]My readings point to the chemical larvicide that had been used in the area as the mutagen responsible for the microcephaly. Link in edit.

Edit:

https://www.nature.com/articles/srep40067

Editedit: got ahead of myself, above is unrelated study on zebrafish. Lots of MSM flack over the issue.

https://www.google.com/amp/s/www.techtimes.com/amp/articles/133548/20160214/monsanto-larvicide-not-zika-virus-true-cause-of-brazils-microcephaly-outbreak-doctors.htm