25
Jul
Research Finds Heightened Toxicity to Aquatic Organisms from Microplastic–Pesticide Interactions
(Beyond Pesticides, July 25, 2025) The scientific literature shows that microplastics (MPs) and pesticides, both ubiquitous throughout the environment, have synergistic effects that threaten aquatic organisms. This means the combined toxicity of the two substances is greater than the sum of two individual exposures. The most recent study to demonstrate this, published in Ecotoxicology, focuses on the impacts of MPs and chlorpyrifos (CPF), a widely used organophosphate insecticide, on cladocerans, a group of microcrustaceans.
As Beyond Pesticides has previously reported, microplastics are found in all environments and threaten not only human health but all wildlife in both aquatic and terrestrial ecosystems. The universal distribution of plastics means that they cannot be avoided. Humans and other organisms take up plastics in the form of microparticles and nanoparticles by inhalation, ingestion, and skin contact every day. Microplastics are about the width of a human hair; nanoplastics are much smaller, about twice the width of a DNA strand. Larger pieces of plastic are ground down to these tiny sizes by weathering, temperature, biological processes, and chemical conditions. (See additional Daily News coverage on the health and environmental hazards of plastics here, here, and here.)
The authors of the current study, in exposing two cladocerans, Ceriodaphnia cornuta (daphnids or water fleas) and Echinisca triserialis (tardigrades or water bears), to MP and CPF both singularly and in combination, are able to assess the short-term (acute) and long-term (chronic) effects for nontarget aquatic organisms and the ecological risks they face from environmental contaminants. As a result, no mortality is observed to MP only treatments while MPs preconditioned with CPF (MP^CPF) show acute effects. Chronic exposure also shows reduced survival and reproductive output in both cladoceran species, with C. cornuta as more vulnerable than E. triserialis.
The researchers state: “A significant delay in age at first reproduction and shorter generation time were observed in the presence of MP^CPF, suggesting MP-mediated enhanced toxicity of CPF, wherein CPF could have accumulated onto the MP surface, thus, intensifying its toxicity. The enhanced toxicity of organic pollutants by MPs in aquatic environments especially in pelagic [open water] organisms is a matter of concern.”
Background
Cladocerans play an important role in the aquatic food web, helping to transfer carbon and nutrients from lower to higher trophic levels. In documenting impacts to cladoceran species, this represents threats to other aquatic organisms and overall biodiversity. “Ingestion of MP particles or the epiplastic substances by these organisms could be the entry point in the food chain that not only affects the population dynamics of C. cornuta and E. triserialis but also other aquatic organisms,” the authors warn.
MP in bodies of water come from various sources including wastewater effluents. “Studies have shown that wastewater treatment plants discharge around 160–300 million MP per day into aquatic habitats,” the researchers note. MPs that are smaller than 2 mm can be easily ingested by cladocerans and other zooplankton.
“Various aquatic organisms such as zooplankton, corals, fish, and marine mammals have been reported to ingest MP directly and/or indirectly leading to the transfer of MP across trophic levels,” the authors share. (See research here and here.) They continue: “The average size range of MP overlaps with the body size of planktonic organisms, and remains suspended in the water column for a long duration. They are easily mistaken with natural food particles, and hence particulate and filter-feeding zooplankton are more likely to ingest MP-preconditioned with dissolved organic contaminants. Thus, MP have the potential to impact a wide range of aquatic organisms including zooplankton.” (See studies here, here, and here.)
These MPs, based on their hydrophobicity (tendency to repel water) and higher surface area, can easily adsorb (adhere to the surface) pesticide molecules. The adsorption of pesticides on MP surfaces is extensively covered in scientific literature, such as with the insecticides malathion and carbofuran and the fungicide carbendazim. (See research here, here, and here.)
For the present study, CPF was chosen as the pesticide to analyze, as it is “representative of a highly occurring group of pollutants in the aquatic environment, such as organophosphate pesticides, which have been included in various monitoring programs.” Studies show CPF in surface and ground water, as well as larger bodies of water, that then impacts aquatic community structure and ecosystem processing. (See here, here, and here.) Previous research also shows CPF can be sorbed onto plastic surfaces. (See Beyond Pesticides’ Daily News coverage on chlorpyrifos here.)
“Thus, understanding the combined effects of MP and insecticides on aquatic organisms such as zooplankton is vital for thorough environmental evaluation and effective environmental management of aquatic ecosystems,” the researchers note. They continue, “In the natural environment, MP co-exists with organic pollutants, and the present study explores the response of the combined effects of MP and insecticide, CPF on pelagic [open water] and littoral [shallow water] cladoceran species.”
Study Methodology and Results
The two cladocerans utilized in this study represent species throughout the water column that are important in aquatic food chains. C. cornuta prefers open-water habitats while E. triserialis is typically found in shallower water and is known for its adaptability to various environmental conditions. “Furthermore, these species are the preferred diet of planktivorous fish, playing pivotal roles in transferring carbon through freshwater food webs, and serving as reliable indicators of aquatic ecosystem health,” the authors write.
