Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Pesticides

WHAT’S KNOWN ON THIS SUBJECT: Exposure to AUTHORS: Maryse F. Bouchard, PhD,a,b David C. Bellinger, 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, diagnostic criteria for ADHD. and Brigham and Women’s Hospital, Boston, Massachusetts KEY WORDS attention-deficit/hyperactivity disorder, pesticides, organophosphates, National Health and Nutrition Examination Survey ABBREVIATIONS abstract DAP—dialkyl OBJECTIVE: The goal was to examine the association between urinary DMAP—dimethyl alkylphosphate DEAP—diethyl alkylphosphate concentrations of dialkyl phosphate metabolites of organophosphates OR—odds ratio and attention-deficit/hyperactivity disorder (ADHD) in children 8 to 15 CI—confidence interval years of age. ADHD—attention-deficit/hyperactivity disorder NHANES—National Health and Nutrition Examination Survey METHODS: Cross-sectional data from the National Health and Nutrition DISC-IV—Diagnostic Interview Schedule for Children IV Examination Survey (2000–2004) were available for 1139 children, who PIR—poverty/income ratio were representative of the general US population. A structured inter- DSM-IV—Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition view with a parent was used to ascertain ADHD diagnostic status, on The Canadian Institutes for Health Research played no role in the 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, RESULTS: One hundred nineteen children met the diagnostic criteria and approval of the manuscript. for ADHD. Children with higher urinary dialkyl phosphate concentra- www.pediatrics.org/cgi/doi/10.1542/peds.2009-3058 tions, especially dimethyl alkylphosphate (DMAP) concentrations, were doi:10.1542/peds.2009-3058 more likely to be diagnosed as having ADHD. A 10-fold increase in DMAP Accepted for publication Feb 23, 2010 concentration was associated with an odds ratio of 1.55 (95% confi- Address correspondence to Maryse F. Bouchard, PhD, University dence interval: 1.14–2.10), with adjustment for gender, age, race/eth- of Montreal, Department of Environmental and Occupational Health, CP 6128 Succursale Centre-Ville, Montreal, QC H3C 3J7, nicity, poverty/income ratio, fasting duration, and urinary creatinine Canada. E-mail: [email protected] concentration. For the most-commonly detected DMAP metabolite, di- PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275). methyl , children with levels higher than the median of Copyright © 2010 by the American Academy of Pediatrics detectable concentrations had twice the odds of ADHD (adjusted odds FINANCIAL DISCLOSURE: The authors have indicated they have ratio: 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–e1277

