Marine Primary Productivity as a Potential Indirect Source of Selenium and Other Trace Elements in Atmospheric Deposition

Machine learning-assisted source tracing in domestic-industrial wastewater: A fluorescence information-based approach

An emergency water pollution incident poses a significant risk to the proper functioning of wastewater treatment plants, particularly in domestic-industrial integrated facilities. Source tracing is recognized as an effective method to mitigate ongoing impacts. Machine learning-assisted traceability is emerging as a more efficient and faster method compared to traditional methods. In this study, a total of 712 sets of characterization wastewater information from effluent samples from14 discharge enterprises across 6 different sectors, as well as domestic wastewater was collected using 3-dimensional fluorescence spectroscopy. After data cleaning and augmentation, a feature fingerprint database of wastewater was constructed to train a traceability model. Several machine learning algorithms, including Back Propagation neural network (BP), Random Forest (RF), Support Vector Machine (SVM), Naive Bayes (NB) and K-Nearest Neighbors (KNN), were selected for constructing the traceability framework. Subsequently, an advanced Particle Swarm Optimization Random Forest model (PSO-RF), capable of automatically optimizing model parameters, was proposed and applied to trace the sources of wastewater in integrated wastewater treatment plant. The PSO-RF achieved and accuracy of 96.55 % in sector identification and 94.25 % in manufacturer identification. As part of the validation process, laboratory simulations were conducted using blended wastewater with different volume ratios of domestic and industrial wastewater to evaluated the potential application of PSO-RF. The results consistently demonstrated PSO-RF's effectiveness, particularly in tracing pharmaceutical wastewater sources, maintaining an accuracy of over 85 %. This work presents a novel strategy for tracing abnormal sources during emergency pollutant incidents, providing essential support for integrating artificial intelligence (AI) into meticulous wastewater management.

Reactions of hypobromous acid with dimethyl selenide, dimethyl diselenide and other organic selenium compounds: kinetics and product formation

Selenium (Se) is an essential micronutrient for many living organisms particularly due to its unique redox properties. We recently found that the sulfur (S) analog for dimethyl selenide (DMSe), i.e. dimethyl sulfide (DMS), reacts fast with the marine oxidant hypobromous acid (HOBr) which likely serves as a sink of marine DMS. Here we investigated the reactivity of HOBr with dimethyl selenide and dimethyl diselenide (DMDSe), which are the main volatile Se compounds biogenically produced in marine waters. In addition, the reactivity of HOBr with further organic Se compounds was tested, i.e., SeMet (as N-acetylated-SeMet), and selenocystine (SeCys2 as N-acetylated-SeCys2), as well as the phenyl-analogs of DMSe and DMDSe, respectively, diphenyl selenide (DPSe) and diphenyl diselenide (DPDSe). Apparent second-order rate constants at pH 8 for the reactions of HOBr with the studied Se compounds were (7.1 ± 0.7) × 107 M-1 s-1 for DMSe, (4.3 ± 0.4) × 107 M-1 s-1 for DMDSe, (2.8 ± 0.3) × 108 M-1 s-1 for SeMet, (3.8 ± 0.2) × 107 M-1 s-1 for SeCys2, (3.5 ± 0.1) × 107 M-1 s-1 for DPSe, and (8.0 ± 0.4) × 106 M-1 s-1 for DPDSe, indicating a very high reactivity of all selected Se compounds with HOBr. The reactivity between HOBr and DMSe is lower than for DMS and therefore this reaction is likely not relevant for marine DMSe abatement. However, the high reactivity of SeMet with HOBr suggests that SeMet may act as a relevant quencher of HOBr.

