Nearly a month after the “tear gas feast” by the Hong Kong police, Apple Daily and a group of chemical engineers took 15 samples of soil and water from the campus of the Chinese University of Hong Kong. Laboratory tests still found 0.1 to 1 mg of remnant per kg of soil and 1 to 10 mg of remnant per kg of leaves near the Number 2 Bridge. The area of influence extended as far as New Asia College, located at the peak of the campus. On 11 November at noon, the Police briefly discharged tear gas at the “Four Pillars”, the entrance of CUHK on Tai Po Road, and CS was detected at Fulton House, 200 metres away (see table).
CS (o-chlorobenzylidene malononitrile) is an extremely fine powder that atomizes during the tear gas explosion and then disperses into the air. Its area of influence reaches as far as the New Asia College at the peak of the campus, though no CS was found in the water samples. Professor David Hui S. C. of the Department of Medicine and Drug Therapeutics, Faculty of Medicine, The Chinese University of Hong Kong points out that exposure to 0.004 mg of CS per minute in the air is enough to sting the eyes, and 4 mg will irritate the respiratory tract. The chemical engineer in charge of testing urged the Government to take the lead to test and disclose the corresponding data.
The chemical engineer in charge of the test, Mr. Lee Ho-kee, explained, “Unlike dioxin, CS is a synthetic substance and should not be found in the natural environment. The residue we recovered can be inferred to be caused by the discharging of tear gas by the police”. He added that CS was found in the leaves of trees near Number 2 Bridge at 1 to 10 mg/kg, which yielded more results than soil because the leaves were lighter. “We hope that the government will take the lead in conducting tests so that the public will know how serious the tear gas contamination is and how long it lingers, and that professionals cleaners should be deployed to clean the streets instead of ordinary cleaning staffs”, he said.
Chan King-ming, an associate professor in the School of Life Sciences at CUHK, who took samples for the university, said, “Researches suggests that the CS half-life is one to two weeks, and three-quarters should still be present on the 17th November (the sampling date). Hong Kong’s urban ventilation is not as good as that of foreign countries, and the half-life (of CS in Hong Kong) may be longer than the average. Police fired tear gas in the densely populated downtown area of Hong Kong, even into residential buildings and shops. If it remains for more than two weeks, where can Hong Kong people go? How long should the old and the infirm hide from it?
Some CUHK staff indicated that they could only work from home, due to the effect of remnant on the trachea. Some residents also said that they had diarrhea for a week after eating near the postgraduate dormitory, which is not far from Number 2 Bridge.