An interlaboratory round robin study on the analysis of toxaphene in a cod liver oil standard reference material

An inter-laboratory round robin analysis of toxaphene in a National Institute of Standards Cod Liver Oil #1588 was carried out. Analysis was performed by GC-ECD, electron capture negative ion GCMS (ECNI GCMS) and electron impact GC/MS in high resolution single ion monitoring mode (EI-HRSIM). Results of the analyses by GC-ECD, ECNI and HRSIM were 4.22±2.45 ppm, 3.95±1.57 ppm, and 2.35±0.06 ppm respectively. Due to the wide inter-laboratory variation in workup, GC conditions, detection method, and quantitation algorithms used, no one set of factors stood out as the cause of the variation in results.     

Droplet digital PCR is a cost-effective method for analyzing long cell-free DNA in maternal plasma: Application in preeclampsia

Objective

Long cell-free DNA (cfDNA) can be found in the plasma of pregnant women and cancer patients. We investigated if droplet digital PCR (ddPCR) can analyze such molecules for diagnostic purposes using preeclampsia as a model.

Method

Plasma samples from ten preeclamptic and sixteen normal pregnancies were analyzed. Two ddPCR assays targeting a single-copy gene, VCP, and one ddPCR assay targeting LINE-1 repetitive regions were used to measure the percentages of long cfDNA >533, 1001, and 170 bp, respectively. The LINE-1 assay was developed as guided by in silico PCR analyses to better differentiate preeclamptic and normal pregnancies.

Results

Preeclamptic patients had a significantly lower median percentage of long cfDNA than healthy pregnant controls, as determined by the LINE-1 170 bp assay (28.9% vs. 35.1%, p < 0.0001) and the VCP 533 bp assay (6.6% vs. 8.7%, p = 0.014). The LINE-1 assay provided a better differentiation than the VCP 533 bp assay (area under ROC curves, 0.94 vs. 0.79).

Conclusion

ddPCR is a cost-effective approach for unlocking diagnostic information carried by long cfDNA in plasma and may have applications for the detection of preeclampsia. Further longitudinal studies with larger cohorts are required to assess the clinical utility of this test.     

Preliminary measurements of aromatic VOCs in public transportation modes in Guangzhou,China

This study examined the exposure level of aromatic volatile organic compounds (VOCs) in public transportation modes in Guangzhou, China. A total of 40 VOC samples were conducted in four popular public commuting modes (subway, taxis, non-air-conditioned buses and air-conditioned buses) while traversing in urban areas of Guangzhou. Traffic-related VOCs (benzene, toluene, ethylbenzene, m/p-xylene and o-xylene) were collected on adsorbent tubes and analyzed by thermal desorption (TD) and gas chromatography/mass-selective detector (GC/MSD) technique. The results indicate that commuter exposure to VOCs is greatly influenced by the choice of public transport. For the benzene measured, the mean exposure level in taxis (33.6 microg/m(3)) was the highest and was followed by air-conditioned buses (13.5 microg/m(3)) and non-air-conditioned buses (11.3 microg/m(3)). The exposure level in the subway (7.6 microg/m(3)) is clearly lower than that in roadway transports. The inter-microenvironment variations of other target compounds were similar to that of benzene. The target VOCs were well correlated to each other in all the measured transports. The concentration profile of the measured transport was also investigated and was found to be similar to each other. Based on the experiment results, the average B/T/E/X found in this study was about (1.0/4.3/0.7/1.4). In this study, the VOC levels measured in evening peak hours were only slightly higher than those in afternoon non-peak hours. This is due to the insignificant change of traffic volume on the measured routes between these two set times. The out-dated vehicle emission controls and slow-moving traffic conditions may be the major reasons leading elevated in-vehicle exposure level in some public commuting journeys.     

Trace metals in mussels from mariculture zones, Hong Kong

In 1997, concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and nickel (Ni) were analysed in green-lipped mussels (Perna viridis) from three mariculture zones located in the north-east (Kat O), south (Lo Tik Wan) and to the west (Ma Wan) of Hong Kong. Spatial differences in the concentration of metals were found, chromium and copper were higher at Ma Wan and Lo Tik Wan compared to Kat O in the north-east. In contrast, the highest levels of lead (mean = 4.37 microg/g dry wt) were recorded at Kat O. There were no differences in the level of nickel between the study sites. A comparison of the metal concentrations in mussels with the results of a previous study seven years before, in 1990, showed a twofold increase in the mean levels of cadmium for all three sites. However, levels of the other metals in 1997 were lower by 12-32% for chromium, 32-39% for copper and 24-25% for nickel. The greatest reductions were recorded for lead: Kat O (39%), Ma Wan (51%) and Lo Tik Wan (75%). This may be related to the introduction of lead-free petrol in 1991. Despite the apparent reduction in some heavy metal bioaccumulation between 1990 and 1997, from a public health risk perspective, the data suggest a continued need for monitoring of heavy metals in mussels from mariculture zones.     

