Review and Analysis of Inhalation Dosimetry Methods for Application to Children’s Risk Assessment

Abstract

Young children have a greater ventilation rate per body weight or pulmonary surface area as compared to adults. The implications of this difference for inhalation dosimetry and children's risk assessment were evaluated in runs of the U.S. Environmental Protection Agency (U.S. EPA) 1994 reference concentration (RfC) methodology and the ICRP 1994 inhalation dosimetry model. Dosimetry estimates were made for 3-mo-old children and adults for particles and Category 1 and 2 reactive gases in the following respiratory-tract regions: extrathoracic (ET), tracheobronchial (BB), bronchioles (bb), and pulmonary (PU). Systemic dosimetry estimates were made for nonreactive (Category 3) gases. Results suggest similar ET dosimetry for children and adults for all types of inhaled materials. BB dosimetry was also similar across age groups except that the dosimetry of ultrafine particles in this region was twofold greater in 3-mo-old children than in adults. In contrast, the bb region generally showed higher dosimetry of particles and gases in adults than in children. Particle dose in the PU region was two- to fourfold higher in 3-mo-old children, with the greatest child/adult difference occurring for submicron size particles. Particulate dosimetry estimates with the default RfC methodology were below those found with the ICRP model for both adults and children for submicrometer sized particles. There were no cases in which reactive gas dosimetry was substantially greater in the respiratory regions of 3-mo-old children. Estimates of systemic dose of Category 3 gases were greater in 3-mo-old children than in adults, especially for liver dose of metabolite for rapidly metabolized gases. These analyses support the approach of assuming twofold greater inhalation dose in children than adults, although there are cases in which this differential can be greater and others where it can be less.

Enhancement of ICRP's Lung Deposition Model for Pathogenic Bioaerosols

“…It is evident from Figure 3d that infants, for all pathogens studied here, appear to be at a greater risk compared to adults. These findings for infants are consistent with prior studies done with polydisperse radionuclides using the ICRP model (Ginsberg et al 2005) and reactive gases using the NCRP model (Ginsberg et al 2008). Interestingly, our studies are also consistent with Cho et al (2005) who found significantly more deposition of different species of fungi in the lower airways of infants compared to adults.…”

“…The surface areas of the extrathoracic, tracheobronchial, and alveolar regions for 176 cm adults are 160, 2363, and 777417 cm 2 , respectively, while for 60-cm infants they are 40, 1570, 37704 cm 2 , respectively (Ginsberg et al 2005(Ginsberg et al , 2010. Again, as in Figure 3c, the upper bounds of NRDA i are plotted for three different bioaerosols in Figure 3d.…”

“…Given the significantly lower breathing flow rates in infants, the normalized dose ET, TB, Al, and TD are lower for all bioaerosols. However, infants and children have significantly smaller lung and lung area compared to adults (ICRP 1994;Ginsberg et al 2005Ginsberg et al , 2008Ginsberg et al , 2010. Thus to compare the lung loading among infants and adults, the numerator and denominator of Equation (22) are divided with the respective lung surface areas (A i ) to get the normalized relative dose per unit area (NRDA) at section i:…”

Expressing urine from a gel disposable diaper for biomonitoring using phthalates as an example

“…Therefore, infants potentially receive a greater exposure of lung surface to airborne compounds on a body weight basis (Bennett et al, 1996). Ginsberg et al (2005) indicated that the particle dose in the pulmonary region is also likely to be two to four times higher in three-month-old children than in adults, particularly for submicrometre-size particles. The skin surface area relative to body weight is greater in children than in adults, such that the potential dose received following dermal exposure is likely to be about three times greater in infants than in adults (Clewell et al, 2002).…”

New developments in aerosol dosimetry

“…Dosimetric modeling for children inhaling both gases and particles has been recently reviewed (Ginsberg et al, 2005(Ginsberg et al, , 2008Foos & Sonawane, 2008;. Children have age-dependent airway sizes, ventilation patterns, and time-activity behaviors, all of which potentially increase their air-pollutant doses over those of adults.…”