Particulate Rare Earth Elements Research Articles

Provenance Indication of Rare Earth Elements in Lake Particulates from Environmentally Sensitive Regions

The provenance of lake particulate matter in environmentally sensitive areas is crucial to understanding regional environmental and climatic changes. This study investigated two regions in the Northeast Tibetan Plateau, China: Region I (Keluke, Tuosu, and Gahai Lakes) and Region II (Qinghai Lake and nearby rivers). The results showed that: (1) The two regions have greater differences in the enrichment of rare earth elements (REEs) and heterogeneity in spatial distribution, both of which are characterized by relative enrichment of LREE and depletion of HREE, but to different degrees; (2) the source and formation of particulate matter in two regions are consistent. Particulate matter in Region I (Keluke and Tuosu Lakes) predominantly originates from granite rocks, which undergo weathering and transportation through rivers. Region II (Qinghai Lake and nearby rivers) particulate matter is affected by chemical weathering and partial recycling of detrital material. Diagenesis had a minimal impact on the particulate REEs. (3) This study primarily provides a preliminary understanding of REEs in lake particles, assessing particle changes during the water-to-sediment process and their provenance indication. Future studies will incorporate the solid fugacity (solid speciation) of REEs in particles, contributing to a comprehensive understanding of rare earth element geochemical processes. This study provides valuable insights into REEs distribution, source, and geochemical behavior in the Tibetan Plateau, underscoring the importance of REEs in understanding provenance processes, and is indicative of provenance studies in other climate change-sensitive regions of the world.

Early diagenetic mobilization of rare earth elements and implications for the Ce anomaly as a redox proxy

The Rare Earth Elements (REE) archived in carbonate rocks retain a wealth of information on paleo-seawater chemistry and local-regional redox conditions. However, interpretations are often ambiguous due to the potential for REE remobilization in marine environments. In this regard, many carbonate rocks that retain primary seawater isotopic signatures exhibit non-seawater-like REE patterns, implying either unusual REE behaviour in seawater or diagenetic overprinting of otherwise well-preserved rock samples. Here, we apply sequential leaching to constrain the possible effects of different REE-bearing phases on measured carbonate REE patterns in order to address this quandary. Our results show that the exchangeable phase contains negligible REE, but could be an important host phase for other elements such as Sr, Ba and K. The acidified hydroxylamine hydrochloride leach is shown here not only to dissolve Fe–Mn oxides but also phosphate minerals, which induces middle REE enrichment in corresponding leachates of dolostone samples in our study. The demonstrable Fe–Mn oxide phase in limestone samples is characterized by middle and/or light REE enrichment and positive Eu anomalies, which are attributed to hydrothermal processes and continuing exchange with marine fluids after initial precipitation. The non-seawater-like REE patterns observed in the carbonate phase of otherwise well-preserved limestones resemble those of the co-existing Fe–Mn oxide fraction, and are interpreted to reflect the dissolution of REE carrier phases during early diagenesis. This view is supported by fluid-rock interaction modelling, which shows how REE can be mobilized at relatively low fluid/rock ratios in shallow porewaters. Non-seawater-like REE patterns may therefore be caused by the incorporation of REE from shallow porewaters before final lithification due to an elevated flux of particulate REE carrier phases, e.g. Fe–Mn oxides and organic matter, to the seafloor. In spite of the sensitivity of carbonate REE patterns to early diagenetic exchange, the co-occurrence of non-seawater-like patterns with primary strontium and carbon isotope values suggests that REE should not be viewed as a general indicator for the preservation of other geochemical proxies. Importantly, Ce anomalies of the carbonate phase will also be affected by porewaters, masking primary seawater values. Our results favour a reevaluation of redox interpretations by taking into account REE patterns as a whole.

