Distribution of 2,4-D in air and on surfaces inside residences after lawn applications: comparing exposure estimates from various media for young children.

We collected indoor air, surface wipes (floors, table tops, and window sills), and floor dust samples at multiple locations within 11 occupied and two unoccupied homes both before and after lawn application of the herbicide 2,4-D. We measured residues 1 week before and after application. We used collected samples to determine transport routes of 2,4-D from the lawn into the homes, its subsequent distribution between the indoor surfaces, and air concentration as a function of airborne particle size. We used residue measurements to estimate potential exposures within these homes. After lawn application, 2,4-D was detected in indoor air and on all surfaces throughout all homes. Track-in by an active dog and by the homeowner applicator were the most significant factors for intrusion. Resuspension of floor dust was the major source of 2,4-D in indoor air, with highest levels of 2,4-D found in the particle size range of 2.5-10 [micro]m. Resuspended floor dust was also a major source of 2,4-D on tables and window sills. Estimated postapplication indoor exposure levels for young children from nondietary ingestion may be 1-10 [micro]g/day from contact with floors, and 0.2-30 [micro]g/day from contact with table tops. These are estimated to be about 10 times higher than the preapplication exposures. By comparison, dietary ingestion of 2,4-D is approximately 1.3 [micro]g/day. Key words:. 2,4-D, indoor air, particle size, pesticide exposure, pesticide transport, residential exposure. Environ Health Perspect 109:1185-1191 (2001). [Online 6 November 2001] http://ehpnet1.niehs.nih.gov/docs/2001/109p1185-1191nishioka/abstract.html

A recent review of occupational studies identified numerous cases in which workplace chemicals such as lead, asbestos, and dichlorobenzidine were transported from the workplace to the home. Analyses to document this transport included measurements made in home areas such as the laundry, in clean clothing drawers, and in house dust (1). In some cases, the levels of transported occupational chemicals were sufficiently high to cause an adverse health effect in a resident child or spouse. Other studies of the air and house dust of farmers' and farm workers' homes have shown that pesticide residues are transported from the outside to the indoor environment (2,3). In one study, organophosphate insecticides were detected in the house dust of pesticide applicators living adjacent to treated orchards, as well as in house dust of nonapplicator farm workers living more than 50 feet from the orchard, and in nearby homes of families not engaged in agricultural activities (2). Spray drift, volatilization, soil/foliar resuspension, track-in on shoes, and/or transport on clothing are assumed to have played important roles in the transport of pesticide residues in these agricultural studies.

Agricultural spray drift and residue resuspension rates have been measured for nonvolatile amine salt formulations of 2,4-dichlorophenoxyacetic acid (2,4-D) and dicamba (4-6). Because both mechanisms involve the airborne transport of submicronto micron-size particles and/or aerosols (7), it is reasonable to assume that fine particles containing 2,4-D can be resuspended from residential turf by wind, penetrate the exterior of the home through cracks and crevices, windows, and doors, and be deposited on interior surfaces. Field simulation studies following lawn applications of 2,4-D, chlorpyrifos, and chlorothalonil have shown that residential track-in of pesticide residues can occur, and that walking over treated turf as much as one week after application can transport residues on shoes from turf to carpets (8,9).

The study reported here was performed in single-story midwestern homes to determine the occurrence and distribution of 2,4-D residues on surfaces and in air within the home--before, during, and after the lawn application of this herbicide. We used these data to describe quantitatively the effects of transport factors and to estimate potential indoor residential exposures of young children. We took samples at seven occupied homes at which the homeowner had applied 2,4-D to the turf, at four occupied homes that had had commercial applications of the same herbicide, and at two nominally unoccupied homes that had had commercial application (e.g., in one unoccupied home, the builder's agent spent 4 hr/day answering the phone there, but entered the home via the garage).

Experimental Methods

Study design. We made assumptions to link sampling methods with both transport mechanisms and exposure pathways. First, specific sampling methods and sampling locations inside the home could be used to assess the magnitude and relative importance of both transport mechanisms and exposure pathways. Second, spray drift, intrusion of resuspended foliar residues, and track-in would contribute to indoor residue levels. Third, foliar resuspension intrusion might be detectable in indoor air on the third day after application; lacking that, this intrusion would cause detectable and equal deposition to floors, sills, and table tops throughout a house. Fourth, track-in would include residues brought in on the applicator's shoes and clothing as well as residues tracked in on subsequent days, and would produce a residue concentration gradient from the entry point. Finally, in-home particle resuspension could overshadow distinct intrusion mechanisms, but the differences among homes and between occupied and unoccupied homes might be used to disaggregate these effects.

Although bias was potentially introduced into this design by conducting the study at the same homes over 2 years, this approach allowed some control for specific activity patterns and factors that were thought to be important. The sampling scheme for each home, summarized in Table 1, lists the sample collection regimen at each home in the matched 1-week preapplication and 1-week postapplication periods. The day on which the application was made constituted day 1 of the postapplication week. Descriptors of important factors for each home and application are given in Table 2. In accordance with U.S. Department of Health and Human Services regulations, the study design, protocol, and informed consent were reviewed and approved by Battelle's Human Subjects Review Board.