Pu Surface Research Articles

A simple and efficient strategy for preparing anticoagulant coatings on biomedical polyurethane surfaces through a fluorinated urethane prepolymer

Developing an efficient yet uncomplicated method to achieve anticoagulant coatings on biomedical PU surfaces remains a challenge. In this research, we have proposed a very simple way to synthesize fluorinated urethane prepolymers (FPUs) that possess extended fluorocarbon side chains and terminal groups, innovatively using a new fluorinated chain extender and a fluorinated terminal capping agent. These FPUs have been utilized as additives to fabricate biomedical PU blends (BPUB). Incorporating a minimal quantity of FPUs, as little as 2.5 %, bestows BPUB with exceptional capabilities to resist protein and platelet adhesion, which can further prevent platelet activation, facilitated by the self-migrating nature of the fluorocarbon chains toward the film's upper surfaces, as substantiated by contact angle measurements and XPS. DSC and TG analysis indicate that the addition of FPUs marginally affects the thermal stability of the BPUB films, yet it reduces the glass transition temperature of the PUs. Remarkably, the BPUB films demonstrate enhanced degradation resistance to physiological solutions, exhibit excellent hemocompatibility, and maintain extremely low cytotoxicity levels. Thus, the FPUs present themselves as highly encouraging candidates for the development of anticoagulant coatings on biomedical polymers.

First-principles study on Ga interactions with Pu surfaces and [formula omitted]-Pu bulk

The Ga-Pu alloy presents a potential solution to address the constraints of Pu metal as a fuel. Therefore, it is imperative to investigate its pertinent properties. In research, surface models were commonly employed for the preliminary exploration of information, including the identification of more stable binding sites. First-principles calculation methods were employed to investigate the adsorption characteristics of Ga atoms at various sites on the surfaces of Pu(100), Pu(110), and Pu(111), as well as their binding behavior within the Plutonium unit cells. The analysis, by adsorption energies, Charge Density Difference, Bader Charge, Electron Localization Function (ELF), Reduced Density Gradient (RDG), and Projected Density of States (PDOS), revealed that when Ga atoms interacted with the surface, they tended to bind more strongly to the Pu(100) long-bridge and Pu(110) TOP 1 sites, with adsorption energies of -2.585eV and -3.150eV, respectively. On the Pu(111) surface, the adsorption energies at the three sites were adsorption comparable, and the binding trends were similar. Upon entering the δ-Pu unit cells, Ga atoms formed a more stable structure after combining at the G, H, and I sites. The stability both on the surfaces and within the δ-Pu unit cells was primarily attributed to metallic bonds, with an additional contribution from mutual attraction due to van der Waals forces in surface adsorption. The adsorption behavior of Ga on the Pu surface and its binding within the δ-Pu unit cell was systematically investigated. This exploration aimed to offer ideas and insights for a comprehensive understanding of Ga-Pu alloys in subsequent studies.

Promoting antibacterial activity of polyurethane blend films by regulating surface-enrichment of SiO2 bactericidal agent

Abstract Polyurethane (PU) blended with nano-bactericidal agents was one of the most ways to obtain PU with antimicrobial properties. However, the bactericidal agent nanoparticles cannot effectively enrich the PU surface to reduce their antimicrobial properties. In this study, nano-silica particles with a large number of polar quaternary ammonium salt (N,N-dimethyl-3-aminopropyl-12-alkyl-ammonium bromide trimethylsilyl, denoted as QAC) can easily enrich the PU surface to endow PU with excellent antibacterial properties after they were blended with PU film. The QAC on the surface of silica with different diameters (denoted as SiO2-Q-X) can endow silica with antimicrobial properties and improve the repulsion between silica and PU to enhance the enrichment on PU surface of silica. A series of SiO2-Q-X/PU blend films were prepared and applied to inhibit the growth of the bacterial colony. The SiO2-Q-X/PU films can inhibit the growth of Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis. The SiO2-Q-X with more polar QAC was easily enriched on the surface of PU and had a better bactericidal effect than those of SiO2-Q-X with a minor polar QAC. Moreover, the aging of the SiO2-Q-X/PU films did not affect their antibacterial effect.

