Beginning in the '90s, a team of US scientists surveyed more than 11 thousand farmers from Iowa and North Carolina. They were asked about their experiences with farm chemicals during their lifetimes.
In 2015, there was a follow-up survey. Almost 12 hundred (10.6%) reported they had either lost, or significantly lost, their sense of smell. And those who reported incidents of unusually high exposure to pesticides during that time, were almost 50% more likely to report the symptom than those who did not. These mishaps are identified in the research as "High Pesticide Exposure Events" or "HPEEs." In them, the farmers either accidentally swallowed, inhaled or spilled the pesticides on their skin.
And those who did not wash thoroughly with soap and water within four hours of exposure, stood a greater chance of developing "OI". In other words, those who washed quickly likely helped reduce their harmful effects.
The pesticides named in the analysis include DDT, an insecticide no longer used in North America. The researchers believe the older farmers reporting symptoms were exposed to it, even before it was banned back in the '60s. DDT and the other insecticide named, lindane, are persistent and can still be found in food, the environment and even human tissue. They belong to a family known as organochlorines. Even before this latest research, organochlorines had been associated with both Parkinson's and dementia.
Four other pesticides are also implicated. They include 2,4-D, a popular weedkiller still in use.