Identification of a novel hydroxylated metabolite of 2,2′,3,5′,6-pentachlorobiphenyl formed in whole poplar plants

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants consisting of 209 congeners. Oxidation of several PCB congeners to hydroxylated PCBs (OH-PCBs) in whole poplar plants has been reported before. Moreover, 2,2′,3,5′,6-pentachlorobiphenyl (PCB95), as a chiral congener, has been previously shown to be atropselectively taken up and transformed in whole poplar plants. The objective of this study was to determine if PCB95 is atropselectively metabolized to OH-PCBs in whole poplar plants. Two hydroxylated PCB95s were detected by high-performance liquid chromatography-mass spectrometry in the roots of whole poplar plants exposed to racemic PCB95 for 30 days. The major metabolite was confirmed to be 4′-hydroxy-2,2′,3,5′,6-pentachlorobiphenyl (4′-OH-PCB95) by gas chromatography-mass spectrometry (GC-MS) using an authentic reference standard. Enantioselective analysis showed that 4′-OH-PCB95 was formed atropselectively, with the atropisomer eluting second on the Nucleodex β-PM column (E2-4′-OH-PCB95) being slightly more abundant in the roots of whole poplar plants. Therefore, PCB95 can at least be metabolized into 4′-OH-PCB95 and another unknown hydroxylated PCB95 (as a minor metabolite) in whole poplar plants. Both atropisomers of 4′-OH-PCB95 are formed, but E2-4′-OH-PCB95 has greater atropisomeric enrichment in the roots of whole poplar plants. A comparison with mammalian biotransformation studies indicates a distinctively different metabolite profile of OH-PCB95 metabolites in whole poplar plants. Our observations suggest that biotransformation of chiral PCBs to OH-PCBs by plants may represent an important source of enantiomerically enriched OH-PCBs in the environment.     

The effects of the Fukushima disaster on nuclear energy debates and policies: a two-step comparative examination

Under what conditions do critical events trigger large-scale public discussion and mobilisation, and can these lead to policy change? In a comparative study of nuclear energy policy after the Japanese Fukushima disaster in March 2011, a theory-development approach is adopted, mobilising data collected from national news agencies’ newswires, public surveys, legislation and parliamentary databases, and newspaper editorials in 12 established democracies between March 2011 and March 2013. The analysis suggests two main hypotheses that can guide future research: critical events are more likely to trigger policy change when intense (contentious) mobilisation from policy challengers aligns with the views of the general public, and is backed by major political allies; and critical events are more likely to trigger intense (contentious) mobilisation when policy challengers articulate their opposition around pre-existing policy debates on the issue and resort to pre-existing organisational and mobilisation resources.     

The three-dimensional structure of 3,3',4,4'-tetrachlorobiphenyl, a dioxin-like polychlorinated biphenyl (PCB)

The crystal structure of PCB 77 (3,3',4,4'-tetrachlorobiphenyl, C(12)H(6)Cl(4)), a dioxin-like PCB congener, is described. The dihedral angle of PCB 77 is 43.94(6) degrees, which is slightly larger than calculated or experimental dihedral angles of biphenyl derivatives in solution but smaller than experimental dihedral angles in the gas phase.     

What stops the ‘diploid male vortex’?—A simulation study for species with single locus complementary sex determination

The survival of hymenopteran populations especially that of ecologically and economically important pollinators and parasitoids, has become a major topic for empirical and theoretical studies. Complementary sex determination (CSD) in Hymenoptera may impose a substantial genetic load through the production of inviable or sterile diploid males. Modelling and laboratory studies have indicated that this genetic load may trigger a ‘diploid male vortex’ leading to rapid extinction of populations.Here we take a broader theoretical approach to analyze why populations exhibiting CSD persist in nature, even if they contain large proportions of homozygous diploid individuals. Using an individual-based model of spatially structured hymenopteran populations, we show that (i) inviability or reduced fertility of homozygous individuals, (ii) female-biased sex ratio, and (iii) strong intra-specific competition can mitigate the negative influence of CSD on population persistence and that (iv) already extremely low dispersal rates will result in long term survival. These findings underline the importance of life history traits for population survival and demonstrate that rather specific conditions must be met to initiate the ‘diploid male vortex’.     

Synthesis of hydroxylated PCB metabolites with the Suzuki-coupling

An improved synthesis of hydroxylated polychlorinated biphenyls (PCBs) which are structurally related to the major hydroxy PCB congeners identified in human plasma is described. The coupling of (chlorinated) aryl boronic acids with bromochloro anisoles using the standard conditions of the Suzuki coupling gave the desired hydroxylated PCB metabolites in good to excellent yields. The approach offers the advantage of high selectivity and good yields compared to conventional methods such as the Cadogan reaction and allows the use of less toxic starting materials.     

Dioxion-/Furan-’Verbrennungsprofile’ aus Hochtemperaturprozessen

Present knowledge assumes that different mechanisms acting downstream in high temperature processes lead to the formation of polychlorinated dibenzo(p)dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Concerning the 17 2,3,7,8-Cl-substituted PCDD/F congeners in particular, there is new evidence for a single-step reaction type (recently reported in this publication series, of. also parts 1 and 2). A formation based on a combination of the several mechanisms, which have been proposed and discussed since 1985, becomes more and more unlikely. Qualitatively the PCDD/F formation downstream from high temperature processes depends rather on a thermodynamically forced single reaction step, and on pure statistical distribution quantitatively. This may be a new ‘Thermostat Synthesis’ instead of ‘de novo’.