In this study, we report that silver ions (Ag
+) from the oxidative dissolution of silver engineered nanoparticles (Ag-ENs) determined the EN toxicity to the marine diatom
Thalassiosira weissflogii. ...Most of the Ag-ENs formed non-toxic aggregates (>0.22 μm) in seawater. When the free Ag
+ concentration (Ag
+
F) was greatly reduced by diafiltration or thiol complexation, no toxicity was observed, even though the Ag-ENs were better dispersed in the presence of thiols with up to 1.08 × 10
−5 M Ag-ENs found in the <0.22 μm fraction, which are orders of magnitude higher than predicted for the natural aquatic environment. The secretion of polysaccharide-rich algal exopolymeric substances (EPS) significantly increased at increasing Ag
+
F. Both dissolved and particulate polysaccharide concentrations were higher for nutrient-limited cells, coinciding with their higher Ag
+ tolerance, suggesting that EPS may be involved in Ag
+ detoxification.
Ag-ENs were found to only have indirect toxic effects on marine phytoplankton as a result of their rapid Ag
+ release.
One of the key risk drivers at radioactive waste disposal facilities is radioiodine, especially 129I. As iodine mobility varies greatly with iodine speciation, experiments with 129I-contaminated ...aquifer sediments from the Savannah River Site located in Aiken, SC, were carried out to test iodine interactions with soils and aquifer sediments. Using tracer 125I− and stable 127I− additions, it was shown that such interactions were highly dependent on I− concentrations added to sediment suspensions, contact time with the sediment, and organic carbon (OC) content, resulting in an empirical particle−water partition coefficient (K d) that was an inverse power function of the added I− concentration. However, K d values of organically bound 127I were 3 orders of magnitude higher than those determined after 1−2 weeks of tracer equilibration, approaching those of OC. Under ambient conditions, organo-iodine (OI) was a major fraction (67%) of the total iodine in the dissolved phase and by implication of the particulate phase. As the total concentration of amended I− increased, the fraction of detectable dissolved OI decreased. This trend, attributed to OC becoming the limiting factor in the aquifer sediment, explains why at elevated I− concentrations OI is often not detected.
Iodine occurs in multiple oxidation states in aquatic systems in the form of organic and inorganic species. This feature leads to complex biogeochemical cycling of stable iodine and its long-lived ...isotope, 129I. In this study, we investigated the sorption, transport, and interconversion of iodine species by comparing their mobility in groundwaters at ambient concentrations of iodine species (10–8 to 10–7 M) to those at artificially elevated concentrations (78.7 μM), which often are used in laboratory analyses. Results demonstrate that the mobility of iodine species greatly depends on, in addition to the type of species, the iodine concentration used, presumably limited by the number of surface organic carbon binding sites to form covalent bonds. At ambient concentrations, iodide and iodate were significantly retarded (K d values as high as 49 mL g–1), whereas at concentrations of 78.7 μM, iodide traveled along with the water without retardation. Appreciable amounts of iodide during transport were retained in soils due to iodination of organic carbon, specifically retained by aromatic carbon. At high input concentration of iodate (78.7 μM), iodate was found to be reduced to iodide and subsequently followed the transport behavior of iodide. These experiments underscore the importance of studying iodine geochemistry at ambient concentrations and demonstrate the dynamic nature of their speciation during transport conditions.
Mercury (Hg) was discharged in the late 1960s into the Penobscot River by the Holtra-Chem chlor-alkali production facility, which was in operation from 1967 to 2000. To assess the transport and ...distribution of total Hg, and recovery of the river and estuary system from Hg pollution, physical and radiochemical data were assembled from sediment cores collected from 58 of 72 coring stations sampled in 2009. These stations were located throughout the lower Penobscot River, and included four principal study regions, the Penobscot River (PBR), Mendall Marsh (MM), the Orland River (OR), and the Penobscot estuary (ES). To provide the geochronology required to evaluate sedimentary total Hg profiles, 58 of 72 sediment cores were dated using the atmospheric radionuclide tracers 137Cs, 210Pb, and 239,240Pu. Sediment cores were assessed for depths of mixing, and for the determination of sediment accumulation rates using both geochemical (total Hg) and radiochemical data. At most stations, evidence for significant vertical mixing, derived from profiles of 7Be (where possible) and porosity, was restricted to the upper ~1–3cm. Thus, historic profiles of both total Hg and radionuclides were only minimally distorted, allowing a reconstruction of their depositional history. The pulse input tracers 137Cs and 239,240Pu used to assess sediment accumulation rates agreed well, while the steady state tracer 210Pb exhibited weaker agreement, likely due to irregular lateral sediment inputs.
