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|In its simplest
form as first suggested in Slide 7, [inhalation exposure] = [air concentration]
x [inhalation rate] x [exposure duration]. The product of the last two terms
in this algorithm may be referred to as a time-related inhalation volume. In this case
with a six-year-old child having spent some time at a playground treated with a wood
preservative, three to four sources of air concentration (typically in m
g/m3 or h g/m3) may need to be
These sources should include: (a) outdoor air at playground; (b) outdoor air away from playground; (c) daytime indoor air; and (d) nighttime indoor air. The indoor air levels between daytime and nighttime might be different in that the toxin or contaminant could also come from shower water or cigarette smoking, which the child could be exposed to while awake.
The inhalation rates for a six-year-old child could vary within the course of a day. Their inhalation rate (typically in m3/hr) at night during resting is often considered to be 2 to 3 times lower than that at other times when they are more active. When the hourly inhalation rate and the air level are multiplied within each activity category, this will give only the air inhaled from that activity for one hour. The exposure duration for each activity must therefore be determined and considered in order to account for the total air inhaled from the total time spent in that activity. The exposure intervals for all activities included in a full day should add up to 24 hours. Another factor that needs to be considered for calculation of the applied dose from the respiratory route is inhalation uptake (that inhaled portion brought to the lungs for intake).