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To date more than 3650 organohalogen compounds are known to be naturally produced by biogeochemical processes. The current
understanding of the abiotic formation of organohalogens during early diagenetic processes in soils and sediments are reviewed
here. Next to volatile alkyl halides and polar organohalogens such as haloacetates there is evidence...
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Conducted isotopic-geochemical study of the Upper Proterozoic rocks of the Nyarovey series was provided from the Polar Urals. U-Pb LA-SF-ICP-MS dating of detrital zircons from metasandstone the lower part of the series showed that the eroded substrate was dominated by Proterozoic rocks. Analysis of the obtained dating allowed us to conclude that th...
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... In addition to anthropogenic production, over 2200 naturally formed Cl org have been identified (e.g., Gribble, 2009; Harper, 1985). In soils, naturally formed Cl org are mainly produced biotically by microorganisms such as fungi and bacteria (Bastviken et al., 2009; Winterton, 2000; Öberg, 2002), but can also be formed abiotically (Schöler and Keppler, 2003 ). Recent results suggest that different tree species and associated microorganisms in the rhizosphere strongly influence both the Cl org and overall Cl levels in soils (Montelius et al., 2015). ...
Much of the total pool of chlorine (Cl) in soil consists of naturally produced organic chlorine (Clorg). The chlorination of bulk organic matter at substantial rates has been experimentally confirmed in various soil types. The subsequent fates of Clorg are important for ecosystem Cl cycling and residence times. As most previous research into dechlorination in soils has examined either single substances or specific groups of compounds, we lack information about overall bulk dechlorination rates. Here we assessed bulk organic matter chlorination and dechlorination rates in coniferous forest soil based on a radiotracer experiment conducted under various environmental conditions (additional water, labile organic matter, and ammonium nitrate). Experiment results were used to develop a model to estimate specific chlorination (i.e., fraction of Cl(-) transformed to Clorg per time unit) and specific dechlorination (i.e., fraction of Clorg transformed to Cl(-) per time unit) rates. The results indicate that chlorination and dechlorination occurred simultaneously under all tested environmental conditions. Specific chlorination rates ranged from 0.0005 to 0.01 d(-1) and were hampered by nitrogen fertilization but were otherwise similar among the treatments. Specific dechlorination rates were 0.01-0.03d(-1) and were similar among all treatments. This study finds that soil Clorg levels result from a dynamic equilibrium between the chlorination and rapid dechlorination of some Clorg compounds, while another Clorg pool is dechlorinated more slowly. Altogether, this study demonstrates a highly active Cl cycling in soils.
... Sediments containing organic matter might also fractionate chlorine isotopes during production and degradation of organochlorine compounds. In this case, changes in δ 37 Cl values will likely depend strongly on the specific reaction pathways involved in halogenation and/or dehalogenation (Aeppli et al., 2013; Futagami et al., 2013; Reddy et al., 2002; Schöler and Keppler, 2003). ...
http://www.sciencedirect.com/science/article/pii/S0012821X15001168
Chlorine stable isotope compositions of two sedimentary sequences and their metamorphic equivalents were measured in order to study fractionation effects during prograde metamorphism and devolatilization. Protoliths (n=25) were collected from a 50 m section of Triassic fluvial and playa-lake strata and Jurassic (Liassic) marine black shales in a well-characterized quarry. Low greenschist to middle amphibolite facies equivalents (n>80) were collected from the Glarus Alps, Urseren Zone, and Lucomagno region. Bulk δ37Cl values are constant within individual sedimentary layers, but vary from −2.0 to +2.4‰ in Triassic rocks and from −3.0 to 0‰ in the black shales. Dolomitic and gypsiferous samples have positive δ37Cl values, but marls and shales are isotopically negative. Bulk Cl contents show only small declines during the earliest stages of metamorphism. Metamorphic equivalents of the Triassic and Liassic protoliths record the same overall ranges in δ37Cl as their protoliths. Samples with highly correlated bulk compositions but different metamorphic grade show no statistically significant difference in δ37Cl. These data lead to the following conclusions: (1) Terrestrial and marine sedimentary rocks display large primary heterogeneities in chlorine isotope composition. As a result, an unambiguous “sedimentary signature” does not exist in the chlorine stable isotope system. (2) No isotopic fractionation is discernable during metamorphic devolatilization, even at low temperatures. Alpine-style metamorphism thus has little to no effect on bulk chlorine isotopic compositions, despite significant devolatilization. (3) Cl is largely retained in the rocks during devolatilization, contrary to the normally assumed hydrophilic behavior of chlorine. Continuous release of mixed-volatile C–O–H fluids likely affected Cl partitioning between fluid and minerals and allowed chlorine to remain in the rocks. (4) There is no evidence for fluid communication across (meta)sedimentary layers except within the Urseren shear zone. These data contribute to a relatively closed-system view of metamorphic devolatilization from anchizone through mid-amphibolite facies conditions.