Composite sediment accumulation rates determined by radionuclides and total Hg for each part of the Penobscot River an/d estuary system (uncertainties reported at 1 σ). Display omitted
•Sediment variability increased from Mendall Marsh/Orland River < Penobscot estuary < Penobscot River.•Generally, sediment mixing was limited (maximum Db ranged from 3-6 cm2 y-1; mixed layers of ~1-3 cm).•A wide range in sediment accumulation rates was observed (0.10-1.85 cm y-1), and was expected.•Extensive lateral transport of sediment (and total Hg) was limited to parts of the Penobscot River.•Sediment (and Hg) accumulation in the Penobscot River was most random, focused inside meanders, and coves.
129
I is commonly either the top or among the top risk drivers, along with
99
Tc, at radiological waste disposal sites and contaminated groundwater sites where nuclear material fabrication or ...reprocessing has occurred. The risk stems largely from
129
I having a high toxicity, a high bioaccumulation factor (90% of all the body's iodine concentrates in the thyroid), a high inventory at source terms (due to its high fission yield), an extremely long half-life (16M years), and rapid mobility in the subsurface environment. Another important reason that
129
I is a key risk driver is that there is uncertainty regarding its biogeochemical fate and transport in the environment. We typically can define
129
I mass balance and flux at sites, but cannot predict accurately its response to changes in the environment. As a consequence of some of these characteristics,
129
I has a very low drinking water standard, which is set at 1 pCi/L, the lowest of all radionuclides in the Federal Register. Recently, significant advancements have been made in detecting iodine species at ambient groundwater concentrations, defining the nature of the organic matter and iodine bond, and quantifying the role of naturally occurring sediment microbes to promote iodine oxidation and reduction. These recent studies have led to a more mechanistic understanding of radioiodine biogeochemistry. The objective of this review is to describe these advances and to provide a state of the science of radioiodine biogeochemistry relevant to its fate and transport in the terrestrial environment and provide information useful for making decisions regarding the stewardship and remediation of
129
I contaminated sites. As part of this review, knowledge gaps were identified that would significantly advance the goals of basic and applied research programs for accelerating
129
I environmental remediation and reducing uncertainty associated with disposal of
129
I waste. Together the information gained from addressing these knowledge gaps will not alter the observation that
129
I is primarily mobile, but it will likely permit demonstration that the entire
129
I pool in the source term is not moving at the same rate and some may be tightly bound to the sediment, thereby smearing the modeled
129
I peak and reducing maximum calculated risk.
