Canopy-forming kelps as California's coastal dosimeter: 131I from damaged Japanese reactor measured in Macrocystis pyrifera

Microplastics as vectors of radioiodine in the marine environment: A study on sorption and interaction mechanism

Radioiodine is one of the long-lived fission products and also an important radionuclide released during nuclear accidents, which generates interest in its environmental fate. Its sorption has been studied in a wide range of materials, but no equivalent study exists for microplastics, an emerging environmental vector. Weathering and biofilm formation on microplastics can enhance radioiodine sorption. For the first time, we're reporting how radioiodine interacts with different types of polyethylene derived microplastics (pristine, irradiated, and biofilm developed microplastics). This study revealed that exposure to radiation and the marine environment significantly alters the physico-chemical properties of microplastics. In particular, in marine-exposed samples, a signature of biofilm development was detected. Speciation study indicates that iodine exists in the iodide form in the studied marine environment. The study revealed that, iodide ions attach to biofilm-developed microplastics via electrostatic, ion-dipole, pore filling, and van der Waals interactions. Pore filling, ion-dipole, and van der Waals interactions may cause iodide binding to irradiated microplastics, whereas pore-filling and van der Waals interactions cause iodide binding to pristine microplastics. The distribution coefficient (K_d) of iodine on microplastics is positively correlated with biofilm biomass, which signifies the role of biofilm in radioiodine uptake. The K_d indicates microplastics are potential iodide accumulators and could be a possible vector in the marine system.

Using medically-derived iodine-131 to track sewage effluent in the Laurentian Great Lakes

Tracking sewage wastewater in a large lake is difficult. Concentrations of pharmaceuticals that can be used as indicator compounds are quickly diluted and not easy to measure. In this study, we examined the potential of using medically-derived iodine-131 (¹³¹I, t_½ = 8.02 d) as a tracer for Milwaukee sewage effluent in Lake Michigan. ¹³¹I activities in sewage effluent from two Milwaukee wastewater treatment plants (WWTPs) were measured in conjunction with ¹³¹I activities in water, sediment and biota in the Milwaukee Outer Harbor and Lake Michigan. ¹³¹I discharge rates from both WWTPS ranged from 34 ± 15 to 1807 ± 24 MBq d^-1, with average and median ¹³¹I discharges of 278 and 129 MBq d^-1. A budget of ¹³¹I in the Milwaukee Outer Harbor - based on measured sediment and water column inventories - showed that ∼11% of the ¹³¹I discharged to the harbor was scavenged to bottom sediments, ∼19% decayed in the harbor water column, and ∼70% was flushed out of the harbor to Lake Michigan. From this budget, we derived a harbor flushing rate of 3.1 days. In Lake Michigan, ¹³¹I activity was found in Cladophora algae (undetected to 91 ± 2 Bq kg^-1) along ∼40 km of shoreline. Benthic trawl samples showed ¹³¹I activity up to 8 km from shore. Calculated ¹³¹I length scales were 30 km alongshore and 3.4 km offshore and corresponded to sewage effluent dispersion rates of ∼2.6 km d^-1 and ∼0.3 km d^-1 in along- and offshore directions. Using ¹³¹I as a tracer of sewage effluent from other coastal municipalities to the Laurentian Great Lakes appears feasible, particularly for larger (>10⁵) population centers.

Japanese Food Data Challenge the Claimed Link between Fukushima's Releases and Recently Observed Thyroid Cancer Increase in Japan

Internal, high-dose exposure with radioiodine is known to increase the risk for thyroid cancer in children and adolescents. Ingestion of contaminated food is generally regarded a dominant route of internal exposure. We analyzed the huge data set of the post-Fukushima food monitoring campaign and deployed a conservative model for the estimation of the doses to the general public in a worst-case scenario. Our data suggest that the committed equivalent ingestion doses to the thyroids of the affected Japanese public, even in the utmost conservative approach, remained below the limit on ingestion of radioiodine in foodstuffs and beverages of 50 mSv (as thyroid equivalent dose). This level of 50 mSv is also the intervention level for the administration of stable iodine, mainly after inhalation. Our study hence suggests that, based on the food data, the internal exposure of Japanese residents was too low to cause a statistically discernible increase in thyroid cancer, even if the contribution from inhalation is taken into account. The data also indicate that the governmental efforts in the food monitoring campaign were successful and cut the thyroid doses to the public by a factor of approximately 3 compared to a scenario without any monitoring.

