Contamination of an Afro-tropical river with nicotine from tobacco farming and its implications for ecological and human health

Tobacco cultivation is associated with ecological and human health risks due to nicotine, an emerging aquatic contaminant. In tobacco-growing areas, nicotine can enter aquatic ecosystems through plant secretions and tobacco stalks used as organic fertilizer. Using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction method and liquid chromatography-tandem mass spectrometry (LC-MS/MS), this study aimed to (i) quantify nicotine residues in the Bua River, which flows through a central tobacco-growing region in Malawi - the country with the highest proportion of arable land dedicated to tobacco farming globally - and (ii) assess ecological risks in water and sediment, as well as potential human health risks from contaminated fish. The highest geometric mean concentrations were detected in fish tissues, particularly Clarias gariepinus (10.29 ± 2.09 μg/kg) compared to Oreochromis shiranus (1.35 ± 6.79 μg/kg), sediment (0.93 ± 3.54 μg/kg), and surface water (0.67 ± 1.96 μg/L). Nicotine levels were associated with several water quality parameters. Findings revealed that nicotine residues occur at ecologically concerning levels, posing high ecological risks to freshwater invertebrates and fish populations. Although nicotine levels in fish muscle do not currently pose human health risks under prevailing consumption rates, cumulative exposure from tobacco farming activities may elevate risks. This study provides evidence of substantial ecological risks that may disrupt trophic balances and alter aquatic communities. It recommends regular monitoring to assess long-term impacts, enable timely ecological responses, and minimize cumulative risks.