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Approximately 40 organophosphate A few epidemiological studies sug- Children who received newborn care pesticides are registered with the US gested that organophosphate expo- in an ICU or premature nursery (n ϭ Environmental Protection Agency for sure was associated with adverse neu- 167) and those with birth weights of use in the United States.1 In 2001, 73 rodevelopmental outcomes, but no Ͻ2500 g (n ϭ 126) were excluded be- million pounds of organophosphates studies have addressed possible risks cause these are important risk factors were 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 Ͻ20 drinking water, and residential pesti- amined the cross-sectional associa- mg/dL) and 1 outlier with respect to cide use important sources of expo- tion between urinary DAP metabolite urinary DAP concentrations. Children sure.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 ϭ 43; fasting to pesticides for infants and children lence in children 8 to 15 years of age. duration, n ϭ 38; urinary creatinine would be the diet, according to the level, n ϭ 1). National Academy of Sciences.3 The METHODS US Pesticide Data Program’s 2008 Re- Study Design and Population ADHD Assessment port indicates that detectable concen- The National Health and Nutrition Ex- The Diagnostic Interview Schedule for trations of the organophosphate mala- amination Survey (NHANES) is a Children IV (DISC-IV), a structured diag- thion were found in 28% of frozen population-based, health survey of nostic interview designed for use in ep- blueberry samples, 25% of strawberry 18 noninstitutionalized US residents con- idemiological studies, was used to samples, and 19% of celery samples.4 ducted by the National Center for assess the presence of ADHD on the Children are generally considered to Health Statistics of the Centers for Dis- basis of slightly modified criteria from be at greatest risk from organophos- ease Control and Prevention. The the Diagnostic and Statistical Manual phate toxicity, because the developing NHANES uses a complex, multistage, of Mental Disorders, Fourth Edition 19 brain is more susceptible to neurotoxi- probability sampling design, with over- (DSM-IV). The interview was con- cants5 and the dose of pesticides per sampling of certain subgroups. Partic- ducted with the mother or another body weight is likely to be larger for ipants completed household surveys, caretaker over the telephone by children. 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. The phate exposure), compared with other mobile centers.16 We used data from DISC-IV has evidence of substantial va- 18 18 age groups in the US population.6 Chil- 2000–2004, years for which ADHD was lidity, reliability for both its English 20,21 dren have reduced expression of de- assessed in children 8 to 15 years of and Spanish versions, and success- toxifying enzymes, which contributes age; diagnoses were available for 3998 ful use via telephone in DSM-IV field tri- 22 to their vulnerability.7,8 Epidemiologi- children. Urinary DAP metabolite levels als. The use of DISC-IV data is re- cal studies linking exposure to organo- were measured for a random sub- stricted for confidentiality reasons; and neurodevelopment sample of the NHANES participants. therefore, we accessed the data have focused on populations with high From 2000 to 2002, the sampling rate through the National Center for Health levels 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 the with 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 inattentive in 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 the havioral problems, poorer short-term stitutional review board, and all par- presence, during the previous 12 memory 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 www.aappublications.org/news by guest on September 25, 2021 with significant impairment in Ն2 set- diethyl alkylphosphate (DEAP) mole- Data Analyses 23 tings (eg, at school and home). The cules (diethyl phosphate, diethyl thio- We used the complex samples module DSM-IV criterion that symptoms must phosphate, and diethyl dithiophos- of SPSS 17.0 (SPSS Inc, Chicago, IL) to not occur in conjunction with another phate). DMAP metabolites are derived conduct all analyses, with accounting neuropsychiatric 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 sample degradation of O,O-diethyl-substituted toms must have been present before 7 weights were used to obtain robust lin- organophosphates such as chlorpyri- years of age, because our hypothesis earized SEs and unbiased point esti- fos. The measurements were per- was that urinary DAP concentrations mates. The threshold for statistical formed through lyophilization and would be associated with increased significance was set at P Ͻ .05. All sta- chemical derivatization, followed by odds of concurrent ADHD. tistical tests were 2-sided. The DAP me- analysis through isotope-dilution gas The DISC-IV identified 119 cases of tabolite concentrations were divided chromatography-tandem mass spec- ADHD, but 30 children did not meet the by the respective molecular weights trometry.24 Stable-isotope analogues diagnostic criteria although the parent before being summed to yield DEAP, were used as internal standards for reported use of doctor-prescribed 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 and year. Because the diagnostic interview might have different relationships to precision, with low analytical limits of addresses the presence of symptoms, the outcomes,12 they were examined detection. Concentrations below the children whose symptoms were well separately. Because the distributions detection limit were imputed a value controlled with medication would not 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 Urinary fore, we also conducted analyses in creatinine concentrations were deter- transformations (base 10) were ap- which ADHD cases were defined as ei- mined using an automated colorimet- plied. Correlates of urinary DAP metab- ther meeting the DISC-IV diagnostic cri- ric method based on a modified Jaffe olite concentrations were examined teria or regularly taking ADHD medica- reaction on a Beckman Synchron AS/ with a general linear model. Logistic tion during the previous year. ASTRA clinical analyzer (Beckman In- regression analyses were used to esti- struments, Inc., Brea, CA) at the mate odds ratios (ORs) and 95% confi- Measurement of Urinary Fairview University Medical Center, dence intervals (CIs) for ADHD (any Metabolites of Organophosphate Minneapolis, Minnesota.26 subtype) and ADHD subtypes, per 10- Pesticides fold increases in total DAP, DMAP, and During 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 in surements were shipped on dry ice American, or other/multiracial), PIR subpopulation analyses and, because to 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 Ն28 different organ- ries), BMI (in quartiles), blood lead race/ethnicity, PIR, fasting time, and ophosphates, were measured in concentrations (logarithmically trans- logarithmically transformed urinary urine 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 for phates.3 The urinary DAP metabolites no), and time since last consuming urine dilution) were included in the measured were 3 dimethyl alkylphos- food or drink, recorded at the time of models because they are important phate (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 sensitivity and dimethyl dithiophosphate) and 3 hours]). analyses. Because individual urinary

