Óxido nitroso y medio ambiente

Emisiones de óxido nitroso de la desnitrificación en las redes de arroyos y ríos Nitrous oxide emission from denitrification in stream and river networks. Beaulieu JJ, Tank JL, Hamilton SK, Wollheim WM, Hall RO Jr, Mulholland PJ, Peterson BJ, Ashkenas LR, Cooper LW, Dahm CN, Dodds WK, Grimm NB, Johnson SL, McDowell WH, Poole GC, Valett HM, Arango CP, Bernot MJ, Burgin AJ, Crenshaw CL, Helton AM, Johnson LT, O'Brien JM, Potter JD, Sheibley RW, Sobota DJ, Thomas SM. Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA. beaulieu.jake@epa.gov Proc Natl Acad Sci U S A. 2011 Jan 4;108(1):214-9. Epub 2010 Dec 20. Abstract Nitrous oxide (N(2)O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N(2)O via microbial denitrification that converts N to N(2)O and dinitrogen (N(2)). The fraction of denitrified N that escapes as N(2)O rather than N(2) (i.e., the N(2)O yield) is an important determinant of how much N(2)O is produced by river networks, but little is known about the N(2)O yield in flowing waters. Here, we present the results of whole-stream (15)N-tracer additions conducted in 72 headwater streams draining multiple land-use types across the United States. We found that stream denitrification produces N(2)O at rates that increase with stream water nitrate (NO(3)(-)) concentrations, but that <1% of denitrified N is converted to N(2)O. Unlike some previous studies, we found no relationship between the N(2)O yield and stream water NO(3)(-). We suggest that increased stream NO(3)(-) loading stimulates denitrification and concomitant N(2)O production, but does not increase the N(2)O yield. In our study, most streams were sources of N(2)O to the atmosphere and the highest emission rates were observed in streams draining urban basins. Using a global river network model, we estimate that microbial N transformations (e.g., denitrification and nitrification) convert at least 0.68 Tg*y(-1) of anthropogenic N inputs to N(2)O in river networks, equivalent to 10% of the global anthropogenic N(2)O emission rate. This estimate of stream and river N(2)O emissions is three times greater than estimated by the Intergovernmental Panel on Climate Change http://www.pnas.org/content/108/1/214.full.pdf+html     Efectos biológicos del óxido nitroso: revisión mecanística y toxicológica Biologic effects of nitrous oxide: a mechanistic and toxicologic review. Sanders RD, Weimann J, Maze M. Department of Anaesthetics, Pain Medicine, and Intensive Care, Imperial College London, Chelsea and Westminster Hospital, London, United Kingdom. Anesthesiology. 2008 Oct;109(4):707-22. Abstract Nitrous oxide is the longest serving member of the anesthesiologist's pharmacologic armamentarium but remains a source of controversy because of fears over its adverse effects. Recently, the Evaluation of Nitrous oxide In a Gas Mixture for Anaesthesia (ENIGMA) trial reported that nitrous oxide use increases postoperative complications; further preclinical reports have suggested that nitrous oxide may contribute to neurocognitive dysfunction in the young and elderly. Therefore, nitrous oxide's longevity in anesthetic practice is under threat. In this article, the authors discuss the evidence for the putative toxicity of nitrous oxide, from either patient or occupational exposure, within the context of the mechanism of nitrous oxide's action. Although it would seem prudent to avoid nitrous oxide in certain vulnerable populations, current evidence in support of a more widespread prescription from clinical practice is unconvincing http://journals.lww.com/anesthesiology/pages/articleviewer.aspx?year=2008&issue=10000&article=00020&type=abstract     Óxido nitroso: un efecto toxicológico globalizado para ser considerado Nitrous oxide: a global toxicological effect to consider. Parker NW, Behringer EC. Anesthesiology. 2009 May;110(5):1195; author reply 1196. To the Editor:-The recent review article by Sanders et al. was informative and comprehensive, with the exception of one important toxicological detail. Nitrous oxide is known to have a significant global climatologic impact as a naturally occurring greenhouse gas. After carbon dioxide and methane, nitrous oxide is the third most climatologically significant greenhouse gas. Greenhouse gases act like a warming blanket in the troposphere and prevent radiative cooling. Nitrous oxide is a particularly potent greenhouse gas with 300 times the global warming potential of carbon dioxide over 100 yr, according to the Intergovernmental Panel on Climate Change. It seems prudent to include the climatologic effects of nitrous oxide as a biologic effect of the gas. http://journals.lww.com/anesthesiology/Citation/2009/05000/Nitrous_Oxide __A_Global_Toxicological_Effect_to.49.aspx

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