Applicators are likely to work for more than one grower in a season. Workers also could harvest celery for another grower when they are not harvesting broccoli; yet both crops could have been treated with the same pesticide.

In terms of long-term inhalation exposure, one cannot be too sure what the pattern of population or occupational mobility is. That is, how likely is a person living within the vicinity for years? Even if residents can be assumed to live in a community for years, there is still an uncertainty about how much time they stay indoors versus outdoors. Often times, the outdoor and indoor air levels are not the same. A six-year-old child can have very different oral exposure to a contaminant compared to a two-year-old. A three-year-old child may still stay home or in a day care center where meals are provided frequently. Yet a six-year-old would spend more time learning in school.