NaFeEDTA fortified soy sauce showed higher iron absorption rate in Chinese females

Objective NaFeEDTA was considered as a promising iron fortificant for controlling iron deficiency anemia. Soy sauce is a suitable food carrier for iron fortification and is a popular condiment in China. Iron absorption rates of NaFeEDTA and FeSO4 were observed and compared in adult female subjects. Methods The stable isotope tracer method was used in Chinese females consuming a typical Chinese diet. Ten healthy young Chinese women were selected as subjects in the 15-day study. A plant-based diet was used based on the dietary pattern of adult women in the 1992 National Nutrition Survey. Six milligram of 54Fe in 54FeSO4 soy sauce and 3 mg 58Fe in Na58FeEDTA soy sauce were given to the same subjects in two days. Food samples and fecal samples were collected and analyzed. Results Iron absorption rates of NaFeEDTA and FeSO4 were 10.51%±2.83 and 4.73%±2.15 respectively. The 58Fe(NaFeEDTA) absorption was significantly higher than that of 54Fe(FeSO4)(P<0.01). The iron absorption rate from NaFeEDTA was 1.2 times higher than that from FeSO4 in Chinese adult women consuming a typical Chinese diet. Conclusion The higher absorption rate of NaFeEDTA suggested that NaFeEDTA would be a better iron fortificant used in soy sauce for the controlling of iron deficiency anemia in China.     

Global tree intrinsic water use efficiency is enhanced by increased atmospheric CO2 and modulated by climate and plant functional types

We conducted a meta-analysis of carbon and oxygen isotopes from tree ring chronologies representing 34 species across 10 biomes to better understand the environmental drivers and physiological mechanisms leading to historical changes in tree intrinsic water use efficiency (iWUE), or the ratio of net photosynthesis (A_net) to stomatal conductance (g_s), over the last century. We show a ∼40% increase in tree iWUE globally since 1901, coinciding with a ∼34% increase in atmospheric CO₂ (C_a), although mean iWUE, and the rates of increase, varied across biomes and leaf and wood functional types. While C_a was a dominant environmental driver of iWUE, the effects of increasing C_a were modulated either positively or negatively by climate, including vapor pressure deficit (VPD), temperature, and precipitation, and by leaf and wood functional types. A dual carbon–oxygen isotope approach revealed that increases in A_net dominated the observed increased iWUE in ∼83% of examined cases, supporting recent reports of global increases in A_net, whereas reductions in g_s occurred in the remaining ∼17%. This meta-analysis provides a strong process-based framework for predicting changes in tree carbon gain and water loss across biomes and across wood and leaf functional types, and the interactions between C_a and other environmental factors have important implications for the coupled carbon–hydrologic cycles under future climate. Our results furthermore challenge the idea of widespread reductions in g_s as the major driver of increasing tree iWUE and will better inform Earth system models regarding the role of trees in the global carbon and water cycles.

