In the Breton capital of Rennes, the air quality monitoring group Airbreizh has detected several pesticides in recent air samples. One of the substances found is lindane, an insecticide that has been banned for agricultural use since 1998 and for biocidal purposes since 2005. These findings were made at Thabor Park in Rennes, where Airbreizh has been monitoring air quality since 2022. Among the detected pesticides, three are of particular concern: pendimethalin, a herbicide used to prevent weed growth; prosulfocarb, a widely used herbicide in the cultivation of cereals, potatoes, and onions; and lindane, a highly toxic insecticide. Lindane is classified as a potential carcinogen by the International Agency for Research on Cancer (IARC) and is also considered a persistent organic pollutant, meaning it can remain in the environment for long periods. According to Airbreizh, lindane is the most frequently detected pesticide among the hundred substances they monitor and is present in all their measurements. Killian Guillaume, a doctoral student at the School of Public Health, suggests that lindane might have been used in the past for treating flower beds or for pest control in older wooden structures and livestock buildings, but its use has long been discontinued. Lindane is found in various environments, including water, soil, air, and dust, and has even been detected in human bodily fluids such as breast milk, blood, and urine, according to the National Agency for Food, Environmental and Occupational Health Safety (Anses). Its presence is not limited to Rennes or Brittany, as it has been found across France. Despite a national monitoring system established in 2018 with seventeen stations, there is currently no specific national regulation for pesticides in the air. A similar monitoring station located in the commune of Mordelles, 20 kilometers from Rennes, highlights the impact of agricultural pesticide use on air quality. This station, situated in a peri-urban area near large farms, has recorded results similar to those at Thabor Park, despite being farther from agricultural plots. Pesticides can travel significant distances through a process known as drift, where up to 90% of the pesticide may not reach its intended target and instead becomes airborne. Additionally, pesticides on the ground can be re-suspended into the air by the movement of animals, people, or machinery. The concentration of lindane in the center of Rennes is ten times higher than in agricultural areas, with levels recorded at 0.2 nanograms per cubic meter in Thabor compared to 0.03 ng/m³ in Mordelles in 2024. The city has launched a study to determine if other neighborhoods are affected by this pollution. Six sensors have been placed in parks and residential areas, and results are expected by early 2027. The health effects of pesticides in the air are not well understood. Killian Guillaume notes that while there are studies on the effects of pesticides ingested through food, the impact of inhaling these substances is largely unknown. Laurence Payrastre from the National Institute for Agricultural Research, Food, and Environment (Inrae) explains that inhaled pesticides enter the lungs directly, whereas ingested pesticides pass through the liver, which can help detoxify them. Olivier Cesbron and Killian Guillaume are calling for greater transparency regarding pesticide use in agriculture. While farmers are required to report pesticide use, this data is not made public. Access to this information could help in better understanding and analyzing pesticide concentrations in the air.