Paraquat is something that can cause acute toxicity to the point of death.

Glyphosate is a teddy bear by comparison.

Many chemicals that cause acute toxicity at high doses also have poorly studied chronic toxicity or carcinogenicity issues, either from bioaccumulation or from cumulative low-grade damage. These issues are much less well-studied than chronic effects of less harmful chemicals, specifically because acute toxicity and attempts to avoid it makes objective testing difficult.