Exposure factors defined

When developing the list of substances, EPA considered only the inherent characteristics of a chemical that indicate a severe threat due to exposure. Well-defined criteria were used for toxicity and flammability. However, because of the complexities of site-specific factors and process conditions, EPA was unable to determine any inherent characteristic as an indicator of reactivity. EPA concluded that there was insufficient technical information for developing criteria for identifying reactive substances. 46 Consequently, the January 1994 RMP list of 130 chemicals does not contain any substances listed due to reactive hazards. 

A Dutch smdy (Wilschut et al. 1998, as reviewed in Vermeire et al. 1999) has evaluated route-to-route extrapolation on the basis of absorption or acute toxicity data. Data were collected primarily on dermal and inhalation repeated dose toxicity. An extrapolation factor, defined as the factor that is applied in route-to-route extrapolation to account for differences in the expression of systemic toxicity between exposure routes, was determined for each substance by using data on absorption and acute toxicity data. As experimental data on absorption often were not available, default values for absorption were also used to determine an extrapolation factor. Despite a rather large overall database, relatively few data could be used for the evaluation and the selection criteria were modified in order to include data that initially were considered less suitable for data analysis interspecies extrapolation based on caloric demands was introduced, and a factor of 3 was applied in case a LOAEL instead of a NOAEL was available. The choice of NOAELs for different exposure routes known for a substance suitable for analysis was based primarily on the same effect, but this criterion could not be maintained. 

All of the previously mentioned exposure methods can be used to estimate either chronic exposure (over a period of years) or acute exposure (single day) for the United States population and population subgroups. Both chronic and acute assessments are usually based on a no observed adverse effect level (NOAEL) in an animal species. Acute exposure is defined relative to an acute (single dose) toxicological endpoint (usually a NOAEL) and may be expressed as a margin of exposure (MOE) or as a percentage of an acute reference dose that is based on a NOAEL and an uncertainty factor (see below). 

This case-study addresses the problem of defining, characterizing and propagating uncertainty in an exposure model. Uncertainty analysis is used to assess the impact of data precision on model predictions. A common complaint associated with worst-case approaches to risk assessment is that the use of highly conservative values for each input variable results in significant overestimation of actual risk and/or exposure factors. 

Sievert (Sv) It is a more modem unit that substitutes the rem, as it reflects the biological effect of radiation. It is defined as the absorbed dose in Gy multiplied by a somewhat complicated factor that takes into account for example the quality factor defined above, the part of the body irradiated and the time and volume of exposure. 1 Sv = 100 rems. 

ADIs using LOAELs (if NOAELs are unavailable). This uncertainty factor defines an exposure level below the LOAEL expected to be in the range of a NOAEL. 

Required by OSHA, the employer must provide protection against the effects of noise exposure when the sound levels exceed those shown in Table 8.7. When the daily noise exposure consists of two or more periods of noise exposure at different levels, their combined effect should be considered rather than the individual effects of each. According to OSHA the exposure factor (EF) is defined as [5] ... 

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. 

Moore and Garg (1994) compared exposure factors for jobs associated with WUEDs to jobs without prevalence of such disorders. They found that the intensity of exertion, estimated as a percentage of maximal strength and adjusted for wrist posture and speed of work, was the major discriminating factor. The relationship between the incidence rate for distal upper-extremity disorder and the job risk factors was defined as follows ... 

EPA s Office of Toxic Substances made the following statement concerning the importance of this type of exposure estimation in a recent strategy document (S8) In all decisions under TSCA, the relative risk presented by a chemical will weigh heavily. Two principal factors define risk potential adverse effects... 

Chapter 12 presents a critical discussion of Pb neurotoxicity in human populations. This is broadly held to be the most significant toxic expression of Pb exposures in sensitive human populations, notably developmental neurotoxicity in utero and in the early postnatal developmental window in infants, toddlers, and even older children. Two factors defining effect... 

Ha2ard is the likelihood that the known toxicity of a material will be exhibited under specific conditions of use. It follows that the toxicity of a material, ie, its potential to produce injury, is but one of many considerations to be taken into account in assessment procedures with respect to defining ha2ard. The following are equally important factors that need to be considered physicochemical properties of the material use pattern of the material and characteristics of the environment where the material is handled source of exposure, normal and accidental control measures used to regulate exposure the duration, magnitude, and frequency of exposure route of exposure and physical nature of exposure conditions, eg, gas, aerosol, or Hquid population exposed and variabiUty in exposure conditions and experience with exposed human populations. 

The stringent requirements covering oxidation stability are defined by the test method DIN 51352, Part 2, known as the Pneurop Oxidation Test (POT). This test simulates the oxidizing effects of high temperature, intimate exposure to air, and the presence of iron oxide, which acts as catalyst - all factors highly conducive to the chemical breakdown of oil, and the consequent formation of deposits that can lead to fire and explosion. 

Some established cell lines were derived from malignant tissue. Many of these cell lines can form tumors when injected into susceptible animals. Other established cell lines are not Uunorigenic. However, exposure to carcinogens, and irradiation can cause these cells to form tumors in susceptible animals. In addition, transformation can be caused by spontaneous mutations, by growth factors, and by viral (or oncogenic) transformation (Table 6). Malignant transformation is defined as consisting of the series of events that cause normal cells to develop the capacity to form tumors. 

NOAEL (no-observed-adverse-effect level) is defined as the highest dose at which no adverse effects are observed in the most susceptible animal species. The NOAEL is used as a basis for setting human safety standards for acceptable daily intakes (ADIs), taking into account uncertainty factors for extrapolation from animals to humans and inter-individual variabilities of humans. The adequacy of any margin of safety or margin of exposure must consider the nature and quality of the available hazard identification and dose-response data and the reliability and relevance of the exposure estimations. In some cases, no adverse endpoint can be identified such as for many naturally occurring compounds that are widespread in foods. In that case, an ADI Not Specified is assigned. ... 

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