According to this theory, defective sperm could never reach an egg to fertilize it, so men couldn't be responsible for producing defective children. Now research has shown that the female reproductive tract has ways of moving sperms along whether they are healthy or defective. Researchers used to believe that there was an effective barrier between blood vessels and the tissues where sperm originates in the testes. It is now known that the barrier is not effective against many chemicals. Then of course there's a cultural bias, reaching back to the Salem witch trials, to blame women for trouble.
Chemicals can directly affect the testes, where sperm originates.
The numbers of sperm can be diminished, or some sperm can be damaged, or sperm may even carry toxins directly into the egg. Alternatively, toxins can attack the male nervous system, or endocrine system, affecting the flow of hormones that act as messengers regulating the complex chemical processes that must all work well for conception to occur. No matter what the mechanism of damage may be, there is a growing body of evidence showing that male exposure to toxins can produce defective children. Furthermore nearly all the children were born underweight. It means neither men NOR women can be safely exposed to toxic chemicals.