First-principles study on δ-Pu surface stability

δ-Pu has been widely used due to its outstanding material properties, and surface stability is essential for studying its surface corrosion mechanism. In this work, δ-Pu and its surface stability were analyzed based on first-principles calculations. The third-order Birch–Murnaghan equation of state fitted the calculated data for the δ-Pu cell, and the lattice constant of equilibrium structure was obtained. By constructing the surface models of three conventional crystal directions, (100), (110), and (111), the surface structure was optimized based upon the Quasi-Newton method, and the surface energy and electronic structure were calculated. The results show that the (110) surface energy of δ-Pu was 0.103 eV/Å2, and the (111) surface energy of δ-Pu was 0.052 eV/Å2. Thus, the d-band center of the (111) plane is farther away from the Fermi level than (100) and (110). Among the three typical crystal orientation planes, the surface energy and electronic structure show that the (111) plane was the most stable crystal orientation plane of δ-Pu.

Functionalization of polyurethane for infection‐resistance surface

AbstractPolyurethane (PU) has an eminence potential to be used as a urinary catheter because of its physicochemical properties. The biofilm accumulation on the surface of polyurethane is the biggest hindrance for its usage as a safe and prolonged catheter. Herein, the antimicrobial polyurethane was developed via wet chemistry method. Alkaline hydrolysis using NaOH was used for the generation of hydrophilic (amine) functionality on polyurethane surface. The reactant concentration and reaction time was investigated in terms of good amine functionality. The amine content at optimized condition was found to be ~4 μM/g in 8 h after treating with 10% NaOH. The surface morphology of hydrolyzed polyurethane was characterized using SEM and atomic force microscopy (AFM) technique, which confirmed the formation microdomains on the PU surface due to hydrolysis. Chlorohexidine digluconate (CLX) was used as model drug and CLX was simply incorporated by immersion of the PU in the CLX solution. The immobilization of drug was confirmed using surface chemistry analysis, that is, X‐ray photoelectron spectroscopy and energy‐dispersive X‐ray mapping technique. The cumulative release of drug was observed with varying concentration of drug. Excellent bacteriostatic and bactericidal efficiency were observed for drug immobilized polyurethane against both gram‐positive bacteria S. aureus and gram‐negative bacteria E. coli. The designed CLX‐PU film did not allow the bacteria to adhere on its surface and mitigate the risk of biofilm formation.

Enhanced Hemocompatibility of Silver Nanoparticles Using the Photocatalytic Properties of Titanium Dioxide.

Silver nanoparticles (AgNPs) are widely used because of their excellent antimicrobial properties. However, the poor hemocompatibility limits the application of AgNPs in blood contact materials. General approaches to improve the hemocompatibility of AgNPs-containing surfaces are to construct barrier layers or co-immobilize anticoagulant biomolecules. But such modification strategies are often cumbersome to prepare and have limited applications. Therefore, this study proposes a simple UV-photo-functionalization strategy to improve the hemocompatibility of AgNPs. We loaded AgNPs onto titanium dioxide (TiO2) nanoparticles to form a composite nanoparticles (Ag@TiO2NPs). Then, UV treatment was performed to the Ag@TiO2NPs, utilizing the diffusible photo-induced anticoagulant properties of TiO2 nanoparticles to enhance the hemocompatibility of AgNPs. After being deposited onto the PU surface, the photo-functionalized Ag@TiO2NPs coating showed excellent antibacterial properties against both Gram-positive/Gram-negative bacteria. Besides, In vitro and ex-vivo experiments demonstrated that the photo-functionalized Ag@TiO2NPs coating had desirable hemocompatibility. This modification strategy can provide a new solution idea to improve the hemocompatibility of metal nanoparticles.

Surface and micromechanical analysis of polyurethane plates with hydroxyapatite for bone structure

To analyze the surface topography and mechanical properties of a polyurethane derived from castor oil reinforced with hydroxyapatite (PU–HA) for bone fixation. The surface analysis was performed by Scanning Electron Microscopy (SEM) and the mechanical properties by Vickers microhardness and tensile tests. The SEM images showed that the PU surface presented important characteristics for materials intended for bone fixation, such as an irregular and porous surface. The analysis showed a surface with alternating areas with depressions and elevations of approximately 80±100 µm, presence of pores of 12 µm in size. The microhardness analysis showed values of 0.42±1.01 HV for PU–HA plates, lower in relation to the poly lactic-co-glycolic acid (PLGA) plate (control group). The elastic modulus and ultimate tensile strength of 317.4 MPa, and 35.57 MPa for PLGA sample, 1.187 MPa, and 0.29 MPa for PU–HA sample. The PU produced showed good surface properties, however demands better mechanical properties.

