Exposure peaks

Samples must be representative of the environment in relation to study objeetives and to permit eomparison of data with appropriate standards, i.e. average eoneentrations, time-weighted exposures, peak eoneentrations, ete. Replieate samples may be advisable. 

Peak-above-ceiling exposure limit The short-term exposure peak permitted above the OSHA standard ceiling exposure level. 

Little information is available on the metabolism of -hexane after oral exposure, although it appears to be qualitatively similar to that after inhalation exposure. Peak serum concentrations of the -hexane metabolite 2,5-hexanedione of 24, 44, and 53 g/mL were observed in rats after a single gavage exposure to 570, 1,140, and 4,000 mg/kg -hexane, respectively (Krasavage et al. 1980). Serum 2,5-hexanedione concentrations rose slowly to a peak at 12-16 hours and returned to baseline by 24 hours. 

Little information exists on the toxicology of piperazine dihydrochloride in humans or in animals. Acute human exposures to the dust have reportedly resulted in irritation to the eyes, mild to moderate skin burns, and sensitization. Exposure levels and duration were not available. Occupational exposures have been associated with occasional cases of asthma. In one factory, several cases of asthma were precipitated by a time-weighted average (TWA) exposure of 1.2mg/m although there were brief exposure peaks of lOOmg/m or higher. There were no new cases noted in a workplace... 

Limited studies in rats also show that DNOC is absorbed after inhalation exposure. DNOC was absorbed into the blood of rats exposed to DNOC aerosols for 4 or 5 hours (King and Harvey 1953a, 1954). Exposure to 0.1 mg/m DNOC caused increases in the blood concentration with time. During the 5 hours of exposure, peak blood concentrations did not exceed 60 pg/g (King and Harvey 1953a). At the end of the exposure period, 16-28 pg/g of DNOC were found in the lungs (method unspecified). In a separate experiment, exposure of rats to 100 mg/m for 4 hours caused incremental increases in blood DNOC concentrations peak blood concentrations ranged from 21 to 64 pg/g in 5 rats. 

Even a single exposure, no matter the duration, might result in reproductive or developmental toxicity. Agents that show accumulation with repeated exposures or that have a long half-life will result in greater exposures over time. The pattern of exposure is extremely important in predicting outcome, and it is usually difficult to extrapolate results from one pattern to another unless pharmacokinetic data are available to illuminate the differences. In the case of intermittent exposures, peak exposures and averages over time should be considered. 

MAK [Maximale Arbeitsplatzkonzentration (Maximum Worlq)lace Concentration)] (Deutsche Forschungsgemeinschaft (German Research Association), 2007) is defined analogous to the ACGIH-TLV-TWA. Two exposure peaks/work shift above the MAK are allowed, but the TWA must be maintained. 

Davis JM, Beckett ST, Bolton RE, et al. 1980a. The effects of intermittent high asbestos exposure (peak dose levels) on the lungs of rats. Br J Exp Pathol 61 272-280. 

Of 289 patients exposed to excessive doses of methylphenidate, 31% had symptoms, including most commonly tachycardia, agitation, and lethargy (41). No patient developed severe symptoms, although there was a less favorable outcome with intentional versus unintentional exposure. Peak exposure occurred in 6- to 9-year-old children, in whom therapeutic error was the most common reason for exposure. 

There was no information available on the distribution of PAHs in humans. PAHs appear to be widely distributed in tissues of animals following oral and inhalation exposure peak tissue concentrations occurred earlier with higher exposure levels. Placental transfer of PAHs appears to be limited, and therefore, fetal levels are not as high as maternal levels. 

Human Toxicology. Male volunteer subjects acutely exposed to 70 mg m cinnamic acid for 10 min had only transient minimal irritant symptoms (slight excess lacrimation, mild rhinorrhea, and bouts of nonproductive coughing) with minor increases in breathing rate, tidal volume, and minute volume, which remrned to control values within 5-10 min of the end of exposure peak flow rate, forced vital capacity, and forced expiratory volume were not significantly altered. Pre- and postexposure chest radiographs were normal (Ballantyne and Clifford, 1978). 

Collection of additional information on possible exposure scenarios (including exposure peaks, comparison with similar plants, first measurements etc.). 

Since monitoring is often of time weighted average exposures, peak exposures and therefore possible risks of OPS may be missed. 

The results of exposure of PnBA in the QUV apparatus were measured by FTIR difference spectra typical spectra are shown in Figure A. These spectra were obtained by computer subtraction of the spectrum of unexposed PnBA from the spectrum of PnBA taken after exposure. Peaks below the baseline indicate a decrease in those functional groups while peaks extending above the baseline indicate a gain in those groups. 

In order to determine exposure peaks, special sampHng techniques have to be used. Normal long-term sampling methods for shift concentrations are not suitable without applying modifications. If the measurement time significantiy exceeds the exposure time, it is not possible to draw conclusions about the real exposure level. The sampling time should be exactly matched to the exposure time. Sometimes the real exposure times can be determined by use of directly indicating measurement devices like FID or PID instruments. 

In the European community, the occupational exposure level is defined as the limit of the time-weighted average of a chemical agent in the air within the breathing zone of a worker in relation to a specified reference period, usually 8 h or a work shift. In addition, to avoid adverse health effects, there is a need to set limits for short-term exposure peaks. In the occupational safety legislation of most countries within the European Community the lists of occupational exposure levels include limits for short-term exposure for many substances, either in the form of definite concentration values or so-called short-term exposure factors. In case of factors, the allowed maximum short-term concentration is calculated by multipHca-tion of the OEL by the short-term exposure factor. Typically, many hazardous substances have factors within the range of 1-4. 

With all short-term tasks, an exposure peak has to be taken into consideration, which requires control of compHance with short-term exposure hmits. If a mixture of several substances is present in the air, thermodesorption is an especially suitable method for control of short-term exposure because it provides low detection limits. 

Pig. 7.6 NMR spectra for modified support before and after CO2 exposure (peak assignments are shown in Fig. 7.7). Reprinted from Ref. [48], Copyright 2011, with permission from Elsevier... 

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