Medical experts say that the rise in autism diagnosis is likely due to improved screenings and access to resources, but on Wednesday, RFK Jr. hazarded another guess: The secretary, who holds no medical credentials, chalked the rise in diagnosis up to “environmental toxins.”

Health and Human Services Secretary Robert F. Kennedy Jr. has called autism an “epidemic” and vowed to find the “environmental toxin” responsible. He also called autism a “preventable disease.”

Robert F. Kennedy Jr., the Health and Human Services Secretary, has spoken several times in April about plans to find the origins of autism.