Subnanosecond phase transition dynamics in laser-shocked iron.

Iron is one of the most studied chemical elements due to its sociotechnological and planetary importance; hence, understanding its structural transition dynamics is of vital interest. By combining a short pulse optical laser and an ultrashort free electron laser pulse, we have observed the subnanosecond structural dynamics of iron from high-quality x-ray diffraction data measured at 50-ps intervals up to 2500 ps. We unequivocally identify a three-wave structure during the initial compression and a two-wave structure during the decaying shock, involving all of the known structural types of iron (α-, γ-, and ε-phase). In the final stage, negative lattice pressures are generated by the propagation of rarefaction waves, leading to the formation of expanded phases and the recovery of γ-phase. Our observations demonstrate the unique capability of measuring the atomistic evolution during the entire lattice compression and release processes at unprecedented time and strain rate.

Bioavailability of chemical pollutants in contaminated soils and pitfalls of chemical analyses in hazard assessment.

Decision-making for remediation of industrial wastelands are still based on the concentrations of pollutants of concern measured in soils. In this work, two soils polluted by polycyclic aromatic hydrocarbons (PAHs) and metals were investigated for their toxicity on earthworms (Eisenia fetida), collembolae (Folsomia candida), and higher plants (Brassica chinensis, Lactucca sativa and Avena sativa) in order to study the relationships between chemical contamination and biological effects. Although the level of contamination by PAHs was elevated and commensurate in the two soils, their toxicity profile was quite different. Soil A affected survival and reproduction of invertebrates and growth of higher plants. Surprisingly, soil B, heavily contaminated by metals in addition to PAHs, was devoid of toxicity. Our results indicate that toxicity cannot simply be extrapolated from pollutant concentrations in a complex matrix in which bioavailability of pollutants may be reduced by ageing. Moreover, the use of toxicity data obtained from spiked soils characterized by readily bioavailable pollutants can also be called into question for such extrapolations. Predicting biological effects therefore requires biological tools to avoid any erroneous conclusions that can be drawn from sole extrapolation of analytical results.

Ecotoxicity of a polycyclic aromatic hydrocarbon (PAH)-contaminated soil.

Soil samples from a former cokery site polluted with polycyclic aromatic hydrocarbons (PAHs) were assessed for their toxicity to terrestrial and aquatic organisms and for their mutagenicity. The total concentration of the 16 PAHs listed as priority pollutants by the US Environmental Protection Agency (US-EPA) was 2634+/-241 mg/kgdw in soil samples. The toxicity of water-extractable pollutants from the contaminated soil samples was evaluated using acute (Vibrio fischeri; Microtox test, Daphnia magna) and chronic (Pseudokirchneriella subcapitata, Ceriodaphnia dubia) bioassays and the EC values were expressed as percentage water extract in the test media (v/v). Algal growth (EC50-3d=2.4+/-0.2% of the water extracts) and reproduction of C. dubia (EC50-7d=4.3+/-0.6%) were the most severely affected, compared to bacterial luminescence (EC50-30 min=12+/-3%) and daphnid viability (EC50-48 h=30+/-3%). The Ames and Mutatox tests indicated mutagenicity of water extracts, while no response was found with the umu test. The toxicity of the soil samples was assessed on the survival and reproduction of earthworms (Eisenia fetida) and collembolae (Folsomia candida), and on the germination and growth of higher plants (Lactuca sativa L.: lettuce and Brassica chinensis J.: Chinese cabbage). The EC50 values were expressed as percentage contaminated soil in ISO soil test medium (weight per weight-w/w) and indicated severe effects on reproduction of the collembola F. candida (EC50-28 d=5.7%) and the earthworm E. fetida (EC50-28 d=18% and EC50-56 d=8%, based on cocoon and juvenile production, respectively). Survival of collembolae was already affected at a low concentration of the contaminated soil (EC50-28 d=11%). The viability of juvenile earthworms was inhibited at much lower concentrations of the cokery soil (EC50-14 d=28%) than the viability of adults (EC50-14 d=74%). Only plant growth was inhibited (EC50-17d=26%) while germination was not. Chemical analyses of water extracts allowed us to identify inorganic water-extractable pollutants as responsible for toxicity on aquatic species, especially copper for effects on D. magna and C. dubia. The soil toxicity on collembolae and earthworms could be explained by 4 PAH congeners-fluorene, phenanthrene, pyrene, and fluoranthene. Yet, toxicity of the cokery soil as a whole was much lower than toxicity that could be deduced from the concentration of each congener in spiked soils, indicating that pollutants in the soil became less bioavailable with ageing.