Global plastic litter pollution has been increasing alongside demand since plastic products gained commercial popularity in the 1930's. Current plastic pollutant research has generally assumed that ...once plastics enter the ocean they are there to stay, retained permanently within the ocean currents, biota or sediment until eventual deposition on the sea floor or become washed up onto the beach. In contrast to this, we suggest it appears that some plastic particles could be leaving the sea and entering the atmosphere along with sea salt, bacteria, virus' and algae. This occurs via the process of bubble burst ejection and wave action, for example from strong wind or sea state turbulence. In this manuscript we review evidence from the existing literature which is relevant to this theory and follow this with a pilot study which analyses microplastics (MP) in sea spray. Here we show first evidence of MP particles, analysed by μRaman, in marine boundary layer air samples on the French Atlantic coast during both onshore (average of 2.9MP/m3) and offshore (average of 9.6MP/m3) winds. Notably, during sampling, the convergence of sea breeze meant our samples were dominated by sea spray, increasing our capacity to sample MPs if they were released from the sea. Our results indicate a potential for MPs to be released from the marine environment into the atmosphere by sea-spray giving a globally extrapolated figure of 136000 ton/yr blowing on shore.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Mass independent fractionation (MIF) of stable isotopes associated with terrestrial geochemical processes was first observed in the 1980s for oxygen and in the 1990s for sulfur isotopes. Recently ...mercury (Hg) was added to this shortlist when positive odd Hg isotope anomalies were observed in biological tissues. Experimental work identified photoreduction of aquatic inorganic divalent Hg
II and photodegradation of monomethylmercury species as plausible MIF inducing reactions. Observations of continental receptors of atmospheric Hg deposition such as peat, lichens, soils and, indirectly, coal have shown predominantly negative MIF. This has led to the suggestion that atmospheric Hg has negative MIF signatures and that these are the compliment of positive Hg MIF in the aquatic environment. Recent observations on atmospheric vapor phase Hg
0 and Hg
II in wet precipitation reveal zero and positive Hg MIF respectively and are in contradiction with a simple aquatic Hg
II photoreduction scenario as the origin for global Hg MIF observations.
This study presents a synthesis of all terrestrial Hg MIF observations, and these are integrated in a one-dimensional coupled continent-ocean–atmosphere model of the global Hg cycle. The model illustrates how Hg MIF signatures propagate through the various Earth surface reservoirs. The scenario in which marine photoreduction is the main MIF inducing process results in negative atmospheric Δ
199Hg and positive ocean Δ
199Hg of −0.5‰ and +0.25‰, yet does not explain atmospheric Hg
0 and Hg
II wet precipitation observations. Alternative model scenarios that presume in-cloud aerosol Hg
II photoreduction and continental Hg
II photoreduction at soil, snow and vegetation surfaces to display MIF are necessary to explain the ensemble of natural observations. The model based approach is a first step in understanding Hg MIF at a global scale and the eventual incorporation of Hg stable isotope information in detailed global mercury chemistry and transport models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Anthropogenic activities have led to large-scale mercury (Hg) pollution in the Arctic. It has been suggested that sea-salt-induced chemical cycling of Hg (through 'atmospheric mercury depletion ...events', or AMDEs) and wet deposition via precipitation are sources of Hg to the Arctic in its oxidized form (Hg(ii)). However, there is little evidence for the occurrence of AMDEs outside of coastal regions, and their importance to net Hg deposition has been questioned. Furthermore, wet-deposition measurements in the Arctic showed some of the lowest levels of Hg deposition via precipitation worldwide, raising questions as to the sources of high Arctic Hg loading. Here we present a comprehensive Hg-deposition mass-balance study, and show that most of the Hg (about 70%) in the interior Arctic tundra is derived from gaseous elemental Hg (Hg(0)) deposition, with only minor contributions from the deposition of Hg(ii) via precipitation or AMDEs. We find that deposition of Hg(0)-the form ubiquitously present in the global atmosphere-occurs throughout the year, and that it is enhanced in summer through the uptake of Hg(0) by vegetation. Tundra uptake of gaseous Hg(0) leads to high soil Hg concentrations, with Hg masses greatly exceeding the levels found in temperate soils. Our concurrent Hg stable isotope measurements in the atmosphere, snowpack, vegetation and soils support our finding that Hg(0) dominates as a source to the tundra. Hg concentration and stable isotope data from an inland-to-coastal transect show high soil Hg concentrations consistently derived from Hg(0), suggesting that the Arctic tundra might be a globally important Hg sink. We suggest that the high tundra soil Hg concentrations might also explain why Arctic rivers annually transport large amounts of Hg to the Arctic Ocean.