Rare earth elements (REEs) behavior in a large river across a geological and anthropogenic gradient

To meet the strong demand for green and digital technologies, the production of rare earth elements (REEs) has increased significantly, yet the fate of REEs (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in large rivers with multiple hydrological, geochemical, and anthropogenic gradients in their catchments remains poorly documented. Here we evaluated the spatial and temporal evolution of the concentrations, patterns, and speciation of REEs in surface waters along a 550 km transect of the St. Lawrence River (SLR) (Canada) and its tributaries from 2017 to 2020. Particulate and filtered (<0.45 µm) REEs concentrations increased downstream, suggesting that REEs found in the SLR predominantly originate from nearby tributaries, especially those draining the REE-rich Canadian Shield geological formation. Moreover, filtered concentrations were significantly higher in years that experienced intense spring freshets, indicating greater influence of runoff and surface soil processes on water chemistry of the SLR. Correlations with terrestrial-DOM, WHAM speciation modelling, and standardized patterns showed REEs speciation dominated by organic colloids, even in alkaline sites with low DOC and low terrestrial inputs. Strong positive correlations with Fe and Al suggested co-transport on organic matter and adsorption on oxyhydroxides. Compared to the influence of water chemistry and geology, the overall influence of anthropogenic inputs was generally low, although we observed an influence of increased erosion on particulate REEs and we measured anthropogenic gadolinium (Gd) at the Montréal wastewater outlet. Our results provide an integrative understanding of the fate of REEs through a geochemical and landscape perspective in one of the largest rivers in North America.

Particulate rare earth element behavior in the North Atlantic (GEOVIDE cruise)

Abstract. Particulate concentrations of the 14 Rare Earth Elements (PREE), yttrium, and 232-thorium were measured in 200 samples collected in the epipelagic (ca. 0–200 m) and mesopelagic (ca. 200–1500 m) zones of the North Atlantic during the GEOVIDE cruise (May/June 2014, R/V Pourquoi Pas?, GEOTRACES GA01), providing the most detailed snapshot of the PREE distribution in the North Atlantic so far. Concentrations of particulate cerium (PCe) varied between 0.2 and 16 pmol L−1, while particulate neodymium (PNd) concentrations ranged between 0.1 and 6.1 pmol L−1. Particulate ytterbium (PYb) concentrations ranged between 0.01 and 0.50 pmol L−1. In addition, this study showed that PREE distributions were also controlled by the biological production in the upper sunlit ocean and by remineralization processes in the mesopelagic area. Low surface concentrations combined with normalized PREE patterns displaying a negative Ce anomaly and HREE enrichments pointed to freshly formed biogenic particles imprinting the seawater signature. A significant relationship between biogenic silica (BSi) and PHREE was also observed in the Labrador and Irminger seas, due to the occurrence of strong diatom blooms at the sampling time. In order to identify dissolved-particulate processes independent of the ionic radius, we used PHo∕PY ratios and showed that absorption processes were predominant in the upper ocean, while adsorption processes dominated at deeper depths. This study highlighted different lithogenic fractions of PREE and dispersion depending on the shelf: off the Iberian margin, up to 100 % of the PREE were determined to have a lithogenic origin. This lithogenic input spread westward along an intermediate nepheloid layer (INL), following isopycnals up to 1700 km away from the margin. In contrast, along the Greenland and Newfoundland margins, the circulation maintained lithogenic inputs of PREE along the coasts.

Solar Radiation as the Likely Cause of Acid-Soluble Rare-Earth Elements in Sediments of Fresh Water Humic Lakes

We studied photochemically induced precipitation of rare-earth elements (REEs) in water from a tributary to Plešné Lake and a tributary to Jiřická Pond, Czech Republic. Both tributaries had high concentrations of dissolved organic matter (∼1.8 mmol C L-1). Filtered (0.2 μm) samples were exposed to artificial solar radiation of 350 W m-2 for 48 to 96 h, corresponding to 3 to 6 days of natural solar radiation in summer at the sampling locations. Experiments were performed with altered and unaltered pH ranging from 3.8 to 6.0. The formation of particulate REEs occurred in all exposed samples with the fastest formation observed at the original pH. The formation of particulate metals continued in irradiated samples after the end of irradiation, suggesting that photochemically induced reactions and/or continuing precipitation continue in darkness or in deeper water due to mixing. Results were compared with paleolimnological records in the Plešné Lake sediment. At pH 5.0, the photochemically induced sediment flux was 3509 nmol m-2 y-1 for Ce, corresponding to 42% of the REEs' annual sediment flux in recent sediment layers. Combining the formation rates obtained in the laboratory irradiation experiments and known 1 day incident solar radiation enabled the estimation of a possible REE sediment flux. For Plešné Lake, the photochemically induced formation of particulate REEs explained 10-44% of the REE concentrations in the upper sediment layers. Observed photochemically induced sequestration of REEs into sediments can explain a significant part of the REEs' history in the Holocene sediment.

