Lead

Guideline

The maximum acceptable concentration (MAC) for lead in drinking water is 0.010 mg/L (10 µg/L). It is recommended that faucets be flushed before water is taken for analysis or consumption.

Identity, Use and Sources in the Environment

Lead is the most common of the heavy elements. Several stable isotopes exist in nature, ²⁰⁸Pb being the most abundant. The average molecular weight is 207.2. Lead is a soft metal that resists corrosion and has a low melting point (327°C). It has therefore been used extensively since Roman times and, as a result, has become widely distributed throughout the environment.¹

In 1984, 264 300 tonnes of lead in all forms, including recycled lead, were produced in Canada, and 130 550 tonnes of refined lead were consumed.² In the same year, 67 000 tonnes were used in the production of lead acid storage batteries, and less than 50 000 tonnes (10 000 tonnes from each of the following categories) were used in the production of tetraethyl lead, pigments and chemicals, solder, other alloys and cables.³ From a drinking water perspective, the almost universal use of lead compounds in plumbing fittings and as solder in water distribution systems is important. Distribution systems and plumbing installed before 1945 may be made from lead pipe.⁴

Solid and liquid (sludge) wastes account for about 81% of the lead discharged into the Canadian environment, usually into landfills,⁵ but lead has been dispersed more widely in the general environment through atmospheric emissions. In 1982, leaded gasoline additives accounted for 63% of all atmospheric emissions.⁵ With the introduction of unleaded fuel, emissions from this source declined from a peak of 14 360 tonnes in 1973 to 6500 tonnes in 1983.³ Emissions have declined to virtually nil in 1991⁶ as a result of the phaseout of leaded gasoline in December 1990 under the Gasoline Regulations of the Canadian Environmental Protection Act.⁷

Exposure

Lead is present in tap water as a result of dissolution from natural sources or from household plumbing systems containing lead in pipes, solder or service connections to homes. The amount of lead from the plumbing system that may be dissolved depends upon several factors, including the acidity (pH), water softness and standing time of the water, with soft, acidic water being most plumbosolvent.⁸ Lead concentrations in untreated water were generally less than 1 µg/L in 71 Canadian municipalities in two national surveys conducted in 1976 and 1977.^9,10 Mean levels in tap water samples taken after three to five minutes of flushing (to remove any standing water) were below 1 µg/L (range £1 to 65 µg/L) in the two national surveys and 4 µg/L (range £1 to 48 µ/L) in 64 municipalities in surveys conducted in Ontario between 1981 and 1985.¹¹ The concentration of lead determined from integrated monitoring of all tap water used in the kitchens of 18 homes in Montreal ranged from 0.25 to 2.76 µg/L, with a median of 0.65 µg/L.¹² The median level of lead in drinking water samples collected in five Canadian cities during a duplicate diet study was 2.0 µg/L.¹³ In a recent study in Ontario, the concentration of lead in water actually consumed was determined using a composite sampler in 40 homes at seven locations.¹⁴ The average concentration of lead over a one-week sampling period ranged from 1.1 to 30.7 µg/L, with a median level of 4.8 µg/L. The results of this study are considered to be the most realistic estimate of the intake of lead from drinking water. Using the median concentration of 4.8 µg/L and daily drinking water consumption of 1.5 L for an adult and 0.6 L for a child, the average daily consumption of lead from drinking water is 7.2 µg for an adult and 2.9 µg for a child.

Food can be contaminated by naturally occurring lead in soil as well as by lead from sources such as atmospheric fallout, water used for cooking or the use of lead-soldered cans. The use of lead-soldered cans has been estimated to contribute 13 to 22% of the total dietary intake of lead.¹⁵ Intake of lead from this source has declined markedly in Canada in recent years as the use of cans with lead solder has been phased down by the food processing industry. Based on recent analyses of lead in food in a national market basket study, the intakes of lead from food have been estimated to be 1.1 µg/kg bw per day for children aged one to four years and 0.75 µg/kg bw per day for adults.¹⁶ This represents a drop of 56% between 1985 and 1989 for children.

Annual geometric mean concentrations measured at more than 100 National Air Pollution Surveillance (NAPS) stations across Canada have declined steadily from 0.74 µg/m³ in 1973 to <0.1 µg/m³ (the detection limit) in 1991,^6,17 paralleling the decrease in the use of lead additives in gasoline to their phaseout in December 1990. Some sampling stations in a few Canadian cities still record measurable concentrations of lead in air (e.g., Vancouver, Edmonton, Calgary, Toronto, Hamilton, Montreal), but average concentrations in these cities are not above 0.1 µg/m³. It is difficult to estimate the current average intake of lead from air, as geometric mean concentrations, although well below the detection limit, are not measurable. Intakes for a two-year-old child and an adult have been estimated to be 0.36 and 1.2 µg/d, respectively, based on NAPS data using one-third the detection limit with a sampling height correction factor of 2.* Soils and household dust are significant sources of lead exposure for small children.^20,21 In 1973, in Toronto homes not near point sources, average lead concentrations were 110 µg/g in garden soil and 845 µg/g in household dust.²² There are no recent data for lead concentrations in household dust in urban Canadian homes. Lead in soil and lead in outdoor air are the main contributors to lead in household dust in Canada. Based on Toronto data, average concentrations of lead in soil and air have declined by 43% and 76%, respectively, between 1973 and 1984, or 3.9% and 6.9% per year, respectively.^17,23,24 Using these data,** the concentration of lead in household dust in urban communities can be estimated to be 350 µg/g in 1984 and 140 µg/g in 1990, assuming no airborne lead and a further reduction of 24% for lead in soil between 1984 and 1990.