Hg and Se in Muscle and Liver of Blue Shark (Prionace glauca) from the Entrance of the Gulf of California: An Insight to the Potential Risk to Human Health

The blue shark (Prionace glauca) is the most commonly caught species of Elasmobranchii at the entrance to the Gulf of California. Although fins are the primary target commodity, the entire organism is consumed. This study examined the concentration of Hg and Se in muscle and liver to understand the antagonistic process that occurs between these two elements within the organism. Twenty-two individuals were captured at the Gulf of California inlet between September 2019 and March 2021. Hg was measured by cold vapor atomic absorption, and Se by atomic absorption spectrophotometry in a graphite furnace. All individuals studied showed higher concentrations (µg g-1 wet weight) of Hg (0.69) and Se (2.49) in liver than in muscle (Hg 0.63 and Se 0.08). Although the mean Hg values were below the maximum allowable limits (Hg 1.0 µg g-1 wet weight), the molar ratio (< 1.0) and the negative health benefit value of selenium (HBVSe) in muscle show that additional caution should be taken when consuming this species. We recommend a more thorough study of the antagonistic interaction between Hg and Se to accurately assess the health risk for consumers of blue shark.

Assessing the Intensity of Marine Biogenic Influence on the Lower Atmosphere: An Insight into the Distribution of Marine Biogenic Aerosols over the Eastern China Seas

Marine biological activities make a non-negligible contribution to atmospheric aerosols, leading to potential impacts on the regional atmospheric environment and climate. The eastern China seas are highly productive with significant emissions of biogenic substances, but the spatiotemporal variations of marine biogenic aerosols are not well known. Air mass exposure to chlorophyll a (AEC) can be used to indicate the influence of biogenic sources on the atmosphere to a certain degree. In this study, the 12 year (2009-2020) daily AEC were calculated over the eastern China seas, showing the spatial and seasonal patterns of marine biogenic influence intensity which were co-controlled by surface phytoplankton biomass and boundary layer height. By combining the AEC values, relevant meteorological parameters, and extensive observations of a typical biogenic secondary aerosol component, methanesulfonate (MSA), a parameterization scheme for MSA simulation was successfully constructed. This AEC-based approach with observation constraints provides a new insight into the distribution of marine biogenic aerosols. Meanwhile, the wintertime air mass retention over land exhibited a significant decrease, showing a decadal weakening trend of terrestrial transport, which is probably related to the weakening of the East Asian winter monsoon. Thus, marine biogenic aerosols may play an increasingly important role in the studied region.

Regional Sources and Sinks of Atmospheric Particulate Selenium in the United States Based on Seasonality Profiles

Selenium (Se) is an essential nutrient for humans and enters our food chain through bioavailable Se in soil. Atmospheric deposition is a major source of Se to soils, driving the need to investigate the sources and sinks of atmospheric Se. Here, we used Se concentrations from PM_2.5 data at 82 sites from 1988 to 2010 from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network in the US to identify the sources and sinks of particulate Se. We identified 6 distinct seasonal profiles of atmospheric Se, grouped by geographical location: West, Southwest, Midwest, Southeast, Northeast, and North Northeast. Across most of the regions, coal combustion is the largest Se source, with a terrestrial source dominating in the West. We also found evidence for gas-to-particle partitioning in the wintertime in the Northeast. Wet deposition is an important sink of particulate Se, as determined by Se/PM_2.5 ratios. The Se concentrations from the IMPROVE network compare well to modeled output from a global chemistry-climate model, SOCOL-AER, except in the Southeast US. Our analysis constrains the sources and sinks of atmospheric Se, thereby improving the predictions of Se distribution under climate change.

Watershed seasonality regulating vanadium concentrations and ecological risks in the coastal aquatic habitats of the northwest Pacific

