Simulated experimental investigation of microplastic weathering in marine environment.

Microplastics act as a potential vector for a wide range of contaminants, which have emerged as a major environmental hazard in the modern world. Considering the seriousness of the problem, a simulated laboratory and field experiment were conducted to study the weathering of pristine microplastics following long-term exposure to natural background radiation and the marine environment after being disposed of in the open environment. For the study, polyethylene-originating (HDPE and LDPE) microplastics were chosen. The study revealed that radiation exposure causes surface roughness and cracks, leading to an increased surface area, which can invite a wide spectrum of pollutants to sorb on their surface. Furthermore, we report that the radiation-induced morphological changes favor microbial colonization on the microplastic surface when exposed to the marine environment. The growth of biofilms on the surface of microplastics reduces their hydrophobicity, which may attract a wide variety of polar contaminants. The study led to an interesting finding: that the HDPE microplastic surface is more conducive for biofilm growth in comparison to the LDPE surface.

Removal of uranium(VI) from water using hydroxyapatite coated activated carbon powder nanocomposite.

Synthesis of hydroxyapatite coated activated carbon nanocomposite was carried out by in-situ chemical precipitation method. Different characterizations confirm that, hydroxyapatite successfully coated over activated carbon powder. Extensive sorption studies of U(VI) on the nanocomposite were conducted to know the effect of contact time, humic acid, carbonate, ionic strength and pH. The study revealed that, the composite material is a more efficient sorbent for U(VI) compared to precursors, which removes U(VI) ion without altering physicochemical properties of water. Sorption exhibits multilayer adsorption on heterogeneous surface and follows chemisorptions. Practical applicability of the material was demonsteted by spiking tap water with U(VI) ion at three different initial concentrations (50, 100 and 150 µg L-1) and the tap water was allowed to passed through a cartridge packed with composite. It was observed that, the concentration of U(VI) ion in eluted water reduced to 98.28%, 96.20% and 97.40%, respectively. This revealed that, the material possesses a huge potential for sequestrating dissolved U(VI) ion and can be used as alternate filtering material for dissolved U(VI) in complex natural water system.

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 (Kd) of iodine on microplastics is positively correlated with biofilm biomass, which signifies the role of biofilm in radioiodine uptake. The Kd indicates microplastics are potential iodide accumulators and could be a possible vector in the marine system.

Transfer of radionuclides from soil to selected tropical plants of Indian Subcontinent: A review.

Soil to plant transfer factor (TF) of radionuclides is an important input parameter in dose assessment models. The wide range of TF for each radionuclide reported in the literature for a particular plant type indicates that radionuclide concentration in soil is not the only factor influencing its uptake by the plant. Different soil properties and agricultural practices may influence the TF and these are also a function of the climate. Considering the wide variation in TF data, here we attempt to review the available literature on TF of radionuclides in tropical countries of the Indian subcontinent (India, Bangladesh, and Sri Lanka). TF under equilibrium conditions are not available for all radionuclides, in such cases TF of naturally existing stable analogs elements were compiled. With an emphasis on, transfer of radionuclides from soil to the edible compartment of the plant; the TF data for 21 elements are compiled for 12 plant groups classified as per IAEA, Technical Reports Series No. 472. The article also presents the analysis and discussion of the extent and limitations of the compiled data. The compiled TF may be useful in assessing the food chain transfer of radionuclides when site-specific information is not available.

A review of soil to rice transfer of radionuclides in tropical regions of Indian subcontinent.

In radioecological studies, soil to plant transfer factors (TF) is commonly used to estimate the food chain transfer of radionuclides, which is an important parameter to assess ingestion doses to humans. Rice is an important (Oryza sativa L.) staple crop in tropical countries and is the major food crop consumed all over the world. Out of the seven countries (India, Pakistan, Bangladesh, Nepal, Bhutan, and the island nations like Sri Lanka and Maldives) of the Indian subcontinent, Bangladesh, Sri Lanka, and Maldives along with a major region of India fall under tropical climate class according to Köppen climate classification. Because, the soil to rice TF under equilibrium conditions are not available for all radionuclides, TF of naturally existing stable elements, which are analogues of radionuclides were compiled. This review paper presents the collection of the TF data of soil to grain and stems & shoots of rice plant for eighteen elements. Data were generated mainly from different sub climatic regions of the tropical environment of India and Bangladesh. An overview of the compilation, analysis, and discussion of the extent and limitations of the data is presented.

A revised IAEA data compilation for estimating the soil to plant transfer of radionuclides in tropical environments.

A revision of the International Atomic Energy Agency (IAEA) Technical Report Series No. 472 (TRS 472) transfer parameter data for root uptake of radionuclides by crops in tropical environments was conducted under the IAEA Modelling and Data for Radiological Impact Assessments (MODARIA II) programme (2016-2019). Data on concentration ratios between plant and soil (CRplant-soil) were collated and summarised following a specific data selection process based on the Köppen-Geiger classification of tropical (class A) climates. An overview of the data collation and analysis methods is presented together with a comparison of CRplant-soil values between the revised tropical dataset and TRS 472 datasets. The revised dataset of CRplant-soil values for tropical environments is part of the IAEA MODARIA II programme Technical Document on soil to plant transfer of radionuclides in non-temperate environments.

