Novel stable isotope concepts to track antibiotics in wetland systems.

Antibiotics, their transformation products, and the translocation of antibiotic-resistant genes in the environment pose significant health risks to humans, animals, and ecosystems, aligning with the One Health concept. Constructed wetlands hold substantial yet underutilized potential for treating wastewater from agricultural, domestic sewage, or contaminated effluents from wastewater treatment plants, with the goal of eliminating antibiotics. However, the comprehensive understanding of the distribution, persistence, and dissipation processes of antibiotics within constructed wetlands remains largely unexplored. In this context, we provide an overview of the current application of stable isotope analysis at natural abundance to antibiotics. We explore the opportunities of an advanced multiple stable isotope approach, where isotope concepts could be effectively applied to examine the fate of antibiotics in wetlands. The development of a conceptual framework to study antibiotics in wetlands using multi-element stable isotopes introduces a new paradigm, offering enhanced insights into the identification and quantification of natural attenuation of antibiotics within wetland systems. This perspective has the potential to inspire the general public, governmental bodies, and the broader research community, fostering an emphasis on the utilization of stable isotope analysis for studying antibiotics and other emerging micropollutants in wetland systems.

How strongly does diet variation explain variation in isotope values of animal consumers?

Analysis of stable isotopes in consumers is used commonly to study their ecological and/or environmental niche. There is, however, considerable debate regarding how isotopic values relate to diet and how other sources of variation confound this link, which can undermine the utility. From the analysis of a simple, but general, model of isotopic incorporation in consumer organisms, we examine the relationship between isotopic variance among individuals, and diet variability within a consumer population. We show that variance in consumer isotope values is directly proportional to variation in diet (through Simpson indices), to the number of isotopically distinct food sources in the diet, and to the baseline variation within and among the isotope values of the food sources. Additionally, when considering temporal diet variation within a consumer we identify the interplay between diet turnover rates and tissue turnover rates that controls the sensitivity of stable isotopes to detect diet variation. Our work demonstrates that variation in the stable isotope values of consumers reflect variation in their diet. This relationship, however, can be confounded with other factors to the extent that they may mask the signal coming from diet. We show how simple quantitative corrections can recover a direct 1:1 correlation in some situations, and in others we can adjust our interpretation in light of the new understanding arising from our models. Our framework provides guidance for the design and analysis of empirical studies where the goal is to infer niche width from stable isotope data.

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Nitrate pollution in groundwater has become a global concern. One of the most important issues in controlling the nitrate pollution of groundwater is to identify the pollution source quickly and accurately. In this review, we firstly summarized the isotopic background values of potential sources of nitrate pollution in groundwater in 17 provinces (cities, autonomous regions) and 29 study areas in China, which could provide the fundamental database for subsequent research. Secondly, we reviewed the research progress of nitrate isotopes combined with multiple tracers for tracing nitrate in groundwater, and discussed their applicable conditions, advantages, and disadvantages. We found that halides and microorganisms combined with nitrate isotopes could accurately trace the pollution sources of domestic sewage, excrement and agricultural activities. The combination of Δ17O and nitrate isotopes could effectively distinguish the source of atmospheric deposition of nitrate in groundwater. The combination of groundwater age and nitrate isotopes could further determine the time scale of nitrate pollution. In addition, we summarized the application cases and compared the characteristics of mass balance mixing model, IsoSource model, Bayesian isotope mixing model, and EMMTE model for quantitative identification of nitrate pollution in groundwater. For the complexity and concealment of groundwater pollution sources, the coupling of nitrate isotopes with other chemical and biological tracing methods, as well as the application of nitrate isotope quantitative models, are effective tools for reliably identifying groundwater nitrate sources and transformation processes.

[Temporal variability of the isotope compositions of plum rain in Nanjing from event to interannual time scales]. / å—äº¬æ¢ é›¨é™æ°´åŒä½ç´ ç»„æˆä»Žäº‹ä»¶åˆ°å¹´é™ å°ºåº¦çš„å˜åŒ–ç‰¹å¾.