Assessing Fukushima-Derived Radiocesium in Migratory Pacific Predators

The 2011 release of Fukushima-derived radionuclides into the Pacific Ocean made migratory sharks, teleosts, and marine mammals a source of speculation and anxiety regarding radiocesium (^134+137Cs) contamination, despite a lack of actual radiocesium measurements for these taxa. We measured radiocesium in a diverse suite of large predators from the North Pacific Ocean and report no detectable (i.e., ≥ 0.1 Bq kg^-1 dry wt) Fukushima-derived ¹³⁴Cs in all samples, except in one olive ridley sea turtle (Lepidochelys olivacea) with trace levels (0.1 Bq kg^-1). Levels of ¹³⁷Cs varied within and across taxa, but were generally consistent with pre-Fukushima levels and were lower than naturally occurring ⁴⁰K by one to one to two orders of magnitude. Predator size had a weaker effect on ¹³⁷Cs and ⁴⁰K levels than tissue lipid content. Predator stable isotope values (δ¹³C and δ¹⁵N) were used to infer recent migration patterns, and showed that predators in the central, eastern, and western Pacific should not be assumed to accumulate detectable levels of radiocesium a priori. Nondetection of ¹³⁴Cs and low levels of ¹³⁷Cs in diverse marine megafauna far from Fukushima confirms negligible increases in radiocesium, with levels comparable to those prior to the release from Fukushima. Reported levels can inform recently developed models of cesium transport and bioaccumulation in marine species.

The potential role of kelp forests on iodine speciation in coastal seawater

Kelps have a major role in marine and atmospheric iodine cycling in the coastal zone of temperate regions, with potential wide-ranging impacts on ozone destruction in the coastal marine boundary layer. However, little is known about the impact of kelp forests on iodine speciation in coastal sea water. To address this, we examined iodide and iodate concentrations in seawater in and around a giant kelp forest near San Diego, CA, USA, and a nearby site that was not influenced by kelp biology. Our data shows that while both iodide and iodate concentrations remained unchanged during the year at the nearby site, these concentrations changed significantly in and around the kelp forest, and were strongly related to changes in kelp canopy biomass. In particular, iodide reached its highest concentration and iodate reached its lowest concentration during the summer when the kelp canopies were near their maximum, while the opposite pattern was observed during the winter and spring when the kelp canopies were near their minimum. Further, comparisons of these changes with corresponding changes in seawater temperature and wind speed indicated that these relationships were relatively small compared to those with changes in kelp biomass. Together, our data show a strong relationship between kelp biomass and iodine metabolism.

Environmental radionuclide monitoring of Canadian harbours: a decade of analyses in support of due diligence activities by the Royal Canadian Navy

The Royal Canadian Navy has conducted a comprehensive programme of safety, security and environmental monitoring since the first visits of nuclear powered and nuclear capable vessels (NPV/NCVs) to Canadian harbours in the late 1960s. The outcomes of baseline monitoring and vessel visit sampling for the period 2003-2012 are described for vessel visits to Halifax (NS), Esquimalt (BC) and Nanoose (BC). Data were obtained by gamma-ray spectroscopy using high purity germanium detectors. No evidence was found for the release of radioactive fission or activation products by NCV/NPVs during the study period, although anthropogenically produced radionuclides were observed as part of the study's baseline monitoring. Background activities of Cs-137 can be observed in sediments from all three locations which are derived from well-documented radioactivity releases. The detection of I-131 in aquatic plants is consistently observed in Halifax at activities as high as 15,000 Bq kg(-1) dry weight. These data are tentatively assigned to the release of medical I-131, followed by bioaccumulation from seawater. I-131 was also observed in aquatic plants samples from Esquimalt (33 Bq kg(-1)) and Nanoose (20 Bq kg(-1)) for a single sampling following the Fukushima Daiichi accident.

Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts

The environmental impacts of the nuclear accidents of Chernobyl and Fukushima are compared. In almost every respect, the consequences of the Chernobyl accident clearly exceeded those of the Fukushima accident. In both accidents, most of the radioactivity released was due to volatile radionuclides (noble gases, iodine, cesium, tellurium). However, the amount of refractory elements (including actinides) emitted in the course of the Chernobyl accident was approximately four orders of magnitude higher than during the Fukushima accident. For Chernobyl, a total release of 5,300 PBq (excluding noble gases) has been established as the most cited source term. For Fukushima, we estimated a total source term of 520 (340-800) PBq. In the course of the Fukushima accident, the majority of the radionuclides (more than 80%) was transported offshore and deposited in the Pacific Ocean. Monitoring campaigns after both accidents reveal that the environmental impact of the Chernobyl accident was much greater than of the Fukushima accident. Both the highly contaminated areas and the evacuated areas are smaller around Fukushima and the projected health effects in Japan are significantly lower than after the Chernobyl accident. This is mainly due to the fact that food safety campaigns and evacuations worked quickly and efficiently after the Fukushima accident. In contrast to Chernobyl, no fatalities due to acute radiation effects occurred in Fukushima.