We examined total mercury (Hg) distributions in sediments from the Penobscot River and estuary, Maine, a site of extensive Hg releases from HoltraChem (1967–2000). Our objectives were to quantify: ...(1) bottom sediment Hg inventories (upper ~1m; 50–100 y); (2) sediment accumulation rates; and (3) contemporary Hg fluxes to bottom sediments; by sampling the Penobscot River (PBR), Mendall Marsh (MM), the Orland River (OR) and the Penobscot estuary (ES). Hg was rapidly distributed here, and the cumulative total (9.28 metric tons) associated with sediments system-wide was within the range released (6–12 metric tons). Evidence of sediment/Hg remobilization was observed in cores primarily from the PBR, and to a lesser extent the ES, whereas cores from MM, most of the OR, the ES, and half from the PBR exhibited sharp peaks in Hg concentrations at depth, followed by gradual decreases towards the surface. Based on background PBR sediment Hg concentrations (100ngg−1), “elevated” (300ngg−1), or “highly elevated” (600ngg−1) Hg concentrations in sediments, and resulting inventories, we assessed impact levels (“elevated”≥270, or “highly elevated”≥540mgm−2). 71% of PBR stations had “elevated”, and 29% had “highly elevated” Hg inventories; 45% of MM stations had “elevated”, and 27% had “highly elevated” inventories; 80% of OR stations had “elevated” inventories only; and 17% of ES stations had “elevated” inventories only. Most “highly elevated” stations were located within 8km of HoltraChem, in MM, in the PBR, and in the OR. Near-surface sediments in the OR, PBR and MM were all “highly elevated”, while those in the ES were “elevated”, on average. Mean Hg fluxes to bottom sediments were greatest in the OR (554), followed by the PBR (469), then MM (452), and finally the ES (204ngcm−2y−1).
Simple contour map (kriging) showing the distributions of total sedimentary Hg inventories (ngcm−2) throughout the Penobscot system. Display omitted
•Total Hg was rapidly distributed and deposited throughout this system.•The calculated cumulative total sedimentary Hg (9.28 metric tons) throughout the system falls within the range of total Hg (6-12 metric tons) believed to have been released from HoltraChem.•Differences between distributions of total Hg inventories, near-surface (upper 3 cm) total Hg concentrations, and contemporary total Hg fluxes show that total Hg is being redistributed throughout the system.•Mean, near-surface (upper 3 cm) total Hg concentrations are greatest in the Orland River (1,120 ng g-1) > Penobscot River (815 ng g-1) > Mendall Marsh (673 ng g-1) > Penobscot Estuary (526 ng g-1).•Hg(o) values at different sites were similar, though individual total Hg profiles were heterogeneous.
Among the key environmental factors influencing the fate and transport of radionuclides in the environment is natural organic matter (NOM). While this has been known for decades, there still remains ...great uncertainty in predicting NOM-radionuclide interactions because of lack of understanding of radionuclide interactions with the specific organic moieties within NOM. Furthermore, radionuclide-NOM studies conducted using modelled organic compounds or elevated radionuclide concentrations provide compromised information related to true environmental conditions. Thus, sensitive techniques are required not only for the detection of radionuclides, and their different species, at ambient and/or far-field concentrations, but also for potential trace organic compounds that are chemically binding these radionuclides. GC-MS and AMS techniques developed in our lab are reviewed here that aim to assess how two radionuclides, iodine and plutonium, form strong bonds with NOM by entirely different mechanisms; iodine tends to bind to aromatic functionalities, whereas plutonium binds to N-containing hydroxamate siderophores at ambient concentrations.
While low-level measurements are a prerequisite for assessing iodine and plutonium migration at nuclear waste sites and as environmental tracers, it is necessary to determine their in-situ speciation, which ultimately controls their mobility and transport in natural environments. More importantly, advanced molecular-level instrumentation (e.g., nuclear magnetic resonance (NMR) and Fourier-transform ion cyclotron resonance coupled with electrospray ionization (ESI-FTICRMS) were applied to resolve either directly or indirectly the molecular environments in which the radionuclides are associated with the NOM.
•Natural organic matter (NOM), even at trace levels, controls I and Pu geochemistry.•There is a need to detect radionuclide speciation at low concentrations.•Need for knowing interaction of individual moieties of NOM with radionuclides important to fate and transport prediction.
In order to more effectively use iodine isotope ratios,
129
I
/
127
I
, as hydrological and geochemical tracers in aquatic systems, a new high performance liquid chromatography (HPLC) method was ...developed for the determination of iodine speciation. The dissolved iodine species that dominate natural water systems are iodide, iodate, and organic iodine. Using this new method, iodide was determined directly by combining anion exchange chromatography and spectrophotometry. Iodate and the total of organic iodine species are determined as iodide, with minimal sample preparation, compared to existing methods. The method has been applied to quantitatively determine iodide, iodate as the difference of total inorganic iodide and iodide after reduction of the sample by NaHSO
3, and organic iodine as the difference of total iodide (after organic decomposition by dehydrohalogenation and reduction by NaHSO
3) and total inorganic iodide.
