The Relationship Between the Level of Copper, Lead, Mercury and Autism Disorders: A Meta-Analysis

"There was a significant relationship between mercury concentration and autism (SMD (95% CI): 1.96 (0.56,3.35); I2=98.6%; P=0.006); there was also a significant relationship between lead concentration and autism (SMD (95% CI): 2.81 (1.64,3.98); I2=97.8%; P=0.000)."

Source: Pediatric Health, Medicine and Therapeutics