Influence of radioactivity on surface charging and aggregation kinetics of particles in the atmosphere

Radioactivity can influence surface interactions, but its effects on particle aggregation kinetics have not been included in transport modeling of radioactive particles. In this research, experimental and theoretical studies have been performed to investigate the influence of radioactivity on surface charging and aggregation kinetics of radioactive particles in the atmosphere. Radioactivity-induced charging mechanisms have been investigated at the microscopic level, and heterogeneous surface potential caused by radioactivity is reported. The radioactivity-induced surface charging is highly influenced by several parameters, such as rate and type of radioactive decay. A population balance model, including interparticle forces, has been employed to study the effects of radioactivity on particle aggregation kinetics in air. It has been found that radioactivity can hinder aggregation of particles because of similar surface charging caused by the decay process. Experimental and theoretical studies provide useful insights into the understanding of transport characteristics of radioactive particles emitted from severe nuclear events, such as the recent accident of Fukushima or deliberate explosions of radiological devices.

Iodine-129 in seawater offshore Fukushima: distribution, inorganic speciation, sources, and budget

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of (129)I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated (129)I concentrations in surface water were observed with the highest (129)I/(127)I atomic ratio of 2.2 × 10(-9) in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of (129)I, while stable (127)I was mainly in iodate form, reflecting the fact that the major source of (129)I is the direct liquid discharges from the Fukushima NPP. The amount of (129)I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of (129)I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of (129)I from the Fukushima accident was estimated. These Fukushima-derived (129)I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future.

Concentration of strontium-90 at selected hot spots in Japan

This study is dedicated to the environmental monitoring of radionuclides released in the course of the Fukushima nuclear accident. The activity concentrations of β⁻ -emitting ⁹⁰Sr and β⁻/γ-emitting ¹³⁴Cs and ¹³⁷Cs from several hot spots in Japan were determined in soil and vegetation samples. The ⁹⁰Sr contamination levels of the samples were relatively low and did not exceed the Bq⋅g⁻¹ range. They were up four orders of magnitude lower than the respective ¹³⁷Cs levels. This study, therefore, experimentally confirms previous predictions indicating a low release of ⁹⁰Sr from the Fukushima reactors, due to its low volatility. The radiocesium contamination could be clearly attributed to the Fukushima nuclear accident via its activity ratio fingerprint (¹³⁴Cs/¹³⁷Cs). Although the correlation between ⁹⁰Sr and ¹³⁷Cs is relatively weak, the data set suggests an intrinsic coexistence of both radionuclides in the contaminations caused by the Fukushima nuclear accident. This observation is of great importance not only for remediation campaigns but also for the current food monitoring campaigns, which currently rely on the assumption that the activity concentrations of β⁻-emitting ⁹⁰Sr (which is relatively laborious to determine) is not higher than 10% of the level of γ-emitting ¹³⁷Cs (which can be measured quickly). This assumption could be confirmed for the samples investigated herein.

Using animal thyroids as ultra-sensitive biomonitors for environmental radioiodine

In the course of the Fukushima nuclear accident large amounts of radionuclides relevant to the Comprehensive Nuclear-Test-Ban-Treaty (CTBT) were released and detected globally. We could show that the intake of environmental (131)I into the thyroids of animals can be used for verification of the CTBT. Due to continuous accumulation of (131)I, its apparent half-life in the thyroid biomonitor exceeds the physical one, thus making (131)I detectable three weeks longer than using conventional CTBT-grade high volume air samplers. The maximum (131)I activity concentrations (in Bq/kg) found in Austrian animal thyroids after the Fukushima nuclear accident could be correlated with the maximum activity concentrations found in air (Bq/m(3)) in Austria via a factor of 1.1 × 10(6). In fall 2011, a second (much smaller) release of (131)I occurred from a laboratory in Hungary, where this factor was 1.9 × 10(6). Hence thyroid biomonitors offer even some quantitative information, which allows the estimation of the (131)I activity concentrations in air. It could be shown that thyroid biomonitors can work under dry conditions, which potentially makes them the method of choice for CTBTO on-site inspections even in arid environments.