Vanadium is a component of different natural and industrial products and a widely used metal, which, nonetheless, has only garnered attention in recent years owing to its potential risks. Six sampling trips were conducted over different seasons and years, collecting 108 samples from rivers and 232 from the bays and analyzed using high-precision inductively coupled plasma mass spectrometry. This study investigated the sources, spatiotemporal characteristics, and risks of vanadium in the aquatic ecosystems of two typical bays of the Northwest Pacific that have strong links with vanadium-related industries. Likewise, the health and ecological risks were assessed using probabilistic and deterministic approaches. Overall, vanadium concentrations were higher in Jiaozhou Bay (JZB: 0.41-52.7 μg L^-1) than in Laizhou Bay (LZB: 0.39-17.27 μg L^-1), with concentrations higher than the majority of the worldwide studies. Vanadium-realted industries significantly impacted (p < 0.05) the metal concentrations in the rivers with 54.22% (40.73-150%) and 54.45% (27.66%-68.87%) greater concentrations in JZB and LZB rivers. In addition, vanadium exhibited significant seasonal variation, and higher values were quantified during the monsoon period at LZB owing to the greater catchment area. Impacted by smaller freshwater inputs, the post-monsoon period had substantial impacts on JZB, and vanadium in the rivers and bays was significantly higher during the winter. Despite some concentrations being higher than that indicated in the drinking water guidelines established by China, vanadium presents low to null risks to the population as per both approaches. Last, species with limited resilience are likely to face medium to high risks, with an incidence of 65-93% using the probabilistic method and 52-97% using the deterministic assessment.

Vertical distribution and major influencing factors of soil selenium in tropical climate: A case study of Chengmai County, Hainan Island

Soil selenium is of great significance to human health. Soil-forming parent rocks are the most critical factor that influences soil Se levels. Chengmai County, Hainan Island, has a tropical climate and diverse types of parent rocks, in which soil Se content is high. This study investigated the vertical distribution of soil Se from various parent rock substrates under tropical climatic conditions, and the factors that influence these soil Se contents, with 69 vertical soil profiles covering Chengmai County. The vertical distribution of soil Se and correlations with CIA (chemical alteration index), Al₂O₃, TFe₂O₃ (total iron oxide expressed as Fe₂O₃), total iodine, SOC (soil organic carbon), and pH were analysed. As per the results, the mean ± standard error of Se content in the A, B, and C horizons was 0.88 ± 0.13 mg/kg, 0.77 ± 0.08 mg/kg and 0.45 ± 0.05 mg/kg, respectively. The parent rock strictly controlled the horizon distribution of Se in the A-horizon. Soil Se showed A-B-horizons-enrichment in the vertical profile, especially in soil profiles overlying granite and basalt. It is hypothesised that the Se enriched in soils developed from the Tuolie Formation due to the release of Se from the weathering process of Se-rich rocks. Meanwhile, Se in soils developed from granite and basalt is more closely associated with exogenous input. Another crucial factor for the high level of Se in Chengmai County is the tropical climate, which has led the rocks to generally undergo intense chemical weathering. This results in soils rich in clay minerals and Fe/Al oxyhydroxides, which easily absorb and retain Se. Furthermore, the Se content of the B-horizon was generally higher than that of the A-horizon due to leaching. These results provide further knowledge and understanding of the geochemical behaviour of soil Se and guide the evaluation of Se-rich land resources under tropical climatic conditions.

Selenium distribution and speciation in waters of pristine alpine lakes from central-western Pyrenees (France-Spain)

The speciation of both redox reactive and volatile selenium (Se) compounds, barely reported in pristine aquatic environments, has never been investigated in remote alpine lakes, considered as sensitive ecosystems to detect the effect of global change. This work presents an integrated investigation on Se distribution and speciation conducted in 20 high altitude pristine lakes from the central-western Pyrenees. Five seasonal sampling campaigns were carried out after snowmelt (June/July) and in early fall (October) for the period 2017-2019. Concentrations of total dissolved Se (TDSe) ranged from 7 to 78 ng L^-1, with selenate being ubiquitously observed in most cases (median of 61% of TDSe). Selenite was only occasionally detected up to 4 ng L^-1, therefore a fraction of TDSe was presumably in the forms of elemental Se(0) and/or selenides. Depth profiles obtained in different lakes showed the occurrence of such Se(-II, 0) pools in bottom hypoxic to anoxic waters. The production of volatile Se compounds presented a low median total concentration (TVSe) of 33 pg L^-1 (range 3-120 pg L^-1), mainly in the form of dimethylselenide in subsurface samples (median of 82% of TVSe). The Se concentration in lake waters was significantly correlated with the sulphate concentration (ρ = 0.93, p < 0.0001), demonstrating that it is influenced by erosion and dissolution of Se and S-enriched parent bedrocks. In addition, for Se depleted alpine lake-bedrock systems, long-range transport and wet atmospheric depositions represent a major source of Se for lake waters.

