Biomedical subjects

Ivan Holoubek

Publications and source records attributed to Ivan Holoubek.

23 records · Page 2Linked to original sources

PubMed2003

Environmental ice photochemistry: monochlorophenols.

Photolysis of 2- and 4-chlorophenol samples in water ice of the initial concentrations 10(-7) to 10(-2) mol L(-1) is reported. Major phototransformations appeared to be based on the coupling reactions due to chlorophenol aggregation at the grain boundaries of the polycrystalline state. The main products, chlorobiphenyldiols, belong to the family of phenolic halogenated compounds (such as hydroxylated polychlorobiphenyls) that are known xenobiotics found in nature. No photosolvolysis products, that is products from intermolecular reactions between organic and water molecules, were observed at temperatures below -10 degrees C. Raising the temperature to -5 degrees C caused a moderate photosolvolytic activity in the case of 4-chlorophenol (formation of hydroquinone), in contrast to 2-chlorophenol which was almost exclusively transformed into pyrocatechol. It is suggested that photosolvolysis above this temperature occurs in a liquid or quasi-liquid layer that covers the ice crystal surfaces. The results support our model in which significant amounts of some persistent, bioaccumulative, and toxic compounds may be generated by photochemistry of primary pollutants in cold ecosystems and in the upper atmosphere, and may be subsequently released to the environment.

Chlorophenols↗

PubMed2003

Novel approach to monitoring of the soil biological quality.

In this study, a new approach to interpretation of results of the simple microbial biomass and respiration measurements in the soil microbiology is proposed. The principle is based on eight basal and derived microbial parameters, which are standardized and then plotted into sunray plots. The output is visual presentation of one plot for each soil, which makes possible the relative comparison and evaluation of soils in the monitored set. Problems of soil microbiology, such as the lack of benchmarking and reference values, can be avoided by using the proposed method. We found that eight parameters provide enough information for evaluation of the status of the soil microorganisms and, thus, for evaluation of the soil biological quality. The usage of rare parameters (potential respiration PR, ratio of potential and basal respiration PR/BR, biomass-specific potential respiration PR/C(bio), available organic carbon C(ext), and biomass-specific available organic carbon C(ext)/C(bio)) can be recommended, besides classical and well-known parameters (microbial biomass C(bio), basal respiration BR, metabolic coefficient qCO(2)). The combination of basal parameters and derived coefficients can also extend our knowledge about the condition of the soil microorganisms. In monitoring the case studies presented, we observed that soils evaluated to possess good biological quality displayed generally higher values of organic carbon, total nitrogen, clay, and cation exchange capacity. The soils of good biological quality can display higher levels of contaminants. This is probably related with the higher content of organic carbon and clay in these soils.

Aluminum Silicates↗

PubMed2003

Isomer-specific analysis of chlorinated biphenyls, naphthalenes and dibenzofurans in Delor: polychlorinated biphenyl preparations from the former Czechoslovakia.

Technical polychlorinated byphenyl (PCB) preparations--Delors 103, 104, 105, and 106--produced in the former Czechoslovakia were analyzed for their chlorobiphenyl (CB), chloronaphthalene (PCN) and chlorinated dibenzofuran (PCDF) composition and content using high resolution gas chromatography-mass spectrometry techniques. The congener patterns of Delors 103, 104, 105, and 106 resembled Aroclors 1242, 1248, 1254, and 1260. Delors contained PCNs and PCDFs, as impurities, at microgram per gram concentrations. Concentrations of PCNs and PCDFs in Delors were greater than those found in the corresponding Aroclors. The potential for the emissions of PCNs and PCDFs from Delor was estimated to be 3680 and 860 kg, respectively. Non- and mono-ortho PCBs were the major contributors to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents in Delor mixtures.

Benzofurans↗

PubMed2003

Comparison of the effects of UV, H2O2/UV and gamma-irradiation processes on frozen and liquid water solutions of monochlorophenols.

The effects of UV irradiation, both in the presence and absence of hydrogen peroxide, as well as of gamma irradiation on 2- and 4-chlorophenol in a solid water ice matrix have been studied and compared to those effects known to occur in aqueous solutions. While UV photolysis (>280 nm) of monochlorophenols leads to efficient coupling reactions in ice and photosolvolysis products in liquid water; hydroxylation to chlorobenzenediols is the main pathway in the presence of H2O2 in both phases. The results show that the solute molecules accumulate in a layer surrounding the ice crystal walls during the freezing process, where they then react. The radiation chemistry of chlorophenol ice samples involves preferential coupling reactions at -78 degrees C rather than reactions with the OH radicals produced by cleavage of water molecules under the conditions employed (1 kGy h(-1)). The apparent similarities between the chemistry in the UV/H2O2-treated liquid and solid, and y-irradiated liquid and solid samples are discussed. It is suggested that the reactions of OH radicals within polycrystalline ice or snow are important natural processes that should be considered in environmental, ice-core or astrophysical research.

Journal Article↗

PubMed2002

Ice (photo)chemistry. Ice as a medium for long-term (photo)chemical transformations--environmental implications.

This review accounts for the current knowledge about the distribution, accumulation, and chemical/photochemical transformations of persistent, bioaccumulative, and toxic compounds (PBTs) in water ice, especially in the connection with polar regions and atmospheric cloud particles. (Photo)reactions on/in ice are discussed in terms of photochemistry, photobiology, paleochemistry, as well as astrophysics. Authors propose a model, in which a significant amount of some PBTs are generated by (photo)chemistry of primary pollutants in ice, which may subsequently be released to the environment. It is argued that ice photochemistry might play an important role in the chemical transformations in cold ecosystems and in the upper atmosphere, particularly now when the ozone layer is partially depleted.

Air Pollutants↗