Spatial Variability in ADHD-Related Behaviors Among Children Born to Mothers Residing Near the New Bedford Harbor Superfund Site

Abstract

Attention-deficit/hyperactivity disorder (ADHD) has an uncertain etiology, with potential contributions from different risk factors such as prenatal environmental exposure to organochlorines and metals, social risk factors, and genetics. The degree to which geographic variability in ADHD is independent of, or explained by, risk factors may provide etiological insight. We investigated determinants of geographic variation in ADHD-related behaviors among children living near the polychlorinated biphenyl-contaminated New Bedford Harbor (NBH) Superfund site in Massachusetts. Participants were 573 children recruited at birth (1993-1998) who were born to mothers residing near the NBH site. We assessed ADHD-related behaviors at age 8 years using Conners' Teacher Rating Scale-Revised: Long Version. Adjusted generalized additive models were used to smooth the association of pregnancy residence with ADHD-related behaviors and assess whether prenatal organochlorine or metal exposures, sociodemographic factors, or other factors explained spatial patterns. Models that adjusted for child's age and sex displayed significantly increased ADHD-related behavior among children whose mothers resided west of the NBH site during pregnancy. These spatial patterns persisted after adjusting for prenatal exposure to organochlorines and metals but were no longer significant after controlling for sociodemographic factors. The findings underscore the value of spatial analysis in identifying high-risk subpopulations and evaluating candidate risk factors.

Keywords: attention-deficit/hyperactivity disorder; environmental exposures; geographic analysis; sociodemographic risk factors.

Figure 1.

Birth addresses of participants in the New Bedford Cohort, who were born in 1993–1998 and whose mothers were living in 4 towns neighboring the New Bedford Harbor Superfund site (New Bedford, Dartmouth, Acushnet, and Fairhaven, Massachusetts) during pregnancy. The population (shown in green) is distributed around primarily nonresidential open space (shown in gray).

Figure 2.

Spatial distribution of predicted raw scores on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) attention-deficit/hyperactivity disorder Total subscale for children in the New Bedford Cohort, born in 1993–1998. A) Spatial variability of DSM-IV Total raw scores among New Bedford Cohort children is predicted for an 8-year-old boy without adjustment for chemical and nonchemical risk factors. The global P value for the significance of location is 0.003. Contour lines denote areas of significantly increased and decreased scores. Adjustment for umbilical cord serum level of the sum of 4 prevalent polychlorinated biphenyl congeners (congeners 118, 138, 153, and 180), umbilical cord serum ρ,ρ′-dichlorodiphenyl dichloroethylene level, peripartum maternal hair mercury level, and child peak 12- to 36-month blood lead level does not change the results. B) Spatial variability in predicted DSM-IV Total scores is attenuated in an analysis adjusted for Home Observation for Measurement of the Environment (HOME) score (predicted at the 95th percentile, where a higher score is indicative of a better home environment and parenting), and location is no longer significant (P = 0.236). Adjustment for other sociodemographic factors produces similar results.

Figure 3.

Geographic patterns of Home Observation for Measurement of the Environment (HOME) scores for children in the New Bedford Cohort, born in 1993–1998. Areas with higher HOME scores (indicating a better home environment and parenting) are the same areas where predicted raw scores on the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, attention-deficit/hyperactivity disorder Total subscale are lowest (less frequent adverse behavior) (see Figure 2A).