I’m really curious about the incidence of PFAS in adolescence and the relationship with lower testosterone levels. A relationship with testicular cancer seems to point to some relationship with PFAS and the reproductive system.
Sperm count/testosterone level is strongly correlated with body weight; if you account for how much fatter people are nowadays the reduction is much less (e.g. compare a healthy weight person from 1970 to now). Similarly a lot of the reduction in fertility is explained by people nowadays being fatter.