Monsoon rainfall is intensifying pollution and increasing levels of antibiotic resistance genes in two heavily polluted rivers flowing through Dehradun, raising concerns about public exposure to antimicrobial-resistant pathogens according to a recent study.
The Bindal Rao and Rispana rivers, tributaries of the Ganga pass through densely populated areas of Uttarakhand’s capital. Researchers found that monsoon rainfall was associated with a major increase in faecal pollution and antibiotic resistance genes in both rivers.
The research was based on seasonal and multi location sampling carried out in 2019 by researchers from the Indian Institute of Technology (IIT) Roorkee and collaborators. Samples were collected before, during and after the monsoon.
Bindal Rao is a seasonal river that can remain largely dry before the monsoon except near settlements, where wastewater provides a continuous flow. Rispana is perennial. Together, the two rivers carry roughly 28 million litres of municipal wastewater each day before joining downstream to form the Suswa River, which is listed under the Namami Gange river restoration programme.
Researchers observed widespread faecal and human derived pollution along the surveyed stretches. During the monsoon, pollution levels increased by approximately 10 to 1,000 times in relative abundance compared with pre-monsoon samples.
The researchers attribute the increase partly to heavy rainfall washing accumulated sewage, faecal material, solid waste and other contaminants from roads, drains, overflowing septic tanks and informal dumping sites into the rivers.
The study detected elevated levels of several antibiotic resistance genes, particularly sul1 and sul2 associated with sulfonamide resistance ermF associated with macrolide resistance and tetW associated with tetracycline resistance. Some of these genes remained elevated in river sediments even after the monsoon season.
Microbiologist Uli Klümper of Technische Universitat Dresden, who collaborated on the research, said monitoring of antimicrobial resistance should account for seasonal events because heavy rainfall can temporarily increase environmental levels and exposure pathways.
The contamination was found to be relatively uniform along the surveyed river stretches, with no significant difference between samples collected upstream and downstream of sewage treatment plant discharge points. Researchers said this suggests that treated effluent from sewage treatment plants is not the only source of pollution.
Untreated municipal wastewater entering the rivers through open drains, informal sewer connections, septic tanks, greywater outlets and other sources may be sustaining contamination across the river systems.
The study also found significant concentrations of heavy metals including silver, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead and zinc, particularly in sediments. However, researchers did not find a consistent relationship between the concentrations of the analysed metals and the elevated antibiotic resistance genes.
Instead the researchers identified widespread sewage and human derived pollution as the dominant factor associated with the high levels of antibiotic resistance genes.
The issue has wider public health implications because people living along the rivers continue to use them for activities including irrigation, bathing, washing and, in some locations, domestic purposes. During floods and waterlogging, contaminated river water can come into direct contact with larger numbers of people.
Researchers warn that floodwaters carrying antibiotic-resistant bacteria and other pathogens could create additional routes for transmission of infections, adding to the health risks already associated with flooding and water pollution.
The findings also highlight broader gaps in urban wastewater management. A 2021 Central Pollution Control Board assessment cited by the researchers estimated a 78.7% gap between sewage generation and installed sewage-treatment capacity across Indian towns and cities, equivalent to about 22,939 million litres per day.
Experts say improving sewage and septic-tank waste management, preventing solid-waste dumping and protecting river channels from encroachment are necessary to reduce pollution in Dehradun’s urban rivers.
The findings also have implications for major infrastructure projects proposed along the Bindal and Rispana. Experts have raised concerns that development around the rivers could affect drainage and flood management if their ecological and hydrological functions are not adequately considered.
Urban water expert Nidhi Singh of the Centre for Ecology Development and Research said rivers such as Bindal and Rispana contribute to drainage, groundwater recharge and flood regulation, making their condition closely connected with the resilience of Dehradun.
Researchers and environmental experts argue that urban rivers should be treated as essential infrastructure rather than simply as drains. Restoring natural drainage, maintaining floodways, controlling sewage and solid waste and protecting groundwater recharge areas could help reduce both environmental pollution and public-health risks.
With changing rainfall patterns and potentially more intense rainfall events, the researchers say seasonal spikes in pollution and antimicrobial resistance need to be considered alongside conventional river-cleaning and sewage treatment measures.