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    • Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate PesticidesMaryse F. Bouchard, David C. Bellinger, Robert O. Wright and Marc G. Weisskopf Pediatrics; originally published online May 17, 2010; DOI: 10.1542/peds.2009-3058 The online version of this article, along with updated information and services, is located on the World Wide Web at: http://pediatrics.aappublications.org/content/early/2010/05/17/peds.2009-3058 PEDIATRICS is the official journal of the American Academy of Pediatrics. A monthly publication, it has been published continuously since 1948. PEDIATRICS is owned, published, and trademarked by the American Academy of Pediatrics, 141 Northwest Point Boulevard, Elk Grove Village, Illinois, 60007. Copyright © 2010 by the American Academy of Pediatrics. All rights reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275. Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • Attention-Deficit/Hyperactivity Disorder and UrinaryMetabolites of Organophosphate Pesticides WHAT’S KNOWN ON THIS SUBJECT: Exposure to AUTHORS: Maryse F. Bouchard, PhD,a,b David C. Bellinger, organophosphates has been associated with adverse effects on PhD,a,c Robert O. Wright, MD, MPH,a,d,e and Marc G. neurodevelopment, such as behavioral problems and lower Weisskopf, PhDa,e,f cognitive function. Studies have focused, however, on populations Departments of aEnvironmental Health and fEpidemiology, with high levels of exposure, relative to the general population. School of Public Health, Harvard University, Boston, Massachusetts; bDepartment of Environmental and Occupational Health, Faculty of Medicine, University of Montreal, Montreal, WHAT THIS STUDY ADDS: We conducted a study with 1139 Quebec, Canada; Departments of cNeurology and dPediatrics, children 8 to 15 years of age, representative of the US population. School of Medicine, Harvard University, and Boston Children’s The findings showed that children with higher urinary levels of Hospital, Boston, Massachusetts; and eChanning Laboratory, organophosphate metabolites were more likely to meet the Department of Medicine, School of Medicine, Harvard University, and Brigham and Women’s Hospital, Boston, Massachusetts diagnostic criteria for ADHD. KEY WORDS attention-deficit/hyperactivity disorder, pesticides, organophosphates, National Health and Nutrition Examination Surveyabstract ABBREVIATIONS DAP— dialkyl phosphateOBJECTIVE: The goal was to examine the association between urinary DMAP— dimethyl alkylphosphate DEAP— diethyl alkylphosphateconcentrations of dialkyl phosphate metabolites of organophosphates OR— odds ratioand attention-deficit/hyperactivity disorder (ADHD) in children 8 to 15 CI— confidence intervalyears of age. ADHD—attention-deficit/hyperactivity disorder NHANES—National Health and Nutrition Examination SurveyMETHODS: Cross-sectional data from the National Health and Nutrition DISC-IV—Diagnostic Interview Schedule for Children IVExamination Survey (2000 –2004) were available for 1139 children, who PIR—poverty/income ratio DSM-IV—Diagnostic and Statistical Manual of Mental Disorders,were representative of the general US population. A structured inter- Fourth Editionview with a parent was used to ascertain ADHD diagnostic status, on The Canadian Institutes for Health Research played no role inthe basis of slightly modified criteria from the Diagnostic and Statisti- the design and conduct of the study; collection, management,cal Manual of Mental Disorders, Fourth Edition. analysis, and interpretation of the data; and preparation, review, and approval of the manuscript.RESULTS: One hundred nineteen children met the diagnostic criteria www.pediatrics.org/cgi/doi/10.1542/peds.2009-3058for ADHD. Children with higher urinary dialkyl phosphate concentra- doi:10.1542/peds.2009-3058tions, especially dimethyl alkylphosphate (DMAP) concentrations, weremore likely to be diagnosed as having ADHD. A 10-fold increase in DMAP Accepted for publication Feb 23, 2010concentration was associated with an odds ratio of 1.55 (95% confi- Address correspondence to Maryse F. Bouchard, PhD, University of Montreal, Department of Environmental and Occupationaldence interval: 