Quantifying soil accumulation of atmospheric mercury using fallout radionuclide chronometry.

Soils are a principal global reservoir of mercury (Hg), a neurotoxic pollutant that is accumulating through anthropogenic emissions to the atmosphere and subsequent deposition to terrestrial ecosystems. The fate of Hg in global soils remains uncertain, however, particularly to what degree Hg is re-emitted back to the atmosphere as gaseous elemental mercury (GEM). Here we use fallout radionuclide (FRN) chronometry to directly measure Hg accumulation rates in soils. By comparing these rates with measured atmospheric fluxes in a mass balance approach, we show that representative Arctic, boreal, temperate, and tropical soils are quantitatively efficient at retaining anthropogenic Hg. Potential for significant GEM re-emission appears limited to a minority of coniferous soils, calling into question global models that assume strong re-emission of legacy Hg from soils. FRN chronometry poses a powerful tool to reconstruct terrestrial Hg accumulation across larger spatial scales than previously possible, while offering insights into the susceptibility of Hg mobilization from different soil environments.

Plasmodium RNA triphosphatase validation as antimalarial target.

Target-based approaches have traditionally been used in the search for new anti-infective molecules. Target selection process, a critical step in Drug Discovery, identifies targets that are essential to establish or maintain the infection, tractable to be susceptible for inhibition, selective towards their human ortholog and amenable for large scale purification and high throughput screening. The work presented herein validates the Plasmodium falciparum mRNA 5' triphosphatase (PfPRT1), the first enzymatic step to cap parasite nuclear mRNAs, as a candidate target for the development of new antimalarial compounds. mRNA capping is essential to maintain the integrity and stability of the messengers, allowing their translation. PfPRT1 has been identified as a member of the tunnel, metal dependent mRNA 5' triphosphatase family which differs structurally and mechanistically from human metal independent mRNA 5' triphosphatase. In the present study the essentiality of PfPRT1 was confirmed and molecular biology tools and methods for target purification, enzymatic assessment and target engagement were developed, with the goal of running a future high throughput screening to discover PfPRT1 inhibitors.

Forest growth responds more to air pollution than soil acidification.

The forests of central Europe have undergone remarkable transitions in the past 40 years as air quality has improved dramatically. Retrospective analysis of Norway spruce (Picea abies) tree rings in the Czech Republic shows that air pollution (e.g. SO2 concentrations, high acidic deposition to the forest canopy) plays a dominant role in driving forest health. Extensive soil acidification occurred in the highly polluted "Black Triangle" in Central Europe, and upper mineral soils are still acidified. In contrast, acidic atmospheric deposition declined by 80% and atmospheric SO2 concentration by 90% between the late 1980s and 2010s. In this study we oserved that annual tree ring width (TRW) declined in the 1970s and subsequently recovered in the 1990s, tracking SO2 concentrations closely. Furthermore, recovery of TRW was similar in unlimed and limed stands. Despite large increases in soil base saturation, as well as soil pH, as a result of repeated liming starting in 1981, TRW growth was similar in limed and unlimed plots. TRW recovery was interrupted in 1996 when highly acidic rime (originating from more pronounced decline of alkaline dust than SO2 from local power plants) injured the spruce canopy, but recovered soon to the pre-episode growth. Across the long-term site history, changes in soil chemistry (pH, base saturation, Bc/Al soil solution ratio) cannot explain observed changes in TRW at the two study sites where we tracked soil chemistry. Instead, statistically significant recovery in TRW is linked to the trajectory of annual SO2 concentrations or sulfur deposition at all three stands.

Indirect nitrous oxide emission factors of fluvial networks can be predicted by dissolved organic carbon and nitrate from local to global scales.

