Exposure-Dependent Effects

Mallik, B., Masunov, A., Lazaridis, T. Distance and exposure dependent effective dielectric function. J. Comput. Chem. 2002, 23, 1090-9. 

Recently, Dinwiddie et al. [14] reported the effects of short-time, high-temperatme exposures on the temperature dependence of the thermal conductivity of CBCF. Samples were exposed to temperatures ranging from 2673 to 3273 K, for periods of 10, 15, and 20 seconds, to examine the time dependent effects of graphitization on thermal conductivity measured over the temperature range from 673 to 2373 K. Typical experimental data are shown in Figs. 7 and 8 for exposure times of 10 and 20 seconds, respectively. The thermal conductivity was observed to increase with both heat treatment temperature and exposure time. 

Accident frequencies were evaluated separately for the two types of activity mainline transit and rail yard classification. When an accident occurs and the tank car is damaged, the severity of public exposure depends on several factors, including tlie likelihood of a breach in tlie tank car, the severity level of tlie release (i.e., tlie rale or volume of spillage), the likelihood of an explosion, tlie magnitude of tlie explosion, and die dispersion pattern of the unignited vapors. Recall tliat Part II of tliis book deals witli explosions and tlieir effects Part III treats tliis subject of dispersion. Table 21.3.1 smnmarizes tlie transportation risk data for tlie mainline and rail yard segments of tlie tank car journey. 

Hillefors-Berglund M, Liu Y, von Euler G Persistent, specific and dose-dependent effects of toluene exposure on dopamine D2 agonist binding in the rat caudate-putamen. Toxicology 77 223-232, 1993... 

An additional study reported age-dependent effects. Lakshmana and Raju (1994) found that oral treatment of rat pups with endosulfan from postnatal days 2-10 resulted in changes in the concentration of noradrenalin, dopamine, and serotonin in various brain areas that differed either in magnitude or direction from changes seen in pups treated from postnatal days 2-23. While the results from this study do not necessarily indicate that neonates are more sensitive to the toxic effects of endosulfan, they do show that the duration of exposure in neonates is an important parameter to consider. 

Postexposure prophylaxis for perinatal exposure depends upon the mother s HBsAg status.24 Mothers who are HBsAg-positive should have their newborns immunized with both the hepatitis B vaccine and HBIG 0.5 mL. This regimen is 85% effective in preventing the hepatitis B carrier status if administered... 

Delayed. Usual onset of symptoms occurs approximately 2 h after aerosol exposure. Depending on inhaled or ingested dosage, symptoms may appear at times ranging from 30 min to 20 h after exposure. Effects from skin contact may appear 36 h later. Dimethylsulfoxide as a "carrier" increases the percutaneous effect by a factor of at least 25. 

Jett DA, Kuhlmann AC, Farmer SJ, et al. 1997. Age-dependent effects of developmental lead exposure on performance in the Morris water maze. Pharmacol Biochem Behav 57(l-2) 271-279. 

Further details of the above study were discussed in U.S. EPA (1994). After the last exposure, methemoglobin levels were elevated in a dose-dependent manner 17 ppm, 0% to 2.9% (no different from controls) 45 ppm, 2.2% to 5.4% and 87 ppm, 4.2% to 23%. The animals exposed at 45 and 87 ppm were anemic with decreases in RBC counts, hemoglobin content, MCHb concentration, and hematocrit, and accompanying increases in erythropoietin foci, reticuloendothelial cell hypertrophy, and hemosiderin deposition in the spleen. The animals in the 87-ppm exposure group were judged cyanotic. In the 17-ppm exposure group, effects were limited to mild splenic congestion. 

Pillet, S. et al., In vitro exposure of seal peripheral blood leukocytes to different metals reveal a sex-dependent effect of zinc on phagocytic activity, Mar. Pollut. Bull., 40,921,2000. 

No information is available on whether biomarkers for exposure or effect of -hexane validated in adults (exhaled -hexane, 2,5-hexanedion in urine) also are valid for children. Interactions of -hexane with other chemicals have not been reported in children, but have occurred in adults (Altenkirch et al. 1977). Since interactions in adults are dependent on toxickinetic parameters, predicting interactions in children requires greater understanding of the metabolism of -hexane in children. 

The reference sampling rate (/ s,ref) as well as the exposure-specific effect jSj are divided out. For practical applications, it therefore suffices to know how the compound-specific effect depends on the properties of the analytes. Observing that the experimental sampling rates have a similar dependence on log ATow, but show a varying offset for the different studies, the log-transformed sampling rates observed in 19 calibration experiments in 9 studies were fitted as a third order polynomial in log Kq -... 

Areas related to the evaluation of the adversity of an effect are reversibility and irreversibility and adaptation to an exposure. Irreversible effects are always of great concern. Reversible effects may also be of great concern depending on the nature of the effect and on the setting in which they occur. It cannot be mled out that a permanent lesion may have occurred even if the overt effect is transient. Eurthermore, when there is a more or less continuous exposure to a substance, the question of reversibility is not relevant because adaptation systems will be counteracted by new insults. In many cases it is not possible to draw any conclusion on whether an effect is reversible or not as such experimental data are rare, and all significant health effects that can impair function, both reversible and irreversible, should therefore be considered in the hazard assessment. 

Some radiation is helpful and necessary, as in the case of sunlight, which allows us to see the world. The nonionizing radiation of the sun warms us, but too much ultraviolet radiation can cause sunburn or cancer depending on our individual sensitivity. There is clearly a dose - response relationship between exposure and effect, with individual sensitivity playing an important role. Microwave and radiofrequency radiation are incredibly useful in heating and transmitting information. 

The units of analysis should be determined by the needs of the assessment, not by the data that happen to be available. Careful consideration is required to identify which biological, spatial, and temporal units are appropriate for each assessment. This will depend on the nature and degree of spatial and temporal variation in the many factors that affect exposure and effects, including the following ... 

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