Photoelectrochemical degradation of Methylene Blue with -PbO2 electrodes driven by visible light irradiation

-PbO2 electrodes were prepared by electro-deposition and characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and linear sweep voltammetry. We confirmed pure -PbO2 crystals were on the electrode and it had a high oxygen evolution potential. The photoactivity and photoelectrochemical (PEC) properties of the -PbO2 electrode were investigated under visible light irradiation ( > 420 nm) for the decolorization of Methylene Blue. Pseudo first-order kinetics parameter (Kapp) for dye decolorization using the -PbO2 electrode achieved 6.71×10?4 min?1 under visible light irradiation, which indicated its excellent visible light-induced photoactivity. The Kapp of the PEC process was as much as 1.41×10?3 min?1 and was 1.71 times that of visible light irradiation or electrolysis even in the presence of the -PbO2 electrode. A significant synergetic effect was observed in the PEC system. We also employed TiO2 modified -PbO2 electrodes in this test, which revealed that the TiO2 immobilized on the -PbO2 electrode inhibited the visible light-induced PEC efficiency despite the amount of TiO2 used for electrode preparation. The -PbO2 electrode was also superior to the dimensionally stable anode (Ti/Ru0:3Ti0:7O2) in visible light-induced photoactivity and PEC efficiency.     

Understanding the connections between relationship conflict and performance: The intervening roles of trust and exchange

Research shows that relationship conflict has a negative impact on job performance. There is scant theoretical work, however, explaining the interpersonal dynamics that lead to this outcome. A conceptual model is developed that explores how relationship conflict impacts performance through its effects on trust and exchange. We argue that relationship conflict has a detrimental effect on trust motivating coworkers to rely more on calculus‐based trust than on relationship‐based trust. This, in turn, affects the form of exchange coworkers use with one another, leading them to rely on negotiated exchange to the exclusion of reciprocal exchange. This kind of exchange relationship, finally, affects in‐role, extra‐role, and attitudinal outcomes. The literature shows that superordinate goals can mitigate relationship conflict and we use social and self‐categorization theories to explain and explore this effect on both relationship conflict and trust. How trust and exchange might change over time is also explored. Copyright © 2009 John Wiley & Sons, Ltd.     

Herbivores and edaphic factors constrain the realized niche of a native plant

Biotic interactions, such as competition and herbivory, can limit plant species ranges to a subset of edaphically suitable habitats, termed the realized niche. Here we explored the role that herbivores play in restricting the niche of serpentine ecotypes of the native California annual Collinsia sparsiflora. We planted seeds from four populations into a range of natural field environments that varied in the presence/absence of naturally occurring C. sparsiflora and in predicted suitability for growth and survival of the serpentine ecotype of C. sparsiflora. Path analysis was then used to model the direct and herbivore-mediated indirect effects of environmental variables on the survival of C. sparsiflora serpentine ecotypes. We found that C. sparsiflora received more herbivory when planted into areas where serpentine ecotypes of C. sparsiflora were not predicted to persist, and that increased herbivory was associated with decreased survival, suggesting that herbivores may limit the distribution of C. sparsiflora serpentine ecotypes. Additionally, we demonstrated that edaphic environmental variables impacted the survival of C. sparsiflora serpentine ecotypes both directly and indirectly, by altering interactions with herbivores. These indirect effects were probably trait-mediated and probably occurred because edaphic factors may influence plant traits that, in turn, alter attractiveness to herbivores. Although the magnitude of direct effects exceeded the magnitude of indirect effects, many strong herbivore-mediated indirect effects were detected. Thus, interactions between the abiotic environment and insect herbivory contributed to restricting the niche of C. sparsiflora serpentine ecotypes to a subset of available habitat.     

Beyond the ecological: biological invasions alter natural selection on a native plant species

Biological invasions can have strong ecological effects on native communities by altering ecosystem functions, species interactions, and community composition. Even though these ecological effects frequently impact the population dynamics and fitness of native species, the evolutionary consequences of biological invasions have received relatively little attention. Here, I show that invasions impose novel selective pressures on a native plant species. By experimentally manipulating community composition, I found that the exotic plant Medicago polymorpha and the exotic herbivore Hypera brunneipennis alter the strength and, in some instances, the direction of natural selection on the competitive ability and anti-herbivore defenses of the native plant Lotus wrangelianus. Furthermore, the community composition of exotics influenced which traits were favored. For example, high densities of the exotic herbivore Hypera selected for increased resistance to herbivores in the native Lotus; however, when Medicago also was present, selection on this defense was eliminated. In contrast, selection on tolerance, another plant defense trait, was highest when both Hypera and Medicago were present at high densities. Thus, multiple exotic species may interact to influence the evolutionary trajectories of native plant populations, and patterns of selection may change as additional exotic species invade the community.