RESEARCH Open Access Pesticides in house dust from urban and farmworker households in California: an observational measurement study Lesliam Quirós-Alcalá1, Asa Bradman1*, Marcia Nishioka2, Martha E Harnly3, Alan Hubbard4, Thomas E McKone1,5, Jeannette Ferber1, Brenda Eskenazi1 Abstract Background: Studies report that residential use of pesticides in low-income homes is common because of poor housing conditions and pest infestations; however, exposure data on contemporary-use pesticides in low- income households is limited. We conducted a study in low-income homes from urban and agricultural communities to: characterize and compare house dust levels of agricultural and residential-use pesticides; evaluate the correlation of pesticide concentrations in samples collected several days apart; examine whether concentrations of pesticides phased-out for residential uses, but still used in agriculture (i.e., chlorpyrifos and diazinon) have declined in homes in the agricultural community; and estimate resident children’s pesticide exposures via inadvertent dust ingestion. Methods: In 2006, we collected up to two dust samples 5-8 days apart from each of 13 urban homes in Oakland, California and 15 farmworker homes in Salinas, California, an agricultural community (54 samples total). We measured 22 insecticides including organophosphates (chlorpyrifos, diazinon, diazinon-oxon, malathion, methidathion, methyl parathion, phorate, and tetrachlorvinphos) and pyrethroids (allethrin-two isomers, bifenthrin, cypermethrin-four isomers, deltamethrin, esfenvalerate, imiprothrin, permethrin-two isomers, prallethrin, and sumithrin), one phthalate herbicide (chlorthal-dimethyl), one dicarboximide fungicide (iprodione), and one pesticide synergist (piperonyl butoxide). Results: More than half of the households reported applying pesticides indoors. Analytes frequently detected in both locations included chlorpyrifos, diazinon, permethrin, allethrin, cypermethrin, and piperonyl butoxide; no differences in concentrations or loadings were observed between locations for these analytes. Chlorthal-dimethyl was detected solely in farmworker homes, suggesting contamination due to regional agricultural use. Concentrations in samples collected 5-8 days apart in the same home were strongly correlated for the majority of the frequently detected analytes (Spearman r = 0.70-1.00, p < 0.01). Additionally, diazinon and chlorpyrifos concentrations in Salinas farmworker homes were 40-80% lower than concentrations reported in samples from Salinas farmworker homes studied between 2000-2002, suggesting a temporal reduction after their residential phase-out. Finally, estimated non-dietary pesticide intake for resident children did not exceed current U.S. Environmental Protection Agency’s (U.S. EPA) recommended chronic reference doses (RfDs). Conclusion: Low-income children are potentially exposed to a mixture of pesticides as a result of poorer housing quality. Historical or current pesticide use indoors is likely to contribute to ongoing exposures. Agricultural pesticide use may also contribute to additional exposures to some pesticides in rural areas. Although children’s non-dietary intake did not exceed U.S. EPA RfDs for select pesticides, this does not ensure that children are free of any health risks as RfDs have their own limitations, and the children may be exposed indoors via other pathways. The * Correspondence: abradman@berkeley.edu 1Center for Environmental Research and Children’s Health (CERCH), School of Public Health, University of California, 1995 University Avenue Suite 265, Berkeley, CA 94704, USA Full list of author information is available at the end of the article Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 © 2011 Quirós-Alcalá et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. frequent pesticide use reported and high detection of several home-use pesticides in house dust suggests that families would benefit from integrated pest management strategies to control pests and minimize current and future exposures. Background Young children are particularly vulnerable to adverse health effects that may result from pesticide exposures. For example, in utero and/or postnatal chronic expo- sures to organophosphorous (OP) pesticides have been associated with poorer neurodevelopment in children [1-5], and altered fetal growth [6], and shortened gesta- tional duration [7]. Animal studies have also shown that neonatal exposures to other contemporary-use pesticides such as pyrethroids are associated with impaired brain development [8], changes in open-field behaviors, and increased oxidative stress [9]. Pesticides have been measured in residential environ- ments, most notably in indoor dust [10-17]. Poor housing conditions in low-income homes, such as overcrowding and housing disrepair, are associated with pest infesta- tions and increased home pesticide use in both urban and agricultural communities [18,19], potentially increas- ing pesticide residues indoors. Additionally, the presence of farmworkers in the home and/or proximity of homes to nearby fields in agricultural communities have been associated with higher indoor pesticide concentrations [13,20]. Several studies indicate that pesticide residues persist indoors due to the lack of sunlight, rain, temperature extremes, microbial action, and other factors that facili- tate degradation [15]. Semi- and non-volatile pesticides (e.g., OPs and pyrethroids) have chemical properties that increase binding affinity for particles and the ten- dency to adsorb onto household surfaces such as carpet or dust, also prolonging their