Variation of Rare Earth Elements (REEs) in the Sulu and Celebes Seas of Malaysian waters during PMSE 09’ expedition using analytical and chemometric techniques

This study provides a dataset of rare earth elements (REEs) in the seawater of Sulu and Celebes Seas of Malaysian waters during the PMSE 09’ expedition, which was conducted to define the pattern of REEs in both seas. Samples were collected, filtered and pre-concentrated on-board ship then analyzed by using ICP-MS. Generally, the spatial distribution pointed out a high concentration of REEs in vicinities with high number of local settlements and Borneo Island riverine flush-outs. The chemometric analysis has showed the competition of binding sites between REEs and salt ions. The REEs normalized against NPDW evidence the influence of South China Sea waters lessen with the increase in water depth. Additionally, the studied area shows that both seas are affected by local river drainage from Borneo Island, Indonesia and Philippine archipelagos.Keywords: dissolved REEs; particulate REEs; Sulu Sea; Celebes Sea; environmetric analysis

Sources of rare earth elements in shells and soft-tissues of bivalves from Tokyo Bay

Abstract Five species of bivalves (Japanese littleneck, blue mussel, trough shell, Stimpson's quahog, and Japanese dosinia) were collected from three different sites in Tokyo Bay and their shells and soft tissues were analyzed for rare earth element (REE) concentrations. Their REE compositions were compared with those of sediment and seawater at corresponding sites. To estimate the digestive strength of the bivalves, different acids were used to extract the elements in sediment for comparison of REE compositions. The REE concentrations of soft tissues were higher than those of shells. The REE abundance patterns of both shells and soft tissues resembled those of sediments or suspended particles rather than those dissolved in seawater, except for mussels. REE composites calculated by mixing particulate and dissolved REEs at much greater ratios for particulate REEs can explain the REE composition of both shells and soft-tissues. In the case of mussel shells, the contribution of REEs dissolved in seawater is important, but despite this most of mussel REEs similarly originate from suspended particles in seawater. This implies that a simple projection to seawater REEs from the REE composition of shells would be difficult. The apparent partitioning coefficients of REEs over Ca in shells ranged from 0.1 to 10 against REEs/Ca of seawater.

Rare earth elements in the sediments of Lake Baikal

Lake Baikal is the deepest and probably oldest lake on Earth. Its water column is pervasively oxic and sedimentation rates are very low which leads to the formation of a dynamic iron (Fe) and manganese (Mn) enrichment below the Mn(II)/O2 boundary. These often massive accumulations can be buried within the reducing part of the sediments and give rise to complex and cryptic redox cycles. The mobility of rare earth elements (REEs) is influenced by the dissolution and reduction dynamics of the ferromanganese oxides. The present study offers an overview of the REE chemistry in Lake Baikal and its catchment area and more specifically REE distribution in five 11- to 26-cm-long sediment cores situated across the lake at different water depths. We analysed and discussed normalised REE patterns and their consequential cerium (Ce) anomalies. While particulate REE concentrations are mainly influenced by processes above or near the surface of Lake Baikal, such as the development of a widespread negative Ce anomaly, processes occurring during early diagenesis in the sediment are most reflected in pore water REEs. The dissolution of ferromanganese oxides at the Mn(II)/O2 boundary remobilizes significant amounts of REE into the pore water whereby some are likely adsorbed onto colloidal Fe oxides. However, besides the tendency of Ce being associated with Mn-oxides, pore water REEs fractionate predominantly around the buried Fe/Mn accumulation where light REEs preferentially adsorb onto Fe-oxides.

