36Cl is a naturally occurring radionuclide produced mainly in the atmosphere. In addition to its natural production, 36Cl has been introduced in significant quantities by humans into the environment because of nuclear bomb tests or nuclear accidents. Natural inputs, together with anthropogenic inputs, contribute to an ambient background activity of 36Cl in the environment. In addition to these inputs, other potential future inputs associated to civil nuclear activities (decommissioning of nuclear power plants, waste disposals) should be anticipated. A good understanding of sources of 36Cl in the environment, including an assessment of their variability, accumulation in soil, and fate in environmental media and at interfaces, is therefore necessary in the context of nuclear activities assessment. Considering this background, we propose here a review of knowledge relating to the sources, exchanges, accumulation, and fate of 36Cl in the environment. It addresses: (i) the identification and quantification of natural and anthropogenic sources and fallout of 36Cl in the environment, and the factors of spatial and temporal variability, including solar cycles and events, latitudinal geomagnetic effect, latitudinal differences in Stratosphere-Troposphere Exchange, distance from the sea, and local precipitation; (ii) the assessment of the exchange processes at the interface between atmosphere and soils, i.e. dry and wet deposition; (iii) the assessment of 36Cl accumulation, fate and speciation in soils and the factors of variability, in particular chlorination/dechlorination processes; (iv) the bioaccumulation processes of 36Cl in plants, i.e. root uptake, foliar absorption and translocation.
Microbial biofilms are increasingly recognised as chemically active interfaces that determine whether radionuclides remain dissolved, accumulate in sediments or enter secondary transport pathways. Their extracellular polymeric substances (EPS) supply diverse binding ligands, create steep microenvironmental gradients and retain redox-active cofactors, thereby coupling sorption to metabolic and mineral-mediated transformations. Yet these same properties complicate claims of durable immobilisation: adsorbed radionuclides may desorb, biomass-associated reduced species may be less persistent than crystalline minerals, and detachment can convert a local sink into a mobile carrier. This review critically examines the interaction of microbial biofilms with uranium, technetium, neptunium, plutonium, caesium, strontium and selected redox-sensitive co-contaminants in contaminated soils, groundwater and surface-water sediments. Particular attention is given to molecular EPS composition, coordination chemistry, extracellular electron transfer, U(IV) product identity, Fe–Mn–S coupling, phosphate mineralisation and redox reversal. Recent evidence from contaminated-aquifer biofilms, field bioaugmentation, flow-through reactors and molecular spectroscopy is assessed by distinguishing instantaneous removal, retained inventory, mineralogical persistence and cumulative contaminant export. A mechanistic risk framework is proposed in which long-term performance depends on the evolving relationship among biofilm physiology, aqueous ligands, oxidant fluxes, hydraulic connectivity and particle mobilisation. The central implication is that biofilm-enhanced sequestration should be judged by radionuclide mass balance and post-disturbance stability rather than by short-term decreases in dissolved concentration alone.
More than a decade after the 2011 Fukushima Daiichi Nuclear Power Plant accident, the internal redistribution of 137Cs within Japanese cedar (Cryptomeria japonica) wood remains an important unresolved question for timber safety and radiological forest management. This study provides the first post-2020, compartment-level, multi-height 137Cs dataset for Japanese cedar at the Yamakiya Experimental Forest (Kawamata Town, Fukushima Prefecture; ∼1000 – 3000 kBq m−2 deposition). In 2024, wood cores were extracted at tree-base (∼0.4 m), breast height (1.3 m), and upper-trunk (10 m) from three model trees using a 12-mm increment borer, divided into the three youngest sapwood annual rings (SW1-3) and consequent 5 annual rings samples of bulk sapwood (SW) and heartwood (HW), and measured for 137Cs activity by a high-purity Ge-detector. A water-leaching fractionation protocol (distilled water, 20:1 water-to-fresh-mass ratio, 24 h orbital shaking) was applied to each sample to resolve 137Cs into a leachable fraction and a residual matrix-bound fraction. The heartwood-to-sapwood (HW/SW) 137Cs concentration ratio averaged approximately 2.0 across the three trees by 2024 confirming continued heartwood enrichment beyond the system-level quasi-equilibrium reached around 2020. Vertical 137Cs distributions were broadly uniform across all three sampling heights, contrasting with the height-dependent gradients of the early post-accident period. The leachable fraction was dominant in both sapwood and heartwood, with total concentrations strongly correlated with leached (R2 = 0.4–0.9) but not matrix-bound concentrations, indicating that 137Cs in cedar wood is predominantly present in a hydrated, water-soluble ionic form. Proportion of the leached 137Cs activity averaged 0.57 ± 0.15 for sapwood and 0.51 ± 0.14 for heartwood. The study significantly contributes to understanding of 137Cs distribution and cycling in Japanese cedar.
Uranium, thorium, plutonium and americium are determined in soil, sediment, water and air for radiation protection and source attribution, but the change in measurement techniques since Chernobyl has not been quantified. This review combines a critical synthesis of method papers with a bibliometric data set of 32,181 OpenAlex records (1986–2026; 3254 naming a technique), analysed by trend tests, correspondence analysis, principal component analysis and Ward clustering and cross-checked in IAEA INIS, to test three hypotheses. H1, that mass spectrometry has replaced decay counting, was only partly supported: the share of analytical records naming inductively coupled plasma mass spectrometry (ICP-MS) rose from 19% in 1990–99 to 41% in 2016–25 (Mann–Kendall τ = +0.43, p < 0.001) and thermal ionisation mass spectrometry, neutron activation and fission track declined, but alpha spectrometry fell only from 21% to 15%, gamma spectrometry stayed near 29%, and the two families have shared mentions roughly equally since 2011. H2, that technique use is organised by the analytical problem, was supported: the only bootstrap-stable cluster grouped alpha spectrometry with sector-field ICP-MS and accelerator mass spectrometry (AMS) as a transuranic ultra-trace group, and correspondence analysis separated transuranic from natural-series methods (47.9% of inertia). H3, that the transition is not an artefact of one index, was supported (Spearman ρ = 0.83 between OpenAlex and INIS). Detection limits for 239Pu range from 10 fg (alpha spectrometry) to 0.2 fg (AMS). Priorities are comparable detection-limit reporting, wider access to AMS and ICP-MS/MS, and monitoring of 241Am ingrowth until the mid-2030s.
