Feasibility of using rural waste products to increase the denitrification efficiency in a surface flow constructed wetland

A surface flow constructed wetland (CW) was set in the Lerma gully to decrease nitrate (NO3 -) pollution from agricultural runoff water. The water flow rate and NO3 - concentration were monitored at the inlet and the outlet, and sampling campaigns were performed which consisted of collecting six water samples along the CW flow line. After two years of operation, the NO3 - attenuation was limited at a flow rate of ~2.5 L/s and became negligible at ~5.5 L/s. The present work aimed to assess the feasibility of using rural waste products (wheat hay, corn stubble, and animal compost) to induce denitrification in the CW, to assess the effect of temperature on this process, and to trace the efficiency of the treatment by using isotopic tools. In the first stage, microcosm experiments were performed. Afterwards, the selected waste material was applied in the CW, and the treatment efficiency was evaluated by means of a chemical and isotopic characterization and using the isotopic fractionation (e) values calculated from laboratory experiments to avoid field-scale interference. The microcosms results showed that the stubble was the most appropriate material for application in the CW, but the denitrification rate was found to decrease with temperature. In the CW, biostimulation in autumn-winter promoted NO3 - attenuation between two weeks and one month (a reduction in NO3 - between 1.2 and 1.5 mM was achieved). After the biostimulation in spring-summer, the attenuation was maintained for approximately three months (NO3 - reduction between 0.1 and 1.5 mM). The e15NNO3/N2 and e18ONO3/N2 values obtained from the laboratory experiments allowed to estimate the induced denitrification percentage. At an approximate average flow rate of 16 L/s, at least 60% of NO3 - attenuation was achieved in the CW. The field samples exhibited a slope of 1.0 for d18O-NO3 - versus d15N-NO3 -, similar to those of the laboratory experiments (0.9–1.2). Plant uptake seemed to play a minor role in NO3 - attenuation in the CW. Hence, the application of stubble in the CW allowed the removal of large amounts of NO3 - from the Lerma gully, especially when applied during the warm months, but its efficacy was limited to a short time period (up to three months). © 2019 Elsevier B.V

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2–4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Nitrate and nitrite reduction by ferrous iron minerals in polluted groundwater: Isotopic characterization of batch experiments

Since nitrate (NO3−) has been related to human health and environmental problems, safe and sustainable strategies to remediate polluted water bodies must be investigated. This work aims to assess the feasibility of using ferrous iron (Fe (II))-containing minerals to stimulate microbial denitrification while avoiding pollution swapping (e.g. accumulation of the by-products nitrite (NO2−) or nitrous oxide (N2O)). To accomplish the objective, samples obtained from several batch experiments were characterized chemically and isotopically. Magnetite, siderite and olivine were tested micro-sized and magnetite was also tested nano-sized. In microbial experiments, NO3− polluted groundwater was employed as inoculum. In these experiments, NO3− reduction to nitrogen gas (N2) was only completed in microcosms containing magnetite nanoparticles, suggesting an increased Fe (II) availability from nano-sized compared to micro-sized magnetite. In abiotic experiments, no reactivity was observed between NO3− or NO2− and micro-sized magnetite, siderite or olivine, while NO2− was rapidly reduced when dissolved Fe2+ was added. These results point to the need of a certain amount of dissolved Fe2+ to stimulate the abiotic NO2− reduction by Fe (II) oxidation. For the microbial NO3− reduction by magnetite nanoparticles, the calculated ε15NNO3 was −33.1¿ (R2 = 0.86), ε18ONO3 was −10.7¿ (R2 = 0.74) and ε15NNO3/ε18ONO3 was 3.1. For the abiotic NO2− reduction by Fe2+, the ε15NNO2 ranged from −14.1 to −17.8¿ (R2 > 0.89). Considering the wide range of ε15NNO2 reported in the literature, it is not likely that NO2− isotopic characterization can be useful at field-scale to distinguish abiotic from microbial NO2− reduction. Nevertheless, the measured δ15N for N2O in microbial and abiotic tests, allowed determining if it was an intermediate or a final product of the reactions by comparing these results with the modelled isotopic composition calculated using the ε15N values determined for the substrates. Hence, isotopic data confirmed that the product of the microbial NO3− reduction was innocuous N2 while the product of the abiotic NO2− reduction was N2O. The latter reaction would be advantageous to avoid NO2− accumulation during denitrification only if the generated N2O is further reduced by microorganisms

Geochemical and isotopic study of abiotic nitrite reduction coupled to biologically produced Fe(II) oxidation in marine environments

Estuarine sediments are often characterized by abundant iron oxides, organic matter, and anthropogenic nitrogen compounds (e.g., nitrate and nitrite). Anoxic dissimilatory iron reducing bacteria (e.g., Shewanella loihica) are ubiquitous in these environments where they can catalyze the reduction of Fe(III) (oxyhydr)oxides, thereby releasing aqueous Fe(II). The biologically produced Fe(II) can later reduce nitrite to form nitrous oxide. The effect on nitrite reduction by both biologically produced and artificially amended Fe(II) was examined experimentally. Ferrihydrite was reduced by Shewanella loihica in a batch reaction with an anoxic synthetic sea water medium. Some of the Fe(II) released by S. loihica adsorbed onto ferrihydrite, which was involved in the transformation of ferrihydrite to magnetite. In a second set of experiments with identical medium, no microorganism was present, instead, Fe(II) was amended. The amount of solid-bound Fe(II) in the experiments with bioproduced Fe(II) increased the rate of abiotic NO2− reduction with respect to that with synthetic Fe(II), yielding half-lives of 0.07 and 0.47 d, respectively. The δ18O and δ15N of NO2− was measured through time for both the abiotic and innoculated experiments. The ratio of ε18O/ε15N was 0.6 for the abiotic experiments and 3.1 when NO2− was reduced by S. loihica, thus indicating two different mechanisms for the NO2− reduction. Notably, there is a wide range of the ε18O/ε15N values in the literature for abiotic and biotic NO2− reduction, as such, the use of this ratio to distinguish between reduction mechanisms in natural systems should be taken with caution. Therefore, we suggest an additional constraint to identify the mechanisms (i.e. abiotic/biotic) controlling NO2− reduction in natural settings through the correlation of δ15N-NO2- and the aqueous Fe(II) concentration.This study was supported by projects CGL2017-87216-C4-1-R, CGL2017-82331-R and CEX2018-000794-S funded by the Spanish Ministry of Science and Innovation and AEI/FEDER funded by the European Union, and by MAG (2017 SGR 1733) financed by the Catalan Government. R. Margalef-Marti wishes to thank the Spanish Government for the Ph.D. grant BES-2015-072882. The authors are indebted to Jordi Bellés (IDAEA-CSIC), Natàlia Moreno (IDAEA-CSIC) and Xavier Alcové (SCTT-Barcelona University) for laboratory assistance and XRD analyses, respectively. The isotopic analyses were prepared at the MAiMA-UB research group laboratory and analyzed at the scientific and technical services of Barcelona University (CCiT-UB). We acknowledge Max Giannetta for his scientific discussions during the manuscript elaboration. We also wish to thank the Editor and three anonymous reviewers for their constructive comments that have improved the quality of the paper.Peer reviewe