What makes radiation protection so challenging?

This commentary explores the challenges in radiation safety that derives from the inherent complexity of social-ecological systems. The framework needed to address the challenges acknowledges the characteristics of wicked problems in this era of postnormal science. My objective for this piece is to summarize relevant characteristics of social-ecological systems that underscore the importance, even the necessity, of adopting a holistic approach to radiation safety. This work builds on several publications that have come out of the ecosystems approach working group of the International Union of Radioecology. The nature of wicked problems is that they require meaningful engagement among diverse groups of affected stakeholders so that negotiated consensus regarding assessment and management for radiation safety can be achieved. I conclude by stating that this approach is complementary to the reference animal and plant approach, that it is consistent with the views for postnormal science, and it conforms with the United Nations Sustainable Development Goals (SDGS) that were adopted in 2015.

From tangled banks to toxic bunnies; a reflection on the issues involved in developing an ecosystem approach for environmental radiation protection.

The objective of this paper is to present the results of discussions at a workshop held as part of the International Congress of Radiation Research (Environmental Health stream) in Manchester UK, 2019. The main objective of the workshop was to provide a platform for radioecologists to engage with radiobiologists to address major questions around developing an Ecosystem approach in radioecology and radiation protection of the environment. The aim was to establish a critical framework to guide research that would permit integration of a pan-ecosystem approach into radiation protection guidelines and regulation for the environment. The conclusions were that the interaction between radioecologists and radiobiologists is useful in particular in addressing field versus laboratory issues where there are issues and challenges in designing good field experiments and a need to cross validate field data against laboratory data and vice versa. Other main conclusions were that there is a need to appreciate wider issues in ecology to design good approaches for an ecosystems approach in radioecology and that with the capture of 'Big Data', novel tools such as machine learning can now be applied to help with the complex issues involved in developing an ecosystem approach.

Dose assessment in environmental radiological protection: State of the art and perspectives.

Exposure to radiation is a potential hazard to humans and the environment. The Fukushima accident reminded the world of the importance of a reliable risk management system that incorporates the dose received from radiation exposures. The dose to humans from exposure to radiation can be quantified using a well-defined system; its environmental equivalent, however, is still in a developmental state. Additionally, the results of several papers published over the last decade have been criticized because of poor dosimetry. Therefore, a workshop on environmental dosimetry was organized by the STAR (Strategy for Allied Radioecology) Network of Excellence to review the state of the art in environmental dosimetry and prioritize areas of methodological and guidance development. Herein, we report the key findings from that international workshop, summarise parameters that affect the dose animals and plants receive when exposed to radiation, and identify further research needs. Current dosimetry practices for determining environmental protection are based on simple screening dose assessments using knowledge of fundamental radiation physics, source-target geometry relationships, the influence of organism shape and size, and knowledge of how radionuclide distributions in the body and in the soil profile alter dose. In screening model calculations that estimate whole-body dose to biota the shapes of organisms are simply represented as ellipsoids, while recently developed complex voxel phantom models allow organ-specific dose estimates. We identified several research and guidance development priorities for dosimetry. For external exposures, the uncertainty in dose estimates due to spatially heterogeneous distributions of radionuclide contamination is currently being evaluated. Guidance is needed on the level of dosimetry that is required when screening benchmarks are exceeded and how to report exposure in dose-effect studies, including quantification of uncertainties. Further research is needed to establish whether and how dosimetry should account for differences in tissue physiology, organism life stages, seasonal variability (in ecology, physiology and radiation field), species life span, and the proportion of a population that is actually exposed. We contend that, although major advances have recently been made in environmental radiation protection, substantive improvements are required to reduce uncertainties and increase the reliability of environmental dosimetry.

Coordinating ecological restoration options analysis and risk assessment to improve environmental outcomes.

Ecological risk assessment as currently practiced has hindered consideration of ecosystem services endpoints and restoration goals in the environmental management process. Practitioners have created barriers between procedures to clean up contaminated areas and efforts to restore ecosystem functions. In this article, we examine linkages between contaminant risk assessment approaches and restoration efforts with the aim of identifying ways to improve environmental outcomes. We advocate that project managers and other stakeholders use an ecological planning framework, with restoration options included upfront in the risk assessment. We also considered the opportunities to incorporate ecosystem services as potential assessment endpoints in the Problem Formulation stages of a risk assessment. Indeed, diverse perspectives of stakeholders are central to understand the relevance of social, cultural, economic, and regional ecology as influences on future use options for the landscape being restored. The measurement endpoints used to characterize the existing ecological conditions for selected ecosystem services can also be used to evaluate restoration success. A regional, landscape, or seascape focus is needed throughout the risk assessment process, so that restoration efforts play a more prominent role in enhancing ecosystem services. In short, we suggest that practitioners begin with the question of "how can the ecological risk assessment inform the decision on how best to restore the ecosystem?"

Plant toxicity testing to derive ecological soil screening levels for cobalt and nickel.