1.14 –2.10), with adjustment for gender, age, race/eth- Health, CP 6128 Succursale Centre-Ville, Montreal, QC H3C 3J7,nicity, poverty/income ratio, fasting duration, and urinary creatinine Canada. E-mail: maryse.bouchard@umontreal.caconcentration. For the most-commonly detected DMAP metabolite, di- PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275).methyl thiophosphate, children with levels higher than the median of Copyright © 2010 by the American Academy of Pediatricsdetectable concentrations had twice the odds of ADHD (adjusted odds FINANCIAL DISCLOSURE: The authors have indicated they haveratio: 1.93 [95% confidence interval: 1.23–3.02]), compared with chil- no financial relationships relevant to this article to disclose.dren with undetectable levels. Funded by the National Institutes of Health (NIH).CONCLUSIONS: These findings support the hypothesis that organo-phosphate exposure, at levels common among US children, may con-tribute to ADHD prevalence. Prospective studies are needed to estab-lish whether this association is causal. Pediatrics 2010;125:e1270–e1277e1270 BOUCHARD et al Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • ARTICLESApproximately 40 organophosphate A few epidemiological studies sug- Children who received newborn carepesticides are registered with the US gested that organophosphate expo- in an ICU or premature nursery (nEnvironmental Protection Agency for sure was associated with adverse neu- 167) and those with birth weights ofuse in the United States.1 In 2001, 73 rodevelopmental outcomes, but no 2500 g (n 126) were excluded be-million pounds of organophosphates studies have addressed possible risks cause these are important risk factorswere used in both agricultural and res- among children with average levels of for developmental disorders.17 We ex-idential settings. The Environmental exposure. By using data for a repre- cluded 24 children with extremely di-Protection Agency considers food, sentative sample of US children, we ex- lute urine (creatinine levels of 20drinking water, and residential pesti- amined the cross-sectional associa- mg/dL) and 1 outlier with respect tocide use important sources of expo- tion between urinary DAP metabolite urinary DAP concentrations. Childrensure.2 Residential pesticide use is com- concentrations and attention-deficit/ with missing data were excluded (pov-mon, but the major source of exposure hyperactivity disorder (ADHD) preva- erty/income ratio [PIR], n 43; fastingto pesticides for infants and children lence in children 8 to 15 years of age. duration, n 38; urinary creatininewould be the diet, according to the Na- level, n 1).tional Academy of Sciences.3 The US METHODSPesticide Residue Program Report’s Study Design and Population ADHD Assessment2008 indicates that detectable concen- The Diagnostic Interview Schedule for The National Health and Nutrition Ex-trations of the organophosphate mala- Children IV (DISC-IV), a structured diag- amination Survey (NHANES) is athion were found in 28% of frozen blue- nostic interview designed for use in ep- population-based, health survey ofberry samples, 25% of strawberry idemiological studies,18 was used to noninstitutionalized US residents con-samples, and 19% of celery samples.4 assess the presence of ADHD on the ducted by the National Center forChildren are generally considered to Health Statistics of the Centers for Dis- basis of slightly modified criteria frombe at greatest risk from organophos- ease Control and Prevention. The the Diagnostic and Statistical Manualphate toxicity, because the developing NHANES uses a complex, multistage, of Mental Disorders, Fourth Editionbrain is more susceptible to neurotoxi- probability sampling design, with over- (DSM-IV).19 The interview was con-cants5 and the dose of pesticides per sampling of certain subgroups. Partic- ducted with the mother or anotherbody weight is likely to be larger for ipants completed household surveys, caretaker over the telephone bychildren. Children 6 to 11 years of age which included questions about demo- trained interviewers, 2 to 3 weeks af-have the highest urinary concentra- graphic features and health history, ter the physical examination. The inter-tions of dialkyl