Higher sea surface temperature in the Indian Ocean during the Last Interglacial weakened the South Asian monsoon.

SignificanceUnderstanding the drivers of South Asian monsoon intensity is pivotal for improving climate forecasting under global warming scenarios. Solar insolation is assumed to be the dominant driver of monsoon variability in warm climate regimes, but this has not been verified by proxy data. We report a South Asian monsoon rainfall record spanning the last ∼130 kyr in the Ganges-Brahmaputra-Meghna river catchment. Our multiproxy data reveal that the South Asian monsoon was weaker during the Last Interglacial (130 to 115 ka)-despite higher insolation-than during the Holocene (11.6 ka to present), thus questioning the widely accepted model assumption. Our work implies that Indian Ocean warming may increase the occurrence of severe monsoon failures in South Asia.

The marriage between stable isotope ecology and plant metabolomics - new perspectives for metabolic flux analysis and the interpretation of ecological archives.

Even though they share many thematical overlaps, plant metabolomics and stable isotope ecology have been rather separate fields mainly due to different mass spectrometry demands. New high-resolution bioanalytical mass spectrometers are now not only offering high-throughput metabolite identification but are also suitable for compound- and intramolecular position-specific isotope analysis in the natural isotope abundance range. In plant metabolomics, label-free metabolic pathway and metabolic flux analysis might become possible when applying this new technology. This is because changes in the commitment of substrates to particular metabolic pathways and the activation or deactivation of others alter enzyme-specific isotope effects. This leads to differences in intramolecular and compound-specific isotope compositions. In plant isotope ecology, position-specific isotope analysis in plant archives informed by metabolic pathway analysis could be used to reconstruct and separate environmental impacts on complex metabolic processes. A technology-driven linkage between the two disciplines could allow to extract information on environment-metabolism interaction from plant archives such as tree rings but also within ecosystems. This would contribute to a holistic understanding of how plants react to environmental drivers, thus also providing helpful information on the trajectories of the vegetation under the conditions to come.

Resin acid δ13C and δ18O as indicators of intra-seasonal physiological and environmental variability.

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top-canopy twigs and breast-height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra-seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C-enriched C-1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water-soluble carbohydrates, possibly caused by discrimination against 18O during O2-based diterpene oxidation and 35%-50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within-tree and among-tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long-term proxy for physiological and environmental changes.

Evaluation of lipid extraction methods for fatty acid quantification and compound-specific δ13C and δ2Hn analyses.

Lipids, with fatty acids (FA) as a crucial subset, have become a focal point for diverse medical, physiological, and ecological studies. However, a comprehensive assessment of the various pre-analytical FA extraction methods published in the scientific literature remains lacking. In this study, we examined the efficacy of seven well-established sample preparation methods, specifically focusing on their effectiveness in total lipid and fatty acid extraction and their impact on compound-specific stable hydrogen (δ2H) and carbon (δ13C) isotope values. We also considered the repercussions of FA removal efficacy on residual bulk tissue δ2Hn analysis, because lipids typically have low δ2H values. Our findings showed that in most cases chloroform-based extraction methods outperformed those without chloroform. While discrepancies were not as evident for smaller organisms, such as plankton, marked variations were discernible in the extraction efficiencies for muscle and liver samples, which was also manifested in the residual bulk tissue δ2Hn results. Notably, most extraction methods had little effect on specific δ13C or δ2H isotope values of FA; instead, an emphasis should be on using an extraction method that achieves optimal baseline peak separation of the chromatograms for C and H isotope measurements.

Shortened food chain length in a fished versus unfished coral reef.

