Step 4: Risk Characterization

The equation developed from the exposure-response model can be rewritten as

(3)

or

(4)

Once the risk (percent sensitized) is set, the relationship can be solved for concentration in the reservoir, since the value of years will be known for a given population. Alternatively, if the duration and concentration are known, the risk (percent sensitized) can be estimated. For example, assuming 5 years of exposure at a concentration of 2 µg/g, the risk of sensitization would be 32 percent.

These calculations are based on data that were abstracted from reports by researchers using various methods, and must therefore be considered "soft"; the results are presented only as an example of how a risk assessment for sensitization could be performed.

CONCLUSIONS AND RECOMMENDATIONS

Some of the issues to be considered when undertaking a risk assessment for aeroallergens have been discussed and an example has been given by using data from the literature on dust mite exposure and the development of sensitization. The data can be described by a linear model and indicates that there is a positive relationship between cumulative exposure to dust mite allergen and the risk of sensitization.

Some residual sensitization (i.e., approximately 10 percent in this example) will occur irrespective of exposure to dust mite allergen according to these estimates. This finding is consistent with the knowledge that other factors may also result in sensitization. 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.

Variability in the methods used in the multiple study protocols reported to date is high. More uniformity in the collection of exposure data would be useful in the risk assessment process. Although reservoir sampling has yielded meaningful results that assist in remediating exposure, further development



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