Only one member of each household selected was eligible to enroll. Overall 1,038 potential participants were contacted by mail and/or telephone, after screening 817 were eligible, and 403 were enrolled and completed the interview on residential pesticides. After limiting to ages 50 and older, 359 PEG participants qualified for this analysis. Eligibility criteria for control recruitment in the CGEP study were the same as for PEG and we again relied on tax assessor’s parcel listings to randomly select residences. But for CGEP, population control subjects were recruited through home visits made by trained field staff, who determined eligibility and enrolled the controls at the door step. This was done in an effort to increase enrollment success and representativeness of the sample population compared to the general population in the three target counties. Recruitment of CGEP participants is ongoing, as of January 2011: 6891 homes were visited, 1355 individuals were found possibly eligible and 601 enrolled. At the time of analysis 314 interviews with data on home pesticide use were available for our analysis. Limiting to individuals age 50 and older, the sample used for our analysis contained 297 CGEP participants. All studies used telephone interviews to obtain data on pesticide exposure. Interviews for PEG and CGEP were conducted by trained staff at the University of California, Los Angeles. PEG interviews were conducted from November 2001 to November 2007 and CGEP interviews used for this analysis were conducted from March 2009 to December 2010. Interviews for SUPERB were conducted by trained staff at the University of California, Davis. The SUPERB study collected data in three tiers, but only data from the telephone interviews administered in the first year of Tier 1 will be used here. SUPERB Tier 1, year 1 interviews were conducted from October 2006 to May 2008. In all three studies we recorded product names, purposes of use, and frequency of indoor and outdoor pesticide use, professional pesticide applications, and applications of pet flea/tick treatments. The questionnaires used for all three studies asked comparable, if not the same questions for each of the above items of interest . Only SUPERB collected information on the area and rooms treated, the size of treated indoor and outdoor areas,drying racks and information on cleaning after and ventilation practices during and after indoor applications.
Prior to the SUPERB interview, participants were given a list with pictures of current pesticide products in order to facilitate the recall of product names and brands. Most data collected for SUPERB pertained specifically to insecticide usage in the last year. SUPERB also contained a small subset of questions pertaining to indoor and outdoor pesticide use frequency from ages 18–50, for this age period it was possible for participants to report use of any type of pesticide. PEG and SUPERB recorded self-reported information on pesticide storage and personal protection methods used during application. The emphasis of PEG and CGEP was less on recent but more on lifetime residential pesticide usage. Thus, product names, purposes of use, and frequency of use of specific pesticides were collected for four periods of the participant’s lifetime: young adult , adult , middle age , and senior . It is important to note that not all participants had reached the age of 65 at the time of interview, therefore questions regarding the 65 and older period often had a smaller sample size than the three younger age periods. PEG and CGEP participants did not receive additional materials to aid with their recall of product names and brands. We relied only on the product names recalled by participants and the purpose of using the reported pesticide. If a participant could not remember data was recorded as missing. Relying on pesticide product information and years of use reported by PEG/CGEP participants, we utilized the California Department of Pesticide Registry online database to identify the pesticide products’ active ingredients [19]. The CDPR database contains information on pesticide formulations sold in California as far back as 1945. This extensive database allowed us to identify active ingredients for pesticides that participants reported using throughout their lifetime in a time specific manner. When participants did not provide sufficient information to accurately identify the correct product, active ingredient information was treated as missing. When the product was identifiable, among active ingredients, the one with the highest concentration was considered the main active ingredient. A chemical class was then assigned to the corresponding main active ingredient of a particular product. Chemical class information was primarily identified from CDPR and the Pesticide Action Network Pesticide Database . For analysis, we assigned active ingredients to one of the following chemical classes: pyrethroids, organophosphates, nitrogen containing lactones, carbamate, halogenated, metals/inorganic compounds, organochlorine, and botanicals .
In some cases a product’s chemical composition changed over time, thus we assumed subjects were exposed to all possible active ingredients in a product during the reported years of usage. Depending on the composition of the product, some were assigned more than one main ingredient and chemical class. We used data from all three studies to evaluate pesticide use throughout a person’s lifetime. We generated frequencies and percentages to describe the prevalence of various pesticide usage and exposure related behaviors. Most variables were multinomial rather than normally distributed. We also compared pesticide use within age groups by education and race. In many instances breaking our study population into smaller subgroups for comparison purposes created small cell sizes, necessitating the use of Fisher’s exact test. Another goal was to compare pesticide use during younger and older adulthood. In order to pool data from all three studies, it was necessary to reorganize the data, defining younger adulthood and older adulthood in each study in a slightly different manner prior to pooling; i.e., as <45 vs. ≥45 for CGEP and PEG and <50 and ≥50 years of age in SUPERB. Because our data on use of pesticides during younger and older adulthood was dichotomous we employed the Phi coefficient to compare pesticide usage across age groups. Data analysis was conducted using SAS 9.2 . Overall 89% of participants from all three study populations used indoor and/or outdoor pesticides at some point during their lifetimes, 72% of participants from all three studies reported ever using pesticides outdoors and 74% ever using pesticides indoors at any point during their lifetime. Our data on ever use frequency are comparable to previous studies that investigated residential pesticide use. In an older study by Savage et al. for the EPA region IX, which contains California and other western states, 62% of all participants reported ever using pesticides in the yard, 28% reported using pesticides in the garden, and 83% of households reported ever using pesticides inside their home within 12 months of being interviewed. A more recent study conducted by Colt et al. in Los Angeles, Detroit, Iowa, and Seattle reported that 94% of subjects had ever used insecticides in or around their current or former residences during a 30 year period prior to interview. In our study we found that 18% of individuals had used indoor pesticides only during their lifetime, 16% had used outdoor pesticides only,cannabis drying and 56% had used both. We speculate that many factors may contribute to this pattern of use, such as type of dwelling and urban versus suburban or rural address.
