Download or read book An Investigation of the Major Transformations and Loss Mechanisms of Mercury and Selenium in the Surface Ocean written by Brian P Dimento and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The importance of methylmercury (CH3Hg) photochemical degradation, an understudied process in marine ecosystems, was investigated in variety of coastal and oceanic waters from the northeastern U.S. as well as the Atlantic, Pacific and Arctic Oceans. Degradation rate constants ranged from 0.87 to 1.67 day-1,but did not correlate with the environmental parameters measured. Further experiments investigating the reaction mechanism observed little effect of nitrate, chloride, and bromide ions. CH3Hg loss per year due to photodegradation was modeled across latitudes from the Equator to the Arctic using water column integrated rates determined for coastal wetlands, estuaries and the open ocean. A global photochemical demethylation rate of 25.3 Mmol yr-1 was calculated, representing an important flux in the biogeochemical cycle of CH3Hg. Air-sea exchange of elemental mercury (Hg0), another important process in the biogeochemical cycle of Hg, was investigated on the U.S. GEOTRACES cruise in the Arctic Ocean in 2015. High resolution measurements of Hg0 in surface waters and the atmosphere were used to calculate evasional fluxes, and Hg concentrations determined in aerosols and precipitation were used to estimate atmospheric deposition. Overall, concentrations of dissolved Hg0 were near saturation in ice-free waters (32 ± 30 fM), but were highly enriched under contiguous ice (101 ± 98 fM, up to 544 fM). Predicted peaks in Hg0 evasion, although blocked by the sea ice barrier, were as high as 270 pmol m-2 h-1. From these estimates we can better predict the effect of a changing climate on Hg dynamics in the Arctic. The photochemical cycling of selenium (Se), an essential micronutrient, was also studied in marine waters. Inorganic Se(IV) and Se(VI) were found in nutrient-type distributions in samples collected during the Metzyme cruise on the equatorial Pacific Ocean in 2011. Photochemically mediated redox transformation pathways studied could not explain the enhanced concentrations of Se(IV) observed, indicating that a biological process is likely involved. Photodegradation was an important sink of dimethyl selenide ((CH3)2Se) in a variety of natural waters, with reaction rate constants ranging from 18.1 to 47.0 day-1. The global loss of (CH3)2Se due to photodegradation was estimated at 28.0 Gmol yr-1.
Download or read book Occurrence of Selenium and Mercury in Surface Water Wind River Indian Reservation Wyoming 1995 written by Melanie L. Clark and published by . This book was released on 1996 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book JV Task 96 Phase 2 Investigating the Importance of the Mercury Selenium Interaction written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to improve the understanding of the mercury issue, it is vital to study mercury's effects on selenium physiology. While mercury present in the environment or food sources may pose health risks, the protective effects of selenium have not been adequately considered in establishing regulatory policy. Numerous studies report that vulnerability to mercury toxicity is inversely proportional to selenium status or level. However, selenium status has not been considered in the development of the reference dosage levels for mercury exposure. Experimental animals fed low-selenium diets are far more vulnerable to mercury toxicity than animals fed normal selenium, and animals fed selenium-rich diets are even more resistant. Selenium-dependent enzymes in brain and endocrine tissues can be impaired by excessive mercury exposure, apparently because mercury has an extremely high binding affinity for selenium. When selenium becomes bound to mercury, it is unable to participate in the metabolic cycling of selenoprotein synthesis. Because of mercury-dependent impairments of selenoprotein synthesis, various antioxidant and regulatory functions in brain biochemistry are compromised. This report details a 2-year