Concerns rise over glyphosate use to combat water hyacinth invasions in wetlands

Water hyacinth, a silent ecological crisis in India’s waterbodies

Have you ever noticed a green layer of dense plants on freshwater water bodies such as rivers,  ponds, lakes in cities where you live? These are the commonly occurring water hyacinth (Eichhornia crassipes), a fast growing aquatic plant often found in freshwater ecosystems that normally provides shelter and feeding grounds for a range of aquatic species.

However, under conditions where water bodies are polluted with a high nutrient load, these free floating and highly invasive aquatic plants can proliferate even more rapidly thus posing a risk to the natural habitat .The explosive growth of water hyacinth (Eichhornia crassipes) in urban waterways is one of the most challenging ecological crises facing  aquatic ecosystems in urban India.

This prolific invader transforms lakes, streams, and rivers into thick vegetative mats, out-competing native aquatic life forms. Its exponential growth costs India’s urban administrators millions of rupees annually in removal and control measures.

A report by the Indian Institute of Science mentions the growth rate of water hyacinth to be between 250-400 kg of dry plant material per acre per day when allowed to grow in water bodies enriched with domestic sewage.

Impacts of water hyacinth invasion

• The dense surface cover created by water hyacinth mats poses severe public health risks, as it provides ideal breeding conditions for mosquitoes that transmit malaria, West Nile virus, and other vector-borne diseases.

• It's decomposing plant matter depletes dissolved oxygen levels that can suffocate fish and other aquatic organisms. In this process, nutrients are released that trigger harmful algal blooms that further degrade water quality and threaten wildlife and human health. Sometimes the cover is so uniform that water birds have mistaken them for a ground.

• The ecological damage extends beyond direct impacts on aquatic life. Water hyacinth outcompetes native vegetation, disrupts food webs, and alters entire ecosystems. Its thick growth blocks sunlight from reaching submerged plants, while its extensive root systems trap sediments and alter water flow patterns.

• The economic toll includes not only direct control costs but also losses in fisheries, recreational activities, and hydroelectric power generation due to clogged waterways and infrastructure.

• Furthermore, there are economic impacts of hyacinth covered lakes. The dense mats hinder the movement of fishing boats, reduce the catch of fish, or damage fishing gear. As hyacinth is sucked into water distribution systems, it clogs the pipes and reduces water flows. Stagnant, light deprived water under the mats creates breeding grounds for disease vectors like mosquitoes.

India's wetlands struggle with water hyacinth infestations

The East Kolkata Wetlands, a Ramsar site of international importance, span over 12,500 hectares and provide ecological services like water purification, flood control, and support for biodiversity. This wetland has been severely affected by water hyacinth invasion. The hyacinth mats have reduced the water purification capacity and threatened the livelihoods of thousands of fishermen who depend on these waters.

Kerala's Vembanad Lake, another Ramsar site, has been persistently affected by hyacinth growth. The plant has impeded the movement of houseboats, affected tourism, and reduced fish populations because of depleted oxygen levels. The local administration has been spending considerable money on mechanical removal, but the plant regenerates within weeks.

Bellandur and Varthur, two lakes in Bengaluru, provide stark examples of water hyacinth proliferation in urban settings. The plant thrives on the high nutrient content from untreated sewage, forming thick mats that occasionally lead to the infamous toxic foam spilling on the roads of Bengaluru. Restoration efforts have been impeded by the persistent regrowth of water hyacinth. The removal costs run into crores of Rupees.

The Yamuna River in Delhi is case where hyacinth populations have exacerbated the pollution. The plant's dense growth traps plastic waste and other pollutants, creating floating islands that further degrade water quality and harm the river's ecosystem. City administration has employed mechanical harvesters and manual removal methods, that have strained the limited financial resources.

In Mumbai’s Powai Lake, water hyacinth has been responsible for the reduced dissolved oxygen level and this has affected the lake's aquatic life. It has also impacted the activities of the Indian Institute of Technology Bombay's rowing club.