How terrestrial plants respond to more frequent, and often prolonged, environmental stressors will have profound impacts on, and feedbacks to, the Earth-climate system at regional to continental scales (1, 2). Central to these feedbacks are plant stomata, microscopic pores on the leaves of plants that act as a control valve over the fluxes of carbon dioxide (C_a) into the leaf during photosynthesis and water vapor (H₂O) out of the leaf during transpiration. Importantly, changes in stomatal aperture do not affect the fluxes of C_a and H₂O equally, as the sum of resistances for the diffusion of C_a from the atmosphere to mesophyll cells where Rubisco is located are much greater than those for H₂O from the surface of leaf mesophyll cells to the atmosphere (3). Indeed, as stomatal aperture changes, so does water use efficiency (WUE), or the ratio of C_a uptake to H₂O released from the leaf to canopy scale (4). Consequently, understanding the environmental factors driving changes in leaf physiology is of paramount concern in the context of climate change as small changes in tree WUE can have major effects on the carbon and hydrologic cycles over large geographical areas (1, 5).Approaches using tree ring carbon isotopes (6–9), eddy-flux measurements (4, 9, 10), atmospheric carbon isotope composition analysis (11), and Earth system modeling techniques (9–13) have shown trends of recently increasing WUE. These increases can occur by stimulation of leaf photosynthetic rates (A_net) (14, 15), reduced stomatal conductance to water (g_s) (14, 15), or some combination of the two. A fundamental physiological response found in numerous C_a enrichment experiments is that WUE of many plants is improved as a result of increasing C_a stimulating photosynthesis and causing partial stomatal closure (14, 16). However, environmental factors distinct from C_a, such as vapor pressure deficit (VPD), precipitation, and temperature, have independent effects on A_net and g_s and, therefore, may modulate the response of WUE to rising C_a, especially across functionally distinct plant groups with differences in wood anatomy (9) and leaf morphology (17). Despite this, few studies have thoroughly examined the effects of multiple environmental factors over controls of WUE, and even fewer have considered the underlying component parts, A_net and g_s (9, 13, 17–20). This has, in part, been due to the complexity of partitioning H₂O gas fluxes at ecosystem scales (21), in addition to the difficulty in attributing changes in isotopically derived intrinsic water use efficiency (iWUE) (the ratio of A_net to stomatal conductance to water, g_s) to A_net or g_s without the accompaniment of physiological measurements (18, 19).A promising technique couples carbon isotopically derived estimates of iWUE with oxygen isotope leaf water enrichment above source water (∆¹⁸O_lw; derived from tree ring δ¹⁸O and source water δ¹⁸O assumed to be ∼δ¹⁸O_{precipitation}) to provide a qualitative attribution of changes in iWUE to underlying A_net and g_s (9, 20, 22–29). As ∆¹⁸O_lw is inversely related to g_s (26–30), if increases in iWUE were due to increases in A_net, then Δ¹⁸O_lw should be constant or decrease with iWUE. However, if increases in iWUE were due to decreases in g_s, or a combination of a decrease in g_s and an increase in A_net, Δ¹⁸O_lw would increase with iWUE (9, 25, 30). As such, there currently exists a wealth of previously untapped long-term records of tree physiological responses to environmental change within numerous dendrochronological studies from around the world, providing a historical view of how iWUE has changed globally over the last century. In this analysis, we 1) synthesize published data from tree ring carbon and oxygen isotope chronologies to examine global trends in tree ring–derived iWUE, 2) identify those environmental factors, and their interactions, that best explain multidecadal to centurial trends in iWUE, and 3) investigate the potential underlying changes in A_net and g_s through an analysis of coupled tree ring–derived iWUE and ∆¹⁸O_lw over time (9, 20, 22, 23, 25).Using 113 unique tree ring carbon and oxygen isotope chronologies comprising 36 different species across 84 sites globally (Fig. 1A and SI Appendix, Table S1), we show tree-level iWUE increased, on average, by ∼40% (0.35% y⁻¹, iWUE = 0.23*y − 369.16) over the last century (1901–2015) (Fig. 1B). We statistically identified a breakpoint in the combined iWUE chronology at 1963, after which iWUE increased linearly at a rate of 0.39 ± 0.01 µmol CO₂⋅mol⁻¹ H₂O⋅y⁻¹ (1.67% y⁻¹), or ∼3.9 times faster than the previous 63 y (F = 207.14, P < 0.0001) (Fig. 1B and SI Appendix, Fig. S1). This change in the rate at which tree iWUE increased after 1963 coincided with a statistical breakpoint in C_a at 1969 where CO₂ began increasing 4.1 times faster than between 1901 and 1969 (SI Appendix, Fig. S2) (31), and is similar to the trend in iWUE from a recent global synthesis by Adams et al. (32) who also showed a similar breakpoint in the 1960s. When considering individual chronologies, the increases in iWUE were widespread, with 93% (105 of 113 chronologies) of those examined having positive trends over 1901–2015 and 84% (95 of 113) of those examined having positive trends over 1963–2015 (SI Appendix, Table S1). These data for trees during the Anthropocene spanning 10 biomes in six continents that represent a spectrum of leaf and wood types reinforce reports of increasing iWUE in the United States (9), Europe (6, 8), and tropical forests (7), in addition to a recent compilation of global iWUE trends (32).Open in a separate windowFig. 