This is an interesting theory, you would need to find birthrates matching the industrial pollution rate, which my guess is it doesn't totally. I'm sure it's a measure of multiple factors where a big one is teenagers are having less sex and first sexual encounter is later. https://opa.hhs.gov/adolescent-health/adolescent-sexual-and-reproductive-health/data-and-statistics-on-adolescent-sexual-and-reproductive-health (Look at figure 1)