persistence indoors [11]. For example, pyrethroid pesticides have low vapor pres- sures, and high octanol/water (Kow) and water/organic carbon (Koc) partition coefficients which facilitate parti- tioning into lipids and organic matter and binding to particulate matter in dust [21]. Because of this, several studies suggest that house dust is an important pathway of pesticide exposure for children [11,15,17,22]. Young children are particularly vulnerable to inadvertent inges- tion of pesticide-contaminated dust due to their fre- quent hand-to-mouth activity and contact with indoor surfaces [15]. California (CA) has intense agricultural pesticide use [23], including OP insecticides. Due to their potential health effects in children, formulations of the OP insec- ticides, chlorpyrifos and diazinon, were voluntarily phased out for residential uses between 2001 and 2004 [24,25]. One study showed that this residential phase- out resulted in decreased air concentrations among low- income households in New York City [26]. However, these OPs are still used in agriculture and trends in resi- dential contamination of these compounds have not been studied in agricultural communities, where pesti- cide drift and transport from fields on work clothing may impact indoor pesticide concentrations [20]. It is also widely accepted that house dust is a reservoir for environmental contaminants with concentrations remaining fairly stable [11]; however, to our knowledge, only one study [27] has documented the temporal stabi- lity of pesticides in house dust focusing on the OP pesti- cide chlorpyrifos. Additionally, exposure data on other contemporary-use pesticides (e.g., pyrethroids) in low- income households is limited. In this study, we charac- terized and compared house dust levels of agricultural and residential-use pesticides from low-income homes in an urban community (Oakland, CA) and an agricul- tural community (Salinas, CA). We evaluated the corre- lation of several semi- and non-volatile pesticide concentrations in samples collected several days apart from the same general area in the home; and examined whether house dust concentrations of chlorpyrifos and diazinon declined in Salinas, CA after the U.S. Environ- mental Protection Agency’s (EPA) voluntary residential phase-out of these compounds. Finally, we estimated resident children’s potential non-dietary ingestion expo- sures to these indoor contaminants to determine if exposures via this pathway exceeded current U.S. EPA recommended guidelines. Methods Study Population Study participants included families with children between 3 and 6 years of age who were participating in a 16-day biomonitoring exposure study (to be presented elsewhere) conducted during July through September 2006. Through community health clinics and organiza- tions serving low-income populations, we recruited a convenience sample of 20 families living in Oakland, CA, (an urban community in Alameda county) and 20 families living in Salinas, CA (an agricultural community with intense agricultural pesticide use in Monterey county). Participating families were Mexican American or Mexican immigrants and all Salinas households included at least one household member who worked in agriculture. The University of California, Berkeley Com- mittee for the Protection of Human Subjects approved Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 2 of 15 all study procedures and we obtained written informed consent from parents upon enrollment. Data Collection After obtaining informed consent from parents, bilingual staff administered a validated questionnaire [10] to ascertain demographic information on the children and household members, as well as information on factors potentially related to pesticide exposures such as: the presence of pest infestations and storage and use of pes- ticides in the previous “0-6 days”, “7-30 days”, “31-90 days” and “ >90 days”. We also conducted a home inspection to obtain information on housing quality and residential proximity to the nearest agricultural field or orchard. On dust collection days, parents were also asked if any pesticide applications had occurred in/ around the home in the preceding 24 hours. Dust Sample Collection Using standard protocols [28], we collected dust samples from an area 1 to 2 m2 with a High Volume Small Sur- face Sampler (HVS3) which collects particles >5 μm. Most dust samples were collected from carpets where parents indicated children spent time playing, except for two homes with no carpets or rugs, for which we col- lected samples from upholstered furniture using an attachment on the HVS3. To assess the consistency of concentrations within homes, we collected up to two dust samples, 5-8 days apart, from the same general location in each home. Dust samples were then manu- ally sieved to obtain the fine fraction (<150 μm), which is more likely to adhere to human skin [15]. This frac- tion was stored at -80°C prior to shipment to Battelle Memorial Institute in Columbus, Ohio for laboratory analysis. Laboratory Analysis Of the 40 homes sampled, 15 Salinas farmworker and 13 Oakland urban homes had sufficient sample mass (≥ 0.5 g) for analysis after measurement of other analytes (to be presented elsewhere). We analyzed two dust sam- ples per home except for one home in each location from which one sample was analyzed, yielding a total of 54 dust samples. For this study, a total of 25 analytes were measured in every sample. Analytes measured included the OP insecticides chlorpyrifos, diazinon, malathion, methidathion, methyl parathion, phorate, tetrachlorvinphos, and one oxidation product of