Leaves of higher plants as biomonitors of radionuclides (137Cs, 40K, 210Pb and 7Be) in urban air

Emerging paradigms into bioremediation approaches for nuclear contaminant removal: From challenge to solution

The release of radionuclides, including Cesium-137 (137Cs), Strontium-90 (90Sr), Uranium-238 (238U), Plutonium-239 (239Pu), Iodine-131 (131I), etc., from nuclear contamination presents profound threats to both the environment and human health. Traditional remediation methods, reliant on physical and chemical interventions, often prove economically burdensome and logistically unfeasible for large-scale restoration efforts. In response to these challenges, bioremediation has emerged as a remarkably efficient, environmentally sustainable, and cost-effective solution. This innovative approach harnesses the power of microorganisms, plants, and biological agents to transmute radioactive materials into less hazardous forms. For instance, consider the remarkable capability demonstrated by Fontinalis antipyretica, a water moss, which can accumulate uranium at levels as high as 4979 mg/kg, significantly exceeding concentrations found in the surrounding water. This review takes an extensive dive into the world of bioremediation for nuclear contaminant removal, exploring sources of radionuclides, the ingenious resistance mechanisms employed by plants against these harmful elements, and the fascinating dynamics of biological adsorption efficiency. It also addresses limitations and challenges, emphasizing the need for further research and implementation to expedite restoration and mitigate nuclear pollution's adverse effects.

A strategy for bioremediation of nuclear contaminants in the environment

Radionuclides released from nuclear contamination harm the environment and human health. Nuclear pollution spread over large areas and the costs associated with decontamination is high. Traditional remediation methods include both chemical and physical, however, these are expensive and unsuitable for large-scale restoration. Bioremediation is the use of plants or microorganisms to remove pollutants from the environment having a lower cost and can be upscaled to eliminate contamination from soil, water and air. It is a cheap, efficient, ecologically, and friendly restoration technology. Here we review the sources of radionuclides, bioremediation methods, mechanisms of plant resistance to radionuclides and the effects on the efficiency of biological adsorption. Uptake of radionuclides by plants can be facilitated by the addition of appropriate chemical accelerators and agronomic management, such as citric acid and intercropping. Future research should accelerate the use of genetic engineering and breeding techniques to screen high-enrichment plants. In addition, field experiments should be carried out to ensure that this technology can be applied to the remediation of nuclear contaminated sites as soon as possible.

Radioactivity of soil in Croatia I: naturally occurring decay chains

The assessment of environmental radioactivity much relies on radionuclide content in soil. This stems from the significant contribution of soil to both external and internal exposure to ionising radiation via direct emission of gamma radiation and soil-to-plant radionuclide transfer, respectively. This motivated us to carry out a systematic research on the radioactivity of soil in Croatia to obtain relevant data that can be used as a basis for understanding the related effects of geomorphological, biogeographical, and climatological properties of the environment. We collected samples of the surface layer of uncultivated soil (0–10 cm) at 138 sites from all over the country and measured them for radionuclide activity concentrations by means of high-resolution gamma-ray spectrometry. This resulted in radioactivity maps containing data on activity concentrations of representative radionuclides in the environment. In this paper, which is the first in our two-part presentation, we focus on the naturally occurring ²³²Th and ²³⁸U decay chains and their correlations with the diversity of Croatian regions. For both of the chains, activity concentrations were the highest in the Dinaric region, the lowest in the Pannonian region, and intermediate in the Adriatic region. Relatively high concentrations of ²²⁶Ra in the soil of the Dinaric region implied a possibility of an enhanced emanation of its progeny ²²²Rn into the air. Activity concentrations of ²¹⁰Pb were additionally elevated in areas with dense vegetation, most probably due to an atmospheric deposition of airborne ²¹⁰Pb onto the surface of plants and their eventual decomposition on the ground.

Using deciduous trees as bioindicators of trace element deposition in a small urban watershed, Indianapolis, IN, USA

Annual and multiyear records of trace element deposition are difficult to develop using monitoring systems but have proven feasible using plant material in several settings. Here, we used material from several tree species (Populus deltoides W. Bartram ex Marshall, Platanus occidentalis L., and Ginkgo biloba L.) to detect atmospheric deposition of trace elements (Cd, Cu, Pb, and Zn) in six localities along a transect from near-urban to far-urban in southeastern Indianapolis, IN, and one control site. We captured soil (legacy footprint), bark (multiannual record), and leaves (seasonal record) across a broad swath of the urban landscape and using a multi-metal approach. Tree bark, leaf, and proximal soil samples were collected and analyzed for their trace element content. The highest trace metal concentrations occurred at the near-urban sites, with particularly high Cu and Pb values. The highest Zn values were found at one of the far-urban sites, which is located near a large brownfield that was a former coal and coke storage and processing facility. No correlation was found between soil trace element composition and that of bark and leaves, perhaps indicating a disconnect between legacy inputs recorded in soils and current inputs recorded in the biological materials. Overall, the tree species analyzed served well as trace element bioindicators, although less so for G. biloba, and thus this approach is promising for further understanding the role that airborne pollution and deposition play in urban watersheds.