1.Tree locations from which chronologies of iWUE and ∆¹⁸O_lw were developed (A) and group mean-centered iWUE by species within site over the period 1901–2015 (B). The color of data points in A and B correspond to the biome from which trees were growing, while the size of the circle in A corresponds to the number of trees used in the development of each carbon and oxygen isotope-derived chronology, respectively. The vertical dashed line in B occurs at the year 1963 where the rate of change in iWUE increases. The solid lines in B denote the average trend in iWUE for the period before (1901–1963) and after (1963–2015) the identified breakpoint. Data for iWUE trends and the number of trees per chronology are listed in SI Appendix, Table S1.Globally, differences in vegetation physiognomy may have large impacts on iWUE, and despite much work examining plant physiological processes within biomes, there have been few large-scale comparisons of historical tree iWUE across biomes at a global scale (6, 8, 9, 12, 32). In this study, we found the rate of increase of iWUE from 1963 to 2015 differed among the 10 biomes represented (F = 7.21, P < 0.001) and ranged between 0.101 ± 0.07 µmol CO₂⋅mol⁻¹ H₂O⋅y⁻¹ for trees growing in deserts and xeric shrublands to 0.611 ± 0.07 µmol CO₂⋅mol⁻¹ H₂O⋅y⁻¹ for Mediterranean forests, woodlands, and scrub (SI Appendix, Fig. S3A and Table S2). Like deserts and xeric shrublands, the rate of iWUE increase since 1963 for trees growing in the tundra and in temperate grasslands, savannas, and shrublands was low, with a mean across the three biomes of 0.131 µmol CO₂⋅mol⁻¹ H₂O⋅y⁻¹. All other biomes exhibit mean rates of iWUE increase after 1963 greater than 0.409 µmol CO₂⋅mol⁻¹ H₂O⋅y⁻¹ (SI Appendix, Table S2). Furthermore, mean iWUE over 1963–2015 ranged from a low of 59.9 µmol CO₂⋅mol⁻¹ H₂O in tropical and subtropical moist broadleaf forests to a high of 91.5 µmol CO₂⋅mol⁻¹ H₂O in temperate conifer forests (SI Appendix, Fig. S3A).When considering changes in iWUE since 1963 with respect to wood anatomy, the rate of iWUE increase was ∼21% higher for conifers relative to diffuse porous trees (P = 0.022), but we found no difference in the rate of iWUE increase between conifer trees and ring porous trees (P = 0.61) or between diffuse porous trees and ring porous trees (P = 0.27) (SI Appendix, Fig. S4A). Our results are similar to climate-corrected iWUE trends from tree rings presented by Frank et al. (6) in European forests, but are in contrast to work by Saurer et al. (33) and Wang et al. (34) using tree rings and flux tower measurements, respectively, who showed broadleaf deciduous trees (i.e., ring porous and diffuse porous) in the Northern hemisphere having greater rates of increase in iWUE than conifer trees over the last century. It is important to note, however, that minor discrepancies among absolute iWUE values and their trends over time in these studies when compared to ours may have resulted from the formulation (i.e., our inclusion of a photorespiratory term) (35) and methodology differences (i.e., tree ring, flux tower) (36). We found no differences in the rate of iWUE increase since 1963 among trees with different leaf functional types (F = 1.05, P = 0.37) (SI Appendix, Fig. S4C). Additionally, we found mean iWUE during 1963–2015 was different among all wood types (F = 782.96, P < 0.001), being the highest in conifer species and lowest in ring porous species (SI Appendix, Fig. S4B), consistent with recent findings from 12 tree species at eight forested sites in the United States (9). Of important note, the patterns in mean iWUE for each wood type fall along a gradient of hydraulic conductivity and safety trade-offs (37). Conifer trees, which have relatively low hydraulic conductivity, but are more resistant to drought induced cavitation and embolism, had the highest mean iWUE, in contrast to ring porous trees, which have higher hydraulic conductivity, but are more vulnerable to hydraulic failure, which had lower mean iWUE (38–40). Mean iWUE was also different among trees with different leaf types, with needleleaf evergreen trees being the highest, followed by needleleaf deciduous trees, broadleaf evergreen trees, and finally broadleaf deciduous trees (SI Appendix, Fig. S4D).Changes in climate and C_a have strong effects on vegetation function from the leaf (14, 15) to global scale (13, 41, 42), yet how environmental change has influenced iWUE across large spatial scales over the last century is not fully resolved. Guerrieri et al. (9) and Frank et al. (6) recently showed increasing C_a and climate change have led to increased iWUE in tree species across the United States and Europe, but whether this response is conserved across biomes experiencing a much larger range in climate is still unknown. To address this knowledge gap, we used linear mixed effects (LME) models to examine the importance of environmental factors in driving tree iWUE. Across all species and study locations from 1963–2015, LME model results explained as much as ∼89% of the variance in iWUE and indicated a strong, positive relationship with C_a and growing season vapor pressure deficit (VPD_grw) and a negative relationship with growing season precipitation (PPT_grw), although a large proportion of the total variance was attributed to differences among sites (Table 1 and SI Appendix, Table S3). Remaining unaccounted variance may include nonclimatic factors, such as nitrogen availability or acidic air pollution, which are known to have important influences over iWUE (19, 43, 44), but these were not included in the studies from which we extracted isotopic data. When extending this analysis to changes in iWUE over the last 115 y (1901–2015), LME model main effects were remarkably consistent with data from 1963–2015, with the exception of growing season temperature (TMP_grw) having a marginally positive effect on iWUE across the 115-y chronology (SI Appendix, Table S4), which suggests TMP_grw is becoming more important in recent years.Table 1.LME model results and parameters for the best model (lowest AICc) examining the drivers of tree ring–derived iWUE for the period 1963–2015