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TABLE 1 Concentrations of Urinary DAP Metabolites (N ϭ 1139) tection limit were between 35.7% and N Below Detection Urinary Metabolite Level, nmol/L 80.0%, depending on the metabolite Limit, n (%) Geometric Interquartile (Table 1). Most children (93.8%) had Mean Range Minimum Maximum Ն1 detectable metabolite, of the 6 Diethyl 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 0.3 650 ysis, higher DAP concentrations were Diethyl dithiophosphate 1139 911 (80.0) 0.5 0.3–0.3 0.2 36 Dimethyl 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 Ͻ .001), younger age Dimethyl dithiophosphate 1133 664 (58.3) 1.7 0.4–7.3 0.3 7006 (P ϭ .03), lower blood lead concentra- DEAPs 1139 253 (22.2) 11.0 2.1–35.0 0.8 5905 ϭ ϭ DMAPs 1139 209 (18.3) 41.3 10.1–130.7 4.5 10 068 tions (P .06), and higher PIR (P Total 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: 1.15 DAP 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 ϭ .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 associated phate. Cases were categorized as be- mates were 7.6% (95% CI: 5.5%–10.4%) with DAP metabolite concentrations low the limit of detection or lower or for inattentive subtype, 1.5% (95% CI: (all P Ͼ .3). higher than the median of detectable 0.8%–2.7%) for hyperactive/impulsive concentrations adjusted for creatinine subtype, and 3.0% (95% CI: 2.1%–4.3%) Any Subtype of ADHD levels. for combined subtype. When children The odds of meeting the DISC-IV crite- taking ADHD medication were included RESULTS 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 for Our study sample included 1139 chil- The proportions of children with uri- covariates attenuated the estimates dren 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 which Male, n (%)a 2247 (51.2) (N ϭ 4578) 570 (53.2) (N ϭ 1139) the association was statistically signif- Race/ethnicity, n (%)a Non-Hispanic white 1138 (59.6) (N ϭ 4578) 325 (63.3) (N ϭ 1139) icant even after adjustment (OR: 1.55 Black 1533 (16.0) (N ϭ 4578) 342 (13.2) (N ϭ 1139) [95% CI: 1.14–2.10]). When children Mexican American 1555 (11.7) (N ϭ 4578) 382 (11.6) (N ϭ 1139) taking ADHD medication were included Other/multiracial 352 (12.7) (N ϭ 4578) 90 (12.0) (N ϭ 1139) PIR, n (%)a as case subjects, slightly higher effect Ͻ1.0 1390 (23.4) (N ϭ 4145) 363 (21.4) (N ϭ 1139) estimates were obtained for DMAPs 1.0–1.84 1009 (20.7) (N ϭ 4145) 274 (21.3) (N ϭ 1139) (adjusted OR: 1.72 [95% CI: 1.31–2.28]). ϭ ϭ 1.85–3.0 730 (20.6) (N 4145) 214 (21.6) (N 1139) A 10-fold difference in DMAP concen- Ͼ3.0 1016 (35.3) (N ϭ 4145) 288 (35.8) (N ϭ 1139) Maternal smoking during pregnancy, n (%)a 697 (19.8) (N ϭ 4509) 152 (17.7) (N ϭ 1125) trations corresponds approximately to ADHD, n (%)a the increase from the 25th to 75th per- Any subtype 295 (12.2) (N ϭ 2859) 119 (12.1) (N ϭ 1139) centile of children’s concentrations Inattentive subtype 133 (5.9) (N ϭ 2865) 69 (7.6) (N ϭ 1139) Hyperactive subtype 81 (3.2) (N ϭ 2860) 21 (1.5) (N ϭ 1139) (Table 1). DEAP metabolite levels were Combined subtype 81 (3.1) (N ϭ 2865) 29 (3.0) (N ϭ 1139) not significantly associated with the Age, weighted mean Ϯ SE, mo 144 Ϯ 0.6 (N ϭ 4578) 143 Ϯ 1.0 (N ϭ 1139) odds of ADHD, whether cases were de- BMI, weighted mean Ϯ SE, kg/m2 20.8 Ϯ 0.1 (N ϭ 4502) 20.6 Ϯ 0.2 (N ϭ 1139) Blood lead level, weighted mean Ϯ SE, ␮g/dL 1.4 Ϯ 0.04 (N ϭ 4036) 1.4 Ϯ 0.04 (N ϭ 1093) fined strictly according to the DISC-IV Maternal age at birth, weighted mean Ϯ SE, y 26.3 Ϯ 0.2 (N ϭ 4432) 26.4 Ϯ 0.3 (N ϭ 1107) criteria or included children taking a Proportions were weighted. ADHD medication (Table 3).

