A growing number of U.S. communities have discovered per- and polyfluoroalkyl substances (PFASs, oftencalled PFCs) in drinking water. Epidemiological studies have reported negative associations between pediatricPFAS exposure and immune function, and suggest that current drinking water guidelines may not adequatelyprotect children from immunotoxicity. In 2016, the National Toxicology Program concluded that two PFASs,PFOA and PFOS, are presumed immune hazards based on human and animal studies. A key knowledge gapis whether exposure to drinking water contaminated by AFFF firefighting foams with complex PFAS mixturescauses clinically relevant immunotoxicity. Communities seek guidance for interpreting blood and water testresults and information on health effects, water treatment, remediation, and strategies to engage local officials. This project will leverage existing researcher-community partnerships to address concerns about healtheffects from PFASs in drinking water and develop tools and materials to support impacted communities. Wewill engage with two communities with AFFF-contaminated drinking water, the Pease International Tradeport inPortsmouth, NH, and Hyannis, MA, and evaluate potential immune responses and explore metabolomicsprofiles among young children. We will develop an online resource center to serve PFAS-affected communitiesnationwide with educational materials, data tools, and opportunities to connect with other communities. We willexplore the exposure experience of affected communities by conducting in-depth interviews and ethnographicresearch. Project partners include environmental health and social science researchers and communityactivists with a well-established collaboration. This community-engaged research project has three aims:Aim 1. Quantify associations of child serum PFOA, PFOS, PFHxS, and total PFASs with a) serum antibody levels following diphtheria and tetanus (DTaP) vaccinations and b) metabolomic profiles.Aim 2. Develop the PFAS Exchange, an online resource center with educational materials, data interpretation tools, tap water testing, and resources to connect communities, provide report-back materials for participants, and engage with residents of affected communities, medical professionals, and other stakeholders.Aim 3. Assess individual, family, and community-level experience of residents in areas impacted by PFAS- contaminated drinking water.The proposed study is innovative in developing novel web-based tools to visualize and interpret personalexposure data, and will be the first to evaluate immunotoxicity and apply novel metabolomics methods in U.S.children exposed to AFFF-contaminated drinking water in early life. It will improve public health by supportingefforts to reduce exposures and health impacts of PFAS contamination through engagement, education, andresearch. This project fulfills the Research to Action mission by addressing community concerns about healtheffects of contaminated drinking water and involving community members throughout.