Spatial distribution and environmental impact factors of soil selenium in Hainan Island, China

Selenium is an essential micronutrient for the human body, given its various health benefits. However, Se deficiency is widespread globally, and dietary adjustment is a feasible way to supplement people's Se daily intake. The Multi-purpose Regional Geochemical Survey (NMPRGS) conducted in Hainan Island found an abundance of Se-rich soil. These Se resources have been utilized to grow naturally Se-rich produce. However, insufficient research has been conducted into the spatial distribution and enrichment of soil Se in Hainan Island. This paper analysed the effect of the environmental impact factors (parent rock, precipitation, etc.) on soil Se, using data from the NMPRGS database. The results showed that, in comparison to the baseline value of Chinese soil, the enrichment degree of Se in the topsoil of Hainan Island was higher, but its distribution was uneven. The parent rock, precipitation, soil type, and soil characteristics all affect the concentration and spatial distribution of regional soil Se. Geographically weighted regression showed that Iodine, pH, SOC, and TFe₂O₃ have a non-stationarity spatial relationship with Se. There was a significant correlation between soil Se and Chemical alteration index (CIA) in granite areas, while CIA was also related to mean annual precipitation (MAP). The concentration enrichment factor values of Se show that the external input of Se in high MAP areas is significantly higher than that in low MAP areas. Based on these results, three important environmental impact factors on soil Se enrichment at the regional scale in Hainan Island were defined: 1) Se-rich rocks; 2) precipitation; 3) SOC. These results can provide guidance for the planning and layout of Se-rich agriculture.

Selenium in Soil-Plant-Microbe: A Review

Selenium (Se) plays an important role in geochemistry and is an essential trace element for humans and animals. This review summarizes the transformation and accumulation of Se in the plant-soil-microbe system. As one of the important reservoirs of Se, soil is an important material basis of its entry into the food chain through plants. Soil with an appropriate amount of Se is beneficial for plant growth and plays a valuable role in a stress-resistant environment. Among the many migration and transformation pathways, the transformation of Se by microorganisms is particularly important and is the main form of Se transformation in the soil environment. In this review, the role and form transformation of Se in plants, soil, and microorganisms; the role of Se in plants; the form, input, and output of Se in soil; the absorption and transformation of Se by plants; and the role of microorganisms in Se transformation are presented. In addition to describing the migration and transformation laws of Se in the environment, this review expounds on the main directions and trends of Se research in the agricultural field as well as current gaps and difficulties in Se-related research. Overall, this reviews aims to provide necessary information and theoretical references for the development of Se-rich agriculture.

The Pedosphere as a Sink, Source, and Record of Anthropogenic and Natural Arsenic Atmospheric Deposition

