So they use formamide to make the synthetic folic acid.
https://www.chemanalyst.com/NewsAndDeals/NewsDetails/the-making-of-folic-acid-understanding-the-vitamin-b9-production-process-37676
Formamide is a reproductive toxin (teratogen). Female lab workers of child-bearing age must
be made aware that fetus exposure to formamide may result in developmental abnormalities.
Formamide is also an irritant to skin, eye, and respiratory tract.
Formamide is slightly combustible.
https://www.ehs.harvard.edu/sites/default/files/lab_safety_guideline_formamide.pdf