The chemical acrylamide is produced when starchy food is heated to a high temperature. The darker the toast, the more acrylamide is produced. The United Kingdom’s Food Standard Agency recommends going for a golden color or lighter, when you toast bread.
Another hint is don’t keep your raw potatoes in the refrigerator because this causes an increase in the levels of acrylamide.
We don’t know for sure how much acrylamide humans can handle, so my recommendation is NOT to eat burnt anything.