The sun pumps out the entire electromagnetic spectrum. Further since the age of radio nearly the entire populated parts of Earth have been blanketed in EM radiation. According to the original Peter Gowan article, the 49er's practice field registered 8.5 milligauss (mG) and their practice facility reads between 13-21 mG. Normal electromagnetic exposure is between 0.5 and 3 mG. 49er players are being exposed to far greater radiation levels than normal, because their facility is located near a power substation. Below is the source:
Could Chronic EMF Exposure from a Nearby Substation Be Causing the 49ers' Epidemic of Tendon Ruptures?