The 1958 Food Additives Amendment gave the U.S. Food and Drug Administration (FDA) the authority and responsibility to require manufacturers to provide safety assessments for all new food additives. The evaluation needed to demonstrate that the new additive ingredients would not cause adverse health impacts before the additive ingredients could be added to foods and sold to the public (1). These additive ingredients include food dyes, flavors, preservatives, and more.
The amendment also included a clause championed by U.S. Representative James Delaney to forbid any new, added ingredient shown to cause cancer in humans or animals from entering the food system. The Delaney clause set the allowable carcinogenic additive limit to zero.
The initial goal of the clause was to prevent potentially harmful, cancer-causing ingredients from entering the food system, which on the surface seems completely reasonable: Zero detectable cancer-causing ingredients means zero additive-induced cancer cases.
However, science is an evolving process. The scientific information and tools available to lawmakers and regulators in 1958 were minimal compared to what we know today (just as 2021 knowledge will look extremely limited in 2084).
In 1958, few ingredients were known to be carcinogenic. Additionally, analytical chemistry and evaluation tools used to detect these levels were not as sophisticated and developed as the tools and processes available to us now (1).
In 1958, scientists would look at an ingredient’s toxicological profile in parts per thousand or parts per million; we now can evaluate at parts per trillion. Keep in mind, a part per million is a tiny measurement representing one part in a whole entity of one million parts.
For example, there are more than 10 million bricks in the Empire State building, which means ten bricks is 1 part per million (ppm).
Ted-Ed put together a video that helpfully explains parts per million.
When we talk about parts per billion (ppb) or parts per trillion (ppt), it's an even smaller number. While billion or trillion sounds like it would be a larger quantity, it's a much smaller quantity by a much larger magnitude.
For example:
1 ppm = 0.000001 of 1
1 ppb = 0.000000001 of 1
1 ppt = 0.000000000001 of 1
We can say with near certainty that the lawmakers and regulators in 1958 were not considering researchers' current ability to detect 1 ppt of an ingredient with relative ease.