Caffeine and Mosquito Repellent Are Quietly Seeping Into India’s Rivers and Groundwater

Every cup of coffee, every spray of insect repellent, and every flush of a toilet leaves a chemical fingerprint on the water around us. Two of the most persistent fingerprints belong to caffeine and N,N-diethyl-meta-toluamide, better known as DEET, the active ingredient in most mosquito repellents. A new comprehensive review published in Discover Sustainability by Daggupati Sridhar of VIT Bhopal University, Sundaram Parimalarenganayaki of Vellore Institute of Technology, and E. Sreehari of Manipal Institute of Technology has pulled together two decades of evidence, spanning 2002 to 2026, showing just how thoroughly these everyday compounds have penetrated India’s rivers, aquifers, and wastewater systems. The picture that emerges is one of quiet, pervasive contamination that conventional water treatment was never designed to stop.

The significance of these two molecules lies partly in what they represent. Caffeine is consumed almost universally by urban populations, metabolized incompletely, and excreted in urine, which makes it an exceptionally reliable tracer of domestic wastewater. If caffeine shows up in a stream or a shallow well, human sewage is almost certainly reaching it. DEET tells a parallel story: washed off skin during bathing and laundering, it follows the same route from bathrooms to drains to rivers. Because neither compound is produced industrially in ways that would confuse the signal, environmental scientists increasingly treat them as anthropogenic markers, chemical smoke alarms for sewage intrusion that might otherwise go undetected.

The review documents detections across many of India’s most important river basins, including the Ganga, the Yamuna, the Cooum in Chennai, and the Godavari, as well as in urban aquifers beneath Delhi, Chennai, Pune, and Vellore. Reported concentrations generally fall between tens and several thousand nanograms per liter. While such levels are far below the doses that produce pharmacological effects in humans, they are high enough to be measured routinely and high enough to raise questions about chronic, low-level exposure of aquatic ecosystems. The pattern of contamination tracks population density and sewage infrastructure closely, with the highest burdens appearing where untreated or partially treated wastewater enters waterways directly.

The pathways delivering these compounds into the environment are varied and, in many cases, structurally entrenched. Domestic wastewater discharge remains the dominant source, but the review identifies septic tank leakage, landfill leachate infiltration, and inadequate sewage networks as significant contributors. In cities where sewer coverage lags behind population growth, large volumes of greywater and blackwater reach storm drains and open channels without any treatment at all. Even where treatment plants exist, they were engineered to remove organic matter, suspended solids, and pathogens, not trace organic micropollutants. Caffeine and DEET therefore slip through activated sludge systems with only partial efficiency, exiting with the treated effluent or partitioning into sewage sludge that may later be applied to land.

Perhaps the most consequential finding concerns groundwater. The review highlights the environmental persistence and mobility of both compounds, properties that allow them to migrate from contaminated surface waters into shallow aquifers through natural recharge processes. Riverbank filtration, infiltration ponds, and leaking sewer lines all provide conduits. Once contaminants reach an aquifer, removal becomes dramatically harder, because groundwater lacks the sunlight, microbial communities, and mixing that help break down organic pollutants in surface waters. For cities that depend heavily on shallow urban wells, this represents a slow-moving contamination problem that could take years to manifest in drinking water and decades to reverse.

The ecological implications are still being mapped, but the review synthesizes ecotoxicological studies indicating potential sub-lethal effects on aquatic organisms. Sub-lethal does not mean harmless: chronic exposure to low concentrations can alter behavior, reproduction, growth, and enzyme activity in fish, amphibians, and invertebrates without killing them outright. Such effects are notoriously difficult to detect in population surveys but can accumulate across food webs and generations. Human exposure assessments reviewed in the paper suggest possible long-term risks from contaminated drinking-water sources, particularly where communities draw water from wells hydraulically connected to polluted rivers or septic fields. The authors are careful to frame these as risks requiring further assessment rather than established public health crises, but the direction of the evidence is clear enough to warrant attention.

Detecting compounds at nanogram-per-liter concentrations demands serious analytical firepower, and the review notes that most studies relied on liquid chromatography coupled with tandem mass spectrometry, known as LC-MS/MS, or gas chromatography with mass spectrometry, GC-MS. These techniques separate complex chemical mixtures and then identify molecules by their mass-to-charge signatures, allowing unambiguous detection even in dirty environmental matrices like sewage effluent or sediment-laden river water. The growing adoption of high-resolution analytical platforms across Indian laboratories reflects a broader global trend: as instruments become more sensitive, the list of pharmaceuticals and personal care products detectable in water keeps lengthening, and caffeine and DEET consistently appear near the top of detection frequency tables worldwide.

On the treatment side, the review offers a measured but cautiously encouraging assessment. Conventional wastewater treatment plants generally achieve only partial removal of both compounds, confirming that standard biological processes are insufficient on their own. Advanced technologies, however, perform considerably better. Advanced oxidation processes, which generate highly reactive hydroxyl radicals capable of degrading stubborn organic molecules, activated carbon adsorption, membrane filtration, and nature-based systems such as constructed wetlands have all demonstrated removal efficiencies ranging from moderate to greater than 90 percent, depending on the specific process and its operating conditions. Constructed wetlands hold particular appeal for India, offering a low-cost, low-energy option that can be scaled to smaller communities where centralized advanced treatment is economically unrealistic.

The authors argue that technology alone will not solve the problem without parallel institutional reform. Their recommendations center on three pillars: integrated monitoring frameworks that systematically track emerging contaminants across surface water, groundwater, and effluent; improved wastewater infrastructure to close the gap between sewage generation and sewage treatment; and policy changes that formally include emerging contaminants in India’s water-quality regulations. At present, most national and international water quality standards specify limits for pathogens, nutrients, heavy metals, and a handful of legacy pesticides, but set no thresholds for pharmaceuticals and personal care products. Without regulatory limits, there is little driver for utilities to invest in the advanced treatment steps capable of removing them.

The global context underscores that India’s challenge is shared but unevenly distributed. Caffeine and DEET are detected in rivers and aquifers on every inhabited continent, and wealthy nations grapple with the same treatment gaps. The difference lies in scale and infrastructure: India’s enormous population, rapid urbanization, and expanding consumption of pharmaceuticals and personal care products combine with incomplete sewage coverage to concentrate the problem. The review’s synthesis makes a compelling case that these two humble molecules, one from the coffee cup and one from the repellent bottle, should be read as sentinels for a much larger class of unregulated pollutants. Watching them, and building the monitoring, treatment, and policy systems to respond, may determine how cleanly the country’s water can carry its people through the coming decades.

Subject of Research: Occurrence, transport, ecological risks, and treatment of caffeine and DEET as emerging contaminants in Indian aquatic environments

Article Title: 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

Article References: 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. (n.d.). https://doi.org/10.1007/s43621-026-04859-2

Image Credits: AI Generated

DOI: 10.1007/s43621-026-04859-2

Keywords: caffeine, DEET, emerging contaminants, water pollution, groundwater contamination, wastewater treatment, India, river basins, ecotoxicology, LC-MS/MS, constructed wetlands, water quality regulation