Precipitation in the plum rain period accounts for 40%-50% of annual precipitation in the monsoon region. To clarify the temporal variability of the isotopic composition of precipitation during the plum rain period from event to interannual time scale and identify the influencing factors, we analyzed the isotopic composition of precipitation and its influencing factors in Nanjing from 2015 to 2022. By using the Hybrid Single-particle Lagran-gian Integrated Trajectory (HYSPLIT) model with specific humidity analysis, we investigated the water vapor source and influencing factors. The results showed that 1) the isotopic abundance of atmospheric precipitation was depleted in the summer and enriched in winter. dx was lower in summer and higher in winter. The isotopic abundance of precipitation from the plum rain was depleted compared to mean value of the whole-year. 2) There was no significant correlation between δ2H and δ18O of the plum rain (precipitation) with local meteorological factors. However, dx was lower in light rain, reflecting the effect of sub-cloud evaporation. The average dx was higher during plum rain period in years with more total plum rain precipitation. 3) The low-latitude South China Sea and the western Pacific Ocean source area provided water vapor for the plum rain. The shift of moisture source region led to abrupt changes in precipitation isotopes. Our results could provide data support for studies on precipitation isotopes in the monsoon region, as well as a reference point for further understanding the precipitation mechanism of the plum rain and stu-dying the seasonal variability of atmospheric circulation in the East Asian monsoon region.

Elevated lead mobility in sediments of a eutrophic drinking water reservoir during spring and summer seasons: Insights from isotopic signatures.

Lead (Pb) pollution in sediments remains a major concern for ecosystem quality due to the robust interaction at the sediment/water interface, particularly in shallow lakes. However, understanding the mechanism behind seasonal fluctuations in Pb mobility in these sediments is lacking. Here, the seasonal variability of Pb concentration and isotopic ratio were investigated in the uppermost sediments of a shallow eutrophic drinking lake located in southeast China. Results reveal a sharp increase in labile Pb concentration during autumn-winter period, reaching ∼ 3-fold higher levels than during the spring-summer seasons. Despite these fluctuations, there was a notable overlap in the Pb isotopic signatures within the labile fraction across four seasons, suggesting that anthropogenic sources are not responsible for the elevated labile Pb concentration in autumn-winter seasons. Instead, the abnormally elevated labile Pb concentration during autumn-winter was probably related to reduction dissolution of Fe/Mn oxides, while declined labile Pb concentration during spring-summer may be attributed to adsorption/precipitation of Fe/Mn oxides. These large seasonal changes imply the importance of considering seasonal effects when conducting sediment sampling. We further propose a solution that using Pb isotopic signatures within the labile fraction instead of the bulk sediment can better reflect the information of anthropogenic Pb sources.

Using stable isotopes to inform water resource management in forested and agricultural ecosystems.

Present and future climatic trends are expected to markedly alter water fluxes and stores in the hydrologic cycle. In addition, water demand continues to grow due to increased human use and a growing population. Sustainably managing water resources requires a thorough understanding of water storage and flow in natural, agricultural, and urban ecosystems. Measurements of stable isotopes of water (hydrogen and oxygen) in the water cycle (atmosphere, soils, plants, surface water, and groundwater) can provide information on the transport pathways, sourcing, dynamics, ages, and storage pools of water that is difficult to obtain with other techniques. However, the potential of these techniques for practical questions has not been fully exploited yet. Here, we outline the benefits and limitations of potential applications of stable isotope methods useful to water managers, farmers, and other stakeholders. We also describe several case studies demonstrating how stable isotopes of water can support water management decision-making. Finally, we propose a workflow that guides users through a sequence of decisions required to apply stable isotope methods to examples of water management issues. We call for ongoing dialogue and a stronger connection between water management stakeholders and water stable isotope practitioners to identify the most pressing issues and develop best-practice guidelines to apply these techniques.

Characterization of the inhalable fraction (< 10 µm) of soil from highly urbanized and industrial environments: magnetic measurements, bioaccessibility, Pb isotopes and health risk assessment.

