Dominant exposure

Humans, fish, and wildlife are exposed to PCBs from a number of different exposure routes, including respiration, water consumption, food consumption, and dermal contact with contaminated water, soil, etc. However, the dominant exposure route is food consumption, and especially the consumption of fish. This is because PCBs bioaccumulate effectively in fats and lipids [35]. As a result, most PCB congeners (including the most toxic ones) biomagnify in the food web, which means that the higher levels of the food web will have greater concentrations than lower ones (see full discussion in the section on food web dynamics). As a result, adverse effects have been observed in fish-eating animals and birds, and in humans that have consumed fish (occupationally exposed workers are not considered in this discussion). 

Stapleton et al. (2005) were the hrst to hnd elevated levels of PBDEs in house dust and to posit that exposure to dust could be an important exposure route. This was followed by confirmation of dust as the dominant exposure route to PBDEs and that diet was secondary for North Americans (Jones-Otazo et al, 2005 Lorber, 2008). Dust, as the main exposure route, was able to account for those women with much higher PBDE concentrations and some of the geographic differences seen among continents (Harrad et al, 2008b). Wu et al (2007) confirmed the dust exposure hypothesis by finding a clear relationship between PBDE concentrations in the breast milk and household dust for 46 mothers in the Northeast US. Further, Zota et al (2008) found that blood serum levels of residents of several counties in California were twofold higher than that in the US as a whole, and concluded that this was consistent with 4-10 times higher dust concentrations. Betts (2008) provides an excellent overview of the subject. 

Health effects associated with excess for the dominant exposure route(s)... 

It is important to examine in a little more detail the significance of uptake via food, although biomagnification in a wider context in field situations is discussed in Section 3.5.4. As a general rule, it has been accepted that uptake via food rather than in the dissolved state directly from the water mass is the dominant exposure route for compounds with log Pow > 5 (Connolly and Pedersen 1988) (Thomann 1989). This alternative exposure route is not, however, generally taken into consideration in laboratory studies since it is difficult — and indeed may be impossible — to distinguish between direct uptake via the food and simultaneous desorption from the food that results in direct... 

Each approach has its characteristic advantages and disadvantages due to the underlying technology and the materials issues involved (see the remainder of this section). In contrast, SLR schemes are relatively simple processes, can have moderate levels of resolution and etch resistance, and good hnearity, but they suffer from reflective swing problems and small depths of focus, and are limited to low aspect ratios. Irrespective of the resist process approach chosen, chemical amplification continues to be the dominant exposure mechanism of the imaging layer. 

Not only does the performance depend on the nature of the foreign metal but also on the preferential surface exposed. Thus, the Pt3Ni(lll)-skin surface exhibits the highest catalytic activity recorded for the ORR, i.e. a total 90-fold increase with respect to that of Pt/C. This value corresponds to a TOF (turn-over frequency) of 2800 s a value well above the figures reported for Pt/C and PtM/C of 25 s and = 60 s respectively. Wu et have reported a facile method for synthesizing PtgNi nanoparticles with a dominant exposure of 111 facets. 

Exposure of a person may be external or internal and may be incurred by various exposure pathways (see Section 9.3). External exposure may be due to direct irradiation from the source, airborne radionuclides in the air (immersion or exposure to an overhead plume), or radionuclides deposited onto the ground and onto a person s clothing and skin. Internal exposure follows from the inhalation of radioactive material either directly from a plume or resuspended from contaminated surfaces, from the ingestion of contaminated food and water, or through contaminated wounds. Total effective dose can be calculated by taking into account all dominant exposure pathways by which persons were exposed. 

Wu et al. [23] recently reported an approach to the preparation of tmncated-octahedral PtsNi (tjO-PtsNi) catalysts that have dominant exposure of 111 facets. Three sets of PtsNi nanocrystals were generated with various truncated-octahedral crystal populations. 