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IJS, KISLJ, NUK, SBMB, UL, UM, UPUK
Gaseous elemental mercury (GEM) is the dominant form of mercury in the atmosphere. Its conversion into oxidized gaseous and particulate forms is thought to drive atmospheric mercury wet deposition to ...terrestrial and aquatic ecosystems, where it can be subsequently transformed into toxic methylmercury. The contribution of mercury dry deposition is however largely unconstrained. Here we examine mercury mass balance and mercury stable isotope composition in a peat bog ecosystem. We find that isotope signatures of living sphagnum moss (Δ199Hg = −0.11 ± 0.09‰, Δ200Hg = 0.03 ± 0.02‰, 1σ) and recently accumulated peat (Δ199Hg = −0.22 ± 0.06‰, Δ200Hg = 0.00 ± 0.04‰, 1σ) are characteristic of GEM (Δ199Hg = −0.17 ± 0.07‰, Δ200Hg = −0.05 ± 0.02‰, 1σ), and differs from wet deposition (Δ199Hg = 0.73 ± 0.15‰, Δ200Hg = 0.21 ± 0.04‰, 1σ). Sphagnum covered during three years by transparent and opaque surfaces, which eliminate wet deposition, continue to accumulate Hg. Sphagnum Hg isotope signatures indicate accumulation to take place by GEM dry deposition, and indicate little photochemical re-emission. We estimate that atmospheric mercury deposition to the peat bog surface is dominated by GEM dry deposition (79%) rather than wet deposition (21%). Consequently, peat deposits are potential records of past atmospheric GEM concentrations and isotopic composition.
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IJS, KILJ, NUK, PNG, UL, UM
The tundra plays a pivotal role in the Arctic mercury
(Hg) cycle by storing atmospheric Hg deposition and shuttling it to the
Arctic Ocean. A recent study revealed that 70 % of the atmospheric Hg
...deposition to the tundra occurs through gaseous elemental mercury (GEM or Hg(0))
uptake by vegetation and soils. Processes controlling land–atmosphere
exchange of Hg(0) in the Arctic tundra are central, but remain
understudied. Here, we combine Hg stable isotope analysis of Hg(0) in the
atmosphere, interstitial snow air, and soil pore air, with Hg(0) flux
measurements in a tundra ecosystem at Toolik Field Station in northern
Alaska (USA). In the dark winter months, planetary boundary layer (PBL)
conditions and Hg(0) concentrations were generally stable throughout the day
and small Hg(0) net deposition occurred. In spring, halogen-induced
atmospheric mercury depletion events (AMDEs) occurred, with the fast
re-emission of Hg(0) after AMDEs resulting in net emission fluxes of Hg(0).