Soil in urban and industrial areas is one of the main sinks of pollutants. It is well known that there is a strong link between metal(loid)s bioaccessibility by inhalation pathway and human health. The critical size fraction is < 10 µm (inhalable fraction) since these particles can approach to the tracheobronchial region. Here, soil samples (< 10 µm) from a highly urbanized area and an industrialized city were characterized by combining magnetic measurements, bioaccessibility of metal(loids) and Pb isotope analyses. Thermomagnetic analysis indicated that the main magnetic mineral is impure magnetite. In vitro inhalation analysis showed that Cd, Mn, Pb and Zn were the elements with the highest bioaccessibility rates (%) for both settings. Anthropogenic sources that are responsible for Pb accumulation in < 10 µm fraction are traffic emissions for the highly urbanized environment, and Pb related to steel emissions and coal combustion in cement plant for the industrial setting. We did not establish differences in the Pb isotope composition between pseudo-total and bioaccessible Pb. The health risk assessment via the inhalation pathway showed limited non-carcinogenic risks for adults and children. The calculated risks based on pseudo-total and lung bioaccessible concentrations were identical for the two areas of contrasting anthropogenic pressures. Carcinogenic risks were under the threshold levels (CR < 10-4), with Ni being the dominant contributor to risk. This research contributes valuable insights into the lung bioaccessibility of metal(loids) in urban and industrial soils, incorporating advanced analytical techniques and health risk assessments for a comprehensive understanding.

Towards the compatibility of stable isotope data: review of related concepts, recent progress with reference materials and current challenges.

Comparing and combining stable isotope datasets from different laboratories and different years is essential for many research areas, such as isotope hydrology, greenhouse gas observations, food studies, isotope forensics, palaeo-reconstructions, etc. Data compatibility (i.e. the ability to combine data) is related to the data quality. The prerequisite for data comparability is data normalization to a common stable isotope scale (often referred to as calibration) based on reliable reference materials (RMs) with accurately assigned values and uncertainties. Still, that does not guarantee the data compatibility (mutual agreement). Albeit metrological concepts related to data compatibility and measurement uncertainty have been developed and applied to analytical chemistry in general, these concepts have not yet been fully applied to stable isotope research. This can affect daily calibrations, analytical data and, therefore, data compatibility. In addition, IRMS users often prepare different laboratory standards themselves. Thereafter, users should then understand the contemporary concepts used for assigning RM value and uncertainty, as well as the limitations and potential problems associated with RMs. The history of RMs, preparation reports and also some problems in the past provide lessons to be learned. These include the δ13C drift of LSVEC (the second anchor on the δ13C scale before 2017), revisions to the value assignment principles, the introduction of replacements for LSVEC, related disputes and the potential underestimation of uncertainties for secondary RMs. The review describes metrological concepts related to isotopic scales, RMs and calibration hierarchies and data compatibility. The main RMs and their uncertainties are reviewed through the lens of metrology concepts. Additional focus is given to the VPDB scale for δ13C and issues of scale discontinuity, which can significantly reduce data compatibility in δ13C. The given examples of value and uncertainty assignment for RMs should be viewed as an example of value and uncertainty calculation in daily practice.

Introducing Isotòpia: A stable isotope database for Classical Antiquity.

We present Isotòpia, an open-access database compiling over 36,000 stable isotope measurements (δ13C, δ15N, δ18O, δ34S, 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 207Pb/206Pb, and 208Pb/206Pb) on human, animal, and plant bioarchaeological remains dating to Classical Antiquity (approximately 800 BCE - 500 CE). These were recovered from different European regions, particularly from the Mediterranean. Isotòpia provides a comprehensive characterisation of the isotopic data, encompassing various historical, archaeological, biological, and environmental variables. Isotòpia is a resource for meta-analytical research of past human activities and paleoenvironments. The database highlights data gaps in isotopic classical archaeology, such as the limited number of isotopic measurements available for plants and animals, limited number of studies on spatial mobility, and spatial heterogeneity of isotopic research. As such, we emphasise the necessity to address and fill these gaps in order to unlock the reuse potential of this database.

Determination of contamination sources and geochemical reactions in groundwater of a mine area using Cu, Zn, and S-O isotopes.