Direct exploitation through fishing is driving dramatic declines of wildlife populations in ocean environments, particularly for predatory and large-bodied taxa. Despite wide recognition of this pattern and well-established consequences of such trophic downgrading on ecosystem function, there have been few empirical studies examining the effects of fishing on whole system trophic architecture. Understanding these kinds of structural impacts is especially important in coral reef ecosystems-often heavily fished and facing multiple stressors. Given the often high dietary flexibility and numerous functional redundancies in diverse ecosystems such as coral reefs, it is important to establish whether web architecture is strongly impacted by fishing pressure or whether it might be resilient, at least to moderate-intensity pressure. To examine this question, we used a combination of bulk and compound-specific stable isotope analyses measured across a range of predatory and low-trophic-level consumers between two coral reef ecosystems that differed with respect to fishing pressure but otherwise remained largely similar. We found that even in a high-diversity system with relatively modest fishing pressure, there were strong reductions in the trophic position (TP) of the three highest TP consumers examined in the fished system but no effects on the TP of lower-level consumers. We saw no evidence that this shortening of the affected food webs was being driven by changes in basal resource consumption, for example, through changes in the spatial location of foraging by consumers. Instead, this likely reflected internal changes in food web architecture, suggesting that even in diverse systems and with relatively modest pressure, human harvest causes significant compressions in food chain length. This observed shortening of these food webs may have many important emergent ecological consequences for the functioning of ecosystems impacted by fishing or hunting. Such important structural shifts may be widespread but unnoticed by traditional surveys. This insight may also be useful for applied ecosystem managers grappling with choices about the relative importance of protection for remote and pristine areas and the value of strict no-take areas to protect not just the raw constituents of systems affected by fishing and hunting but also the health and functionality of whole systems.

Dietary plasticity and broad North Atlantic origins inferred from bulk and amino acid-specific δ15N and δ13C favour killer whale range expansions into Arctic waters.

Killer whales (Orcinus orca) occur seasonally in the eastern Canadian Arctic (ECA), where their range expansion associated with declining sea ice have raised questions about the impacts of increasing killer whale predation pressure on Arctic-endemic prey. We assessed diet and distribution of ECA killer whales using bulk and compound-specific stable isotope analysis (CSIA) of amino acids (AA) of 54 skin biopsies collected from 2009 to 2020 around Baffin Island, Canada. Bulk ECA killer whale skin δ15N and δ13C values did not overlap with potential Arctic prey after adjustment for trophic discrimination, and instead reflected foraging history in the North Atlantic prior to their arrival in the ECA. Adjusted killer whale stable isotope (SI) values primarily overlapped with several species of North Atlantic baleen whales or tuna. Amino acid (AA)-specific δ15N values indicated the ECA killer whales fed primarily on marine mammals, having similar glutamic acid δ15N-phenylalanine δ15N (δ15NGlx-Phe) and threonine δ15N (δ15NThr) as mammal-eating killer whales from the eastern North Pacific (ENP) that served as a comparative framework. However, one ECA whale grouped with the fish-eating ENP ecotype based δ15NThr. Distinctive essential AA δ13C of ECA killer whale groups, along with bulk SI similarity to killer whales from different regions of the North Atlantic, indicates different populations converge in Arctic waters from a broad source area. Generalist diet and long-distance dispersal capacity favour range expansions, and integration of these insights will be critical for assessing ecological impacts of increasing killer whale predation pressure on Arctic-endemic species.

Compound-specific stable isotope analyses of fatty acids indicate feeding zones of zooplankton across the water column of a subalpine lake.

Spatial and temporal zooplankton feeding dynamics across the water column of lakes are key for understanding site-specific acquisition of diet sources. During this 6-week lake study, we examined stable carbon (δ13C) and nitrogen (δ15N) isotopes and conducted compound-specific fatty acid (FA) stable isotope analysis (CSIA) of edible seston in the epi-, meta-, and hypolimnion, and zooplankton of Lake Lunz, Austria. We predicted that CSIA of essential FA can discern the foraging grounds of zooplankton more accurately than the commonly used bulk stable isotopes. The δ13C and δ15N values of seston from different lake strata were similar, whereas a dual CSIA approach using stable carbon and hydrogen isotopes of FA (δ13CFA and δ2HFA) provided sufficient isotopic difference in essential FA to discern different lake strata-specific diet sources throughout the study period. We present a CSIA model that suggests strata-specific foraging grounds for different zooplankton groups, indicating higher preference of cladocerans for feeding on epilimnetic diet sources, while calanoid copepods retained more hypolimnetic resources. The CSIA approach thus yields strata-specific information on foraging strategies of different zooplankton taxa and provides more details on the spatial and temporal trophodynamics of planktonic food webs than commonly used bulk stable isotopes.