Analytical accuracy was tested: (1) against certified reference material, SRM 1549, powdered milk (NIST); (2) through the method of standard additions; and (3) by comparison to values of environmental waters measured independently by inductively coupled plasma mass spectrometry (ICP-MS). The method has been successfully applied to measure the concentrations of iodide species in rain, surface and ground water, estuarine and seawater samples. The detection limit was ∼1
nM (0.2
ppb), with less than 3% relative standard deviation (R.S.D.) for samples determined by standard additions to an iodide solution of 20
nM in 0.1
M NaCl.
This technique is one of the few methods sensitive enough to accurately quantify stable iodine species at nanomolar concentrations in aquatic systems across a range of matrices, and to quantitatively measure organic iodine. Additionally, this method makes use of a very dilute mobile phase, and may be applied to small sample volumes without pre-column concentration or post-column reactions.
Radionuclides reach the environment from natural or anthropogenic sources and are equilibrating over time with different phases through sorption and precipitation reactions onto inorganic phases and ...macromolecular natural organic matter (NOM). Strong binding to NOM can occur by chelation of clustered binding sites (i.e., binding sites from different branches in the macromolecule) in the absence of conventional chelating sites. Despite many years of research and strong evidence of its significance, transport of many radionuclides is still modeled without taking into consideration NOM as a redox regulator and a sorbent or chelating agent.
Microbially mediated chelation and incorporation reactions can control a number of radionuclides, e.g., plutonium (Pu) and iodine (I) isotopes, leading to retardation or mobilization, depending on whether the carrier compound is in solution or particle-bound. The presence of NOM in contaminated soils complicates conventional remediation techniques for I, where base has been added to either increase the cation exchange capacity of soils or to promote direct co-precipitation of the cationic radionuclide in the waste stream. Even though Pu at waste sites did not have to be remediated, base addition would likely also bring surprises. This addition may then have unexpected consequences; while promoting the immobilization of inorganic Pu, it has been shown to also remobilize inorganic-I and low-molecular weight organic compounds that are bound to I and Pu.
Iodine occurs in multiple oxidation states in aquatic systems, existing not only as inorganic species (iodide (I−) and iodate (IO3−)), but also as organic species where I is covalently bound to aromatic moieties. Thus, stable iodine, 127I, and its long-lived isotope, 129I, a major by-product of nuclear fission, undergo complex biogeochemical cycling in the environment, which renders them less mobile than when assuming that all I is in the form of the highly mobile form of iodide.
In the laboratory and the field, plutonium strongly associates with NOM, when present, and is strongly chelated by specific moieties such as hydroxamate siderophores and other N-containing compounds. As a consequence, its mobility is controlled by the transport behavior of the anionic organic forms rather than the much more strongly sorbing cationic form of Pu(IV). NOM, even at trace levels, can play a significant role in controlling the fate and transport of radionuclides.
•Iodine in the environment occurs in multiple oxidation states in aquatic systems, existing not only as inorganic species (iodide (I−) and iodate (IO3−)), but also as organic species where I is covalently bound to aromatic moieties.•Thus, stable iodine, 127I, and its longlived isotope, 129I, a major by-product of nuclear fission, undergo complex biogeochemical cycling in the environment, which renders them less mobile than when assuming that all I is in the form of the highly mobile form of iodide.•Plutonium also strongly associates with natural organic matter whereby it is strongly chelated by specific moieties such as hydroxamate siderophores and other nitrogen containing compounds.•As a consequence, its mobility is controlled by the transport behavior of the anionic organic forms rather than the much more strongly sorbing cationic form of Pu(IV).
A
bstract
The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The ...electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections,
dσ/dp
and
dσ/d
cos(
θ
), and the total cross-sections in a limited phase-space in momentum and scattering angle (
p >
300 MeV/c and
θ ≤
45°) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.
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