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When fungicides impact more than just fungi, is chlorothalonil a concern?

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Plant protection products have sowed seeds of controversy within the agricultural, scientific and regulatory communities. Conversations seem to surround the impact of these chemicals on the ecosystem.

Looking at the bee colony collapse disorder, we posted a blog discussing possible stressor neonicotinoids. Herbicides such as glyphosate are also believed to have contributed to the problem.1 If that’s not enough, researchers have added fungicides, such as chlorothalonil, as a probable cause for the decline of the bee population. 2-3 These fungicides have been found in bumblebees and in honeybee hive residues, and have been shown to increase the likelihood of Nosema ceranae infection in honeybees.3-9

I think this quote sums up my thoughts:

“Insecticides work; they kill insects. Fungicides have been largely overlooked because they are not targeted for insects, but fungicides may not be quite as benign—toward bumblebees—as we once thought. This surprised us” ~Scott McArt, Assistant Professor of Entomology, Cornell University

It is only recently that regulatory agencies have taken notice and action. The recent chlorothalonil ban by the European Union is the latest example. The regulation set a deadline of November 20, 2019 for all existing stock to be sold or distributed, with a use-up date for all products of May 20, 2020. Switzerland followed suit in December when it issued a statement withdrawing authorization of chlorothalonil products with immediate effect. 

So, what is chlorothalonil?

Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile) is a broad spectrum non-systematic agricultural fungicide. It is used on a wide variety of food and cereal crops, as well as large grassed areas like golf courses. Available commercially in many different formulations and brand names, it is used to prevent mildew and mold contamination. Chlorothalonil has been used globally for over 50 years and is the world’s most popular fungicide.

Why should your testing labs be concerned about chlorothalonil?

These decisions were taken following the EFSA’s (European Food Safety Authority’s) scientific assessment, which points to concerns around the chemical’s impact on aquatic life and human health. It concluded that the approval criteria were not satisfied for a wide range of reasons.

In a statement, the European Commission said: “There are also serious environmental concerns, notably high risks are identified for fish and amphibians and great concerns are raised concerning contamination of groundwater by metabolites of the substance.” According to the World Health Organization (WHO), chlorothalonil can cause kidney and stomach damage in humans and renal tumors in rodents and dogs. The chemical has been linked to declining bee populations.

While the EU and Switzerland are the first to ban chlorothalonil, the world is watching. Will other countries or regions follow? In the meantime, scientists testing for pesticide residues in food or environmental samples need to be prepared.

What are the limits of chlorothalonil residue testing?

Before prohibition was on the agenda, chlorothalonil was regulated in some markets. This was in the form of legal or advisory maximum residue level (MRL) on chlorothalonil residues and its metabolite SDS-3701.

Where these standards exist, they set concentration limits in agricultural (animal and plant) commodities, as well as soil, groundwater and drinking water. While they vary between countrIES, the Codex Alimentarius Commission serves as a reference for international food trade, with MRL of 0.01 mg/kg upwards depending on the sample type.

With the recent ban coming into force, it’s expected that food and environmental testing will play an important role. This will not only ensure adherence to the ban but also measure its effectiveness. We would expect the food supply, as well as soil and water environments, to be free of residues in due course. Chlorothalonil is moderately persistent, with a half-life ranging from several days to 6 months, even up to 1 year after successive application.

What are the analytical challenges for pesticide residue testing laboratories?

It is important to be aware of the relevant chlorothalonil standards and limits in your region. Ideally, your analytical methods will need to be capable of monitoring this fungicide in all commodity groups with an LOQ of 0.01 mg/kg, and within any regulatory guidelines.

For most labs, this means being able to test for more compounds in a wider range of samples at low concentrations with good accuracy and reproducibility. The keywords here are sensitivity, selectivity and specificity.

How do you achieve sensitive and rapid chlorothalonil analysis?

The prevalence of multi-residue liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses for the quantification of pesticides in food and environmental samples has been steadily increasing for many years. It is a minimum requirement for most laboratories working in these fields.

Modern tandem quadrupoles can detect regulated compounds at very low levels with minimal sample preparation. They offer a sensitive, simple, robust and rapid simultaneous determination of a wide variety of pesticide analytes in different samples. See what SCIEX pesticide testing solutions can offer. If you have any questions, feel free to comment here or email me at


  1. Motta, E. V. S., Raymann, K., & Moran, N. A. (2018). Glyphosate perturbs the gut microbiota of honeybees. Proceedings of the National Academy of Sciences115(41), 10305–10310. doi: 10.1073/pnas.1803880115
  2. Mcart, S. H., Urbanowicz, C., Mccoshum, S., Irwin, R. E., & Adler, L. S. (2017). Landscape predictors of pathogen prevalence and range contractions in US bumblebees. Proceedings of the Royal Society B: Biological Sciences284(1867), 20172181. doi: 10.1098/rspb.2017.2181
  3. Calderone, N. W. (2012). Insect Pollinated Crops, Insect Pollinators and US Agriculture: Trend Analysis of Aggregate Data for the Period 1992–2009. PLoS ONE7(5). doi: 10.1371/journal.pone.0037235
  4. Pettis, J. S., Vanengelsdorp, D., Johnson, J., & Dively, G. (2012). Pesticide exposure in honey bees results in increased levels of the gut pathogen Nosema. Naturwissenschaften99(2), 153–158. doi: 10.1007/s00114-011-0881-1
  1. Pettis, J. S., Lichtenberg, E. M., Andree, M., Stitzinger, J., Rose, R., & Vanengelsdorp, D. (2013). Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae. PLoS ONE8(7). doi: 10.1371/journal.pone.0070182
  2. Botías, C., David, A., Hill, E. M., & Goulson, D. (2017). Quantifying exposure of wild bumblebees to mixtures of agrochemicals in agricultural and urban landscapes. Environmental Pollution222, 73–82. doi: 10.1016/j.envpol.2017.01.001
  3. Mullin, C. A., Frazier, M., Frazier, J. L., Ashcraft, S., Simonds, R., Vanengelsdorp, D., & Pettis, J. S. (2010). High Levels of Miticides and Agrochemicals in North American Apiaries: Implications for Honey Bee Health. PLoS ONE5(3). doi: 10.1371/journal.pone.0009754
  4. Sanchez-Bayo, F., & Goka, K. (2014). Pesticide Residues and Bees – A Risk Assessment. PLoS ONE9(4). doi: 10.1371/journal.pone.0094482
  5. Mcart, S. H., Fersch, A. A., Milano, N. J., Truitt, L. L., & Böröczky, K. (2017). High pesticide risk to honey bees despite low focal crop pollen collection during pollination of a mass blooming crop. Scientific Reports7(1). doi: 10.1038/srep46554

About me, KC Hyland

As a technical marketing scientist, I combine my expertise with the latest information from around the globe. I support and develop mass spectrometry solutions for food, environmental and cannabis testing applications. I have more than 13 years of research experience in environmental chemistry and have been with SCIEX since 2014. I am passionate about the role of science in our future as we strive to build a socially just and environmentally conscious world.


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