... This compartment receives significant fluxes of inorganic halides via the deposition of sea salt aerosols, combustion processes, and from weathering processes of rocks as well as vertically intruding salt diapirs. VOX have been found in natural soils as well as sediments of hyper-/saline salt lakes (Schöler and Keppler, 2003; Weissflog et al., 2005). A number of studies is dealing with the release of organohalogens from coastal marshes and other wetlands, where halogenation was suggested to depend on fungal and bacterial activity (e.g. ...
Due to their negative water budget most recent semi-/arid regions are characterized by vast evaporates (salt lakes and salty soils). We recently identified those hyper-saline environments as additional sources for a multitude of volatile halogenated organohalogens (VOX). These com-pounds can affect the ozone layer of the stratosphere and play a key role in the production of aerosols. A remote sensing based analysis was performed in the Southern Aral Sea basin, providing information of major soil types as well as their extent and spatial and temporal evolution. VOX production has been determined in dry and moist soil sam-ples after 24 h. Several C1-and C2 organohalogens have been found in hyper-saline topsoil profiles, including CH 3 Cl, CH 3 Br, CHBr 3 and CHCl 3 . The range of organohalogens also includes trans-1,2-dichloroethene (DCE), which is re-ported here to be produced naturally for the first time. Us-ing MODIS time series and supervised image classification a daily production rate for DCE has been calculated for the 15 000 km 2 ranging research area in the southern Aralkum. The applied laboratory setup simulates a short-term change in climatic conditions, starting from dried-out saline soil that is instantly humidified during rain events or flooding. It describes the general VOX production potential, but allows only for a rough estimation of resulting emission loads. VOX emissions are expected to increase in the future since the area of salt affected soils is expanding due to the regressing Aral Sea. Opportunities, limits and requirements of satellite based rapid change detection and salt classification are discussed.
... Benthic organisms such as this have been regarded as indicators of low molecular weight Br org in sediments [Fielman et al., 2001]. Br org may also form abiotically in sediments during early diagenetic processes as insoluble Fe(III)–oxides are reduced [Keppler et al., 2000; Schöler and Keppler, 2003]. [34] Much of sediment NOM, however, originates in surface waters, as detrital matter from organisms in the euphotic zone that ultimately settles on the sediment surface. ...
Organobromine (Brorg) compounds, commonly recognized as persistent, toxic anthropogenic pollutants, are also produced naturally in terrestrial and marine systems. Several enzymatic and abiotic bromination mechanisms have been identified, as well as an array of natural Brorg molecules associated with various marine organisms. The fate of the carbon-bromine functionality in the marine environment, however, remains largely unexplored. Oceanographic studies have noted an association between bromine (Br) and organic carbon (Corg) in marine sediments. Even so, there has been no direct chemical evidence that Br in the sediments exists in a stable form apart from inorganic bromide (Brinorg), which is widely presumed conservative in marine systems. To investigate the scope of natural Brorg production and its fate in the environment, we probed Br distribution and speciation in estuarine and marine sediments using in situ X-ray spectroscopy and spectromicroscopy. We show that Brorg is ubiquitous throughout diverse sedimentary environments, occurring in correlation with Corg and metals such as Fe, Ca, and Zn. Analysis of sinking particulate carbon from the seawater column links the Brorg observed in sediments to biologically produced Brorg compounds that persist through humification of natural organic matter (NOM). Br speciation varies with sediment depth, revealing biogeochemical cycling of Br between organic and inorganic forms as part of the burial and degradation of NOM. These findings illuminate the chemistry behind the association of Br with Corg in marine sediments and cast doubt on the paradigmatic classification of Br as a conservative element in seawater systems.
... Inorganic chloride (Cl inorg ) delivered to soil through atmospheric deposition can undergo plant uptake, leaching, and reactions to form organochlorine (Cl org ). Natural chlorination may occur through biotic [Bastviken et al., 2009; Niedan et al., 2000; Reina et al., 2004] and abiotic [Fahimi et al., 2003; Holmstrand et al., 2006; Keppler et al., 2000; Schoeler and Keppler, 2002] processes under environmental conditions. Accumulated evidence indicates that Cl inorg converts to Cl org during the decay and humification of plant material on the soil surface [Asplund and Grimvall, 1991; Asplund et al., 1989; Flodin et al., 1997; Hjelm et al., 1995; Müller and Schmitz, 1985; Myneni, 2002b; Öberg, 2002]. ...