Tissue-specific carbon isotope patterns of amino acids in southern sea otters.

The measurement of stable isotope values of individual compounds, such as amino acids (AAs), has become a powerful tool in animal ecology and ecophysiology. As with any emerging technique, questions remain regarding the capabilities and limitations of this approach, including how metabolism and tissue synthesis impact the isotopic values of individual AAs and subsequent multivariate patterns. We measured carbon isotope (δ13C) values of essential (AAESS) and nonessential (AANESS) AAs in bone collagen, whisker, muscle, and liver from ten southern sea otters (Enhydra lutris nereis) that stranded in Monterey Bay, California. Sea otters in this population exhibit high degrees of individual dietary specialization, making this an excellent dataset to explore differences in AA δ13C values among tissues in a wild population. We found the δ13C values of the AANESS glutamic acid, proline, serine, and glycine and the AAESS threonine differed significantly among tissues, indicating possible isotopic discrimination during tissue synthesis. Threonine δ13C values were higher in liver relative to bone collagen and muscle, which may indicate catabolism of threonine for gluconeogenesis, an interpretation further supported by correlations between the δ13C values of threonine and its gluconeogenic products glycine and serine in liver. This intraindividual isotopic variation yielded different ecological interpretations among tissues; for 6/10 of the sea otter individuals analyzed, at least one tissue indicated reliance on a different primary producer source than the other tissues. Our results highlight the importance of gluconeogenesis in a carnivorous marine mammal and indicate that metabolic processes influence AAESS and AANESS δ13C values and multivariate AA δ13C patterns.

Lipid biomarkers and stable isotopes uncover paleovegetation changes in extremely species-rich forest-steppe ecosystems, Central Europe.

The historical development of the vegetation of semi-dry grasslands in Central Europe is not satisfactorily understood. Long-term continuity of open vegetation or, conversely, deep-past forest phases are considered possible sources of the current extreme species diversity of these ecosystems. We aimed to reveal the trajectory of paleovegetation development in these ecosystems through detailed analysis of terrestrial in-situ soil geoarchives. We measured the bulk soil carbon and nitrogen contents, lipid molecular distribution, and compound-specific stable carbon and hydrogen isotopic signatures of mid- and long-chain n-alkanes extracted from soil and modern plant material tissues (i.e., deciduous and Pinus leaves and grass/herbaceous species). The C23-C33 n-alkane homologues were identified in soils with different abundances. Normally, C27 and C29 n-alkanes were the most abundant homologues in tree-leaf samples, while grass-derived n-alkanes were mostly C31 and C33 homologues. Soils were largely dominated by C29 and C31 n-alkanes. Odd-numbered C27-C33 soil n-alkane δ13C values ranged from -36.2‰ to -23.2‰, whereas their δ2H values showed a wider range of variability that fluctuated from -224‰ to -172‰. Molecular distribution in combination with radiocarbon analysis of soil organic matter (SOM) and δ13C and δ2H values of n-alkanes revealed a large contribution of C3 trees (both deciduous and coniferous trees/pine trees) as the main source of n-alkanes between the late Pleistocene and early Holocene (ca 15,000-8200 calibrated year before present/cal year BP). A clear shift toward more grassy/herbaceous vegetation was observed from the early Holocene (ca 11,700-8200 cal year BP) onwards. Distribution patterns of lipids and soil geochemical parameters showed that plants are the main source of SOM and that biodegradation and kinetic isotope fractionation are not the main reasons for 13C enrichment in soil profiles. Past C3 vegetation shifts as well as paleoclimate changes (i.e., aridity) can have played a role in the observed 13C depth profiles.

Efficient acid hydrolysis for compound-specific δ15N analysis of amino acids for determining trophic positions.