multiclient-funded research program designed to examine the interactions between mercury and selenium in animal models. The studies explored the effects of dietary intakes of toxic amounts of methylmercury and the protective effects of the normal dietary range of selenium in counteracting mercury toxicity. This study finds that the amounts of selenium present in ocean fish are sufficient to protect against far larger quantities of methylmercury than those present in typical seafoods. Toxic effects of methylmercury exposure were not directly proportional to mercury concentrations in blood, brain, or any other tissues. Instead, mercury toxicity was proportional to molar ratios of mercury relative to selenium. In order to accurately assess risk associated with methylmercury or mercury exposures, mercury-selenium ratios appear to be far more accurate and effective in identifying risk and protecting human and environmental health. This study also finds that methylmercury toxicity can be effectively treated by dietary selenium, preventing the death and progressive disabilities that otherwise occur in methylmercury-treated subjects. Remarkably, the positive response to selenium therapy was essentially equivalent regardless of whether or not toxic amounts of methylmercury were still administered. The findings of the Physiologically Oriented Integration of Nutrients and Toxins (POINT) models of the effects of mercury and selenium developed in this project are consistent with the hypothesis that mercury toxicity arises because of mercury-dependent inhibition of selenium availability in brain and endocrine tissues. This appears to occur through synergistic effects of mercury-dependent inhibition of selenium transport to these tissues and selective sequestration of the selenium present in the tissues. Compromised transport of selenium to the brain and endocrine tissues would be particularly hazardous to the developing fetus because the rapidly growing tissues of the child have no selenium reserves. Therefore, maternal consumption of foods with high mercury-selenium ratios is hazardous. In summation, methylmercury exposure is unlikely to cause harm in populations that eat selenium-rich diets but may cause harm among populations that consume certain foods that have methylmercury present in excess of selenium.
Download or read book Mechanisms of Mercury Transformation in Bottom Sediments written by and published by . This book was released on 1973 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Mercury as a Global Pollutant written by Donald B. Porcella and published by Springer. This book was released on 2014-08-23 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: ACKNOWLEDGEMENTS xiv PART I MERCURY AND HUMAN HEALTH B. WHEATLEY and S. PARADIS I Exposure of Canadian Aboriginal Peoples to Methylmercury 3-11 M. GIRARD and C. DUMONT I Exposure of James Bay Cree to Methylmercury during Pregnancy for the Years 1983-91 13-19 M. RICHARDSON, M. MITCHELL, S. COAD and R. RAPHAEL I Exposure to Mercury in Canada: A Multimedia Analysis 21-30 M. RICHARDSON, M. EGYED and D. J. CURRIE I Human Exposure to Mercury may Decrease as Acidic Deposition Increases 31-39 L. E. FLEMING, S. WATKINS, R. KADERMAN, B. LEVIN, D. R. AVYAR, M. BIZZIO, D. STEPHENS and J. A. BEAN I Mercury Exposure in Humans through Food Consumption from the Everglades of Florida 41-48 J. M. GEARHART, H. J. CLEWELL III, K. S. CRUMP, A. M. SHIPP and A. SILVERS I Pharmacokinetic Dose Estimates of Mercury in Children and Dose-Response Curves of Performance Tests in a Large Epidemiological Study 49-58 I. SKARE I Mass Balance and Systemic Uptake of Mercury Released from Dental Amalgam Fillings 59-67 J. DELLINGER, N. KMIECIK, S. GERSTENBERGER and H. NGU I Mercury Contamina tion of Fish in the Ojibwa Diet: I. Walleye Fillets and Skin-On versus Skin-Off Sampling 69-76 J. DELLINGER, L. MALEK and M. BEATTIE I Mercury Contamination of Fish in the Ojibwa Diet: II. Sensory Evoked Responses in Rats Fed Walleye 77-83 H. AKAGI, O. MALM, F. J. P. BRANCHES, Y. KINJO, Y. KASHIMA, J. R. D. GUIMARAES, R. B. OLIVEIRA, K. HARAGUCHI, W. C. PFEIFFER, Y.
