Development of a house dust standard reference material for the determination of organic contaminants

National-level health survey studies, such as the National Human Exposure Assessment Survey field program, have targeted the determination of organic contaminants in house dust in an effort to characterize human exposure in the domestic environment. As the effort to further understand human health effects in relation to organic contaminants associated with indoor dust accelerates, the need for an indoor dust Standard Reference Material (SRM) that is characterized for organic contaminants has become critical. To meet this need, a new organic contaminant house dust SRM has been developed. SRM 2585 Organic Contaminants in House Dust is intended for use in evaluating analytical methods for the determination of selected polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyl (PCB) congeners, chlorinated pesticides, and polybrominated diphenyl ether (PBDE) congeners in house dust and similar matrices. The material may also be useful for evaluation and comparison of methods or instruments used for sampling in the indoor environment. Moreover, because of the material's extensive characterization (140 organic contaminant concentrations), the material may be useful in toxicity studies related to indoor air (in vitro or in vivo). The determination of the concentrations of PAHs (including alkyl-PAHs and PAHs with molecular mass 300 and 302), PCBs, and chlorinated pesticides is reported here, and these results are compared to values reported in the literature for house dust.     

Determination of methylmercury and butyltin compounds in marine biota and sediments using microwave-assisted acid extraction,solid-phase microextraction,and gas chromatography with microwave-induced plasma atomic emission spectrometric detection

A method is described for the determination of methylmercury and butyltin compounds in marine sediment and tissue using microwave-assisted acid extraction or digestion and solid-phase microextraction (SPME) followed by analysis using gas chromatography with microwave-induced plasma atomic emission spectrometric detection (GC-MIP-AES). Using the SPME-GC-MIP-AES method, enrichment factors for methylmercury and butyltin compounds of 50-100 were achieved, as compared to the typical hexane extraction, and measurements in marine tissue and sediment matrixes were possible at 1-2 microg/kg (methylmercury) and 10-100 ng/kg (butyltins). The SPME-GC-MIP-AES method was validated using several marine sediment and tissue matrix certified reference materials (CRMs) with certified values for methylmercury and butyltin compounds. The SPME-GC-MIP-AES method was used to measure methylmercury in four marine tissue CRMs ranging from oyster tissue at 13.0 +/- 1.0 microg/kg to fish tissue at 397 +/- 13 microg/kg (as Hg dry mass). Results from the SPME-GC-MIP-AES method were used in conjunction with results from other techniques to assign certified values for methylmercury in oyster, mussel, and fish tissue CRMs. Mono-, di-, and tributyltin were measured in three sediment CRMs at concentration levels of (0.08 +/- 0.03)-(0.35 +/- 0.05) mg/kg (as Sn dry mass).     

Extraction of Residual Chlorinated Pesticides from Cotton Matrix as Part of a Certification Method for Cotton Reference Material

As a part of developing a certified testing method for residual pesticides analysis in cotton materials using gas chromatography (GC), the target pesticides listed in Oko-tex standards should be isolated from a homogenized cotton matrix. The sample homogeneity and extraction procedures are the most effective steps in this analysis. Any error in this procedure must lead to incorrect results. Two extraction methods with different solvents, e.g., methanol, hexane, hexane/acetone (1:1 v/v), and dichloromethane were used throughout this work. Extraction methods were soxhlet (SOX) and accelerated solvent extraction (ASE). The resulted extracts were concentrated then injected into a GC equipped with an Electron Capture Detector (ECD). The qualitative results, when compared with those of the NIST standard reference material (SRM-2261) certified by the National Institute of Standards and Technology, USA, proved that the ASE and SOX techniques with dichloromethane as extracting solvent are more selective for all concerned pesticides for homogenized cotton samples. The ASE extraction with dichlormethane is better for hexachlorobenzene, gamma-HCH, heptachlor, Cis-chlordane, trans-nonchlor, and SOX extraction technique with dichloromethane is better for Heptachlor epoxide, 4,4′-DDE, Dieldrin, 2,4′-DDD, 4,4′-DDT, and Mirex with broading in the resulted peaks.     

Determination of Levoglucosan in Particulate Matter Reference Materials

Source identification is critical for the effective management of air pollution. The ratio of levoglucosan (1,6-anhydro- β -D-glucose) to organic carbon has been used to identify and quantify the contribution of biomass combustion to the organic carbon content in aerosols. Therefore, accurate levoglucosan measurements in particulate matter are important. This study determined levoglucosan concentrations in urban dust Standard Reference Materials (SRMs) 1649a and 1648 available from the National Institute of Standards and Technology (NIST) as well as two particulate matter samples with particle sizes nominally 2.5 μ m and smaller collected in Baltimore, MD. Levoglucosan was extracted using both pressurized fluid and Soxhlet techniques. Quantification was performed with gas chromatography/mass spectrometry (GC/MS) using a deuterated levoglucosan internal standard and two different GC columns. Levoglucosan concentrations were 81.1 μ g g^?1 with a standard deviation of 9.4 μ g g^?1 (n = 9) for SRM 1649a, 107 μ g g^?1 with a standard deviation of 18 μ g g ^?1 (n = 8) for SRM 1648, 225 μ g g^?1 (standard deviation of 41 μ g g^?1 n = 4) and 138 μ g g^?1 (standard deviation of 39 μ g g ^{? 1} n = 5) for the two fine particulate matter samples collected in Baltimore, MD.     

