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31.
32.
Medications for pregnant women: A balancing act between the interests of the mother and of the fetus
Drug entry into the adult brain is controlled by efflux mechanisms situated in various brain barrier interfaces. The effectiveness of these protective mechanisms in the embryo, fetus and newborn brain is less clear. The longstanding belief that “the” blood-brain barrier is absent or immature in the fetus and newborn has led to many misleading statements with potential clinical implications. Here we review the properties of brain barrier mechanisms in the context of drug entry into the developing brain and discuss the limited number of studies published on the subject. We noticed that most of available literature suffers from some experimental limitations, notably that drug levels in fetal blood and cerebrospinal fluid have not been measured. This means that the relative contribution to the overall brain protection provided by individual barriers such as the placenta (which contains similar efflux mechanisms) and the brain barriers cannot be separately ascertained. Finally, we propose that systematic studies in appropriate animal models of drug entry into the brain at different stages of development would provide a rational basis for use of medications in pregnancy and in newborns, especially prematurely born, where protection usually provided by the placenta is no longer present. 相似文献
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The size of particles in urban air varies over four orders of magnitude (from 0.001 μm to 10 μm in diameter). In many cities
only particle mass concentrations (PM10, i.e. particles <10 μm diameter) is measured. In this paper we analyze how differences
in emissions, background concentrations and meteorology affect the temporal and spatial distribution of PM10 and total particle
number concentrations (PNC) based on measurements and dispersion modeling in Stockholm, Sweden. PNC at densely trafficked
kerbside locations are dominated by ultrafine particles (<0.1 μm diameter) due to vehicle exhaust emissions as verified by
high correlation with NOx. But PNC contribute only marginally to PM10, due to the small size of exhaust particles. Instead
wear of the road surface is an important factor for the highest PM10 concentrations observed. In Stockholm, road wear increases
drastically due to the use of studded tires and traction sand on streets during winter; up to 90% of the locally emitted PM10
may be due to road abrasion. PM10 emissions and concentrations, but not PNC, at kerbside are controlled by road moisture.
Annual mean urban background PM10 levels are relatively uniformly distributed over the city, due to the importance of long
range transport. For PNC local sources often dominate the concentrations resulting in large temporal and spatial gradients
in the concentrations. Despite these differences in the origin of PM10 and PNC, the spatial gradients of annual mean concentrations
due to local sources are of equal magnitude due to the common source, namely traffic. Thus, people in different areas experiencing
a factor of 2 different annual PM10 exposure due to local sources will also experience a factor of 2 different exposure in
terms of PNC. This implies that health impact studies based solely on spatial differences in annual exposure to PM10 may not
separate differences in health effects due to ultrafine and coarse particles. On the other hand, health effect assessments
based on time series exposure analysis of PM10 and PNC, should be able to observe differences in health effects of ultrafine
particles versus coarse particles. 相似文献
35.
Emo Chiellini Andrea Corti Salvatore D’Antone Norman C. Billingham 《Journal of Polymers and the Environment》2007,15(3):169-178
Most of the standardized biodegradation tests used to assess the ultimate biodegradation of environmentally degradable polymers
are based solely on the determination of net evolved carbon dioxide. However, under aerobic conditions, it has to be considered
that heterotrophic microbial consortia metabolize carbon substrates both to carbon dioxide and in the production of new cell
biomass. It is generally accepted that in the relatively short term, 50% of the carbon content of most organic substrates
is converted to CO2, with the remaining carbon being assimilated as biomass or incorporated into humus. The latter is particularly important
when the metabolism of the organic matter occurs in a soil environment. A straightforward relationship between the free-energy
content of a carbon substrate (expressed as the standard free-energy of combustion) and its propensity for conversion to new
microbial biomass rather than mineralization to CO2 has been established. This can potentially lead to underestimation of biodegradation levels of test compounds, especially
when they consist of carbon in a fairly low formal oxidation state and relatively high free-energy content. In the present
work, the metabolism of different kind of carbon substrates, especially in soil, is reviewed and compared with our own experimental
results from respirometric tests. The results show that conversion of highly oxidized materials, such as the commonly used
reference materials, cellulose or starch, to CO2 may be significantly overestimated. The addition of glucosidic material to soil leads to greatly increased respiration and
is accompanied by a very low conversion to biomass or humic substances. In contrast, relatively less oxidized substrates metabolize
more slowly to give both CO2 and biomass to an extent which may be significantly underestimated if glucosidic materials are used as the reference. The
need for an overall carbon balance taking into account both the carbon immobilized as biomass and that volatized as CO2 must be considered in standard respirometric procedures for assessing the biodegradability of slowly degrading macromolecules. 相似文献
36.
Factors effecting Zn+2 uptake by the water hyacinth Eichhonnia cnassipes, were examined. Two phases of zinc uptake were observed throughout the uptake range (1000 – 0.001 ppm). Initially a rapid uptake phase of 4 hours followed by a slower, near linear uptake phase extending past 48 hours. Stirring the solution enhanced uptake, suggesting uptake is partially diffusion limited. Increasing pH from 3 to 5 enhanced zinc uptake. As solution volume was increased, more zinc was removed. With increasing amounts of Hg+2 or Cd+2, the zinc removal rate decreased, suggesting a competition for binding sites on the roots. The presence of complexing agents during the uptake phase reduced zinc uptake. The inability of complexing agents to recover all zinc removed by a plant suggests a translocation to sites within the plant. 相似文献
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The investigation concerns the impact of the new school environment on a group of 50 male and female children aged 11–16 years, who leave home to reside temporarily at boarding school, in terms of the characteristics of problems and worries reported and the incidence of spontaneous reports of homesickness. More problems relating to the school than to the home environment were reported but proportionally more worry units were reported associated with home problems for both males and females. There was no sex differences in this respect. The reported level of spontaneously reported homesickness was 16% and there were no sex differences. Factors such as age, geographical distance of move and decision to go away to school were not influential in determining the level of reported problems or incidence of spontaneous reports of homesickness. A relationship was found with level of problems reported and recent life history but the result proved difficult to interpret. 相似文献
40.
Melamine-based organoclay to sequester atrazine 总被引:4,自引:0,他引:4
Sequestration of aqueous atrazine by organoclays prepared from the surfactant 6-piperazin-1-yl-N,N'-bis-(1,1,3,3-tetramethyl-butyl)-(1,3,5)triazine-2,4-diamine and Gonzales bentonite was assessed using 14C-labeled atrazine. Organoclays with varying ratios of surfactant to clay were evaluated with respect to their ability to sequester atrazine from an aqueous solution. Organoclays containing 100-200 g kg-1 surfactant on a total weight basis provided the most efficient adsorption of atrazine, with apparent KOC values exceeding 5000 l kg-1 at these loading fractions. Less than 12% of sequestered atrazine was released during four sequential day long washings, supporting our expectation that the majority of the reaction of atrazine with the surfactant lead to irreversible chemical bond formation through nucleophilic aromatic substitution. 相似文献