From the Cover: Dietary changes of large herbivores in the Turkana Basin,Kenya from 4 to 1 Ma

A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites that range from forest to grassland shows that most extant East and Central African large herbivore taxa have diets dominated by C₄ grazing or C₃ browsing. Comparison with the fossil record shows that faunal assemblages from ca. 4.1–2.35 Ma in the Turkana Basin had a greater diversity of C₃–C₄ mixed feeding taxa than is presently found in modern East and Central African environments. In contrast, the period from 2.35 to 1.0 Ma had more C₄-grazing taxa, especially nonruminant C₄-grazing taxa, than are found in modern environments in East and Central Africa. Many nonbovid C₄ grazers became extinct in Africa, notably the suid Notochoerus, the hipparion equid Eurygnathohippus, the giraffid Sivatherium, and the elephantid Elephas. Other important nonruminant C₄-grazing taxa switched to browsing, including suids in the lineage Kolpochoerus-Hylochoerus and the elephant Loxodonta. Many modern herbivore taxa in Africa have diets that differ significantly from their fossil relatives. Elephants and tragelaphin bovids are two groups often used for paleoecological insight, yet their fossil diets were very different from their modern closest relatives; therefore, their taxonomic presence in a fossil assemblage does not indicate they had a similar ecological function in the past as they do at present. Overall, we find ecological assemblages of C₃-browsing, C₃–C₄-mixed feeding, and C₄-grazing taxa in the Turkana Basin fossil record that are different from any modern ecosystem in East or Central Africa.The expansion of C₄ biomass beginning in the late Miocene marks a major vegetation change in the history of Earth. Today C₄ plants comprise ca. 50% of net primary productivity (NPP) in the tropics (1) yet contributed less than 1% of NPP only 10 million years ago. C₄ plants are primarily grasses and sedges, although C₄ photosynthesis is known to be used in ∼20 plant families (2, 3). C₄ photosynthesis is an adaptation to low (ca. <500 ppm by volume) concentrations of CO₂ in Earth’s atmosphere along with high growing-season temperatures (4). Although genetic evidence indicates an Oligocene origin of C₄ photosynthesis in the grasses (5, 6), macrofossil evidence for C₄ photosynthesis in grasses is extremely sparse (7, 8).The expansion of C₄ biomass has been documented through stable isotopes in paleosols (9–12), grass phytoliths (13), herbivore tooth enamel (14–16), and biomarkers in deep-sea sediments (17, 18). At 10 Ma in Africa, Asia, and North America, the δ¹³C values for equid tooth enamel indicate a diet dominated by C₃ vegetation; by ca. 7 Ma, equids in Africa have a diet dominated (>75%) by C₄ vegetation (14, 15). In East Africa today there is a distinct difference in diets of major herbivores, with most mammals either being predominantly browsing (>ca. 75% C₃) or grazing (>ca. 75% C₄), and there are relatively few mixed feeders (Fig. 1).Open in a separate windowFig. 1.δ¹³C₁₇₅₀ values for tooth enamel (or equivalent) for >1,900 mammals from East and Central Africa (principal localities in SI Appendix, Table S1; data from Dataset S1).A recent study of the early transition of C₃ to C₄ dietary change in the Turkana Basin from 10 Ma to ca. 4 Ma (15) showed that equids were the earliest mammals to fully exploit the C₄ dietary resource, attaining a predominantly C₄-grazing diet by 7 Ma. Other mammal groups (hippopotamids, elephantids, and bovids) changed to a C₄ diet later than did the equids. In this paper we document dietary changes in the major Artiodactyla-Perissodactyla-Proboscidea (APP) taxa in the Turkana Basin between ca. 4 Ma and 1 Ma and compare those to dietary preferences of extant APP taxa in East and Central Africa. The Turkana Basin has an excellent stratigraphy (19–22) with excellent preservation of fossils from 4 to 1 Ma; this study focuses on fossils recovered from the Koobi Fora, Kanapoi, and Nachukui Formations of northern Kenya.We compare dietary changes within the major APP taxa through the past 4 Ma in the formations listed above using >900 individual fossils that represent the major taxa collected within the principal stratigraphic intervals of these formations. Fossil mammalian diets are compared with those of >1,900 extant mammal individuals sampled from >30 different regions and habitats in eastern and central Africa. We compare the ecosystem structure (C₃ browsers, C₃/C₄ mixed diets, and C₄ grazers) through the Pliocene and Pleistocene and document changes in ungulate diets over time.     

Dietary change among hominins and cercopithecids in Ethiopia during the early Pliocene