A long-term stable and flexible glucose sensor coated with poly(ethylene glycol)-modified polyurethane

• A flexible glucose sensor with long service life and good consistency is proposed. • GOx is coated on the electrode surface by a self-developed electrospray apparatus. • PU surface is modified by chemical grafting to improve its biocompatibility. Flexible biosensors have the great potential to be applied in medical diagnosis, wearable devices, fermentation and other fields. This paper proposes a manufacturing scheme of a flexible enzymatic glucose sensor coated with polyurethane modified by poly(ethylene glycol), PU-PEG, as a protective membrane, which can overcome the problems of poor consistency and short service life of the electrochemical sensor. A platinum-black electrode formed by electroplating platinum-black nanoparticles onto a flexible gold electrode is used as an enzyme carrier. The enzyme is electrosprayed evenly onto the electrode to avoid aggregation and to control quality. Glutaraldehyde is used as a cross-linking agent to immobilise the enzyme layer. Additionally, using PU-PEG as the protective membrane improves the anti-interference performance, controls the enzymatic reaction rate and makes long-term stable operation of the sensor possible. The experimental results show that the linear range of the sensor is 0.5 ~ 25 mM, the minimum detection limit is 0.25 mM, and the sensitivity is as high as 3.418 μA/mM. The measurement results of the sensors show good consistency, with a maximum absolute deviation of only 5.52%. The effective working time in 37℃ bovine serum with a glucose concentration of 5 mM is up to 23 days.

Metallic and anti-metallic properties of hydrogen adsorbed AnO2 (An = Th, U, and Pu) surfaces

The effect of atomic hydrogen adsorption on AnO2 (An = Th, U, and Pu) surfaces is studied in the framework of density functional theory and Hubbard-corrected density functional theory. Several adsorption coverages (1/3, 1/2, 2/3, and 1 monolayer) are considered. For the band insulator ThO2, surface metallicity induced by hydrogen adsorption is observed due to the electron donation of the hydrogen to the surface. But this effect is found to be strongly suppressed by electronic correlation for the Mott insulators UO2 and PuO2 because the electrons from the adsorbed hydrogen atoms occupy the localized 5f orbitals of the surface U/Pu atoms.

Source, Spatial Distribution and Migration of <sup>239+240</sup>Pu in Chinese Soils

The source, spatial distribution, typical vertical distribution and migration of 239+240 Pu in Chinese 647 surface soils and 66 soil cores are investigated in this study. To provide a complete spatial distribution of 239+240 Pu in Chinese surface soil, an overall pattern of and mechanism for 239+240 Pu migration in Chinese core soil, we summarize and analyze the 239+240 Pu surface and vertical distributions in literature. Comprehensive statistical analysis suggests four typical distributions in Chinese soil cores. It is found that the 239+240 Pu vertical distribution is closely related to the soil type and the 239+240 Pu migration. The result indicates that global fallout is the major source of 239+240 Pu in Chinese soils, with the average 240 Pu/ 239 Pu atom ratios around 0.18. Abnormally low 240 Pu/ 239 Pu ratios are detected in Jiuquan region and northern Xinjiang province in Northwest China, which can be attributed to nuclear weapons tests. To further investigate the migration behaviors of 239+240 Pu in soil cores in China, we apply the Convection Dispersion Equation (CDE) model and find that 239+240 Pu apparent convection velocities ranges from 0.00032±0.00031 cm/a to 0.473±0.083 cm/a. As shown in four typical vertical 239+240 Pu activity distribution soil cores, the deepened 239+240 Pu activity maximum value position implies a fast 239+240 Pu migration rate or apparent convection velocity. This study for the first time suggests a significant linear correlation ( R 2 =0.847) between depth of 239+240 Pu maximum value (cm) and apparent convection velocity (v, cm/a), and we speculate that v usually does not exceed 0.5 cm/a. A significant linear correlation is also identified between apparent dispersion coefficient (D, cm 2 /a) and v 2 in Chinese soil cores.

