6.6. Lead (Pb)

6.6. Lead (Pb)

6.6.1. Behaviour, effects, emissions

Lead is a pollutant in air mainly through its use as an additive to gasoline, in the form of organic lead compounds: tetraethyl and tetramethyl lead. Also, many metal smelters (lead, copper, zinc, iron, steel) emit significant amounts of lead to the atmosphere. Lead occurs in the atmosphere mainly in particulate form (in the fine particle fraction), but a small part occurs in vapour form as organic lead compounds.

The previously very widespread use of lead in gasoline has been substantially reduced in most parts of Europe since early 1980 especially, through the reduction of lead in gasoline, from typically 0.7-0.8 g/l to less than 0.15 g/l, and through the use of lead-free gasoline needed by catalyst cars.

Human exposure to lead is through inhalation of airborne lead and ingestion of lead in foodstuffs and beverages. While most airborne lead is man-made, an appreciable proportion of that in food and water is of natural origin. Nevertheless both deposition of airborne lead, and lead from other man-made sources (e.g. pipes and solders) contribute to dietary intake. Blood lead concentrations are a good indicator of recent exposure to lead from all sources, and adverse health effects tend to increase in severity with increasing blood lead level.

EPA standards are based upon the concept of a relationship between ambient air lead and blood lead concentrations, and presume that a blood lead level of
0.15 µg/ml (mean value for children) can be achieved at an ambient air lead level of 1.5 µg/m3 .

The most sensitive body systems to the effects of lead are the haematopoietic system, the nervous system and the renal system. In addition, lead has been shown to affect the normal functions of the reproductive, endocrine, hepatic, cardiovascular, immulogic and gastrointestinal systems. The most sensitive group to lead poisoning is children. Some studies indicate that children with high levels of lead accumulated in their baby teeth experience more behavioural problems, lower IQs and decreased ability to concentrate, although these findings are currently controversial.

Examples of some "lowest-observed-effect" levels for children (identified by the EPA) are: disturbance of haem synthesis via enzyme inhibition at 0.1 µg/ml, anaemia at 0.4 µg/ml, encephalopathic symptoms at 0.8 µg/ml.

Lead is generally toxic to both plants and animals, and although no serious effects are generally seen at current environmental levels, it is widely considered prudent to limit further dispersal of lead as far as is possible.

6.6.2. Air Quality Limit and Guide Values

EU Limit value and WHO Guideline value for lead is given in Table 6.25. The WHO Guideline value is lower than the EU Limit value by a factor 2-4.

Table 6.25: EU Limit Value for Pb (µg/m3). EU Council Directive 82/884/EEC. WHO Guideline value (µg/m3).