Unfortunately our three studies did not collect any or comparable information about such factors. We also examined frequency of pesticide use by race and education in each of the four age periods, young adult , adult , middle age , and senior . We found that there was no statistically significant difference of outdoor pesticide frequency of use by race. For indoor pesticide frequency of use, the only statistically significant finding was that nonwhites, ages 16–24, appeared to use indoor pesticides more frequently than whites ages 16–24. When examining frequency of outdoor pesticide use by education the only statistically significant difference in use during lifetime was seen after age 65 , such that individuals with <12 years of education appeared to use outdoor pesticides more frequently. Individuals with <12 years of education used indoor pesticides significantly more frequently throughout most of their adult lives In PEG and CGEP, lifetime frequency of pesticide use, both indoors and outdoors, increased with increasing age .We speculate that increased use of pesticides during middle age may be a reflection of changes in lifestyle during middle age. For example, individuals in middle age may be more likely to own their homes, whereas young adults may still live with family or rent an apartment. A homeowner may be more likely to apply residential pesticides in his/her home compared to an apartment tenant who does not have or take care of yards and gardens and may rely on a landlord to eliminate pests. Relying on information from all three studies we found that 50% of participants had ever used outdoor pesticides during younger adulthood and 63% had ever used outdoor pesticides during older adulthood . More than half of all participants had ever applied pesticides indoors during both younger and older adulthood . Outdoor and indoor pesticide use during younger adulthood was positively correlated with pesticide use during older adulthood . Our findings suggest that people are likely to use pesticides throughout their lifetimes, albeit at relatively low frequency. While the overall frequency of pesticide use was low, as people age there seems to be an increase in use. Our results also show that use of pesticides at younger ages may be related to use of pesticides at older ages. However, further studies are necessary to examine whether general attitudes toward pesticide use, which may be influenced by occupation or education, influence an individual to adopt and continue residential pesticide use throughout lifetime. Additionally it appears that at certain ages, race and education may also influence frequency of pesticide use. Higher use frequencies among older adults are important since pesticides may act more strongly as neurotoxins due to the nervous system’s inability to properly handle and repair damage from toxins during this stage of life. Future risk assessment for pesticides may need to take into account a possible increased vulnerability for older adulthood exposures as well as considering the accumulation of effects from even low-level exposures over a person’s lifetime. According to reports in our PEG and CGEP studies, organophosphates, halogenated pesticides, botanicals, and organochlorines were used more often outdoors, while pyrethroids, carbamates, and aromatic, nitrogen containing lactones were the most common active ingredients in pesticides used indoors. Metal/inorganic pesticides were used both in- and outdoors in similar proportion . However it is important to acknowledge that chemical classes found in consumer use pesticides have changed over the years due to the introduction of new chemicals and regulations limiting use of certain chemicals. For example pyrethroids have only become more common in the past twenty-five to thirty years, while regulations restricted the use of many organochlorines especially for residential and indoor uses. Therefore many individuals in our sample would likely not have used pyrethroids as young adults but also would have decreased their residential use of organochlorines and organophosphates as older adults.Both indoors and outdoors, pesticides were most commonly applied as sprays when participants were asked to report method ever used or method used in the last year . Ever usage of bait and granule varies greatly between indoor and outdoor pesticides; however use of bait and granule is more similar for indoor and outdoor use if we consider their use only in the last year. Participants also reported other application methods for indoor pests, e.g., foggers, gel, and stakes, and for outdoor application, e.g., powder, candles, foam, strips, and traps . Some of the differences in methods used over lifetime versus used in the past year may be due to the fact that PEG and CGEP collected data on any type of pesticide over lifetime, while in SUPERB use in the last year focused specifically on insecticide use. Relatively few participants reported the use of foggers in all three studies. In the case of PEG and CGEP it is possible that participants may have reported foggers as sprays. In SUPERB foggers were clearly separated from sprays. Foggers are a major source of potential insecticide exposure to residential users as they release far more chemical into the environment than the other methods of application mentioned here.