Other sources of lead intake include ceramic ware, activities involving arts and crafts, peeling paint and renovations resulting in dust or fumes from paint.²⁵ No allowance has been made for the contribution of lead from these sources, because they occur on a highly sporadic basis and because no quantitative data are available. It has been pointed out²⁵ that old paint has been an important source of excess lead intake for inner-city children living in older housing stock in the United States. This may not be as important in Canada as in the United States, because Canada's stock of older housing is smaller relative to the total stock available. However, these sources, as well as occurrences of high lead concentrations in drinking water in some older houses, can be extremely important for a small number of children.

Total intakes and uptakes of lead from all sources are shown in Table 1 for children and adults in urban areas. The relative contribution of water to average intake is estimated to be 9.8% and 11.3% for children and adults, respectively. Total intake of lead from three of the four major sources--air, food and dust--appears to have dropped significantly since the mid-1980s as a result of regulatory and voluntary actions to control lead from air (via gasoline) and food (via cans). For young children, average daily intake is calculated to be about 29 µg/d, down from 70 µg/d calculated on the basis of 1984 to 1986 data, and is now below the intake of 48 µg/d for a two-year-old based on the World Health Organization's (WHO) provisional tolerable weekly intake (PTWI) of 25 µg/kg bw, equivalent to approximately 3.5 µg/kg bw per day.²⁶

Table 1. Total intake^a and uptake^b of lead (µg/d)

		Child (two years old, 13.6 kg)		Adult (70 kg)
Medium	Concentration	Intake (%)	Uptake (%)	Intake (%)	Uptake (%)
a Assumed volume of air inhaled per day is 20 m3 for adults and 6 m3 for children. Assumed drinking water consumption is 1.5 L/d for adults and 0.6 L/d for children. Intake of lead estimated to be 1.1 µg/kg bw per day for children and 0.75 µg/kg bw per day for adults.16 Assumed quantity of dirt ingested is 20 mg/d for adults and 80 mg/d for young children.27,28 Numbers may not be exact due to rounding. b Absorption of inhaled lead is assumed to be 40% for adults and children. Absorption of lead in food and drinking water is assumed to be 50% for children and 10% for adults. Absorption of lead from dirt and dust is assumed to be 30% for children and 10% for adults.21
Air	0.06 µg/m3	0.36 (1.2)	0.14 (1.1)	1.2 (1.9)	0.48 (7.1)
Water	4.8 µg/L	2.9 (9.8)	1.45 (11.6)	7.2 (11.3)	0.72 (10.7)
Food	Various	15.0 (50.9)	7.5 (60.2)	52.5 (82.4)	5.25 (78.0)
Dust, dirt	140 µg/g	11.2 (38.0)	3.36 (27.0)	2.8 (4.4)	0.28 (4.2)
Total		29.5	12.5	63.7	6.7

Analytical Methods and Treatment Technology

Atomic absorption spectrometry (AAS) may be used to determine concentrations of lead and other metals in water. Detection limits of less than 1 µg/L can be achieved;¹² however, practical quantitation limits (PQLs) are usually 1 to 3 µg/L during routine monitoring studies.¹¹ Inductively coupled plasma atomic emission spectrometry (ICP-AES) is frequently used in routine monitoring analyses, because of speed, relative freedom from interference by other components in the sample and lower cost per analysis. This technique is preferable to AAS when multi-element analysis is required. The detection limit is 1 to 2 µg/L and the PQL is about 7 to 10 µg/L.²⁹ Because the maximum acceptable concentration (MAC) for lead in drinking water is intended to apply to average concentrations in distributed water, sampling should be carried out on flushed samples at the point of consumption.

Conventional water treatments, including settling, aluminum sulphate (alum) or ferric sulphate coagulation and filtration are reasonably effective in removing lead from treated drinking water. Lime softening at elevated pH is also effective in removal of lead. However, because the majority of lead in drinking water is introduced after leaving the treatment plant as a result of leaching from materials in the distribution system or household plumbing, corrosion control is a more effective method of preventing high concentrations of lead at the point of consumption. Adjustment of the pH from less than 7 to 8 or 9 and moderate increases in alkalinity, measured as carbonate, to more than 30 mg/L reduce the plumbosolvency of acidic waters and minimize leaching.^30,31 Corrosion inhibitors such as zinc orthophosphate or silicate-based inhibitors may also be added. Although water treatment can reduce tap water lead concentrations substantially, water treatment alone may be inadequate to reduce lead to concentrations below 10 µg/L when water is supplied through leaded distribution systems and lead concentrations are high.³² Other effective methods of treatment, which are also suitable for home use, include reverse osmosis and ion exchange using a strong acid cation resin; activated adsorption has also been reported to be effective in some cases.