Assessment of per- and polyfluoroalkyl substances in wastewater from selected wastewater treatment plants in Kampala and Jinja Cities, Uganda

Abstract

Over the past two decades, the rapid urbanization and industrialization in Uganda have generated wastewater containing emerging contaminants such as per- and polyfluoroalkyl substances (PFASs). This study assessed PFASs contamination from Bugolobi (Kampala) and Kirinya (Jinja) wastewater treatment plants (WWTPs) by analysing 80 influent and effluent samples for 15 PFASs using LC-MS/MS. Ten PFASs were detected, ranging from nondetectable levels (n.d) to 372.4 ng/L (mean: 20.94 ± 0.42 ng/L), levels that are comparable in magnitude to those reported for WWTPs in other African countries. At Bugolobi, influent concentrations ranged from n.d to 190.01 ng/L (mean: 60.85 ± 1.03 ng/L), while effluent concentrations varied from n.d to 372.4 ng/L (mean: 237.91 ± 7.06 ng/L). At Kirinya, levels ranged from n.d to 29.37 ng/L (mean: 17.58 ± 3.54 ng/L; influent) and n.d to 30.21 ng/L (mean: 7.79 ± 0.85 ng/L; effluent), dominated by short-chain compounds (PFBS, PFBA). Mass loadings were higher at Bugolobi (5,353.56 mg/day, 1.95 kg/year) than at Kirinya (93.62 mg/day, 0.034 kg/year). Despite discharge loads falling below permissible thresholds, the persistence and mobility of short-chain PFASs underscore the need for strict pollution control strategies. PFSAs exhibited higher removal (72.45% Bugolobi; 36.45% Kirinya) than PFCAs (-127.38% Bugolobi; -20.50% Kirinya), with negative efficiencies likely reflecting precursor transformation, desorption, or apparent concentration increases due to volume reduction rather than true production of PFASs. Bugolobi (~82.59%; aggregate) outperformed Kirinya (~25.19%) due to the advanced conventional treatment technology used. Ecological risk assessment revealed higher risks at lower trophic levels (many RQs >1; algae), at Bugolobi (impacting Daphnia and fish) compared to Kirinya (most RQs <1), potentially due to lower influx and partial mitigation by its pond-based system. These findings underscore WWTPs as point sources of PFASs that may find their way into neighbouring aquatic ecosystems, resulting in ecological risks to organisms.