Evaluation of the potential for caesium transfer from contaminated soil to the food chain as a consequence of uptake by edible vegetables

Steep declines in radioactive caesium after 30 years of monitoring alpine plants in mountain areas of central Norway

The Chernobyl accident exposed large areas of northern Europe to radiocaesium (137Cs). We investigated temporal and spatial variation in concentrations of radiocaesium among five functional groups of alpine plants at two mountain areas in central Norway over a 31-year period from 1991 to 2022. Average concentrations of radiocaesium were initially high in lichens and bryophytes at around 4600-6400 Bq/kg dry weight during 1991-1994 but then decreased dramatically over three decades to current concentrations of <200 Bq/kg for all plant groups in 2019-2022. The effective half-life of radiocaesium was estimated to be 4-6 years in lichens and mosses, 7-13 years in herbaceous plants, and 22-30 years in woody plants, which were less than the physical half-life of 30.2 years. Concentrations of radiocaesium were greater at the nutrient-poor site than at the nutrient-rich site, probably due to greater deposition levels at higher elevations and the geographical pattern of the deposition. Functional groups of plants differed with higher concentrations among non-vascular than vascular plants. Common heather Calluna vulgaris was unusual among woody plants with high concentration of radiocaesium, especially in the new shoots. Our new estimates of concentrations and dynamics of radiocaesium for alpine plants in natural environments will be useful for modelling herbivore exposure and evaluating potential impacts on wildlife and human health.

Radioactivity evaluation and radiation dosimetry assessment in Greek honey

Greek honey was examined for ²³⁸U, ²³⁴U, ²¹⁰Pb, ²¹⁰Po, ⁴⁰K, and ¹³⁷Cs levels. ²³⁸U was calculated from 0.013 ± 0.007 Bq kg^-1 to 0.10 ± 0.02 Bq kg^-1 while ²³⁴U ranged from 0.017 ± 0.009 Bq kg^-1 to 0.11 ± 0.03 Bq kg^-1. ²¹⁰Pb measured from 0.04 ± 0.02 Bq kg^-1 to 1.70 ± 0.26 Bq kg^-1 whereas ²¹⁰Po activity determined between 0.02 ± 0.01 Bq kg^-1 and 2.31 ± 0.34 Bq kg^-1. ⁴⁰ K found at the range of 7.9 ± 1.6 Bq kg^-1 to 102.2 ± 19.7 Bq kg^-1 and ¹³⁷Cs 0.3 ± 0.1 Bq kg^-1 up to 0.8 ± 0.1 Bq kg^-1. Uranium isotopes and ²¹⁰Po were determined via alpha spectrometry. ²¹⁰Pb was also indirectly determined by alpha spectrometry. ⁴⁰ K and ¹³⁷Cs were measured through γ-ray spectrometry. An annual dose calculation was performed for different age groups.

Mass balance of metals during the phytoremediation process using Noccaea caerulescens: a pot study

There are two widely used methods to estimate the time taken for phytoremediation for the removal of the target pollutants, i.e., using the data of metal uptake by the harvested parts of the selected plant or using the decrement in average element content between the beginning and end of the remediation. The latter not only depends on sampling points but is also determined by sampling time because even if the soil is initially perfectly homogenized, plant growth itself heterogenizes the soil as time goes by. In this study, phytoremediation was tested on one homogenized soil obtained from various soil samples taken within an e-waste dismantling and recycling site, and the remediation time for different points of bulk and rhizosphere soil was estimated using the two methods. Phytoremediation efficiency, as assessed by the change in soil metal concentrations over 100 days, widely varied depending on which of the six soil compartments of the pot was sampled, and the standard deviations of Cd, Zn, Pb, and Cu increased as the experiment proceeded, indicating the inaccuracy of this method. When applied to rhizosphere soil, this method led to a large overestimation of phytoremediation efficiency for Cd and Zn, which was 81- and 77-fold that was obtained by measuring the actual amount of metals taken up by Noccaea caerulescens. The significant difference between the two methods indicated that the blended soil became heterogeneous during the phytoremediation process because the species extracted metals from different soil parts, manifested by the variation in the metal content. The gap between these two estimation methods decreased when the soil was mixed thoroughly at the end of the experiment. This work shows that calculating the metal decontamination efficiency based on the measurement of the actual amount of metal taken by the plant is more robust than estimating it based on the evolution of soil metal concentration over time. In addition, our study reveals that using N. caerulescens may not be appropriate in Pb- or Cu-polluted soil, since this species mobilized these metals but did not extract them.

Biometric traits of onion (Allium cepa L.) exposed to 137Cs and 243Am under hydroponic cultivation

To elucidate the features of bioaccumulation and phytotoxic effects of long-lived artificial radionuclides, a hydroponic experiment was carried out with the cultivation of onion (Allium cepa L.) in low-mineralized solutions spiked with ¹³⁷Cs (250 kBq L^-1) or ²⁴³Am (9 kBq L^-1). After the 27-day growth period, ≈70% of ¹³⁷Cs and ≈14% of ²⁴³Am were transferred from the solutions to onion biomass with transfer factor values ≈ 400 and ≈ 80, respectively. Since the bioaccumulation of both radionuclides mainly took place in the roots of onion (77% ¹³⁷Cs and 93% ²⁴³Am of the total amount in biomass), edible organs - bulbs and leaves - were protected to some extent from radioactive contamination. At the same time, the incorporation of the radionuclides into the root tissues caused certain changes in their biometric (geometric and mass) traits, which were more pronounced under the ²⁴³Am-treatment of onion. Exposure to ²⁴³Am significantly reduced the number, length, and total surface area of onion roots by 1.3-2.6 times. Under the influence of ¹³⁷Cs, the dry-matter content in roots decreased by 1.3 times with a corresponding increase in the degree of hydration of the root tissues. On the whole, the data obtained revealed the specific features of ¹³⁷Cs and ²⁴³Am behaviour in "hydroponic solution - plant" system and suggested that biometric traits of onion roots could be appropriate indicators of phyto(radio)toxicity.

Morpho-Physiological and Metal Accumulation Responses of Hemp Plants (Cannabis Sativa L.) Grown on Soil from an Agro-Industrial Contaminated Area

Hemp is a promising plant for phytomanagement. The possibility to couple soil restoration to industrial crop cultivation makes this plant attractive for the management of contaminated sites. In this trial, Cannabis sativa L. plants were grown in a greenhouse on soils from two sites of “Valle del Sacco” (Lazio Region, Italy), a wide area contaminated by agro-industrial activities. One site was representative of moderate and diffuse metal(loid) multi-contamination, above the Italian concentration limit for agriculture (MC—moderately contaminated). The second site showed a metal(loid) content below the aforementioned limit, as a typical background level of the district (C—control). After 90 days, biometric and physiological parameters revealed satisfactory growth in both soil types. MC-grown plants showed a slight, but significant reduction in leaf area, root, and leaf biomass compared with C-grown plants. Chlorophyll content and chlorophyll fluorescence parameters, namely the quantum yield of primary photochemistry (Fv/Fm) and the Performance Index (PIABS), confirmed the good physiological status of plants in both soils. Metal(loid) analyses revealed that As, V, and Pb accumulated only in the roots with significant differences in MC- and C-grown plants, while Zn was found in all organs. Overall, preliminary results showed a satisfactorily growth coupled with the restriction of toxic metal translocation in MC-grown hemp plants, opening perspectives for the phytomanagement of moderately contaminated areas.