A middle-school in Nazareth was exposed to an extreme mercury contamination after students removed the toxic substance from the school lab and spread it in the yard as a hoax, Yedioth Ahronoth reported. Schools must contact the Environmental Protection Ministry immediately in the event that students or faculty members may be exposed to toxic materials in school grounds, but the school delayed the report for three days, for reason which have yet to be determined. Ministry inspectors found extreme contamination in the school yard – four times higher than the legal definition of a "severe contamination" and shut the school down immediately. According to available details, the students got hold of 2lbs of liquid mercury – which looks like tiny, harmless silver spheres – and began playing with them in the yard and is some of the classrooms. According to an Environmental Protection Ministry source, the school called the incident in last Thursday afternoon and inspectors were on the ground within hours. The ministry's hazmat unit was stunned to find that the contamination was school-wide, stretching some 8,000 sq-feet. Mercury contamination readings measured at 39 micrograms per cube of air – when 10mcg per cube is considered a severe contamination. The ministry suspects that the mercury was not stored properly, thus allowing the students to access it. An official Environmental Protection Ministry investigation has been launched. Mercury is a heavy, silvery d-block element, considered highly toxic, despite its wide industrial use. Last week, 140 nations joined a new and legally binding international treaty to reduce harmful emissions of mercury. Israel Moskovitz, Tamar Trabelsi-Hadad and Goel Beno contributed to this report Follow Ynetnews on Facebook and Twitter