Phytotoxicity tests were performed to set ecological soil screening levels for cobalt (Co) and nickel (Ni) following the American Society for Testing and Materials international E1963-98 Standard Guide for Conducting Terrestrial Plant Toxicity Tests. Two soils (a modified artificial soil mixed with 5% organic matter, pH 5.01, and a native riverine sandy soil with 0.1% organic matter, pH 6.3) were treated with cobalt(II) chloride or nickel chloride and allowed to age for four weeks before initiating tests. Alfalfa, barley, radish, perennial rye, and brassica were used to determine the appropriate range of concentrations and to select the most sensitive plant species for definitive tests. The tests were designed to have one to three test concentrations below the 20% effects concentration (EC20), and five to six test concentrations above the EC20. Definitive tests for each chemical used two soil matrices, three plant species, and replicates at 10 nominal concentrations, including negative control. Soil chemical concentrations were determined before planting and on completion of the phytotoxicity tests. Threshold responses interpreted as the EC20 for each species endpoint were calculated from regression analyses. The geometric mean of the EC20 values (excluding emergence, mortality, and nodule numbers) for each species resulted in values of 30.6 mg/kg for Co and 27.9 mg/kg for Ni.

BIOLOGICAL NITROGEN INFLUX IN AN OHIO RELICT PRAIRIE.

The principal contributors of biologically fixed N in natural grassland ecosystems appear to be asymbiotic bacteria and heterocystous cyanobacteria. The environmental factors of light, moisture, and temperature play important roles in the magnitude of the N2 -fixation activity. Biological N2 -fixation was measured in the Elizabeth's Prairie section of the Lynx Prairie Preserve, Adams County, Ohio, during 15 site visits beginning 29 March through 8 November 1980. In situ N2 -fixation activity was measured using the acetylene-reduction technique. The percentage cover of cyanobacterial colonies (Nostoc sp.) was determined using Point-Frame Analysis. Soil and air temperatures and soil water potentials also were measured. Intact soil cores with a surface cover of Nostoc were collected and returned to the laboratory to quantify the effect of decreasing water potential on the N2 (C2 H2 )ase activity of Nostoc. The N2 (C2 H2 )ase activity of Nostoc on the intact soil cores displayed a linear response of approximately 10% decrease in N2 (C2 H2 )ase activity per one bar decrease in soil water potential. The cyanobacteria contributed almost all of the biologically fixed N at the site until late June. From late June through to mid September, heterotrophic diazotrophs played the major role in the N2 -fixation activity. These changes are attributed to fluctuations in Nostoc sp. colony cover, temperature, and soil water potentials. Extrapolation of the measured rates, and assuming an average of 10 hr per day of activity, Nostoc sp. is shown to have contributed 4.60 ± 1.17 kg N ha-1 yr-1 . Heterotrophic diazotrophs contributed an estimated 3.19 ± 1.18 kg N ha-1 yr-1 . The total biological N2 -fixation for the site was calculated at 8.2 ± 2.55 kg N ha-1 yr-1 , from additional measurements which estimated total diazotrophic activity of the site. These rates of N2 -fixation are among the highest reported for temperate grassland habitats.

N2 (C2 H2 )ASE ACTIVITY BY ALNUS INCANA SSP. RUGOSA (BETULACEAE) IN THE NORTHERN HARDWOOD FOREST.

Field assays of N2 (C2 H2 )ase activity were performed with intact nodules from a pure alder site (alder) and a mixed alder-aspen site (aspen). Assays were performed between 12 June and 12 August 1980 and in May 1981. N2 (C2 H2 )ase rates are expressed as g N g nodule oven-dry wt-1 hr-1 (g N g-1 hr-1 ). Diurnal N2 (C2 H2 )ase activity showed an increase in both sites between 0600 and midday, then decreased to a low by 1800. Nighttime activity in the May 1981 assay was approximately 25% of the daytime peak. Mean (±SE) 1200 hr N2 (C2 H2 )ase activity (µg N g-1 hr-1 ) for all sizes in the alder stand rose from 24.56 ± 6.56 on 12 June to 73.96 ± 28.37 on 26 June and declined to 9.20 ± 2.56 by 12 August. In the aspen stand activity decreased from the 12 June rate of 21.81 ± 4.59 to 3.64 ± 1.87 on 24 July but then increased to 30.00 ± 7.39 by 12 August. Based on diurnal assays, the seasonal mean N influx (µg N g-1 hr-1 ) is statistically higher (P 0.05) in the alder stand with a value of 26.70 compared to 14.63 in the aspen stand. Small size class shrubs had significantly higher (P < 0.05) N2 (C2 H2 )ase activity (µg N g-1 hr-1 ) in diurnal assays than medium or large class shrubs. The estimated mean (±SE) N2 (C2 H2 )ase activity (mg N g-1 season-1 ) for all sizes was 44.4 ± 18.6 in the alder stand compared to 16.2 ± 5.2 in the aspen stand. Nodule excavations showed the g shrub-1 in the alder stand to be 16.48 ± 10.29, 38.57 ± 12.34 and 29.11 ± 7.15 for small, medium and large size shrubs and 12.73 ± 3.23, 28.21 ± 4.36 and 56.45 ± 16.23 for respective sizes in the aspen stand. Seasonal N influx was 4.69 kg ha-1 in the alder stand and 0.84 kg ha-1 in the aspen stand, representing 17.9% of the alder stand. Nitrogen feedback inhibition from uric acid-N influx and allelochemic interference from aspen are discussed as explanations for the differences in N influx in the two stands.