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Absence of Effect-Measure Modification Between Polychlorinated Biphenyls and Methylmercury on ADHD-Like Behaviors in the New Bedford Cohort

Sagiv, Sharon*†; Bellinger, David*‡; Altshul, Larisa*; Amarasiriwardena, Chitra*; Korrick, Susan*†

doi: 10.1097/01.ede.0000362449.40526.e6
Abstracts: ISEE 21st Annual Conference, Dublin, Ireland, August 25–29, 2009: Symposium Abstracts

*Harvard School of Public Health, Boston, MA, United States; †Brigham and Women's Hospital, Boston, MA, United States; and ‡Children's Hospital, Boston, MA, United States.


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Background and Objective:

Two prior studies report effect modification between polychlorinated biphenyls (PCBs) and methylmercury (MeHg) on neurodevelopmental outcomes in children, including behavior and cognition. We previously reported minor to moderate main effect associations of low-level prenatal PCBs and MeHg with ADHD-like behaviors, such as inattention and impulsivity in the New Bedford cohort. We investigated a synergistic relationship between PCBs and MeHg on ADHD-like behaviors at 8 years of age using the NES2 Continuous Performance Test (CPT) and the Conners’ Rating Scale for Teachers (CRS-T).

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Participants came from a prospectively followed cohort of children born between 1993 and 1998 to mothers residing near a PCB-contaminated harbor and Superfund site in New Bedford, Massachusetts. Prenatal PCB exposure was measured in cord serum and maternal hair was collected 10 days postpartum and measured for total mercury (Hg), as a proxy for MeHg. We assessed additive effect modification between PCBs and Hg on: 1) sustained attention (errors of omission) and impulse control (errors of commission) measured with the CPT, and 2) Conners’ ADHD Index, DSM-IV Inattention, DSM-IV Impulsivity-Hyperactive and DSM-IV Total (combined subtypes) measured with the CRS-T, with multivariable regression models using the likelihood ratio test.

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Median (and range) cord serum levels for the sum of four prevalent PCB congeners (118, 138, 153, 180) and hair Hg levels for the 485 subjects with data on both toxicants was 0.18 (0.01–4.41) ng/g serum and 0.4 (0.03–0.5) ppm, respectively. The Spearman correlation coefficient between PCBs and Hg was 0.4. No statistically significant or consistent additive effect modification between PCBs and Hg was observed for any of the CPT and CRS-T outcomes.

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We did not observe additive effect modification between PCBs and Hg on ADHD-like behaviors. Our findings do not support synergism between these toxicants at these low exposure levels.

© 2009 Lippincott Williams & Wilkins, Inc.