The U.S. Environmental Protection Agency (EPA) is issuing this Request for Applications (RFA) to better understand the impacts of per- and poly-fluoroalkyl substances (PFAS) on water quality and availability across the U.S. The Agency is seeking new information on 1) the fate and transport of short (C4 to C7) and long-chain ( C8) PFAS in the environment, including per- and poly-fluorinated carboxylic acids, sulfonic acids, and ethers, and associated precursor and transformation products; 2) comprehensive human and ecosystem exposure to PFAS; and 3) PFAS toxicity, modes of action, physiologically-based pharmacokinetics and pharmacodynamics, and other topics related to hazard assessment. Proposals may address any or all of these topic areas in support of the development of robust risk assessments for human and ecological exposure to PFAS in water.