Ján Mihalík

Particle size distribution of radioactive aerosols after the Fukushima and the Chernobyl accidents.

Following the Fukushima accident, a series of aerosol samples were taken between 24th March and 13th April 2011 by cascade impactors in the Czech Republic to obtain the size distribution of (131)I, (134)Cs, (137)Cs, and (7)Be aerosols. All distributions could be considered monomodal. The arithmetic means of the activity median aerodynamic diameters (AMADs) for artificial radionuclides and for (7)Be were 0.43 and 0.41 μm with GDSs 3.6 and 3.0, respectively. The time course of the AMADs of (134)Cs, (137)Cs and (7)Be in the sampled period showed a slight decrease at a significance level of 0.05, whereas the AMAD pertaining to (131)I increased at a significance level of 0.1. Results obtained after the Fukushima accident were compared with results obtained after the Chernobyl accident. The radionuclides released during the Chernobyl accident for which we determined the AMAD fell into two categories: refractory radionuclides ((140)Ba, (140)La (141)Ce, (144)Ce, (95)Zr and (95)Nb) and volatile radionuclides ((134)Cs, (137)Cs, (103)Ru, (106)Ru, (131)I, and (132)Te). The AMAD of the refractory radionuclides was approximately 3 times higher than the AMAD of the volatile radionuclides; nevertheless, the size distributions for volatile radionuclides having a mean AMAD value of 0.51 μm were very close to the distributions after the Fukushima accident.

Fractionation of 137Cs and Pu in natural peatland

High Cs-137 concentrations in plants growing on peatland inspired us to investigate the quantity of its bioavailable fraction in natural peat. Our investigation aims to: a) estimate the quantity of bioavailable Cs-137 and Pu present in peat, b) verify the similarity of Cs-137 and K-40 behaviours, and c) perform a quantification of Cs-137 and Pu transfer from peat to plants. We analysed the vertical distribution of Cs-137 and Pu isotopes in the peat and their concentrations in plants growing on these places. Bioavailability of radionuclides was investigated by sequential extraction. Sequential analyses revealed that it was the upper layer which contained the majority of Cs-137 in an available form while deeper layers retained Cs-137 in immobile fractions. We can conclude that 18% of all Cs-137 in the peat is still bioavailable. Despite of the low quantity of bioavailable fraction of Cs-137 its transfer factor reached extremely high values. In the case of Pu, 64% of its total amount was associated with fulvic/humic acids which resulted in the high transfer factor from peat to plants. 27 years after the Chernobyl nuclear accident, the significant part of radionuclides deposited in peatland is still bioavailable.

Release of 137 Cs from plant mass in course of biodegradation

AbstractThis investigation was focused on the role of humic acid-like compounds during the biodegradation of plant mass contaminated with 137Cs. The experiments were set up to distinguish cases of external and internal contamination. The results showed that 137Cs was associated with humic acid-like compounds in eluates from biomass and especially with their lighter fraction. The 137Cs in detritus was markedly mobile and only minor amounts were retained in biomass. These two variants differed in the rate of 137Cs release: while in the internally contaminated biomass the rate decreased during composting, in the externally contaminated biomass the rate increased.

Redistribution of Cs 137 introduced into montmorillonite in association with organic matter coming from biomass composting

The adsorption and later bioavailability of 137Cs from the system humic acid (HA)/humic acid like compounds (HALC) and montmorillonite was investigated. The setup of the experiments should approach as much as possible natural conditions when 137Cs is introduced into soil with HALC from decomposed biomass. The significant differences were found in the trials containing various HA/HALC and also pure montmorillonite. The 137Cs was more available when it reached soil in association with HALC originated from compost than when it was adsorbed on stable humic acids. Moreover, the long term interaction of 137Cs with HALC led to decrease of 137Cs adsorbed on montmorillonite and increase of its bioavailable fraction. UV-Vis spectrometry and infrared spectroscopy showed the clear difference between HA, fresh HALC and old HALC which could partially explain the different results.

Natural Radionuclides, Rare Earths and Heavy Metals Transferred to the Wild Vegetation Covering a Phosphogypsum Stockpile at Barreiro, Portugal

In Portugal, the industrial production of phosphate fertilizers, has been dealing with a specific raw material—north African phosphate rock—with a high content of trace metals and natural radioactive elements mainly from the 238U decay series. A disabled phosphate plant located in the vicinity of the river Tejo estuary has produced phosphoric acid for several decades (1950–1989) and dumped tons of phosphogypsum (PG) on retention lagoons, formerly decanted and deposited into a stockpile. This paper deals with the assessment of radionuclides, rare earth elements (REEs) and heavy metals transfer to plants (fam. Plantaginaceae, Plantago sp.) and mosses (fam. Bryaceae, Bryum sp.) growing naturally on the PG pile. In Plantago sp., the concentration ratio (CR, plant tissue/PG) was 0.187 for 226Ra and 0.293 for 210Pb. The translocation factor (TF, aerial parts/roots) was 0.781 for 226Ra and 0.361 for 210Pb. In contradiction to the high CR, the leachability of 226Ra from PG was low, lower than 2%. The results confirmed the role of mosses as biomonitors. A high quantity of contaminants collected in its biomass confirmed the hypothesis of their significant transport by air and rain water. High concentrations of heavy metals (As, Cd, Zn, W) in samples collected on the stockpile are an evidence of their transport from former industrial zones in the surroundings and present even more important risk for public health and environment than natural radionuclides and REEs from the PG stockpile.