It's worse then just health problems. People have died as a result of olive oil being cut with phenylamine, most notoriously in Sapin in 1981. An estimated 2100 people died. The survivors were still protesting as of a couple of years ago.
Why would anyone cut olive oil with with phenylamine? The former is dirt cheap. Wikipedia comes in clutch and reveals the root cause:
"Spanish regulations of the time allowed imports of rapeseed oil only for industrial use, and only if it has been denatured with aniline to prevent use as food"
The article goes on to reveal that the deaths were likely caused by something else:
"The WHO has since then tried to recreate the poisoning in laboratory animals with less-than-satisfactory results"
"when these three substances were given to laboratory animals, OOPAP was not acutely toxic, PAP was toxic only after injection, but not after oral administration, and OPAP was toxic only after injection of high doses.[3] Therefore, none of these three substances is thought to cause TOS.[3] Similar results were obtained after administration of fatty acid anilides"
"Spanish regulations of the time allowed imports of rapeseed oil only for industrial use, and only if it has been denatured with aniline to prevent use as food"
https://en.wikipedia.org/wiki/Toxic_oil_syndrome
The article goes on to reveal that the deaths were likely caused by something else:
"The WHO has since then tried to recreate the poisoning in laboratory animals with less-than-satisfactory results"
"when these three substances were given to laboratory animals, OOPAP was not acutely toxic, PAP was toxic only after injection, but not after oral administration, and OPAP was toxic only after injection of high doses.[3] Therefore, none of these three substances is thought to cause TOS.[3] Similar results were obtained after administration of fatty acid anilides"