The Anthropocene has led to global-scale contamination of the biosphere through diffuse atmospheric dispersal of arsenic. This review considers the sources arsenic to soils and its subsequent fate, identifying key knowledge gaps. There is a particular focus on soil classification and stratigraphy, as this is central to the topic under consideration. For Europe and North America, peat core chrono-sequences record massive enhancement of arsenic depositional flux from the onset of the Industrial Revolution to the late 20th century, while modern mitigation efforts have led to a sharp decline in emissions. Recent arsenic wet and dry depositional flux measurements and modern ice core records suggest that it is South America and East Asia that are now primary global-scale polluters. Natural sources of arsenic to the atmosphere are primarily from volcanic emissions, aeolian soil dust entrainment, and microbial biomethylation. However, quantifying these natural inputs to the atmosphere, and subsequent redeposition to soils, is only starting to become better defined. The pedosphere acts as both a sink and source of deposited arsenic. Soil is highly heterogeneous in the natural arsenic already present, in the chemical and biological regulation of its mobility within soil horizons, and in interaction with climatic and geomorphological settings. Mineral soils tend to be an arsenic sink, while organic soils act as both a sink and a source. It is identified here that peatlands hold a considerable amount of Anthropocene released arsenic, and that this store can be potentially remobilized under climate change scenarios. Also, increased ambient temperature seems to cause enhanced arsine release from soils, and potentially also from the oceans, leading to enhanced rates of arsenic biogeochemical cycling through the atmosphere. With respect to agriculture, rice cultivation was identified as a particular concern in Southeast Asia due to the current high arsenic deposition rates to soil, the efficiency of arsenic assimilation by rice grain, and grain yield reduction through toxicity.

Atmospheric iodine, selenium and caesium depositions in France: I. Spatial and seasonal variations

The spatial distribution and seasonal variations of atmospheric iodine (I), selenium (Se) and caesium (Cs) depositions remain unclear and this precludes adequate inputs for biogeochemical models. We quantified total concentrations and fluxes of these elements in rainfalls from 27 monitoring sites in France with contrasted climatic conditions; monthly measurements were taken over one year (starting in 2016/09). Since speciation of I and Se can impact their behaviour in the environment, analysis of their inorganic compounds was also conducted. Our results showed that annual I concentrations in rainfall were much higher than those of Se and Cs (annual means = 1.56, 0.044 and 0.005 μg L^-1, respectively). The annual iodine concentrations were highly positively correlated with those of marine elements (i.e. Na, Cl and Mg), involving higher I concentrations under oceanic climate than for transition, continental and mountainous ones. Furthermore, common patterns were found between Se concentrations and both marine and terrestrial components consistent with the various sources of Se in atmosphere. The association of Cs with two anthropogenic components (i.e. NH₄⁺ and NO₃^-) used in agriculture supports the hypothesis of its terrestrial origin (i.e. from atmospheric dusts) in rainfall. We found higher rainfall concentrations of I during the warmest months for all climates. However, no specific seasonal trend occurred for Se and Cs. On annual average, rainfall contained mostly unidentified selenium compounds (inorganic Se proportions = 25-54%) and equal proportions of inorganic and unidentified I compounds. Concentrations of iodate were higher under oceanic climate consistent with an iodine marine-origin.

Selenium volatilization from tundra soils in maritime Antarctica

Maritime Antarctica harbors a large number of penguins and seals that provide considerable input of selenium (Se) originating as guano into terrestrial ecosystems. Subsequent Se emissions via biomethylation and volatilization from these sources of Se have not been studied. Here, penguin colony soils (PCS) and adjacent tundra marsh soils (TMS), seal colony soils (SCS) and adjacent tundra soils (STS), and normal upland tundra soils (NTS) were collected in maritime Antarctica. For the first time, Se volatilization and speciation were investigated in these soils through incubation experiments using chemo-trapping method. The Se contents in PCS, SCS, STS and TMS were highly enriched compared with NTS, with organic matter-bound Se accounting for 70%-80%. Laboratory incubations yielded the greatest Se volatilization rates (VR_Se) in PCS (0.20 ± 0.01 μg kg^-1 d^-1), followed by SCS (0.14 ± 0.01 μg kg^-1 d^-1) at low temperature (4 °C). Soil frozen-thawing induced 1-4 fold increase in VR_Se, and the VR_Se continuously increased until the soils fully thawed. The VR_Se showed a significant positive correlation (R² = 0.96, p < 0.01) with soil temperature. Methylated Se species were dominated by dimethylselenide (DMSe) in PCS and dimethyldiselenide (DMDSe) in SCS. Our results imply that the combination of climate warming, frozen-thawing processes, and high-Se inputs from sea animals will significantly increase tundra soil Se volatilization in maritime Antarctica. High VR_Se from penguin colony soils, and significantly elevated Se levels in the mosses close to penguin colony, suggest that volatilization of Se from penguin colony soils play an important role in the mobilization and regional biogeochemical cycling of Se in maritime Antarctica.

