Physiological daily inhalation rates for free-living individuals aged 1 month to 96 years, using data from doubly labeled water measurements:: A proposal for air quality criteria, standard calculations and health risk assessment

Reported disappearance rates of oral doses of doubly labeled water ((H2O)-H-2 and (H2O)-O-18) in urine, monitored by gas-isotope-ratio mass spectrometry for an aggregate period of over 30,000 days and completed with indirect calorimetry and nutritional balance measurements, have been used to determine physiological daily inhalation rates for 2210 individuals aged 3 weeks to 96 years. Rates in m(3)/kg-day for healthy normal-weight individuals (n = 1252) were higher by 6 to 21% compared to their overweight/ obese counterparts ( n = 679). Rates for healthy normal-weight males and females drop by about 66 to 75% within the course of a lifetime. Infants and children between the age of 3 weeks to less than 7 years inhale 1.6 to 4.3 times more air (0.395 +/- 0.048 to 0.739 +/- 0.071 m(3)/kg-day, mean +/- S. D., n = 581) than adults aged 23 to 96 years (0.172 +/- 0.037 to 0.247 +/- 0.039 m(3)/kg-day, n = 388). The 99th percentile rate of 0.725 m(3)/kg-day based on measurements for boys aged 2.6 to less than 6 months is recommended for air quality criteria and standard calculation for non-carcinogenic compounds pertaining to individuals of any age or gender ( normality confirmed using the Shapiro-Wilk test, p = 0.05). This rate is 2.5-fold more protective than the daily inhalation estimate of 0.286 m(3)/kg-day published by the Federal Register in 1980 (i.e., 20 m(3)/day for a 70-kg adult). It ensures that very few newborns aged 1 month and younger, less than 1% of infants aged 2.6 to less than 6 months and of course no older individuals up to 96 years of age inhale more toxic chemicals than the associated reference dose, when air concentration reaches the resulting air quality criteria and standard values. This rate is also protective for underweight, overweight, and obese individuals. Finally, as far as newborns are concerned, a rate of 0.956 m(3)/kg-day based on the 99th percentile estimates is recommended for short-term criteria and standard calculations for toxic chemicals that yield adverse effects over instantaneous to short-term duration.