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The task force set up by the Government on July 15 to investigate the cause of excessive lead in drinking water in public rental housing estates announced its preliminary findings today (September 25).
The preliminary findings revealed that leaded solder joints installed in the inside service were the cause of excessive lead in drinking water in Kai Ching Estate and Kwai Luen Estate Phase 2. Copper alloy fittings also leached lead but did not result in excessive lead in water.
Speaking at a press conference today, the Chairman of the task force, Mr Wong Chung-leung, said, "In the past two months, the task force held seven meetings and visited Kai Ching Estate and Kwai Luen Estate Phase 2 where excessive lead in drinking water was found. It dismantled more than 100 components (44 copper pipes, 28 valves, three meters, 12 taps and 47 solder joints) from the water supply chains. For control purposes, 22 components were also taken from a supply chain at Hung Hei House at Hung Fuk Estate in Yuen Long, where lead content in the water samples collected was found to be well below the World Health Organization (WHO) Provisional Guideline Value (PGV), i.e. 10 micrograms per litre, for similar testing."
Also attending the media briefing, member of the task force Dr Chan Hon-fai explained the methodology of testing. He said that the task force had conducted leaching tests, elemental analyses of various components, mathematic modelling and lead isotopic analysis. The test results indicated that copper alloy valves, taps and solder joints of copper pipes with diameters below 76 millimetres dismantled from the water supply chain of Hong Ching House at Kai Ching Estate leached lead, with solder joints found to be leaching the highest amount of lead. Elemental analysis of solder joints showed that their lead content reached 41 per cent, 585 times the British Standard (BS) of 0.07 per cent lead.
The task force calculated the amount of lead leaching and the contribution from all pipe components by using the 24-hour leaching test results as the base. The analysis of the materials in copper pipes showed that they contained a very small amount of lead, meeting the BS. The level of lead leaching was even lower than the detectable level. As for copper alloy fittings, including valves, meters and taps, the BS specifies the lead content for different types of copper alloy, including the ratio of lead content. On the assumption that only copper alloy fittings leached lead, the leaching rate was calculated at 2.7 mcg per litre under mathematic modelling, well below the WHO PGV of 10 mcg per litre. The result was supported by the situation in Hung Fuk Estate, where stainless steel pipes, copper pipes with lead-free solder and copper alloy fittings were used and the lead content in the water samples collected complied with the WHO PGV. The task force, therefore, considered that excessive lead content in Kai Ching Estate and Kwai Luen Estate Phase 2 was not caused by the copper alloy fittings but the leaded solder joints.
The task force also made use of lead isotopic analysis to identify the source of lead. While the lead isotopic ratios of leaded solder and copper alloy fittings were found in two distinctive clusters, the mean value of the water samples with excessive lead closely agreed with the mean value of leaded solder. In other words, lead in water came from leaded solder.
Apart from investigating the leaching of lead, the task force examined the leaching rate of three other heavy metals - chromium, cadmium and nickel - in all the components dismantled from the water supply chains. Nickel was found in the leaching test of kitchen taps and washing machine taps at the units of Hong Ching House at Kai Ching Estate. As the taps contained a very small amount of water, however, nickel could be flushed away within one to two seconds after turning on the taps. The amounts of chromium and cadmium leached from all the components were undetectable (below 1 mcg per litre).
Separately, the task force found that some valves and taps installed were not those submitted to the Water Authority (WA) before the commencement of plumbing works, although they were on the WA's directory list of pipes and fittings. Some valves and taps installed did not comply with the BS requirements in respect of lead content. However, leaching test results revealed that the non-conforming valves and taps did not contribute to excessive lead in water.
The task force made the following recommendations:
1. Prevent use of leaded solder and non-conforming pipes and fittings:
(a) An enhanced system for site inspection and testing during construction of plumbing works
* Qualified persons (e.g. a building services engineer or a building services inspector) to carry out adequate and regular field inspection;
*Conduct systematic non-destructive tests of soldering joints during construction (e.g. conducting a quick lead test or using an x-ray forensic spectrometer);
* Arrange random sampling and testing of soldering materials delivered to the site;
(b) Stipulate the testing of four additional heavy metals (lead, chromium, cadmium and nickel) for water samples and testing the lead content of solder joints in newly completed inside service by Licensed Plumber and Authorised Person;
2. The WA to explore the use of pipe materials free from the risk of misuse of leaded joints in plumbing works, e.g. using silver brazing or compression joints for copper pipes or stainless steel pipes;
3. The Housing Authority to consider requiring the adoption of central procurement for solder materials; and
4. The WA to consider reviewing relevant legislation.
The task force reminded the public to take note of the following:
1. If water has been standing in pipes for a long time (for instance, after several hours of non-use, overnight, over a weekend or after a holiday), run water at the tap for about two minutes before using it for drinking or food preparation;
2. As hot water increases the amount of lead that may leach from pipe materials, use only water from a cold-water tap for cooking and drinking;
3. Use other pipe materials with very low risk of excessive lead in drinking water, such as stainless steel pipes, galvanised iron pipes or copper pipes with compression joints or soldered by silver brazing; and
4. For details, please refer to the brochure titled "Hong Kong's Water Supply - Reducing Lead in Drinking Water" which can be obtained in the Public Enquiry Service Centres in all Home Affairs Department District Offices and all estate management offices of the Housing Department or downloaded from the Information Services Department's designated website: www.isd.gov.hk/drinkingwater .
The task force aims to issue the final report in October.
Ends/Friday, September 25, 2015
Issued at HKT 17:39
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