Free volume,mobility, and structural relaxations in poly(ethylene oxide)/poly(methyl methacrylate) blends

Time-dependent structural relaxations in a melt-mixed 38/62 vol% poly(ethylene oxide)/atactic poly(methyl methacrylate) blend were studied using several techniques: differential scanning calorimetry, pressure-volume-temperature analysis, positron annihilation lifetime spectroscopy, dynamic mechanical analysis, and solid-state nuclear magnetic resonance. The internal volume (free volume hole size) and the external volume (specific volume) of the blend are found to decrease with aging time. The time scale of the volume changes is the same, suggesting that internal and external volumes can be calculated from each other. Increasing mobility of poly(ethylene oxide), composition fluctuations, and shifting glass transition temperatures are observed upon aging. Phase separation in terms of spinodal decomposition below an upper critical solution temperature occurs within minutes and results in two amorphous phases of different composition. Subsequent crystallization then causes further structural changes.     

Certification of a Diesel Particulate Related Standard Reference Material (SRM 1975) for PAHs

Standard Reference Materials (SRMs) are Certified Reference Materials issued by the National Institute of Standards and Technology (NIST). Three of these materials, SRMs 1975 (Diesel Particulate Extract), 2975 (Diesel Particulate Matter, Industrial Forklift), and 1650 (Diesel Particulate Matter) are diesel particulate-related materials that are well characterized for PAH isomer distributions. SRM 1975 is a methylene chloride extract of industrial forklift diesel particulate matter and it was developed originally in response to the needs of the bioassay community for a natural environmental extract. Thirty-nine PAHs (or combinations of PAHs) were determined in SRM 1975 using various combinations of four different methods of analysis. SRM 1975 will be issued with certified concentrations for eight PAHs. In addition, reference concentrations will be provided for additional PAHs, including many alkyl substituted isomers such as methylphenanthrenes, methylpyrenes, and methylfluoranthenes. Reference values for the mutagenic activity of the extract will also be provided. The approach and results for the certification of PAH concentrations in SRM 1975 are described in this paper.     

Extraocular light exposure does not suppress plasma melatonin in humans

Light affects the circadian axis in at least two ways. It can cause the acute suppression of pineal melatonin synthesis, and/or a phase-shift of the circadian oscillator. As recent evidence has suggested that extraocular light exposure may cause phase-shifts of the circadian clock, we have investigated whether suppression of melatonin can be induced by the same type of light exposure. In the first study subjects' eyes were exposed to white light (2250 lux for 30 mins) via a fibre optic cable. As expected, suppression of nighttime plasma melatonin levels (61 +/- 6%) was observed. In the second study, light of the same quality but higher intensity (14,000 or 67,500 lux for 180 mins) was delivered in the same manner to the popliteal region behind the subjects' knees, whilst shielding their eyes. No suppression of plasma melatonin levels (4 +/- 7%) was detected in any of the subjects. Thus, extraocular photoreception, if it exists in mammals, does not affect the suprachiasmatic nucleipineal pathway.     

Culturing and characterization of human periodontal ligament fibroblasts—a preliminary study

The periodontal ligament (PDL) is believed to harbour cells with the capacity to regenerate the periodontium consisting of the PDL layer and surrounding alveolar bone and cementum. Fibroblast, the predominant cell type, is implicated in PDL tissue regeneration and repair. In this study, PDL fibroblasts (PDLF) from healthy human premolar and molar explants were cultured and characterized in vitro. Protein expression profiles were analysed and compared to gingival fibroblasts (GF) and alveolar bone osteoblasts (OB). Alkaline phosphatase (ALP) expression was higher in all induced cultures. Western blotting showed that all three cell types expressed osteonectin (ON) and osteopontin (OPN). Conversely, bone sialoprotein (BSP II) was down-regulated in PDLF and GF upon induction. Von Kossa staining revealed mineralised matrix for all induced cultures. This study showed the response of PDLF in protein expression, and pointed to its potential application in periodontal regeneration.     

Adaptive cyberdefense for survival and intrusion tolerance

While providing some resistance against cyberattacks, current approaches to securing networked and distributed information systems are mainly concerned with static prevention measures. For example, signature-based systems can only detect known attacks and tend to provide brittle, all-or-nothing protection. New work in survivability and intrusion tolerance focuses on augmenting existing information systems with adaptive defenses. A middleware-based survivability toolkit lets applications use network-and host-based mechanisms in their own defense.     

Analytical Methods for Determination of Polycyclic Aromatic Hydrocarbons (PAHs) — A Historical Perspective on the 16 U.S. EPA Priority Pollutant PAHs

The identification of 16 polycyclic aromatic hydrocarbons (PAHs) as priority pollutants by the U.S. Environmental Protection Agency (EPA) in 1976 has been a primary driver for analytical methods development for the determination of PAHs. In this article, the historical development of methods in liquid chromatography (LC) and gas chromatography (GC) to separate these 16 PAHs is discussed. In LC a significant effort was the search for and the fundamental understanding of the unique stationary phase capable of achieving the desired separation of the 16 EPA PAHs. For GC methods, the focus on stationary phase development has been the separation of critical isomers with a broader scope than the 16 EPA PAHs. The current routine LC and GC methods for the 16 EPA PAHs are well established; however, new advances in analytical techniques beyond LC and GC are discussed. Many analysts are now interested in more than just the 16 EPA PAHs (e.g., higher molecular mass PAHs and alkyl-substituted PAHs) and analytical methods have emerged to address these needs. Reference materials and their use in the determination of PAHs are discussed.