DESIGN AND CONTINUOUS OPERATION OF A SOLAR CONVECTION DRIER WITH AN AUXILIARY HEATING SYSTEM

A solar drier of the through-draft type (4 trays at 0.5 m² surface area) with natural air convection and an auxiliary gas heating system was constructed. General relationships between the climatic conditions of the ambient air, product load and drying characteristics were established. Test runs with the drier as continuous equipment were carried out over a period of 24 h, using carrot dice as experimental material. Air flow rates through the dryer between 100 and 140 kg/h and overall drying rates between 1.5 and 2 kg/h were reached. The overall energy efficiency coefficient for the hybrid heating system amounted to 27 % as compared to 31 to 37 % for the solar energy heating alone and to 22 to 27 % for gas heating energy alone. A combination of continuous drying in the first stage with subsequent batch-wise finish drying in the same or a supplementary drier seems to be advantageous.     

Passive sampling combined with ecotoxicological and chemical analysis of pharmaceuticals and biocides - evaluation of three Chemcatcher™ configurations

Passive sampling is a tool to monitor the presence and concentrations of micropollutants in the aquatic environment. We investigated the duration of integrative sampling and the effects of flow rate on the performance of three configurations of the Chemcatcher - a sampler for polar organic compounds. Chemcatchers were fitted with Empore™ styrenedivinylbenzene (SDB) XC disks (XC), SDB-RPS disks (RPS) or SDB-RPS disks covered with a polyethersulfone membrane (RPS-PES). Samplers were either exposed to treated sewage effluent for 5 days at various flow rates, or at a single flow rate with overlapping exposures of 3-24 days. Chemical analysis focused on a set of pharmaceuticals and biocides and ecotoxicological analysis measured inhibition of photosystem II in algae. For compounds with log K_OW > 2, both XC and RPS disks respond dynamically to higher flow rates; uptake increased up to five-fold when flow increased from 0.03 to 0.37 m s⁻¹. At a flow rate of 0.13 m s⁻¹ the integrative window of SDB disks approached 6 days for more hydrophobic compounds (log K_OW > 3.5). The RPS-PES configuration was less affected by flow and also showed an extended integrative window (up to 24 days). The membrane causes a lag phase of up to 2.3 days which thwarts a sound interpretation of data from sampling periods of less than 10 days.     

Zur Warmfestigkeit austenitischer Ventilstähle mit hohem Stickstoffgehalt

On the hot strength of austenitic valve steels with a high nitrogen content Exhaust valves are made of CrMnNi steels with about 1 wt% of (C + N) and additions of W, Mo and Nb. Remelting under pressure allows to raise N and do without C. After solution annealing the formation of discontinuous N‐perlite during aging is suppressed by ∼ 1 wt% of Nb whereby the creep strength is increased. The size and distribution of continuously precipitated nitrides in N‐steels are finer than those of carbides and nitrides in (C + N)‐steels. Thus the creep strength of the former is superior at 700 °C. However, at 800 °C σ‐phase leads to a breakdown of creep strength. The reason is seen in a lower stability of N‐austenite as compared to (C + N)‐austenite, which shows a higher concentration of free electrons and more short range atomic ordering.     

Comparative ecotoxicological hazard assessment of beta-blockers and their human metabolites using a mode-of-action-based test battery and a QSAR approach

We analyzed nontarget effects of the beta-blockers propranolol, metoprolol, and atenolol with a screening test battery encompassing nonspecific, receptor-mediated, and reactive modes of toxic action. All beta-blockers were baseline toxicants and showed no specific effects on energy transduction nor endocrine activity in the yeast estrogen and androgen screen, and no reactive toxicity toward proteins and DNA. However, in a phytotoxicity assay based on the inhibition of the photosynthesis efficiency in green algae, all beta-blockers were 10 times more toxic than their modeled baseline toxicity. Baseline- and phytotoxicity effects increased with hydrophobicity. The beta-blockers showed concentration addition in mixture experiments, indicating a mutual specific nontarget effect on algae. Using literature data and quantitative structure-activity relationships (QSAR), we modeled the total toxic potential of mixtures of the beta-blockers and their associated human metabolites for the phytotoxicity endpoint with two scenarios. The realistic scenario (I) assumes that the metabolites lose their specific activity and act as baseline toxicants. In the worst-case scenario (II) the metabolites exhibitthe same specific mode of action as their parent drug. For scenario (II), metabolism hardly affected the overall toxicity of atenolol and metoprolol, whereas propranolol's hazard potential decreased significantly. In scenario (I), metabolism reduced the apparent EC50 of the mixture of parent drug and metabolite even further. The proposed method is a simple approach to initial hazard assessment of pharmaceuticals and can guide higher tier testing. It can be applied to other classes of pollutants, e.g., biocides, as well as to environmental transformation products of pollutants.     

