Lead
(endorsed 1996)
Guideline
Based on health considerations, the concentration of lead in drinking water should not exceed 0.01 mg/L.
General description
Lead can be present in drinking water as a result of dissolution from natural sources, or from household plumbing systems containing lead. These may include lead in pipes, or in solder used to seal joints. The amount of lead dissolved will depend on a number of factors including pH, water hardness and the standing time of the water.
Lead is the most common of the heavy metals and is mined widely throughout the world. It is used in the production of lead acid batteries, solder, alloys, cable sheathing, paint pigments, rust inhibitors, ammunition, glazes and plastic stabilisers. The organo-lead compounds tetramethyl and tetraethyl lead are used extensively as anti-knock and lubricating compounds in gasoline.
Drinking water concentrations of lead reported overseas are usually less than 0.002 mg/L, but concentrations of 0.1 mg/L have been reported in Scotland where lead pipes and soft, acidic water are contributing factors.
Approximately 80% of the daily intake of lead is from the ingestion of food, dirt and dust. Food contains small but significant quantities of lead, which can increase when acidic food is stored in lead-glazed ceramic pottery or lead-soldered cans. The use of lead-free solders is becoming more widespread in the food processing industry. The average Australian adult dietary intake of lead is approximately 0.1 mg per day.
Typical values in Australian drinking water
In major Australian reticulated supplies, total lead concentrations range up to 0.01 mg/L, with typical concentrations less than 0.005 mg/L.
Treatment of drinking water
Lead concentrations in drinking water can be reduced by conventional methods of water treatment using coagulants or lime softening.
Measurement
The concentration of lead in drinking water can be determined by graphite furnace atomic absorption spectroscopy (APHA Method 3500-Pb Part B 1992). The limit of determination is 0.005 mg/L.
Health considerations
Lead can be absorbed by the body through inhalation, ingestion or placental transfer. In adults, approximately 10% of ingested lead is absorbed but in children this figure can be 4 to 5 times higher. After absorption, the lead is distributed in soft tissue such as the kidney, liver, and bone marrow where it has a biological half-life in adults of less than 40 days, and in skeletal bone where it can persist for 20 to 30 years.
In humans, lead is a cumulative poison that can severely affect the central nervous system. Infants, fetuses and pregnant women are most susceptible. Placental transfer of lead occurs in humans as early as the 12th week of gestation and continues throughout development.
Many epidemiological studies have been carried out on the effects of lead exposure on the intellectual development of children. Although there are some conflicting results, on balance the studies demonstrate that exposure to lead can adversely affect intelligence.
These results are supported by experiments using young primates, where exposure to lead causes significant behavioural and learning difficulties of the same type as those observed in children.
Other adverse effects associated with exposure to high amounts of lead include kidney damage, interference with the production of red blood cells, and interference with the metabolism of calcium needed for bone formation.
Epidemiological studies have found no association between lead and tumour incidence. Kidney tumours, however, have been reported in rats, mice and hamsters fed lead salts in their diet, but only at doses above 27 mg/kg body weight per day. Gliomas (brain tumours) have also been reported in rats. In addition, lead salts given orally to rats have increased the carcinogenic activity of known carcinogens.
Tests for mutagenicity using strains of bacteria have largely been negative. Tests using mammalian cells have been inconclusive, with some studies reporting negative results and some reporting chromosome damage.
The International Agency for Research on Cancer has concluded that lead is possibly carcinogenic to humans (Group 2B, inadequate human data but sufficient evidence in animals for inorganic lead compounds) (IARC 1987).
Derivation of guideline
The guideline value for lead in drinking water is based on a World Health Organization assessment and was determined by the need to protect young children, infants and pregnant women, the groups most at risk. The value was determined as follows:
where:
0.0035 mg/kg body weight per day is the lead intake which, based on metabolic studies with infants, does not result in an increase in lead retention (Ziegler et al. 1978, Ryu et al. 1983).
13 kg is the average weight of a child at 2 years of age.
0.2 is the proportion of total lead intake attributable to water consumption. Sufficient data are available to indicate that 80% of intake is from food, dirt and dust.
1 L/day is the average amount of water consumed by a young child.
The NHMRC in 1993 established guidelines for lead in Australians, which provide the basis for establishing acceptable levels of lead in air, food, soil and water. Pending an assessment of the impact of this review on the guideline value for lead, the guideline should be regarded as an interim value.
References
APHA Method 3500-Pb Part B (1992). Lead: Atomic Absorption Spectrometric method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.
IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.
NHMRC (National Health and Medical Research Council) (1993) Revision of Australian Guidelines for Lead in Blood and Lead in Ambient Air, 115th Session, NHMRC, Commonwealth of Australia, Canberra.
Ryu JE, Ziegler EE, Nelson SE, Fomon SJ (1983). Dietary intake of lead and blood lead concentration in early infancy. American Journal of Disease of Children, 137:886–891.
Zeigler EE, Edwards BB, Jensen RL, Mahaffey KR, Fomon SJ (1978). Absorption and retention of lead by infants. Pediatric Research, 12:29–34.
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