Daily Archives: January 2, 2013

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Fluoride challenged in 1960…

Pages from [1960] The Fluoridations Fallacy by R.F. Boyd Gaudin, B.Sc., A.C.G.I., A.M

Selenium guideline too high?

Marco Vinceti, Catherine M. Crespi, Francesca Bonvicini, Carlotta Malagoli, Margherita Ferrante, Sandra Marmiroli, Saverio Stranges. The need for a reassessment of the safe upper limit of selenium in drinking water. Science of The Total Environment, Volume 443, 15 January 2013, Pages 633–642.

Results of recent epidemiologic studies suggest the need to reassess the safe upper limit in drinking water of selenium, a metalloid with both toxicological and nutritional properties. Observational and experimental human studies on health effects of organic selenium compounds consumed through diet or supplements, and of inorganic selenium consumed through drinking water, have shown that human toxicity may occur at much lower levels than previously surmised. Evidence indicates that the chemical form of selenium strongly influences its toxicity, and that its biological activity may differ in different species, emphasizing the importance of the few human studies on health effects of the specific selenium compounds found in drinking water. Epidemiologic studies that investigated the effects of selenate, an inorganic selenium species commonly found in drinking water, together with evidence of toxicity of inorganic selenium at low levels in from in vitro and animal studies, indicate that health risks may occur at exposures below the current European Union and World Health Organization upper limit and guideline of 10 and 40 μg/l, respectively, and suggest reduction to 1 μg/l in order to adequately protect human health. Although few drinking waters are currently known to have selenium concentrations exceeding this level, the public health importance of this issue should not be overlooked, and further epidemiologic research is critically needed in this area.

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Solar irradiance does indeed affect climate….

L. E. A. Vieira, S. K. Solanki, N. A. Krivova, and I. Usoskin. Evolution of the solar irradiance during the Holocene. Astronomy & Astrophysics, manuscript no. TSIversion08, March 29, 2011

Context. Long-term records of solar radiative output are vital for understanding solar variability and past climate change. Measurements of solar irradiance are available for only the last three decades, which calls for reconstructions of this quantity over longer time scales using suitable models.

Aims. We present a physically consistent reconstruction of the total solar irradiance for the Holocene.

Methods. We extend the SATIRE (Spectral And Total Irradiance REconstruction) models to estimate the evolution of the total (and partly spectral) solar irradiance over the Holocene. The basic assumption is that the variations of the solar irradiance are due to the evolution of the dark and bright magnetic features on the solar surface. The evolution of the decadally averaged magnetic flux is computed from decadal values of cosmogenic isotope concentrations recorded in natural archives employing a series of physics-based models connecting the processes from the modulation of the cosmic ray flux in the heliosphere to their record in natural archives. We then compute the total solar irradiance (TSI) as a linear combination of the jth and jth + 1 decadal values of the open magnetic flux. In order to evaluate the uncertainties due to the evolution of the Earth’s magnetic dipole moment, we employ four reconstructions of the open flux which are based on conceptually different paleomagnetic models.

Results. Reconstructions of the TSI over the Holocene, each valid for a different paleomagnetic time series, are presented. Our analysis suggests that major sources of uncertainty in the TSI in this model are the heritage of the uncertainty of the TSI since 1610 reconstructed from sunspot data and the uncertainty of the evolution of the Earth’s magnetic dipole moment. The analysis of the distribution functions of the reconstructed irradiance for the last 3000 years, which is the period that the reconstructions overlap, indicates that the estimates based on the virtual axial dipole moment are significantly lower at earlier times than the reconstructions based on the virtual dipole moment. We also present a combined reconstruction, which represents our best estimate of total solar irradiance for any given time during the Holocene.

Conclusions. We present the first physics-based reconstruction of the total solar irradiance over the Holocene, which will be of interest for studies of climate change over the last 11 500 years. The reconstruction indicates that the decadally averaged total solar irradiance ranges over approximately 1.5 W/m2 from grand maxima to grand minima.

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Alaska cooling trend since 2000…..

G. Wendler, L. Chen and B. Moore. The First Decade of the New Century: A Cooling Trend for Most of Alaska. The Open Atmospheric Science Journal, 2012, 6, 111-116.

During the first decade of the 21st century most of Alaska experienced a cooling shift, modifying the long-term warming trend, which has been about twice the global change up to this time. All of Alaska cooled with the exception of Northern Regions. This trend was caused by a change in sign of the Pacific Decadal Oscillation (PDO), which became dominantly negative, weakening the Aleutian Low. This weakening results in less relatively warm air being advected from the Northern Pacific. This transport is especially important in winter when the solar radiation is weak. It is during this period that the strongest cooling was observed. In addition, the cooling was especially pronounced in Western Alaska, closest to the area of the center of the Aleutian Low. The changes seen in the reanalyzed data were confirmed from surface observations, both in the decrease of the North-South atmospheric pressure gradient, as well as the decrease in the mean wind speeds for stations located in the Bering Sea area.

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Assessing potential hazards from drugs in drinking water

Richard J. Bull, James Crook, Margaret Whittaker, Joseph A. Cotruvo. Therapeutic dose as the point of departure in assessing potential health hazards from drugs in drinking water and recycled municipal wastewater. Regulatory Toxicology and Pharmacology. Volume 60, Issue 1, 1 June 2011, Pages 1–19.

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The detection of drugs in drinking water sources has raised questions related to safety. In the absence of regulatory or other official guidance, water utilities are faced with a problem of which drugs should be monitored and the detection limits that should be required. The US FDA summarizes data required for drug approval and post marketing adverse reaction reporting. The use of these data as a means of arriving at concentrations in water where adverse health effects are minimal or non-existent was explored. The minimum therapeutic dose was assumed an appropriate point of departure. Appropriate uncertainty factors could be applied depending upon the qualitative and quantitative nature of the data that are available. Assumptions inherent in US FDA’s approval of drugs for use in subsets of the population relative to the broader concerns that arise for exposures of the entire population had to be considered. Additional questions are; whether the drug under consideration is carcinogenic, carries pregnancy and lactation warnings, approval for limited vs. chronic use, exposures to multiple compounds that could act in additive or synergistic ways, and the seriousness of toxicities that are observed. Aside from these considerations, a combined uncertainty factor of 1000 appeared adequate.

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