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Grandbois RM, Santschi PH, Xu C, Mitchell JM, Kaplan DI, Yeager CM. Iodide uptake by forest soils is principally related to the activity of extracellular oxidases. Front Chem 2023; 11:1105641. [PMID: 36936531 PMCID: PMC10019592 DOI: 10.3389/fchem.2023.1105641] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Accepted: 02/14/2023] [Indexed: 03/06/2023] Open
Abstract
129I is a nuclear fission decay product of concern because of its long half-life (16 Ma) and propensity to bioaccumulate. Microorganisms impact iodine mobility in soil systems by promoting iodination (covalent binding) of soil organic matter through processes that are not fully understood. Here, we examined iodide uptake by soils collected at two depths (0-10 and 10-20 cm) from 5 deciduous and coniferous forests in Japan and the United States. Autoclaved soils, and soils amended with an enzyme inhibitor (sodium azide) or an antibacterial agent (bronopol), bound significantly less 125I tracer (93%, 81%, 61% decrease, respectively) than the untreated control soils, confirming a microbial role in soil iodide uptake. Correlation analyses identified the strongest significant correlation between 125I uptake and three explanatory variables, actinobacteria soil biomass (p = 6.04E-04, 1.35E-02 for Kendall-Tau and regression analysis, respectively), soil nitrogen content (p = 4.86E-04, 4.24E-03), and soil oxidase enzyme activity at pH 7.0 using the substrate L-DOPA (p = 2.83E-03, 4.33E-04) and at pH 5.5 using the ABTS (p = 5.09E-03, 3.14E-03). Together, the results suggest that extracellular oxidases, primarily of bacterial origin, are the primary catalyst for soil iodination in aerobic, surface soils of deciduous and coniferous forests, and that soil N content may be indicative of the availability of binding sites for reactive iodine species.
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Affiliation(s)
- Russell M. Grandbois
- Laboratory for Environmental and Oceanographic Research, Department of Marine Sciences, Texas A&M University—Galveston, Galveston, TX, United States
| | - Peter H. Santschi
- Laboratory for Environmental and Oceanographic Research, Department of Marine Sciences, Texas A&M University—Galveston, Galveston, TX, United States
| | - Chen Xu
- Laboratory for Environmental and Oceanographic Research, Department of Marine Sciences, Texas A&M University—Galveston, Galveston, TX, United States
| | - Joshua M. Mitchell
- Chemical Diagnostics and Engineering, Los Alamos National Laboratory, Los Alamos, NM, United States
| | - Daniel I. Kaplan
- Savannah River Ecology Laboratory, University of Georgia, Aiken, SC, United States
| | - Chris M. Yeager
- Chemical Diagnostics and Engineering, Los Alamos National Laboratory, Los Alamos, NM, United States
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Roulier M, Carasco L, Orjollet D, Bueno M, Pannier F, Le Hécho I, Nicolas M, Coppin F. Iodine distribution and volatilization in contrasting forms of forest humus during a laboratory incubation experiment. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2022; 248:106872. [PMID: 35430501 DOI: 10.1016/j.jenvrad.2022.106872] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 03/19/2022] [Accepted: 03/22/2022] [Indexed: 06/14/2023]
Abstract
Radionuclides 129I (t1/2 = 15.7 × 106 years) and 131I (t1/2 = 8.02 days) are both introduced into the environment as a result of nuclear human activities. Environmental transfer pathways and fluxes between and within ecosystems are essential information for risk assessment. In forest ecosystems, humus degradation over time could result in re-mobilization and then downward migration and/or volatilization of intercepted 129I. In order to estimate the scale of these processes, humus (mull and moder forms) sampled under deciduous and coniferous forests were spiked with 125I- (t1/2 = 59.4 days), as a surrogate for 129I, in order to study the evolution of its water-soluble and organic fractions as well as the volatilization rate during humus degradation at laboratory scale. To our knowledge, this is the first time that interactions between iodine and contrasting forms of forest humus have been investigated. The evolution of native stable iodine (127I) pools in unspiked humus was also studied. The nature of the humus' organic matter appears to be a factor that impacts on the proportions of water-soluble and organic fractions of iodine and on their evolution. Iodine-125 was mainly organically bound (fraction for mulls and moders: ∼54-59 and 41-49%, respectively) and no clear evolution was observed within the 4-month incubation period. A large decrease in 125I water-solubility occurred, being more marked for mull (from ∼14-32 to 3-7%) than for moder (from ∼21-37 to 7-19%) humus. By contrast, a significant fraction was not extractible (∼38-43%) and varied in inverse proportion to the water-soluble fraction, suggesting a stabilization of iodine in humus after wet deposit. The nature of the humus organic matter also impacted on 125I volatilization. Although of the same order of magnitude, the total volatilization of 125I was higher for moders (∼0.039-0.323%) than for mulls (∼0.015-0.023%) within the 4-month incubation period. Volatilization rates for mulls were correlated with the water-soluble fraction, implying that volatilization of 125I could occur from the humus solution. Our results showed that humus is thus a zone of iodine accumulation by association with organic matter and that potential losses by lixiviation are significantly more important compared to volatilization.
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Affiliation(s)
- Marine Roulier
- Institute of Radiological Protection and Nuclear Safety IRSN, PSE-ENV/SRTE/LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France; CNRS/Univ. Pau & Pays de l'Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254, Avenue du Président Angot, 64000, Pau, France.
| | - Loïc Carasco
- Institute of Radiological Protection and Nuclear Safety IRSN, PSE-ENV/SRTE/LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
| | - Daniel Orjollet
- Institute of Radiological Protection and Nuclear Safety IRSN, PSE-ENV/SRTE/LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
| | - Maïté Bueno
- CNRS/Univ. Pau & Pays de l'Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254, Avenue du Président Angot, 64000, Pau, France.
| | - Florence Pannier
- CNRS/Univ. Pau & Pays de l'Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254, Avenue du Président Angot, 64000, Pau, France.
| | - Isabelle Le Hécho
- CNRS/Univ. Pau & Pays de l'Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254, Avenue du Président Angot, 64000, Pau, France.
| | - Manuel Nicolas
- Office National des Forêts ONF, Direction forêts et risques naturels, Département recherche, développement, innovation, Boulevard de Constance, 77300, Fontainebleau, France.
| | - Frédéric Coppin
- Institute of Radiological Protection and Nuclear Safety IRSN, PSE-ENV/SRTE/LR2T, CE Cadarache, 13115, Saint Paul les Durance Cedex, France.
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Sachs S, Bernhard G. Influence of humic acids on the actinide migration in the environment: suitable humic acid model substances and their application in studies with uranium—a review. J Radioanal Nucl Chem 2011. [DOI: 10.1007/s10967-011-1084-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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