The incorporation of C₄ resources into hominin diet signifies increased dietary breadth within hominins and divergence from the dietary patterns of other great apes. Morphological evidence indicates that hominin diet became increasingly diverse by 4.2 million years ago but may not have included large proportions of C₄ foods until 800 thousand years later, given the available isotopic evidence. Here we use carbon isotope data from early to mid Pliocene hominin and cercopithecid fossils from Woranso-Mille (central Afar, Ethiopia) to constrain the timing of this dietary change and its ecological context. We show that both hominins and some papionins expanded their diets to include C₄ resources as early as 3.76 Ma. Among hominins, this dietary expansion postdates the major dentognathic morphological changes that distinguish Australopithecus from Ardipithecus, but it occurs amid a continuum of adaptations to diets of tougher, harder foods and to committed terrestrial bipedality. In contrast, carbon isotope data from cercopithecids indicate that C₄-dominated diets of the earliest members of the Theropithecus oswaldi lineage preceded the dental specialization for grazing but occurred after they were fully terrestrial. The combined data indicate that the inclusion of C₄ foods in hominin diet occurred as part of broader ecological changes in African primate communities.The Pliocene is a critical time in human evolution when almost all early hominins became committed terrestrial bipeds and expanded their diets to include a wider range of resources than their ancestors. Recent stable isotope studies of Australopithecus afarensis teeth indicate that hominins had increased their dietary breadth to include significant amounts of C₄ or crassulacean acid metabolism (CAM) resources by 3.4 Ma (1), which is in contrast to its putative ancestor, Australopithecus anamensis, whose diet was limited to predominantly C₃ foods (2). The expansion in hominin diets to include significant amounts of C₄ and CAM resources indicates a transition toward more open-country foods, because C₃ plants include trees, shrubs, forbs, and cool-growing season grasses, whereas C₄ plants are primarily warm-growing season grasses and sedges, and CAM plants include cacti and succulents (3). This dietary expansion may have made it easier for hominins to survive in a greater range of environments or in environments that were more variable. However, we do not know when hominins started to include large proportions of C₄ resources in their diets, nor do we fully understand the ecological context of these changes (1, 4).We use stable carbon isotope ratios of fossil hominin and cercopithecid teeth from Woranso-Mille in the western part of the central Afar Rift in Ethiopia (Fig. S1) to refine the timing of hominin dietary expansion to include C₄ resources. We also report isotope data from other mammals and soil carbonates to evaluate the environmental context and the diagenetic integrity of the isotope data. We use stable carbon isotope ratios, or δ¹³C values, of fossil teeth to evaluate the dietary proportion of plants that use the C₃ vs. C₄ photosynthetic pathway, based on the premise that C₃ and C₄ plants have distinct carbon isotope signatures and that the δ¹³C value of tooth enamel reflects the carbon isotope composition of an animal’s diet (5). Fossil teeth from the Woranso-Mille paleontological study area are well-suited to fill the temporal gap in the isotopic record of hominin diet because they are part of a record of Pliocene mammalian fossils that spans 3.76–3.2 Ma (6–11). The hominin fossils from Woranso-Mille include those that are morphologically intermediate between Au. anamensis and Au. afarensis, some that are definitively Au. afarensis, and others that represent additional species (7–9, 12). The cercopithecids include multiple species of colobines and at least two papionins (10). Theropithecus oswaldi cf. darti is the most common cercopithecid in the assemblages (>90% of identifiable cercopithecid specimens; 40% of the total identifiable mammal specimens) (6, 10); it represents the oldest and most primitive representative of the long-lasting T. oswaldi lineage whose morphology became increasingly specialized for grazing throughout the Pliocene and into the Pleistocene (13). The carbon isotope data from cercopithecids sympatric to hominins at Woranso-Mille make it possible to evaluate the ecological context for dietary changes in hominins.Open in a separate windowFig. S1.Map with locations of sites discussed in text and listed in Datasets S2 and S5. Woranso-Mille, Middle Awash (Aramis, Asa Issie, Asa Koma), Dikika, Gona (Segala Noumou), and Hadar and are in the Afar region in Ethiopia. Lomekwi, Allia Bay, and Kanapoi are in the Omo-Turkana region of Kenya. Imagery is from NASA''s Earth Observatory from August 2004 (72).     

From the Cover: Strong evidence for the continued contribution of lead deposited during the 20th century to the atmospheric environment in London of today

Although leaded gasoline was banned at the end of the last century, lead (Pb) remains significantly enriched in airborne particles in large cities. The remobilization of historical Pb deposited in soils from atmospheric removal has been suggested as an important source providing evidence for the hypothetical long-term persistency of lead, and possibly other pollutants, in the urban environment. Here, we present data on Pb isotopic composition in airborne particles collected in London (2014 to 2018), which provide strong support that lead deposited via gasoline combustion still contributes significantly to the lead burden in present-day London. Lead concentration and isotopic signature of airborne particles collected at a heavily trafficked site did not vary significantly over the last decade, suggesting that sources remained unchanged. Lead isotopic composition of airborne particles matches that of road dust and topsoils and can only be explained with a significant contribution (estimate of 32 ± 10 to 43 ± 9% based on a binary mixing model) of Pb from leaded gasoline. The lead isotopes furthermore suggest significant contributions from nonexhaust traffic emissions, even though isotopic signatures of anthropogenic sources are increasingly overlapping. Lead isotopic composition of airborne particles collected at building height shows a similar signature to that collected at street level, suggesting effective mixing of lead within the urban street canyon. Our results have important implications on the persistence of Pb in urban environments and suggest that atmospheric Pb reached a baseline in London that is difficult to decrease further with present policy measures.

