Exposure characterization

The approach to exposure assessment is not as internationally harmonized as hazard assessment. A synopsis of current activities regarding exposure assessment for industrial chemicals in a number of OECD Member countries has been published (OECD 2006). The executive summary of this document states that while there is a significant level of sharing of approaches used for hazard characterization for risk assessment, this is not the case for exposure characterization. Although broad consistency in the overall approaches used by different countries in conducting exposure assessment exists, there is variation in policy-related factors, including the regulatory context for assessment and the way that information is applied, as well as in the types of approaches and tools used. 

Total allocations of less than 100% of the tolerable intake are recommended to account for, e.g., those media for which exposure has not been characterized, and cross-route exposure. The proportion of the total intake, which is not allocated, should vary according to the adequacy of the exposure characterization from all media. 

In exposure characterization, credible and relevant data are analyzed to describe the source(s) of stressors, the distribution of stressors in the environment, and the contact or co-occurrence of stressors with ecological receptors. An exposure profile is developed that identifies receptors and exposure pathways, describes the intensity and spatial and temporal extent of exposure, describes the impact of variability and uncertainty on exposure estimates, and presents a conclusion about the likelihood that exposure will occur. 

TVOC is an indicator for the presence of VOCs indoors. The TVOC indicator can be used in relation to exposure characterization and source identification but for VOCs only. In risk assessment, the TVOC indicator can only be used as a... 

Travis, K.Z. and P. Hendley (2001). Probabilistic aquatic risk assessment of pyrethroids IV. Landscape-level exposure characterization. Environ. Toxicol. Chem., 20 679-686. 

The ecological risk assessment was conducted in accordance with the USEPA guidance document Guidelines for Ecological Risk Assessment (USEPA, 1998) . A four-step assessment process was adopted problem formulation, exposure characterization, characterization of ecological effects and risk evaluation. 

Comparative Toxicokinetics. The animal data indicate that the nervous system is a sensitive target of toxicity for aluminum following oral exposure, as summarized in the Data Needs sections on Neurotoxicity. Although the interpretation of the human data is limited by poor exposure characterization, the occupational exposure studies suggest that neurotoxicity is also a sensitive end point following inhalation exposure (Hanninen et al. 1974 Hosovski et al. 1990 Rifat et al. 1990 Sim et al. 1997 Sjogren et al. 1996 White et al. 1992). The toxicokinetic properties of aluminum have been extensively studied in human and animals. The results of these studies suggest that the absorption, distribution, and excretion properties of aluminum are similar across species. 

BENEFITS OF USING PROBABILISTIC TECHNIQUES INSTEAD OF DEFAULT CONSTANTS 307 PROBABILISTIC EXPOSURE CHARACTERIZATION 308 POPULATIONS OF INDIVIDUALS 310 CONCLUSIONS AND RECOMMENDATIONS 312 REFERENCES 313... 

Risk characterization is a combination of two components (1) a toxicological characterization of each pesticide having a common mechanism for the given toxicity endpoint and exposure duration, and (2) the exposure characterization for a specified population. Exposure characterization is illustrated in the case study and is also discussed later in this chapter. The methodology for combining the exposure characterization with the toxicological information to form the dose and risk characterizations is discussed in the remainder of this section. 

Monte Carlo techniques allow the exposure characterizations for the different subpopulations to be properly aggregated into a population characterization which reflects the relative subpopulation sizes and the different exposure distributions in each subpopulation without having to assume the worst-case for the population or a specific subpopulation. For example, Figure 8.8 shows how the population of herbicide handlers involved in the production of com crops is related to its component subpopulations. The Monte Carlo simulation for the population of herbicide handlers involved in the production of com crops can be carried out in such a way that 97 % of the iterations in the simulation are expected to be for Grower and 3% for Commercial , and among the iterations for Grower one-third are expected to be for Mixer/Loader , etc. Thus, a Monte Carlo simulation correctly characterizes a population by sampling its... 