Streams and rivers are important sources of nitrous oxide (N2 O), a powerful greenhouse gas. Estimating global riverine N2 O emissions is critical for the assessment of anthropogenic N2 O emission inventories. The indirect N2 O emission factor (EF5r ) model, one of the bottom-up approaches, adopts a fixed EF5r value to estimate riverine N2 O emissions based on IPCC methodology. However, the estimates have considerable uncertainty due to the large spatiotemporal variations in EF5r values. Factors regulating EF5r are poorly understood at the global scale. Here, we combine 4-year in situ observations across rivers of different land use types in China, with a global meta-analysis over six continents, to explore the spatiotemporal variations and controls on EF5r values. Our results show that the EF5r values in China and other regions with high N loads are lower than those for regions with lower N loads. Although the global mean EF5r value is comparable to the IPCC default value, the global EF5r values are highly skewed with large variations, indicating that adopting region-specific EF5r values rather than revising the fixed default value is more appropriate for the estimation of regional and global riverine N2 O emissions. The ratio of dissolved organic carbon to nitrate (DOC/NO3 - ) and NO3 - concentration are identified as the dominant predictors of region-specific EF5r values at both regional and global scales because stoichiometry and nutrients strictly regulate denitrification and N2 O production efficiency in rivers. A multiple linear regression model using DOC/NO3 - and NO3 - is proposed to predict region-specific EF5r values. The good fit of the model associated with easily obtained water quality variables allows its widespread application. This study fills a key knowledge gap in predicting region-specific EF5r values at the global scale and provides a pathway to estimate global riverine N2 O emissions more accurately based on IPCC methodology.

Incorporation of Hydrophilic Macrocycles Into Drug-Linker Reagents Produces Antibody-Drug Conjugates With Enhanced in vivo Performance.

Antibody-drug conjugates (ADCs) have begun to fulfil their promise as targeted cancer therapeutics with ten clinical approvals to date. As the field matures, much attention has focused upon the key factors required to produce safe and efficacious ADCs. Recently the role that linker-payload reagent design has on the properties of ADCs has been highlighted as an important consideration for developers. We have investigated the effect of incorporating hydrophilic macrocycles into reagent structures on the in vitro and in vivo behavior of ADCs. Bis-sulfone based disulfide rebridging reagents bearing Val-Cit-PABC-MMAE linker-payloads were synthesized with a panel of cyclodextrins and crown ethers integrated into their structures via a glutamic acid branching point. Brentuximab was selected as a model antibody and ten ADCs with a drug-to-antibody ratio (DAR) of 4 were prepared for biological evaluation. In vitro, the ADCs prepared showed broadly similar potency (range: 16-34 pM) and were comparable to Adcetris® (16 pM). In vivo, the cyclodextrin containing ADCs showed greater efficacy than Adcetris® and the most efficacious variant (incorporating a 3'-amino-α-cyclodextrin component) matched a 24-unit poly(ethylene glycol) (PEG) containing comparator. The ADCs bearing crown ethers also displayed enhanced in vivo efficacy compared to Adcetris®, the most active variant (containing a 1-aza-42-crown-14 macrocycle) was superior to an analogous ADC with a larger 24-unit PEG chain. In summary, we have demonstrated that hydrophilic macrocycles can be effectively incorporated into ADC reagent design and offer the potential for enhanced alternatives to established drug-linker architectures.

Linking soil phosphorus with forest litterfall resistance and resilience to cyclone disturbance: A pantropical meta-analysis.

