The Chinese University said on Friday that tests it has had carried out since police fired massive amounts of tear gas on its campus in Sha Tin last month show the soil and water there do not contain hazardous amounts of toxic chemicals and no clean-up is necessary. Riot officers used more than 2,300 canisters of tear gas as they battled with protesters at the university for hours on November 12. Students and teaching staff were quick to raise concerns that the campus could be contaminated with toxins, and the university decided to appoint an independent laboratory to collect and test air, water and soil samples. On Friday, the institution's management released the findings of some of the water and soil tests. It said the amount of dioxins, cyanide, polychlorinated biphenyls (PCBs) and Polycyclic Aromatic Hydrocarbons (PAHs) in the soil samples were all well below the risk level set out by the Environmental Protection Department. "Risks to human health arising from exposure to [the] soil are minimal and measures to protect public health, including a clean-up, would not be necessary," the university said. As for the water, it said the levels of the chemicals were all below limits set by the Environmental Protection Agency in the United States. "This implies that the health hazards from these contaminants in soil and water samples are negligible," the university statement added. No results were released for the tests on the air around the campus and the university said it would make public other findings once they become available.