The IUR Forum: Worldwide Harmonisation of Networks to Support Integration of Scientific Knowledge and Consensus Development in Radioecology.

During the past decades, many specialised networks have formed to meet specific radioecological objectives, whether regional or sectorial (purpose-oriented). Regional networks deal with an array of radioecological issues related to their territories. Examples include the South Pacific network of radioecologists, and the European network of excellence in radioecology. The latter is now part of the European platform for radiation protection. Sectorial networks are more problem-oriented, often with wider international representativeness, but restricted to one specific issue, (e.g. radioactive waste, low-level atmospheric contamination, modelling). All such networks, while often working in relative isolation, contribute to a flow of scientific information which, through United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR's) efforts of synthesis, feeds into the radiation protection frameworks of protecting humans and the environment. The IUR has therefore prompted a co-construction process aimed at improving worldwide harmonisation of radioecology networks. An initiative based on an initial set of 15 networks, now called the IUR FORUM, was launched in June 2014. The IUR Forum agreed to build a framework for improved coordination of scientific knowledge, integration and consensus development relative to environmental radioactivity. Three objectives have been collectively assigned to the IUR FORUM: (1) coordination, (2) global integration and construction of consensus and (3) maintenance of expertise. One particular achievement of the FORUM was an improved description and common understanding of the respective roles and functions of the various networks within the overall scene of radioecology R&D. It clarifies how the various networks assembled within the IUR FORUM interface with UNSCEAR and other international regulatory bodies (IAEA, ICRP), and how consensus on the assessment of risk is constructed. All these agencies interact with regional networks covering different geographical areas, and with other networks which address specific topics within radiation protection. After holding its first Consensus Symposium in 2015, examining the possible ecological impact of radiation from environmental contamination, the IUR FORUM continues its work towards improved radiation protection of humans and the environment. We welcome new members.

DNA damage caused by chronic transgenerational exposure to low dose gamma radiation in Medaka fish ( Oryzias latipes ).

The effect of transgenerational exposure to low dose rate (2.4 and 21 mGy/day) gamma irradiation on the yield of DNA double-strand breaks and oxidized guanine (8-hydroxyguanine) has been studied in the muscle and liver tissue of a model organism, the Japanese medaka fish. We found the level of unrepaired 8-hydroxyguanine in muscle tissue increased nonlinearly over four generations and the pattern of this change depended on the radiation dose rate, suggesting that our treatment protocols initiated genomic instability and an adaptive response as the generations progressed. The yield of unrepaired double-strand breaks did not vary significantly among successive generations in muscle tissue in contrast to liver tissue in which it varied in a nonlinear manner. The 8-hydroxyguanine and DSB radiation yields were significantly higher at 2.4 mGy/day than at 21 mGy/day in both muscle and liver tissue in all generations. These data are consistent with the hypothesis of a threshold for radiation-induced activation of DNA repair systems below which tissue levels of DNA repair enzymes remain unchanged, leading to the accumulation of unrepaired damage at very low doses and dose rates.

Are radiosensitivity data derived from natural field conditions consistent with data from controlled exposures? A case study of Chernobyl wildlife chronically exposed to low dose rates.

The discrepancy between laboratory or controlled conditions ecotoxicity tests and field data on wildlife chronically exposed to ionising radiation is presented for the first time. We reviewed the available chronic radiotoxicity data acquired in contaminated fields and used a statistical methodology to support the comparison with knowledge on inter-species variation of sensitivity to controlled external γ irradiation. We focus on the Chernobyl Exclusion Zone and effects data on terrestrial wildlife reported in the literature corresponding to chronic dose rate exposure situations (from background ~100 nGy/h up to ~10 mGy/h). When needed, we reconstructed the dose rate to organisms and obtained consistent unbiased data sets necessary to establish the dose rate-effect relationship for a number of different species and endpoints. Then, we compared the range of variation of radiosensitivity of species from the Chernobyl-Exclusion Zone with the statistical distribution established for terrestrial species chronically exposed to purely gamma external irradiation (or chronic Species radioSensitivity Distribution - SSD). We found that the best estimate of the median value (HDR50) of the distribution established for field conditions at Chernobyl (about 100 µGy/h) was eight times lower than the one from controlled experiments (about 850 µGy/h), suggesting that organisms in their natural environmental were more sensitive to radiation. This first comparison highlights the lack of mechanistic understanding and the potential confusion coming from sampling strategies in the field. To confirm the apparent higher sensitive of wildlife in the Chernobyl Exclusion Zone, we call for more a robust strategy in field, with adequate design to deal with confounding factors.