Research in the last 20 years has shown that chlorine undergoes transformations between inorganic and organic forms as part of a complex biogeochemical cycle in terrestrial systems. Natural organochlorine production appears to be associated with the decomposition of plant material on the soil surface, though the chlorine cycle budget implies that a proportion of natural organochlorine enters soil through plant litter and atmospheric deposition as well. Organochlorine compounds may form through biotic and abiotic pathways, but the rates and magnitude of production in the field remain undefined. We have performed a time-dependent trace of chlorine concentration through forest ecosystems, revealing distinct fractions of naturally produced organochlorine in plant biomass. Aliphatic organochlorine constitutes an intrinsic component of healthy leaves that persists through senescence and humification of the plant material, making a substantial contribution to the pool of soil organochlorine. Plant leaves also contain soluble aromatic organochlorine compounds that leach from leaf litter during early decay stages. As decay progresses, high concentrations of insoluble aromatic organochlorine accrue in the humus, through de novo production as well as adsorption. The rates of aromatic organochlorine production and degradation vary seasonally and conversely. This study presents the first unambiguous evidence that there exist multiple pools of chlorinated organic matter in the soil environment and that leaf litter deposition makes a significant and refractory contribution to the soil organochlorine pool, providing key insights into the biogeochemical chlorine cycle.
... According to the findings of Hoekstra et al. (7) that natural soils could be generally considered as a source of trihalomethanes, we investigated THM formation by applying small organic compounds as starting materials employing Fentonlike reaction conditions (18)(19)(20). The use of these model compounds is necessary for a better comprehension of the reaction mechanism (21)(22)(23)(24). The molecules chosen were in principle polyhydroxylated benzenes (e.g., catechol, resorcin, and hydroquinone) which are representative for some structural elements of humic substances in soil. ...
... To investigate the THM formation mechanism in soil we used a single surrogate compound (catechol) to represent the multitude of organic species present in soil (21). This permits mechanistic details to be examined. ...
... In addition to these non-specific natural chlorination products, individual chlorinated metabolites have been isolated from soil fungi and lichen for decades (Yosioka et al., 1968; Turner and Aldridge, 1983; Wijnberg, 1998; Gribble, 2003 ). Abiotic (nonenzymatic ) chlorination has also been shown to occur naturally and is thought to be catalyzed by metal ions in the low-pH soil environment (Keppler et al., 2000; Schoeler and Keppler, 2002; Fahimi et al., 2003; Holmstrand et al., 2006). This evidence collectively indicates that terrestrial Cl undergoes complex biogeochemical transformations. ...
... Metals such as Fe are often the key cofactors in the reaction centers of haloperoxidative enzymes (Sundaramoorthy et al., 1995). In addition, abiotic (non-enzymatic) metal-catalyzed chlorination of aliphatic and aromatic substrates has been documented in natural systems (Keppler et al., 2000; Schoeler and Keppler, 2002; Fahimi et al., 2003; Holmstrand et al., 2006) and as part of biomimetic synthetic schemes in the laboratory (Delaude and Laszlo, 1990; Walker et al., 1997). Microscopic observations suggest that numerous aromatic Cl org hotspots may be associated with fungal activity on weathered leaf surfaces. ...
Natural organochlorine (Clorg) is ubiquitous in soil humus, but the distribution and cycling of different Cl species during the humification of plant material is poorly understood. Our X-ray spectromicroscopic studies indicate that the distributions of Clorg and inorganic Cl-(Clinorg) in oak leaf material vary dramatically with decay stage, with the most striking changes occurring at the onset of weathering. In healthy or senescent leaves harvested from trees, Clinorg occurs in sparsely distributed, highly localized ``hotspots'' associated with trichomes as well as in diffuse concentration throughout the leaf tissue. The Clinorg associated with trichomes exists either in H-bonded form or in a solid salt matrix, while the Clinorg in diffuse areas of lower Cl concentration appears exclusively in H-bonded form. Most solid phase Clinorg leaches from the leaf tissue during early weathering stages, whereas the H-bonded Clinorg appears to leach away slowly as degradation progresses, persisting through advanced weathering stages. In unweathered leaves, aromatic and aliphatic Clorg were found in rare but concentrated hotspots. In weathered leaves, by contrast, aromatic Clorg hotspots are prevalent, often coinciding with areas of elevated Fe or Mn concentration. Aromatic Clorg is highly soluble in leaves at early weathering stages and insoluble at more advanced stages. These results, combined with optical microscopy, suggest that fungi play a role in the production of aromatic Clorg in weathering leaf material. Aliphatic Clorg occurs in concentrated hotspots in weathered leaves as well as in diffuse areas of low Cl concentration. The distribution and speciation of Cl in weathering oak leaves depicted by this spectromicroscopic study provides new insight into the formation and cycling of Clorg during the decay of natural organic matter.