It was found that that in the case of soft beta and X-ray radiation the IPs behave as an ideal gas counter with the 100% absorption efficiency if they are exposed in the middle of exposure range ( 10 to 10 photons/ pixel area) and that the relative uncertainty in measured intensity is determined primarily by the quantum fluctuations of the incident radiation (1). The thermal neutron absorption efficiency of the present available Gd doped IP-Neutron Detectors (IP-NDs) was found to be 53% and 69%, depending on the thicknes of the doped phosphor layer ( 85pm and 135 pm respectively). No substantial deviation in the IP response with the spatial variation over the surface of the IP was found, when irradiated by the homogeneous field of X-rays or neutrons and deviations were dominated by the incident radiation statistics (1). 

Optical Lithography. Optical Hthography uses visible or ultraviolet light as the exposure media, and is the dominant Hthographic process used for patterning IC wafers. The linewidth limit is near 0.4 p.m, although some narrower features may be possible (34). The masks typically are made from patterned, opaque chromium films on glass. 

There is some evidence for chemically mediated endocrine disruption in amphibians. The egg yolk protein, vitellogenin, is inducible in amphibians by exposure to DDT. " Males of the short clawed toad Xenopus laevis given 250 fig/g or 1 fig/g o,p -DDT for seven days have been shown to produce vitellogenin, although the induction was less than that achieved by treatment with 1 fig/g of either 17/1-oestradiol or diethylstilboestrol. Research has also shown that endocrine disrupting chemicals can alter sex ratios in wild populations of certain species PCB congeners and organochlorine compounds have been linked with male domination of sex ratios in polluted compared to unpolluted sites. ... 

Table 1 contains the metal-to-metal engineering property requirements for Boeing Material Specification (BMS) 5-101, a structural film adhesive for metal to metal and honeycomb sandwich use in areas with normal temperature exposure. The requirements are dominated by shear strength tests. Shear strength is the most critical engineering property for structural adhesives, at least for the simplistic joint analysis that is commonly used for metal-to-metal secondary structure on commercial aircraft. Adhesive Joints are purposefully loaded primarily in shear as opposed to tension or peel modes as adhesives are typically stronger in shear than in Mode I (load normal to the plane of the bond) loading. 

For example, given a BWR-1 release (Table 8,2-1), typical weather conditions, no rain and less than one mile from the accident immersion, inhalation, and ground produce about the same magnitude doses for exposure times of several hours or less. The exposure from a cloud ceases once the cloud has passed, but exposure may continue from the ground until the area is decontaminated or evacuated. If the exposure time is long, the ground dose can eventually dominate. Tables 9-6 and 9-7 in NUREG/CR-2300 show examples of the relative importance of these pathways. 

The biotransformation of a given chemical compound in experimental animals and in humans may differ. Furthermore, high doses of chemical compounds are used in studies with experimental animals, and this may cause alterations in biotransformation of the tested chemicals that do not occur at the lower doses relevant to the human exposure situation. For example, a metabolic pathway dominating at low doses may become saturated, and a salvage metabolic pathway, e.g., one that produces reactive intermediates of the compound, may become involved in the biotransformation of the chemical. Since this intermediate could never be produced at the exposure levels encountered in humans, the overall result... 

Malignant hyperthermia (MH) is an autosomal-dominant pharmacogenetic disorder that is triggered by exposure to inhalation of general anesthetics, such as halothane. In susceptible individuals, these drugs can induce tachycardia, a greatly increased body metabolism, muscle contracture and an elevated body temperature (above 40°C) with a rapid rate of increase. Many cases of MH are linked to a gene for type 1 ryanodine receptor (RyRl). 

From this, it can be seen that the optimum choice of 3D technique depends on the observing strategy appropriate to the particular scientific investigation. However there are other, second-order, considerations to be considered which violate this datacube theorem. These include whether the individual exposures are dominated by photon noise from the background or the detector, and the stability of the instrument and background over a long period of stepped exposures. 

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