HANGZHOU, June 26 -- Nine industrial plants in east China's Zhejiang Province have been fined and suspended after their emissions were blamed for a spate of nosebleeds in a nearby middle school, authorities said on Thursday. From March to May, 18 students suffered nosebleeds in Huangjiabu Township Middle School in the city of Yuyao, school medical room records show. He Dongfeng, father of a student at the school, said his son suffered a bleeding nose about three weeks ago, together with three or four of his classmates. He reported a sour and metallic smell in the air near the school. Huangjiabu Township High School is near Huangjiabu Township's industrial zone, a 133-hectare area that is home to 31 plants, including nine metal finishing and six dyeing plants. Zheng Qilong, deputy head of the township, said authorities could not deny, but also did not have any evidence of, a connection between industrial pollution and the students' nosebleeds. According to doctors, toxic air can cause bleeding from the nose if the density of particulate matter is high enough. Another possible reason is that long-term exposure to toxic air may damage the coagulation function of blood platelets, leading to nosebleeds. Yang Sheng, an official with Huangjiabu's environmental protection bureau, said based on complaints from teachers and students of the high school, environmental authorities have carried out plant inspections and fined and suspended nine of them.