A five-minute primer on an issue making headlines
The government has said heavy metal contaminants and organic chemicals were found in seabed soil samples collected at the Tamar site in 2003. But they did not test for dioxins at the time.
On Friday, environment minister Sarah Liao Sau-tung said studies in 2002 revealed dioxin levels 30 to 50 times lower than the internationally permissible level. The Civic Party is calling for a Legislative Council meeting this week to discuss claims by environmentalist Laurie Wan Shek-luen that the site is highly contaminated with dioxins from its previous role as a British military dockyard.
What are dioxins?
They are a family of chemical compounds created though combustion processes such as waste incineration. Similar to DDT, dioxins work their way up the food chain to accumulate in humans and wildlife. The most toxic - and unfortunately, the most common - is 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD). Most people mean TCDD when they refer to dioxin contamination.
How toxic is it?
This dioxin builds up in the body's tissues. Too much of it will disfigure a person's face by causing a persistent acne called chloracne. In animals, it results in birth defects, miscarriages, mutations, damage to the immune system, diabetes and cancer.