While tropical cyclone regimes are shifting with climate change, the mechanisms underpinning the resistance (ability to withstand disturbance-induced change) and resilience (capacity to return to pre-disturbance reference) of tropical forest litterfall to cyclones remain largely unexplored pantropically. Single-site studies in Australia and Hawaii suggest that litterfall on low-phosphorus (P) soils is more resistant and less resilient to cyclones. We conducted a meta-analysis to investigate the pantropical importance of total soil P in mediating forest litterfall resistance and resilience to 22 tropical cyclones. We evaluated cyclone-induced and post-cyclone litterfall mass (g/m2 /day), and P and nitrogen (N) fluxes (mg/m2 /day) and concentrations (mg/g), all indicators of ecosystem function and essential for nutrient cycling. Across 73 case studies in Australia, Guadeloupe, Hawaii, Mexico, Puerto Rico, and Taiwan, total litterfall mass flux increased from ~2.5 ± 0.3 to 22.5 ± 3 g/m2 /day due to cyclones, with large variation among studies. Litterfall P and N fluxes post-cyclone represented ~5% and 10% of the average annual fluxes, respectively. Post-cyclone leaf litterfall N and P concentrations were 21.6 ± 1.2% and 58.6 ± 2.3% higher than pre-cyclone means. Mixed-effects models determined that soil P negatively moderated the pantropical litterfall resistance to cyclones, with a 100 mg P/kg increase in soil P corresponding to a 32% to 38% decrease in resistance. Based on 33% of the resistance case studies, total litterfall mass flux reached pre-disturbance levels within one-year post-disturbance. A GAMM indicated that soil P, gale wind duration and time post-cyclone jointly moderate the short-term resilience of total litterfall, with the nature of the relationship between resilience and soil P contingent on time and wind duration. Across pantropical forests observed to date, our results indicate that litterfall resistance and resilience in the face of intensifying cyclones will be partially determined by total soil P.

A general pattern of trade-offs between ecosystem resistance and resilience to tropical cyclones.

Tropical cyclones drive coastal ecosystem dynamics, and their frequency, intensity, and spatial distribution are predicted to shift with climate change. Patterns of resistance and resilience were synthesized for 4138 ecosystem time series from n = 26 storms occurring between 1985 and 2018 in the Northern Hemisphere to predict how coastal ecosystems will respond to future disturbance regimes. Data were grouped by ecosystems (fresh water, salt water, terrestrial, and wetland) and response categories (biogeochemistry, hydrography, mobile biota, sedentary fauna, and vascular plants). We observed a repeated pattern of trade-offs between resistance and resilience across analyses. These patterns are likely the outcomes of evolutionary adaptation, they conform to disturbance theories, and they indicate that consistent rules may govern ecosystem susceptibility to tropical cyclones.

Light and flow regimes regulate the metabolism of rivers.

Mean annual temperature and mean annual precipitation drive much of the variation in productivity across Earth's terrestrial ecosystems but do not explain variation in gross primary productivity (GPP) or ecosystem respiration (ER) in flowing waters. We document substantial variation in the magnitude and seasonality of GPP and ER across 222 US rivers. In contrast to their terrestrial counterparts, most river ecosystems respire far more carbon than they fix and have less pronounced and consistent seasonality in their metabolic rates. We find that variation in annual solar energy inputs and stability of flows are the primary drivers of GPP and ER across rivers. A classification schema based on these drivers advances river science and informs management.

Land Use Overrides Stream Order and Season in Driving Dissolved Organic Matter Dynamics Throughout the Year in a River Network.

Anthropogenic land use has increased nutrient concentrations and altered dissolved organic matter (DOM) character and its bioavailability. Despite widespread recognition that DOM character and its reactivity can vary temporally, the relative influence of land use and stream order on DOM characteristics is poorly understood across seasons and the entire flow regime. We examined DOM character and 28-day bioavailable dissolved organic carbon (BDOC) across a river network to determine the relative roles of land use and stream order in driving variability in DOM character and bioavailability throughout the year. DOM in 1st-order streams was distinct from higher stream orders with lower DOC concentrations, less aromatic (specific ultraviolet absorbance at 254 nm (SUVA254)), more autochthonous (fluorescence index), and more recently produced (ß/α) DOM. Across all months, variability in DOM character was primarily explained by land use, rather than stream order or season. Land use and stream order explained the most DOM variation in transitional and winter months and the least during dry months. BDOC was greater in watersheds with less aromatic (SUVA254) and more recent allochthonous DOM (ß/α) and more development and impervious surface. With continued development, the bioavailability of DOM in the smallest and most impacted watersheds is expected to increase.

Rate of Posterior Capsule Rupture in Phacoemulsification Cataract Surgery by Residents with Institution of a Wet Laboratory Course.