phosphate (DAP) me- and blood and urine samples were col- view was conducted by bilingual inter-tabolites (markers of organophos- lected during physical examinations at viewers in English or Spanish. Thephate exposure), compared with other mobile centers.16 We used data from DISC-IV has evidence of substantial va-age groups in the US population.6 Chil- 2000 –2004, years for which ADHD was lidity,18 reliability for both its English18dren have reduced expression of de- assessed in children 8 to 15 years of and Spanish20,21 versions, and success-toxifying enzymes, which contributes age; diagnoses were available for 3998 ful use via telephone in DSM-IV field tri-to their vulnerability.7,8 Epidemiologi- children. Urinary DAP metabolite levels als.22 The use of DISC-IV data is re-cal studies linking exposure to organo- were measured for a random sub- stricted for confidentiality reasons;phosphates and neurodevelopment sample of the NHANES participants. therefore, we accessed the datahave focused on populations with high From 2000 to 2002, the sampling rate through the National Center for Healthlevels of exposure, relative to the gen- was 50% for ages 6 to 11 years and Statistics Research Data Center.eral population.9,10 Prenatal organo- 33% for ages 12 to 15 years. From 2003 The DISC-IV scoring algorithms deter-phosphate exposure was associated to 2004, the sampling rate was 33% for mine ADHD diagnostic status for thewith increased risk of pervasive devel- all ages. Measurements of urinary DAP previous year, as well as ADHD sub-opmental disorders, as well as delays levels were available for 1481 children type, that is, predominately inattentivein mental development at 2 to 3 years among those with ADHD diagnoses. subtype, predominately hyperactive/of age.11,12 Postnatal organophosphate The NHANES was approved by the Na- impulsive subtype, or combined sub-exposure has been associated with be- tional Center for Health Statistics in- type. The diagnosis is based on thehavioral problems, poorer short-term stitutional review board, and all par- presence, during the previous 12memory and motor skills, and longer ticipants provided written informed months, of symptoms related to inat-reaction times in children.13–15 consent. tention, hyperactivity, and impulsivity,PEDIATRICS Volume 125, Number 6, June 2010 e1271 Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • with significant impairment in 2 set- diethyl alkylphosphate (DEAP) mole- Data Analysestings (eg, at school and home).23 The cules (diethyl phosphate, diethyl thio- We used the complex samples moduleDSM-IV criterion that symptoms must phosphate, and diethyl dithiophos- of SPSS 17.0 (SPSS Inc, Chicago, IL) tonot occur in conjunction with another phate). DMAP metabolites are derived conduct all analyses, with accountingneuropsychiatric disorder is not as- from O,O-dimethyl-substituted organo- for the multistage probability sam-sessed by the DISC-IV. We chose not to phosphate pesticides such as malathi- pling design of the NHANES. Strata, pri-use the DSM-IV criterion that symp- on; DEAP metabolites result from the mary sampling units, and sampletoms must have been present before 7 degradation of O,O-diethyl-substituted weights were used to obtain robust lin-years of age, because our hypothesis organophosphates such as chlorpyri- earized SEs and unbiased point esti-was that urinary DAP concentrations fos. The measurements were per- mates. The threshold for statisticalwould be associated with increased formed through lyophilization and significance was set at P .05. All sta-odds of concurrent ADHD. chemical derivatization, followed by tistical tests were 2-sided. The DAP me-The DISC-IV identified 119 cases of analysis through isotope-dilution gas tabolite concentrations were dividedADHD, but 30 children did not meet the chromatography-tandem mass spec- by the respective molecular weightsdiagnostic criteria although the parent trometry.24 Stable-isotope analogues before being summed to yield DEAP,reported use of doctor-prescribed were used as internal standards for DMAP, and total DAP concentrations. each of the metabolites, which re-ADHD medication during the previous Because DMAP and DEAP metabolites sulted in