Compound-specific isotope analysis of nitrogen in amino acids (CSIA-AA, δ15NAA) has gained increasing popularity for elucidating energy flow within food chains and determining the trophic positions of various organisms. However, there is a lack of research on the impact of hydrolysis conditions, such as HCl concentration and hydrolysis time, on δ15NAA analysis in biota samples. In this study, we investigated two HCl concentrations (6 M and 12 M) and four hydrolysis times (2 h, 6 h, 12 h, and 24 h) for hydrolyzing and derivatizing AAs in reference materials (Tuna) and biological samples of little egret (n = 4), night heron (n = 4), sharpbelly (n = 4) and Algae (n = 1) using the n-pivaloyl-iso-propyl (NPIP) ester approach. A Dowex cation exchange resin was used to purify amino acids before derivatization. We then determined δ15NAA values using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The results revealed no significant differences (p > 0.05) in δ15NAA values among samples treated with different HCl concentrations or hydrolysis times, particularly for δ15NGlx (range: 21.0-23.5‰) and δ15NPhe (range: 4.3-5.4‰) in Tuna (12 M). Trophic positions (TPs) calculated based on δ15NAA at 2 h (little egret: 2.9 ± 0.1, night heron: 2.8 ± 0.1, sharpbelly: 2.0 ± 0.1 and Algae: 1.3 ± 0.2) were consistent with those at 24 h (3.1 ± 0.1, 2.8 ± 0.1, 2.2 ± 0.1 and 1.1 ± 0.1, respectively), suggesting that a 2-h hydrolysis time and a 6 M HCl concentration are efficient pretreatment conditions for determining δ15NAA and estimating TP. Compared to the currently used hydrolysis conditions (24 h, 6 M), the proposed conditions (2 h, 6 M) accelerated the δ15NAA assay, making it faster, more convenient, and more efficient. Further research is needed to simplify the operational processes and reduce the time costs, enabling more efficient applications of CSIA-AA.

Reevaluating the timing of Neanderthal disappearance in Northwest Europe.

Elucidating when Neanderthal populations disappeared from Eurasia is a key question in paleoanthropology, and Belgium is one of the key regions for studying the Middle to Upper Paleolithic transition. Previous radiocarbon dating placed the Spy Neanderthals among the latest surviving Neanderthals in Northwest Europe with reported dates as young as 23,880 ± 240 B.P. (OxA-8912). Questions were raised, however, regarding the reliability of these dates. Soil contamination and carbon-based conservation products are known to cause problems during the radiocarbon dating of bulk collagen samples. Employing a compound-specific approach that is today the most efficient in removing contamination and ancient genomic analysis, we demonstrate here that previous dates produced on Neanderthal specimens from Spy were inaccurately young by up to 10,000 y due to the presence of unremoved contamination. Our compound-specific radiocarbon dates on the Neanderthals from Spy and those from Engis and Fonds-de-Forêt demonstrate that they disappeared from Northwest Europe at 44,200 to 40,600 cal B.P. (at 95.4% probability), much earlier than previously suggested. Our data contribute significantly to refining models for Neanderthal disappearance in Europe and, more broadly, show that chronometric models regarding the appearance or disappearance of animal or hominin groups should be based only on radiocarbon dates obtained using robust pretreatment methods.

Massive and rapid predominantly volcanic CO2 emission during the end-Permian mass extinction.

