Toxic Skies: Pesticides discovered drifting through France’s clouds

Next time when you are on cloud nine, beware! The clouds drifting above France are not as pure as they seem. A pioneering Franco-Italian study has revealed that they carry traces of pesticides — including chemicals banned more than a decade ago.

Researchers from the University of Clermont Auvergne and the French National Centre for Scientific Research (CNRS) analyzed six cloud water samples collected between 2023 and 2024 at the Puy de Dôme massif in Auvergne. To their surprise, they found 32 different pesticides . Even more troubling, a third of the samples contained concentrations above regulatory limits for drinking water.

The study went further, offering the first-ever estimate of pesticide presence across all low and medium-altitude clouds in mainland France. The results suggest that between 6 and 139 tonnes of pesticides could be drifting overhead.“Frankly, for the sake of our beautiful green and blue planet, we were hoping not to find pesticides in the clouds,” said lead researcher Angelica Bianco , who described her team as “cloud hunters.”

Capturing the Uncatchable

Studying clouds is no easy task. Unlike rivers or soil, they are fleeting and contain only tiny water droplets. To capture them, the researchers used a specialized collector known as a “boogie” at the Puy de Dôme Observatory. The site is one of the few in France where clouds are present nearly 40 percent of the time.

The process is delicate: an operator must be on site to set up, collect, and dismantle the equipment, all while preventing contamination. A typical sample amounts to just a few millilitres of liquid, after hours of effort. Yet these drops contained pesticides ranging from herbicides and fungicides to insecticides and biocides.

Unexpected Findings

The biggest surprise came from samples drawn from air masses that had traveled high over the Atlantic Ocean. Even there, far from farmland, pesticides were detected.

Though concentrations were small — in the nano- to microgram-per-litre range — the cumulative effect across billions of tons of cloud water is staggering.

“Naively, I didn’t think we’d find tons of pesticides in the clouds,” Bianco said. “But the estimate triggered the strongest reactions, and for good reason. It shows the hidden scale of the pollution we are spreading into the environment.”

A Full Circle of Pollution

The findings complete what scientists now see as a global cycle: pesticides seep into soils, rivers, lakes, and groundwater, fall back in rain, and now appear in the clouds themselves. Once airborne, they can travel across continents and reach remote regions like the Arctic, previously thought untouched by such pollution.

Clouds also act as chemical reactors, where sunlight can break down these compounds into new substances — some of which were also detected in the samples.

What Next?

With only six samples from a single site, the study is just the beginning. Bianco hopes to extend the research across more locations and seasons.

Still, the message is clear: even the skies above us are no longer free from pesticides . What falls from the clouds may not just be rain — but the residue of human activity carried on the wind.