First-principles study of co-adsorption behavior of O2 and CO2 molecules on δ-Pu(100) surface

First principles calculation is performed to study the co-adsorption behaviors of O2 and CO2 on δ-Pu(100) surface by using a slab model within the framework of density functional theory (DFT). The results demonstrate that the most favorable co-adsorption configurations are Tv-C4O7 and Tp1-C2O8, with adsorption energy of –17.296 eV and –23.131 eV for CO2-based and O2-based system, respectively. The C and O atoms mainly interact with the Pu surface atoms. Furthermore, the chemical bonding between C/O and Pu atom is mainly of ionic state, and the reaction mechanism is that C 2s, C 2p, O 2s, and O 2p orbitals overlap and hybridize with Pu 6p, Pu 6d, and Pu 5f orbital, resulting in the occurrence of new band structure. The adsorption and dissociation of CO2 molecule are obviously promoted by preferentially occupying adsorbed O atoms, therefore, a potential CO2 protection mechanism for plutonium-based materials is that in CO2 molecule there occurs complete dissociation of CO2 → C + O + O, then the dissociated C atom combines with O atom from O2 dissociation and produces CO, which will inhibit the O2 from further oxidizing Pu surface, and slow down the corrosion rate of plutonium-based materials.

Novel hydrophobic and oleophobic surfaces using polyurethane with hydrogenated polyisoprene soft segment

Hydrophobic and oleophobic surfaces are of industrial as well as scientific interests. The conventional fluorine-based methods are well established but have critical limitations and drawbacks. We surprisingly found that a polyurethane polymer with hydrogenated polyisoprene soft segments shows a remarkable hydrophobic and oleophobic surface, which is comparable to those of fluorine-based polymers. Hydroxyl-terminated hydrogenated polyisoprene (HHPIP) and 4, 4′-diphenylmethane diisocyanate (MDI) were used to synthesize HHPIP-MDI polyurethane (HHPIP-MDI PU), which showed the remarkable surface properties. The contact angles of water and n-hexadecane on one of HHPIP-MDI PUs (104.7° and 30.8°) were significantly higher than those on polyethylene (94.7° and 6.5°), respectively. The results verified the hydrophobicity and oleophobicity of the HHPIP-MDI PU surface. The HHPIP-MDI PUs exhibited a low surface free energy (23.0 mN/m). Furthermore, we compared the dispersive and polar components of the surface free energy of HHPIP-MDI PU surfaces with other polymers and found that the balance between dispersive and polar components was different from those of conventional fluorocarbon polymers. The unique hydrophobic and oleophobic surface of HHPIP-MDI PUs is most probably originated from the low density HHPIP layer constrained by the hard urethane segments.

Diffusion behavior of hydrogen in oxygen saturated and unsaturated plutonium dioxide: An ab initio molecular dynamics study

As the plutonium (Pu) oxides are the crucial issue of the Pu surface and corrosion science and some impurities like hydrogen (H) are virtually impossible to exclude from them in realistic environments, understanding the dynamical behaviors of hydrogen (H) in Pu oxides is essential for the protections and applications of Pu. Here we perform systematic ab initio molecular dynamics (AIMD) calculations to reveal the diffusion behaviors of impurity H in the oxygen saturated (OS) and oxygen unsaturated (OU) Pu dioxide (PuO 2 ). The considered variation ranges of the concentration of interstitial H (θ: H to Pu ratio), the concentration of oxygen vacancy (OV) (n ov : OV to O ratio), and the temperature were 1 32 ∼ 14 32 , 0 ∼ 8 64 , and 300 ∼ 800 K, respectively. The root mean square displacements, radial distribution functions, Bader charge, electronic density of states, and the three-dimensional diffusion coefficients were extracted and analyzed in detail. Results indicate that the H diffusion is inhibited mainly due to the formation of hydroxyl with the host O both in the OS and OU PuO 2 . In the OU PuO 2 the O atoms will transport due to the presence of large concentration of H. The octahedral interstitial site in the OS PuO 2 and the OV in the OU PuO 2 provide a metastable and favorable capturing effect to the interstitial H, respectively. The diffusion coefficient in the OU PuO 2 is smaller than that of in the OS PuO 2 and decreases with n ov essentially as the OV plays the role of a trap for H diffusion. Our conclusions may provide potential guidance for Pu surface and corrosion science. • The mechanisms of inhibit hydrogen diffusion in different plutonium dioxides were confirmed. • Two different capturing effects to hydrogen in saturated and unsaturated PuO 2 were found. • The diffusion coefficients of hydrogen in different plutonium dioxides were obtained. • The variation tendencies of the hydrogen diffusion coefficients were discussed.