Three experimental units each with different experimental focus were designed, fabricated and delivered to NASA Langley. The first unit contains four passive and four active films samples to be exposed to combined atomic oxygen and vacuum UV. The second unit contains 11 passive and four active samples to be exposed only to vacuum UV (see Fig. 2). The third unit has two passive samples with different thicknesses of protective aluminum layers to be exposed to atomic oxygen and vacuum UV. All passive samples will be characterized, both in terms of chemical and physical properties, after the mission and compared with pre-exposure characterization to determine the effects of the space environmental exposure. Thin foil-type thermocouples are attached and logged underneath the samples to measure actual temperatures experienced. By recording the temperature it will be possible to correlate the deflection properties with temperature conditions of the active samples. 

Waldman J (1995) Approaches for exposure characterization and data needs for hazardous waste site assessment. Environmental Health Perspectives 103 99-104. 

Being able to predict the human health risk from exposure to airborne chemicals can be complex, requiring reliable analysis of human exposure. While the basic principles of risk assessment are applicable to various conditions of exposure, characterizing how an individual s health status can significantly influence the threshold for effects can be a most challenging component of the risk assessment process. One needs to consider the overall scientific weight-of-evidence to predict whether or not an individual may be uniquely susceptible to certain... 

Another approach to evaluating exposure uses chemical, biochemical, or physiological evidence (e.g., biomarkers) of a previous exposure. This approach has been used primarily for assessing chemical exposures and is particularly useful when a residue or biomarker is diagnostic of exposure to a particular chemical. These types of measurements are most useful for exposure characterization when they can be quantitatively linked to the amount of stressor originally contacted by the organism. Pharmacokinetic models are sometimes used to provide this linkage. 

Fajen JM, McCammon CS. 1988. Exposure characterization study of workers exposed to hydrazines. Cincinnati, OH National Institute for Occupational Safety and Health. 261-295. 

Vena, J State University of New York at Buffalo Buffalo, New York The New York Angler Study Exposure characterization and reproductive and developmental health... 

Mendola P, Vena JE, Buck GM. 1995b. Exposure characterization, reproductive and developmental health in the New York State angler cohort study. Great Lakes Res Rev 1(2) 41 3. 

Vena JE, Buck GM, Kostyniak P, et al. 1996. The New York angler cohort study Exposure characterization and reproductive and developmental health. Toxicol Ind Health 12 (3-4) 327-334. 

Two studies in school children (He et al. 1994 Zhang et al. 1995) showed that over-exposure to manganese in drinking water and food was associated with poorer performance in school and on neurobehavioral tests as compared to non-exposed children. The exposed and control children in these studies were reportedly well-matched and the reports indicated that hair manganese was inversely related to performance on neurobehavioral exams and in school. However, there were several limitations in the reporting of the study, including the lack of analysis for lead or mercury, which are neurotoxins, and the lack of definitive exposure characterization. 

The analysis phase is directed by the products of the problem formulation and is further divided into characterization of exposure and characterization of effects steps. Exposure characterization uses the properties of the chemicals and the receiving environment to estimate the extent to which the organisms will be exposed. Effects characterization determines the effects of varying dose or other measures of exposure on organisms, populations or communities. 

A modifying factor (MF) may also be applied to the calculation of an RfD to account for uncertainties that are not specifically addressed by the individual UFs. For example, deficiencies in the key study, such as a statistically minimal sample size or poor exposure characterization, may warrant the use of an MF greater than 1. Conversely, allowance is made for the use of an MF of less than 1 if the use of the standard default UFs results in a RfD that, in the professional judgment of the risk assessors, is excessively low this might occur in the case of essential elements. If all the uncertainties in the derivation of a RfD are addressed by the use of the five Uncertainty Factors, then the default value for the MF is 1. 

Bausano, )., Boyd, S., Lesko, )., and Case, S.W. (2004) Composite life under sustained compression and one-sided simulated fire exposure characterization and prediction. Proceeding of the International SAMPE Symposium, Long Beach, CA, 2004 [CD ROM]. 

Composite life under sustained compression and one-sided simulated fire exposure characterization and prediction. Composites Part A, 37 (7), 1092-1100. 

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