Transfer kinetics of polar organic compounds over polyethersulfone membranes in the passive samplers POCIS and Chemcatcher

Passive samplers for polar organic compounds often use a polyethersulfone (PES) membrane to retain the particulate sorbent material (e.g., in a POCIS; polar organic chemical integrative sampler) or to reduce the sampling rate and thus extend the kinetic regime (e.g., in a Chemcatcher). The transport kinetics over the PES membrane are evaluated here in a short-term (6 days) and a long-term (32 days) experiment with POCIS and Chemcatchers. Passive samplers were placed in a channel with flowing river water that was spiked with 22 organic chemicals including pharmaceuticals, pesticides and biocides; with logK(ow) (logarithmic octanol-water partitioning coefficient) values between -2.6 and 3.8. Samplers were removed at intervals and membranes and sorbent material were extracted and analyzed with LC-MS/MS. Uptake kinetics of the compounds fell between two extremes: (1) charged chemicals and chemicals of low hydrophobicity did not accumulate in PES and rapidly transferred to the sorbent (e.g., diclofenac) and (2) more hydrophobic chemicals accumulated strongly in the PES and appeared in the sorbent after a lag-phase (e.g., diazinon and diuron). Sorption kinetics were modeled with a three-compartment first-order kinetic model to determine uptake and elimination rate constants and partitioning coefficients. Water PES partitioning coefficients fitted with the model correlated well with experimentally determined values and logK(ow). Sampling rates of Chemcatcher (0.02-0.10 L/d) and POCIS (0.02-0.30 L/d) showed similar patterns and correlated well. Thus the samplers are interchangeable in practical applications. Longer lag-phases may pose problems when calculating time-weighted average aqueous concentrations for short passive sampling windows and for a correct integrative sampling of fluctuating concentrations.     

Significance of xenobiotic metabolism for bioaccumulation kinetics of organic chemicals in Gammarus pulex

Bioaccumulation and biotransformation are key toxicokinetic processes that modify toxicity of chemicals and sensitivity of organisms. Bioaccumulation kinetics vary greatly among organisms and chemicals; thus, we investigated the influence of biotransformation kinetics on bioaccumulation in a model aquatic invertebrate using fifteen (14)C-labeled organic xenobiotics from diverse chemical classes and physicochemical properties (1,2,3-trichlorobenzene, imidacloprid, 4,6-dinitro-o-cresol, ethylacrylate, malathion, chlorpyrifos, aldicarb, carbofuran, carbaryl, 2,4-dichlorophenol, 2,4,5-trichlorophenol, pentachlorophenol, 4-nitrobenzyl-chloride, 2,4-dichloroaniline, and sea-nine (4,5-dichloro-2-octyl-3-isothiazolone)). We detected and identified metabolites using HPLC with UV and radio-detection as well as high resolution mass spectrometry (LTQ-Orbitrap). Kinetics of uptake, biotransformation, and elimination of parent compounds and metabolites were modeled with a first-order one-compartment model. Bioaccumulation factors were calculated for parent compounds and metabolite enrichment factors for metabolites. Out of 19 detected metabolites, we identified seven by standards or accurate mass measurements and two via pathway analysis and analogies to other compounds. 1,2,3-Trichlorobenzene, imidacloprid, and 4,6-dinitro-o-cresol were not biotransformed. Dietary uptake contributed little to overall uptake. Differentiation between parent and metabolites increased accuracy of bioaccumulation parameters compared to total (14)C measurements. Biotransformation dominated toxicokinetics and strongly affected internal concentrations of parent compounds and metabolites. Many metabolites reached higher internal concentrations than their parents, characterized by large metabolite enrichment factors.     

