Occurrence of Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) in the Transboundary Guarani Aquifer System within a Highly Urbanized Context in the Sinos River Basin

The Guarani Aquifer System (GAS) is a transboundary sedimentary aquifer source of public water supply for millions of people in Brazil, Argentina, Uruguay, and Paraguay, known for the high quality of its groundwaters. However, under surface conditions in an urban environment with poor sanitation and intense industrial activity, water quality can degrade due to the input of a wide range of contaminants, including per and polyfluoroalkyl substances (PFAS). PFAS are anthropogenic substances widely used in industry for their unique properties, such as hydrophobicity and chemical stability. However, in the environment, they exhibit high persistence and potential health risks to humans and other organisms. In this study, 28 PFAS were investigated in the GAS within the context of the Sinos River Basin, located in southern Brazil, a region known for its lack of sewage treatment, uncontrolled urbanization, and strong leather, metallurgical and electroplating industries. Fifteen groundwater samples were collected from tubular wells and springs, and five samples were taken from the Sinos River. In five groundwater samples least two PFAS were detected, with the total PFAS (ΣPFAS) up to 16.78 ng/L, with PFOA and PFBA being the most frequent. In surface waters of the Sinos River, ΣPFAS ranged from 0.98 to 71.09 ng/L, with 6:2 FTS and PFOSA being the most frequently detected. Our study is the first one to identify the background of PFAS in the GAS and suggests the need for long-term monitoring of the aquifer, as its characteristics may promote the retention of these highly persistent compounds, likely associated with the use of pesticides and the leather and electroplating industries.