natural chemicals and their synthetic analogues

The introduction of Registration, Evaluation and Authorisation of Chemicals (REACH), requires companies to register and risk assess all substances produced or imported in volumes of >1 tonne per year. Extrapolation methods which use existing data for estimating the effects of chemicals are attractive to industry, and comparative data are therefore increasingly in demand. Data on natural toxic chemicals could be used for extrapolation methods such as read-across. To test this hypothesis, the toxicity of natural chemicals and their synthetic analogues were compared using standardised toxicity tests. Two chemical pairs: the napthoquinones, juglone (natural) and 1,4-naphthoquinone (synthetic); and anthraquinones, emodin (natural) and quinizarin (synthetic) were chosen, and their comparative effects on the survival and reproduction of collembolans, earthworms, enchytraeids and predatory mites were assessed. Differences in sensitivity between the species were observed with the predatory mite (Hypoaspis aculeifer) showing the least sensitivity. Within the chemical pairs, toxicity to lethal and sub-lethal endpoints was very similar for the four invertebrate species. The exception was earthworm reproduction, which showed differential sensitivity to the chemicals in both naphthoquinone and anthraquinone pairs. Differences in toxicity identified in the present study may be related to degree of exposure and/or subtle differences in the mode of toxic action for the chemicals and species tested. It may be possible to predict differences by identifying functional groups which infer increased or decreased toxicity in one or other chemical. The development of such techniques would enable the use of read-across from natural to synthetic chemicals for a wider group of compounds

Recovery of the Red Forest from a fire event

Severe and acute radiation from the Chernobyl accident killed coniferous trees in a 4-6 km2 area of forest, now known as the ‘Red Forest’. In July 2016, an accidental fire burnt c.80% of this area presenting a unique opportunity to study the effect of fire on radionuclide biogeochemistry and the impact of radiation on the recovery of forest ecosystems exposed to a secondary stressor (fire). The RED FIRE project built upon pre-fire baseline measurements collected by the TREE project and data from collaborating Ukrainian scientists; this gave us an opportunity to contrast pre- versus post-fire ecosystem states. The objectives of the project were to assess the impact of fire on radionuclide mobility in soil and determine if there was any impact of radiation on the recovery of the forest ecosystem. To achieve these objectives we used some approaches novel to radioecology: bait lamina sticks to measure soil biological activity; aerial drone vegetation and contamination mapping; wildlife camera traps and bioacoustic recorders. This poster concentrates on our studies of the recovery of vegetation and soil biological activity following the fire. In April 2016 (pre-fire), we deployed bait lamina sticks at 18 sites in the Chernobyl Exclusion Zone (11 in the Red Forest) to investigate soil biological activity across a range of ambient dose rates (13-220 μSvh-1). The bait lamina sticks are 10 cm long PVC strips with 16 small holes along their length; the holes are filled with bait (food); loss of bait provides a measure of soil biological activity. In September 2016, to assess ecosystem recovery post-fire, we deployed bait lamina at 20 sites in the Red Forest, including the 11 sites previously used in April 2016; they were re-deployed in spring and autumn 2017. A summary of the results from these studies are presented. In September 2016, at each of the 18 bait lamina sites, vegetation cover was recorded using photographs. Sites were marked so that subsequent vegetation recovery could be monitored using photographs and by an on-ground vegetation survey; species present at each plot were identified and the percentage cover was recorded in September 2017. In March 2017, aerial drone flights were also used to provide a photogrammetric analysis of vegetation cover; the area will be reflown in summer 2018. A summary of the results from these studies is also presented. Acknowledgements: RED FIRE (https://www.ceh.ac.uk/redfire) was funded under a NERC Urgency Grant (NE/P015212/1). Deployment of the camera traps was conducted as part of the TREE project (http://www.ceh.ac.uk/tree) which is co-funded by the Natural Environmental Research Council, Environment Agency and Radioactive Waste Management Ltd

Wildfires in the Chornobyl Exclusion Zone

Wildfires are an annual event in the Chornobyl Exclusion Zone (CEZ), with more than 1250 fires recorded between 1993 and 2014 in the Ukrainian CEZ. Severe and acute radiation from the Chornobyl accident killed most coniferous trees in an area of approximately 4-6 km2 to the west of the power plant. This area, now known as the 'Red Forest', subsequently partially regenerated with understory vegetation and deciduous trees. In July 2016, a fire burnt c.80% of the Red Forest presenting a unique opportunity to study the effect of fire on radionuclide biogeochemistry and the impact of radiation on the recovery of forest ecosystems exposed to a secondary stressor (fire). In early April 2020, fires started to burn in the Ukrainian CEZ and eventually spread over the subsequent month to become the largest wildfire in the 34-year history of the CEZ. The total area burnt has been estimated to be 870 km2 or about one-third of the land area of the Ukrainian CEZ. This presentation will discuss the results of our studies following both of these major fire events. In autumn 2016 we established 60 study plots in the Red Forest incorporating burnt and unburnt areas; control plots (n=9) were also established in a deciduous woodland approximately 4.5 km to the west of the Red Forest study area. Over the next year, we monitored changes in soil biological activity (using ‘bait lamina’ sticks); soil biological activity data for many of the plots were available from before the fire. Over the period September 2016 to September 2017 motion activated cameras (n=21) were established across the Red Forest to capture information on the presence of medium-large mammal species. Data from a preceding motion-activated camera study at sites across the Chornobyl Exclusion Zone (https://tree.ceh.ac.uk/content/exposure-uncertainty) are available for comparison to the Red Forest observations. To study small mammals, trapping grids were established at eight sites (including burnt and unburnt sites) in the Red Forest during summer 2018. Results (trapping success and number of species) from the Red Forest trapping study can be compared to historical data held by Chornobyl Center. There is the possibility that a fire in a contaminated area, such as the Red Forest, could change the bioavailability of radionuclides in the ecosystem. Samples of ash and soil were subjected to extractions to determine the likely contribution of ash to readily available pools of Sr-90 and Cs-137. There has previously been concern over likely inhalation doses to people as a consequence of fires in the Chornobyl Exclusion Zone. We will present dose estimates for the 2020 fires to firefighters and local population

Assessing soil biodiversity across Great Britain: national trends in the occurrence of heterotrophic bacteria and invertebrates in soil

An assessment of the biodiversity of soils was a component of the Countryside Survey 2000 (CS2000). This was the first integrated survey of soil biota and chemical properties at a national scale. A total of 1052 soil samples were collected across Great Britain during CS2000 and analysed for a range of soil microbial and invertebrate characteristics resulting in the production of a series of robust datasets. A principal objective was to use these datasets to investigate relationships between soil biota and environmental factors such as geographical location, vegetation, land use, land cover, soil type and pollutant levels as first stages in characterising the inherent biodiversity of British soils and investigating the potential of soil biodiversity as indicators of soil health at a regional or national scale. Preliminary results for culturable heterotrophic, invertebrate taxa, Acari, Collembola and Oribatid mites are presented here to illustrate the nature of the data collected and the patterns of soil biodiversity in relation to large-scale regional, vegetation and soil characteristics across the British countryside