Advanced Infill Designs for 3D Printed Shape-Memory Components.

Poly(lactic acid) (PLA) is one of the most often used polymers in 3D printing based on the fused deposition modeling (FDM) method. On the other hand, PLA is also a shape memory polymer (SMP) with a relatively low glass transition temperature of ~60 °C, depending on the exact material composition. This enables, on the one hand, so-called 4D printing, i.e., printing flat objects which are deformed afterwards by heating them above the glass transition temperature, shaping them and cooling them down in the desired shape. On the other hand, objects from PLA which have been erroneously deformed, e.g., bumpers during an accident, can recover their original shape to a certain amount, depending on the applied temperature, the number of deformation cycles, and especially on the number of broken connections inside the object. Here, we report on an extension of a previous study, investigating optimized infill designs which avoid breaking in 3-point bending tests and thus allow for multiple repeated destruction and recovery cycles with only a small loss in maximum force at a certain deflection.

Dumped munitions: New insights into the metabolization of 2,4,6-trinitrotoluene in Baltic flatfish.

Livers from dab (Limanda limanda), plaice (Pleuronectes platessa) and flounder (Platichthys flesus) sampled from the Baltic Sea were used to determine the interaction of flatfish CYP1A enzymes with 2,4,6-trinitrotoluene (TNT) in vitro. Competitive inhibition of 7-ethoxyresorufin-O-deethylase (EROD) and 7-methoxyresorufin-O-deethylase (MROD) could be demonstrated for all three flatfish species. The highest inhibition of CYP1A activities was measured in liver samples of flounder resulting in a half maximal inhibitory concentration (IC50) of 28.1 µM TNT. Due to their lower inhibition (EROD IC50 65.2 µM TNT, MROD IC50 40.3 µM TNT), dab liver samples were used to conduct in vitro metabolization experiments with TNT. The metabolization of TNT in fish was investigated with post-mitochondrial fractions (PMF) of dab liver as a model system after adding different cofactors. Rapid and time-dependent enzymatic degradation of TNT was observed. The concentrations of 4-amino-2,6-dinitrotoluene and 2-amino-4,6-dinitrotoluene increased in the samples over time. Additionally, 2,2,6,6-tetranitro-4,4-azoxytoluene was detected in one sample. The results of this study indicate that in vitro experiments are useful to investigate the xenobiotic metabolism of fish under controlled conditions prior to field studies. The metabolites found can serve as target compounds for marine monitoring of TNT contamination in munition dumpsites.

First evidence of explosives and their degradation products in dab (Limanda limanda L.) from a munition dumpsite in the Baltic Sea.

Corrosion and disintegration of munition shells from the World Wars increase the risk that explosives are released into the marine environment, exposing a variety of organisms. Only few studies investigated contamination of fish with explosives in the field under environmental conditions. Here we present a comprehensive study on the contamination status of dab (Limanda limanda) from a munition dumpsite and from reference sites in the Baltic Sea. Bile of 236 dab from four different study sites, including a dumpsite for conventional munitions, was investigated and explosive compounds were detected by high performance liquid chromatography-mass spectrometry. Five explosive compounds were identified, including 2,4,6-trinitrotoluene, 4-amino-2,6-dinitrolouene, and hexahydro-1,3,5-trinitro-1,3,5-triazine. 48% of the samples from the dumpsite contained at least one explosive compound. The results prove that toxic explosive compounds from a dumpsite in the Baltic Sea are accumulated by flatfish and may therefore pose a risk to fish health and human food safety.

Studying the metabolism of toxic chemical warfare agent-related phenylarsenic chemicals in vitro in cod liver.