diazinon, diazinon-oxon; the pyrethroid insecticides bifenthrin, allethrin (two isomers), cypermethrin (four isomers), cis- and trans-permethrin, deltamethrin, esfen- valerate, imiprothrin, and prallethrin; the pesticide synergist commonly added to pyrethroid formulations piperonyl butoxide; the herbicide chlorthal-dimethyl; and the fungicide iprodione. We selected target analytes based on regional agricultural and non-agricultural use as reported in the California Department of Pesticide Regulation Pesticide Use Reporting database [29], active ingredients in pesticides used or stored indoors, detec- tion in our prior studies [10,13], and laboratory feasibil- ity. Select physico-chemical properties of the target analytes and information on county-level agricultural and non-agricultural pesticide use in both study loca- tions are provided in the Additional files section (Addi- tional file 1 Table A1). To measure analytes, we modified a previously pub- lished laboratory method [10,13]. Briefly, 0.5 g dust ali- quots were fortified with 250 ng of two surrogate recovery standards (SRSs)–fenchlorphos and 13C12- trans-permethrin–and extracted using ultrasonication in 1:1 hexane:acetone. We used solid phase extraction for sample cleanup, concentrated extracts to 1 mL and then fortified them with an internal standard, dibromobiphe- nyl. Concentrated extracts were analyzed with an elec- tron impact gas chromatrography mass spectrometer in the multiple ion detection mode (Phenomenex ZB-35 column, 30 m × 0.25 mm ID, 0.25 μm film) with tem- peratures programmed from 130-340°C at 6°C/min. For each sample analysis set, we analyzed seven calibration curve solutions ranging from 2 to 750 ng/mL (five times higher for deltamethrin) and used a linear least squares regression and the internal method of quantification to prepare calibration curves. A solvent method blank, matrix spike sample (spike = 250 ng), and duplicate study sample were included in each sample analysis set for quality assurance and quality control purposes. We also determined the relative percent difference of the duplicate samples for each analyte measured to ensure that the analytical precision was within acceptable limits. No analytes were detected in the four solvent method blanks, indicating no laboratory contamination. Analyte recoveries in four randomly-selected matrix spike sam- ples averaged 117 ± 19% for OP analytes, 115 ± 16% for pyrethroid analytes, 82 ± 5% for chlorthal-dimethyl, 112 ± 14% for iprodione; and average SRS recoveries were 113 ± 6% and 128 ± 5% for fenchlorphos and 13C12- trans-permethrin, respectively. The average relative per- cent difference in concentration for the 12 analytes detected in duplicate samples was 14 ± 18% (n = 43 dif- ference values spread across 12 analytes), indicating good analytical precision. Data Analysis We first summarized demographic characteristics and computed descriptive statistics for all analytes by loca- tion. For subsequent analyses, we focused on analytes frequently detected (i.e., detection frequencies, DF ≥50%). Concentrations below the limit of detection Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 3 of 15 (LOD) were assigned a value of LOD/√2 [30] and results were considered significant at p < 0.05. We used Fisher’s Exact tests to determine if analyte detection frequencies differed between locations. To assess differences in concentrations between study loca- tions, we used linear regression models with a general- ized estimating equations (GEE) approach [31] in order to report robust inference that accounts for the non- independence of repeated samples within households. Given the limited number of homes sampled and the homogeneity of the study population, we excluded demographic characteristics as covariates in GEE mod- els. We also examined location differences using analyte loadings, ng/m2 [21]. We calculated loadings by multi- plying analyte concentrations by the sieved fine mass and dividing by the area sampled. To determine the correlation of analyte concentrations between the first and second collections, we computed Spearman rank-order correlations. To examine temporal trends of chlorpyrifos and diazi- non concentrations in farmworker homes after the resi- dential phase-out, we used Wilcoxon Mann-Whitney tests to compare dust concentrations in the 15 (n = 29 samples) Salinas farmworker households sampled in 2006 from our present study with dust concentrations from a subset of 82 Salinas farmworker homes of parti- cipants in the CHAMACOS study [13] sampled between 2000 and 2002 (2000, n = 33; 2001, n = 36; 2002, n = 13), and 20 similar households sampled by Bradman et al. [10] in 2002. The same laboratory (Battelle Mem- orial Institute) and collection methods were used in all studies. In addition, we restricted comparisons to those study homes located in the same zip codes as the homes in the present study. If multiple dust samples were avail- able from any of the study homes in the same year, including the present study, the mean analyte dust con- centration was used in our analyses. There were no demographic or household differences between our pre- vious studies and the present study; e.g., all households had at least one farmworker residing in the home and study participants generally represented the farmworker population in Salinas Valley: primarily Mexican or of Mexican descent; Spanish-speaking; low literacy; low income; and frequently reported pesticide applications in the home and wearing work clothes and shoes indoors. Homes were also located >200 feet from the nearest agricultural field. Using the California Depart- ment of Pesticide Regulation Pesticide Use Reporting (PUR) database [29], we also computed county-level agricultural and non-agricultural usage of these OP pes- ticides during 1999-2007 to determine whether temporal changes in residential dust concentrations were concur- rent with regional use patterns. Non-agricultural uses included applications for landscape maintenance, public health, commodity fumigation, rights-of-way, and struc- tural pest control applications by licensed applicators which are reported to the state. Finally, to determine if exposures via the non-dietary ingestion pathway exceed U.S. EPA guidelines for the children in the present study, we calculated hazard quo- tients (HQ) for the majority of the detected analytes. We focused on the children given their unique vulner- abilities to environmental toxicants [32]. We calculated the HQ as the ratio of the child’s potential daily toxicant intake at home via non-dietary ingestion (mg/kg/day) to the specific toxicant chronic reference dose, RfD, (mg/ kg/day). The potential daily toxicant intake was calcu- lated as follows: PDI(mg/kg/day) = (Cdust × IR)/BWchild, where Cdust is the analyte dust concentration in the child’s home (mg/g), IR is the dust intake rate–assumed to be 0.10 g/day (100 mg/day) [33], and BWchild is the child’s body weight (kg) obtained at the initial visit. We used chronic RfDs because children ingest small amounts of dust every day [33]. Chronic oral RfDs were available for 14 of the detected pesticides. For those pes- ticides that have been re-registered in response to the Food Quality Protection Act [34], chronic population adjusted doses (cPAD) were used as the reference dose. An HQ >1.0 would suggest that the child’s exposure via non-dietary ingestion, independent of other exposure routes, may exceed the U.S. EPA’s RfD. All statistical analyses were performed using Stata 10 for Windows (StataCorp, College Station, TX). Results Household demographics and pesticide use Except for farmworker status, demographic characteris- tics were similar in both study locations (Table 1). Parti- cipating households were within 200% of the poverty line and approximately 50% or more of the homes had at least six household members. Although not statisti- cally significant, pest sightings were more commonly reported in Oakland urban homes compared to Salinas farmworker homes. Most participants reported using pesticides indoors in the three months preceding the study (67% and 85% of farmworker and urban homes, respectively) and the most common location of use was the kitchen. Hand-held pyrethroid sprays were the most common formulation and application method in both locations; applications were mostly targeted at ants and cockroaches. Participants from three homes (one Salinas farmworker home and two Oakland urban homes) reported applying pyrethroid insecticides between the two sampling dates. No products with OP insecticides were stored or reported applied in the homes, at the Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 4 of 15 Table 1 Demographic and household characteristics for study participants from farmworker homes in Salinas, CA and urban homes in Oakland, CAa Salinas farmworker homes (n = 15) Oakland urban homes (n = 13) n (%) n (%) Maternal education (highest grade completed) < completed 9th grade or lower 8 (53.3) 8 (61.5) Grades 10-12 (no diploma) 3 (20.0) 1 (7.7) High school diploma/GED or technical school 2 (13.3) 4 (30.8) College graduate 2 (13.3) — Paternal education (highest grade completed) < completed 9 th grade or lower 12 (85.7) 10 (83.3) Grades 10-12 (no diploma) 1 (7.1) 1 (8.3) High school diploma/GED or technical school 1 (7.1) 1 (8.3) College graduate — — Family income relative to federal poverty levelb ≤ Poverty level 10 (66.7) 9 (69.2) > Poverty level but <200% poverty level 5 (33.3) 4 (30.8) Number of household members 3-5 8 (53.3) 5 (38.5) > 6 7 (46.7) 8 (61.5) Reported rodent sighting in the home Yes 2 (13.3) 3 (23.1) No 13 (86.7) 10 (76.9) Reported cockroach sighting in the home Yes 3 (20.0) 5 (38.5) No 12 (80.0) 8 (61.5) Reported pesticide application in the last 3 months Yes 10 (66.7) 11 (84.6) No 5 (33.3) 2 (15.4) Farmworkers wore work clothing indoorsc Yes 12 (80.0) — No 2 (20.0) Farmworkers wore work shoes indoorsc Yes 7 (50.0) — No 7 (50.0) Farmworkers living in the home (past 3 months) 0 — 11 (84.6)d 1-3 15 (100.0) 2 (15.4) Farmworkers currently living in the home 0 1 (6.7) — 1-3 11 (73.3) — 4-7 3 (20.0) — Distance of home to nearest field/orchard 50-20 feet 1 (6.7) — > 200 feet-1/4 mile 3 (20.0) — > 1/4 mile 11 (73.3) — a. No statistically significant differences were observed between locations for demographic factors unrelated to farmworker status. b. Families’ poverty levels were based on U.S. Department of Health and Human Services thresholds for 2006. Source: http://aspe.hhs.gov/POVERTY/06poverty.shtml. c. One participant in the Salinas group reported that the father was a farmworker during the eligibility screening; however, the father was not living in the home during the sample collection period so information is only available for 14 of the 15 farmworker households for this demographic characteristic. d. Two participants reported having a parent or parent’s sibling working in a field/golf course doing maintenance/landscaping work potentially involving pesticide use; however, they were not doing this work during sample collection. Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 5 of 15 workplace or on pets. Most participants from Salinas households (80%) reported that farmworkers residing in the home wore their work clothing indoors and about half of them also wore their work shoes indoors. Approximately 27% of Salinas farmworker homes were located <1/4 mile from the nearest agricultural field or orchard. Dust Levels: Trends and location differences We detected 21 of the 25 analytes measured (Table 2). The majority of homes (93%) had at least three analytes detected in dust; 79% of the homes (n = 22) had at least six analytes detected and <1% (n = 2) of Salinas farm- worker homes had up to 14 analytes detected in one sample. Cis- and trans-permethrin were the only insecticides detected in every home. Commonly detected OP pesticides included diazinon and chlorpyrifos. Diazi- non was detected in 79% and 52% of the samples col- lected from Salinas farmworker and Oakland urban homes, respectively. Chlorpyrifos was detected in 55% and 36% of the samples collected from Salinas farmwor- ker homes and Oakland urban homes, respectively. Other commonly detected analytes in samples collected from both locations included: allethrin (DF ≥ 80%), cypermethrin (DF ≥ 55%), and piperonyl butoxide (DF ≥ 86%). Detection frequencies were only significantly dif- ferent between locations for chorthal-dimethyl, which was detected solely in Salinas farmworker homes. Median concentrations of diazinon, chlorpyrifos, per- methrins, allethrin, and chlorthal-dimethyl were higher Table 2 Limits of detection and summary statistics for pesticide dust concentrations (ng/g) in samples collected in 2006 from low-income farmworker and urban homesa,b Salinas farmworker homes (n = 29 samples collected from 15 homes) Oakland urban homes (n = 25 samples collected from 13 homes) LOD (ng/g) DF min p25 p50 p75 p95 max DF min p25 p50 p75 p95 max Organophosphates Diazinon 4 79 – 8.21 14.4 18 35.8 56.4 52 – – 6.98 18.1 133 139 Chlorpyrifos 10 55 – – 21.9 28 135 200 36 – – – 34.9 43.7 56.4 Malathion 10 7 – – – – 52.2 70.8 12 – – – – 877 1160 Tetrachlorvinphos 50 10 – – – – 252 271 4 – – – – – 15.8 Diazinon-oxon 4 ND – – – – – – 4 – – – – – 4.73 Methidathion 10 ND – – – – – – ND – – – – – – Methyl Parathion 10 ND – – – – – – ND – – – – – – Phorate 10 ND – – – – – – ND – – – – – – Pyrethroids cis-permethrin 4 100 45.9 84.9 568 908 5930c 6300c 100 11.6 84.4 291 946 21600 26700 trans-permethrin 4 100 88.4 144 952 1380 9170c 9690c 100 18.4 166 504 1620 36400 46800 Allethrind 10 83 – 18.4 57.1 129 652c 694 80 – 20.376 50.5 158 276 289 Cypermethrine 20 55 – – 230 918 4540 13500 64 – – 587 1050 5990 13100 Bifenthrin 10 14 – – – – 23.8 23.9 44 – – – 45 2050 2120 Sumithrin 10 24 – – – – 591 807 8 – – – – 104 116 Deltamethrin 250 17 – – – – 3780 5590 12 – – – – 13000 16300 Imiprothrin 50 7 – – – – 253 2140 4 – – – – – 160 Prallethrin 2 ND – – – – – – 4 – – – – – 33.6 Esfenvalerate 50 3 – – – – – 66.5 ND – – – – – – Other Piperonyl butoxidef 2 86 – 30.9 92.3 283 9060 9350 96 – 51.6 353 751 40300 46600 Chlorthal-dimethylg 2 97 – 13.3 16.3 23.5 34.1 34.8 ND – – – – – – Iprodioneh 100 ND – – – – – – ND – – – – – – a. Two samples were obtained from each home in both locations except for one home in each location due to inadequate sample volume. b. Samples were collected from carpets or area rugs with the exception of three samples from two farmworker homes which were collected from furniture due to the absence of a carpet. c. Denotes that the reported concentration was observed in a furniture sample. d. Reported as the sum of two isomers (cis/trans) isomers. e. Reported as the sum of four isomers. f. Insecticide synergist. g. Phthalate herbicide h. Dicarboximide fungicide. Abbreviations and notation: LOD = limit of detection; DF = detection frequency (based on the number of samples obtained); ND or ‘–’ indicates that analyte was not detected or detected LOD Range of Intake (mg/kg/day)c p50 p75 p95 Max Organophosphates Min Max diazinon 0.0002 36 – 7.0 × 10-07 2.5 × 10-04 4.3 × 10-04 1.6 × 10-03 3.5 × 10-03 chlorpyrifos 0.00003 25 – 1.1 ×10-06 – 4.9 × 10-03 2.3 × 10-02 3.8 × 10-02 malathion 0.07 5 – 4.9 × 10-06 – – 2.8 × 10-06 7.0 × 10-05 tetrachlorvinphos 0.04 4 – 1.5 × 10-06 – – 2.2 × 10-05 3.9 × 10-05 Pyrethroids cis-permethrind 0.25 54 5.4 × 10-08 1.3 × 10-04 9.7 × 10-06 2.0 × 10-05 8.4 × 10-05 5.1 × 10-04 trans-permethrind 0.25 54 8.6 × 10-08 2.2 × 10-04 1.7 × 10-05 3.2 × 10-05 1.6 × 10-04 8.9 × 10-04 cypermethrin 0.06 32 – 6.4 × 10-05 2.5 ×10-05 8.4 × 10-05 4.8 × 10-04 1.1 × 10-03 bifenthrin 0.015 15 – 1.1 × 10-05 – 4.4 × 10-06 2.6 × 10-05 7.5 × 10-04 sumithrin 0.0007 9 – 3.7 × 10-06 – – 3.2 × 10-03 5.2 × 10-03 deltamethrin 0.0033 8 – 9.0 × 10-05 – – 6.7 × 10-03 2.7 × 10-02 prallethrin 0.025 1 – 1.9 × 10-07 – – – 7.4 × 10-06 esfenvalerate 0.02 1 – 4.4 × 10-07 – – – 2.2 × 10-05 Others chlorthal-dimethyl 0.01 28 – 1.8 × 10-07 3.0 × 10-06 7.2 × 10-06 1.5 × 10-05 1.8 × 10-05 piperonyl butoxide 0.16 49 – 2.2 × 10-04 5.0 × 10-06 1.7 × 10-05 2.5 × 10-04 1.4 × 10-03 a. A hazard quotient (HQ) was calculated as the ratio of the potential dust intake to the respective analyte reference dose (RfD). The HQ was only calculated for those analytes for which an RfD was available. b. Chronic population adjusted doses (cPADs) were used as the reference dose for chlorpyrifos (cPAD for children and females 13-50 years of age) and deltamethrin. Sources: IRIS database http://cfpub.epa.gov/ncea/iris/index.cfm?fuseaction=iris.showSubstanceList and EPA’s Pesticide Registration Status: http://www.epa.gov/opp00001/reregistration/status.htm. c. Intake was calculated by multiplying the toxicant dust concentration by an ingestion rate of 0.10 g/day (100 mg/day) then dividing by the child-specific body weight (kg). d. The RfD available for “permethrin” was used for each individual isomer in our calculations. Notation: ‘–’ Value is not reported since dust concentrations were less than the limit of detection. Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 9 of 15 dust concentrations from samples collected 5-8 days apart suggests that, for some pesticides, measurements in house dust may be relatively stable indicators of potential indoor exposure over this time frame. To our knowledge, this is the first study to evaluate the correlation of con- centrations within homes for several pesticides over a short sampling period. Although the detection frequency for chlorpyrifos and diazinon was higher in Salinas than Oakland, we did not observe statistically significant differences in pesticide concentrations or loadings between locations. This is notable given that >28,000 and 65,000 kgs of chlorpyri- fos and diazinon, respectively, were applied for agricul- tural purposes in Monterey County in 2006 (Additional File 1 Table A1) and minimal applications (65 kgs and 3 kgs of chlorpyrifos and diazinon, respectively) occurred in Alameda County. Previously, we showed a significant correlation with local agricultural use and chlorpyrifos dust concentrations (but not diazinon) for homes throughout the Salinas Valley [13]. Mapping of dust concentrations and agricultural use suggests that chlorpyrifos dust concentrations are higher in the center of the Valley (south of the city of Salinas), where agri- cultural use is higher [13]. Farmworker homes in the present study were from the city of Salinas where the impact of drift from agricultural applications may have been lower. Additionally, our small sample size may have prevented us from observing significant differences in concentrations between locations for these OP pesti- cides as well as other analytes. Malathion was not frequently detected in homes from either location; however, higher levels were observed in urban homes. This pesticide is used in agriculture and is also registered for use in home gardens, as a building perimeter treatment, as a wide-area spray for mosqui- toes, and by prescription for head-lice control [37]. However, no parents reported treating their children for lice or using it themselves in their gardens. The main county uses for this OP pesticide in 2006 in the urban region were landscape maintenance and structural pest control [38]. These applications were reported more than 25 km away from the nearest study home, thus it is not readily apparent why higher levels were observed in urban homes although it should be noted that we only sampled a small number of homes. We generally observed significantly lower house dust concentrations of chlorpyrifos and diazinon in the pre- sent study compared to levels measured in dust from homes located in the same zip codes sampled between 2000 and 2002 [10,13], suggesting that indoor concen- trations in the city of Salinas are decreasing despite con- tinued agricultural use in the area. In New York City, air concentrations for these OP pesticides in low-income homes also significantly decreased between 2001 and 2004 [26]. The temporal declines in indoor concentra- tions reported here and in the New York City study may reflect the decreasing usage of these OP pesticides for home or structural applications per the U.S. EPA’s residential phase-out. Nonetheless, despite declining concentrations indoors, detection of these OP pesticides, especially in Oakland where there was little agricultural or structural use, underscores their persistence indoors. Compared to other studies in farmworker populations (Table 6), we observed lower median concentrations for chlorpyrifos [10,13,17,22,39,40] and diazinon [10,13,40]. These farmworker studies generally reported a wider range of concentrations for these two OP pesticides and collected dust samples prior to the residential phase-out. One study by Curl et al. [22] reported a wider range of diazinon concentrations, but comparable median con- centrations (10 ng/g). Although malathion was not fre- quently detected in our farmworker homes, a wider range of concentrations was reported in previous farm- worker studies (Table 6) [10,22,40]. To our knowledge, only one other study has reported OP pesticide concen- trations in low-income urban homes [41]. This study reported higher median concentrations for chlorpyrifos and diazinon in low-income urban housing units in Bos- ton, MA. Homes in this study were sampled just after or during the residential phase-out of chlorpyrifos and dia- zinon, respectively (between July 2002 and August 2003). Pyrethroids were detected in house dust in several study homes. Similar to low-income urban housing units in Boston, MA [41], pyrethroids and PBO were detected in higher concentrations and used more fre- quently in our study homes compared to other pesti- cides. This finding is consistent with the fact that pyrethroid insecticide formulations for residential appli- cations have largely replaced OP pesticide residential formulations [42,43]. Although over 19,000 kgs of per- methrin were applied in Monterey County in 2006 for agricultural purposes [44], we did not observe significant differences in permethrin concentrations (or loadings) between locations. Allethrin and cypermethrin were also widely detected in most homes. Our findings suggest that home use likely contributed to the presence of pyr- ethroid pesticides in house dust since pyrethroids were commonly used indoors and negligible to no agricultural applications took place at the county level (except for permethrin). It is also possible that structural pest con- trol applications influenced indoor detection of certain pyrethroids in some homes. For example, it is estimated that ~80% of the non-agricultural cypermethrin use reported in Alameda County in 2006 was for structural pest control [38]. The presence of pyrethroids in house dust is also consistent with their physical and chemical properties, including high octanol:water partition Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 10 of 15 Table 6 Dust concentrations for select organophosphorous pesticides and pyrethroids from select U.S. farmworker studies (ng/g)a Author Population Location Collection method Sampling Dates Pesticides LOD (ng/g) b DF% n Range (ng/g) Median Mean (SD) Harnly et al. 2009c Farmworkers (CHAMACOS longitudinal birth cohort) Salinas Valley, CA HVS3 2000-2002 Organophosphates: Chlorpyrifos 2 91 177-197 2.9-7850 74 NR Diazinon 2 86 4.7-2870 26 Pyrethroids: cis-Permethrin 5 98 16-168000 344 trans- Permethrin 5 98 146-265000 467 Others: Chlorthal- dimethyl 2 98 2.3-271 22 Bradman et al. 2006d Farmworkers Salinas Valley, CA HVS3 June- September 2002 Organophosphates: Chlorpyrifos 2 95 20 4.0) and low vapor pres- sures (Additional File 1 Table A1). To our knowledge, only two studies [10,13] have measured pyrethroid dust concentrations in farmworker homes. Similar to the pre- sent study, permethrins were the most frequently detected pyrethroids indoors. Median cis- and trans- permethrin concentrations in our farmworker homes were higher than those observed in a previous study [10]. The detection of chlorthal-dimethyl in all Salinas farmworker homes and none of the Oakland urban homes is consistent with other Salinas Valley studies showing an association between agricultural use and house dust contamination [13] and a positive correlation between outdoor and indoor air concentrations [10]. This herbicide had relatively high agricultural use (~ 33,970 kgs) in the Salinas Valley and is not found in home-use pesticides. Chlorthal-dimethyl also has a high log Kow value and low vapor pressure (Additional File 1 Table A1), and may be bound to particulate matter at room temperature. Over 16,000 kgs of malathion and iprodione were used in 2006 for agricultural applications (Additional File 1 Table A1); however, they were not commonly detected in farmworker homes from the city of Salinas. For some of these pesticides, e.g., iprodione, LODs were higher than for other analytes. Other factors including physico- chemical properties, e.g., high vapor pressure and low log Kow values (≤3), may have resulted in lower detec- tion frequencies. These pesticides were also not fre- quently detected in dust samples from our previous study in the city of Salinas [10]. This study has several limitations. Location differ- ences in pesticide dust levels have been reported previously when using loadings rather than concentra- tions [21]; however, our small sample size limits statis- tical power and may have prevented us from observing statistically significant differences between locations for concentrations and/or loadings. Additionally, although homes with insufficient sample mass were demographically similar to those with adequate sample mass, exclusion of these homes may have introduced some bias and prevented us from detecting a differ- ence in pesticide concentrations and/or loadings between locations. We also focused on low-income homes and thus the results may not be generalizable to other populations. Although estimated intakes for select pesticides were below EPA RfDs (i.e., HQ <1.0), it should not be concluded that intakes below RfDs are “acceptable” or free of any health risks. For exam- ple, recent studies have identified mechanisms of OP pesticide toxicity that were not considered in defining current U.S. EPA RfDs (e.g., suppressed expression of serotonin transporter genes) [45]. Moreover, RfDs do not account for differences in vulnerability to pesticide toxicity due to genetic factors, such as paraoxonase (PON1) polymorphisms [46]. Additionally, our intake calculations for pesticides do not account for other exposure pathways (e.g., inhalation or diet); nor did we consider that some children could have pica or other behaviors that could increase or decrease intake. Although we surveyed participants on their usage of pesticides indoors, we were not always able to corro- borate whether formulation ingredients were present at high concentrations as the pesticide containers were not always available to confirm the active ingredients. Lastly, children in the homes sampled are clearly exposed to multiple indoor contaminants and our hazard evaluation does not account for exposure to complex mixtures. Conclusions Studies of contaminants in low-income homes, including our study, have been limited in sample size and, often, selection of participants has not been random. In addi- tion, collection methods, analytical techniques, analytes measured, and timing of data collection differ. To our knowledge, only one other study has assessed indoor dust concentrations of pyrethroids in low-income homes in an urban setting [41]. Nonetheless, the results from these studies indicate that low-income children are potentially exposed to a mixture of pesticides. Agricul- tural pesticide use may contribute to additional expo- sures to some pesticides in rural areas; historical or current residential use is also likely to contribute to ongoing exposures. Although children’s non-dietary intake did not exceed U.S. EPA RfDs for select pesti- cides, this does not ensure that children are free of any health risks as RfDs have their own limitations, and the children may be exposed indoors via other pathways. The frequent pesticide use reported among participating households in this and previous studies of low-income homes [18,19,41] and high detection of several home- use pesticides in house dust suggests there is a need to educate families on the potential health impacts of pesti- cide use and effective integrated pest management stra- tegies to control pests and reduce exposures to household occupants [42]. Particular at-risk populations are those living in households with poorer housing qual- ity, where there may be greater needs for pest control [18,19]. Additional research is needed to quantify exposures and potential health effects from these compounds, par- ticularly frequently used pesticides such as pyrethroids. Such research should consider the complex mixture of chemicals found in indoor environments, include both environmental and biomonitoring measurements to assess cumulative exposures, and consider exposures in homes of different socioeconomic status. Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 13 of 15 Additional material Additional file 1: Table A1. Select analyte chemical and physical properties and amounts applied in 2006 for agricultural and non- agricultural purposes in the counties where our homes were sampled. This file contains information on select chemical and physical properties for the analytes measured in dust samples as well as information on their usage at the county level in the year in which samples were collected. Additional file 2: Table A2. Summary statistics for dust loadings (ng/ m2) in samples collected in 2006 from low-income urban and farmworker homes. This file contains information on select summary statistics on analyte dust loadings in the homes sampled. List of Abbreviations CDPR: California Department of Pesticide Regulation; cPAD: Chronic Adjusted Population Dose; DF: Detection frequency; GEE: Generalized Estimating Equation; HQ: Hazard Quotient; HVS3: High Volume Small Surface Sampler; Koc: Water:Organic Carbon Partition Coefficient; Kow: Octanol:Water Partition Coefficient; LOD: Limit of Detection; OP: Organophosphorous; PBO: Piperonyl butoxide; PDI: Potential daily intake; PON1: Paraoxonase 1; PUR: Pesticide Use Reporting; RfD: Reference Dose; SRS: Surrogate Recovery Standard; U.S. EPA: United States Environmental Protection Agency. Acknowledgements Work was supported by EPA (RD 83171001, Science to Achieve Results-STAR- Graduate Fellowship Program F5D30812), NIEHS (PO1ES009605), UC MEXUS, and the UC Berkeley Center for Latino Policy Research. This work is solely the responsibility of the authors and does not necessarily represent the official views of the funders. We thank our staff and community partners including Dr. Pescetti and the staff from Clinica de la Raza for helping with recruitment efforts, our study participants, and Dr. Rupali Das, Dr. Katharine Hammond, Marta Lutsky, Dr. Mark Nicas, and Dr. Rosana Weldon for editorial comments. Author details 1Center for Environmental Research and Children’s Health (CERCH), School of Public Health, University of California, 1995 University Avenue Suite 265, Berkeley, CA 94704, USA. 2Battelle Memorial Institute, 505 King Avenue, Columbus, OH 43201, USA. 3California Department of Public Health, Environmental Health Investigations Branch, 850 Marina Bay Parkway P-3, Richmond, CA 94804, USA. 4Division of Biostatistics, School of Public Health, University of California, Berkeley 50 University Hall, MC 7356, Berkeley, CA 94720, USA. 5Lawrence Berkeley National Laboratory, One Cyclotron Road, Mail stop 90R3058, Berkeley, CA 95720, USA. Authors’ contributions LQA: conceived of the study; participated in the design, coordination, and implementation of all study field activities; conducted the statistical analysis; and drafted the manuscript; AB: conceived of the study; participated in the design, coordination, and implementation of all study field activities; and helped to draft the manuscript; MN: responsible for laboratory analysis of dust samples and quality assurance and control, and helped to draft the laboratory analysis section of the manuscript; MEH: provided assistance with previous CHAMACOS data used in the analysis of temporal trends of phased-out pesticides and helped to draft the manuscript; AH: contributed to the statistical phase and helped to draft the data analysis and results section of the manuscript; TEM: helped to draft the manuscript; JF: responsible for cleaning the data and providing feedback on the manuscript; BE: conceived of the study; participated in the design, coordination, and implementation of all study field activities; and helped to draft the manuscript. 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Holland N, Furlong C, Bastaki M, Richter R, Bradman A, Huen K, Beckman K, Eskenazi B: Paraoxonase polymorphisms, haplotypes, and enzyme activity in Latino mothers and newborns. Environ Health Perspect 2006, 114:985-991. doi:10.1186/1476-069X-10-19 Cite this article as: Quirós-Alcalá et al.: Pesticides in house dust from urban and farmworker households in California: an observational measurement study. Environmental Health 2011 10:19. Submit your next manuscript to BioMed Central and take full advantage of: • Convenient online submission • Thorough peer review • No space constraints or color figure charges • Immediate publication on acceptance • Inclusion in PubMed, CAS, Scopus and Google Scholar • Research which is freely available for redistribution Submit your manuscript at www.biomedcentral.com/submit Quirós-Alcalá et al. Environmental Health 2011, 10:19 http://www.ehjournal.net/content/10/1/19 Page 15 of 15