A traditional way to directly monitor the amount of pesticide that people eat relies on collecting and analyzing samples of duplicate meals prepared at home by study participants. New insights into this approach may make the study method even more useful to researchers [EHP 109:145-150]. Environmental scientist David Macintosh of the University of Georgia at Athens and colleagues find that the duplicate' meal strategy shows a seasonal variation in the average concentration of pesticide found in foods throughout the year. Moreover, the amount of pesticide ingested by an individual varies widely from sampling to sampling.
Seventy-five participants, ages 12-84 years, prepared duplicate home meals for four consecutive days. Samples of each of the four meals were blended into a composite for each person, then analyzed by gas-liquid chromatography. In 379 food samples collected during six sampling periods spaced throughout 12 months, the researchers measured seven organochlorine pesticides no longer in use but still of concern because of their persistence in the environment (including DDT), two organophosphorus insecticides commonly used in agricultural and home settings (malathion and chlorpyrifos), and one triazine herbicide (atrazine).
Three pesticides--malathion, chlorpyrifos, and p,p'-DDE--were detected in at least 20% of all the food samples. Depending on the time of year, average concentrations of these pesticides differed two- to threefold, with the highest concentrations detectable in spring and summer, and the lowest concentrations in the winter months. Overall, 75% of the food samples contained malathion at a mean concentration of 1.8 micrograms per kilogram (pg/kg) of food, 38% contained chlorpyrifos at a mean concentration of 0.7 [micro]g/kg, and 21% contained p,p'-DDE at a mean concentration of 0.2 [micro]g/kg. These corresponding exposure concentrations are up to 100-fold lower than safety limits set by the U.S. Environmental Protection Agency and the World Health Organization--a pleasant surprise to the researchers, who consider the amounts to present no health concerns.
Furthermore, pesticide concentrations for individuals varied from one sampling time to another. For example, for one person, chlorpyrifos concentrations ranged from nondetectable in one sample to 24 [micro]g/kg in another. Therefore, pesticide concentrations in a single sample from an individual are not a reliable indicator of concentrations in other composite samples of their food. This is the first time that seasonal variation and individual fluctuation of dietary pesticide exposure have been reported in a study of this size.
Future researchers can obtain better information on pesticide consumption more economically by paying attention to the time of year in which samples are collected. For instance, if researchers want to capture the maximum short-term exposure to organophosphorus pesticides in the diet, they should sample in the summertime. If they're after long-term average exposure, food samples need to be monitored throughout the year.
The researchers also suggest that epidemiologists, who are concerned with the health outcomes of pesticide exposure, can use this new information in the design of future studies. Knowing that a onetime sampling does not give a reliable measure of intermediate or long-term exposure, epidemiologists can address the reliability issue by either enrolling more people in a study, obtaining repeated measurements, or making statistical adjustments to risk estimates to compensate for low reliability.