The end-Permian mass extinction event (∼252 Mya) is associated with one of the largest global carbon cycle perturbations in the Phanerozoic and is thought to be triggered by the Siberian Traps volcanism. Sizable carbon isotope excursions (CIEs) have been found at numerous sites around the world, suggesting massive quantities of 13C-depleted CO2 input into the ocean and atmosphere system. The exact magnitude and cause of the CIEs, the pace of CO2 emission, and the total quantity of CO2, however, remain poorly known. Here, we quantify the CO2 emission in an Earth system model based on new compound-specific carbon isotope records from the Finnmark Platform and an astronomically tuned age model. By quantitatively comparing the modeled surface ocean pH and boron isotope pH proxy, a massive (∼36,000 Gt C) and rapid emission (∼5 Gt C yr-1) of largely volcanic CO2 source (∼-15%) is necessary to drive the observed pattern of CIE, the abrupt decline in surface ocean pH, and the extreme global temperature increase. This suggests that the massive amount of greenhouse gases may have pushed the Earth system toward a critical tipping point, beyond which extreme changes in ocean pH and temperature led to irreversible mass extinction. The comparatively amplified CIE observed in higher plant leaf waxes suggests that the surface waters of the Finnmark Platform were likely out of equilibrium with the initial massive centennial-scale release of carbon from the massive Siberian Traps volcanism, supporting the rapidity of carbon injection. Our modeling work reveals that carbon emission pulses are accompanied by organic carbon burial, facilitated by widespread ocean anoxia.

Source differentiation of BTEX compounds in groundwater contaminated due to refinery activities.

This study aims to identify sources of groundwater contamination in a refinery area using integrated compound-specific stable isotope analysis (CSIA), oil fingerprinting techniques, hydrogeological data, and distillation analysis. The investigations focused on determination of the origin of benzene, toluene, ethylbenzene, and xylenes (BTEX), and aliphatic hydrocarbons as well. Groundwater and floating oil samples were collected from extraction wells for analysis. Results indicate presence of active leaks in both the northern and southern zones. In the northern zone, toluene was found to primarily originate from oil products like aviation turbine kerosene (ATK or aviation fuel), kerosene, regular gasoline, and diesel fuel. Additionally, stable isotope ratios of carbon and hydrogen for ethylbenzene, o-xylene (ortho xylene) and p-xylene (para xylene) in zone A suggested the pollution originated from gasoline within the northern zone. The origin of super gasoline (with higher octane) identified in southern zone using δ13C and δ2H values of toluene in the floating oil and groundwater samples. Further, biodegradation of toluene likely occurred in southern zone according to δ13C and δ2H. The findings underscore the critical importance of integrating CSIA and fingerprinting techniques to effectively address the challenges of source identification and relying solely on each method independently is insufficient. Accordingly, comparing the GC-MS results of floating oil samples with ATK and jet fuel (JP4) standards can be effectively utilized for source differentiation. However, this method showed no practical application to distinguish different types of diesel or gasoline. The accuracy and reliability of source identification of BTEX compounds may significantly improve when hydrogeological data incorporates with stable isotopes analysis. Additionally, the results of this study will elevate the procedures for fuel-related contaminants source identification of the polluted groundwater that is crucial to develop effective remediation strategies.

Molecular 14 C evidence for contrasting turnover and temperature sensitivity of soil organic matter components.

Climate projection requires an accurate understanding for soil organic carbon (SOC) decomposition and its response to warming. An emergent view considers that environmental constraints rather than chemical structure alone control SOC turnover and its temperature sensitivity (i.e., Q10 ), but direct long-term evidence is lacking. Here, using compound-specific radiocarbon analysis of soil profiles along a 3300-km grassland transect, we provide direct evidence for the rapid turnover of lignin-derived phenols compared with slower-cycling molecular components of SOC (i.e., long-chain lipids and black carbon). Furthermore, in contrast to the slow-cycling components whose turnover is strongly modulated by mineral association and exhibits low Q10 , lignin turnover is mainly regulated by temperature and has a high Q10 . Such contrasts resemble those between fast-cycling (i.e., light) and mineral-associated slow-cycling fractions from globally distributed soils. Collectively, our results suggest that warming may greatly accelerate the decomposition of lignin, especially in soils with relatively weak mineral associations.

Variation in gut microbial contribution of essential amino acids to host protein metabolism in a wild small mammal community.