Measurement of PuO2 film thickness by electron probe microanalysis (EPMA) calibration curve method

Plutonium (Pu) surfaces are highly reactive toward oxygen containing species and, therefore, invariably covered with oxides (e.g. PuO2) during transport and handling. The actual thickness of the surface oxide may dictate if a plutonium part is suitable for a certain application. As a result, a cost-effective, quick, non-destructive, yet reliable means to measure the oxide layer thickness formed on Pu samples is desirable. In this study, the cross-sections of a series of room temperature grown oxides on Pu samples were trenched by focus ion beam (FIB) then observed by scanning electron microscopy (SEM) to measure the surface oxide thicknesses, which were then combined with the corresponding oxygen k-ratios provided by electron probe microanalysis (EPMA) to form calibration curves. Oxide thickness measurements for the calibration curves were made on samples within the typical SEM observable range for PuO2 (35–400 nm). The portion of the calibration curve in the thinner oxide region (<35 nm) were approximated via Pouchou and Pichoir’s ϕ(ρz) theory. Two specimens with micrometer-thick PuO2 standards (one formed at room temperature and the other at higher temperature with a higher level of crystallinity) were made for the k-ratios in this study, allowing EPMA users to choose the standard that best suits their needs. If the surface corrosion is known to be PuO2 (from the environment in which the Pu sample is stored) or if the stoichiometry of the surface oxide is confirmed by a preliminary/compliment technique, these calibration curves allow EPMA users to quickly and efficiently determine PuO2 thicknesses from the measured oxygen k-ratios of their samples. The methodology presented in this study can also be used as a template for creating calibration curves for oxides grown on other actinides.

A Facile Activation Method for Improving the Wettability of Polyurethane Surfaces

This work reports the activation of polyurethane film surfaces in order to enrich them with polar groups such as -NH2, -OH, -COOH or radicals, which further allows immobilization of several bioactive compounds. UV-activation was used to introduce new groups on the polymer surface without affecting the bulk properties. The current arising species improve the wettability of the PU surfaces as it was observed from the static contact angle measurements. The structure and composition of the new PU surfaces were analyzed by using ATR-FTIR spectroscopy. The results suggested the possibility of modifying the PU surfaces in a shorter time periods, in order to provide many sites to attach other biomacromolecules by polar interaction or hydrogen bonding.

Low‐pressure plasma surface modification of polyurethane films with chitosan and collagen biomolecules

ABSTRACTPolyurethane (PU) was synthesized using castor oil and a trade grade of hexamethylene diisocyanate, and then PU films were prepared for wound dressing applications. The PU films were then plasma treated with the low‐pressure nitrogen plasma to functionalize with peroxide and hydroperoxide groups in order to attach with acrylic acid monomers. Therefore, the polyacrylic acid polymer branches were formed on the film surfaces. Carboxylic acid groups were activated by N‐(3‐dimethylaminopropyl)‐N′‐ethyl carbodiimide hydrochloride/N‐hydroxysuccinimide and bonded with chitosan and collagen biomolecules. Untreated, nitrogen plasma treated, polyacrylic acid grafted, and finally chitosan and collagen‐immobilized PU films were characterized by several tests. The tests included the attenuated total reflectance Fourier transform infrared spectroscopy, static contact angle, atomic force microscopy, scanning electron microscopy, fibroblast L929 cell culture, and antibacterial activity assay to evaluate their in vitro cytocompatibility. The results confirmed that chitosan and collagen were immobilized successfully on the PU surfaces. The chitosan‐immobilized PU and collagen‐immobilized PU improved the adhesion and proliferation of fibroblast cells compared to untreated PU films. The chitosan‐modified PU films exhibit the best antibacterial properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47567.

Sorption kinetics of plutonium (V)/(VI) to three montmorillonite clays

Pu(V) adsorbed to the surface of montmorillonite clay can be reduced to Pu(IV). In this work, the role of clay structural Fe on this surface mediated reduction reaction was investigated by quantifying Pu(V)/(VI) sorption rates under atmospheric (oxic) conditions to three montmorillonite clays with variable Fe content (SWy-1: 2.6 wt % Fe; STx-1: 0.6 wt % Fe; Barasym synthetic mica-montmorillonite: 0.01 wt % Fe) at pH 4, pH 6, and pH 8. The experiments were performed over a period of one year, a timescale at which the sorption rates were expected to capture both adsorption and surface mediated reduction processes. At pH 6 and pH 8, the rate of sorption was positively correlated with structural Fe content. However, by 360 d, the extent of sorption was independent of Fe. Moreover, in the case of the synthetic montmorillonite it was not apparent that sorption equilibrium had been achieved by the end of the experiment. There was minimal difference in sorption rates between the clays at pH 4, suggesting that structural Fe content may be less important in Pu(V)/(VI) reduction at low pH. The results indicate that at circumneutral pH, structural Fe will affect the kinetics of Pu surface mediated reduction on montmorillonite clays but not necessarily the equilibrium Pu sorption affinity at environmentally relevant timescales. The differences in rates on the three clays emphasize the need to perform long-term sorption experiments (>1 year) to adequately capture the equilibrium processes controlling the uptake of Pu under atmospheric conditions. Comparison to other minerals indicates that the sorption rates can vary by as much as five orders of magnitude depending on the structure and composition of the surface.