An invitation to contribute to a strategic research agenda in radioecology.

With intentions of integrating a portion of their respective research efforts into a trans-national programme that will enhance radioecology, eight European organisations recently formed the European Radioecology ALLIANCE (www.er-alliance.org). The ALLIANCE is an Association open to other organisations throughout the world with similar interests in promoting radioecology. The ALLIANCE members recognised that their shared radioecological research could be enhanced by efficiently pooling resources among its partner organizations and prioritising group efforts along common themes of mutual interest. A major step in this prioritisation process was to develop a Strategic Research Agenda (SRA). An EC-funded Network of Excellence in Radioecology, called STAR (Strategy for Allied Radioecology), was formed, in part, to develop the SRA. This document is the first published draft of the SRA. The SRA outlines a suggested prioritisation of research topics in radioecology, with the goal of improving research efficiency and more rapidly advancing the science. It responds to the question: "What topics, if critically addressed over the next 20 years, would significantly advance radioecology?" The three Scientific Challenges presented within the SRA, with their 15 associated research lines, are a strategic vision of what radioecology can achieve in the future. Meeting these challenges will require a directed effort and collaboration with many organisations the world over. Addressing these challenges is important to the advancement of radioecology and in providing scientific knowledge to decision makers. Although the development of the draft SRA has largely been a European effort, the hope is that it will initiate an open dialogue within the international radioecology community and its stakeholders. This is an abbreviated document with the intention of introducing the SRA and inviting contributions from interested stakeholders. Critique and input for improving the SRA are welcomed via a link on the STAR website (www.star-radioecology.org).

Investigating the embryo/larval toxic and genotoxic effects of γ irradiation on zebrafish eggs.

Eggs/larval of freshwater fish (Danio rerio) were exposed to low dose rates of external gamma radiation (from 1 to 1000 mGy d(-1)) over a 20-day period, with the objective of testing the appropriateness of the 10 mGy d(-1) guideline suggested by the IAEA. The present study examines different endpoints, mortality and hatching time and success of embryos as well as the genotoxicity of γ-irradiations (after 48 h). The 20-day embryo-larval bioassay showed an enhanced larval resistance to starvation after chronic exposure to γ irradiation (from low 1 mGy d(-1) to high dose rate 1000 mGy d(-1)) and an acceleration in hatching time. Gamma irradiation led to increased genotoxic damage Ito zebrafish egg (40-50% DNA in tail in Comet assay) from the lowest dose rate (1 mGy d(-1)). Possible mechanisms of γ radiotoxicity and implications for radioprotection are discussed.

Cesium accumulation by aquatic organisms at different trophic levels following an experimental release into a small reservoir.

The rates of accumulation and subsequent loss of stable cesium (¹³³Cs) by organisms at different trophic levels within plankton-based and periphyton-based food chains were measured following the addition of ¹³³Cs into a small reservoir near Aiken, South Carolina, USA. An uptake parameter u (L kg⁻¹ d⁻¹ dry mass) and a loss rate parameter k (d⁻¹) were estimated for each organism using time-series measurements of ¹³³Cs concentrations in water and biota, and these parameters were used to estimate maximum concentrations, times to maximum concentrations, and concentration ratios (C(r)). The maximum ¹³³Cs concentrations for plankton, periphyton, the insect larva Chaoborus punctipennis, which feeds on plankton, and the snail Helisoma trivolvis, which feeds on periphyton, occurred within the first 14 days following the addition, whereas the maximum concentrations for the fish species Lepomis macrochirus and Micropterus salmoides occurred after 170 days. The C(r) based on dry mass for plankton and C. punctipennis were 1220 L kg⁻¹ and 5570 L kg⁻¹, respectively, and were less than the C(r) of 8630 L kg⁻¹ for periphyton and 47,700 L kg⁻¹ for H. trivolvis. Although the C(r) differed between plankton-based and periphyton-based food chains, they displayed similar levels of biomagnification. Biomagnification was also indicated for fish where the C(r) for the mostly nonpiscivorous L. macrochirus of 22,600 L kg⁻¹ was three times less than that for mostly piscivorous M. salmoides of 71,500 L kg⁻¹. Although the C(r) for M. salmoides was greater than those for periphyton and H. trivolvis, the maximum ¹³³Cs concentrations for periphyton and H. trivolvis were greater than that for M. salmoides.

