30
Sep
Transport of Pesticides in Clouds Causes Transcontinental Contamination, Study Finds
(Beyond Pesticides, September 30, 2025) A pioneering study has measured the concentrations of pesticides in clouds. Prior to this, rainwater has been tested and found to be a common depositor of pesticides. But there is far less information about the role of clouds themselves. The findings add to general scientific understanding that pesticides go everywhere: into soils, water bodies, and the bodies of plants and animals—even when they are not intentionally applied. There are many studies of pesticide concentrations, including their metabolites, so-called “inert†ingredients, and degradation products, in soil, water and the atmosphere. The study was published in Environmental Science & Technology last August by a team of scientists from the University of Clermont Auvergne and the Laboratoire Phytocontrol in France and the University of Torino in Italy.
Clouds are collections of water droplets, as opposed to molecular gases or aerosols, which are simply fine particles or liquid droplets of any substance capable of becoming airborne. Aerosol and gas-phase chemicals are known to travel widely in the atmosphere and do not require the presence of water to do so. Contaminants in rain have been studied to some extent, but rain is a separate analytical category from clouds. A study published last month found 14 pesticides in rainwater in an agricultural area of Brazil. The authors noted that rainwater must be considered a source of pesticide exposure and should not be used as drinking water, but did not report on whether the pesticides arrived by atmospheric transport. Local sources are more likely—Brazil leads the world in pesticide usage, at more than 800 tons a year.
No environment, no matter how pristine it seems, escapes atmospheric pollutants. The more volatile a chemical is, the more it will spread in the atmosphere. For example, one study found endangered marmots on Vancouver Island contaminated with PCBs, PBDEs, hexachlorobenzene, and other industrial compounds, likely originating in Asia. There is also a well-known conveyor belt of atmospheric pollutants from lower latitudes to the Arctic, where the local environments become reservoirs: tundra, permafrost, ice, water, plants and animals. The exposure of polar bears to PCBs notoriously leads to endocrine disruption and failing reproduction in the species. One of the manifold concerns about climate change is that these Arctic reservoirs are releasing long-sequestered chemicals back into the atmosphere for further transport. For details, see Beyond Pesticides’ June 2023 analysis of an important study in Nature Communications.
The French cloud study analyzed six cloud water samples collected at an atmospheric station in south-central France in late summer 2023 and spring 2024. The samples were collected from the upper margin of the boundary layer, which is the air mass closest to the Earth and influenced by planetary factors, and from the free troposphere, which is the next highest layer where the air behaves with less terrestrial influence. The scientists searched for 446 compounds categorized as “pesticides, biocides, their transformation products and additives.†They found 32 compounds comprising three fungicides, seven insecticides, one biocide and eight transformation products. Among the pesticides were atrazine, cypermethrin, DEET, metolachlor, tributyltin, and fipronil. Mesotrione (a broadleaf herbicide for field corn), DMST (a metabolite of the fungicide tolylfluanid, used on apples, grapes, hops and tomatoes), and triphenyl phosphate (a plasticizer related to the fungicide tributyltin) were found in the highest concentrations. Two samples had total pesticide concentrations above the European drinking water limit. See Beyond Pesticides’ Gateway on Pesticide Hazards and Safe Pest Management for information on all of the above pesticides. The biocide, anthraquinone, is used as a bird repellent at golf courses and airports and as a seed treatment to discourage birds from eating them. According to EPA, anthraquinone is classed as “likely to be carcinogenic to humans.â€
The authors note that there was no correlation of any class of pesticide with either sampling period, which would have been likely had the pesticides been locally applied. This point, along with the presence of pesticides banned in France, supports the idea that long-range transport from countries where those pesticides are legal is involved. Other studies of aerosols and rain have come to the same conclusion. Further, neither the concentrations nor the types of pesticides found in clouds resembled those in local streams, adding support to the long-range transport concept.
Intriguingly, the study analysis includes “back-trajectory†tracing of the history of various air masses crossing the sample site. In one sample, part of the air mass originated in Spain. This sample had relatively high pesticide concentrations. Other sources included the Atlantic Ocean and northwest France. Samples with air masses coming from the ocean or from land areas covered by forest, natural grasslands and vineyards had the lowest concentrations.
The authors also compare results from aerosol studies with their cloud samples, finding significant differences. In one aerosol study, 58 pesticides were found in boundary layer sites, but only eight of those were found in the cloud samples. Two pesticides in cloud samples (fipronil and cypermethrin) did not appear in any aerosol samples. The authors also note that pesticide transformation products were found in clouds but not aerosols, suggesting that chemical processes in the clouds are converting the actual pesticide formulations in a way that does not occur to aerosols circulating freely in the atmosphere.
Atmospheric transport of pollutants has been acknowledged in science for decades, but its recognition in regulation and policy is much less discernible. One important indicator from a study of persistent organic pollutants in blood and breast milk samples from Arctic populations is that levels of regulated pollutants, such as certain “forever chemicals,†the DDT breakdown compound DDE, and PCBs have declined over time, while the unregulated pollutants have increased. The consequences of exposure to pesticides are as well known as those to PCBs, PFAS, and numerous other chemical bad actors.
According to public health and environmental advocates, the evidence that pesticides are traveling the globe in clouds, as well as in gaseous and particulate form, descending as rain, fog, snow and ice, and adding to the damage from direct exposures, spray drift, food consumption, and other sources, should be the straw that breaks the camel’s back of corporate regulatory capture. It is a sad moment, advocates say, to realize that clouds and rain are not the natural refreshment they used to be. But that same evidence—that eliminating pesticides makes a significant difference in human and ecosystem health—shows that changes can be made. Harmful trends can be reversed. Speaking out to regulators and elected officials, local and national organizing, changing your domestic ecosystem by going organic—all of these push the planet toward healing. See the multiple resources at www.beyondpesticides.org for ways to accomplish all of these things.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Are Clouds a Neglected Reservoir of Pesticides?
Bianco et al.
Environmental Science & Technology September 2025
https://pubs.acs.org/doi/10.1021/acs.est.5c03787
Pesticides in rainwater: A two-year occurrence study in an unexplored environmental compartment in regions with different land use in the State of São Paulo – Brazil
Dias et al.
Chemosphere March 2025
https://www.sciencedirect.com/science/article/abs/pii/S0045653525000335
Climate Crisis Unleashes Pesticide Contamination from Thawing Permafrost, Elevating Global Emergency
Beyond Pesticides, June 8, 2023
https://beyondpesticides.org/dailynewsblog/2023/06/climate-crisis-unleashes-pesticide-contamination-from-thawing-permafrost-elevating-global-emergency/
Arctic Glaciers Entrap Pesticides and Other Environmental Pollutants from Global Drift and Release Hazardous Chemicals as They Melt from Global Warming
Beyond Pesticides, August 20, 2020
https://beyondpesticides.org/dailynewsblog/2020/08/arctic-glaciers-entrap-pesticides-and-other-environmental-pollutants-from-global-drift-and-release-hazardous-chemicals-as-they-melt-from-global-warming/
Pesticides Found in Marine Atmosphere Over Deep Atlantic Ocean, Documented for the First Time
Beyond Pesticides, April 16, 2025
https://beyondpesticides.org/dailynewsblog/2025/04/pesticides-found-in-marine-atmosphere-over-deep-atlantic-ocean-documented-for-the-first-time/
