Cadmium ions, for example, apparently can enter both mature and immature sperm cells. Once inside, these cadmium ions can cause molecules forming the cellular backbone to spontaneously disassemble. Products of this disassembly can apparently tell the cell to self-destruct. When this occurs inside the testis, the number of sperm produced decrease. In severe cases, this can produce male sterility.
Several factors influence the severity of cadmium effects.
The level of cadmium in the blood is one factor. A second is the occurrence of varicose veins in the testes. A consequence of these varicose veins appears to be to increase the force driving metal ions from blood into the parts of the testes where sperm develop, thereby increasing the amount of cadmium the developing sperm see. A third factor seems to be the type of calcium ion channel the individual man has on his sperm. Some types are associated with greater sensitivity to cadmium poisoning than others.