Molecular weight determination of the hepatic vasopressin receptor with a high-affinity photoprobe

We report here a study of photoaffinity labeling of the V1a-vasopressin receptor with high-affinity, V1-specific radioiodinated antagonist ligands: one containing an azidophenylalanine residue ([beta,beta-dimethyl-beta-mercaptopropionyl(1), p-azido-Phe2,Val4,Lys8,D-Tyr9] vasopressin), two others containing nitrophenylalanine, and one, highly similar but without a photosensitive function, as control. All analogues competed in the dark for the same binding site with vasopressin. Long-wavelength UV irradiation of rat liver membranes incubated in presence of the radio-iodinated azido photolabel produced a specifically labeled protein band at 53 kDa in SDS-PAGE. Identical experiments with the nitrophenylalanyl peptides produced only non-specific labeling and control experiments with the non-photosensitive analogue produced no labeling at all. Chemical crosslinking of 3H-VP to the same membrane preparation produced a result identical to that of the azido photolabel, confirming the receptor nature of the labeled protein. Deglycosylation of the labeled receptor with endoglycosidase F reduced the observed molecular weight of 53 kDa to 43 kDa. The molecular parameters reported herein of the presumed hepatic vasopressin receptor confirm the values deduced from the molecular cloning of the rat V1a receptor.     

Luciferase assembly after transport into mammalian microsomes involves molecular chaperones and peptidyl-prolyl cis/trans-isomerases

The assembly of a heterodimeric luciferase was studied after de novo synthesis of corresponding precursor proteins in reticulocyte lysate and concomitant transport into dog pancreas microsomes. This cytosolic luciferase from a prokaryotic organism (Vibrio harveyi) was specifically used as a model protein to investigate (i) whether the eukaryotic cytosol and the microsomal lumen have similar folding capabilities and (ii) whether the requirements of a polypeptide for certain molecular chaperones and folding catalysts are determined by the polypeptide or the intracellular compartment. The two luciferase subunits were fused to the preprolactin signal peptide. Data indicate that efficient assembly of luciferase occurs in the mammalian microsomes. Furthermore, it was observed that luciferase assembly can be separated in time from synthesis and membrane transport, depends on ATP hydrolysis, is partially sensitive to cyclosporin A and FK506, and in the absence of lumenal proteins is less efficient as compared with the presence of lumenal proteins. Thus, heterodimeric luciferase depends on functionally related molecular chaperones and folding catalysts during its assembly in either the eukaryotic cytosol or the microsomal lumen.     

Subcellular distribution and function of Rab3A, B, C, and D isoforms in insulin-secreting cells

Insulin-secreting cells express four GTPases of the Rab3 family. After separation of extracts of INS-1 cells on a sucrose density gradient, the bulk of the A, B, and C isoforms was recovered in the fractions enriched in insulin-containing secretory granules. Rab3D was also mainly associated with secretory granules, but a fraction of this isoform was localized on lighter organelles. Analyses by confocal microscopy of immunostained HIT-T15 cells transfected with epitope-tagged constructs confirmed the distribution of the Rab3 isoforms. Transfection of HIT-T15 cells with GTPase-deficient mutants of the Rab3 isoforms decreased nutrient-induced insulin release to different degrees (D>B>A>C), while overexpression of Rab3 wild types had minor or no effects. Expression of the same Rab3 mutants in PC12 cells provoked an inhibition of K+-stimulated secretion of dense core vesicles, indicating that, in beta-cells and neuroendocrine cells, the four Rab3 isoforms play a similar role in exocytosis. A Rab3A/C chimera in which the carboxyterminal domain of A was replaced with the corresponding region of C inhibited insulin secretion as Rab3A. In contrast, a Rab3C/A chimera containing the amino-terminal domain of C was less potent and reduced exocytosis as Rab3C. This suggests that the degree of inhibition obtained after transfection of the Rab3 isoforms is determined by differences in the variable amino-terminal region.