2015 Event Water pollution in Rio de Janeiro may pose health hazards to participants in the Summer 2016 Olympics; the World Health Organization has asked the International Olympic Committee to expand its list of tested substances to protect the athletes 2014 Event The British government raises its terror threat level to 'severe' due to concern over the number of participants in Middle Eastern conflicts who have been traveling to and from the U.K. and who may seek to instigate terrorist actions inside the country 1988 Event Greatest number of participants, 31,678, on a bicycle tour, London 1973 Event NCAA makes urine testing mandatory for participants 1957 Event Trial begins in Budapest against participants october uprising 1952 Event PGA approves allowing black participants
