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Arsenic (As)
Arsenic comes from natural sources such as erosion of soils, rocks, or a variety of human activities, e.g. use as pesticides, wood preservatives, dyes, paints, glass-making, electronics manufacturing and leather tanning.
The monitoring results show that levels of arsenic in marine water and sediments samples collected in Inner Deep Bay were generally higher as compared with other areas, which might be related to the higher background level of arsenic in soil of the northwestern New Territories. Nevertheless, the concentrations of As in marine water samples were far below the US standard for protection of aquatic organisms. The levels in sediment samples in the territory were generally below the US standard for protection of benthic organisms, while the levels in sediment samples collected from Deep Bay were comparable with the US standard. The total arsenic concentrations in fish and shellfish samples collected also met Hong Kong’s food standards (6 and 10 mg/kg wet weight respectively).
Barium (Ba)
Anthropogenic sources of barium include processing of barium minerals and manufacturing of barium products. Barium is also released to the atmosphere during the burning of coal, fossil fuels and waste.
Barium was commonly detected in Hong Kong marine sediments at a level of 13 - 50 mg/kg dry weight and higher levels were recorded for sediments samples obtained from central Victoria Harbour and Deep Bay. Overall, the levels in Hong Kong’s sediments were below the US standard for protection of benthic organisms.
Beryllium (Be)
Beryllium is commonly used in the electronics and mechanical industries. Beryllium particles in the air are produced from ore crushing, oil or coal combustion in electric power generation. Beryllium can be found in the wastewater from iron, steel and non-ferrous manufacturing industries.
Beryllium in Hong Kong marine sediments was at a level of between 0.9 – 2.5 mg/kg dry weight. No international safety guideline for beryllium in marine sediment can be found so far for comparison.
Cadmium (Cd)
The sources of cadmium in the environment include burning of fossil fuels, incineration of municipal wastes and emissions from zinc, lead and copper smelters. Wastewater from metal-plating, plastic industries as well as pigment and battery manufacturing plants may also be sources of cadmium pollution in the environment.
The levels of cadmium in all sea water samples collected were below the reporting limit of analysis (<0.5 μg/L).
Copper (Cu)
Copper is a major metal used in the electroplating and printed circuit board industries. Other sources of copper include domestic use of copper containing chemicals and corrosion of household copper pipes.
Copper was commonly found in marine sediments, highest in central Victoria Harbour (140 - 163 mg/kg dry weight). Areas away from urban centres, e.g. outer Deep Bay, Mirs Bay, Southern waters had much lower levels (10 – 27 mg/kg dry weight). The levels in the Victoria Harbour exceeded the Upper Chemical Exceedance Level (110 mg/kg dry weight) for copper stipulated in the Appendix A of the Works Bureau Technical Circular (Works) No. 34/2002 Management of Dredged / Excavated Sediment. The elevated level was likely related to the discharges from electroplating and PCB manufacturing industries in the 60s-80s, before the implementation of the Waste Disposal (Chemical Waste) (General) Regulation in 1992.
Mercury (Hg)
Mercury is a naturally occurring metal derived from weathering and erosion of rocks and soil, and from volcanic activities. Anthropogenic mercury generally comes from fossil fuel combustion, mining, smelting and solid waste incineration. Wastewater generated from industries and dental clinics if not properly treated can also be important sources of mercury in the aquatic environment.
Monitoring data show that mercury was generally low (<0.05 – 0.24 mg/kg dry weight) in all marine sediment samples collected, except in central Victoria Harbour where slightly higher levels (0.46 – 0.49 mg/kg dry weight) were observed. Nevertheless, the sediment mercury levels in central Victoria Harbour remain below the Lower Chemical Exceedance Level (0.5 mg/kg dry weight) for mercury stipulated in Appendix A of the Works Bureau Technical Circular (Works) No. 34/2002 Management of Dredged / Excavated Sediment.
Selenium (Se)
Selenium is a naturally occurring element widely distributed in the environment. Sources of selenium include irrigation of soils naturally high in selenium and ash pond discharges from coal combustion power plants.
The levels of selenium in marine sediments and biota samples collected were generally between <0.2 – 1.8 mg/kg dry weight and 0.2 – 1.2 mg/kg wet weight respectively. Sediment selenium levels were generally below the US level for protection of benthic organisms except for the Victoria Harbour and Tolo Harbour.
Silver (Ag)
Silver is used as an oxidizing agent in photography, silver plating and is found in electric conductors and equipment. Other uses of silver include as a disinfectant in water purification, in surgical cements, and in making jewelry, medical equipment and batteries.
The monitoring data show that the levels of silver in marine sediments were mostly at the range between <0.2 to 1 mg/kg dry weight. Selected sediment samples with concentrations that exceeded the Lower Chemical Exceedance Level (1 mg/kg dry weight) of the Works Bureau Technical Circular (Works) No. 34/2002 Management of Dredged / Excavated Sediment were found in central Victoria Harbour (4.7 – 8.5 mg/kg dry weight), inner Deep Bay (0.7 – 1.1 mg/kg dry weight) and Junk Bay (1.5 – 2.6 mg/kg dry weight) respectively, which could be attributed to the uncontrolled industrial discharges in the 70s and 80s prior to implementation of the Waste Disposal (Chemical Waste) (General) Regulation in 1992.
Thallium (Tl)
Thallium is commonly found in natural-ores containing copper, gold, zinc and cadmium. Anthropogenic sources of thallium include gaseous emission from cement factories and coal burning in power plants.
The monitoring results show that the levels of thallium in marine sediments of Hong Kong were from non-detectable to 0.8 mg/kg dry weight. No international safety guideline for thallium in marine sediments can be found so far for comparison.
Tin (Sn)
Tin compounds occur naturally in soil. Tin is used to line containers for food and beverages and is present in trace amounts in domestic products such as toothpaste, perfumes and soaps.
The monitoring results show that tin was generally present in marine sediments at low levels (2 – 10 mg/kg dry weight). Higher levels were detected in central Victoria Harbour (11 - 21 mg/kg dry weight) and Junk Bay (5 - 17 mg/kg dry weight). The higher concentrations in central Victoria Harbour and Junk Bay might be related to historical discharges from electroplating and printed circuit board industries as well as metal refining factories in Tsuen Wan and Kwun Tong. No international safety guideline for tin in marine sediments can be found so far for comparison.
Zinc (Zn)
Zinc is ubiquitous in the environment. Anthropogenic zinc mainly comes from metal smelters as well as production of brass, bronze, die castings metals, alloys, rubbers and paints.
In general, the level of zinc in Hong Kong’s marine water was mainly between <10 – 80μg/L and lower than the US standard for protection of aquatic organisms.
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