To determine contamination sources and pathways, the use of multiple isotopes, including metal isotopes, can increase the reliability of environmental forensic techniques. This study differentiated contamination sources in groundwater of a mine area and elucidated geochemical processes using Cu, Zn, S-O, and O-H isotopes. Sulfate reduction and sulfide precipitation were elucidated using concentrations of dissolved sulfides, δ34SSO4, δ18OSO4, and δ66Zn. The overlying contaminated soil was possibly responsible for the contamination of groundwater at <5 mbgl, which was suggested by low δ65Cu values (0.419-1.120‰) reflecting those of soil (0.279-1.115‰). The existence of dissolved Cu as Cu(I) may prevent the increase in δ65Cu during leaching of contaminated soil in the sulfate-reducing environment. In contrast, the groundwater at >5 mbgl seemed to be highly affected by the contamination plume from the adit water, which was suggested by high SO42- concentrations (407-447 mg L-1) and δ65Cu (0.252-2.275‰) and δ66Zn (-0.105‰-0.362‰) values at a multilevel sampler approaching those of the adit seepages. Additionally, the O-H isotopic ratios were distinguished between <5 mbgl and >5 mbgl. Using δ65Cu and δ66Zn to support the determination of groundwater contamination sources may be encouraged, particularly where the isotopic signatures are distinct for each source.

Lead Isotope Signatures and Source Identification of Heavy Metals in Vegetable Soils Irrigated with Swine Wastewater of Jiangxi Province, China.

The rapid development of livestock and poultry industry in China has caused serious environment pollution problems. To understand the heavy metals accumulation and identify their sources, 7 heavy metals contents and lead isotope ratios were determined in 24 soil samples from vegetable fields irrigated with swine wastewater in Dongxiang County, Jiangxi Province, China. The results showed that the concentration of Cr, Ni, Cu, Zn, As, Cd and Pb in the swine wastewater irrigated vegetable soils varied from 38.5 to 86.4, 7.57 to 30.6, 20.0 to 57.1, 37.5 to 174, 9.18 to 53.1, 0.043 to 0.274 and 12.8 to 37.1 mg/kg, respectively. The soils were moderately to heavily polluted by As, moderately polluted by Cr, Ni, Cu, Zn and Cd, and unpolluted to moderately polluted by Pb. Sampling soils were classified as moderately polluted according to the Nemerow comprehensive pollution index. Lead isotope and Principal Component Analysis (PCA) analysis indicated that swine wastewater irrigation and atmospheric deposition were the primary sources of the heavy metals.

Spatiotemporal and multi-isotope assessment of metal sedimentation in the Great Lakes.

This study investigates spatiotemporal dynamics in metal sedimentation in the North American Great Lakes and their underlying biogeochemical controls. Bulk geochemical and isotope analyses of n = 72 surface and core sediment samples show that metal (Cu, Zn, Pb) concentrations and their isotopic compositions vary spatially across oligotrophic to mesotrophic settings, with intra-lake heterogeneity being similar or higher than inter-lake (basin-scale) variability. Concentrations of Cu, Zn, and Pb in sediments from Lake Huron and Lake Erie vary from 5 to 73 mg/kg, 18-580 mg/kg, and 5-168 mg/kg, respectively, but metal enrichment factors were small (<2) across the surface- and core sediments. The isotopic signatures of surface sediment Cu (δ65Cu between -1.19‰ and +0.96‰), Zn (δ66Zn between -0.09‰ and +0.41‰) and Pb (206/207Pb from 1.200 to 1.263) indicate predominantly lithogenic metal sourcing. In addition, temporal trends in sediment cores from Lake Huron and Lake Erie show uniform metal concentrations, minor enrichment, and Zn and Pb isotopic signatures suggestive of negligible in-lake biogeochemical fractionation. In contrast, Cu isotopic signatures and correlation to chlorophyll and macronutrient levels suggest more differentiation from source variability and/or redox-dependent fractionation, likely related to biological scavenging. Our results are used to derive baseline metal sedimentation fluxes and will help optimize water quality management and strategies for reducing metal loads and enrichment in the Great Lakes and beyond.

Calcium isotope fractionation by intracellular amorphous calcium carbonate (ACC) forming cyanobacteria.

