PROJECT SUMMARY Non-persistent pesticides are the cornerstone of modern agriculture, yet their routine application is particularly worrisome to child-bearing and lactating women in view of studies linking maternal exposures to increased risk of autism and neurodevelopmental problems in infants. The majority of studies to date have linked prenatal exposures to autism spectrum disorders and impairments in social and cognitive domains. Data on risks associated with early postnatal exposures via breast milk appears to be lacking, despite recent evidence showing the presence of non-persistent pesticides in breast milk. Additionally, it is not known which circulating pesticides accumulate in breast milk, and whether postnatal exposure risks to the infant are elevated for compounds that preferentially partition into breast milk. The goal of this proposal is to quantify an array of non-persistent pesticides in maternal breast milk and serum collected postnatally, in order to 1) relate pesticide concentrations in breast milk to the risk of neurodevelopmental impairments; 2) understand the extent of non-persistent pesticide partitioning from serum into breast milk; and 3) determine whether compounds that preferentially bioconcentrate in milk pose more of a risk to infant neurodevelopment compared to those that partition less. These objectives will be addressed in the “Markers of Autism Risk in Babies - Learning Early Signs” (MARBLES) cohort, which enrolled pregnant mothers who have had a previous child with autism spectrum disorders and therefore are at high risk of delivering another child who develops autism or atypical neurodevelopment in social and cognitive domains. We hypothesize that non-persistent pesticides that highly partition into breast milk, will be associated with increased risk of autism spectrum disorders and atypical neurodevelopment. This research will provide new information on the neurodevelopmental risks associated with early postnatal exposure to non-persistent pesticides, and determine whether these risks are specific to compounds that preferentially partition from blood to breast milk. Identifying non-persistent compounds in breast milk that may adversely impact neurodevelopment in the child, provides the basis for actively monitoring these chemicals in at-risk individuals.