Contrasting cesium dynamics in neighboring deep and shallow warm-water reservoirs.

To measure the long term retention and seasonal dynamics of an initial 4 kg addition of (133)Cs into an 11.4-ha, 157,000 m(3) reservoir (Pond 4, near Aiken, South Carolina, USA), the concentrations and inventories of (133)Cs in the water column were measured at periodical intervals for 522 days following the 1 August, 1999 release. After rapid declines in concentrations and inventories during the first 90 days, the (133)Cs concentrations in the water column declined at an average proportional rate of 0.004 d(-1). However, there were periods of less rapid and more rapid rates of declines, and these were correlated with periods of increasing and decreasing K concentrations in the water column. The decline rates were less and the K concentrations greater in the winter than in the summer. In the deeper, neighboring monomictic reservoirs of Par Pond and Pond B, a yearly cycle of increasing and decreasing (137)Cs concentrations in the water column is driven by anoxic remobilization of Cs from the sediments into a persistent summer hypolimnion. In Pond 4, whose mean depth of 1.6 m is too shallow to support a persistent anoxic hypolimnion, the pattern of yearly dynamics for K and Cs appear to be related to the accumulation and release of these elements from the extensive, seasonal macrophyte communities. The contrasting results between Pond 4 and Pond B suggest that a full appreciation of the relative importance of 1) anoxic remobilization and 2) accumulation and release by macrophytes in these systems remains to be established.

Communication of radiation-induced signals in vivo between DNA repair deficient and proficient medaka (Oryzias latipes).

Radiation-induced bystander effects are established consequences of exposure to ionizing radiation. The operation of this mechanism has been seen in vitro and also between fish, mammals, and plants in vive where stress signals from treated organisms induce responses in neighbors. In vitro research shows that DNA repair deficient cells produce more toxic bystander responses. To test this in vivo two strains of Japanese medaka were tested. One is a mutant, repair deficient strain (ric2) and the other, the wildtype repair proficient strain (CAB). Irradiated fish swam with unirradiated partners in a strain mix and match protocol. The data suggest that medaka produce signals, when exposed to radiation, that induce unirradiated fish ofthe same strain swimming with them to produce an altered response to that seen in bystanders to sham irradiated fish. More apoptosis was seen in bystanders to repair deficient fish. When the strains are mixed, the bystanders of either strain respond like the donor strain. Measurements of Bcl-2 and cmyc proteins in the explants confirmed these observations. A possible role for p53 was also identified in that the use of reporters with mutant p53 demonstrated that CAB signals killed all the reporter cells by apoptosis. Use of a similar but p53 wildtype cell line had no such effect. The data add to the body of knowledge showing that bystander signals operate at hierarchical levels of organization greater than the individual and may therefore have relevance in radioecology and (eco)systems biology.

Cesium accumulation by fish following acute input to lakes: a comparison of experimental and Chernobyl-impacted systems.

