{"id":39587,"date":"2025-09-17T00:01:08","date_gmt":"2025-09-17T04:01:08","guid":{"rendered":"https:\/\/beyondpesticides.org\/dailynewsblog\/?p=39587"},"modified":"2025-09-16T11:06:02","modified_gmt":"2025-09-16T15:06:02","slug":"study-of-biological-diversity-effects-of-pesticide-mixtures-highlights-underestimated-risks-to-ecosystems","status":"publish","type":"post","link":"https:\/\/beyondpesticides.org\/dailynewsblog\/2025\/09\/study-of-biological-diversity-effects-of-pesticide-mixtures-highlights-underestimated-risks-to-ecosystems\/","title":{"rendered":"Study of Biological Diversity Effects of Pesticide Mixtures Highlights Underestimated Risks to Ecosystems"},"content":{"rendered":"

(Beyond Pesticides<\/em>, September 17, 2025) A study in Environmental Science & Technology<\/em><\/a> finds additive effects of a synthetic pyrethroid insecticide (cypermethrin) and two fungicides (azoxystrobin and prochloraz) on biological control, biomass of major invertebrate trophic groups (position in food web), and soil ecosystem processes in arable systems (land suitable for growing crops). The study authors further highlight the failure of pesticide regulations to consider elaborate trophic interactions and pesticide mixtures<\/a>, as well as additive and synergistic effects<\/a> within their assessments, calling attention to the complexity of real-world exposures and the lack of research to fully understand the implications of chemical use for agricultural and land management purposes.<\/p>\n

\u201cArable systems have a high dependence on diverse natural biota to support pest control, soil bioturbation, and nutrient recycling,\u201d the researchers write. These communities rely on a balance of organisms within various trophic levels in order to function and provide vital ecosystem services<\/a>. Disruptions caused by environmental contaminants, such as pesticides to nontarget organisms<\/a>, impact entire ecosystems and overall biodiversity<\/a>. As the authors state, current risk assessments underestimate the real-world risks of petrochemical pesticides and synthetic fertilizers that, despite a wide body of science connecting exposure to deleterious health and environmental effects, are still not fully understood.<\/p>\n

There are complex interactions of chemical mixtures that occur as a result of the \u201dchemical soup<\/a>\u201d present in the environment, with underlying mechanisms that are incompletely comprehended. Rather than relying on a precautionary approach<\/a> to protect health and the environment, the U.S. Environmental Protection Agency (EPA) utilizes unenforceable mitigation<\/a> strategies to \u201creduce risks\u201d and allows registrations based on insufficient scientific research. The risk assessment incorporates the assumption of 100% compliance with mitigation measures. (See more on the precautionary principle here<\/a>, here<\/a>, and here<\/a>, as well as EPA failures here<\/a> and here<\/a>.)<\/p>\n

Background and Relevance<\/strong><\/p>\n

The use of pesticides has grown exponentially since World War II, with many wartime chemicals transitioning to the consumer market<\/a>, including the organochlorines (e.g., DDT) and organophosphates (e.g., malathion, chlorpyrifos). \u201cThe potential nontarget effects<\/a> on biodiversity from these pesticides have required the development of regulatory procedures to mitigate risk,\u201d the authors explain. They continue: \u201cHowever, there is increasing concern that these fail to adequately capture the real-world consequences. Part of this failing relates to a focus during the regulatory process on single active ingredients, an emphasis on a restricted number of established model species (e.g., nontarget arthropods like honeybees, earthworms, springtails, and enchytraeids) from which risk is inferred and the lack of continuous instruction on the timing and dose of pesticide application.\u201d<\/p>\n

The use of a limited group of model species, in particular, is concerning as they \u201cfail to capture how differential species sensitivity propagates through trophic interactions to affect wider system-level processes,\u201d the researchers emphasize. (See more information in Daily News<\/em> coverage on varying sensitivity between species and risk assessment deficiencies here<\/a> and here<\/a>.)<\/p>\n

The pesticides included in the experiment are cypermethrin<\/a>, a synthetic pyrethroid<\/a> insecticide, and two fungicides, azoxystrobin<\/a> and prochloraz<\/a>, which documentation shows cause health and environmental effects ranging from toxicity to aquatic organisms and bees to neurotoxicity, endocrine disruption, and oxidative stress.<\/p>\n

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

The study, performed in an open growing area in Southern England, uses arable communities of pests (aphids and weevils), predators (e.g., beetles, spiders, and mites), and soil biota (including mites and earthworms) to assess interactions between cypermethrin, azoxystrobin, and prochloraz as well as within trophic interactions as a result of exposure to these active ingredients. \u201cThis study is intended to provide new insights into the risks posed by pesticide synergisms<\/a> within the context of trophically complex communities critical to the support of agricultural ecosystem services,\u201d the authors summarize.<\/p>\n

They continue: \u201cIn this study, we use a model arable mesocosm<\/a> [controlled, semi-natural experimental ecosystem] approach to test the interacting effects of a widely used pyrethroid cypermethrin in combination with an azole fungicide prochloraz that has an established biochemical mechanism resulting in synergisms<\/a>. We also tested the effects of the strobilurin fungicide azoxystrobin, for which there is little evidence for synergisms with pyrethroids.\u201d<\/p>\n

The results reveal that despite previous research supporting cypermethrin and prochloraz having increased interactions, cypermethrin and azoxystrobin have a greater than additive effect. \u201cThe synergism between cypermethrin and prochloraz was relatively small compared to that between cypermethrin and azoxystrobin,\u201d the researchers state. \u201cHowever, the synergism between cypermethrin and prochloraz was expected due to the inhibition of the cytochrome P450 monooxygenases,\u201d which are proteins essential for metabolism.<\/p>\n

The study analyzes the effects of the three pesticides individually and in pairwise combinations to establish how \u201ckey aspects of arable farming systems, including aphid pest control by ladybirds, biomass of key trophic levels, overall community food web structure, and soil organic matter recycling\u201d is impacted following exposure. The methodology includes a description of the 35 mesocosms containing blended loam topsoil with organic matter and a seeded soil surface with a mixture of organic powdered oats and dried yeast flakes to provide resources for soil microfauna.<\/p>\n

Two months before the application of the pesticides, field beans were transplanted into the soil, and then a sequential addition of arthropod communities began to build up the trophic levels of detritivores (animals that feed on dead organic matter), herbivore pests, and predators. In total, the experiment includes seven treatments ranging from the control (no pesticides) to each active ingredient individually and in pairs.<\/p>\n

Assessments following pesticide applications incorporate arthropod sampling and soil sampling, with an assessment of decomposition rates of the breakdown of organic matter by soil macrofauna. Trophic links are also estimated using the WebBuilder function of its statistical package \u201cto predict trophic interactions between the terrestrial and soil arthropod communities for each mesocosm.\u201d These links are based on observed and established species feeding relationships within the mesocosm.<\/p>\n

Within the experiment, the arable crop mesocosm system records show 30 taxonomic units (including species, genus, and order classifications), representing a total of 317,064 individuals from the trophic levels of detritivores, herbivores, and predators over the 4-week sampling period. Impacts on the organisms throughout the experiment show:<\/p>\n