Determination of oxoanions and water-soluble species of arsenic, selenium, antimony, vanadium, and chromium eluted in water from airborne fine particles (PM2.5): effect of acid and transition metal content of particles on heavy metal elution

Heavy metals in particulate matter (PM) are of great concern, and their effects on the environment and human health depend on their solubilities and species present. In this study, the solubility of As, Se, Sb, V and Cr and their species eluted in water was investigated. As, Se, Sb, and V were present mostly in fine particles, and they were predominantly water-soluble in fine particles (<2.5 μm, PM_2.5) but insoluble in coarse particles (>2.5 μm). Solubility of Cr was poor even in fine particles. It was found that for fine particles, solubilities of the heavy metals were related to the nitrate and sulfate contents. This suggests that the higher the acidity of the particles, the higher the solubility of the heavy metals. Oxoanions of the five kinds of heavy metals in water extracts of fine particles were determined by inductively coupled plasma mass spectrometry preceded by ion chromatography. The results suggested the presence of atmospheric oxidation during the aerosol transportation. Also, the As(iii)/As(v) (arsenite/arsenate) ratios for the fine particle extracts were related to the transition metal concentrations, which indicated that Fe, Cu, etc. in fine particles affected the As redox equilibrium. It was suggested that the heavy metals exist as complexes with iron hydroxide and dissolved organic matter in addition to the free oxoanions. These investigations were performed for PM samples collected in winter and summer in Kumamoto, west Japan, where the site is strongly exposed to westerly winds from continental East Asia. The obtained results improve our understanding of the behavior of the heavy metals in airborne PM after depositing on a wet environment and biota.

Exposure to Dimethyl Selenide (DMSe)-Derived Secondary Organic Aerosol Alters Transcriptomic Profiles in Human Airway Epithelial Cells

Dimethyl selenide (DMSe) is one of the major volatile organoselenium compounds released from aquatic and terrestrial environments through microbial transformation and plant metabolism. The detailed processes of DMSe leading to secondary organic aerosol (SOA) formation and the pulmonary health effects induced by inhalation of DMSe-derived SOA remain largely unknown. In this study, we characterized the chemical composition and formation yields of SOA produced from the oxidation of DMSe with OH radicals and O₃ in controlled chamber experiments. Further, we profiled the transcriptome-wide gene expression changes in human airway epithelial cells (BEAS-2B) after exposure to DMSe-derived SOA. Our analyses indicated a significantly higher SOA yield resulting from the OH-initiated oxidation of DMSe. The oxidative potential of DMSe-derived SOA, as measured by the dithiothreitol (DTT) assay, suggested the presence of oxidizing moieties in DMSe-derived SOA at levels higher than typical ambient aerosols. Utilizing RNA sequencing (RNA-Seq) techniques, gene expression profiling followed by pathway enrichment analysis revealed several major biological pathways perturbed by DMSe-derived SOA, including elevated genotoxicity, DNA damage, and p53-mediated stress responses, as well as downregulated cholesterol biosynthesis, glycolysis, and interleukin IL-4/IL-13 signaling. This study highlights the significance of DMSe-derived SOA as a stressor in human airway epithelial cells.

