Molybdenum disulfide as a filler for a polymeric matrix at an ultralow content: Polystyrene case

For the first time, polystyrene (PS)/molybdenum disulfide (MoS2) nanocomposites were produced using the melt compounding technique. The nanocomposites presented better thermo stability due to improvements in heat dissipation. Mechanical evaluations of the nanocomposites showed that when only 0.002 wt% of MoS2 was added to PS, it was possible to achieve an improvement of 27, 93.7, and 100% in the tensile strength, elongation at break, and toughness, respectively. Thermo-mechanical results indicated strong intermolecular and physical interactions between filler and polymer matrix contributing to effectiveness of the reinforcement. Very low number of agglomerates was observed by microtomography and Raman spectroscopy, mainly for the system with 0.002% wt.% of MoS2. The results proved that the use of bidimensional particles, even with ultralow content (<0.05 wt%), can improve the mechanical performance of polymeric matrices by a combination of well-done particle synthesis, right choice of processing strategy and good interaction between filler and matrix

Toxicity and bioaccumulation of phenanthrene in Enchytraeus albidus (Oligochaeta: Enchytraeidae)

Polycyclic aromatic compounds, such as phenanthrene (PHE), tend to accumulate in the soil compartment, where they may be retained for many years because of their persistency and hydrophobicity. The toxicity and bioaccumulation of these chemicals in soil biota and potential biomagnification along the food chain is an issue of concern. The main goal of this study was to determine the toxicity and bioaccumulation of PHE in Enchytraeus albidus (Oligochaeta: Enchytraeidae) in a natural standard soil (LUFA 2.2) following standard test guidelines. Phenanthrene dose-relatedly affected the survival and reproduction of E. albidus with median lethal concentration and median effective concentration (EC50) values of 135 and 33mg/kg dry soil, respectively. A toxicokinetics study, performed at a nontoxic soil concentration of 8mg/kg, showed uptake and elimination rate constants of 4.91kg soil per kilogram fresh weight animal per day and 0.236 per day, respectively and a bioaccumulation factor (BAF) of 20.8kg soil per kilogram fresh weight animal. These results show that the three-week exposure in the toxicity test with E. albidus is sufficiently long to reach equilibrium, but also that PHE may accumulate to considerable levels, possibly causing a risk for predators. © 2010 SETAC © 2011 SETAC