Environmental Engineering Reference
In-Depth Information
the combustion of motor vehicle fuels, and ingestion of lead-based paint and
contaminated dust and soil by children.
The combustion of lead-amended gasoline has likely been the single
greatest source of lead contamination of both the environment and humans.
In North America, the phase-out of leaded gasoline and implementation of
strict regulatory limits on primary and secondary lead smelters has resulted
in a decline of atmospheric lead emissions of over 99% in the past 3 decades.
Unlike a variety of other trace elements, lead is not required in the body
to mediate any biochemical or physiological function. It is a very toxic
substance, and increasingly, what once were considered to be low levels of
exposure have become the subject of major public health concern. Total body
burdens of lead in modern day humans are several hundred times greater
than those of our preindustrial ancestors.
A. Lead in the indoor environment
Because of its widespread use and the nature of individual uses, it is not
surprising that lead is a common contaminant of indoor spaces. Indoor lead
contamination has been associated with lead aerosols produced from motor
vehicle operation and lead and other nonferrous metal smelter emissions;
the passive transport of lead dusts into vehicles and residences on the cloth-
ing and shoes of workers exposed to lead in lead-generating or lead-using
industries (lead brought home) and other activities; home hobbies such as
making stained-glass windows, munitions, fishing weights, etc.; deteriorat-
ing or damaged interior lead-based paint (LBP); and the passive transport
of lead-contaminated residential soils indoors by people and pets. Significant
lead contamination of household surface dusts is widespread in North Amer-
ican and European homes that have a history of LBP use.
1. Lead-based paint
Lead compounds such as white lead and lead chromate have been used as
white pigments in paints for centuries. In addition to their pigment proper-
ties, lead compounds were valued because of their durability and resistance
to weathering. Though used in interior and exterior paints, lead was more
commonly used in exterior white paints. An old house with exterior lead-
based paint is pictured in
Figure 2.12
.
Lead compounds have also been used
in the production of varnishes and primers. Red lead, or litharge (Pb
3
O
4
),
has been widely used in the manufacture of weather-resistant metal coatings.
Such coatings were used on bridges and other steel structures and occasion-
ally on exterior residential metal products.
Lead poisoning of young children associated with LBP was initially
recognized by public health authorities in the U.S. in the late 1940s and early
1950s. As a consequence, the paint industry voluntarily limited the lead
content in paint to 1% solids by weight in 1955. Regulatory action subse-
quently limited this to 0.5% by weight in 1971 and 0.06% in 1978. Pre-1978
