In February 1987, a shocking incident occurred in Mexico City, the capital of Mexico, when thousands of birds suddenly fell from the sky and died. Examination of the bird carcasses revealed high concentrations of lead, cadmium, and mercury in their hearts, lungs, and livers. These heavy metals had accumulated in the birds’ bodies due to severe air pollution in the city. Residents of Mexico City, exposed to this polluted air, experienced symptoms such as headaches, insomnia, fatigue, and vomiting, and in severe cases, even reported hallucinations and delusions. At that time, experts warned against breastfeeding young children because breast milk contained significant amounts of heavy metals.