I know that its hard for someone to understand who doesn't work with farm chemicals on a regular basis but Roundup is on the low side in terms of toxicity. Here's a copy of a Material Safety Data Sheet that all those who handle herbicides need to maintain for employee access: http://greenhouse.ucdavis.edu/pest/pmsds/Roundup.PDF Almost anything is toxic, even salt, if the dose is high enough. The question that must be…
Carbon monoxide is toxic. If I breath it while walking a previously fired forest, I feel bad today. If I breath too much I die. But if I get out alive tomorrow my body will be fine.
Carcinogen work in totally different ways. If I contact or breath it I will feel fine today but I will have created damage to some of my cells DNA. This damage will create other damages when 5 years from no my cells transcribe some genes in a chain reaction, or will accumulate errors over time.
Five years from now one of the damaged cells will start replicating itself without control, and I will get cancer.
We get cancer by indirect ways, and delayed in time, on people that are not isolated so it is hard to get the cause effect relationship.
I worked in a Hospital for some time. On oncology got people that smoke 3-4 cigarettes packages a day that got pulmonary cancer, but they were seriously convinced that smoking had nothing to do with it.
It took decades to establish a relationship between smoking and cancer, and that was with half of the population smoking. With smaller populations it becomes harder and harder.