Decreased sperm count can occur due to radiation exposure after receiving a threshold of at least:

Decreased sperm count as a result of radiation exposure typically occurs after surpassing a threshold of around 150 milligray (mGy). At this level, the radiation exposure is significant enough to impact the function and production of sperm in the testes, leading to potential fertility issues.

Radiation has a harmful effect on the rapidly dividing cells found in the testes, where sperm production occurs. As the dose increases, the damage to these sensitive tissues can result in a decrease in both sperm count and quality. Studies have shown that exposure below approximately 150 mGy tends not to lead to observable changes in sperm parameters, which is why this threshold is significant in the context of radiation biology.

Additionally, doses higher than this threshold can lead to more pronounced effects, including potential long-term impacts on sperm health and fertility.