Methylmercury (MeHg) is a powerful neurotoxicant in humans. In terms of biomarkers of MeHg exposure, hair and blood have long been used in epidemiological studies as the biomarkers of choice. In fact, total hair mercury (Hg) content as well as organic blood Hg concentrations reflects exposure to organic Hg from food consumption. Extensive studies, establishing a constant and linear relation between MeHg intake versus Hg levels in hair and blood, were conducted by governmental officials to establish guidelines on safe levels of MeHg exposure, which were translated into threshold daily fish consumption rates (usually expressed as μg MeHg per kg bodyweight). Nowadays, in most epidemiologic studies blood or hair mercury (Hg) level is commonly used as a valid proxy to estimate human exposure to methylmercury (MeHg) through fish consumption without relating this signal to actual fish consumption patterns among populations. Human variability in mercury toxicokinetics was identified and measurement error has been pointed out to be a substantial contributor to observed variability, particularly where dietary information is retrospective and self-reported. However, experimental evidence indicates that significant variability among individuals may exist in the biokinetics of mercury. Also recent findings from previous population-based studies through COMERN initiative also revealed that MeHg metabolic processes might greatly vary across populations. In fact, it is unlikely that the magnitude of the difference measured between observed and expected levels of mercury, given the reported intake, can be entirely explained by laboratory measurement errors or reporting bias. 相似文献
The Tso Morari Complex, which is thought to be originally the margin of the Indian continent, is composed of pelitic gneisses and schists including mafic rock lenses (eclogites and basic schists). Eclogites studied here have the mineral assemblage Grt + Omp + Ca-Amp + Zo + Phn + Pg + Qtz + Rt. They also have coesite pseudomorph in garnet and quartz rods in omphacite, suggesting a record of ultrahigh-pressure metamorphism. They occur only in the cores of meter-scale mafic rock lenses intercalated with the pelitic schists. Small mafic lenses and the rim parts of large lenses have been strongly deformed to form the foliation parallel to that of the pelitic schists and show the mineral assemblages of upper greenschist to amphibolite facies metamorphism. The garnet–omphacite thermometry and the univariant reaction relations for jadeite formation give 13–21 kbar at 600 °C and 16–18 kbar at 750 °C for the eclogite formation using the jadeite content of clinopyroxene (XJd = 0.48).
Phengites in pelitic schists show variable Si / Al and Na / K ratios among grains as well as within single grains, and give K–Ar ages of 50–87 Ma. The pelitic schist with paragonite and phengite yielded K–Ar ages of 83.5 Ma (K = 4.9 wt.%) for paragonite–phengite mixture and 85.3 Ma (K = 7.8 wt.%) for phengite and an isochron age of 91 ± 13 Ma from the two dataset. The eclogite gives a plateau age of 132 Ma in Ar/Ar step-heating analyses using single phengite grain and an inverse isochron age of 130 ± 39 Ma with an initial 40Ar / 36Ar ratio of 434 ± 90 in Ar/Ar spot analyses of phengites and paragonites. The Cretaceous isochron ages are interpreted to represent the timing of early stage of exhumation of the eclogitic rocks assuming revised high closure temperature (500 °C) for phengite K–Ar system. The phengites in pelitic schists have experienced retrograde reaction which modified their chemistry during intense deformation associated with the exhumation of these rocks with the release of significant radiogenic 40Ar from the crystals. The argon release took place in the schists that experienced the retrogression to upper greenschist facies metamorphisms from the eclogite facies conditions. 相似文献
The three most important components necessary for functioning of an operational flood warning system are: (1) a rainfall measuring
system; (2) a soil moisture updating system; and, (3) a surface discharge measuring system. Although surface based networks
for these systems can be largely inadequate in many parts of the world, this inadequacy particularly affects the tropics,
which are most vulnerable to flooding hazards. Furthermore, the tropical regions comprise developing countries lacking the
financial resources for such surface-based monitoring. The heritage of research conducted on evaluating the potential for
measuring discharge from space has now morphed into an agenda for a mission dedicated to space-based surface discharge measurements.
This mission juxtaposed with two other upcoming space-based missions: (1) for rainfall measurement (Global Precipitation Measurement,
GPM), and (2) soil moisture measurement (Hydrosphere State, HYDROS), bears promise for designing a fully space-borne system
for early warning of floods. Such a system, if operational, stands to offer tremendous socio-economic benefit to many flood-prone
developing nations of the tropical world. However, there are two competing aspects that need careful assessment to justify
the viability of such a system: (1) cost-effectiveness due to surface data scarcity; and (2) flood prediction uncertainty
due to uncertainty in the remote sensing measurements. This paper presents the flood hazard mitigation opportunities offered
by the assimilation of the three proposed space missions within the context of these two competing aspects. The discussion
is cast from the perspective of current understanding of the prediction uncertainties associated with space-based flood prediction.
A conceptual framework for a fully space-borne system for early-warning of floods is proposed. The need for retrospective
validation of such a system on historical data comprising floods and its associated socio-economic impact is stressed. This
proposal for a fully space-borne system, if pursued through wide interdisciplinary effort as recommended herein, promises
to enhance the utility of the three space missions more than what their individual agenda can be expected to offer. 相似文献
Field investigations of the Deccan Trap lava sequence along a 70 km traverse in the Narsingpur-Harrai-Amarwara area of central
India indicate twenty lava flows comprising a total thickness of around 480 m. Primary volcanic structures like vesicles and
cooling joints are conspicuous in this volcanic succession and are used to divide individual flows into three well-defined
zones namely the lower colonnade zone, entablature zone, and the upper colonnade zone. The variable nature of these structural
zones is used for identification and correlation of lava flows in the field. For twenty lava flows, the thicknesses of upper
colonnade zones of eight flows are ∼5 m while those of eight other flows are ∼8 m each. The thicknesses of upper colonnade
zones of remaining four flows could not be measured in the field. Using the thicknesses of these upper colonnade zones and
standard temperature-flow thickness-cooling time profiles for lava pile, the total cooling time of these sixteen Deccan Trap
lava flows has been estimated at 12 to 15 years. 相似文献