Strong hydroclimatic controls on vulnerability to subsurface nitrate contamination across Europe.

Subsurface contamination due to excessive nutrient surpluses is a persistent and widespread problem in agricultural areas across Europe. The vulnerability of a particular location to pollution from reactive solutes, such as nitrate, is determined by the interplay between hydrologic transport and biogeochemical transformations. Current studies on the controls of subsurface vulnerability do not consider the transient behaviour of transport dynamics in the root zone. Here, using state-of-the-art hydrologic simulations driven by observed hydroclimatic forcing, we demonstrate the strong spatiotemporal heterogeneity of hydrologic transport dynamics and reveal that these dynamics are primarily controlled by the hydroclimatic gradient of the aridity index across Europe. Contrasting the space-time dynamics of transport times with reactive timescales of denitrification in soil indicate that ~75% of the cultivated areas across Europe are potentially vulnerable to nitrate leaching for at least one-third of the year. We find that neglecting the transient nature of transport and reaction timescale results in a great underestimation of the extent of vulnerable regions by almost 50%. Therefore, future vulnerability and risk assessment studies must account for the transient behaviour of transport and biogeochemical transformation processes.

Droplet millifluidics for kinetic study of transketolase.

We present a continuous-flow reactor at the millifluidic scale coupled with an online, non-intrusive spectroscopic monitoring method for determining the kinetic parameters of an enzyme, transketolase (TK) used in biocatalysis for the synthesis of polyols by carboligation. The millifluidic system used is based on droplet flow, a well-established method for kinetic chemical data acquisition. The TK assay is based on the direct quantitative measurement of bicarbonate ions released during the transketolase-catalysed reaction in the presence of hydroxypyruvic acid as the donor, thanks to an irreversible reaction: bicarbonate ions react with phosphoenolpyruvate (PEP) in the presence of PEP carboxylase as the first auxiliary enzyme. The oxaloacetate formed is reduced to malate by NADH in the reaction catalysed by malate dehydrogenase as the second auxiliary enzyme. The extent of oxidation of NADH was measured by spectrophotometry at 340 nm. This system gives a direct, quantitative, generic method to evaluate the TK activity versus different substrates. We demonstrate the accuracy of this strategy to determine the enzymatic kinetic parameters and to study the substrate specificity of a thermostable TK from thermophilic microorganism Geobacillus stearothermophilus, offering promising prospects in biocatalysis. Millifluidic systems are useful in this regard as they can be used to rapidly evaluate the TK activity towards various substrates, and also different sets of conditions, identifying the optimal operating environment while minimizing resource consumption and ensuring high control over the operating conditions.

Ascorbic acid-2-0-beta-glucuronide, a new metabolite of vitamin C identified in human urine and uremic plasma.

A new metabolite of ascorbic acid has been isolated by a multi-step chromatographic procedure both from normal human urine and uremic plasma. Nuclear Magnetic Resonance studies, and chemical and enzymic analyses indicated that the compound is a conjugated structure consisting of equimolar ascorbic and beta-D-glucuronic acids. We determined the pKa value of the ascorbic acid moiety of the compound on the basis of variations of ultraviolet absorbances as a function of pH. Results showed that glucuronic acid is coupled to the 2-position of ascorbic acid.

Reintroduction: challenges and lessons for basic ecology.

Ecology is a subject where theoretical predictions are often difficult to test experimentally in the field. To address this challenge, the Ecological Society of America suggested exploiting large-scale environmental management decisions in a scientific way. This 'adaptive management' constitutes one of the purposes of the Sustainable Biosphere Initiative. Meanwhile, in the current context of the biodiversity crisis, translocations and particularly reintroductions of threatened species are becoming more numerous. It is time for ecologists and wildlife managers to collaborate on these unique opportunities for large-scale studies.

Study of psychosocial parameters related to the survival rate of renal transplantation in children.

The purpose of the present study was to assess the effect of intelligence, schooling, psychomotor, emotional, and social status on renal graft survival in children. Sixty-two cadaver renal transplant recipients were evaluated retrospectively and the influence of sex, age, weight, and the use of cyclosporin A (CyA) on the success rate of the graft from 1 to 5 years later was analyzed. Psychological and social scores were devised and included as factors predictive of survival of the graft. Univariate analysis showed that the following variables predicted renal graft survival: the use of CyA (P = 0.0002), pre-transplant dialysis (P = 0.04), weight at the time of transplantation (P = 0.072), and psychological scores (P = 0.064). Association analysis demonstrated that pre-transplantation dialysis was only a chance association and therefore the parameter was discarded. Multivariate analysis showed that the predictive parameters were the use of CyA, sex, weight in kilograms, and the psychological score. An equation was then derived from variables that predict the probability that a specific patient's graft will survive more than t months. This equation is the estimated survival distribution function and is as follow: S (t) = Exp {-Exp[-(0.8882x1 - 1.827x2 + 0.037x3 - 0.1746x4) + ln t - 4.7862]} where S (t) = the survival at t months post transplantation, x1 = sex (male 1, female 2), x2 = CyA (yes 1, no 2), x3 = weight in kilograms, and x4 = psychological score. The major impact of psychological factors on renal graft survival was surprising.