The Physical Environment
Exposure to an environmental agent is the
first step in a sequence of environmentally
related health effects. Exposure may occur
at any point as people move through several
environments during the course of a
day. Adult environments include home,
work, and errands outside home and
work. Infants and children spend time at
home, school, day care, and play. Because
the environments of children are typically
different from those of adults and may
vary according to the age of the child, children’s
exposure to environmental agents
may be different from exposures of adults
and may vary with the developmental stage
of the child. In addition, different patterns
of exposure to a toxin may yield different health effects. For example, nitrates in
well water may cause the hemoglobin in
blood to become methemoglobin. If too
many nitrates are ingested, this chemical
change can cause insufficient oxygen to
reach the body tissues.2 However, if the
nitrates are ingested at a rate that is slow
enough for the enzymes in the blood to
convert the methemoglobin back to
hemoglobin, no health effect will occur.