Exposure to Lead

7. Direct human exposure to lead occurs not only through inhalation of particulate lead in ambient air, but also through ingestion of contaminated food, water and dust, and from occupational sources. In children and infants, ingestion of lead-containing dust following transfer from hand to the mouth is also important.
8. Food is the main source of lead intake for most people. Levels in food routinely monitored in the United Kingdom by the Ministry of Agriculture Fisheries and Food show that beverages, vegetables and milk are the main food groups containing lead. Lead may enter food through the deposition of dust and rain, containing the metal, on crops. In root crops, the contribution of deposited lead to the lead content of the edible portion of the plant is probably slight, but in leafy crops and cereals it may be more important. The amount of lead on food plants may be reduced through washing during food processing. Uptake of lead directly from the soil by food plants will also contribute to lead intake. However, only a small proportion of lead in soil is available for plant uptake and species differ widely in their uptake. Other ways in which lead may get into food include through food-processing activities, glazed ceramic dishes, lead crystal ware and now rarely, lead solder in cans.
9. Drinking water may also be a source of lead exposure in the United Kingdom. The current lead standard for drinking water is 50 µg/l* at consumers' taps. In 1993 the World Health Organisation recommended a guideline value of 10 µg/l and this value has been included in the European Commission's revised Drinking Water Directive. Water leaving treatment works usually has concentrations of less than 10 µg/l. However, in areas where lead pipes, storage tanks or other fixtures and fittings are still in use, and the water is able to dissolve it, lead can leach into water resulting in occasional breaches of the current lead standard of 50 µg/l. Water supplies are treated to minimise this.
10. Soil and dust are major sources of exposure for children, who transfer dirt from their hands to their mouths, and dust can be the major component of their lead intake. In most rural and remote areas lead in soil is derived mainly from natural geological sources, but in urban and industrial areas soil lead is derived mainly from man's activity. Additionally, the application of sewage sludge to agricultural land may increase the lead content of soil. Lead in outdoor dust is derived from the deposition of dust produced by lead-based paint, combustion of leaded petrol and from industrial sources such as lead smelters. The major source of lead in indoor dust is peeling and flaking of lead-based paints in older properties, although dust and soil from outdoors may also enter buildings.
11. Although normally only a small fraction of total lead intake occurs through inhalation, lead in air may also contribute to exposure indirectly, for example, through deposition in dust and on crops.

* 1 µg/l is one millionth of a gram of lead in 1 litre of water