Hydrogen peroxide/UV treatment on polylactide/polyurethane blends for biomedical applications

Biodegradable polymers should be non-toxic, possess low immunogenicity and good mechanical properties. Due to their hydrophobicity and their low surface energy cells only poorly attach, spread and proliferate on these biodegradable polyesters. Therefore, the surface of these polyesters should usually be modified and already several approaches have been presented to increase their cell affinity. In this research the influence of hydrogen peroxide combined with ultra violet irradiation on wettability, morphology and mechanical properties of PU/PLA blends as well as their pure components. It was clearly visible that both pure PU and PLA acted completely different form PU/PLA blend during treatment. The wettability of pure polymers changed after H2O2/UV, PU surface became more hydrophilic, whereas PLA becomes slightly hydrophobic. Due to micropores and microcracks visible on surfaces resulted from breaking ester linkage, deterioration of their mechanical properties was also observed. The exposure of PU/PLA films to H2O2/UV irradiation showed the change of wettability toward more hydrophilic and increase of mechanical properties because of specific affinity to the etching process.

A First-Principles Study of Hydrogen Diffusivity and Dissociation on δ-Pu (100) and (111) Surfaces

The diffusivity and chemical reactivity of hydrogen on the δ-Pu (100) and (111) surfaces has been studied with density functional theory using both spin-polarization and spin–orbit coupling calculations. Comparison of the total electronic density of states and atomic hydrogen diffusion energies indicates that spin-polarization yields accurate results, with spin–orbit coupling yielding slightly smaller barriers to hopping between adsorption sites. On the (100) surface, both sets of calculations indicate that the dissociation reaction for molecular hydrogen is highly active at ambient conditions and results in the hydrogen ions bonded within the Pu surface, similar to hydride formation. In contrast, calculations on the (111) surface indicate a lower barrier for dissociation without the formation of the hydride-like end product. Our results help quantify the effect of spin–orbit coupling on hydrogen surface chemistry on δ-Pu. In addition, we observe that the degree of resulting corrosion could depend on the ...

Temporal evolution of 137Cs, 237Np, and 239+240Pu and estimated vertical 239+240Pu export in the northwestern Mediterranean Sea

The evolution of 137Cs, 237Np and 239+240Pu at the DYFAMED station (NW Mediterranean) is discussed in relation to physical processes, downward fluxes of particles, and changes in the main input sources. The data set presented in this study represents the first complete 237Np vertical profiles (0.12–0.27μBqL−1), and constitutes a baseline measurement to assess future changes. A similar behavior of Cs and Np has been evidenced, confirming that Np behaves conservatively. While the 137Cs decrease has been driven by its radioactive decay, the vertical distribution of 237Np has not substantially changed over the last decade. In the absence of recent major inputs, a homogenization of their vertical distribution occurred, partly due to deep convection events that became more intense during the last decade. In contrast, 239+240Pu surface levels in the NW Mediterranean waters have fallen in the past four decades by a factor of 5. This decrease in surface has been balanced by higher concentrations in the deep-water layers. A first estimate of the downward 239+240Pu fluxes in the NW Mediterranean Sea is proposed over more than two decades. This estimation, based on the DYFAMED sediment trap time-series data and published 239+240Pu flux measurements, suggests that sinking particles have accounted for 60–90% of the upper layer (0–200m) Pu inventory loss over the period 1989–2013. The upper layer residence time of Pu is estimated to be ~28years, twice as long as the residence time estimated for the whole western Mediterranean (~15years). This difference highlights the slow removal of Pu in the open waters of the NW Mediterranean and confirms that most of the Pu removal occurs along the coastal margin where sedimentation rates are high.