A review on the occurrence, pathways, risks, and treatment of caffeine (CAF) and N,N-diethyl-meta-toluamide (DEET) in Indian aquatic environments with global perspectives

Emerging Contaminants (ECs) such as pharmaceuticals and personal care products are increasingly detected in aquatic environments due to rapid urbanization, expanding consumption patterns, and incomplete removal by conventional wastewater treatment systems. Among these compounds, caffeine (CAF) and N,N-diethyl-meta-toluamide (DEET) have gained attention as reliable anthropogenic tracers of domestic wastewater contamination. This review critically evaluates the occurrence, sources, transport pathways, ecological risks, and treatment strategies of CAF and DEET in Indian aquatic environments while integrating relevant global perspectives. A comprehensive assessment of peer-reviewed literature published between 2002 and 2026 was conducted using major scientific databases to synthesize current knowledge on these contaminants in surface water, groundwater, and wastewater systems. The findings indicate that CAF and DEET are widely detected across major Indian river basins including the Ganga, Yamuna, Cooum, and Godavari, as well as in urban aquifers of cities such as Delhi, Chennai, Pune, and Vellore. Reported concentrations generally range from tens to several thousand ng/L, primarily associated with domestic wastewater discharge, septic leakage, landfill leachate infiltration, and inadequate sewage infrastructure. The review further highlights the environmental persistence and mobility of these compounds, which enable their migration from surface water systems into shallow groundwater through recharge processes. Ecotoxicological studies reveal potential sub-lethal effects on aquatic organisms, while human exposure assessments suggest possible long-term risks from contaminated drinking-water sources. The reviewed studies predominantly employed liquid chromatography–tandem mass spectrometry (LC–MS/MS) and gas chromatography–mass spectrometry (GC–MS) for contaminant detection, reflecting the increasing adoption of high-resolution analytical techniques for trace organic micropollutants. Although conventional wastewater treatment plants generally achieve only partial removal of CAF and DEET, advanced treatment technologies including advanced oxidation processes, activated carbon adsorption, membrane filtration, and nature-based systems such as constructed wetlands have demonstrated removal efficiencies ranging from moderate to greater than 90%, depending on the treatment process and operating conditions. The review emphasizes the need for integrated monitoring frameworks, improved wastewater infrastructure, and policy inclusion of ECs in water-quality regulations to safeguard India’s surface and groundwater resources.