Purpose To determine if a structured surgical wet laboratory curriculum for ophthalmology residents reduced the rate of posterior capsule rupture (PCR) in phacoemulsification cataract surgery. Setting James A. Haley Veterans' Hospital, Tampa, FL. Design Retrospective cohort study. Methods The study assessed resident-performed phacoemulsification cataract cases from 2011 to 2017, after the creation of a wet laboratory course. Primary outcome measure was PCR. If present, timing of complication, dropped lens fragments, and the need for anterior vitrectomies were noted. Self-reported rates of PCR prior to institution of a wet laboratory course (2010-2011) were compared with cases done by residents who completed the course (2011-2017). Results A total of 3,445 cases were reviewed of which 2.44% (84 cases) noted PCR. Of these, 19% (16) had dropped lens fragments, and 60.7% (51) required anterior vitrectomy. Sixty-nine cases documented timing of PCR with the majority, 58%, occurring during phacoemulsification. When comparing rates of PCR in cases done prior to the presence of a wet laboratory course versus after, there was a significant reduction observed (5.20% before vs. 2.44% after). Conclusion In the presence of a wet laboratory curriculum, the rate of PCR decreased dramatically. The average rate was lower than those reported at other training programs (2.6-9.9%). Most PCR occurred during phacoemulsification, suggesting need for further focused instruction in this step.

Shifting stoichiometry: Long-term trends in stream-dissolved organic matter reveal altered C:N ratios due to history of atmospheric acid deposition.

Dissolved organic carbon (DOC) and nitrogen (DON) are important energy and nutrient sources for aquatic ecosystems. In many northern temperate, freshwater systems DOC has increased in the past 50 years. Less is known about how changes in DOC may vary across latitudes, and whether changes in DON track those of DOC. Here, we present long-term DOC and DON data from 74 streams distributed across seven sites in biomes ranging from the tropics to northern boreal forests with varying histories of atmospheric acid deposition. For each stream, we examined the temporal trends of DOC and DON concentrations and DOC:DON molar ratios. While some sites displayed consistent positive or negative trends in stream DOC and DON concentrations, changes in direction or magnitude were inconsistent at regional or local scales. DON trends did not always track those of DOC, though DOC:DON ratios increased over time for ~30% of streams. Our results indicate that the dissolved organic matter (DOM) pool is experiencing fundamental changes due to the recovery from atmospheric acid deposition. Changes in DOC:DON stoichiometry point to a shifting energy-nutrient balance in many aquatic ecosystems. Sustained changes in the character of DOM can have major implications for stream metabolism, biogeochemical processes, food webs, and drinking water quality (including disinfection by-products). Understanding regional and global variation in DOC and DON concentrations is important for developing realistic models and watershed management protocols to effectively target mitigation efforts aimed at bringing DOM flux and nutrient enrichment under control.

Distinctive Patterns and Controls of Nitrous Oxide Concentrations and Fluxes from Urban Inland Waters.

Inland waters are significant sources of nitrous oxide (N2O), a powerful greenhouse gas. However, considerable uncertainty exists in the estimates of N2O efflux from global inland waters due to a lack of direct measurements in urban inland waters, which are generally characterized by high carbon and nitrogen concentrations and low carbon-to-nitrogen ratios. Herein, we present direct measurements of N2O concentrations and fluxes in lakes and rivers of Beijing, China, during 2018-2020. N2O concentrations and fluxes in the waters of Beijing exceeded previous estimates of global rivers due to the high carbon and nutrient concentrations and high aquatic productivity. In contrast, the N2O emission factor (N2O-N/DIN, median 0.0005) was lower than global medians and the N2O yield (ΔN2O/(ΔN2O + ΔN2), average 1.6%) was higher than those typically observed in rivers and streams. The positive relationship between N2O emissions and denitrifying bacteria as well as the Michaelis-Menten relationship between N2O emissions and NO3--N concentrations suggested that bacteria control the net production of N2O in waters of Beijing with N saturation, leading to a low N2O emission factor. However, low carbon-to-nitrogen ratios are beneficial for N2O accumulation during denitrification, resulting in high N2O yields. This study demonstrates the significant N2O emissions and their distinctive patterns and controls in urban inland waters and suggests that N2O emission estimates based on nitrogen loads and simple emission factor values are not appropriate for urban inland water systems.