The formation of intracellular amorphous calcium carbonate (ACC) by various cyanobacteria is a widespread biomineralization process, yet its mechanism and importance in past and modern environments remain to be fully comprehended. This study explores whether calcium (Ca) isotope fractionation, linked to ACC-forming cyanobacteria, can serve as a reliable tracer for detecting these microorganisms in modern and ancient settings. Accordingly, we measured stable Ca isotope fractionation during Ca uptake by the intracellular ACC-forming cyanobacterium Cyanothece sp. PCC 7425. Our results show that Cyanothece sp. PCC 7425 cells are enriched in lighter Ca isotopes relative to the solution. This finding is consistent with the kinetic isotope effects observed in the Ca isotope fractionation during biogenic carbonate formation by marine calcifying organisms. The Ca isotope composition of Cyanothece sp. PCC 7425 was accurately modeled using a Rayleigh fractionation model, resulting in a Ca isotope fractionation factor (Δ44Ca) equal to -0.72 ± 0.05‰. Numerical modeling suggests that Ca uptake by these cyanobacteria is primarily unidirectional, with minimal back reaction observed over the duration of the experiment. Finally, we compared our Δ44Ca values with those of other biotic and abiotic carbonates, revealing similarities with organisms that form biogenic calcite. These similarities raise questions about the effectiveness of using the Ca isotope fractionation factor as a univocal tracer of ACC-forming cyanobacteria in the environment. We propose that the use of Δ44Ca in combination with other proposed tracers of ACC-forming cyanobacteria such as Ba and Sr isotope fractionation factors and/or elevated Ba/Ca and Sr/Ca ratios may provide a more reliable approach.

Applicability of self-consistent reaction field (SCRF) method to DFT estimation of hydrogen isotope separation factors in reversible processes.

In earlier quantum chemical calculations of isotope effects, chemical species in the liquid phase were generally treated as existing in the gas phase. In recent years, however, advances in computational programs have made it easier for the self-consistent reaction field (SCRF) method to handle chemical species in the liquid phase, and as a result, it has become easier to apply the SCRF method to isotope effect calculations. This paper concerns the scope of application of the DFT-SCRF method to reversible processes for hydrogen isotope enrichment. It is found that the applicability of the method depends on the type of the intermolecular interaction in the liquid phase and the degree of hydrogen isotope effect (separation factor) on which the process is based. When the magnitude of the isotope effect of the separation system is greater than 10-1, the simple SCRF method is fully applicable; when the magnitude is around 10-2, SCRF with a dimer model, in which the monomer is replaced by a dimer, is applicable for the analysis of the liquid phase with relatively strong intermolecular interactions. Anharmonic correction to the separation factor calculated based on harmonic frequencies may be effective to systems with the liquid phase with weak intermolecular interactions.

Spatial ecology of moose in Sweden: Combined Sr-O-C isotope analyses of bone and antler.

The study of spatial (paleo)ecology in mammals is critical to understand how animals adapt to and exploit their environment. In this work we analysed the 87Sr/86Sr, δ18O and δ13C isotope composition of 65 moose bone and antler samples from Sweden from wild-shot individuals dated between 1800 and 1994 to study moose mobility and feeding behaviour for (paleo)ecological applications. Sr data were compared with isoscapes of the Scandinavian region, built ad-hoc during this study, to understand how moose utilise the landscape in Northern Europe. The 87Sr/86Sr isoscape was developed using a machine-learning approach with external geo-environmental predictors and literature data. Similarly, a δ18O isoscape, obtained from average annual precipitation δ18O values, was employed to highlight differences in the isotope composition of the local environment vs. bone/antler. Overall, 82% of the moose samples were compatible with the likely local isotope composition (n = 53), suggesting that they were shot not far from their year-round dwelling area. 'Local' samples were used to calibrate the two isoscapes, to improve the prediction of provenance for the presumably 'non-local' individuals. For the latter (n = 12, of which two are antlers and ten are bones), the probability of geographic origin was estimated using a Bayesian approach by combining the two isoscapes. Interestingly, two of these samples (one antler and one bone) seem to come from areas more than 250 km away from the place where the animals were hunted, indicating a possible remarkable intra-annual mobility. Finally, the δ13C data were compared with the forest cover of Sweden and ultimately used to understand the dietary preference of moose. We interpreted a difference in δ13C values of antlers (13C-enriched) and bones (13C-depleted) as a joint effect of seasonal variations in moose diet and, possibly, physiological stresses during winter-time, i.e., increased consumption of endogenous 13C-depleted lipids.

Transformation of Mercurous [Hg(I)] Species during Laboratory Standard Preparation and Analysis: Implication for Environmental Analysis.

