In 1981, over six hundred people in Spain died from a mystery illness. Panic mounted as people across Europe read the news. Eventually, the epidemic was declared the result of food contamination — but some scientists think there's more to the story.
In May 1981, a small child died from what seemed to the staff of a local hospital to be pneumonia. Before long, his entire family was in the hospital. This was unusual enough. Families are exposed to each other's diseases, but few diseases are that virulent. Soon, though, it looked like there was a resurgence of the plague in Spain. People across the country went to hospitals in droves, all with similar symptoms - nausea, vomiting, and a steadily increasing trouble taking a breath. Significantly, families tended to come in together.
This is what caused officials to believe that the "plague" was not a disease. They searched the houses of the affected families and found one thing - olive oil that was not actually olive oil. The oily substance, which had been sold as cheap olive oil by forty different merchants, was actually rapeseed oil, or colza oil. Colza is grown across Europe, and its oil is generally used for industrial lubricants. This batch of oil had been dosed with aniline, a herbicide, to make sure nobody ate it. The merchants in the market got hold of it anyway. Sometimes they removed the aniline, and sometimes they did not.
The Spanish government instituted an oil exchange policy, taking the contaminated oil off the streets. The government spent much of the 1980s building a case against the 40 merchants who had sold the contaminated oil.
Some epidemiologists think that it was, instead, covering its own errors. They claim the oil wasn't to blame. Many scientists believed the aniline contaminated oil theory. The most prominent among these was Sir Richard Doll, whose previous work included making the connection between cigarettes and lung cancer. Others, including two scientists hired by the Spanish government to track the epidemic, don't believe the oil was the cause. The timeline, they claim, is off. People, as a whole, began getting better before the announcement about the tainted oil was made, and before the exchange program began.
They believe that "toxic oil syndrome" is organophosphate poisoning. Organophosphates are pesticides, but early in the 20th century they enjoyed a less savory reputation. They were once used as nerve gases, and were banned (for that use) by the Geneva Conventions. Among the signs of organophosphate poisoning are nausea, vomiting, and difficulty breathing - although they also cause muscle twitches and a host of other symptoms.
So while some people believe the poisoned oil is to blame for the plague, others think that pesticides were leaked near homes and resulted in the death of hundreds.