Per- and Polyfluoroalkyl Substances (PFAS) in the Rusizi River System, Burundi: A Multi-Compartment Assessment from Tributaries to Lake Tanganyika.

Per- and polyfluoroalkyl substances (PFAS) are global pollutants, yet data from tropical freshwater ecosystems remain scarce. This study provides the first assessment of PFAS occurrence in the Rusizi delta (Burundi), from tributaries to Lake Tanganyika, by analyzing water, sediment, macrophytes, and fish, and by evaluating human health risks from fish consumption. In water, only PFOA (<0.60-7.80 ng/L) was detected and showed a uniform spatial distribution. Sediment concentrations were largely below quantification limits, likely reflecting unfavorable sorption conditions. Macrophytes were dominated by short-chain PFAS, particularly PFBS, without consistent species- or site-specific patterns, supporting their potential as biomonitors of cumulative PFAS exposure. Fish exhibited the highest PFAS diversity, with more diverse profiles in liver than muscle, although tissue-specific patterns were often absent. PFBS was dominant across fish species, and emerging PFAS (e.g., PFBS and NaDONA) were frequently detected. Human health risks from fish consumption were, except for children, mostly below EFSA tolerable weekly intake values for regulated PFAS, but potential concern for adolescents and adults emerged when PFAS were expressed as PFOA equivalents. This study provides essential baseline data for tropical freshwater systems and highlights the need for expanded PFAS monitoring and risk assessment in data-poor regions.