Download or read book Mechanisms of Mercury Transformation in Bottom Sediments written by Peter A. Krenkel and published by . This book was released on 1973 with total page 343 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1977 with total page 1064 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Selected Water Resources Abstracts written by and published by . This book was released on 1978-07 with total page 662 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Environment Abstracts Annual 1991 written by Bowker Editorial Staff and published by R. R. Bowker. This book was released on 1992-03 with total page 1792 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Earth Materials and Health written by National Research Council and published by National Academies Press. This book was released on 2007-05-09 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: A range of natural earth materials, like arsenic or fluoride, have long been linked to significant human health effects. Improved understanding of the pervasive and complex interactions between earth materials and human health will require creative collaborations between earth scientists and public health professionals. At the request of the National Science Foundation, U.S. Geological Survey, and National Aeronautics and Space Administration, this National Research Council book assesses the current state of knowledge at the interface between the earth sciences and public health disciplines. The book identifies high-priority areas for collaborative research, including understanding the transport and bioavailability of potentially hazardous earth materials, using risk-based scenarios to mitigate the public health effects of natural hazards under current and future climate regimes, and understanding the health risks that result from disturbance of earth systems. Geospatial information - geological maps for earth scientists and epidemiological data for public health professionals - is identified as one of the essential integrative tools that is fundamental to the activities of both communities. The book also calls for increased data sharing between agencies to promote interdisciplinary research without compromising privacy.
Download or read book Monitored Natural Attenuation of Inorganic Contaminants in Ground Water written by and published by . This book was released on 2007 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: V.3 ... consists of individual chapters that describe 1) the conceptual background for radionuclides, including tritium, radon, strontium, technetium, uranium, iodine, radium, thorium, cesium, plutonium-americium and 2) data requirements to be met during site characterization.
Download or read book Mercury Hazards to Living Organisms written by Ronald Eisler and published by CRC Press. This book was released on 2006-03-14 with total page 333 pages. Available in PDF, EPUB and Kindle. Book excerpt: Complex and ever changing in its forms and functions, the element mercury follows a convoluted course through the environment and up the food chain. The process is complicated further by the fact that the difference between tolerable natural background levels and harmful effects in the environment is exceptionally small and still not completely und
Download or read book Poisoning in the Modern World written by Ozgur Karcioglu and published by BoD – Books on Demand. This book was released on 2019-06-19 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over 400 years ago, Swiss alchemist and physician Paracelsus (1493-1541) cited: "All substances are poisons; there is none that is not a poison. The right dose differentiates a poison from a remedy." This is often condensed to: "The dose makes the poison." So, why are we overtly anxious about intoxications?In fact, poisons became a global problem with the industrial revolution. Pesticides, asbestos, occupational chemicals, air pollution, and heavy metal toxicity maintain high priority worldwide, especially in developing countries. Children between 0 and 5 years old are the most vulnerable to both acute and chronic poisonings, while older adults suffer from the chronic effects of chemicals. This book aims to raise awareness about the challenges of poisons, to help clinicians understand current issues in toxicology.
Download or read book Diet and Health written by National Research Council and published by National Academies Press. This book was released on 1989-01-01 with total page 765 pages. Available in PDF, EPUB and Kindle. Book excerpt: Diet and Health examines the many complex issues concerning diet and its role in increasing or decreasing the risk of chronic disease. It proposes dietary recommendations for reducing the risk of the major diseases and causes of death today: atherosclerotic cardiovascular diseases (including heart attack and stroke), cancer, high blood pressure, obesity, osteoporosis, diabetes mellitus, liver disease, and dental caries.
Download or read book New Scientist written by and published by . This book was released on 1975 with total page 884 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Selected Water Resources Abstracts written by and published by . This book was released on 1978-10 with total page 800 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Toxicological Profile for Selenium Update written by John Risher and published by DIANE Publishing. This book was released on 2011-05 with total page 457 pages. Available in PDF, EPUB and Kindle. Book excerpt: Selenium (SE) and its compounds are used in photographic devices, gun gluing, plastics, paints, anti-dandruff shampoos, vitamin and mineral supp., fungicides, and glass. It is also used to prepare drugs and as a nutritional feed supp. for poultry and livestock. This profile includes: (a) The exam¿n. of toxicologic info. and epidemiologic evaluations on SE to ascertain the levels of significant human exposure for the substance and the chronic health effects; (b) A determination of whether adequate info. on the health effects of SE is avail. to determine levels of exposure that present a significant risk to human health (SRHH); and (c) Ident¿n. of toxicologic testing needed to identify the types of exposure that may present SRHH. Illus. A print on demand pub.
