Neuropsychological effects of chronic low-dose exposure to polychlorinated biphenyls (PCBs): A cross-sectional study

BACKGROUND: Exposure to indoor air of private or public buildings contaminated with polychlorinated biphenyls (PCBs) has raised health concerns in long-term users. This exploratory neuropsychological group study investigated the potential adverse effects of chronic low-dose exposure to specific air-borne low chlorinated PCBs on well-being and behavioral measures in adult humans. METHODS: Thirty employees exposed to indoor air contaminated with PCBs from elastic sealants in a school building were compared to 30 non-exposed controls matched for education and age, controlling for gender (age range 37–61 years). PCB exposure was verified by external exposure data and biological monitoring (PCB 28, 101, 138, 153, 180). Subjective complaints, learning and memory, executive function, and visual-spatial function was assessed by standardized neuropsychological testing. Since exposure status depended on the use of contaminated rooms, an objectively exposed subgroup (N = 16; PCB 28 = 0.20 μg/l; weighted exposure duration 17.9 ± 7 years) was identified and compared with 16 paired controls. RESULTS: Blood analyses indicated a moderate exposure effect size (d) relative to expected background exposure for total PCB (4.45 ± 2.44 μg/l; d = 0.4). A significant exposure effect was found for the low chlorinated PCBs 28 (0.28 ± 0.25 μg/l; d = 1.5) and 101 (0.07 ± 0.09 μg/l; d = 0.7). Although no neuropsychological effects exceeded the adjusted significance level, estimation statistics showed elevated effect sizes for several variables. The objectively exposed subgroup showed a trend towards increased subjective attentional and emotional complaints (tiredness and slowing of practical activities, emotional state) as well as attenuated attentional performance (response shifting and alertness in a cued reaction task). CONCLUSION: Chronic inhalation of low chlorinated PCBs that involved elevated blood levels was associated with a subtle attenuation of emotional well-being and attentional function. Extended research is needed to replicate the potential long-term low PCB effects in a larger sample

A theoretical study of standard heat of formation of systems involving in the zinc reduction of silicon tetrachloride

The gas phase zinc reduction of silicon tetrachloride produces the silicon for solar cells. While this reaction provides a new low-cost production route for silicon materials for photovoltaic cells, little is known about the chemistry of this process. Theoretical methods, based on quantum chemistry predictions, in the gas phase, are now fully capable of providing molecular thermochemistry and kinetic parameters with sufficient accuracy for modeling purposes. This kind of kinetic information is crucial for reactor design and scale-up of reaction systems. In this spirit, we have developed two test sets, one for silicon and another for zinc compounds, for evaluating the performance of various computational methods: density functional theory (B3LYP, BH and HLYP, BMK, and M05-2X), and composite methods (G3 and CBS-QB3). The new generation of DFT methods BMK and M05-2X and the composite CBS-QB3 method allow to predict the standard heat of formation, Delta H-f(0), of the silicon compounds with MAD of, respectively, 7, 13, and 15 kJ mol(-1), whereas the previous DFT methods are less reliable. At least triple zeta, for basis set, is needed in order to predict correctly the standard heat of formation. For the zinc compounds, BMK, B3LYP, and CBS-QB3 are the best performing methods for the calculation of Delta H-f(0) with MADs of 24, 25, and 28 kJ mol(-1), respectively. We recommend BMK and CBS-QB3 methods for investigating the new solar silicon process