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941.
In mammals, serum paraoxonase (PON1) is tightly associated with high-density lipoprotein (HDL) particles. In human populations, PON1 exhibits a substrate dependent activity polymorphism determined by an Arg/Gln (R/Q) substitution at amino acid residue 192. The physiological role of this protein appears to be involvement in the metabolism of oxidized lipids. Several studies have suggested that the PON1R192 allele may be a risk factor in coronary artery disease. PON1 also plays an important role in the metabolism of organophosphates including insecticides and nerve agents. The PON1R192 isoform hydrolyzes paraoxon rapidly, but diazoxon, soman and sarin slowly compared with the PON1Q192 isoform. Both PON1 isoforms hydrolyze phenylacetate at approximately the same rate, while PON1R192 hydrolyzes chlorpyrifos oxon slightly faster than PONQ192. Animal model studies involving injection of purified rabbit PON1 into mice clearly demonstrated the ability of PON1 to protect cholinesterases from inhibition by OP compounds. The consequence of having low PON1 levels has been addressed with toxicology studies in PON1 knockout mice. These mice showed dramatically increased sensitivity to chlorpyrifos oxon, diazoxon and some increased sensitivity to the respective parent compounds. These observations are consistent with earlier studies that showed a good correlation between high rates of OP hydrolysis by serum PON1 and resistance to specific OP compounds. They are also consistent with the observations that newborns have an increased sensitivity to OP toxicity, due in part to their not expressing adult PON1 levels for weeks to months after birth, depending on the species. Together, these studies point out the importance of considering the genetic variability of PON1192 isoforms and levels as well as the developmental time course of PON1 appearance in serum in developing risk assessment models 相似文献
942.
John A. Bukowski R. Jeffrey Lewis John F. Gamble Nancy C. Wojcik Robert J. Laumbach 《人类与生态风险评估》2002,8(4):735-765
This review explores the recent epidemiological literature to identify possible risk factors for childhood asthma development, as well as the proportion of cases that might be attributable to each factor. Tobacco smoke and house-dust-mite allergy are the only environmental risk factors with firmly established roles in asthma development. Together with genetics, these risk factors probably account for much of childhood asthma development. Suggestive risk factors include cockroach, pet, and mold allergens; low birth weight; small family size; and viral infection. More theoretical risk factors include insufficient breastfeeding, obesity/inactivity, ambient ozone, and living in non-farm settings. National/international trends suggest several risk factors that could play major roles in the rising prevalence of asthma. The “tighter” building construction of modern housing and the increasing time that children spend indoors has undoubtedly increased indoor allergen exposures. Children also spend more time in sedentary activities, with a concomitant decrease in physical activity and increase in obesity. Modern “hygiene” and the changing nature of childhood infection may have also increased asthma prevalence. Mechanisms have been suggested implicating ambient air pollution in asthma development, and there is limited epidemiological evidence supporting this hypothesis. However, this evidence does not resolve why pollution levels have been decreasing throughout the period that asthma rates have risen 相似文献
943.
David A. Bella 《人类与生态风险评估》2002,8(1):55-73
Salmon in the U.S. Pacific Northwest are in widespread decline despite countless environmental assessment studies and billions of dollars spent. Having been involved in environmental assessment for more than three decades, I am forced to conclude that this decline tells us that our established practices of assessment and management are fundamentally deficient. Rather than studying the salmon, we should examine our own practices. These practices presume that, if individual actions are found to be beneficial through analytical assessments, the cumulative outcomes of many actions will also be beneficial. This “linear” presumption is embedded in institutions, analytical methods, and assessment practices. For a whole class of emerging problems, including declining salmon, this presumption is fundamentally wrong. Declining salmon provide a warning that our own analytical habits of thought and notions of progress are leading to outcomes that are both destructive and contrary to our best intentions. This paper is a response to this warning. 相似文献
944.
Tree rings and forest management in Europe 总被引:1,自引:0,他引:1
945.
Byung-Ki Hur Dae-Won Cho Ho-Jung Kim Chun-Ik Park Hyung-Joon Suh 《Biotechnology and Bioprocess Engineering》2002,7(1):10-15
Environmental and medium factors were investigated as basic data for optimizing DHA production when usingThraustochytrium aureum. To study the effect of environmental conditions, the rotation speed and culture temperature were, changed. Plus the trend
of the growth characteristics, lipid content in the biomass, and DHA content in lipids were evaluated according to various
initial glucose concentrations. The biomass, lipid, and DHA analyses showed that the physiological characteristics ofT. aureum were closely related with the environmental and medium conditions, as in the case of other marine microorganisms. For example,
a low rotation speed of 50 rpm lowered the cell growth rate as well as the DHA content in the lipids. A low temperature had
a negative effect on the cell growth, yet a positive effect on the lipid content in the biomass. Different initial glucose
concentrations had no effect on the lipid content in the biomass or DHA content in the lipids, yet did affect the cell growth.
Accordingly, these results show that environmental and medium factors must be synthetically considered in order to optimize
DHA production when usingT. aureum. 相似文献
946.