Hg(I) may control Hg redox kinetics; however, its metastable nature hinders analysis. Herein, the stability of Hg(I) during standard preparation and analysis was studied. Gravimetric analysis showed that Hg(I) was stable in its stock solution (1000 mg L-1), yet completely disproportionated when its dilute solution (10 µg L-1) was analyzed using liquid chromatography (LC)-ICPMS. The Hg(I) dimer can form through an energetically favorable comproportionation between Hg(0) and Hg(II), as supported by density functional theory calculation and traced by the rapid isotope exchange between 199Hg(0)aq and 202Hg(II). However, the separation of Hg(0) and Hg(II) (e.g., LC process) triggered its further disproportionation. Polypropylene container, increasing headspace, decreasing pH, and increasing dissolved oxygen significantly enhanced the disproportionation or redox transformations of Hg(I). Thus, using a glass container without headspace and maintaining a slightly alkaline solution are recommended for the dilute Hg(I) stabilization. Notably, we detected elevated concentrations of Hg(I) (4.4-6.1 µg L-1) in creek waters from a heavily Hg-polluted area, accounting for 54-70% of total dissolved Hg. We also verified the reductive formation of Hg(I) in Hg(II)-spiked environmental water samples, where Hg(I) can stably exist in aquatic environments for at least 24 h, especially in seawater. These findings provide mechanistic insights into the transformation of Hg(I), which are indicative of its further environmental identification.

Vertebral microchemistry as an indicator of habitat use of the oceanic whitetip shark Carcharhinus longimanus in the central and eastern Pacific Ocean.

The oceanic whitetip shark, Carcharhinus longimanus, is a highly migratory, epipelagic top predator that is classified as critically endangered. Although this species is widely distributed throughout the world's tropical oceans, its assumed mobility and pelagic behavior limit studies to derive required lifetime data for management. To address this data deficiency, we assessed variation in the habitat use of C. longimanus by oceanic region and over ontogeny through time series trace element and stable isotope values conserved along the vertebral centra (within translucent annulus bands) of 13 individuals sampled from the central and eastern Pacific Ocean. Elemental ratios of Mg:Ca, Mn:Ca, Fe:Ca, Zn:Ca, and Ba:Ca varied significantly among individuals from both sampling regions while principal component analysis of combined standardized elements revealed minimal overlap between the two areas. The limited overlap was also in agreement with stable isotope niches. These findings indicate that C. longimanus exhibit a degree of fidelity to sampling regions but also connectivity in a proportion of the population. The relatively stable Sr:Ca ratio supports its occurrence in oceanic environments. The decreasing trends in Ba:Ca, Mn:Ca, and Zn:Ca ratios, as well as in carbon and nitrogen isotope values along vertebral transects, indicate that C. longimanus undergo a directional habitat shift with age. Combined elemental and stable isotope values in vertebral centra provide a promising tool for elucidating lifetime data for complex pelagic species. For C. longimanus, management will need to consider subpopulation movement behavior in the Pacific to minimize the potential for localized depletions. Further work is now required to sample individuals across the entire Pacific and to link these findings with genetic and movement data to define population structure.

The Roles of Diet and Habitat Use in Pesticide Bioaccumulation by Juvenile Chinook Salmon: Insights from Stable Isotopes and Fatty Acid Biomarkers.

Stable isotopes (SI) and fatty acid (FA) biomarkers can provide insights regarding trophic pathways and habitats associated with contaminant bioaccumulation. We assessed relationships between SI and FA biomarkers and published data on concentrations of two pesticides [dichlorodiphenyltrichloroethane and degradation products (DDX) and bifenthrin] in juvenile Chinook Salmon (Oncorhynchus tshawytscha) from the Sacramento River and Yolo Bypass floodplain in Northern California near Sacramento. We also conducted SI and FA analyses of zooplankton and macroinvertebrates to determine whether particular trophic pathways and habitats were associated with elevated pesticide concentrations in fish. Relationships between DDX and both sulfur (δ34S) and carbon (δ13C) SI ratios in salmon indicated that diet is a major exposure route for DDX, particularly for individuals with a benthic detrital energy base. Greater use of a benthic detrital energy base likely accounted for the higher frequency of salmon with DDX concentrations > 60 ng/g dw in the Yolo Bypass compared to the Sacramento River. Chironomid larvae and zooplankton were implicated as prey items likely responsible for trophic transfer of DDX to salmon. Sulfur SI ratios enabled identification of hatchery-origin fish that had likely spent insufficient time in the wild to substantially bioaccumulate DDX. Bifenthrin concentration was unrelated to SI or FA biomarkers in salmon, potentially due to aqueous uptake, biotransformation and elimination of the pesticide, or indistinct biomarker compositions among invertebrates with low and high bifenthrin concentrations. One FA [docosahexaenoic acid (DHA)] and DDX were negatively correlated in salmon, potentially due to a greater uptake of DDX from invertebrates with low DHA or effects of DDX on FA metabolism. Trophic biomarkers may be useful indicators of DDX accumulation and effects in juvenile Chinook Salmon in the Sacramento River Delta.