Risk assessments of environmental lead (Pb) exposure have drawn the conclusion that it is not possible to identify a blood Pb level below which no adverse impact is detectable (1, 2). Even very low blood Pb levels in children are associated with a loss of full-scale intelligence quotient (IQ) score, and the curve steepens at lower blood Pb levels, with a greater loss of IQ points per unit of blood Pb in the lowest exposure groups (1, 2). Although currently available research has included subjects with very low blood Pb, it is not possible for such studies to go to zero Pb, but it is prudent to treat Pb as a nonthreshold toxin (3). Bellinger estimated full-scale IQ point losses in the early 2000s in the US child population associated with six medical conditions, four neurodevelopmental disorders, two socioeconomic, nutritional, and psychosocial factors, and three environmental chemical exposures (methylmercury, organophosphate pesticides, and Pb) (1). Pb exposure ranked second among all fifteen risk factors, behind only preterm birth and first among the environmental chemical exposures. Much of the summed IQ loss occurred among the lowest-exposed groups due to their larger numbers, and even if population blood Pb levels have declined since the Bellinger study and more children have hence moved into the lower exposure groups (4), the total IQ loss across the population may remain substantial.A major policy achievement in our efforts to reduce Pb in the environment has been the global phaseout of Pb from gasoline at the end of the last century, which resulted in a drastic decrease of atmospheric Pb concentration, especially in urban and remote areas of Europe and North America. While exposure to Pb from paints, Pb pipes, and Pb-containing toys are now recognized as the main cause of elevated blood Pb levels in children in nonindustrial environments, Pb remains an environmental pollutant of great concern (5), as its ongoing existence in the environment affects environmental quality in cities and is raising particular concerns regarding long-term exposure (6). A significant association between Pb concentration in particulate matter smaller than 10 µm (PM₁₀) and the US population’s blood was recently demonstrated (7), suggesting that inhalation and/or ingestion of coarse particles might be an important pathway for human exposure to Pb. Viewed in this context, Pb in the environment remains a significant threat to public health, and it is absolutely essential to accurately identify and monitor the sources and pathways of Pb in the urban environment.While it has been suggested that Pb sources in urban environments today include local and/or distant emissions from industries, coal burning, and traffic (exhaust and nonexhaust emissions) (8–11), recent works studying Pb contamination of airborne particles in (peri-)urban environments (10, 12) have suggested that ongoing contributions of lead released into the environment by leaded gasoline combustion during the last century remain an important but underestimated source. If confirmed more widely, then abatement strategies aimed at eliminating Pb fully from the urban environment need to be adjusted. It is very important to note that these recent findings are in line with an early study of Pb in sediments and water of the San Francisco Bay, suggesting already in the early 2000s that recycling of legacy Pb from leaded gasoline may be a continuing threat to environmental health (13, 14). Furthermore, a shift in Pb concentrations within size distribution, from the fine range (PM_2.5) to the coarse range (PM₁₀), has been highlighted after the ban of leaded gasoline in the United States and Europe and ascribed to a change in dominant Pb sources consisting of industrial emissions and road dust resuspension instead of direct vehicle exhausts (15).Alkyl Pb motor fuel additives were used in the United Kingdom from the 1930s until phaseout was completed at the end of 1999. Although added in an organometallic form, Pb emissions from vehicles were predominantly in the form of a fine aerosol of inorganic Pb salts (16). The maximum permitted level of Pb in UK motor fuel was 0.84 g ⋅ L⁻¹. The limit fell successively to 0.40 g ⋅ L⁻¹ in 1981 and 0.15 g ⋅ L⁻¹ in 1986. At its peak in the early 1980s, of the order of 7,000 tons per year of Pb were emitted from road traffic exhaust in the United Kingdom, which had fallen to just 30 tons by the year 2000 (17). Until its final ban, leaded gasoline combustion remained the most important source of Pb emissions in the UK atmosphere (17). In the early 1980s, annual average airborne Pb concentrations at background sites in central London were around 500 to 600 ng ⋅ m⁻³, which fell to around 300 ng ⋅ m⁻³ in the second half of the 1980s and then dropped progressively to around 20 ng ⋅ m⁻³ in 2000. Airborne concentrations now are generally less than 10 ng ⋅ m⁻³ and have remained steady over the last decade (18).Using Pb isotope composition of atmospheric particles has been a crucial tool in tracing the origin of Pb in the environment and identifying leaded gasoline as a dominant source during the 20th century (19). Following the removal of Pb additives from gasoline in Europe, Pb isotope ratios of atmospheric particles generally changed toward more radiogenic values due to the increase in the relative contribution of other Pb sources (19). Such an evolution was recorded in London airborne particles between 1998 and 2001 during the final phasing out of leaded gasoline in the United Kingdom (20). However, this trend was no longer observed a decade later, leading to the suggestion that leaded gasoline remained an important source of atmospheric Pb (9).The aim of this study was to test if remobilization of historical gasoline-derived Pb remains today an important and persistent source of Pb in London and the urban environment. To this end, we studied the Pb isotope composition of airborne particles collected in central London between 1995 and 2018 using new and historical data and quantified the possible contribution of historical gasoline Pb. London is representative of many large cities in developed countries, where particle emissions from industries and coal combustion are now relatively low, and where traffic emissions and dust resuspension represent dominant sources of airborne particles. Therefore, it constitutes an ideal site to study the persistence of Pb in urban environments almost 20 y after the complete phaseout of leaded gasoline. The variability of Pb concentration and isotopic composition was determined in PM₁₀ and total suspended particles (TSP_passive) during 1 mo at a heavily trafficked site in central London (Marylebone Road site [MR]), where particle emissions are dominated by traffic. The data were compared with the previously published isotopic composition of potential Pb sources and PM₁₀ from this historically monitored site. In addition, the variability of Pb isotopic composition in TSP_passive collected between 2014 and 2018 at building height in central London (Imperial College London site [IC]) is reported to determine mixing and source contributions within the urban canyon.     

