Antibiotic Residues in Pakistan’s River Jhelum Raise Ecological Alarm While Human Risks Stay Low

A new study of the River Jhelum in Pakistan has found measurable residues of six widely used antibiotics at every monitoring station along the river, with the macrolide azithromycin reaching the highest concentration of 20.30 micrograms per liter. The research, published in the journal Environmental Geochemistry and Health, combined high-performance liquid chromatography with photodiode-array detection, pollution indices, and geographic information system-based spatial interpolation to map how pharmaceutical contamination varies along one of the country’s most important waterways. The findings arrive at a moment when the World Health Organization has warned of widespread resistance to common antibiotics worldwide, making the environmental dimension of antimicrobial resistance impossible to ignore.

The research team, led by Bakhtawar Fatima and Adeel Mahmood of Government College Women University in Sialkot, together with colleagues from institutions in Pakistan and Saudi Arabia, collected surface-water samples from ten monitoring sites representing upstream, midstream, and downstream reaches of the river during a post-monsoon sampling campaign. This design allowed the investigators to trace how antibiotic loads change as the river moves through populated and agricultural terrain. Post-monsoon sampling is particularly informative because seasonal runoff can mobilize contaminants from soils, wastewater outfalls, and livestock areas, delivering a snapshot of the pollution burden after peak hydrological activity.

Analytically, the study targeted six antibiotics spanning several drug classes: azithromycin, a macrolide; ofloxacin, ciprofloxacin, and levofloxacin, all fluoroquinolones; linezolid, an oxazolidinone; and cefixime, a cephalosporin. These compounds were quantified using high-performance liquid chromatography coupled with photodiode-array detection, a technique that separates complex environmental mixtures and identifies compounds by their characteristic light absorption spectra. The measured concentrations followed a clear hierarchy: azithromycin at 20.30 micrograms per liter, ofloxacin at 12.70, ciprofloxacin at 8.03, linezolid at 4.55, cefixime at 1.40, and levofloxacin at 0.51 micrograms per liter.

The dominance of azithromycin is significant for several reasons. Macrolide antibiotics are known to persist in aquatic environments and are frequently reported at elevated levels in rivers across Asia, as global reviews of macrolide contamination in surface waters have documented. Azithromycin consumption surged during the COVID-19 pandemic, and researchers in Pakistan have separately reported increased antimicrobial resistance against the drug during that period, attributing it in part to irrational utilization. The new Jhelum data suggest that heavy use of this class is leaving a chemical fingerprint in the river system, with azithromycin showing the greatest pollution burden across all monitoring sites investigated, while levofloxacin exhibited comparatively limited contamination.

To characterize the overall contamination pattern, the team applied two complementary assessment frameworks. Single-factor pollution indices evaluate each antibiotic individually against reference thresholds, while a comprehensive pollution index aggregates the contributions of all six compounds into a single measure of combined contamination. According to the comprehensive assessment, the investigated river transect carries substantial combined antibiotic pollution. The researchers then used GIS-based spatial interpolation to visualize how contamination is distributed across the river’s length, a technique that converts discrete measurements from ten sampling points into a continuous surface showing pollution gradients between upstream, midstream, and downstream reaches.

The ecological risk assessment produced the study’s most striking result. Using risk quotient analysis, a screening approach that compares measured environmental concentrations with predicted no-effect concentrations for aquatic organisms, azithromycin yielded the highest ecological risk quotient of 17.41. A risk quotient above one signals high predicted ecological risk under the applied screening framework, so a value exceeding seventeen indicates that the concentrations found in the Jhelum are far above levels considered safe for aquatic life. Fluoroquinolones such as ofloxacin and ciprofloxacin, which also registered elevated concentrations, are similarly associated with concerns for aquatic organisms, including effects on photosynthetic microbes and invertebrates that form the base of riverine food webs.

The ecological implications extend beyond individual toxicity. Antibiotic residues in surface water exert selective pressure on bacterial communities, promoting the proliferation of antibiotic resistance genes that can move between environmental and clinical settings. Research on swine farming, for example, has shown elevated proliferation of resistant bacteria and resistance genes in groundwater connected to agricultural areas. Short-term exposure to antibiotics has also been shown to cause long-term disturbance in gut microbial metabolism and molecular ecological networks, underscoring how persistent low-level contamination can reorganize microbial ecosystems. In a river like the Jhelum, which supports fisheries, irrigation, and domestic water use along its course, such microbial shifts carry consequences for both biodiversity and public health.

On the human health side, the picture is more reassuring, at least under the screening assumptions applied. The team calculated hazard quotients for non-carcinogenic risks, and all values remained below unity, the threshold that would indicate potential concern. This means that, based on the measured concentrations and standard exposure assumptions, the antibiotic residues in the river water do not currently pose significant non-carcinogenic health risks to people. The authors are careful to frame this as a screening-level result; hazard quotients near or below one do not eliminate concerns about chronic low-dose exposure, mixture effects, or the indirect pathway through antimicrobial resistance, which the World Health Organization identifies as one of the top global public health threats.

The Jhelum findings fit into a broader pattern documented across South Asia and beyond. Reviews of antibiotic contamination in the major river systems of South Asian countries, studies of urban rivers in northwest Pakistan, and a landmark global assessment of pharmaceutical pollution of the world’s rivers published in the Proceedings of the National Academy of Sciences all point to the same conclusion: pharmaceutical residues in waterways are a planetary problem, with the highest concentrations typically found in low- and middle-income countries where wastewater treatment infrastructure lags behind pharmaceutical consumption. Pakistan’s national antimicrobial consumption data show significant trends before and after the COVID-19 pandemic, adding context to the residues now detected in its rivers.

The authors argue that their findings strengthen the case for improved wastewater management, pharmaceutical discharge controls, and systematic monitoring of antibiotic residues in the River Jhelum. Because conventional wastewater treatment plants are often not designed to remove pharmaceutical compounds, effluents can pass through treatment and enter rivers largely intact. Targeted interventions, such as upgraded treatment technologies, take-back programs for unused medications, stewardship of antibiotic prescribing in human and veterinary medicine, and routine surveillance at fixed monitoring stations, would together reduce the input of these emerging contaminants. The study, funded through a large research project at King Khalid University in Saudi Arabia, provides a baseline against which future monitoring can measure whether such interventions are working, and it adds the River Jhelum to the growing map of the world’s antibiotic-contaminated waterways.

Subject of Research: Occurrence, spatial distribution, and ecological and human health risks of antibiotic residues in the River Jhelum, Pakistan

Article Title: Occurrence, spatial distribution, and ecological and human health risks of antibiotic residues in the River Jhelum

Article References: Occurrence, spatial distribution, and ecological and human health risks of antibiotic residues in the River Jhelum. (n.d.). https://doi.org/10.1007/s10653-026-03539-4

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03539-4

Keywords: antibiotic residues, River Jhelum, Pakistan, azithromycin, ecological risk, human health risk assessment, antimicrobial resistance, emerging contaminants, surface water pollution, HPLC, GIS spatial analysis, wastewater management