19
Sep
Agricultural Pesticide Residues in River–Lake Systems Threaten Nontarget Organisms in Aquatic Ecosystems
(Beyond Pesticides, September 19, 2025) In Water Science and Engineering, a study investigating the occurrence and distribution of agricultural pesticides in a river–lake system of the Taihu Lake Basin in China through surface runoff finds adverse effects on nontarget organisms that threaten ecological security. In evaluating the risks to aquatic organisms, the researchers highlight how pesticide residues in surface water and sediments jeopardize the entire food web, as risks are present throughout multiple trophic levels (positions in the food chain).
The results show that in surface waters, the fungicide carbendazim is the dominant pollutant with 23.66% of the contamination. Within the sediment samples, the fungicide tebuconazole is the primary contributor at 28.57%. Overall, fungicides are the main type of pesticide present in the tested river water and sediments. These compounds account for 76.86% and 85.10% of contamination, respectively. The authors also note that pesticide concentrations in both water and sediments in the rivers increase while moving downstream.
“Ecological risk assessment revealed high mixed risks to algae, daphnia [water fleas], and fish, with risk levels rising along with trophic levels of aquatic organisms,” the researchers state. They continue, “[C]ertain pesticides posed high risks to algae even at low concentrations, indicating more targeted toxicity for lower trophic organisms.” This is concerning, as pesticide residues from agricultural areas around the world enter aquatic environments through surface runoff, atmospheric deposition, rainfall, and other pathways. These chemicals then pose a risk to aquatic organisms and entire ecosystems, as they create toxic health effects and destabilize ecosystem functioning.
As the study notes, China is among the largest producers and consumers of pesticides worldwide, with previous research finding the country applying pesticides at rates 1.5-4.0 times higher per hectare than the global average. Studying river–lake systems, which are interconnected ecosystems where rivers connect to lakes, allowing for the transport, transformation, and storage of water, nutrients, and sediment, highlights how hydrological conditions in these bodies of water can affect the levels of pesticides that then expose aquatic organisms.
In summarizing the need for this research, the authors say, “While many studies have examined the storage characteristics of pesticides in surface water, research on the transport dynamics of pesticides in rivers and lakes remains insufficient, limiting accurate assessment of pesticide exposure scenarios and ecological risks.”
Study Methodology and Results
The researchers established 23 sites throughout Gehu Lake, Taihu Lake, and the rivers connecting them, taking water and sediment samples to analyze. In performing chromatographic and mass spectrometric analyses, the study was able to identify pesticide residues present and perform ecological risk assessments.
In the surface waters, a total of 34 pesticides are detected, with fifteen pesticides, including the fungicides carbendazim and hexaconazole, in 100% of samples. Twenty-five of the pesticides have detection rates above 50%. Within the sediment samples, a total of 20 pesticides are detected. Notably, pesticide pollution is more severe in the sediments of Gehu Lake, followed by the connecting rivers and then Taihu Lake. The levels within the sediment reveal carbendazim and tebuconazole in 100% of samples, while the fungicides prometryn, hexaconazole, and propiconazole are detected above 90%. Fungicides are the most detected contaminants in both the water and sediment samples.
“Pesticide contamination in rivers within the river–lake system intensified downstream, with average total concentrations increasing by 33%,” the authors write. They continue: “Notably, the concentrations of key pollutants carbendazim and hexaconazole increased by 19% and 65%, respectively. Propiconazole, isocarbofos [insecticide], and ten other pesticides exhibited concentration increases exceeding 50%. In river sediments, carbendazim concentrations increased by over 80% in downstream sediments, while prometryn levels rose more than fourfold. These results highlight the critical role of rivers as conduits for pollutant transport to the lakes and water exchange in the river–lake system.”
In terms of risks to aquatic organisms, the study finds propiconazole, carbendazim, phorate sulfone (metabolite of the organophosphate insecticide phorate), and forchlorfenuron (synthetic plant growth regulator) all pose high ecological risks to algae. The researchers note that, “Chronic exposure to such pesticides can alter algal community composition, destabilizing the foundational food webs of aquatic ecosystems and threatening biodiversity.”
In daphnia, tebuconazole and carbendazim constitute the highest calculated ecological risk, jointly accounting for over 80%, and represent the risks to aquatic invertebrate populations from pesticide exposure. In determining the ecological risk values in fish, the data show that tebuconazole poses a consistently high risk at all sampling sites, contributing 69.34% to the overall risk. Imidacloprid (neonicotinoid insecticide), carbendazim, hexaconazole, propiconazole, and tetraconazole also present high risks at more than 60% of the sampling sites.
Overall, the ecological risks of pesticides to aquatic organisms increase throughout the trophic levels. “Tebuconazole, identified as the primary pollutant in both surface water and sediments, contribute[s] to ecological risks across three trophic levels in the descending order of fish (69.37%), daphnia (17.55%), and algae (0.12%), indicating strong bioconcentration potential of pesticides in aquatic organisms,” the researchers state.
Previous Research
Scientific literature cited within the current study adds to a wide body of science connecting pesticide exposure to deleterious impacts on nontarget organisms. Results include:
- Exposure of Oryzias latipes to the herbicide atrazine “induces transgenerational genetic abnormalities such as hermaphroditism and organ feminization.” (See study here.)
- A study finds that the insecticide parathion-methyl inhibits photosynthesis and impairs cyanobacterial growth.
- “Glyphosate [herbicide] has been shown to destabilize aquatic plant community structure, and metolachlor [herbicide] exposure leads to reduced aquatic population richness and biodiversity loss.” (See here, here, and here.)
- Tebuconazole is toxic to daphnia, significantly inhibiting their reproduction, and “exhibits cumulative toxicity, potentially accumulating in fish via the food chain and causing liver toxicity.” (See research here and here.)
- Carbendazim induces heritable DNA damage in daphnia populations.
- Fenbuconazole (fungicide) and metolachlor exposure in fish causes developmental toxicity and hepatotoxicity. (See here, here, and here.)
Resources and Daily News coverage from Beyond Pesticides on waterway contamination highlights how water is being polluted at unprecedented rates, with pesticides, industrial chemicals, nutrients, metals, and other contaminants. Environmental and health advocates say it is essential that these pesticide contaminants not invade waterways and drinking water. Improper oversight and lax enforcement mean that many of these pesticides do, in fact, continue to contaminate the environment. (See the Pesticides and You article entitled Poisoned Waterways here and additional Daily News articles here, here, here, and here.)
Take Action
To prevent the deleterious health effects to aquatic organisms from pesticide exposure, as outlined here, as well as the broader impacts on biodiversity, human health, and the environment, a widespread transition to organic agriculture and land management is necessary. (See more on the health and environmental benefits of organic practices here and here.)
Help support the organic solution by buying organic products (on a budget!), growing your own organic food, becoming a Parks Advocate with the Parks for a Sustainable Future program, and taking action with Action of the Week.
For more information, see Beyond Pesticides’ previous action: >> Tell your U.S. Representative and Senators to ensure that agencies reaffirm U.S. commitment to restoring and maintaining the chemical, physical, and biological integrity of all the nation’s protected water resources.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Qin, Y. et al. (2025) Occurrence and ecological risk of typical pesticides in a river–lake system, Water Science and Engineering. Available at: https://www.sciencedirect.com/science/article/pii/S1674237025000833.
