The main objective of this project is to study the effects of low-level intrauterine toxin exposures on memory and learning in school age children. Specifically, the neurodevelopmental effects of intrauterine exposures to common environmental contaminants-polychlorinated biphenyls (PCBs), dichlorodiphenyl dichloroethene (DDE), methylmercury (MeHg), and lead (Pb)-- at levels occurring in the general environment will be studied. The neurodevelopmental toxicities of postnatal Pb exposure will also be studied. The study will benefit from extensive information that is available for an established cohort of 790 children born to mothers residing in communities adjacent to a PCB- contaminated harbor (and Superfund site) in Massachusetts. Biomarkers of multiple in utero exposure measures were obtained for these children at birth, and detailed developmental assessments were performed during the first six months of life. The proposed study will be conducted as a follow- up evaluation of these children as they achieve school age with three major hypotheses. Low-level in utero PCB, DDE, MeHg, and Pb exposures and postnatal Pb exposures are associated with: (1) Long-term toxicity to memory and other skills necessary for successful learning. (2) Impaired learning as assessed by achievement testing, and achievement that is blow expectation compared with general cognitive ability. (3) Chronic behavioral disturbances, in particular those associated with attention disorders. A secondary hypothesis of the study will be to assess the relationship of neighborhood and related contextual variables (e.g., income and racial distribution within neighborhoods) with the developmental outcomes of interest. A corollary to this hypothesis is assessment of whether proximity to the PCB-contaminated site is associated with adverse developmental effects independent of individual exposure measures. As part of this research, assessments of memory, learning, language skills, general cognition, and attentions; standardized achievement testing; and teacher and parental behavioral assessments will be obtained for 500 six-to eight-year olds. Results of these assessments will be compared with cord serum and/or breast milk levels of PCB, DDE, and Pb; preschool blood Pb levels; and peripartum maternal hair mercury levels. The ultimate goals of this study are to address uncertainties regarding the relationship of these exposures with childhood abilities and behaviors that are critical to successful learning and to do so at exposure levels characteristic of the current U.S. population.