During the short snow-free growing season in summer, vegetation uptake of
atmospheric Hg(0) enhanced atmospheric Hg(0) net deposition to the Arctic
tundra. At night, when PBL conditions were stable, ecosystem uptake of
atmospheric Hg(0) led to a depletion of atmospheric Hg(0). The night-time
decline of atmospheric Hg(0) was concomitant with a depletion of lighter
Hg(0) isotopes in the atmospheric Hg pool. The enrichment factor,
ε202Hgvegetationuptake=-4.2 ‰ (±1.0 ‰) was consistent
with the preferential uptake of light Hg(0) isotopes by vegetation. Hg(0)
flux measurements indicated a partial re-emission of Hg(0) during daytime,
when solar radiation was strongest. Hg(0) concentrations in soil pore air
were depleted relative to atmospheric Hg(0) concentrations, concomitant with
an enrichment of lighter Hg(0) isotopes in the soil pore air, ε202Hgsoilair-atmosphere=-1.00 ‰
(±0.25 ‰) and E199Hgsoilair-atmosphere=0.07 ‰ (±0.04 ‰). These
first Hg stable isotope measurements of Hg(0) in soil pore air are
consistent with the fractionation previously observed during Hg(0) oxidation
by natural humic acids, suggesting abiotic oxidation as a cause for observed
soil Hg(0) uptake. The combination of Hg stable isotope fingerprints with
Hg(0) flux measurements and PBL stability assessment confirmed a dominant
role of Hg(0) uptake by vegetation in the terrestrial–atmosphere exchange of
Hg(0) in the Arctic tundra.
Past and present anthropogenic mercury (Hg) release to ecosystems causes neurotoxicity and cardiovascular disease in humans with an estimated economic cost of $117 billion USD annually. Humans are ...primarily exposed to Hg via the consumption of contaminated freshwater and marine fish. The UNEP Minamata Convention on Hg aims to curb Hg release to the environment and is accompanied by global Hg monitoring efforts to track its success. The biogeochemical Hg cycle is a complex cascade of release, dispersal, transformation and bio-uptake processes that link Hg sources to Hg exposure. Global change interacts with the Hg cycle by impacting the physical, biogeochemical and ecological factors that control these processes. In this review we examine how global change such as biome shifts, deforestation, permafrost thaw or ocean stratification will alter Hg cycling and exposure. Based on past declines in Hg release and environmental levels, we expect that future policy impacts should be distinguishable from global change effects at the regional and global scales.
Monomethylmercury (MMHg) is a potent toxin that bioaccumulates and magnifies in marine food webs. Recent studies show abundant methylated Hg in deep oceans (>1000 m), yet its origin remains ...uncertain. Here we measured Hg isotope compositions in fauna and surface sediments from the Mariana Trench. The trench fauna at 7000-11000 m depth all have substantially positive mass-independent fractionation of odd Hg isotopes (odd-MIF), which can be generated only in the photic zone via MMHg photo-degradation. Given the identical odd-MIF in trench fauna and North Pacific upper ocean (<1000 m) biota MMHg, we suggest that the accumulated Hg in trench fauna originates exclusively from MMHg produced in upper oceans, which penetrates to depth by sorption to sinking particles. Our findings reveal little in-situ MMHg production in deep oceans and imply that anthropogenic Hg released at the Earth's surface is much more pervasive across deep oceans than was previously thought.
Mercury (Hg) photochemical redox reactions control atmospheric Hg lifetime and therefore play an important role in global Hg cycling. Oxidation of Hg(0) to Hg(II) is currently thought to be a ...Br-initiated two-stage reaction with end-products HgBr2, HgBrOH, HgBrONO, HgBrOHO. Atmospheric photoreduction of these Hg(II) compounds can take place in both the gas and aqueous phase. Here we present new experimental observations on aqueous Hg(II) photoreduction rates in the presence of dissolved organic carbon and halides and compare the findings to rainfall Hg(II) photoreduction rates. The pseudo first-order, gross photoreduction rate constant, kred, for 0.5 μM Hg(II) in the presence of 0.5 mg/ L of dissolved organic carbon (DOC) is 0.23 h−1, which is similar to the mean kred (0.15 ± 0.01 h−1(σ, n = 3)) in high altitude rainfall and at the lower end of the median kred (0.41 h−1, n = 24) in continental and marine waters. Addition of bromide (Br−) to experimental Hg(II)-DOC solutions progressively inhibits Hg(II) photoreduction to reach 0.001 h−1 at total Br− of 10 mM. Halide substitution experiments give Hg(II)Xn(n-2) photoreduction rate constants of 0.016, 0.004 h−1, and < detection limit for X = Cl−, Br−, and I− respectively and reflect increasing stability of the Hg(II)-halide complex. We calculate equilibrium Hg(II) speciation in urban and high-altitude rainfall using Visual Minteq, which indicates Hg(II)-DOC to be the dominant Hg species. The ensemble of observations suggests that atmospheric gaseous HgBr2, HgCl2, HgBrNO2, HgBrHO2 forms, scavenged by aqueous aerosols and cloud droplets, are converted to Hg(II)-DOC forms in rainfall due to abundant organic carbon in aerosols and cloud water. Eventual photoreduction of Hg(II)-DOC in aqueous aerosols and clouds is, however, too slow to be relevant in global atmospheric Hg cycling.
