Soil microbial communities play a crucial role in maintaining ecosystem health, driving key processes such as nutrient cycling, organic matter decomposition, and soil fertility. However, these microbial populations are highly sensitive to environmental changes and chemical stressors, including pesticides. The preprint "Evaluating the effects of environmental disturbances and pesticide mixtures on soil microbial endpoints," provides valuable insights into how soil microbial communities respond to environmental fluctuations and pesticide exposure (Drocco et al., 2025). By integrating experimental soil microcosms with targeted microbial assessments, the study offers a comprehensive view of the resilience and vulnerability of soil microbiota under multiple stress conditions.

The study aimed to assess how temperature and humidity fluctuations, along with pesticide exposure, impact soil microbial communities. A total of 250 soil microcosms were subjected to three different environmental conditions: heat disturbance, high humidity simulating heavy rain, or a control with no disturbance. Following a three-day recovery period, the microcosms were exposed to different pesticide active ingredients—clopyralid (herbicide), cypermethrin (insecticide), and pyraclostrobin (fungicide)—either individually or in combination at standard (1x) and elevated (10x) agronomic doses.

By evaluating microbial endpoints related to diversity and community structure, the researchers were able to determine how environmental disturbances and chemical exposure influence soil microbial functions (Bacmaga et al., 2015). Of particular interest was the focus on microbial guilds involved in nitrification, a critical process for soil nitrogen cycling and agricultural productivity (Dominati et al., 2010).

The study’s findings reveal a complex interplay between environmental stressors and pesticide exposure on microbial communities. Some key observations showed that heat and high humidity significantly altered microbial diversity and composition before pesticide application. This suggests that climate-driven disturbances can precondition microbial communities, potentially influencing their subsequent responses to chemical exposure. Moreover, the pesticide effects depend on dose and combination, while individual pesticides had measurable impacts on microbial endpoints, their effects were amplified when applied in mixtures or at elevated doses. This underscores the importance of considering real-world pesticide applications, where mixtures are commonly used. Furthermore, the results indicate that the microbial guilds involved in nitrification appeared to be disproportionately affected by pesticide exposure, raising concerns about long-term soil fertility and nitrogen availability in treated soils.

These findings have significant implications for sustainable agriculture and soil health management. Understanding how soil microbiota respond to environmental and chemical stressors can inform strategies to mitigate negative impacts, such as adopting precision agriculture techniques, improving pesticide formulations, and implementing soil conservation practices.

Despite its valuable contributions, the study has some limitations. The controlled microcosm approach, while useful for isolating specific variables, may not fully capture the complexity of field conditions. Long-term effects of pesticide exposure were also not assessed, leaving questions about microbial recovery and ecosystem stability over extended periods. Future research should focus on field-based experiments and long-term monitoring to validate and expand on these findings.

In conclusion, the current study highlights the intricate interactions between environmental stressors and pesticide exposure on soil microbial communities. By leveraging a robust experimental design and providing open-access data and statistical scripts, the research enhances our understanding of soil microbial dynamics and their implications for agricultural sustainability. As climate change and intensive pesticide use continue to shape soil ecosystems, such studies are essential for developing resilient and sustainable soil management practices.

References

Bacmaga, M., et al., 2015. Microbial and enzymatic activity of soil contaminated with a mixture of diflufenican + mesosulfuron-methyl + iodosulfuron-methyl-sodium. Environ Sci Pollut Res Int. 22: 643-56, https://doi.org/10.1007/s11356-014-3395-5 

Dominati, E., et al., 2010. A framework for classifying and quantifying the natural capital and ecosystem services of soils. Ecological Economics. 69: 1858-1868, https://doi.org/10.1016/j.ecolecon.2010.05.002 

Drocco, C., Coors, A., Devers-Lamrani, M., Martin-Laurent, F., Rouard, N., Spor A. 2025. Evaluating the Effects of Environmental Disturbances and Pesticide Mixtures on N-cycle related Soil Microbial Endpoints. ver.3 peer-reviewed and recommended by PCI Ecotoxicology and Environmental Chemistry, https://doi.org/10.1101/2024.01.22.576671

For many decades, the macrocyclic lactone drug ivermectin is extensively used in veterinary medicine and agriculture, as well as human medicine. Residues of ivermectin excreted in cattle dung remain persistent in soils (Mougin et al., 2003), biologically active and threaten non-target soil and coprophagous organisms such as dung flies and beetles (Lumaret et al., 2012). Ivermectin affects highly beneficial and taxonomically diverse groups inhabiting dung pats, including flies, parasitic wasps, as well as coprophilus and predatory dung beetles (Villar et al., 2022). Ivermectin resistance is well document in insects, but it seems to take longer and to be less effective than resistance to insecticides or other antiparasitic drugs, because of different physiological mechanisms involved in resistance (Seaman et al., 2015).

In that context, Gonzalez-Tokman et al. (2024) compared the reproductive success of a line of dung beetles (Euoniticellus intermedius, Scarabaeinae) exposed to a moderate concentration of invermectin during 18 generations, and a control line of beatles that was maintained free of antiparasitic drug. They carried-out toxicity experiments with increasing ivermectin concentrations to determine if sensitivity to ivermectin was reduced after some generations of exposure, possibly by acquiring resistance by means of transgenerational effects. Thus, dung beetles did not generate resistance to ivermectin after 18 generations of continuous exposure, and quantitative genetic analyses showed only low genetic variation in response to ivermectin.

The results published by Gonzalez-Tokman et al. (2024) indicated a low potential of beetles for adaptation to the drug, and suggest for non-target invertebrate groups a possible risk of extinction in ivermectin-contaminated pastures. These effects can greatly impact grassland ecology, lower their quality and reduce the area available and palatable to livestock.

References

Mougin, C., Kollmann, A., Dubroca, J., Ducrot, P.-H., Alvinerie, M., Galtier, P., 2003. Fate of the veterinary medicine ivermectin in soil. Environ. Chem. Letters 1, 131-134. https://doi.org/10.1007/s10311-003-0032-9

Lumaret, JP., Errouissi, F., Floate, K., Römbke, J., Wardhaugh, K., 2012. A review on the toxicity and non-target effects of macrocyclic lactones in terrestrial and aquatic environments. Current Pharmaceutical Biotechnology 13(6), 1004-60. https://doi.org/10.2174/138920112800399257

Villar, D., & Schaeffer, D.J., 2022. Ivermectin use on pastured livestock in Colombia: parasite resistance and impacts on the dung community. Revista Colombiana De Ciencias Pecuarias, 36(1), 3-12. https://doi.org/10.17533/udea.rccp.v36n1a2

Seaman, J.A., Alout, H., Meyers, J.I., Stenglein, M.D., Dabiré, R.K., Lozano-Fuentes, S., Burton, T.A., 471 Kuklinski, W.S., Black, W.C., Foy, B.D., 2015. Age and prior blood feeding of Anopheles gambiae influences their susceptibility and gene expression patterns to ivermectin-containing blood meals. BMC Genomics 16, 797. https://doi.org/10.1186/s12864-015-2029-8 

González-Tokman, D., Arellano-Torres, A., Baena-Díaz, F., Bustos, C., Martínez M., I., 2024. Ivermectin resistance in dung beetles exposed for multiple generations, bioRxiv ver. 3 peer-reviewed and recommended by Peer Community in Ecotoxicology and Environmental Chemistry. https://doi.org/10.1101/2023.05.08.539900