Large quantities of chemical warfare agents (CWAs), such as phenylarsenic chemicals, were disposed by sea-dumping after World War II. Nowadays, the release of these toxic chemicals from munitions poses a potential threat to living organisms. This study investigates the fate of these chemicals in fish by exposing selected CWA-related phenylarsenic chemicals and their oxidation products to cod (Gadus morhua) liver S9 fraction in vitro. Clark I (DA), Adamsite (DM) and their corresponding oxidation products as well as triphenylarsine oxide (TPA[ox]) and phenylarsonic acid (PDCA[ox]) were used as chemicals in in vitro experiments. Glutathione (GSH) conjugates of DA, DM and PDCA-related chemicals were found to be the most dominant metabolites, and methylated metabolites were detected as well, suggesting that these compounds are metabolised in the presence of cod liver enzymes. TPA[ox] was the only compound tested that did not form a GSH conjugate or methylated metabolite, indicating a different biotransformation pathway for this compound. Furthermore, hydroxylated metabolites were detected for each tested chemical. Due to their reactive nature, GSH conjugates may be difficult to detect in fish samples from CWA dumpsites. In contrast, both methylated and hydroxylated metabolites of phenylarsenic chemicals are promising target chemicals for the detection of CWA-related contamination in fish.

Nitroaromatic compounds damage the DNA of zebrafish embryos (Danio rerio).

Lethal and sublethal effects of trinitrotoluene (TNT) and its degradation products 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT) to zebrafish embryos (Danio rerio) were investigated in a 120 h exposure scenario. Lethal concentrations (LC50) were 4.5 mg/l for TNT, 13.4 mg/l for 2-ADNT and 14.4 mg/l for 4-ADNT. Embryos exposed to 2-ADNT or 4-ADNT revealed a high proportion of chorda deformations among the surviving individuals. Genotoxicity of the nitroaromatic compounds in zebrafish embryos was investigated by comet assay isolating cells from whole embryos after 48 h in vivo exposure. Significant genotoxicity was induced by all three compounds tested, in comparison to the corresponding controls at 0.1 mg/l and 1.0 mg/l as lowest tested concentrations. The genotoxicity caused by TNT was about three to four times higher than that of 2-ADNT and 4-ADNT. To our knowledge, this is the first study demonstrating the genotoxicity of TNT in fish embryos by in vivo exposure. The results are discussed in the context of dumped munition in the marine environment.

The ecotoxic potential of a new zero-valent iron nanomaterial, designed for the elimination of halogenated pollutants, and its effect on reductive dechlorinating microbial communities.

The purpose of this study was to assess the ecotoxic potential of a new zero-valent iron nanomaterial produced for the elimination of chlorinated pollutants at contaminated sites. Abiotic dechlorination through the newly developed nanoscale zero-valent iron material and its effects on dechlorinating bacteria were investigated in anaerobic batch and column experiments. The aged, i.e. oxidized, iron material was characterization with dynamic light scattering, transmission electron microscopy and energy dispersive x-ray analysis, x-ray diffractometry and cell-free reactive oxygen measurements. Furthermore, it was evaluated in aerobic ecotoxicological test systems with algae, crustacean, and fish, and also applied in a mechanism specific test for mutagenicity. The anaerobic column experiments showed co-occurrence of abiotic and biological dechlorination of the common groundwater contaminant perchloroethene. No prolonged toxicity of the nanomaterial (measured for up to 300 days) towards the investigated dechlorinating microorganism was observed. The nanomaterial has a flake like appearance and an inhomogeneous size distribution. The toxicity to crustacean and fish was calculated and the obtained EC50 values were 163 mg/L and 458 mg/L, respectively. The nanomaterial showed no mutagenicity. It physically interacted with algae, which had implications for further testing and the evaluation of the results. Thus, the newly developed iron nanomaterial was slightly toxic in its reduced state but no prolonged toxicity was recorded. The aquatic tests revealed a low toxicity with EC50 values ≥ 163 mg/L. These concentrations are unlikely to be reached in the aquatic environment. Hence, this nanomaterial is probably of no environmental concern not prohibiting its application for groundwater remediation.