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•Addition of Br− to Hg(II)-DOC solutions progressively inhibits Hg(II) photoreduction.•Hg(II)-halide (Cl−, Br− and I−) photoreduction rate reflects increasing complex stability.•Hg(II)-Halide complexes are converted to Hg(II)-DOC forms in rainfall.•Hg(II)-DOC is the dominant Hg species in rainfall.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The isotopic composition of atmospheric total gaseous mercury (TGM) and particle-bound mercury (PBM) and mercury (Hg) in litterfall samples have been determined at urban/industrialized and rural ...sites distributed over mainland China for identifying Hg sources and transformation processes. TGM and PBM near anthropogenic emission sources display negative δ202Hg and near-zero Δ199Hg in contrast to relatively positive δ202Hg and negative Δ199Hg observed in remote regions, suggesting that different sources and atmospheric processes force the mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) in the air samples. Both MDF and MIF occur during the uptake of atmospheric Hg by plants, resulting in negative δ202Hg and Δ199Hg observed in litter-bound Hg. The linear regression resulting from the scatter plot relating the δ202Hg to Δ199Hg data in the TGM samples indicates distinct anthropogenic or natural influences at the three study sites. A similar trend was also observed for Hg accumulated in broadleaved deciduous forest foliage grown in areas influenced by anthropogenic emissions. The relatively negative MIF in litter-bound Hg compared to TGM is likely a result of the photochemical reactions of Hg2+ in foliage. This study demonstrates the diagnostic stable Hg isotopic composition characteristics for separating atmospheric Hg of different source origins in China and provides the isotopic fractionation clues for the study of Hg bioaccumulation.
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IJS, KILJ, NUK, PNG, UL, UM
Understanding the sources and transformations of mercury (Hg) in the free troposphere is a critical aspect of global Hg research. Here we present one year of observations of atmospheric Hg speciation ...and gaseous elemental Hg (GEM) isotopic composition at the high-altitude Pic du Midi Observatory (2860 m above sea level) in France. Biweekly integrated GEM from February 2012 to January 2013 revealed significant variations in δ202HgGEM (−0.04‰ to 0.52‰) but not in Δ199HgGEM (−0.17‰ to −0.27‰) or Δ200HgGEM (−0.10‰ to 0.05‰). δ202HgGEM was negatively correlated with CO and reflected air mass origins from Europe (high CO, low δ202HgGEM) and from the Atlantic Ocean (low CO, high δ202HgGEM). We suggest that the δ202HgGEM variations represent mixing of recent low δ202HgGEM European anthropogenic emissions with high δ202HgGEM northern hemispheric background GEM. In addition, Atlantic Ocean free troposphere air masses showed a positive correlation between δ202HgGEM and gaseous oxidized Hg (GOM) concentrations, indicative of mass-dependent Hg isotope fractionation during GEM oxidation. On the basis of atmospheric δ202HgGEM and speciated Hg observations, we suggest that the oceanic free troposphere is a reservoir within which GEM is readily oxidized to GOM.
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IJS, KILJ, NUK, PNG, UL, UM
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