Maritime Deposition of Organic and Inorganic Arsenic

The speciation of arsenic in wet and dry deposition are ambiguously described in current literature. Presented here is a 2 year study quantifying arsenic species in atmospheric deposition collected daily from an E. Atlantic coastal, semirural site, with comparative urban locations. Inorganic arsenic (As_i) was the principal form of arsenic in wet deposition, with a mean concentration of 0.54 μmol/m³. Trimethylarsine oxide (TMAO) was found to be the dominant form of organic arsenic, determined as above the LoD in 33% of wet deposition samples with a mean concentration of 0.12 μmol/m³. Comparison with codeposited trace elements and prevailing weather trajectories indicated that both anthropogenic and marine sources contribute to atmospheric deposition. Analysis of dry deposition revealed it to be a less significant input to the land-surface for As_i, contributing 32% of that deposited by wet deposition. Dry deposition had a larger proportion of As_i than that found in wet deposition, with TMAO making up only 12% of the sum of species. In comparison, urban sites showed large spatial and temporal variations in organic arsenic deposition, indicating that local sources of methylated species may be likely and that further understanding of biogenic arsine evolution and degradation are required to adequately assess the atmospheric arsenic burden and subsequent contribution to terrestrial ecosystems.

Source apportionment of selenium and influence factors on its bioavailability in intensively managed greenhouse soil: A case study in the east bank of the Dianchi Lake, China

Selenium (Se) is an essential trace element for humans and animals. In China, intensive agricultural inputs in greenhouse vegetable production (GVP) have resulted in great changes in Se concentration and bioavailability in soil, which have great influences on Se flux to living organisms through food chains. It is crucial to understand the factors on Se concentration and bioavailability in greenhouse soil. Thus, we chose the east bank of the Dianchi Lake, a typical GVP area covering 177 km² in Southwest China, as the study area to quantify source contributions to soil Se and estimate relative importance of influence factors on its bioavailability in GVP with a receptor model (absolute principal component scores-multiple linear regression, APCS-MLR) after principal component analysis (PCA). According to the enrichment factor (EF), total Se in greenhouse soil was accumulated at a minor level (1 < EF < 3) by long-term and intensive fertilization. Source contributions to total Se decreased in the sequence of parent materials > fertilization > atmospheric deposition. It suggested that fertilization, especially manure, might be an important way to increase total Se in greenhouse soils in Se-deficient areas. The bioavailability of Se was affected by several factors, among of which total Se was the foremost one. In comparison with organic matter and clay, Fe/Al oxides exerted more controls on Se bioavailability, which was dependent on pH. Increasing Olsen P was helpful in improving soil Se bioavailability in greenhouse. More attention should be paid to soil physicochemical characteristics when Se-containing fertilizers are applied to increase Se levels in greenhouse vegetables.

Marine versus Continental Sources of Iodine and Selenium in Rainfall at Two European High-Altitude Locations

The essential elements selenium (Se) and iodine (I) are often present in low levels in terrestrial diets, leading to potential deficiencies. Marine I and Se emissions and subsequent atmospheric wet deposition has been suggested to be an important source of I and Se to soils and terrestrial food chains. However, the contribution of recycled moisture of continental origin to I and Se to precipitation has never been analyzed. Here we report concentrations and speciation of I and Se, as well as of bromine (Br), sulfur (S), and DOC-δ¹³C signatures for weekly collected precipitation samples (in the period of April 2015 to September 2016) at two high altitude sites, i.e., Jungfraujoch (JFJ; Switzerland) and Pic du Midi (PDM; France). Analysis of precipitation chemistry and moisture sources indicate combined marine and continental sources of precipitation and Se, I, Br, and S at both sites. At JFJ, concentrations of I and Se were highest when continental moisture sources were dominant, indicating important terrestrial sources for these elements. Furthermore, correlations between investigated elements and DOC-δ¹³C, particularly when continental moisture source contributions were high, indicate a link between these elements and the source of dissolved organic matter, especially for I (JFJ and PDM) and Se (JFJ).