a high degree of accuracy andyear. Because the diagnostic interview might have different relationships to precision, with low analytical limits ofaddresses the presence of symptoms, the outcomes,12 they were examined detection. Concentrations below thechildren whose symptoms were well separately. Because the distributions detection limit were imputed a valuecontrolled with medication would of total DAP, DMAP, and DEAP concen- corresponding to the value of the de-meet the diagnostic criteria. There- trations were skewed, logarithmic tection limit divided by √2.25 Urinaryfore, we also conducted analyses in transformations (base 10) were ap- creatinine concentrations were deter-which ADHD cases were defined as ei- plied. Correlates of urinary DAP metab- mined using an automated colorimet-ther meeting the DISC-IV diagnostic cri- olite concentrations were examined ric method based on a modified Jaffeteria or regularly taking ADHD medica- with a general linear model. Logistic reaction on a Beckman Synchron AS/tion during the previous year. regression analyses were used to esti- ASTRA clinical analyzer (Beckman In- struments, Inc., Brea, CA) at the mate odds ratios (ORs) and 95% confi-Measurement of Urinary dence intervals (CIs) for ADHD (any Fairview University Medical Center,Metabolites of Organophosphate subtype) and ADHD subtypes, per 10- Minneapolis, Minnesota.26Pesticides fold increases in total DAP, DMAP, andDuring the physical examination, Other Covariates DEAP metabolite concentrations (in“spot” urine specimens were collected The following variables were consid- nanomoles per liter). Results are pre-from participants, divided into ali- ered as potential confounders: gender, sented for crude analyses and ad-quots, and stored cold (2– 4°C) or fro- age (in months), child race/ethnicity justed analyses. Gender- and age-zen. Samples collected for DAP mea- (non-Hispanic white, black, Mexican related differences were examined insurements were shipped on dry ice American, or other/multiracial), PIR subpopulation analyses and, becauseto the Centers for Disease Control (the ratio of self-reported family in- there were no differences in effect es-and Prevention’s National Center for come to the family’s appropriate pov- timates and no significant interaction,Environmental Health. Six urinary erty threshold value, on the basis of these variables were included as co-DAP metabolites, resulting from the Census data, recoded into 4 catego- variates in the models. In addition,degradation of 28 different organ- ries), BMI (in quartiles), blood lead race/ethnicity, PIR, fasting time, andophosphates, were measured in concentrations (logarithmically trans- logarithmically transformed urinaryurine to provide an indicator of the formed), maternal age at birth, mater- creatinine concentrations (as recom-body burden of common organophos- nal smoking during pregnancy (yes or mended by Barr et al,26 to adjust forphates.3 The urinary DAP metabolites no), and time since last consuming urine dilution) were included in themeasured were 3 dimethyl alkylphos- food or drink, recorded at the time of models because they are importantphate (DMAP) molecules (dimethyl blood and urine sampling (recorded potential confounders; other covari-phosphate, dimethyl thiophosphate, on a scale of 1 [0 –2 hours] to 7 [21–24 ates also were examined in sensitivityand dimethyl dithiophosphate) and 3 hours]). analyses. Because individual urinarye1272 BOUCHARD et al Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • ARTICLESTABLE 1 Concentrations of Urinary DAP Metabolites (N 1139) tection limit were between 35.7% and N Below Detection Urinary Metabolite Level, nmol/L 80.0%, depending on the metabolite Limit, n (%) (Table 1). Most children (93.8%) had Geometric Interquartile Mean Range Minimum Maximum 1 detectable metabolite, of the 6Diethyl phosphate 1133 534 (46.9) 4.7 0.9–28.1 0.4 5902 DAPs measured. In a multivariate anal-Diethyl thiophosphate 1121 487 (42.8) 2.0 0.4–7.6 0.3 650Diethyl dithiophosphate 1139 911 (80.0) 0.5 0.3–0.3 0.2 36 ysis, higher DAP concentrations wereDimethyl phosphate 1139 581 (51.0) 10.7 2.8–39.0 2.8 1324 associated with higher creatinine con-Dimethyl thiophosphate 1139 407 (35.7) 