Herbivory is a dominant feeding strategy among animals, yet herbivores are often protein limited. The gut microbiome is hypothesized to help maintain host protein balance by provisioning essential macromolecules, but this has never been tested in wild consumers. Using amino acid carbon (δ13 C) and nitrogen (δ15 N) isotope analysis, we estimated the proportional contributions of essential amino acids (AAESS ) synthesized by gut microbes to five co-occurring desert rodents representing herbivorous, omnivorous and insectivorous functional groups. We found that herbivorous rodents occupying lower trophic positions (Dipodomys spp.) routed a substantial proportion (~40%-50%) of their AAESS from gut microbes, while higher trophic level omnivores (Peromyscus spp.) and insectivores (Onychomys arenicola) obtained most of their AAESS (~58%) from plant-based energy channels but still received ~20% of their AAESS from gut microbes. These findings empirically demonstrate that gut microbes play a key functional role in host protein metabolism in wild animals.

Stable isotope analyses of amino acids reveal the importance of aquatic resources to Mediterranean coastal hunter-gatherers.

Determining the degree to which humans relied on coastal resources in the past is key for understanding long-term social and economic development, as well as for assessing human health and anthropogenic impacts on the environment. Prehistoric hunter-gatherers are often assumed to have heavily exploited aquatic resources, especially those living in regions of high marine productivity. For the Mediterranean, this view has been challenged, partly by the application of stable isotope analysis of skeletal remains which has shown more varied coastal hunter-gatherer diets than in other regions, perhaps due to its lower productivity. By undertaking a more specific analysis of amino acids from bone collagen of 11 individuals from one of the oldest and best-known Mesolithic cemeteries in the Mediterranean, at El Collado, Valencia, we show that high levels of aquatic protein consumption were achieved. By measuring both carbon and nitrogen in amino acids, we conclude that some of the El Collado humans relied heavily on local lagoonal fish and possibly shellfish, rather than open marine species. By contrast to previous suggestions, this study demonstrates that the north-western coast of the Mediterranean basin could support maritime-oriented economies during the Early Holocene.

Dual C-Br Isotope Fractionation Indicates Distinct Reductive Dehalogenation Mechanisms of 1,2-Dibromoethane in Dehalococcoides- and Dehalogenimonas-Containing Cultures.

Brominated organic compounds such as 1,2-dibromoethane (1,2-DBA) are highly toxic groundwater contaminants. Multi-element compound-specific isotope analysis bears the potential to elucidate the biodegradation pathways of 1,2-DBA in the environment, which is crucial information to assess its fate in contaminated sites. This study investigates for the first time dual C-Br isotope fractionation during in vivo biodegradation of 1,2-DBA by two anaerobic enrichment cultures containing organohalide-respiring bacteria (i.e., either Dehalococcoides or Dehalogenimonas). Different εbulkC values (-1.8 ± 0.2 and -19.2 ± 3.5‰, respectively) were obtained, whereas their respective εbulkBr values were lower and similar to each other (-1.22 ± 0.08 and -1.2 ± 0.5‰), leading to distinctly different trends (ΛC-Br = Δδ13C/Δδ81Br ≈ εbulkC/εbulkBr) in a dual C-Br isotope plot (1.4 ± 0.2 and 12 ± 4, respectively). These results suggest the occurrence of different underlying reaction mechanisms during enzymatic 1,2-DBA transformation, that is, concerted dihaloelimination and nucleophilic substitution (SN2-reaction). The strongly pathway-dependent ΛC-Br values illustrate the potential of this approach to elucidate the reaction mechanism of 1,2-DBA in the field and to select appropriate εbulkC values for quantification of biodegradation. The results of this study provide valuable information for future biodegradation studies of 1,2-DBA in contaminated sites.

Novel Insights into Uptake, Translocation, and Transformation Mechanisms of 2,2',4,4'-Tetra Brominated Diphenyl Ether (BDE-47) in Wheat (Triticum aestivum L.): Implication by Compound-Specific Stable Isotope and Transcriptome Analysis.

