This factsheet on lead and its associated health effects has been produced in view of public concern over the incident of lead in drinking water in some public housing estates.
What is lead?
Lead is a naturally occurring heavy metal which usually presents in very small amounts in the environment. Lead and its compounds may be found in products such as batteries, lead-based paints, lead-containing ceramics, lead solder and leaded petrol. In everyday life, lead is found everywhere and exposure seems inevitable. Notwithstanding this, it is always good for health to achieve the lowest possible lead level in the body.
What is the recommended limit of lead in drinking water?
The World Health Organization’s Guidelines for Drinking-water Quality has set a provisional guideline value of not more than 10 micrograms per litre for lead. According to the test result of the Water Supplies Department, exposure to the level of lead found in drinking water of the affected buildings is unlikely to cause acute toxicity. Every effort should be made to achieve drinking water that is as safe as practicable.
Sources of exposure
Industries with particularly high potential exposures include construction work involving welding; cutting, brazing or polishing on lead surfaces and application of lead solder; most smelter operations either as a trace contaminant or as a major product; secondary lead smelters where lead is recovered from batteries; and firing ranges.
Lead may be contaminated with hazardous concentrations in lead paint, cosmetics and herbal medicines. Common exposure sources of lead with very low level for general public include urban dust, contaminated food and contaminated water.
Health effects of lead
Lead can enter the human body by ingestion, inhalation and skin absorption. When lead is absorbed into the body in excessive amount, it is toxic to many organs and systems. Depending on the lead level inside the body, significant exposure to lead is associated with a wide range of effects, including neurodevelopmental effects, anaemia, high blood pressure, gastrointestinal symptoms, impaired renal function, neurological impairment, impaired fertility and adverse pregnancy outcomes. Infants, young children, pregnant women and lactating women are more likely to be affected by its adverse effects.
Before the incident of lead in drinking water is resolved, those living in the affected estates are advised to take the following precautionary measures:
- If lead should be present in the plumbing system, the longer water has been standing in the pipes, for instance, after several hours of non-use, overnight, over a weekend or after a holiday, the more lead it may contain. Flushing works by removing the water with the most lead from the drinking water system. Running water at a tap, usually for two to three minutes, prior to using it for drinking or food preparation will often reduce lead levels in the water.
- As hot water increases the amount of lead that may leach from the pipe materials, use only water from the cold-water tap for cooking and drinking.
- Alternative source of water without elevated lead, such as distilled water or water from water filters certified by American NSF 53 Standard for removal of lead, could be used for cooking and drinking.
- Since the absorption of inorganic lead via skin is not effective, use of water from the affected buildings for any purpose other than ingestion, such as showering, tooth brushing and face washing, should not pose a health threat.
- It will be advisable for infants, young children, pregnant women and lactating women to use alternative sources of drinking water such as distilled water for cooking and drinking as an additional precautionary measure.
- It is safe to use the distilled water to substitute tap water in preparing formula milk, but the same method of preparation including boiling of distilled water should be followed.
- Mineral water contains levels of mineral which may exceed the requirement of infants and young children, and hence should not be used to prepare formula milk.
- Eat a balanced diet with adequate intake of calcium, iron and vitamin C to minimise the amount of lead absorbed in the body.
- Some domestic water filters (such as those certified by American NSF 53 Standard for removal of lead) can reduce the lead level in water. Nevertheless, no filter will give the claimed performance unless it is operated strictly according to the manufacturer's operational conditions with regular maintenance including timely change of core parts. Without proper maintenance, filters may also become an ideal breeding ground for growth of micro-organisms. As chlorine level in water will be reduced by activated charcoal in the filters, the water from filters should be boiled to kill germs before drinking.
Other general health advice
- Do not allow children to chew or mouth painted surfaces of toys or furniture that may have been painted with lead-based paint.
- Clean the dust in your house regularly if it might be decorated with lead-based paint, especially when the paint is in deteriorating conditions. Wash children's hands and faces frequently to remove any lead dusts and soil.
- Keep all lead contaminated / contained products away from children. Some types of pigments that are used as make-up (e.g. surma or kohl) or hair colouring dye may contain lead.
Testing of blood lead level
Whole blood lead level is internationally recognised as the most accurate and reliable method for screening and diagnosis to assess the risk of lead on health. For children, pregnant women and lactating women, a blood lead level of equal to or more than 5 microgram/dL requires further assessment. For adults, a blood lead level of equal to or more than 10 microgram/dL required further assessment. Hair and urine tests for lead are not suitable for screening and diagnosis. They are therefore not advisable.
In responding to this incident, professional staff of HA and the DH have worked closely to develop a management protocol for persons whose blood lead levels would be found to be abnormal. After detailed review of local and international literature and research by experts, reference value and the care plan have been established. The management team considered it most important for the source of contamination to be eliminated and for lead in the body to be excreted over time. The key feature of the care plan is to make reference to the blood lead levels detected, and stratify management actions according to assessment of health risk. In summary –
- if the blood lead level is normal, there is no significant health risk and no follow-up required;
- if the blood lead level is at borderline raised level, there is potential health risk, hence health evaluation and follow-up required.
- if the blood lead level is at significantly raised level, there is risk of lead poisoning, hence medical assessment and follow-up required.
Management of a raised blood lead level
The most important management is to identify and remove the source of exposure. When exposure stops, lead in the body will be gradually reduced through excretion in urine and bile. It is important to have a balanced diet with adequate amounts of vitamins and minerals, especially calcium and iron, as good nutrition lowers the amount of swallowed lead that is absorbed into the bloodstream. Patients who are symptomatic with high blood lead levels (i.e. more than 44 micrograms/dL in the more easily affected group and more than 50 micrograms/dL for adults) should be evaluated for further management, including chelation therapy.