There are over one hundred mineralized lakes in Khakasia with areas in excess of 0.01 km2 including periodically dry lakes. These saline lakes are situated within the Chebakovo-Balakhtinskaya and Yuzhno-Minusinsk depressions of the Minusinsk intermontane trough, bounded by Kuznetsk Alatau, Western and Eastern Sayan mountains. The depressions are characterised by steppe landscape, low topographic relief and an arid climate (annual rainfall ca. 300 mm y–1). The mineralisation of the various lakes ranges from some 2 to 150 g l–1. Mg++, Na+ and Ca++ cations, SO4
= and Cl– anions dominate the composition of soluble salts. The degree of variation of the lakes' mineralisation increases in dry periods. The majority of lakes are associated with synclinal structures and terrigenous red-bed Upper Devonian clastic deposits which bear indicators of accumulation in an evaporite environment (the presence of gypsum layers). Some mineral lakes are situated in Carboniferous carbonate-terrigenous deposits, containing scattered pyroclastics and features of evaporite sedimentation. The high salinity of the lakes is explained (i) by the availability of readily soluble minerals in Palaeozoic strata (gypsum, anhydrite, halite and others), which may be dissolved in groundwater and transported to lake catchments, and (ii) by the high degree of surface water evaporation due to the arid climate. The mineralized waters of some lakes can be recommended for balneological purposes. A deterioration is noted in the ecological status of some saline lakes due to anthropogenic contamination. 相似文献
947.
In this paper we ask whether succession in a rocky subtidal community varies in space and time, and if so how much affect that variation has on predictions of community dynamics and structure. We describe succession by Markov chain models based on observed frequencies of species replacements. We use loglinear analysis to detect and quantify spatio‐temporal variation in the transition matrices describing succession. The analysis shows that space and time, but not their interaction, have highly significant effects on transition probabilities. To explore the ecological importance of the spatio‐temporal variability detected in this analysis, we compare the equilibria and the transient dynamics among three Markov chain models: a time‐averaged model that includes the effects of space on succession, a spatially averaged model that include the effects of time, and a constant matrix that averages over the effects of space and time. All three models predicted similar equilibrium composition and similar rates of convergence to equilibrium, as measured by the damping ratio or the subdominant Lyapunov exponent. The predicted equilibria from all three models were very similar to the observed community structure. Thus, although spatial and temporal variation is statistically significant, at least in this system this variation does not prevent homogeneous models from predicting community structure. 相似文献
948.
949.
Marieke Gorrée Jeroen B. Guinée Gjalt Huppes Lauran van Oers 《The International Journal of Life Cycle Assessment》2002,7(3):158-166
Linoleum is a floor covering consisting mainly of linseed oil, other vegetable oils, wood flour and limestone on a carrier
of jute. Forbo-Krommenie B.V. commissioned the Centre of Environmental Science (CML) to carry out an Environmental Life Cycle
Assessment for linoleum floors. The goal of this study was to assess the environmental performance of linoleum floors, indicating
possible options for improvement, and assessing the sensitivity of the results to methodological choices. The functional unit
was defined as: 2000 m2 linoleum produced in 1998, used in an office or public building over a period of 20 years. The method followed in this study
is based on a nearly final draft version of the LCA guide published by CML in corporation with many others, which is an update
of the guide on LCA of 1992.
From the contribution analysis, the main contributing processes became clear. In addition, the sensitivity analysis by scenarios
showed that the type of maintenance during use and the pigments used can have a large influence on the results. Major data
gaps of the study were capital goods and unknown chemicals. Sensitivity analysis also showed that these gaps can lead to an
underestimation. Based on this study, some options to improve the environmental performance of linoleum were formulated and
advice for further LCA studies on linoleum was given. 相似文献
950.
Summary
In vitro plantlets of Phalaenopsis ‘Happy Valentine’, Neofinetia falcate Hu, Cymbidium kanran Makino, and Cymbidium goeringii Reichb. f. were grown under photoautotrophic [high photosynthetic photon flux (PPF), high CO2 concentration, and increased number of air exchanges] and heterotrophic (low PPF, low CO2 concentration, no air exchanges) culture conditions. After 40 d of culture, a significant difference in plantlet growth was
observed between the two cultures. Total fresh and dry mass were on average 1.5 times greater in photoautotrophic culture
than in heterotrophic culture. Higher net photosynthetic rates were also observed for Phalaenopsis in photoautotrophic culture. In photoautotrophic culture, little difference was observed in air temperature between the inside
and outside of the culture vessel, whereas in heterotrophic culture, air temperature inside the culture vessel was 1–2°C higher
than that outside the culture vessel. Relative humidity inside the culture vessel was remarkably different between the two
cultures: 83–85% in photoautotrophic culture and 97–99% in heterotrophic culture. These results indicated that growth and
net photosynthetic rate of in vitro orchid plantlets were susceptible to the culture environments such as PPF, CO2 concentration, relative humidity (RH), and the number of air exchanges, which would allow a more efficient micropropagation
system for these orchid plants. 相似文献