Understanding the solid phase chemical fractionation of uranium in soil and effect of ageing.

The aim of the present work is to understand the solid phase chemical fractionation of Uranium (U) in soil and the mechanism involved. This study integrated batch experiments of U(VI) adsorption to soil, study of U in different soil fractions, ageing impact on fractionation of U and spectroscopic investigation of adsorbed U(VI) using X-ray Photoelectron Spectroscopy (XPS). For the study three soils, pedogenically different (S1: Igneous, S2: Sedimentary and S3: Metamorphic) were amended with U(VI) and chemical fractionation of U was studied by sequential extraction after an interval of one month and 12 months. It was found that there occurs a significant rearrangement of U in different fractions with ageing and no correlation was observed between the U content in different fractions and the adsorbents of respective fractions such as soil organic matter (SOM), Fe/Mn oxides (hydroxides) carbonates, soil cation exchange capacity (CEC). XPS study revealed that surface enrichment of U mainly governed by the carbonate minerals and SOM, whereas bulk concentration was controlled by the oxides (hydroxides) of Si and Al. Occlusion of U-Fe-oxides (hydroxides) on silica was identified as an important mechanism for bulk enrichment (Increase in residual fraction) and depletion of U concentration in reducible fraction.

Impact of particle size, temperature and humic acid on sorption of uranium in agricultural soils of Punjab.

Batch experiments were conducted to study the sorption of uranium (U) onto soil in deionised water as a function of its dosage, temperature and humic acid (HA). Furthermore, soils were characterized for particle sizes in the form of sand (>63 µm), silt (>2-<63 µm) and clay (<2 µm). The textural analysis revealed that soils were admixture of mainly sand and silt along with a small abundance of clay. X-ray diffraction analysis indicates that clay factions ranging from 2.8 to 5% dominated by quartz and montmorillonite. Experimental results indicated that soil with high abundance of clays and low sand content has relatively high U sorption which could be due to availability of high exchange surfaces for metal ions. However, at low concentration of HA, sorption of U was maximum and thereby decreased as the HA concentration increased. The maximum sorption may be due to increase in the negative active surface sites on HA and further decrease could be attributed to saturation of sorption site and surface precipitation. Conversely, the thermodynamic data suggested that the sorption is spontaneous and enhanced at higher temperature.

Thermodynamic parameters of U (VI) sorption onto soils in aquatic systems.

The thermodynamic parameters viz. the standard free energy (∆Gº), Standard enthalpy change (∆Hº) and standard entropy change (∆Sº) were determined using the obtained values of distribution coefficient (kd) of U (VI) in two different types of soils (agricultural and undisturbed) by conducting a batch equilibrium experiment with aqueous media (groundwater and deionised water) at two different temperatures 25°C and 50°C. The obtained distribution coefficients (kd) values of U for undisturbed soil in groundwater showed about 75% higher than in agricultural soil at 25°C while in deionised water, these values were highly insignificant for both soils indicating that groundwater was observed to be more favorable for high surface sorption. At 50°C, the increased kd values in both soils revealed that solubility of U decreased with increasing temperature. Batch adsorption results indicated that U sorption onto soils was promoted at higher temperature and an endothermic and spontaneous interfacial process. The high positive values of ∆Sº for agricultural soil suggested a decrease in sorption capacity of U in that soil due to increased randomness at solid-solution interface. The low sorption onto agricultural soil may be due to presence of high amount of coarse particles in the form of sand (56%). Geochemical modeling predicted that mixed hydroxo-carbonato complexes of uranium were the most stable and abundant complexes in equilibrium solution during experimental.

Distribution, enrichment and principal component analysis for possible sources of naturally occurring and anthropogenic radionuclides in the agricultural soil of Punjab state, India.

Enrichment factor (EF) of elements including geo-accumulation indices for soil quality and principal component analysis (PCA) were used to identify the contributions of the origin of sources in the studied area. Results of (40)K, (137)Cs, (238)U and (232)Th including their decay series isotopes in the agricultural soil of Mansa and Bathinda districts in the state of Punjab were presented and discussed. The measured mean radioactivity concentrations for (238)U, (232)Th and (40)K in the agricultural soil of the studied area differed from nationwide average crustal abundances by 51, 17 and 43 %, respectively. The sequence of the EFs of radionuclides in soil from the greatest to the least was found to be (238)U > (40)K > (226)Ra > (137)Cs > (232)Th > (228)Ra. Even though the enrichment of naturally occurring radionuclides was found to be higher, they remained to be in I(geo) class of '0', indicating that the soil is uncontaminated with respect to these radionuclides. Among non-metals, N showed the highest EF and belonged to I(geo) class of '2', indicating that soil is moderately contaminated due to intrusion of fertiliser. The resulting data set of elemental contents in soil was also interpreted by PCA, which facilitates identification of the different groups of correlated elements. The levels of the (40)K, (238)U and (232)Th radionuclides showed a significant positive correlation with each other, suggesting a similar origin of their geochemical sources and identical behaviour during transport in the soil system.