| Autism Spectrum Disorders in Relation to Distribution of Hazardous Air Pollutants in the San Francisco Bay Area Gayle C. Windham,1 Lixia Zhang,2 Robert Gunier,1 Lisa A. Croen,3 and Judith K. Grether1 1Division of Environmental and Occupational Disease Control, California Department of Health Services, Richmond, California, USA; 2Impact Assessment, Inc., La Jolla, California, USA; 3Kaiser Permanente Medical Care Program Division of Research, Oakland, California, USA Abstract
Objective: To explore possible associations between autism spectrum disorders (ASD) and environmental exposures, we linked the California autism surveillance system to estimated hazardous air pollutant (HAP) concentrations compiled by the U.S. Environmental Protection Agency. Methods: Subjects included 284 children with ASD and 657 controls, born in 1994 in the San Francisco Bay area. We assigned exposure level by census tract of birth residence for 19 chemicals we identified as potential neurotoxicants, developmental toxicants, and/or endocrine disruptors from the 1996 HAPs database. Because concentrations of many of these were highly correlated, we combined the chemicals into mechanistic and structural groups, calculating summary index scores. We calculated ASD risk in the upper quartiles of these group scores or individual chemical concentrations compared with below the median, adjusting for demographic factors. Results: The adjusted odds ratios (AORs) were elevated by 50% in the top quartile of chlorinated solvents and heavy metals [95% confidence intervals (CIs) , 1.1–2.1], but not for aromatic solvents. Adjusting for these three groups simultaneously led to decreased risks for the solvents and increased risk for metals (AORs for metals: fourth quartile = 1.7 ; 95% CI, 1.0–3.0 ; third quartile = 1.95 ; 95% CI, 1.2–3.1) . The individual compounds that contributed most to these associations included mercury, cadmium, nickel, trichloroethylene, and vinyl chloride. Conclusions: Our results suggest a potential association between autism and estimated metal concentrations, and possibly solvents, in ambient air around the birth residence, requiring confirmation and more refined exposure assessment in future studies. Key words: air toxics, autism, autism spectrum disorders, diesel, mercury, metals, neurodevelopment, neurotoxicants, solvents, vinyl chloride. Environ Health Perspect 114: 1438–1444 (2006) . doi:10.1289/ehp.9120 available via http://dx.doi.org/ [Online 21 June 2006]
Address correspondence to G. Windham, Division of Environmental and Occupational Disease Control, California Department of Health Services, 850 Marina Bay Parkway, Building P, Richmond, CA 94804 USA. Telephone: (510) 620-3638. Fax: (510) 620-3720. E-mail: gwindham@dhs.ca.gov We thank M. Falade and A. Hertz for geocoding, B. Hopkins and M. Anderson for autism data linkage and management, D. Smith for helpful comments, L. Lotspeich for expert clinical review, the California Centers for Autism and Developmental Disabilities Research and Epidemiology staff for data collection, and the California Department of Developmental Services regional centers and Kaiser Permanente Medical Care Program for provision of data on autism. Funding was provided for data analyses by the Agency for Toxic Substances and Disease Registry and for surveillance and analyses by the Centers for Disease Control and Prevention, as well as by the California Department of Health Services. The authors declare they have no competing financial interests. Received 23 February 2006 ; accepted 21 June 2006.
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