An uptake parameter u (Lkg(-1)d(-1)) and a loss rate parameter k (d(-1)) were estimated for the patterns of accumulation and loss of (133)Cs by three fish species following an experimental (133)Cs addition into a pond in South Carolina, USA. These u and k parameters were compared to similar estimates for fish from other experimental ponds and from lakes that received (137)Cs deposition from Chernobyl. Estimates of u from ponds and lakes declined with increasing potassium concentrations in the water column. Although loss rates were greater in the experimental ponds, the times required to reach maximum Cs concentrations in fish were similar between ponds and lakes, because ponds and lakes had similar retentions of Cs in the water column. The maximum Cs concentrations in fish were largely determined by initial Cs concentrations in the water column. These maximum concentrations in fish and the times required to reach these maxima are potentially useful indicators for assessments of risks to humans from fish consumption.

Radiation-induced untargeted germline mutations in Japanese medaka.

Radiation has been shown to increase mutation frequencies at tandem repeat loci by indirect interactions of radiation with DNA. We studied germline mutations in chronically exposed Japanese medaka (Oryzias latipes) using microsatellite loci. After screening 26 randomly selected loci among unirradiated parents and their 200 offspring, we selected seven highly mutable loci (0.5-1.0 x 10(-2) mutants per locus per gamete) and two bonus loci for further study. To determine if radiation exposure increases mutation frequencies in these loci, medaka were chronically irradiated from subadults through maturation at relatively low dose rates of 68 mGy/d. Total doses for males and females were 10.4 and 3 Gy, respectively. The mean number of mutations for the offspring of exposed families (0.149+/-0.044) was significantly higher (P=0.018) than for control families (0.080+/-0.028), indicating induction of germline mutations from chronic irradiation. This increase in the microsatellite mutation rate is greater than expected from direct interaction of radiation with DNA, suggesting indirect, untargeted mechanism(s) for mutations. This study identified microsatellite loci with a high mutational background in medaka, variation among loci and families as important variables, and demonstrated the usefulness of this fish model for studying radiation-induced germline mutations.

Foliar uptake of cesium from the water column by aquatic macrophytes.

The probable occurrence and rate of foliar absorption of stable cesium (133Cs) from the water column by aquatic macrophyte species was analyzed following the addition of 133Cs into a small reservoir near Aiken, South Carolina, USA. An uptake parameter u (10(3)Lkg(-1)d(-1)) and a loss rate parameter k (d(-1)) were estimated for each species using time series of 133Cs concentrations in the water and plant tissues. Foliar uptake, as indicated by rapid increases in plant concentrations following the 133Cs addition, occurred in two floating-leaf species, Brasenia schreberi and Nymphaea odorata, and two submerged species, Myriophyllum spicatum and Utricularia inflata. These species had values of u> or =0.75 x 10(3)Lkg(-1)d(-1). Less evidence for foliar uptake was observed in three emergent species, including Typha latifolia. Ratios of u to k for B. schreberi, M. spicatum, N. odorata and U. inflata can be used to estimate concentration ratios (CR) at equilibrium, and these estimates were generally within a factor of 2 of the CR for 137Cs for these species in the same reservoir. This correspondence suggests that foliar uptake of Cs was the principal absorption mechanism for these species. Assessments of: (1) the prevalence of foliar uptake of potassium, rubidium and Cs isotopes by aquatic macrophytes and (2) the possible importance of foliar uptake of Cs in other lentic systems are made from a review of foliar uptake studies and estimation of comparable u and k values from lake studies involving Cs releases.

The influence of a whole-lake addition of stable cesium on the remobilization of aged 137Cs in a contaminated reservoir.

To document the short-term dynamics of Cs, 4 kg of (133)Cs were introduced into an 11.4-ha, 157 000 m(3) reservoir previously contaminated with (137)Cs from past reactor operations at the US Department of Energy's Savannah River Site near Aiken, South Carolina, USA. The (133)Cs addition resulted in an increase of 6.1 MBq of (137)Cs (1.9 mug (137)Cs) in the water column over the following 260 days. Possible sources for the increased (137)Cs included (1) release from the sediments, (2) release from the approximately 26 000 kg of aquatic macrophytes that occupied 80% of the reservoir, and (3) wash-in from the pond's watershed. Data are presented to indicate that release from the sediments was the principal source of the (137)Cs increase. The fraction of (137)Cs released from the sediments (0.7%) is consistent with laboratory measurements of (137)Cs desorption from neighboring ponds on the Savannah River Site.

