DEPOSITION OF FINE PARTICLES IN CHILDREN SPONTANEOUSLY BREATHING AT REST

Recent epidemiological studies suggest that children may be more susce ptible than adults to effects of inhaled particulate matter. To determ ine if children receive an increased lung dose of particles compared t o adults we measured fractional deposition (DF) of fine particles in c hildren, age 7-4 yr (n = 16), adolescents, age 74-18 yr (n = 11), and adults, age 19-35 yr (n = 12). Each subject inhaled 2-mu m monodispers e Carnauba wax particles while following a breathing pattern previousl y determined by respiratory inductance plethysmography for that subjec t (i.e., that subject's spontaneous pattern at rest). Breath-by-breath DF (ratio of particles not exhaled/total particles inhaled) was deter mined by photometry at the mouth. Among the children there was no vari ation in DF with subject age or height, but DF was dependent on inters ubject variation in tidal volume (V-t) (p <.001). DF for the children versus the adolescents was 0.22 +/- 0.08(sd) and 0.20 +/- 0.03, respec tively (NS), also not different from the adults, DF = 0.22 +/- 0.09. O n the other hand, the rate of deposition normalized to lung surface ar ea, nD(rate) tended to be greater (35%) in the children versus the com bined group of adolescents and adults for resting breathing of these p articles (p =.07). The variable nD(rate) is a function of the DF, the subject's minute ventilation, and his or her lung size. The increase i n nD(rate) in the children is due to their higher minute ventilation i n relation to their lung size. These results may prove useful in deter mining age-relative risks that may be associated with the inhalation o f pollutant particles in ambient air.