Which sentence contains the central idea of the paragraph?

Referees at sporting events are more likely to suffer hearing loss than their peers. That's because noises louder than 85 decibels can cause permanent hearing damage. Referees' whistles can be as loud as 106 decibels. According to a survey published in the Journal of Occupational and Environmental Hygiene, almost half of the sporting officials surveyed claimed their ears were ringing after a game. This symptom could be caused by damage to their inner ears.