The maximally exposed individual--comparison of maximum likelihood estimation of high quantiles to an extreme value estimate.

The dose to human and nonhuman individuals inflicted by anthropogenic radiation is an important issue in international and domestic policy. The current paradigm for nonhuman populations asserts that if the dose to the maximally exposed individuals in a population is below a certain criterion (e.g., <10 mGy d(-1)) then the population is adequately protected. Currently, there is no consensus in the regulatory community as to the best statistical approach. Statistics, currently considered, include the maximum likelihood estimator for the 95th percentile of the sample mean and the sample maximum. Recently, the investigators have proposed the use of the maximum likelihood estimate of a very high quantile as an estimate of dose to the maximally exposed individual. In this study, we compare all of the above-mentioned statistics to an estimate based on extreme value theory. To determine and compare the bias and variance of these statistics, we use Monte Carlo simulation techniques, in a procedure similar to a parametric bootstrap. Our results show that a statistic based on extreme value theory has the least bias of those considered here, but requires reliable estimates of the population size. We recommend establishing the criterion based on what would be considered acceptable if only a small percentage of the population exceeded the limit, and hence recommend using the maximum likelihood estimator of a high quantile in the case that reliable estimates of the population size are not available.

Effects of radiation on the environment: a need to question old paradigms and enhance collaboration among radiation biologists and radiation ecologists.

A historical perspective is given of the current paradigm that does not explicitly protect nonhuman biota from radiation but instead relies on the concept that if dose limits are set to protect humans, then the environment is automatically protected as well. We summarize recent international questioning of this paradigm and briefly present three frameworks for protecting biota that are being considered by the U.S. Department of Energy, the Canadian Nuclear Safety Commission, and the International Commission on Radiological Protection. We point out a controversial component in each of the three frameworks and suggest topics that need additional research. We emphasize that to properly address radiation protection of the environment, we need to understand how effects are integrated across different levels of biological organization. We caution that the proposed use of molecular end points to estimate ecological risks from radioactive contamination is applicable only if we understand the extent of the impact that molecular damage has on individual organisms and populations of exposed biota. To accomplish the latter, enhanced collaborations are required among the traditionally separate disciplines of radiation biology and radiation ecology.

Low Dose Rate Irradiation Facility: initial study on chronic exposures to medaka.

Uncertainties associated with the effects from chronic low-level exposures to radiation prompted us to construct a Low Dose Rate Irradiation Facility (LoDIF). The facility was designed specifically to test the appropriateness of the 10 mGy d(-1) guideline often espoused as acceptable for protection of aquatic biota from ionizing radiation. Scientists at the 0.4 ha facility use 40 outdoor mesocosms and 137Cs irradiators of three different source strengths to research the effects of chronic low-level irradiation at different levels of biological organization. A description of the facility is included along with results from a pilot study in which Japanese medaka (a small fish native to Asia) were chronically irradiated at the highest dose rate possible within the facility (350+/-150 mGy d(-1)). Irradiated fish produced fewer eggs per day (p=0.03); had a lower percentage of viable eggs (p=0.04), and produced a lower percentage of hatchlings (p=0.05). Although these data are not surprising based on the relatively high dose rates, they are important to future work at the LoDIF because they confirm the utility of our chosen model organism for detecting population-level responses, and they illustrate the statistical power achieved from using replicated mesocosms, in that statistical significance was achieved with few replicates per treatment. Future directions for the LoDIF are presented, as well as an invitation for interested researchers to participate in our studies.

Reduction of crop contamination by soil resuspension within the 30-km zone of the Chernobyl nuclear power plant.

