WINDSOR, Ontario—The discovery of two inactive grenades inside a vehicle led to a seven-hour closure of Canada-bound traffic on the Ambassador Bridge at the busiest border closing with the U.S., Windsor police said Tuesday. The inert grenades were found submerged in an unidentified white powdery substance, police said, leading to the closure from about 9 a.m. to about 4 p.m. Monday. “We would like to thank the public for your patience in this matter,” Windsor police said in a news release. “All necessary precautions were taken for the safety of the community and everyone involved during this incident. … We understand that any incident which causes a closure of an international border can have far-reaching impacts, however, it was imperative during this incident to take all necessary precautions under the circumstances presented.” No criminal charges will be brought against the U.S. man driving the vehicle, police said.