Controlling water hyacinth: Can glyphosate be the answer

The Pune Municipal Corporation (PMC) considered a proposal to use glyphosate, a widely-used commercial herbicide, to control the growth of water hyacinths in local water bodies. Pashan lake, a water body formed by a bund on the Ramnadi, Pune’s smallest river, is perennially infested by hyacinth. The PMC spends considerable money for its removal. Glyphosate could provide a cost-effective solution for controlling the invasive plants, as the dead hyacinth is relatively easier to remove. 

Before proceeding with its application at Pashan Lake, the PMC asked a team of scientists and environmental experts from the CSIR National Chemical Laboratory (CSIR-NCL), the Indian Institute of Science Education and Research (IISER) and the Centre for Sustainable Development, Gokhale Institute of Politics and Economics, Pune, to evaluate the potential environmental impact of using glyphosate in public water bodies.

The agency that proposed the use of glyphosate had conducted one study on a small farm plot. Their study showed that glyphosate residue in the soil was at negligible levels. Based on this study, and a review of literature, they concluded that glyphosate posed no significant health risks in water bodies. However, they did not support it with data on its effects on aquatic environments or long-term ecological impacts, particularly in water bodies.

The Indian Union Ministry of Environment has taken note of concerns raised by several NGOs about the use of glyphosate in Powai Lake and has directed the Maharashtra State Wetland Authority to investigate. In response, the Maharashtra Pollution Control Board (MPCB) has granted conditional approval to the Brihanmumbai Municipal Corporation (BMC) for using glyphosate to manage the invasive hyacinths in the lake. This approval is conditional on the BMC taking steps to prevent untreated sewage from entering the lake, conducting studies on how the herbicide might accumulate in the ecosystem, and regularly testing the water and sediments for contamination. 

Why glyphosate use in wetlands sparks environmental worries

In 2022, the BMC even launched a pilot project that used drones to spray glyphosate over the lake. While this method raised hopes for an effective solution, concerns remain about its ecological impact, particularly on sensitive wildlife like crocodiles, which live in the lake. Many experts argue that rather than introducing another chemical into the ecosystem, it would be more beneficial to tackle the root cause of the problem—pollution—by addressing the sources of contamination in the first place.

Glyphosate-based herbicides (GBHs) are among the most widely used agrochemicals in the world, with millions of tons applied annually to control weeds in agriculture, forestry, and urban environments [1,2,3]. Glyphosate functions by inhibiting 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), a key enzyme in the shikimate pathway, which is essential for the synthesis of aromatic amino acids in plants. Because this pathway is absent in animals, glyphosate has long been assumed to be safe for non-plant life [1,2,3].

• Glyphosate can harm beneficial insects

Recent studies suggest that even low, non-lethal doses of these herbicides may have unintended consequences on beneficial species like fruit flies (Drosophila melanogaster), an important model organism used to study genetics, physiology, and toxicology. One study by Augiar et al. (2016) found that sub-lethal doses of GBHs can trigger oxidative stress in Drosophila [4]. This stress prompts the activation of the insect's antioxidant defense system—a biological response aimed at minimising damage. However, despite these protective mechanisms, researchers observed an increase in lipid peroxidation, a sign of cell membrane damage, suggesting that the defense system might not be entirely effective in preventing harm.

Another study by Talyn et al. (2019) focused on survival rates and found that fruit flies exposed to Roundup®, a common GBH, had significantly higher mortality rates than those in the control group [5]. This suggests that glyphosate-based herbicides can be toxic to non-target insects, even at concentrations typically used in farming.

Small lab-level study conducted in CSIR-NCL showed that fruit-flies treated with recommended commercial dose of GBH resulted in significant mortality within two days. Moreover, survived files also showed developmental and reproductive defects. Beyond survival, research also indicates that GBHs may interfere with insect reproduction. Some studies show that exposure to these herbicides can disrupt the reproductive systems of fruit flies, which could have broader ecological consequences, particularly for pollinators and other beneficial insects [6].