Magnesium isotope geochemistry in arc volcanism

Incorporation of subducted slab in arc volcanism plays an important role in producing the geochemical and isotopic variations in arc lavas. The mechanism and process by which the slab materials are incorporated, however, are still uncertain. Here, we report, to our knowledge, the first set of Mg isotopic data for a suite of arc lava samples from Martinique Island in the Lesser Antilles arc, which displays one of the most extreme geochemical and isotopic ranges, although the origin of this variability is still highly debated. We find the δ²⁶Mg of the Martinique Island lavas varies from −0.25 to −0.10, in contrast to the narrow range that characterizes the mantle (−0.25 ± 0.04, 2 SD). These high δ²⁶Mg values suggest the incorporation of isotopically heavy Mg from the subducted slab. The large contrast in MgO content between peridotite, basalt, and sediment makes direct mixing between sediment and peridotite, or assimilation by arc crust sediment, unlikely to be the main mechanism to modify Mg isotopes. Instead, the heavy Mg isotopic signature of the Martinique arc lavas requires that the overall composition of the mantle wedge is buffered and modified by the preferential addition of heavy Mg isotopes from fluids released from the altered subducted slab during fluid−mantle interaction. This, in turn, suggests transfer of a large amount of fluid-mobile elements from the subducting slab to the mantle wedge and makes Mg isotopes an excellent tracer of deep fluid migration.Arc volcanism records the elemental cycling between the subducting slab and subarc mantle. Of particular interest is the mechanism by which the subducted material is incorporated into the arc lava. Except for the rare case where arc lava is the direct melting product of a subducted slab (1), most scenarios suggest that mantle wedge is the major magma source that melts after being modified by fluids or melts derived from the subducted basalt and sediment (2, 3). In addition, processes such as polybaric crystallization and crustal assimilation can also modify the composition of arc magmas on their way to the surface. These different processes have different implications on subduction dynamics and elemental cycling, but, in many cases, they are difficult to distinguish. One of the best examples comes from studies of island arc lavas from the Lesser Antilles arc (Fig. 1). Geochemical and Sr, Nd, Pb, Hf, and Li isotopic studies suggest that the Lesser Antilles arc lavas incorporated a variable but to some extent significant amount of subducted sediments (4–8). However, the exact mechanism by which the sediment was incorporated into the lavas is still highly debated and involves various processes such as crustal contamination, subarc mantle metasomatism by fluids released from the slab, or melts derived by partial melting of the subducted sediments (4–17).Open in a separate windowFig. 1.(Upper) Geological map of the Lesser Antilles island arc and the two DSDP sites (sites 144 and 543). (Lower) Comparison of Martinique Island basalts with other Lesser Antilles and worldwide island arcs in ⁸⁷Sr/⁸⁶Sr versus ²⁰⁶Pb/²⁰⁴Pb isotopic space (data compiled by Geochemistry of Rocks of the Oceans and Continents database). Modified from ref. 4 with permission from Elsevier; www.sciencedirect.com/science/journal/0012821X.Magnesium isotopes have the potential to provide new and independent constraints on both source composition and processes operating during the formation of arc magmas, not only because Mg is a major element in all magmas but also because surficial and low-temperature processes fractionate Mg isotopes whereas high-temperature magmatic processes do not (18, 19) (Fig. 2). Subducted marine sediments and altered basalts have isotopic compositions different from those of the normal mantle as sampled by global peridotite xenoliths (Fig. 2); however, they generally have low Mg concentrations (18–25, ^*). In comparison, altered abyssal peridotites have Mg concentrations similar to the normal mantle whereas their Mg isotopic compositions are heavier because of the impact of hydrothermal circulation during accretion and residence in the deep ocean (Fig. 2).^†,‡ Finally, although the mechanism is still not well understood, studies of a few arc peridotites show that they also have slightly heavier Mg isotopic composition than the normal mantle (Fig. 2). Given these observed ranges, Mg isotopes may help in understanding the relative contributions of crustal and mantle components to arc magmatism, but no systematic study of either continental or island arc lavas has been carried out yet.Open in a separate windowFig. 2.Magnesium isotopic composition of Martinique arc lavas and subducting forearc sediments (sites 144 and 543). (Data are reported in ​andS2.)S2.) Data sources for the other reservoirs are from several references (18, 22–24, 36, 42, 43,^*,^†,^‡). The vertical solid line and gray bar represent the average δ²⁶Mg and 2 SD of normal mantle, as sampled by global peridotite xenoliths (−0.25 ± 0.04) (18). The short bold black vertical lines represent the mean δ²⁶Mg value of each individual reservoir.Here, we report Mg isotopic data for 27 arc lavas and 17 subducting forearc sediment samples. The lava samples are from the Martinique Island and cover most of the chemical and isotopic variations in the Lesser Antilles arc (4, 5) (Fig. 1). The sediment samples are from Deep Sea Drilling Project (DSDP) sites 543 and 144 (NE and SE of Martinique Island, respectively); they cover the whole compositional spectrum of subducting sediments and range in lithology from chalky ooze to terrigenous and pelagic deposits (6, 7).The sediments display a large range of δ²⁶Mg (−0.76 to +0.52) with an average of −0.10 ± 0.61 (2 SD) (Fig. 2). This mineralogical control is also evident in studies of loess, shale, mudrock, and carbonates as well as leaching experiments that show preferential enrichment of light Mg isotopes in carbonates over silicates (26, 27).

Table S1.

Magnesium isotopic compositions of standards and subducting sediments from DSDP sites 144 and 543 (SE and NE of Martinique Island, respectively)

Influence of cisapride on gastric emptying of solids and liquids monitored by13C breath tests

[¹³C]Acetate and [¹³C]octanoate breath tests were used to analyze the gastric emptying of liquids and solids in healthy controls and patients with functional dyspepsia both with and without cisapride. A standard test meal was labeled with either 150 mg [¹³C]acetate (liquid phase labeled in the water) or with 100 mg [¹³C]octanoate (solid phase labeled in the egg yolk). Six patients with dyspepsia and six healthy controls underwent a 4-hr breath test four times, ie, both the [¹³C]acetate and [¹³C]octanoate test with and without cisapride. Duplicate [¹³C]acetate or [¹³C]octanoate breath tests were performed in another 12 healthy controls in order to assess day-to-day variability of gastric emptying for liquids and solids. The mass spectrometric data were fitted to a power exponential function allowing mathematical analysis of half-emptying times and lag times. In patients with dyspepsia, gastric half emptying times of solids were significantly delayed as compared to the emptying of solids in the controls (203±41 vs 148±35 min;P<0.05). With cisapride, gastric emptying of solids was significantly accelerated (P<0.05) both in the patients (166±58 min) and in the controls (117±27 min). The gastric emptying of liquids did not differ in patients and controls, and cisapride had no effect on the emptying of liquids within the normal range. In the healthy controls, half emptying times both for liquids and solids were reproducible on the two different days (CV_intra: 5.58% for liquis, 20.01% for solids). We conclude that as an entirely noninvasive and nonradioactive tool¹³C-labeled breath tests are well reproducible and allow assessment of the effect of cisapride on the characteristics of gastric emptying.     

Study on Morphology and Chemical States of Surface Active Layer of Th-W Cathode

The surface morphology and chemical states of W-2%ThO₂ thermionic cathode during vacuum high-temperature treatment were investigated in this research. The W-2%ThO₂ thermionic cathode was prepared by a solid-liquid doping method combined with high-temperature sintering. The morphology and distribution of thorium oxide were observed using a transmission electron microscope and scanning electron microscope. The chemical states of elements at different temperatures were analyzed by X-ray photoelectron spectroscopy. Results indicate that the surface morphology and chemical form of the alloy evolve with the increase of temperature. The matrix had a lamellar structure at low temperatures, and the surface was relatively flat. The samples were heated to 500 °C, 1100 °C, and 1300 °C for 1 h. During the heating process, thorium oxide changed from granular to spherical, and the matrix was recrystallized. As the heating temperature rises, diffusion channels appear inside the cathode. As the temperature increases, the high-priced tungsten gradually decreases, and the zero-valent tungsten content increases. The adsorbed oxygen left the cathode surface, and the lattice oxygen increased. The surface oxygen content decreased, and the thorium and tungsten content increased.     

15 N-尿素发射光谱分析法检测幽门螺杆菌感染

目的：建立检测幽门螺杆菌感染的无损伤、无放射性方法－－^15N-尿素发射光谱分析法。方法：对26例受检者^15N-尿素发射光谱分析法检测其幽门螺杆菌感染。结果：诊断特异性为81％，灵敏度为89％，阳性预测值为84％。结论：该方法具有一定的实用意义。