The uptake, translocation, and transformation of 2,2',4,4'-tetra brominated diphenyl ether (BDE-47) in wheat (Triticum aestivum L.) were comprehensively investigated by hydroponic experiments using compound-specific stable isotope analysis (CSIA) and transcriptome analysis. The results indicated that BDE-47 was quickly adsorbed on epidermis of wheat roots and then absorbed in roots via water and anion channels as well as an active process dependent on energy. A small fraction of BDE-47 in roots was subjected to translocation acropetally, and an increase of δ13C values in shoots than roots implied that BDE-47 in roots had to cross at least one lipid bilayer to enter the vascular bundle via transporters. In addition, accompanied by the decreasing concentrations, δ13C values of BDE-47 showed the increasing trend with time in shoots, indicating occurrence of BDE-47 transformation. OH-PBDEs were detected as transformation products, and the hydroxyl group preferentially substituted at the ortho-positions of BDE-47. Based on transcriptome analysis, genes encoding polybrominated diphenyl ether (PBDE)-metabolizing enzymes, including cytochrome P450 enzymes, nitrate reductases, and glutathione S-transferases, were significantly upregulated after exposure to BDE-47 in shoots, further evidencing BDE-47 transformation. This study first reported the stable carbon isotope fractionation of PBDEs during translocation and transformation in plants, and application of CSIA and transcriptome analysis allowed systematically characterize the environmental behaviors of pollutants in plants.

Emissions of the Urban Biocide Terbutryn from Facades: The Contribution of Transformation Products.

Biocides are added to facade paints and renders to prevent algal and fungal growth. The emissions of biocides and their transformation products from building facades during wind-driven rain can contaminate surface waters, soil, and groundwater. Although the emissions of biocide transformation products may be higher than those of the parent biocide, knowledge of the emissions of transformation products over time is scarce. Combining field- and lab-scale experiments, we showed that solar irradiation on facades controls the formation of transformation products and can be used with runoff volume to estimate the long-term emissions of terbutryn transformation products from facades. The slow (t1/2 > 90 d) photodegradation of terbutryn in paint under environmental conditions was associated with insignificant carbon isotope fractionation (Δδ13C < 2 ‰) and caused 20% higher emission of terbutryn-sulfoxide than terbutryn in leachates from facades. This indicated continuous terbutryn diffusion toward the paint surface, which favored terbutryn photodegradation and the concomitant formation of transformation products over time. The emissions of terbutryn transformation products (77 mg m-2) in facade leachates, modeled based on irradiation and facade runoff, were predicted to exceed those of terbutryn (42 mg m-2) by nearly 2-fold after eight years. Overall, this study provides a framework to estimate and account for the long-term emissions of biocide transformation products from building facades to improve the assessment of environmental risks.

Mercury and Sulfur Redox Cycling Affect Methylmercury Levels in Rice Paddy Soils across a Contamination Gradient.

Methylmercury (MeHg) contamination in rice via paddy soils is an emerging global environmental issue. An understanding of mercury (Hg) transformation processes in paddy soils is urgently needed in order to control Hg contamination of human food and related health impacts. Sulfur (S)-regulated Hg transformation is one important process that controls Hg cycling in agricultural fields. In this study, Hg transformation processes, such as methylation, demethylation, oxidation, and reduction, and their responses to S input (sulfate and thiosulfate) in paddy soils with a Hg contamination gradient were elucidated simultaneously using a multi-compound-specific isotope labeling technique (200HgII, Me198Hg, and 202Hg0). In addition to HgII methylation and MeHg demethylation, this study revealed that microbially mediated reduction of HgII, methylation of Hg0, and oxidative demethylation-reduction of MeHg occurred under dark conditions; these processes served to transform Hg between different species (Hg0, HgII, and MeHg) in flooded paddy soils. Rapid redox recycling of Hg species contributed to Hg speciation resetting, which promoted the transformation between Hg0 and MeHg by generating bioavailable HgII for fuel methylation. Sulfur input also likely affected the microbial community structure and functional profile of HgII methylators and, therefore, influenced HgII methylation. The findings of this study contribute to our understanding of Hg transformation processes in paddy soils and provide much-needed knowledge for assessing Hg risks in hydrological fluctuation-regulated ecosystems.