PEDIATRICS Volume 125, Number 6, June 2010 e1273 Downloaded from www.aappublications.org/news by guest on September 25, 2021 TABLE 3 ORs for Any ADHD Subtype for 10-Fold Increases in Urinary DAP Metabolite Levels account for creatinine concentrations (N ϭ 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 ϭ ϭ (n 119) Medication (n 148) concentrations), and results were es- Unadjusted Adjusteda Unadjusted Adjusteda sentially the same as those obtained in DEAPs 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 was a 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, ϭ Thiophosphate Concentration (N 1139) we added a term for year of data col- Dimethyl Thiophosphate OR (95% CI) lection to the models, but this term Concentration Cases Identified With DISC-IV Cases Identified With DISC-IV or was not significant and did not (n ϭ 119) ADHD Medication (n ϭ 148) change the effect estimates appre- a a Unadjusted Adjusted Unadjusted Adjusted ciably. The effect estimates were not ϭ Below detection limit (n 407) 1.0 (reference) affected by adjustments for blood Lower than median (n ϭ 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) Higher than median (n ϭ 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 at a Adjusted for gender, age, race/ethnicity, PIR, and fasting duration. birth, or maternal smoking during b Range: 0.9 to 30.4 nmol ϫ g of creatinine per L; median: 11.2 nmol ϫ g of creatinine per L. pregnancy. Given that ADHD medica- c Range: 30.4 to 7932.0 nmol ϫ g of creatinine per L; median: 97.6 nmol ϫ g of creatinine per L. tion use could change the metabo- lism of pesticides and influence their The associations between DMAP con- phate concentrations above the me- excretion in urine, we excluded the centrations and ADHD were similar for dian of detectable values had twice the 40 children who were taking such girls (with cases defined as meeting odds of ADHD, compared with children medication, but the results were DISC-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 ϭ .48). higher when children taking ADHD Similarly, we examined age differ- medication were included as case Subtypes of ADHD ences 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 ADHD years of age but found no difference (P subtype increased significantly with for interaction ϭ .55). Sensitivity Analyses higher DEAP (adjusted OR for 10-fold The 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 for tected DMAP metabolite (64.3% of chil- concentrations were associated both 10-fold increase in concentration: 2.13 dren) and accounted for 50% of total with greater odds of ADHD and with [1.08–4.20]), and total DAP (adjusted DMAP 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 ϭ 1139) OR (95% CI) Hyperactive/Impulsive Subtype (n ϭ 21) Inattentive Subtype (n ϭ 69) Combined Subtype (n ϭ 29) Unadjusted Adjusteda Unadjusted Adjusteda Unadjusted Adjusteda DEAPs 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.

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The odds of inattentive subtype in- surements of urinary metabolites of ADHD as were those with undetectable creased 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 investigations not 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 as not 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 in DISCUSSION 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 which are indicators of exposure to phates are eliminated from the body concentrations during pregnancy dimethyl-containing organophosphate after 3 to 6 days,28 the detection of were found to be associated with pesticides, and increased odds of DAPs in the urine of most children in- poorer mental and motor development ADHD 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 and criteria used for case identification. direct exposure to DAPs present in reaction time.13 Prenatal exposure to This 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 development ing 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 rather trations are more strongly associated been found on several types of fruits than DEAP metabolites.12 The stronger with a specific subtype of ADHD is un- and vegetables.29 In any case, mis- association with DMAP metabolites clear, 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 might active/impulsive subtype. This study should bias effect estimates toward indicate greater toxicity of these should 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 might nationally 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. A posure 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 cholinergic centrations of DAP metabolites among urinary DEAP metabolites as well, signaling are thought to occur in children did not decrease from 2000 to which was not the case. Another limi- ADHD.31 At doses lower than those 2003–2004. tation is measurement error, in that needed to inhibit acetylcholinesterase, The most important limitation of the the concentrations of individual DMAP certain organophosphates affect present 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 to long-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 animal ing ADHD-like behaviors, serial mea- as likely to be diagnosed as having studies.34,35 Developmental exposure to

PEDIATRICS Volume 125, Number 6, June 2010 e1275 Downloaded from www.aappublications.org/news by guest on September 25, 2021 organophosphates might have persis- pesticide exposure to adverse develop- and should establish appropriate tent effects on multiple neural systems mental outcomes. Our findings sup- temporality. that may underlie ADHD behaviors, port the hypothesis that current levels such as inattention and cognitive defi- of organophosphate pesticide expo- ACKNOWLEDGMENTS cits, 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 research CONCLUSIONS urine samples collected over time for was provided by National Institute of The present study adds to the accumu- better assessment of chronic expo- Environmental Health Sciences grant lating evidence linking higher levels of sure and critical windows of exposure, P30 ES 00002. REFERENCES

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PEDIATRICS Volume 125, Number 6, June 2010 e1277 Downloaded from www.aappublications.org/news by guest on September 25, 2021 Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides Maryse F. Bouchard, David C. Bellinger, Robert O. Wright and Marc G. Weisskopf Pediatrics 2010;125;e1270 DOI: 10.1542/peds.2009-3058 originally published online May 17, 2010;

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Downloaded from www.aappublications.org/news by guest on September 25, 2021 Attention-Deficit/Hyperactivity Disorder and Urinary Metabolites of Organophosphate Pesticides Maryse F. Bouchard, David C. Bellinger, Robert O. Wright and Marc G. Weisskopf Pediatrics 2010;125;e1270 DOI: 10.1542/peds.2009-3058 originally published online May 17, 2010;

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