Experimental nitrogen and phosphorus enrichment stimulates multiple trophic levels of algal and detrital-based food webs: a global meta-analysis from streams and rivers.

Anthropogenic increases in nitrogen (N) and phosphorus (P) concentrations can strongly influence the structure and function of ecosystems. Even though lotic ecosystems receive cumulative inputs of nutrients applied to and deposited on land, no comprehensive assessment has quantified nutrient-enrichment effects within streams and rivers. We conducted a meta-analysis of published studies that experimentally increased concentrations of N and/or P in streams and rivers to examine how enrichment alters ecosystem structure (state: primary producer and consumer biomass and abundance) and function (rate: primary production, leaf breakdown rates, metabolism) at multiple trophic levels (primary producer, microbial heterotroph, primary and secondary consumers, and integrated ecosystem). Our synthesis included 184 studies, 885 experiments, and 3497 biotic responses to nutrient enrichment. We documented widespread increases in organismal biomass and abundance (mean response = +48%) and rates of ecosystem processes (+54%) to enrichment across multiple trophic levels, with no large differences in responses among trophic levels or between autotrophic or heterotrophic food-web pathways. Responses to nutrient enrichment varied with the nutrient added (N, P, or both) depending on rate versus state variable and experiment type, and were greater in flume and whole-stream experiments than in experiments using nutrient-diffusing substrata. Generally, nutrient-enrichment effects also increased with water temperature and light, and decreased under elevated ambient concentrations of inorganic N and/or P. Overall, increased concentrations of N and/or P altered multiple food-web pathways and trophic levels in lotic ecosystems. Our results indicate that preservation or restoration of biodiversity and ecosystem functions of streams and rivers requires management of nutrient inputs and consideration of multiple trophic pathways.

Resolving a paradox-high mercury deposition, but low bioaccumulation in northeastern Puerto Rico.

At a "clean air" trade winds site in northeastern Puerto Rico, we found an apparent paradox: atmospheric total mercury (THg) deposition was highest of any site in the USA Mercury Deposition Network, but assimilation into the local food web was quite low. Avian blood THg concentrations (n = 31, from eight species in five foraging guilds) ranged widely from 0.2 to 32 ng g-1 (median of 4.3 ng g-1). Within this population, THg was significantly greater at a low-elevation site near a wetland compared to an upland montane site, even when the comparison was limited to a single species. Overall, however, THg concentrations were approximately an order of magnitude lower than comparable populations in the continental U.S. In surface soil and sediment, potential rates of demethylation were 3 to 9-fold greater than those for Hg(II)-methylation (based on six radiotracer amendment incubations), but rates of change of ambient MeHg pools showed a slight net positive Hg(II)-methylation. Thus, the resolution of the paradox is that MeHg degradation approximately keeps pace with MeHg production in this landscape. Further, any net production of MeHg is subject to frequent flushing by high rainfall on chronically wet soils. The interplay of these microbial processes and hydrology appears to shield the local food web from adverse effects of high atmospheric mercury loading. This scenario may play out in other humid tropical ecosystems as well, but it is difficult to evaluate because coordinated studies of Hg deposition, methylation, and trophic uptake have not been conducted at other tropical sites.

Half-life extension and non-human primate pharmacokinetic safety studies of i-body AD-114 targeting human CXCR4.