Rare earth elements and Nd isotopes tracing water mass mixing and particle-seawater interactions in the SE Atlantic

Distributions of dissolved and particulate rare earth elements (REEs) and seawater neodymium isotopic composition (εNd) were established in samples from the BONUS GoodHope (BGH) IPY-GEOTRACES cruise in the SE Atlantic sector of the Southern Ocean (36°S-13°E to 57°S-0°, Feb.–Mar. 2008). Close to the South African continent in the subtropical domain, particulate REEs show the highest concentrations and flat PAAS-normalized patterns, clearly tracing their lithogenic origin. Active cerium oxidation onto suspended particles is evidenced by the mirror-image relationship of the cerium anomaly between dissolved and particulate phases. Unradiogenic dissolved neodymium in surface waters (εNd= -17.1) traces the influence of old sedimentary material brought by the Agulhas current and rings to the Cape Basin area. A mass balance calculation suggests that the release of Nd from dissolution of lithogenic material corresponds to a remobilization of 154×106T of sediment per year, i.e., 5% of the total sediment delivered to the southeast African coast annually. At open ocean stations, both dissolved and particulate REEs present negative cerium anomalies, indicating that particles have acquired a marine signature. The increasing REE concentrations with depth, and the strong linear correlations of dissolved REE with silica, indicate that surface removal and deep re-mineralisation of REEs are partially related to the biogeochemical cycle of silicate, which involves biogenic silica (diatoms). Combined with marine carbonates, these authigenic phases could explain the observed REE patterns in suspended particles, except for La. We suggest that the positive La anomalies in both phases are linked to the oceanic barium cycle and the partial dissolution of barite crystals, especially in the Polar Frontal Zone.The εNd composition behaves conservatively in intermediate and deep waters, while input processes affect the isotopic signal of subtropical surface waters and Weddell Gyre bottom waters. An Indian Ocean and an Atlantic variety of AAIW have been isotopically differentiated (εNd=−9.3±0.3 and εNd=−8.0±0.5, respectively). Homogeneous signatures characterize circumpolar waters (εNd from −8.2 to −8.4 for CDW). A binary mixing model has been used to assess the contribution of undiluted NADW reaching southern latitudes.

Using Rare Earth Elements to Control Phosphorus and Track Manure in Runoff

Concern over the enrichment of agricultural runoff with phosphorus (P) from land applied livestock manures has prompted the development of manure amendments that minimize P solubility. In this study, we amended poultry, dairy, and swine manures with two rare earth chlorides, lanthanum chloride (LaCl(3).7H(2)O) and ytterbium chloride (YbCl(3).6H(2)O), to evaluate their effects on P solubility in the manure following incubation in the laboratory as well as on the fate of P and rare earth elements (REEs) when manures were surface-applied to packed soil boxes and subjected to simulated rainfall. In terms of manure P solubility, La:water-extractable P (WEP) ratios close to 1:1 resulted in maximum WEP reduction of 95% in dairy manure and 98% in dry poultry litter. Results from the runoff study showed that REE applications to dry manures such as poultry litter were less effective in reducing dissolved reactive phosphorus (DRP) in runoff than in liquid manures and slurries, which was likely due to mixing limitations. The most effective reductions of DRP in runoff by REEs were observed in the alkaline pH soil, although reductions of DRP in runoff from the acidic soil were still >50%. Particulate REEs were strongly associated with particulate P in runoff, suggesting a potentially useful role in tracking the fate of P and other manure constituents from manure-amended soils. Finally, REEs that remained in soil following runoff had a tendency to precipitate WEP, especially in soils receiving manure amendments. The findings have valuable applications in water quality protection and the evaluation of P site assessment indices.

Elemental characteristics of surface suspended particulates off the Changjiang estuary during the 1998 flood