A field experiment was conducted within the 30-km zone of the Chernobyl Nuclear Power Plant to analyze whether the application of mulching reduced resuspension of 137Cs contaminated soil in oat (Avena sativa) crops. In 1993, we applied a mulch treatment at a dose of 200 g m(-2), and soil resuspension was measured by estimating soil loadings onto plant surfaces from Ti concentrations in plants. In 1994, two mulch doses were applied, 200 and 50 g m(-2), and we estimated the contribution of soil resuspension by using artificial resuspension collection devices (ARC). In the 1993 experiment between 4.6 and 34.4% of the plant's total 137Cs contamination was attributed to external soil contamination. The mean amount of soil-derived 137Cs attached to vegetation was 124.7 Bq kg(-1)(plant) in control plots and 53.7 Bq kg(-1)(plant) in mulched plots. In the 1994 experiment, covering the soil with a mulch layer decreased the radiocesium content in ARC by about 70%. Results obtained in these experiments suggest that soil resuspension was a significant mechanism for plant contamination and that mulching was effective in reducing that contamination.

Comparative bias associated with various estimates of dose to maximally exposed individuals.

Protection of the environment from anthropogenic radiation is a resurging international interest. The paradigm currently in use argues that the population is adequately protected if dose rates to the maximally exposed individuals are below a certain limit. Based on data sampled from natural populations, resource managers need to be able to test the hypothesis that dose rates to the maximally exposed individuals are acceptable. Recognizing the difficulty of sampling the maximally exposed individual within a contaminated environment, risk assessors have used various alternative approaches that vary from changing the paradigm and applying recommended dose rate limits to representatively, rather than maximally, exposed individuals, to using the 95th percentile of the sample mean as an estimator of the population maximum. To determine the effectiveness of numerous proposed alternatives, we used computer simulation techniques to generate a "population" of doses with known distributional qualities and then mathematically "sampled" the population to compare the ability of the various statistics at estimating the known population maximum. The simulation procedure was repeated 1000 times using Monte Carlo techniques, each time producing a measure of the distance between the estimate and the true value. We were thus able to quantify the bias associated with several approaches used to determine compliance with dose rate criteria established by the Department of Energy for protecting biota. The 95th quantile of the sample mean, and the sample maximum underestimated the population maximum by as much as 72 and 44%, respectively. The maximum likelihood estimate (MLE) of the 99.99th percentile was found to be the best predictor of the population maximum, even for small sample sizes of 20 and for both normally and lognormally distributed populations. However, bias associated with the MLE increased significantly if the population's distribution was incorrectly identified. We suggest shifting the regulatory criterion appropriately to argue that if the top 1% (as opposed to the maximum) of the population has a dose rate less than or equal to the regulatory limit then the population is adequately protected, and then using the MLE of the 99th percentile as the least biased sample statistic. Results of this study are also relevant when estimating dose to critical sub-groups of humans whose lifestyles are such that their doses are among the maximum for the population.

Apatite and phillipsite as sequestering agents for metals and radionuclides.

Laboratory and greenhouse studies were conducted to quantify apatite and phillipsite (zeolite) sequestration of selected metal contaminants. The laboratory batch study measured the sorption of aqueous Co2+, Ba2+, Pb2+, Eu3+, and UO2(2+). Apatite sorbed more Co2+, Pb2+, Eu3+, and UO2(2+) from the spike solution than phillipsite, resulting in distribution coefficients (Kd values) of >200,000 L kg(-1). Phillipsite was more effective than apatite at sorbing aqueous Ba2+. Results from the laboratory study were used to design the greenhouse study that used a soil affected by a Zn-Pb smelter from Pribram, Czech Republic. Two application rates (25 and 50 g kg(-1)) of phillipsite and apatite and two plant species, maize (Zea mays L.) and oat (Avena sativa L.), were evaluated in this study. There was little (maize) to no (oat) plant growth in the unamended contaminated soil. Apatite and, to a slightly lesser extent, phillipsite additions significantly enhanced plant growth and reduced Cd, Pb, and Zn concentrations in all analyzed tissues (grain, leaves, and roots). The sequestering agents also affected some essential elements (Ca, Fe, and Mg). Phillipsite reduced Fe and apatite reduced P and Fe concentrations in oat tissues; however, the level of these elements in oat leaves and grains remained sufficient. Sequential extractions of the soil indicated that the Cd, Pb, and Zn were much more strongly sorbed onto the amended soil, making the contaminants less phytoavailable.