According to 16 CFR 1500.3 [Title 16 -- Commercial Practices; Chapter II -- Consumer Product Safety Commission; Subchapter C -- Federal Hazardous Substances Act Regulations; Part 1500 -- Hazardous Substances and Articles; Administration and Enforcement Regulations], a substance is toxic because it presents a chronic hazard if it falls into one of the following categories. (For additional information see the chronic toxicity guidelines at 16 CFR 1500.135.)
(A) For Carcinogens. A substance is toxic if it is or contains a known or probable human carcinogen.
(B) For Neurotoxicological Toxicants. A substance is toxic if it is or contains a known or probable human neurotoxin.
(C) For Developmental or Reproductive Toxicants. A substance is toxic if it is or contains a known or probable human developmental or reproductive toxicant.