Per- and polyfluoroalkyl substances (PFAS) is a collective name for approx. 5000 synthetic chemicals used in a myriad of products, such as nonstick frying pans, waterproof clothing, cosmetics and firefighting foam. They are sometimes called “forever chemicals” as they breakdown very slowly, if at all, in the environment. They are found in indoor and outdoor environments, wildlife and in virtually every human and have been associated with cancer, developmental toxicity, and other negative health effects. Plausible point sources of PFAS are the many sewage treatment plants draining into in the Baltic Sea. Very little is known about the amounts and composition of PFAS coming from STPs as well as the effects from them on the Baltic Sea organisms. We believe that the PFAS currently monitored (commonly around 20 of the 5000 substances) only comprise a small fraction of the total PFASs released. The disparity between the PFAS monitored and the PFAS used, suggests that the exposure to PFASs in the environment is largely underestimated. The aim of this project is to measure the concentrations and composition of PFAS, in water, sediment and organisms in Baltic Sea food webs in the vicinity of STPs by combining methods of determining the different fractions of fluorine; known and unknown PFASs (i.e. fluorine mass balance, FMB). In addition, effects of developmental exposure from emerging and unstudied PFAS will be evaluated in experiments in two Baltic Sea organisms.