Metal wet deposition in the Three Gorges Reservoir (TGR) region of Southwest China

Metal wet deposition has become an environmental concern because of its threats to soil or water quality and human health. This study was to collect rainfall waters in 2016 from seven sites, representing urban, town, rural, and wetland, within the Three Gorges Reservoir (TGR) region of Southwest China, determine the metal concentration and flux (Zn, Mn, Cu, As, Cd, Pb), and identify their possible sources. Results indicated that Zn was the most abundant metal with a concentration of 16.92 μg L^-1 in fall and 19.91 μg L^-1 in winter and flux of 4.71 mg m^-2 in fall, while Cd was the least with a monthly mean concentration of 0.02-0.37 μg L^-1. Among the seven sites, urban (FL) had the highest values of both concentrations of metals (Zn, Cu, Pb) and fluxes of metals (Mn, As), which significantly differed from the other sites. Component and redundancy analysis suggested that fossil fuel and biomass combustion be a potential metal source. Enrichment factors, box model, and potential ecological risk index showed that the TGR water quality could face a high risk due to wet metal deposition, especially Cd. Data could provide a valuable aid in mitigating metal pollution, developing the best watershed management practices, as well as safeguarding water quality and human health in the TGR region or other reservoir regions.

Biovolatilization of Arsenic as Arsines from Seawater

Marine sources of arsenic to the atmosphere are normally dismissed as minor. Here we show that arsenic can be biovolatilized from seawater, and that biovolatilzation is based on organic arsenic species present in the seawater. Even though inorganic arsenic is in great excess in seawaters, it is trimethylarsine (TMA) that is the primary biovolatilized product, with dimethylarsine (DMA) also observed if dimethylarsinic acid (DMAA) is spiked into seawaters. With respect to budgets, 0.04% of the total arsenic in the seawater was biovolatilized over a 2-week incubation period. To test the environmental significance of this finding, wet deposition was analyzed for arsenic species at coastal locations, one of which was the origin of the seawater. It was found that the oxidized product of TMA, trimethylarsine oxide (TMAO), and to a less extent DMAA were widely present. When outputs for arsines (0.9 nmol/m²/d) from seawater and inputs from wet deposition (0.3-0.5 nmol/m²/d) were compared, they were of the same order of magnitude. These findings provide impetus to reexamining the global arsenic cycle, as there is now a need to determine the flux of arsines from the ocean to the atmosphere.

Atmospheric deposition of trace elements to Daya Bay, South China Sea: Fluxes and sources

This study was conducted from October 2015 to March 2017, with the aim of providing the first data on the fluxes and sources of wet and dry deposition of trace elements (TEs) in Daya Bay, South China Sea. Wet deposition flux of TEs was always preponderant and orders of magnitude higher than that of dry deposition owing to the high rainfall frequency in Daya Bay. The total deposition fluxes of TEs in the target area were higher than in most places worldwide, but at a moderate level within China. Wet deposition was highest in summer and lowest in winter, whereas dry deposition showed an opposite seasonal trend. The main sources of TEs in wet deposition were seasalt/dust, fossil fuel combustion, and crustal sources, and in dry deposition, they were dust/metallurgic, fossil fuel, petrochemical industry and crustal sources.

Elevated Trimethylarsine Oxide and Inorganic Arsenic in Northern Hemisphere Summer Monsoonal Wet Deposition

For arsenic speciation, the inputs for wet deposition are not well understood. Here we demonstrate that trimethylarsine oxide (TMAO) and inorganic arsenic are the dominant species in monsoonal wet deposition in the summer Indian subcontinent, Bangladesh, with inorganic arsenic dominating, accounting for ∼80% of total arsenic in this medium. Lower concentrations of both species were found in monsoonal wet deposition in the winter Indian subcontinent, Sri Lanka. The only other species present was dimethylarsinic acid (DMAA), but this was usually below limits of detection (LoD). We hypothesize that TMAO and inorganic arsenic in monsoonal wet deposition are predominantly of marine origin. For TMAO, the potential source is the atmospheric oxidation of marine derived trimethylarsine. For inorganic arsenic, our evidence suggests entrainment of water column inorganic arsenic into atmospheric particulates. These conclusions are based on weather trajectory analysis and on the strong correlations with known wet deposition marine derived elements: boron, iodine, and selenium. The finding that TMAO and inorganic arsenic are widely present and elevated in monsoonal wet deposition identifies major knowledge gaps that need to be addressed regarding the understanding of arsenic's global cycle.