Exposure frequency

Sampling needs vary with the batch being run. Use of same equipment/procedure may lead to operator exposure. Frequency of manual sampling is much higher than in continuous plants. 

Key to fiaure Species Exposure frequency/ duration System NOAEL (ppm) Less serious (ppm) LOAEL (effect) Reference... 

Key to Exposure frequency/ NOAEL LOAEL (effect) Less serious Serious ... 

Exposure Frequency/Duration The duration of the study and the weekly and daily exposure regimen are provided in this column. This permits comparison of NOAELs and LOAELs from different studies. In this case (key number 18). rats were exposed to [substance x] via inhalation for 13 weeks, 5 days per week, for 6 hours per day. 

Key to figure Species Exposure frequency/ durat ion Systett NOAEL (ppm)... 

Paulet and Desbrousses (1970) exposed groups of 10 rats/sex (strain not specified) to chlorine dioxide vapors at a concentrations of 0 or 2.5 ppm (6.9 mg/m ), 7 hours/day for 30 days. The weekly exposure frequency was not reported. Chlorine dioxide-exposed rats exhibited respiratory effects that included lymphocytic infiltration of the alveolar spaces, alveolar vascular congestion, hemorrhagic alveoli, epithelial erosions, and inflammatory infiltrations of the bronchi. The study authors also reported slightly decreased body weight gain and decreased erythrocyte and increased leukocyte levels, relative to controls. Recovery from the pulmonary lesions was apparent in rats examined after a 15-day recovery period. 

Exposure Frequency/Duration The duration of the study and the weekly and... 

EF - Exposure frequency (EF), or frequency of mouthing events Visual observation or videotape events/day... 

The application of human data in risk assessment for children has been detailed in a number of publications (USEPA, 1991 Richter-Reichhelm et al., 2002 IPCS, 2005 Kimmel et al., 2006). In general, the risk assessor should evaluate each human study for its power and potential bias. The power of the study is the study s ability to detect an effect. It is dependent on the size of the study population, the frequency of the effect or the exposure in the population, and the level of risk to be identified. The greater the population size and the effect or exposure frequency, the greater the power of the study. In studies of low power, it is generally not possible to establish the lack of an association between an exposure and an effect, and even positive findings may be difficult to support. Metaanalysis, which combines populations from different studies, may increase the power of the overall database, but the potential for the combination of dissimilar populations must be considered in any risk assessment. 

Similarly, exact solutions can be obtained for products (or quotients) of lognormal distributions (e.g. Burmaster Thompson, 1995). This situation may be possible for some simple exposure assessments if one is working with one equation, such as the product of intake rate, concentration in the intake media (e.g. air, liquid), exposure duration and exposure frequency, divided by an averaging time and body weight, as long as all of the input distributions are lognormal. 

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