{"id":39597,"date":"2025-09-19T00:01:29","date_gmt":"2025-09-19T04:01:29","guid":{"rendered":"https:\/\/beyondpesticides.org\/dailynewsblog\/?p=39597"},"modified":"2025-09-18T10:06:44","modified_gmt":"2025-09-18T14:06:44","slug":"agricultural-pesticide-residues-in-river-lake-systems-threaten-nontarget-organisms-in-aquatic-ecosystems","status":"publish","type":"post","link":"https:\/\/beyondpesticides.org\/dailynewsblog\/2025\/09\/agricultural-pesticide-residues-in-river-lake-systems-threaten-nontarget-organisms-in-aquatic-ecosystems\/","title":{"rendered":"Agricultural Pesticide Residues in River\u2013Lake Systems Threaten Nontarget Organisms in Aquatic Ecosystems"},"content":{"rendered":"

(Beyond Pesticides<\/em>, September 19, 2025) In Water Science and Engineering<\/em><\/a>, a study investigating the occurrence and distribution of agricultural pesticides in a river\u2013lake system of the Taihu Lake Basin in China through surface runoff finds adverse effects on nontarget organisms<\/a> that threaten ecological security. In evaluating the risks to aquatic organisms<\/a>, 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).<\/p>\n

The results show that in surface waters, the fungicide carbendazim<\/a> is the dominant pollutant with 23.66% of the contamination. Within the sediment samples, the fungicide tebuconazole<\/a> 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.<\/p>\n

\u201cEcological risk assessment revealed high mixed risks to algae, daphnia [water fleas], and fish, with risk levels rising along with trophic levels of aquatic organisms,\u201d the researchers state. They continue, \u201c[C]ertain pesticides posed high risks to algae even at low concentrations, indicating more targeted toxicity for lower trophic organisms.\u201d 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.<\/p>\n

As the study notes, China is among the largest producers and consumers of pesticides worldwide, with previous research<\/a> finding the country applying pesticides at rates 1.5-4.0 times higher per hectare than the global average. Studying river\u2013lake 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.<\/p>\n

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.\u201d<\/p>\n

Study Methodology and Results <\/strong><\/p>\n

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<\/a> analyses, the study was able to identify pesticide residues present and perform ecological risk assessments.<\/p>\n

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<\/a>, hexaconazole, and propiconazole<\/a> are detected above 90%. Fungicides are the most detected contaminants in both the water and sediment samples.<\/p>\n

\u201cPesticide contamination in rivers within the river\u2013lake system intensified downstream, with average total concentrations increasing by 33%,\u201d the authors write. They continue: \u201cNotably, 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\u2013lake system.\u201d<\/p>\n

In terms of risks to aquatic organisms, the study finds propiconazole, carbendazim, phorate sulfone (metabolite of the organophosphate insecticide phorate<\/a>), and forchlorfenuron<\/a> (synthetic plant growth regulator) all pose high ecological risks to algae. The researchers note that, \u201cChronic exposure to such pesticides can alter algal community composition<\/a>, destabilizing the foundational food webs of aquatic ecosystems and threatening biodiversity<\/a>.\u201d<\/p>\n

In daphnia, tebuconazole and carbendazim constitute the highest calculated ecological risk, jointly accounting for over 80%, and represent the risks to aquatic invertebrate populations<\/a> 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<\/a> (neonicotinoid insecticide), carbendazim, hexaconazole, propiconazole, and tetraconazole<\/a> also present high risks at more than 60% of the sampling sites.<\/p>\n

Overall, the ecological risks of pesticides to aquatic organisms increase throughout the trophic levels. \u201cTebuconazole, 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<\/a> potential of pesticides in aquatic organisms,\u201d the researchers state.<\/p>\n

Previous Research<\/strong><\/p>\n

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:<\/p>\n