Surface suspended particulate matter (SPM) samples were collected on two latitudinal transects over the Changjiang estuary, covering a wide salinity regime from 8 to 30‰, instantaneously after the largest Changjiang flood peak in August 1998 that caused severe disaster in China. They have been analyzed for 20 major and trace elements and 7 rare earth elements (REEs) using ICP-MS. The SPM concentrations varied a very wide range of up to two orders of magnitude, sharply decreasing southward from 18 mg/l in the Changjiang river mouth to less than 1 mg/l at around 28°N, which may be representative of a background in the East China Sea (ECS) shelf. All selected particulate elements exhibit large variability in space. SPM collected around the Changjiang river mouth was dominated by the lithogenic components approximately accounting for 80% or more of the bulk, and when going south the proportions decreased to less than half of the total. Based on the results of enrichment factor (EF) calculation, elements Fe, Ti, Mn, Ba, Sr, Co, Be, Tl, Nb, V, Ni, and Mo with mean EF values of less than 3 were categorized into the unpolluted group, and elements Zn, Cu, Pb, As, Ag, and Sb with EF values of higher than 5 into the polluted group. This investigation demonstrated that anthropogenic metals could be dispersed over a large extent along the Chinese coast and on the ECS shelf although a majority of terrigenous sediments would be deposited within the Changjiang estuary. Additionally, our study reveals that the Qiantangjiang might contribute non-negligible pollutants to Hangzhou Bay. We therefore argue that the study area has been in moderate pollution, different from most of previous suggestions. Overall, most samples have similar chondrite- and especially UCC-normalized distribution patterns (UCC: upper continental crust); the sample/UCC ratios of REEs generally vary within a factor of 3 and display a flat (or slightly convex) pattern, essentially revealing little fractionation for particulate REEs. We estimated the import fluxes of particulate metals to the Changjiang estuary during the flood period; our results highlight the significance when compared to the annual fluxes. The study provides an informative data set with respect to SPM compositions in the Changjiang estuary during a catastrophic flood for assessing environmental changes in the future after the Three-Gorges Dam's operation and when the Yangtze Valley is going to be more industrialized and urbanized.

Rare earth elements in the modern sediments of the Bay of Biscay (France)

Particulate rare earth elements (REEs) were measured in modern sediment from the Bay of Biscay. Vertical profiles of total and reactive (ascorbate reducible) REEs have been studied in four contrasted sites ranging at water depth from 150 to 2800 m. The focus is on the coupling between the diagenetic conditions and the behavior of particulate REE. Total REEs fraction appears to be affected by the presence of metal sulphides that may act as an important carrier phase for solid REEs. In sediments where sulphate reduction is weak, the transfer from an unknown previous phase, stable in oxic conditions, to another one associated with sulphides seems to be direct, without mobilization in porewaters. In sediments where greater sulphate reduction occurs, we note the formation of an additional “authigenic” phase. Consequently, a threshold level of dissolved sulphide is a prerequisite for the formation of an additional “authigenic” REEs fraction. No direct relationship between the REE asc profiles and authigenic metal oxides have been observed, indicating that authigenic Fe and Mn oxides do not act as an efficient traps in the sediment. Despite particulate REE are mobile in these sediments, no fractionation of the lanthanide series is observed in relation to the redox conditions.

Rare earth element geochemistry of groundwater in the Palouse Basin, northern Idaho–eastern Washington

Concentrations of rare earth elements (REE) were determined in groundwaters from the Palouse Basin, located in northern Idaho and eastern Washington. Samples were taken from wells and springs tapping waters in four different rock units: loess, Wanapum Basalt, Grande Ronde Basalt, and Moscow Mountain Granite. In general, unfiltered aliquots of the waters had higher concentrations of REE than those filtered through a 0.45 μm filter, sometimes by several orders of magnitude, indicating the presence of REE as suspended particles or large colloids. Overall REE concentrations in the waters decrease, and the unfiltered and filtered aliquots become more similar in concentration, with increasing depth within the stratigraphic section (i.e. loess → Wanapum → Grande Ronde). There are some distinctions in NASC (North American Shale Composite)-normalized REE patterns among the four groups of waters, but there is considerable variation among the waters within each group. When normalized to their host rocks, most filtered and many unfiltered aliquots of groundwaters from all four units show depletion of the LREE relative to the HREE. The results are consistent with a model in which meteoric water enters the basalt aquifers via the loess, picking up a heavy particulate and some dissolved REE load, followed by infiltration downward through the units. While moving downwards, the waters are subjected to natural filtration processes in which the particulate REE are largely removed.

Rare earth elements in suspended particulate material of North Atlantic surface waters

On a transect between the northwest and northeast Atlantic Ocean (30°N/60°W to 60°N/2°W; June/July 1996) suspended particulate material (SPM) in 24 near-surface water samples (4 to 22 m 3 with SPM concentrations between 32 and 447 mg m −3) has been collected using a large volume centrifuge system. The samples have been analyzed for Y, the rare earth elements (REEs), and major inorganic and biogenic carrier phases such as Al (clay), Fe, Mn, POC, opal, and CaCO 3. The concentration pattern of particulate REEs roughly follows the SPM distribution. Average values (pmol l −1) are for Y (2.36), La (0.84), Ce (0.82), Pr (0.17), Nd (0.67), Sm (0.14), Eu (0.030), Gd (0.15), Tb (0.024), Dy (0.16), Ho (0.036), Er (0.12), Tm (0.018), Yb (0.13), and Lu (0.022). Extensive variability in negative Ce anomalies have been observed along our transect, with the strongest anomalies in areas of high POC abundances. Significant fractionation between LREEs and HREEs has been found for all major particulate phases. These data are characterized by (1) strong relationships ( p < 0.001) exist between concentrations of nonlithogenic (excess) HREEs (Tb–Lu) and POC values indicating that complexation with organic ligands promotes (temporary) HREE enrichment on solid surfaces. (2) The behavior of particulate Fe and Mn fractions is decoupled. While Fe and Al (clay) phases exhibit preferential uptake of LREEs (La–Gd) with crust-like signatures, particulate excess Mn is strongly coupled to the POC phase ( R 2 = 0.82) and to excess HREEs. We, therefore, suggest that the enrichment of REEs in Mn particles occurs via the formation of biogenic material (probably mediated by bacteria) and is not caused by adsorption onto Mn–oxihydroxides. Another result is that Y, in all studied relationships with the major inorganic and biogenic phases, is very similar to Ho implying their chemistries in surface ocean particulates are dominated by similar valency and ionic radii. The Y/Ho ratios (average of 69 ± 7 mol mol −1) have been very constant along our transect, and lie in between the ratios for seawater (100) and continental crust (50).

Temporal variations in the fractionation of the rare earth elements in a boreal river; the role of colloidal particles.

Rare earth element (REE) data from weekly sampling of the filtered (<0.45 μm) and suspended particulate phase during 18 months in the Kalix River, Northern Sweden, are presented together with data on colloidal particles and the solution fraction (<3 kDa). The filtered REE concentration show large seasonal and temporal variations in the river. Lanthanum varied between approximately 300 and 2100 pM. High REE concentration in the filter-passing fraction is related to increased water discharge and there is a strong correlation between the REE concentration, organic carbon, Al and Fe. Physical erosion of detrital particles plays a minor role for the yearly transport of particulate REE in this boreal river system. The suspended particulate fraction, which is dominated by non-detrital fractions, accounted for only 35% of the yearly total transport of La in the river. Approximately 10% of the REE were transported in detrital particles during winter. At spring-flood in May, about 30% of the LREE and up to 60% of the HREE where hosted in detrital particles. Ultrafiltration of river water during spring-flood shows that colloidal particles dominate the transport of filter-passing REE. Less than 5% of the filtered REE are found in the fraction smaller than 3 kDa. The colloidal fraction shows a flat to slightly LREE enriched pattern whereas the solution fraction (<3 kDa) show an HREE enriched pattern, compared with till in the catchment. Suspended particles show a LREE enriched pattern. Data indicate that the REE are associated with two phases in the colloidal (and particulate) fraction, an organic-rich phase (with associated Al–Fe) and an Fe-rich (Fe–oxyhydroxide) inorganic phase. The Ce-anomaly in the suspended particulate fraction in the river shows systematic variations, and can be used to interpret fractionation processes of the REE during weathering and transport. There was no anomaly at maximum spring-flood but during the ice-covered period the anomaly became more and more negative. The temporal and seasonal variations of the Ce-anomaly in the suspended particulate phase reflect transport of REE–C–Al–Fe-enriched colloids from the upper section of the till (and/or from mires) to the river at storm events.

Behaviour of rare earth elements at the freshwater–seawater interface of two acid mine rivers: the Tinto and Odiel (Andalucia, Spain)

The concentrations of dissolved and suspended particulate rare-earth elements (REE) are reported in acid-sulphate waters from the Odiel and Tinto rivers. Shale normalized patterns are typically convex and high REE concentrations (e.g., Ce=0.43–65 μg.l −1) are present in the waters. The REE content of the suspended load is greater by a factor of up to 3000. In the Odiel river, REE patterns of the particulates are essentially convex and sub-parallel to those of the waters; speciation calculations indicate that SO 4 complexes play a dominant role in controlling the REE distributions. In the Tinto river, the REE patterns of the suspended load are slightly fractionated and a negative Ce anomaly is apparent in several samples, reflecting the local influence of phosphogypsum deposits. Contrasting with normal estuaries, REE are not intensely removed in the low chlorinity zone. A remobilization in relation to Fe reduction is observed in the Tinto river.

Distribution ratio of dissolved and particulate REE in surface coastal seawater.

Dissolved and particulate forms of rare earth elements (REE) in the surface seawater of coastal area were separately determined with Inductively Coupled Plasma ion source Mass Spectrometry (ICP-MS) in order to discuss the REE partitioning between them. Two different samples were prepared on the occasion of each sampling: one sample was acidified before it was filtrated (AF) and another sample was acidified after filtrated (FA). On the two samples (AF and FA) we measured the REE abundances of the filtrate and the collected matter on the filter separately. In either sample, the filtrate showed a “W type tetrad effect”-like variation in the chondrite normalized REE pattern. The partitioning pattern of sample FA shows a clearer “W type tetrad effect”-like variation than that of sample AF, indicating that “labile” showed a “M type tetrad effect”-like variation. Besides Ce anomaly, anomalous behavior of Tb has been observed in the filtrate of the sample FA. Th in the collected shows rather capricious behavior.

Rare earth element distributions in anoxic waters of the Cariaco Trench

The concentrations of dissolved and suspended particulate rare earth elements in the Cariaco Trench are reported. In solution all REE, notably Ce, show a sharp increase just at or below the oxic anoxic interface at 300 meters depth. Particulate concentrations show a complementary decrease at the same depth. The overlying oxic waters exhibit a negative Ce anomaly; the anoxic waters carry a slightly positive Ce anomaly. The particulate Ce anomaly reaches a maximum just above the interface, coinciding with maxima for particulate Mn and Fe and minima for the dissolved Ce anomaly and dissolved Ce, Mn and Fe. Thermodynamic calculations predict that the solubility of Ce(IV)O 2 is greatly enhanced by the steep pϵ-drop at the O 2 H 2S interface whereas oxygenated seawater is grossly oversaturated with dissolved Ce(III). However, the dramatic shifts in pe and absolute total Ce concentration do not affect the relative speciation of Ce in solution, which varies only with pH and not with pϵ because dissolved Ce(IV)-species are negligible. The cycling of Ce across the oxic anoxic boundary is driven largely by its own redox chemistry as with Fe and Mn. The remaining REE, being strictly trivalent, are recycled in association with the dissolution-precipitation of (ferro)manganese oxyhydroxides. The relative turnover rates at the interface are ranked as Mn > Ce = Ce-anomaly > Nd, Sm, Eu, La, Dy, Er . The observed absence of Eu anomalies would render in situ reduction of Eu(III) to Eu(II) unlikely; thermodynamic considerations also rule out the existence of Eu(II) species in low temperature reducing environments.

An application of the activable multiple air tracer for the land and sea breeze experiment.

To study the atmospheric turbulent diffusion and transport of air pollutants, the air tracer technique is an effective means, and several kinds of air tracer material such as sulfur hexafluoride and fluorescent particles have been developed up to now. However, it is difficult to see how much is contributed by the emissions of the respective pollutants to the receptors, and to know the complex transport processes of the tagged air parcels, by simultaneously using these air tracers. Such being the case, a multiple air tracer system has been demanded. Therefore, we applied the activable multiple air tracer method (AMAT system) to the investigation of the land and sea breeze. The AMAT system is that the particulate rare-earth elements are released into the atmosphere with pressurized air through the atomizer as air tracers and collected on filter paper; the samples collected are analyzed quantitatively by the neutron activation technique. The AMAT system is based on the principle that the field experiment with multiple air tracers can be conducted easily by selecting the elements with the suitable characteristics. As the elements, Eu, Dy, Ho and Lu are appropriate. In a comparison experiment between the AMAT and SF6, we could find that there was no discernible difference in the concentration between the AMAT and SF6, with small exceptions. Furthermore, we could get a good agreement between the predicted and the observed concentration of the AMAT in the Niihama Experiment.