Exponent

About: Exponent is a company organization based out in Menlo Park, California, United States. It is known for research contribution in the topics: Population & Risk assessment. The organization has 1589 authors who have published 2680 publications receiving 88140 citations.

Is total mass or mass of alveolar-deposited airborne particles of beryllium a better predictor of the prevalence of disease? A preliminary study of a beryllium processing facility.

Abstract: Cases of chronic beryllium disease (CBD) and beryllium (Be) sensitization continue to be identified among Be industry workers. The currently accepted method for measuring exposure, which involves measuring the total mass of airborne Be per cubic meter, shows an inconsistent doseresponse relationship with the prevalence of CBD. This study was conducted to evaluate which Be aerosol characteristics other than total mass may be more informative in understanding the dose-response relationship between exposure to Be and disease. Personal (n = 53) and general (n = 55) area airborne Be samples were collected in five furnace areas at a Be manufacturing facility where prevalence rates of CBD and Be sensitization had been previously studied among 535 employees with significant Be exposure. In the five furnace areas, particle-size specific personal samples and area samples were collected using an Andersen impactor and a microorifice uniform deposit impactor (MOUDI), respectively. The calculated concentrations were ex...

Corrosion Damage and Wear Mechanisms in Long-Term Retrieved CoCr Femoral Components for Total Knee Arthroplasty

Abstract: Background Metal debris and ion release has raised concerns in joint arthroplasty. The purpose of this study was to characterize the sources of metallic ions and particulate debris released from long-term (in vivo >15 years) total knee arthroplasty femoral components. Methods A total of 52 CoCr femoral condyles were identified as having been implanted for more than 15 years. The femoral components were examined for incidence of 5 types of damage (metal-on-metal wear due to historical polyethylene insert failure, mechanically assisted crevice corrosion at taper interfaces, cement interface corrosion, third-body abrasive wear, and inflammatory cell–induced corrosion [ICIC]). Third-body abrasive wear was evaluated using the Hood method for polyethylene components and a similar method quantifying surface damage of the femoral condyle was used. The total area damaged by ICIC was quantified using digital photogrammetry. Results Surface damage associated with corrosion and/or CoCr debris release was identified in 51 (98%) CoCr femoral components. Five types of damage were identified: 98% of femoral components exhibited third-body abrasive wear (mostly observed as scratching, n = 51/52), 29% of femoral components exhibited ICIC damage (n = 15/52), 41% exhibited cement interface damage (n = 11/27), 17% exhibited metal-on-metal wear after wear-through of the polyethylene insert (n = 9/52), and 50% of the modular femoral components exhibited mechanically assisted crevice corrosion taper damage (n = 2/4). The total ICIC-damaged area was an average of 0.11 ± 0.12 mm 2 (range: 0.01-0.46 mm 2 ). Conclusion Although implant damage in total knee arthroplasty is typically reported with regard to the polyethylene insert, the results of this study demonstrate that abrasive and corrosive damage occurs on the CoCr femoral condyle in vivo.

Increasing Surface Hydrophilicity in Poly(Lactic Acid) Electrospun Fibers by Addition of Pla-b-Peg Co-Polymers:

Abstract: Poly (lactic acid) – b – poly (ethylene glycol) (PLAb-PEG) co-polymers with block lengths of 1000-750, 5000-1000, 1000-5000, and bulk PEG were added to PLA electrospinning dopes to create hydrophilic but non-water soluble nanofibers. PLA-b-PEG block lengths strongly affected the total amount of PEG that could be incorporated, as well as spinnability and fiber morphology. Solutions containing >1% w/w of the lowest molecular weight co-polymer PLA (1000) – b – PEG (750) formed an unspinnable, cloudy gel. Addition of the PLA (5000) – b – PEG (1000) to the base spinning solution influenced fiber diameters and spinnability in the same manner as simply increasing PLA concentration in the spinning dope. Addition of PLA (1000) – b – PEG (5000) resulted in decreased fiber diameters, and allowed for the highest overall co-polymer loading. In final fiber formulations, maximums of 0.9, 2.9 and 9.3 wt% PEG could be achieved using the PLA-b-PEG 1000-750, 5000-1000 and 1000-5000 respectively. PEG (MW = 3350 g/mol) homopolymer was added to the spinning dopes to prepare fibers with 1.0 and 5.0 wt% PEG. The resulting fibers had non-uniform morphology and more variable diameter size than occurred with the addition of PEG in block co-polymer form. Water absorbance by electrospun nonwoven fabrics increased by four times over the control PLA with the addition of 1.0 wt% PEG, and by eighteen times with the addition of 9.3 wt% PEG with the block copolymers. At similar overall PEG loadings, the addition of PLA-b-PEG resulted in a two to four fold increase in water wicking over the addition of PEG homopolymer.

The Key Events Dose-Response Framework: Its Potential for Application to Foodborne Pathogenic Microorganisms

Abstract: The Key Events Dose-Response Framework (KEDRF) is an analytical approach that facilitates the use of currently available data to gain insight regarding dose-response relationships. The use of the KEDRF also helps identify critical knowledge gaps that once filled, will reduce reliance on assumptions. The present study considers how the KEDRF might be applied to pathogenic microorganisms, using fetal listeriosis resulting from maternal ingestion of food contaminated with L. monocytogenes as an initial example. Major biological events along the pathway between food ingestion and the endpoint of concern are systematically considered with regard to dose (i.e., number of organisms), pathogen factors (e.g., virulence), and protective host mechanisms (e.g., immune response or other homeostatic mechanisms). It is concluded that the KEDRF provides a useful structure for systematically evaluating the complex array of host and pathogen factors that influence the dose-response relationship. In particular, the KEDRF supports efforts to specify and quantify the sources of variability, a prerequisite to strengthening the scientific basis for food safety decision making.

Chemical and mutagenic properties of asphalt fume condensates generated under laboratory and field conditions

Abstract: Exposure to asphalt fumes is widely recognized as a potential occupational health concern for paving and roofing workers. Two studies suggest that asphalt fumes generated in the laboratory are carcinogenic to mice. In this study, asphalt fume condensate (AFC) was collected from the head space of an operating hot mix asphalt storage tank and from a laboratory fume-generating apparatus operating at approximately 149 degrees C and 316 degrees C. Salmonella assays for mutagenesis, in vitro chromosomal aberration assays using Chinese hamster ovary (CHO) cells, chemical analyses, and simulated distillations were performed using gas chromatography to characterize the toxicological and chemical properties of AFCs generated by these two methods. The 316 degrees C lab AFC sample was more mutagenic in the Salmonella assay than the 149 degrees C lab AFC sample, with mutagenicity indices (MIs) of 8.3 and 5.3, respectively. AFCs collected from the storage tank were not mutagenic. Chromosomal aberration assays of all AFCs were negative. Chemical analyses and simulated distillations showed substantial differences in the chemical composition of the AFC samples. The 316 degrees C lab AFC sample contained more higher-boiling-point (three- and four-ring) polycyclic aromatic sulfur heterocycle compounds than the 149 degrees C lab AFC sample, and both lab AFC samples contained 5 to 100 times more of these compounds than AFC samples collected from the asphalt storage tank. These results are consistent with other data reported in the scientific literature describing the carcinogenicity of higher-boiling-point sulfur heterocycle compounds. In contrast to other recent studies, the results of this study indicate that the chemical composition and toxicological properties of laboratory-generated asphalt fumes are not representative of those properties of fumes to which workers and the public might be exposed.