Western Australia is a semi-/arid region known for saline lakes with a wide range of geochemical parameters (pH 2.5–7.1, Cl− 10–200 g L−1). This study reports on the haloacetones chloro- and bromoacetone in air over 6 salt lake shorelines. Significant emissions of chloroacetone (up to 0.2 µmol m−2 h−1) and bromoacetone (up to 1. 5 µmol m−2 h−1) were detected, and a photochemical box model was employed to evaluate the contribution of their atmospheric formation from the olefinic hydrocarbons propene and methacrolein in the gas phase. The measured concentrations could not explain the photochemical halogenation reaction, indicating a strong hitherto unknown source of haloacetones. Aqueous-phase reactions of haloacetones, investigated in the laboratory using humic acid in concentrated salt solutions, were identified as alternative formation pathway by liquid-phase reactions, acid catalyzed enolization of ketones, and subsequent halogenation. In order to verify this mechanism, we made measurements of the Henry’s law constants, rate constants for hydrolysis and nucleophilic exchange with chloride, UV-spectra and quantum yields for the photolysis of bromoacetone and 1,1-dibromoacetone in the aqueous phase. We suggest that heterogeneous processes induced by humic substances in the quasi-liquid layer of the salt crust, particle surfaces and the lake water are the predominating pathways for the formation of the observed haloacetones.
Environmental context Natural organohalogens produced in and released from soils are of utmost importance for ozone depletion in the stratosphere. Formation mechanisms of natural organohalogens are reviewed with particular attention to recent advances in biomimetic chemistry as well as in radical-based Fenton chemistry. Iron-catalysed oxidation in biotic and abiotic systems converts organic matter in nature to organohalogens. Abstract Natural and anthropogenic organic matter is continuously transformed by abiotic and biotic processes in the biosphere. These reactions include partial and complete oxidation (mineralisation) or reduction of organic matter, depending on the redox milieu. Products of these transformations are, among others, volatile substances with atmospheric relevance, e.g. CO2, alkanes and organohalogens. Natural organohalogens, produced in and released from soils and salt surfaces, are of utmost importance for stratospheric (e.g. CH3Cl, CH3Br for ozone depletion) and tropospheric (e.g. Br2, BrCl, Cl2, HOCl, HOBr, ClNO2, BrNO2 and BrONO2 for the bromine explosion in polar, marine and continental boundary layers, and I2, CH3I, CH2I2 for reactive iodine chemistry, leading to new particle formation) chemistry, and pose a hazard to terrestrial ecosystems (e.g. halogenated carbonic acids such as trichloroacetic acid). Mechanisms for the formation of volatile hydrocarbons and oxygenated as well as halogenated derivatives are reviewed with particular attention paid to recent advances in the field of mechanistic studies of relevant enzymes and biomimetic chemistry as well as radical-based processes.
Perchlorates have been found on the surface of Mars. Since they are
strongly oxidizing, it is important to discuss how this fact is
reflected both on the existence of organic compounds on the surface of
Mars and possibly life. We have previously reported that perchlorates,
although strongly oxidizing, do not destroy some amino acids, such as
glycine and alanine, among others, and also spare other classes of
organic compounds. Others have found that perchlorates are utilized by
bacteria and Archaea as energy sources. Particularly important are the
findings about Archaea, since they show a combination of a biotic and
abiotic processing of perchlorates, which implies ancient origins of
these pathways, which may have been typical on prebiotic Earth. There
are also numerous reports of the presence of organohalogen compounds on
Earth which are made by natural sources or living organisms. Such
compounds may be simple, such as chloromethane, or very complicated.
They are utilized or produced by living organisms on Earth.
Significantly, some such compounds are extremely stable to high
temperatures, over 400oC, which should be taken into account for the
chemical analyses on Mars. Finally, organohalogen compounds have been
also detected on the meteorites. This combined evidence indicates that
eventual finding of the organohalogen compounds on Mars is expected, and
that the presence of the strongly oxidizing perchlorates does not rule
out life on Mars.
