Peat Formation Concentrates Arsenic Within Sediment Deposits of the Mekong Delta

Mekong River Delta sediment bears arsenic that is released to groundwater under anaerobic conditions over the past several thousand years. The oxidation state, speciation, and distribution of arsenic and the associated iron bearing phases are crucial determinants of As reactivity in sediments. Peat from buried mangrove swamps in particular may be an important host, source, or sink of arsenic in the Mekong Delta. The total concentration, speciation, and reactivity of arsenic and iron were examined in sediments in a Mekong Delta wetland by X-ray fluorescence spectrometry (XRF), X-ray absorption spectroscopy (XAS), and selective chemical extractions. Total solid-phase arsenic concentrations in a peat layer at a depth of 6 m below ground increased 10-fold relative to the overlying sediment. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that arsenic in the peat was predominantly in the form of arsenian pyrite. Arsenic speciation in the peat was examined further at the micron-scale using μXRF and μX-ray absorption near-edge structure (XANES) spectroscopy coupled with principal component analysis. The multiple energy μXRF mapping and μXANES routine was repeated for both iron and sulfur phase analyses. Our μXRF/μXANES analyses confirm arsenic association with pyrite – a less reactive host phase than iron (hydr)oxides under anaerobic conditions. The arsenian pyrite likely formed upon deposition/formation of the peat in a past estuarine environment (∼ 5.5 ka BP), a process that is not expected under current geochemical conditions. Presently, arsenian pyrite is neither a source nor a sink for aqueous arsenic in our sediment profile, and under present geochemical conditions represents a stable host of As under the reducing aquifer conditions of the Mekong Delta. Furthermore, organic carbon within the peat is unable to fuel Fe(III) reduction, as noted by the persistence of goethite which can be reduced microbially with the addition of glucose

SARS-CoV-2 susceptibility and COVID-19 disease severity are associated with genetic variants affecting gene expression in a variety of tissues

Variability in SARS-CoV-2 susceptibility and COVID-19 disease severity between individuals is partly due to genetic factors. Here, we identify 4 genomic loci with suggestive associations for SARS-CoV-2 susceptibility and 19 for COVID-19 disease severity. Four of these 23 loci likely have an ethnicity-specific component. Genome-wide association study (GWAS) signals in 11 loci colocalize with expression quantitative trait loci (eQTLs) associated with the expression of 20 genes in 62 tissues/cell types (range: 1:43 tissues/gene), including lung, brain, heart, muscle, and skin as well as the digestive system and immune system. We perform genetic fine mapping to compute 99% credible SNP sets, which identify 10 GWAS loci that have eight or fewer SNPs in the credible set, including three loci with one single likely causal SNP. Our study suggests that the diverse symptoms and disease severity of COVID-19 observed between individuals is associated with variants across the genome, affecting gene expression levels in a wide variety of tissue types

A first update on mapping the human genetic architecture of COVID-19

peer reviewe

Arsenic Release Metabolically Limited to Permanently Water-Saturated Soil in Mekong Delta

Microbial reduction of arsenic-bearing iron oxides in the deltas of South and Southeast Asia produces widespread arsenic-contaminated groundwater. Organic carbon is abundant both at the surface and within aquifers, but the source of organic carbon used by microbes in the reduction and release of arsenic has been debated, as has the wetland type and sedimentary depth where release occurs. Here we present data from fresh-sediment incubations, in situ model sediment incubations and a controlled field experiment with manipulated wetland hydrology and organic carbon inputs. We find that in the minimally disturbed Mekong Delta, arsenic release is limited to near-surface sediments of permanently saturated wetlands where both organic carbon and arsenic-bearing solids are sufficiently reactive for microbial oxidation of organic carbon and reduction of arsenic-bearing iron oxides. In contrast, within the deeper aquifer or seasonally saturated sediments, reductive dissolution of iron oxides is observed only when either more reactive exogenous forms of iron oxides or organic carbon are added, revealing a potential thermodynamic restriction to microbial metabolism. We conclude that microbial arsenic release is limited by the reactivity of arsenic-bearing iron oxides with respect to native organic carbon, but equally limited by organic carbon reactivity with respect to the native arsenic-bearing iron oxides

Incidence, Patterns, and Impact of Dual Antiplatelet Therapy Cessation Among Patients With and Without Chronic Kidney Disease Undergoing Percutaneous Coronary Intervention: Results From the PARIS Registry (Patterns of Non-Adherence to Anti-Platelet Regimens in Stented Patients).

BACKGROUND: Patients with chronic kidney disease (CKD) experience high rates of ischemic and bleeding events after percutaneous coronary intervention (PCI), complicating decisions surrounding dual antiplatelet therapy (DAPT). This study aims to determine the pattern and impact of various modes of DAPT cessation for patients with CKD undergoing PCI. METHODS AND RESULTS: Patients from the PARIS registry (Patterns of Non-Adherence to Anti-Platelet Regimens in Stented Patients) were grouped based on the presence of CKD defined as creatinine clearance <60 mL/min. After index PCI, time and mode of DAPT cessation (discontinuation, interruption, and disruption) and clinical outcomes (major adverse cardiac events, stent thrombosis, myocardial infarction, and major bleeding [Bleeding Academic Research Consortium type 3 or 5]) were reported. Over 2 years, patients with CKD (n=839) had higher adjusted risks for death (hazard ratio, 3.16; 95% confidence interval, 2.26-4.41), myocardial infarction (hazard ratio, 2.43; 95% confidence interval, 1.65-3.57), and major bleeding (hazard ratio, 2.21; 95% confidence interval, 1.53-3.19) compared with patients without CKD (n=3745). Rates of DAPT discontinuation within the first year after PCI and disruption were significantly higher for patients with CKD. However, DAPT interruption occurred with equal frequency. Associations between DAPT cessation mode and subsequent risk were not modified by CKD status. Findings were unchanged after propensity matching. CONCLUSIONS: Patients with CKD display high and comparable risks for both ischemic and bleeding events after PCI. Physicians are more likely to discontinue DAPT within the first year after PCI among patients with CKD, likely reflecting clinical preferences to avoid bleeding. Risks after DAPT cessation, irrespective of underlying mode, are not modified by the presence or absence of CKD