Hydrochemical systematics and isotope (δ18O, δD and 3H) variations of aquifer system of southern Bengal Basin: implications for groundwater pollution.

Hydrogeological, hydrochemical and isotopic traits of the groundwater in the Quaternary aquifer system in an urban-periurban locality within and encircling the Kolkata-Howrah twin city in the south Bengal Basin have been synthesised to explain the present- and paleo-hydrological processes, surface and groundwater interaction and mixing dynamics of contamination of groundwater. Rock-weathering, evaporation, ion-exchange and active mineral dissolution are the key processes commanding the groundwater chemistry. Freshwater flushing from the recharge zones had thinned the entrapped sea water which has generated the present-day brackish water by a non-uniform fusion. The best-fit line of the plots of δD and δ18O of groundwater samples displays a slope lower than that of local meteoric water line (LMWL) and global meteoric water line (GMWL) which hints that isotopic constitution of the groundwater of the present area is primarily formed by evaporation before or in the recharging process. A wide range of δ18O values in groundwater suggests that these waters are not blended enough to remove dissimilarities in isotope configuration of recharge water. This also suggests that many groundwaters are a result of mixing of present-day recharge and an older integrant recharged under previously cooler climatic conditions. The groundwater samples are more depleted of oxygen at the shallower level. The depleted samples cluster around the Tolly's nala (canal) where upper aquitard is missing or < 10-m thick. The tritium values range between 0.70 and 15.02 which indicate the occurrence of 'sub-modern', 'a mix of modern and sub-modern water' and 'modern water'. It indicates mingling of isotope-depleted water from the Hugli River by means of Tolly's canal with relatively less-depleted groundwater of Kolkata's late Pleistocene aquifer. The tritium values and Cl/Br ratio of groundwater samples adjoining Tolly's canal and elsewhere refer the direct infiltration of 'modern wastewater and freshwater' which mixes with the 'sub-modern water' in the aquifer system.

Finding balance: Tree-ring isotopes differentiate between acclimation and stress-induced imbalance in a long-term irrigation experiment.

Scots pine (Pinus sylvestris L.) is a common European tree species, and understanding its acclimation to the rapidly changing climate through physiological, biochemical or structural adjustments is vital for predicting future growth. We investigated a long-term irrigation experiment at a naturally dry forest in Switzerland, comparing Scots pine trees that have been continuously irrigated for 17 years (irrigated) with those for which irrigation was interrupted after 10 years (stop) and non-irrigated trees (control), using tree growth, xylogenesis, wood anatomy, and carbon, oxygen and hydrogen stable isotope measurements in the water, sugars and cellulose of plant tissues. The dendrochronological analyses highlighted three distinct acclimation phases to the treatments: irrigated trees experienced (i) a significant growth increase in the first 4 years of treatment, (ii) high growth rates but with a declining trend in the following 8 years and finally (iii) a regression to pre-irrigation growth rates, suggesting the development of a new growth limitation (i.e. acclimation). The introduction of the stop treatment resulted in further growth reductions to below-control levels during the third phase. Irrigated trees showed longer growth periods and lower tree-ring δ13 C values, reflecting lower stomatal restrictions than control trees. Their strong tree-ring δ18 O and δ2 H (O-H) relationship reflected the hydrological signature similarly to the control. On the contrary, the stop trees had lower growth rates, conservative wood anatomical traits, and a weak O-H relationship, indicating a physiological imbalance. Tree vitality (identified by crown transparency) significantly modulated growth, wood anatomical traits and tree-ring δ13 C, with low-vitality trees of all treatments performing similarly regardless of water availability. We thus provide quantitative indicators for assessing physiological imbalance and tree acclimation after environmental stresses. We also show that tree vitality is crucial in shaping such responses. These findings are fundamental for the early assessment of ecosystem imbalances and decline under climate change.