13.7 1.9–58.8 0.9 9929 centrations (P .001), younger ageDimethyl dithiophosphate 1133 664 (58.3) 1.7 0.4–7.3 0.3 7006 (P .03), lower blood lead concentra-DEAPs 1139 253 (22.2) 11.0 2.1–35.0 0.8 5905DMAPs 1139 209 (18.3) 41.3 10.1–130.7 4.5 10 068 tions (P .06), and higher PIR (PTotal DAPs 1139 71 (6.2) 68.3 24.4–186.0 6.0 10 195 .10). DAP concentrations were higher for children examined in 2003–2004 (adjusted mean: 18.15 nmol/L; SE: 1.15DAP metabolite levels were below the teristics similar to those of children nmol/L), compared with those exam-analytical limit of detection for a large not included in the sample (Table 2). ined in 2000 (mean: 12.62 nmol/L; SE:proportion of children (Table 1), which One hundred nineteen children met 1.24 nmol/L) and 2001–2002 (mean:might bias effect estimates,27 we the diagnostic criteria for any ADHD 11.69 nmol/L; SE: 1.18 nmol/L), al-conducted further analyses on the subtype, which corresponds to a pop- though not significantly (P .10). Gen-metabolite with the highest detection ulation prevalence of 12.1% (95% CI: der, race/ethnicity, and fasting dura-frequency, namely, dimethyl thiophos- 9.6%–15.1%). The prevalence esti- tion were not significantly associatedphate. Cases were categorized as be- mates were 7.6% (95% CI: 5.5%–10.4%) with DAP metabolite concentrationslow the limit of detection or lower or for inattentive subtype, 1.5% (95% CI: (all P .3).higher than the median of detectable 0.8%–2.7%) for hyperactive/impulsiveconcentrations adjusted for creatinine subtype, and 3.0% (95% CI: 2.1%– 4.3%) Any Subtype of ADHDlevels. for combined subtype. When children The odds of meeting the DISC-IV crite- taking ADHD medication were includedRESULTS ria for ADHD increased with the uri- as case subjects, there were 148 nary concentrations of total DAP me-Descriptive Statistics cases. tabolites (Table 3). Adjustment forOur study sample included 1139 chil- The proportions of children with uri- covariates attenuated the estimatesdren 8 to 15 years of age, with charac- nary DAP concentrations below the de- (for a 10-fold increase in total DAP con- centration, unadjusted OR: 1.31 [95%TABLE 2 Comparison of Characteristics of Children 8 to 15 Years of Age Not Included and Included CI: 1.06 –1.63]; adjusted OR: 1.21 [95% in Study Sample CI: 0.97–1.51]). This association was Not Included Included driven by DMAP metabolites, for whichMale, n (%) a 2247 (51.2) (N 4578) 570 (53.2) (N 1139) the association was statistically signif-Race/ethnicity, n (%)a Non-Hispanic white 1138 (59.6) (N 4578) 325 (63.3) (N 1139) icant even after adjustment (OR: 1.55 Black 1533 (16.0) (N 4578) 342 (13.2) (N 1139) [95% CI: 1.14 –2.10]). When children Mexican American 1555 (11.7) (N 4578) 382 (11.6) (N 1139) taking ADHD medication were included Other/multiracial 352 (12.7) (N 4578) 90 (12.0) (N 1139)PIR, n (%)a as case subjects, slightly higher effect 1.0 1390 (23.4) (N 4145) 363 (21.4) (N 1139) estimates were obtained for DMAPs 1.0–1.84 1009 (20.7) (N 4145) 274 (21.3) (N 1139) (adjusted OR: 1.72 [95% CI: 1.31–2.28]). 1.85–3.0 730 (20.6) (N 4145) 214 (21.6) (N 1139) 3.0 1016 (35.3) (N 4145) 288 (35.8) (N 1139) A 10-fold difference in DMAP concen-Maternal smoking during pregnancy, n (%)a 697 (19.8) (N 4509) 152 (17.7) (N 1125) trations corresponds approximately toADHD, n (%)a the increase from the 25th to 75th per- Any subtype 295 (12.2) (N 2859) 119 (12.1) (N 1139) centile of children’s concentrations Inattentive subtype 133 (5.9) (N 2865) 69 (7.6) (N 1139) Hyperactive subtype 81 (3.2) (N 2860) 21 (1.5) (N 1139) (Table 1). DEAP metabolite levels were Combined subtype 81 (3.1) (N 2865) 29 (3.0) (N 1139) not significantly associated with theAge, weighted mean SE, mo 144 0.6 (N 4578) 143 1.0 (N 1139) odds of ADHD, whether cases were de-BMI, weighted mean SE, kg/m2 20.8 0.1 (N 4502) 20.6 0.2 (N 1139)Blood lead level, weighted mean SE, g/dL 1.4 0.04 (N 4036) 1.4 0.04 (N 1093) fined strictly according to the DISC-IVMaternal age at birth, weighted mean SE, y 26.3 0.2 (N 4432) 26.4 0.3 (N 1107) criteria or included children takinga Proportions were weighted. ADHD medication (Table 3).PEDIATRICS Volume 125, Number 6, June 2010 e1273 Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • TABLE 