Distribution of natural and artificial radionuclides in chernozem soil/crop system from stationary experiments

The present paper focuses on the determination of radiological characteristics of cultivated chernozem soil and crops from long-term field experiments, taking into account the importance of distribution and transfer of radionuclides in the soil-plant system, especially in agricultural cropland. The investigation was performed on the experimental fields where maize, winter wheat, and rapeseed were cultivated. Analysis of radioactivity included determination of the gross alpha and beta activity as a screening method, as well as the activities of the following radionuclides: natural ((210)Pb, (235)U, (238)U, (226)Ra, (232)Th, (40)K, (7)Be) and artificial ((90)Sr and (137)Cs). The activities of natural and artificial ((137)Cs) radionuclides were determined by gamma spectrometry, while the artificial radionuclide (90)Sr was determined by a radiochemical analytical method. Based on the obtained results for the specific activity of (40)K, (137)Cs, and (90)Sr, accumulation factors for these radionuclides were calculated in order to estimate transfer of radionuclides from soil to crops. The results of performed analyses showed that there is no increase of radioactivity that could endanger the food production through the grown crops.

Natural and anthropogenic radioactivity in the environment of Kopaonik mountain, Serbia

To evaluate the state of the environment in Kopaonik, a mountain in Serbia, the activity concentrations of (4) K, (226)Ra, (232)Th and (137)Cs in five different types of environmental samples are determined by gamma ray spectrometry, and radiological hazard due to terrestrial radionuclides is calculated. The mean activity concentrations of natural radionuclides in the soil are higher than the global average. However, with an exception of two sampling locations, the external radiation hazard index is below one, implying an insignificant radiation hazard. Apart from (40)K, content of the natural radionuclides is predominantly below minimum detectable activities in grass and cow milk, but not in mosses. Although (137)Cs is present in the soil, grass, mosses and herbal plants, its specific activity in cow milk is below minimum detectable activity. Amongst the investigated herbal plants, Vaccinium myrtillus L. shows accumulating properties, as a high content of (137)Cs is detected therein. Therefore, moderation is advised in consuming Vaccinium myrtillus L. tea.

Dietary items as possible sources of (137)Cs in large carnivores in the Gorski Kotar forest ecosystem, Western Croatia

The mountain forest ecosystem of Gorski Kotar is distant from any significant sources of environmental pollution, though recent findings have revealed that this region is among the most intense (137)Cs contaminated area in Croatia. Therefore, the aim of this study was to investigate (137)Cs and (40)K load in three large predator species in the mountain forest ecosystem. Radionuclides mass activities were determined by the gamma-spectrometric method in the muscle tissue of brown bear (47), wolf (7), lynx (1) and golden jackal (2). The highest (137)Cs mass activity was found in lynx (153 Bq kg(-1)), followed by brown bear (132 Bq kg(-1)), wolf (22.2 Bq kg(-1)), and golden jackal (2.48 Bq kg(-1)). Analysis of 63 samples of dietary items suggests that they are not all potentially dominant sources of (137)Cs for wildlife. The most important source of radionuclides for the higher parts of the food-chain from the study area were found to be the mushroom species wood hedgehog (Hydnum repandum), with a transfer factor TF of 5.166, and blueberry (Vaccinium myrtillus) as a plant species (TF=2.096). Food items of animal origin indicated higher mass activity of radionuclides and therefore are possible moderate bioindicators of environmental pollution. The results also revealed that possible unknown wild animal food sources are a caesium source in the study region, and further study is required to illuminate this issue.

Radionuclides in some edible and medicinal macrofungal species from Tara Mountain, Serbia

Edible and medicinal macrofungi used in human diet represent not only important sources of nutritive elements but toxic substances as well (heavy metals and radionuclides). Radioactivity levels of four radionuclides ((40)K, (137)Cs, (226)Ra, (228)Ra) were determined in the basidiomata (fruiting bodies of a Basidiomycetes) of six lignicolous (Fomitopsis pinicola, Ganoderma applanatum, Hericium clathroides, Megacollybia platyphylla, Pluteus cervinus, Trametes gibbosa) and three mycorrhizal (Boletus luridus, Boletus sp. 1, Boletus sp. 2) species as well as their soil (wood) substrates by gamma spectrometry (high-resolution high-purity germanium (HPGe) detector). The aim was to investigate their ability for radionuclide absorption according to transfer factors (from soil and wood), to predict potential bioindicator species as well as species with potential risk for human use. Samples were taken during years 2011 and 2012, at two sites in forest ecosystem of Tara Mountain (Serbia). Observed concentration ranges per dry weight were as follows: 29-3,020 Bq/kg ((40)K), 21.9-735 Bq/kg ((137)Cs), 3-39 Bq/kg ((226)Ra), and 2.0-18 Bq/kg ((228)Ra). Obtained results indicate that the type of basidiome (fleshy/tough), most likely due to a different metabolic rate, has a very important role in radionuclide accumulation. The highest activity concentrations of all analyzed radionuclides were found in species with fleshy basidiomata--P. cervinus, H. clathroides, M. platyphylla, and Boletus species. A species-specific influence on radionuclide uptake was more prominent comparing to habitat differences and the role of fungal trophic mode. No significant variations were observed regarding radionuclide activity among the same fungal species from different sampling sites.