To test the effects of exposure to MP and CPF individually and in combination in the two species, polyethylene plastics were crushed and ground, and CPF stock solutions were prepared. Between the control and test groups, the organisms were assessed for mortality and reproductive impacts both acutely (48 hours) and chronically (until the last organism perished).
As the researchers note: “The environmentally relevant concentrations of CPF and MP do not incur instant mortality; rather, they are more likely to affect the physiology, behavior, and survival patterns of the exposed organisms. The physiological responses of an organism, which determine survival and ability to contribute to the next generation, are ecologically more relevant parameters.”
The acute tests for both species reveal concentration-dependent mortality patterns for MPs preconditioned with CPF, but “the absence of mortality in the MP alone treatment condition, in either species at all the concentrations in acute test, suggests that MP alone does not have any toxic effect on the organisms in the short term.” More importantly, within the chronic tests, increased toxicity is observed when MPs are combined with CPF. Decreases in survivorship and reproduction rates, as well as a delay in reproduction, are noted, with higher sensitivity in C. cornuta than E. triserialis.
“These results indicate the synergistic effect of MP by accumulating CPF on the surface of MP at higher concentrations, suggesting that filter-feeding zooplankton may be more susceptible to the effects of MP^CPF compared to the presence of either MP or the insecticide alone in the aquatic environment,” the authors conclude.
In explanation of the sensitivity variations between the two species, the researchers say: “This difference in susceptibility can be attributed to a variety of factors, including their distinct habitat preference, behavior, and respective positions in the food chain. Ceriodaphnia cornuta, a pelagic species, may have greater exposure to contaminants in the water column, making them more susceptible to the effects of CPF and MP. The presence of C. cornuta in the surface and water column enhances the chances of encounter with floating MP, and their filter-feeding mechanism exposes them to higher quantities of MP and associated CPF, as MP has a larger surface area compared to larger plastic particles.” (See scientific literature here, here, and here.)
Previous Research
In Daily News, titled Microplastics Interact with Pesticides, Exacerbating Environmental Health Threats, Studies Find, Beyond Pesticides shares the findings of a literature review of over 90 scientific articles in Agriculture that document how MPs increase the bioavailability, persistence, and toxicity of pesticides used in agriculture. These interactions between MPs and pesticides enhance the threat of pesticide exposure to nontarget organisms, threaten biodiversity, and perpetuate the cycle of toxic chemical use.
Additional research, cited in the Ecotoxicology study, shows:
- Chronic exposure to polyethene MP impacts the growth and reproduction of both the freshwater amphipod Hyalella azteca and Ceriodaphnia dubia.
- Daphnia magna, with chronic exposure to polyethene MP, experience alterations in food uptake rate and immobilization.
- “MP-mediated effects increase with increasing exposure duration and concentration and have been reported to incur mortality through entanglement and blockage of the digestive tract in aquatic organisms.” (See here, here, and here.)
- Previous studies highlight MPs as vectors of toxic compounds in aquatic food chains. (See here and here.)
- “Recent studies have reported the joint toxic effects of CPF and MP on aquatic organisms, such as the fish Oncorhynchus mykiss and copepod Acartia tonsa.”
- “Similarly, previous studies on the effects of MP and CPF showed reduced feeding efficiency, fecundity, and survivorship when Acartia tonsa were exposed to CPF-loaded MP.”
- A study shows bioaccumulation of CPF in the muscles and tissue of Dicentrarchus labrax transferred through MP.
- “Studies have also reported the adverse effects of conditioned MP with pesticides, such as endocrine perturbation, hepatic damage, oxidative stress induction, and enzymatic activity modifications leading to early-life mortality in mussels and sea urchin embryos.” (See here, here, and here.)
A Holistic Solution
Organic agriculture negates microplastic–pesticide interactions that influence aquatic food webs, overall biodiversity, and environmental health. In adopting organic methods for land management, a holistic solution protects the health of all ecosystems and the organisms within them. Organic agriculture embodies an ecological approach to farming that does not rely on or permit toxic pesticides, chemical fertilizers, genetically modified organisms, antibiotics, sewage sludge, or irradiation. The National Organic Standards Board (NOSB) works to continuously improve upon these standards and acts as a lifeline from the government to the organic community as it considers input from the public regarding organic integrity. In this context, Beyond Pesticides has urged the NOSB (see here and here) to phase out the use of plastic in its certification production systems and in the packaging of organic food, as well as protect organic production by denying the petition to allow synthetic “compostable materials.”
Visit Keeping Organic Strong to learn more about the 2025 NOSB meeting from earlier this spring. Reference our previous actions (here and here) regarding plastics in farming, water, and food, and stay informed on other opportunities to engage by signing up to receive our Action of the Week and Weekly News Update emails.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Source:
Rajan, K., Yadav, D. and Kumar, R. (2025) Microplastic contamination worsens the ecotoxicity of chlorpyrifos to cladoceran Ceriodaphnia cornuta (Sars, 1885) and Echinisca triserialis (Brady, 1886), Ecotoxicology. Available at: https://link.springer.com/article/10.1007/s10646-025-02909-5.