3 ORs for Any ADHD Subtype for 10-Fold Increases in Urinary DAP Metabolite Levels account for creatinine concentrations (N 1139) in our analyses. We used creatinine- OR (95% CI) adjusted DAP, DMAP, and DEAP con- Cases Identified With DISC-IV Cases Identified With DISC-IV or ADHD centrations (metabolite/creatinine (n 119) Medication (n 148) concentrations), and results were es- Unadjusted Adjusteda Unadjusted Adjusteda sentially the same as those obtained inDEAPs 1.02 (0.74–1.41) 0.94 (0.69–1.28) 0.88 (0.66–1.18) 0.80 (0.60–1.05) the main analyses, in which adjust-DMAPs 1.66 (1.24–2.22) 1.55 (1.14–2.10) 1.87 (1.42–2.47) 1.72 (1.31–2.28)Total DAPs 1.31 (1.06–1.63) 1.21 (0.97–1.51) 1.48 (1.20–1.82) 1.35 (1.10–1.67) ment for the creatinine level wasa Adjusted for gender, age, race/ethnicity, PIR, fasting duration, and logarithmically transformed urinary creatinine achieved by including it as an indepen-concentration. dent variable along with the other covariates.TABLE 4 ORs for Any ADHD Subtype According to Creatinine Level-Adjusted Urinary Dimethyl To evaluate possible cohort effects, Thiophosphate Concentration (N 1139) we added a term for year of data col- Dimethyl Thiophosphate OR (95% CI) Concentration lection to the models, but this term Cases Identified With DISC-IV Cases Identified With DISC-IV or was not significant and did not (n 119) ADHD Medication (n 148) change the effect estimates appre- Unadjusted Adjusteda Unadjusted Adjusteda ciably. The effect estimates were notBelow detection limit (n 407) 1.0 (reference)Lower than median (n 366)b 1.11 (0.63–1.97) 1.05 (0.57–1.95) 1.36 (0.76–2.44) 1.22 (0.65–2.27) affected by adjustments for bloodHigher than median (n 366)c 1.83 (1.18–2.82) 1.93 (1.23–3.02) 2.04 (1.30–3.22) 2.12 (1.32–3.41) lead concentrations, maternal age ata Adjusted for gender, age, race/ethnicity, PIR, and fasting duration. birth, or maternal smoking duringb Range: 0.9 to 30.4 nmol g of creatinine per L; median: 11.2 nmol g of creatinine per L.c Range: 30.4 to 7932.0 nmol pregnancy. Given that ADHD medica- g of creatinine per L; median: 97.6 nmol g of creatinine per L. tion use could change the metabo- lism of pesticides and influence theirThe associations between DMAP con- phate concentrations above the me- excretion in urine, we excluded thecentrations and ADHD were similar for dian of detectable values had twice the 40 children who were taking suchgirls (with cases defined as meeting odds of ADHD, compared with children medication, but the results wereDISC-IV criteria or taking ADHD medica- with concentrations below the detec- similar (adjusted OR for 10-fold in-tion, adjusted OR: 2.09 [95% CI: 1.39 – tion limit (adjusted OR: 1.93 [95% CI: crease in DMAP levels: 1.80 [95% CI:3.15]) and boys (adjusted OR: 1.60 [95% 1.23–3.02]) (Table 4). The OR was 1.18 –2.76]).CI: 1.09 –2.36]; P for interaction .48). higher when children taking ADHDSimilarly, we examined age differ- medication were included as case Subtypes of ADHDences in DMAP effect estimates for subjects (adjusted OR: 2.12 [95% CI: The odds of meeting the diagnostic cri-children 8 to 11 years and 12 to 15 1.32–3.43]). teria for hyperactive/impulsive ADHDyears of age but found no difference (P subtype increased significantly withfor interaction .55). Sensitivity Analyses higher DEAP (adjusted OR for 10-foldThe metabolite dimethyl thiophos- The urinary creatinine level was a po- increase in concentration: 2.15 [95%phate was the most commonly de- tential confounder because higher CI: 1.06 – 4.40]), DMAP (adjusted OR fortected DMAP metabolite (64.3% of chil- concentrations were associated both 10-fold increase in concentration: 2.13dren) and accounted for 50% of total with greater odds of ADHD and with [1.08 – 4.20]), and total DAP (adjustedDMAP metabolites. Children with higher DAP concentrations. We exam- OR for 10-fold increase in concentra-creatinine-adjusted dimethyl thiophos- ined different analytical approaches to tion: 1.85 [1.04 –3.27]) levels (Table 5).TABLE 5 ORs for Subtypes of ADHD for 10-Fold Increases in Urinary DAP Metabolite Levels (N 1139) OR (95% CI) Hyperactive/Impulsive Subtype (n 21) Inattentive Subtype (n 69) Combined Subtype (n 