One of the most alarming discoveries is glyphosate’s effect on pollinators, particularly honeybees (Apis mellifera) and bumblebees (Bombus terrestris). Studies have found that glyphosate exposure: Impairs learning and memory in bees, making it harder for them to locate flowers and return to their hive [7]. Disrupts gut microbiota, reducing the abundance of beneficial bacteria like Snodgrassella alvi, which help bees fight infections [8]. Lowers colony survival rates, especially when bees are exposed to sub-lethal doses over time.

• Glyphosate can be toxic to fish, algae and invertebrates living on land and water

Research has shown that glyphosate affects various biological pathways in aquatic and terrestrial organisms. Studies have demonstrated its toxicity to fish, algae, and invertebrates, raising concerns about its role in the decline of amphibian and aquatic species. When glyphosate enters water bodies, it breaks down into aminomethylphosphonic acid (AMPA), which retains toxic properties and can persist in the environment [9].

One of the major concerns with glyphosate is its persistence in soil and water. It binds to inorganic clays, organic matter, and sediments in freshwater environments, with a half-life ranging from 12 days to 10 weeks [10]. This prolonged presence increases the risk of accumulation in ecosystems. Additionally, when glyphosate is applied to manage aquatic plants, it has been detected in surface waters for extended periods, potentially affecting non-target species, including beneficial microorganisms in the soil [11,12].

• Glyphosate has been found to pose risks to human health

In addition to its environmental and health risks, glyphosate has shown limited effectiveness in certain applications. A three-year randomized trial in Karnal, Haryana, tested glyphosate and six other herbicides on water hyacinth. The study found that glyphosate was ineffective in controlling the weed, as it regenerated after treatment [23]. This further supports arguments against using glyphosate in aquatic environments.

While the extent of glyphosate’s risks remains a topic of scientific debate, the majority of evidence suggests that it should be used with caution [3,13,24,19]. To fully grasp the ecological consequences of glyphosate, scientists need to focus on longitudinal studies examining these chronic effects on different species—including pollinators, soil microbes, and aquatic organisms—are essential for understanding the broader ecological risks. There should be a search for safer herbicide alternatives, which is crucial for reducing environmental harm. Furthermore, understanding pesticide-environment and pesticide-pesticide interactions is critical for refining pesticide regulations and ensuring that chemical mixtures do not pose unintended ecological risks.

Glyphosate remains a powerful and effective herbicide, but its impact on non-target organisms cannot be ignored. As evidence of ecological harm grows, it is crucial to reevaluate its widespread use and explore safer alternatives.

Glyphosate should not be used to control water hyacinth in wetlands 

A shift from treating symptoms to removing root cause is necessary

Controlling hyacinth is tantamount to treating the symptom. The only real solution would be to treat the root cause – urban untreated sewage. There is no alternative to 100 percent sewage treatment. Unfortunately, the sewage treatment plant (STP) capacity falls woefully short for the rapid growth of the city.

The PMC has put started work on increasing the sewage treatment capacity of the city. The project, funded under the Japan International Cooperation Agency (JICA), includes building 11 STPs and upgradation of some existing ones. After initial delays, the project finally took off. However, even after completion of the JICA project, Pune will face a shortfall in STP capacity (see Table below), without accounting for population growth (which is significant). Unless this issue is addressed, controlling hyacinth will always remain a futile public expenditure.

Dr. Ashish Lele is the Director of CSIR-National Chemical Laboratory, Pune

Dr. Gurudas Nulkar is the Director of Centre for Sustainable Development, Gokhale Institute of Politics and Economics, Pune. He can be contacted at gurudas.nulkar@gipe.ac.in

Dr. Rakesh Joshi is a Scientist at Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune.