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The Level of Dioxins in Air in Hong Kong

The Level of Dioxins in Air in Hong Kong

The Level of Dioxins in Air in Hong Kong

The Dioxin Monitoring Results

There are no major dioxin emission sources in Hong Kong. The trace amount of dioxins comes mainly from different types of combustion processes including vehicle engines, incineration facilities, occasional fires and hill fires. Therefore, the level of dioxins in the air has been very low.

 

The Environmental Protection Department (EPD) has been monitoring the dioxin levels at Central/Western and Tsuen Wan for many years. The monitoring results show that the dioxin levels in Hong Kong are very low and have been decreasing for the past two decades. The annual average in 2021 is about 0.017 pg/m3 and is close to the lower detection limit. (See Fig. 1)

Figure 1: The Annual Trend of Dioxins 1998 - 2021

Fig. 1 The Annual Trend of Dioxins 1998 - 2021

The 24-hr average levels of dioxins in the past 5 years are much lower than the Japan annual standard and the Canada 24-hr standard. As the prevailing wind direction differs in winter and summer, the dioxin concentration levels also vary with the seasons. In General, the levels in winter are higher than that in summer.

Dioxins Produced by Burning Process

According to international literatures (Ref. 1-4), dioxins would be formed during combustion as long as the material has a small amount of chloride such as PVC or salt. In Hong Kong, PVC is commonly found in electric wirings, cables, plastic pipes, plastic floor tiles, auto parts, road plastic fences and traffic cones. There are also folding tables, folding chairs and office chairs which are made of plastic. Since Hong Kong is an offshore city, sea salt is extensively present in our environment. Therefore, burning waste in the open air can indeed produce a small amount of dioxins. The Chinese University of Hong Kong (CUHK) has collected soil samples containing black smoky substance near a charred mattress. The analysis results show that the levels of dioxin concentrations are significantly higher than the background levels as found in the other samples, and consider that this higher levels may be caused by burning plastic or the plastic part of the mattress. This matches with the findings in international literatures. However, the dioxin concentrations found do not pose any health risks.

Environmental Protection Department

 

Jan 2022

 

 

Reference

 

Major sources and emission factors of dioxins

  1. Mengmei Zhang, Alfons Buekens & Xiaodong Li (2017) “Open burning as a source of dioxins.” Critical Reviews in Environmental Science and Technology, 47:8, 543-620, DOI: 10.1080/10643389.2017.1320154.
  2. UNEP (2013) “Toolkit for Identification and Quantification of Releases of Dioxins, Furans and Other Unintentional POPs under Article 5 of the Stockholm Convention.” January 2013.
  3. Takayuki Shibamoto, Akio Yasuhara, and Takeo Katami (2007) “Dioxin Formation from Waste Incineration.” Reviews of Environmental Contamination and Toxicology. 190:1–41.
  4. Schleicher O., Jensen A.A., Blinksbjerg P., Thomsen E., Schilling B. (2002) “Dioxin emissions from biomass fired energy plants and other sources in Denmark.” Organohalogen Compounds 56 (2002), pp. 147-150. (Emissions from BBQ)