29) Unadjusted Adjusteda Unadjusted Adjusteda Unadjusted AdjustedaDEAPs 2.29 (1.25–4.21) 2.15 (1.06–4.40) 0.77 (0.52–1.14) 0.70 (0.49–1.01) 1.29 (0.68–2.43) 1.22 (0.59–2.50)DMAPs 2.26 (1.33–3.86) 2.13 (1.08–4.20) 1.61 (1.10–2.37) 1.47 (0.99–2.19) 1.30 (0.56–2.99) 1.30 (0.48–3.48)Total DAPs 1.95 (1.18–3.22) 1.85 (1.04–3.27) 1.26 (0.91–1.75) 1.14 (0.81–1.61) 1.09 (0.59–2.01) 1.05 (0.51–2.16)a Adjusted for gender, age, race/ethnicity, PIR, fasting duration, and logarithmically transformed urinary creatinine concentration.e1274 BOUCHARD et al Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • ARTICLESThe odds of inattentive subtype in- surements of urinary metabolites of ADHD as were those with undetectablecreased with higher concentrations of organophosphates over a longer time concentrations.DMAP metabolites (adjusted OR: 1.47 period would provide a better assess- The present study uses a larger sam-[95% CI: 0.99 –2.19]), although this did ment of average exposure, but the ple size than previous investigationsnot reach the level of significance. Con- NHANES does not include longitudinal on neurodevelopmental effects of or-centrations of DAP metabolites were follow-up assessments. For organo- ganophosphate exposure, as well asnot significantly associated with the phosphates coming from the diet, the DSM-IV– based diagnostic outcomes.odds of combined subtype. measurement of organophosphate Comparisons across studies are metabolites in a single urine sample difficult because of differences inDISCUSSION may reflect average exposure levels exposure levels, timing of exposure,We report an association between uri- reasonably well, to the extent that diet outcomes assessed, and age at as-nary DMAP metabolite concentrations, is consistent. Given that organophos- sessment. Higher blood chlorpyrifoswhich are indicators of exposure to phates are eliminated from the body concentrations during pregnancydimethyl-containing organophosphate after 3 to 6 days,28 the detection of were found to be associated withpesticides, and increased odds of DAPs in the urine of most children in- poorer mental and motor developmentADHD for children 8 to 15 years of age. dicates continuing exposure. An addi- at 3 years,11 and greater postnatal ex-There was a 55% to 72% increase in the tional consideration is that urinary posure to organophosphates was as-odds of ADHD for a 10-fold increase in DAP levels might reflect not only expo- sociated with difficulties with memory,DMAP concentration, depending on the sure to organophosphates but also attention, motor tasks, behavior,14 andcriteria used for case identification. direct exposure to DAPs present in reaction time.13 Prenatal exposure toThis association was not explained by the environment, resulting from organophosphates also was associ-gender, age, PIR, race/ethnicity, fast- degradation of organophosphates ated with poorer mental developmenting duration, or creatinine concentra- through hydrolysis or photolysis. at 2 years of age and, as in our study,tion. Whether DAP metabolite concen- Significant amounts of DAPs have the association was with DMAP rathertrations are more strongly associated been found on several types of fruits than DEAP metabolites.12 The strongerwith a specific subtype of ADHD is un- and vegetables.29 In any case, mis- association with DMAP metabolitesclear, because of the small numbers of classification of exposure on the ba- could be explained by greater expo-cases, although the association was sis of measurements of urinary DAP sure to organophosphates metabo-stronger for the predominantly hyper- levels should be nondifferential and lized into DMAP metabolites, or it mightactive/impulsive subtype. This study should bias effect estimates toward indicate greater toxicity of theseshould be generalizable to the US pop- the null. organophosphates.ulation because the NHANES sample is Given the cross-sectional nature of our Several biological mechanisms mightnationally representative, unlike previ- analysis, we cannot rule out the possi- underlie an association between or-ous studies of groups with higher ex- bility that children with ADHD engage ganophosphate pesticides and ADHD. Aposure levels.11–15 With respect to the in