Information on human time-activity patterns is often required to interpret environmental exposure data fully and to implement exposure assessment models. Data on short-term time-activity patterns for individuals, such as 1-day measurements, are relatively abundant. The reliability of such data for use in chronic exposure (e.g., 1 or more years) assessments performed for evaluation of health risks is not well understood. As part of the NHEXAS-Maryland investigation, daily time budget data for seven microenvironments were collected from 80 people during as many as six 1-week Cycles over a 12-month period. The data were summarized and analyzed statistically by sampling Cycle, day of week, and individual to characterize long-term average microenvironmental time budgets and to identify their determinants. Median times spent in transit, indoors at home, outside at home, indoors at work or school, outdoors at work or school, indoors at other locations, and outdoors at other locations were found to vary significantly, although not substantively in many cases, by time of year (i.e., Cycle), by day of week, and by individuals. Time budgets for most of the microenvironments also exhibited significant variability by gender, age group, education level, annual household income, and work status. The results indicate that short-term (e.g., 1-day) measures of microenvironmental time budgets for individuals are unlikely to be representative of their long-term patterns. Thus, health risk or epidemiological assessments performed for a population mean or specific quantile may be relatively insensitive to when time budget data were collected. However, the accuracy of such assessments performed for individuals is likely to be greatly improved by collection of time budget data from numerous points in time.

Longitudinal information on human activity patterns is required to perform reliable assessments of chronic exposure to pesticides in nonoccupational settings. As part of a longitudinal, multimedia exposure survey in Maryland, USA, we collected 2521 person -days of information on the frequency of five activities that are potentially important to pesticide exposure in residential settings: preparation of pesticides; application of pesticides; contact with soil on the skin; contact with grass on the skin; and contact with carpet. Logistic regression was used to evaluate the data for variability by time of year, day of week, and several demographic factors. Eight percent of the population reported preparing pesticides on at least one occasion over the year, while 24% of the population applied pesticides at least once. The majority of the population reported contact with soil ( 68% ), grass ( 72% ), and carpet ( 64% ) over the course of a year. Skin contact with soil and grass was found to occur approximately twice as frequently ( p < 0.001 ) in spring and summer periods than in fall and winter periods. Similarly, contact with soil and grass was about 50% ( p < 0.05 ) more likely to occur on weekend days than on weekdays. These results indicate that short -term measurements ( e.g., 1 -day or 1 -week ) of these activities for an individual may not be equivalent to long -term average patterns. We also found that selected demographic characteristics were significant predictors of several of these activities. Thus, some demographic characteristics may be useful in categorizing exposure although it is unlikely that a single short -term measurement will suffice to describe annual average activity or multiple short -term activity periods.