Single domain antibodies that combine antigen specificity with high tissue penetration are an attractive alternative to conventional antibodies. However, rapid clearance from the bloodstream owing to their small size can be a limitation of therapeutic single domain antibodies. Here, we describe and evaluate the conjugation of a single domain i-body, AD-114, which targets CXCR4, to a panel of half-life extension technologies including a human serum albumin-binding peptide, linear and branched PEG, and PASylation (PA600). The conjugates were assessed in murine, rat and cynomolgus monkey pharmacokinetic studies and showed that the branched PEG was most effective at extending circulating half-life in mice; however, manufacturing limitations of PEGylated test material precluded scale-up and assessment in larger animals. PA600, by comparison, was amenable to scale-up and afforded considerable half-life improvements in mice, rats and cynomolgus monkeys. In mice, the circulating half-life of AD-114 was extended from 0.18 h to 7.77 h following conjugation to PA600, and in cynomolgus monkeys, the circulating half-life of AD-114-PA600 was 24.27 h. AD-114-PA600 was well tolerated in cynomolgus monkeys at dose rates up to 100 mg/kg with no mortalities or drug-related clinical signs.

Trace metals in Northern New England streams: Evaluating the role of road salt across broad spatial scales with synoptic snapshots.

Mobilization of trace metals from soils to surface waters can impact both human and ecosystem health. This study resamples a water sample archive to explore the spatial pattern of streamwater total concentrations of arsenic, cadmium, copper, lead, and zinc and their associations with biogeochemical controls in northern New England. Road deicing appears to result in elevated trace metal concentrations, as trace metal concentrations are strongly related to sodium concentrations and are most elevated when the sodium: chloride ratio is near 1.0 (~halite). Our results are consistent with previous laboratory and field studies that indicate cation exchange as a metal mobilization mechanism when road salt is applied to soils containing metals. This study also documents associations among sodium, chloride, dissolved organic carbon, iron, and metal concentrations, suggesting cation exchange mechanisms related to road deicing are not the only mechanisms that increase trace metal concentrations in surface waters. In addition to cation exchange, this study considers dissolved organic carbon complexation and oxidation-reduction conditions affecting metal mobility from soils in a salt-rich environment. These observations demonstrate that road deicing has the potential to increase streamwater trace metal concentrations across broad spatial scales and increase risks to human and ecosystem health.

Nutrient export and elemental stoichiometry in an urban tropical river.

Nutrient inputs to surface waters are particularly varied in urban areas, due to multiple nutrient sources and complex hydrologic pathways. Because of their close proximity to coastal waters, nutrient delivery from many urban areas can have profound impacts on coastal ecology. Relatively little is known about the temporal and spatial variability in stoichiometry of inorganic nutrients such as dissolved silica, nitrogen, and phosphorus (Si, N, and P) and dissolved organic matter in tropical urban environments. We examined nutrient stoichiometry of both inorganic nutrients and organic matter in an urban watershed in Puerto Rico served by municipal sanitary sewers and compared it to two nearby forested catchments using samples collected weekly from each river for 6 yr. Urbanization caused large increases in the concentration and flux of nitrogen and phosphorus (2- to 50-fold), but surprisingly little change in N:P ratio. Concentrations of almost all major ions and dissolved silica were also significantly higher in the urban river than the wildland rivers. Yield of dissolved organic carbon (DOC) was not increased dramatically by urbanization, but the composition of dissolved organic matter shifted toward N-rich material, with a larger increase in dissolved organic nitrogen (DON) than DOC. The molar ratio of DOC:DON was about 40 in rivers draining forested catchments but was only 10 in the urban river. Inclusion of Si in the assessment of urbanization's impacts reveals a large shift in the stoichiometry (Si:N and Si:P) of nutrient inputs. Because both Si concentrations and watershed exports are high in streams and rivers from many humid tropical catchments with siliceous bedrock, even the large increases in N and P exported from urban catchments result in delivery of Si, N, and P to coastal waters in stoichiometric ratios that are well in excess of the Si requirements of marine diatoms. Our data suggest that dissolved Si, often neglected in watershed biogeochemistry, should be included in studies of urban as well as less developed watersheds due to its potential significance for marine and lacustrine productivity.