behaviors that expose them to primary action of organophosphates,importance of these findings, organo- higher levels of organophosphates. If particularly with respect to acute poi-phosphates are among the most this were the case, however, we would soning, is inhibition of acetylcholinest-widely used pesticides, and the con- have expected to see higher levels of erase,30 and disruptions in cholinergiccentrations of DAP metabolites among urinary DEAP metabolites as well, signaling are thought to occur inchildren did not decrease from 2000 to which was not the case. Another limi- ADHD.31 At doses lower than those2003–2004. tation is measurement error, in that needed to inhibit acetylcholinesterase,The most important limitation of the the concentrations of individual DMAP certain organophosphates affectpresent study is the assessment of or- metabolites were below the analytical different neurochemical targets, in-ganophosphate exposure through limit of detection for large proportions cluding growth factors, several neuro-measurement of DAP metabolites in of children. This problem, however, transmitter systems, and second-only 1 spot urine sample. Given that does not apply to the analysis showing messenger systems.32,33 Exposure tolong-term exposure to organophos- that children with levels higher than some of these organophosphate com-phates likely would be necessary to the median of detectable dimethyl thio- pounds was shown to cause hyperac-produce neurochemical changes caus- phosphate concentrations were twice tivity and cognitive deficits in animaling ADHD-like behaviors, serial mea- as likely to be diagnosed as having studies.34,35 Developmental exposure toPEDIATRICS Volume 125, Number 6, June 2010 e1275 Downloaded from pediatrics.aappublications.org by guest on February 9, 2012
    • organophosphates might have persis- pesticide exposure to adverse develop- and should establish appropriatetent effects on multiple neural systems mental outcomes. Our findings sup- temporality.that may underlie ADHD behaviors, port the hypothesis that current levelssuch as inattention and cognitive defi- of organophosphate pesticide expo- ACKNOWLEDGMENTScits, similar to the effects of develop- sure might contribute to the childhood The Canadian Institutes for Health Re-mental nicotine exposure.36,37 burden of ADHD. Future studies should search provided a fellowship to Dr use a prospective design, with multiple Bouchard. Support for this researchCONCLUSIONS urine samples collected over time for was provided by National Institute ofThe present study adds to the accumu- better assessment of chronic expo- Environmental Health Sciences grantlating evidence linking higher levels of sure and critical windows of exposure, P30 ES 00002.REFERENCES 1. US Environmental Protection Agency. 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    • Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate PesticidesMaryse F. Bouchard, David C. Bellinger, Robert O. Wright and Marc G. Weisskopf Pediatrics; originally published online May 17, 2010; DOI: 10.1542/peds.2009-3058Updated Information & including high resolution figures, can be found at:Services http://pediatrics.aappublications.org/content/early/2010/05/17 /peds.2009-3058Citations This article has been cited by 6 HighWire-hosted articles: http://pediatrics.aappublications.org/content/early/2010/05/17 /peds.2009-3058#related-urlsPermissions & Licensing Information about reproducing this article in parts (figures, tables) or in its entirety can be found online at: http://pediatrics.aappublications.org/site/misc/Permissions.xht mlReprints Information about ordering reprints can be found online: http://pediatrics.aappublications.org/site/misc/reprints.xhtmlPEDIATRICS is the official journal of the American Academy of Pediatrics. A monthlypublication, it has been published continuously since 1948. PEDIATRICS is owned, published,and trademarked by the American Academy of Pediatrics, 141 Northwest Point Boulevard, ElkGrove Village, Illinois, 60007. Copyright © 2010 by the American Academy of Pediatrics. Allrights reserved. Print ISSN: 0031-4005. Online ISSN: 1098-4275. Downloaded from pediatrics.aappublications.org by guest on February 9, 2012