The Government has found no evidence that tear gas can cause dioxin poisoning, Secretary for Food & Health Prof Sophia Chan said today.

Prof Chan made the statement in response to questions from lawmakers.

She said that the Department of Health and the Hong Kong Poison Information Centre have reviewed relevant medical literature and scientific evidence but have found no evidence on dioxin poisoning cases caused by the use of tear gas.

Prof Chan said the combustion of any substance could produce different chemicals, including cyanide and dioxin.

The nature, quantity and concentration of chemicals produced would be subject to the duration and temperature of combustion and the substance itself.

Given the short combustion duration of tear gas canisters, any cyanide produced would quickly disperse in the air, she said.

Those exposed to tear gas generally experience mild respiratory and skin irritation, she noted.

As for the impact on the environment, she said tear gas is mainly a particulate compound, and since it is heavier than air, its dispersion is limited.

In terms of food safety, Prof Chan pointed out that the Centre for Food Safety has provided advice on its website on how to prevent food contamination.

Whether contaminants will affect food safety depends on several factors, such as the storage conditions of the food, the duration of exposure and the concentration of contaminants, she said.

Prof Chan added that drinking water in Hong Kong is sourced from imported water from Dongjiang and rainwater from local catchments. Since the sources are located in country parks or remote areas, the drinking water would not be contaminated by chemicals.

When asked if the composition of tear gas rounds and tear spray would be made public, Prof Chan said Police have been sourcing safe and suitable equipment and ammunition.

Police consider that it would be inappropriate to disclose such details as it would affect its operational capability.