Indoor Allergens Assessing and Controlling Adverse Health Effects (1993) / Chapter Skim
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6 Assessing Exposure and Risk
6 Assessing Exposure and Risk
Pages 185-205
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From page 185... ...
The risk assessment section describes the general nature of the process, including exposure assessment, and presents an example that uses dust mite exposure data in assessing the risk of sensitization. EXPOSURE ASSESSMENT Assessing exposure involves numerous techniques to identify contaminants, contaminant sources, environmental exposure media, transport through each medium, chemical and physical transformations of the contaminant, routes of entry to the body, intensity and frequency of contact, and spatial and temporal concentration patterns of the contaminant (NRC, 19911.
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From page 186... ...
ii:::..:, : a. ::#::: :~ Host factors 1 , Biologically Effective Dose (to Critical Target Tissues)
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From page 187... ...
Measurements can be semiquantitative (e.g., "presence or absence" or "low, medium, or highs or, alternatively, modes can be chosen for sampling and analysis that will give accurate, precise documentation for a specific population regarding a more or less well-defined allergen. Although monoclonal antibody immunoassays measure specific allergens, most allergen monitoring includes sampling for indicators rather than the actual aerosolized allergen.
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From page 188... ...
As a substitute, multiple discrete samples can be taken over relatively short periods of time, or long-term samples can be taken and analyzed as a time-weighted average or in discrete units. Sampling for allergens always occurs in a complex environment, and consideration must be given to factors that might modify source strengths, emission rates, accuracy and precision of sample collection, or sample analysis methods and health effects (O'Rourke et al., 1990~.
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From page 189... ...
Air sample collection involves drawing a representative sample of the aerosol into a collection device and removing particles in an unbiased way and in a form that allows appropriate analysis. Volumetric air samples for indoor allergen analysis are usually collected by suction devices.
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From page 190... ...
Modifications of the Hirst spore trap (the Burkard, Kramer-Collins, and Lanzoni spore traps [Solomon et al., 1980bl) are increasingly used for evaluating outdoor allergen aerosols.
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From page 191... ...
. Suction samplers that collect particles by filtration efficiently trap all particles above the rated pore size of the filter.
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From page 192... ...
Sample methods that allow microscopic evaluation include suction impaction (as used in the Burkard and Lanzoni spore traps) and rotating impactors (the rotorod)
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From page 193... ...
Water samples are commonly analyzed for bacterial content using the fluorescent dye acridine orange, which stains nucleic acids inside the bacterial cells (Palmgren et al., 19861. The melanin pigments in many fungus spores mask this fluorescence, and some fungal spore walls apparently prevent entry of the dye.
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From page 194... ...
Exposure AS mentioned earlier in this chapter, many of the methods used for estimating environmental concentrations of aeroallergens are not truly representative of an individual's exposure to actual allergens. For example, ambient air monitoring is often used to represent personal exposure, and indicators rather than specific inhalable allergens are usually monitored.
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From page 195... ...
Use of this technique requires the collection of sufficient mass to measure concentration reliably, a difficult task for aerosols as transient as those of mite fecal particles. Inhaled allergens from other sources can also differ from generally measured arthropods, particles, grains or spores.
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From page 196... ...
RISK ASSESSMENT In general, risk assessment is a process designed to evaluate the potential relationship that may exist between exposure to a particular agent, e.g., aeroallergen, and a particular effect, e.g., sensitization or allergic disease. This section describes a number of issues that may be considered in conducting a risk assessment for aeroallergens and an example using data on environmental levels of dust mite allergen and the occurrence of sensitization.
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From page 197... ...
STEP 2: EXPOSURE ASSESSMENT The measurement of exposure to allergens is a rapidly advancing field. Instrumentation and approaches were described earlier in this chapter; this discussion summarizes some of the issues that arise in using aeroallergen exposure data for a risk assessment.
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From page 198... ...
The exposure-response relationship may be estimated when too little information is available to allow extrapolation from exposure to dose. For noncarcinogens, this effort has traditionally focused on identification of a "threshold exposure" below which no health effects are observed (Pierson et al., 19911; this threshold is now known as the No Observed Adverse Effect Level (NOAEL; Shoaf, 19914.
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From page 199... ...
For aeroallergens, this relationship might be expressed as the number of new cases expected at a given exposure level or the distribution of expected change in the severity of symptoms with changing exposure levels. Example of a Risk Assessment: Exposure to Dust Mite Allergen and Sensitization for Asthma STEP 1: HAZARD IDENTIFICATION When dust mites were first reported in the literature in the 1970s, it was suggested that levels of more than 500 mites/g of dust in a house were likely to produce symptoms of asthma in allergic individuals.
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From page 200... ...
compared children growing up in a suburb of Marseilles, which is a seaport, with those growing up in Brianc~on at an elevation of 6,000 feet. The average concentration of mite allergen in mattress dust from Marseilles was 15.8 ,ug/g, compared with 0.36 ,ug/g in Brianc~on.
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From page 201... ...
For the purposes of this example, sensitization was chosen as the endpoint. STEP 2: EXPOSURE ASSESSMENT Because the common allergens are thought to cause or exacerbate asthma by the inhalation route, measuring inhaled allergen might seem to be the best method for determining exposure (Price et al., 1990; Swanson et al., 1985; Tovey et al., 1981b)
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From page 202... ...
STEP 3: DOSE-RESPONSE ASSESSMENT Exposure is estimated in this example from several different studies that use slightly different protocols for reporting the results from reservoir sampling. For example, Sporik and colleagues (1990)
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From page 203... ...
FIGURE 6-3 An exposure-response analysis of dust mite allergens.
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From page 204... ...
For this reason, information on cross-reactivity of allergenic agents in study subjects is desirable, and important to the analysis of potential mechanisms of sensitization. Research Agenda Item: Determine whether a practical method could be developed to measure concentrations of dust mite allergens that are capable of sensitizing humans.
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From page 205... ...
Improved, standardized methods of collecting and analyzing indoor allergen samples would be particularly valuable in establishing the relationship between reservoir samples, personal exposure measures, levels of activity, and the potential for airborne exposure of sufficient magnitude to induce negative health outcomes. Research Agenda Item: Quantitate the relationship of allergens in reservoirs (and on surfaces)
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