Abstract
Fifteen organochlorine pesticides (OCPs) were determined in sediments from 14 sites in upper, middle and lower reaches of River Rwizi. Duplicate samples were collected at each site, during three sampling regimes covering the wet and dry seasons. Sediments were extracted using acetone: hexane (1:1 mixture) and clean-up was achieved using C18 cartridge. OCPs were determined using gas chromatography-mass spectrometry (GC-MS). Principal component analysis (PCA) was used to assess spatial relationships. To assess ecological health risk, the risk quotient (RQ) based on exposure and toxicity was calculated. Hazard index (HI), based on the sum of ratios of the OCP doses to permitted levels was calculated assess risk to human health. Recoveries of 54.4-93%, linearity (R(2)) > 0.9988, limits of detection (LoD) of 0.34-0.66 ng/kg and limits of quantification (LoQ) of 1.02-2.01 ng/kg were obtained during method validation. The total OCPs concentration was 84.34-159.5 µg/kg dry weight. Presence of OCPs in the sediment may be attributed to environmental persistence, however the presence of endosulfans implies continuing input since they have a relatively short half-life. Ecological risk quotient (RQ) values were 0.01-9780.37 while hazard index (HI) values were all less than 1. The HI for dermal exposure in children was 0.2695 and in adults it was 0.1497, exceeding the negligible risk threshold of H < 0.1. While the risk to human health was low, the high risk posed to ecology by heptachlor (RQ = 9780.37) and endosulfan II (RQ = 835.98) requires immediate mitigation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s44274-025-00465-7.