Lead paint or lead-based paint is paint containing lead, a heavy metal, that is used as pigment, with lead(II) chromate (PbCrO4, "chrome yellow") and lead(II) carbonate(PbCO3, "white lead") being the most common. Lead is also added to paint to speed drying, increase durability, retain a fresh appearance, and resist moisture that causes corrosion. However it is one of the major health and environmental issues with paint. In some countries lead continues to be added to paint intended for domestic use whereas in others regulation exists that prohibits this, though lead paint may still be found in older properties painted prior to the introduction of such regulation e.g. in the U.S. and the U.K. and Australia. Paint with significant lead content is still used in industry and by the military. For example, leaded paint is sometimes used to paint roadways and parking lot lines.
Toxicity
Although lead improves paint performance, it is a dangerous substance. It is especially damaging to children under age six whose bodies are still developing. Lead causes nervous system damage, stunted growth, and delayed development. It can cause kidney damage and affects every organ system of the body. It also is dangerous to adults, and can cause reproductive problems for both men and women. Lead paint is particularly dangerous because it tastes sweet therefore encouraging children to put lead chips and toys with lead dust in their mouths.
One myth related to lead-based paint is that children must eat leaded paint chips to develop lead poisoning. In fact, childhood lead exposure can occur by way of ingestion of lead dust through normal hand-to-mouth contact during which children swallow lead dust dislodged from deteriorated paint or leaded dust generated during remodeling or painting.
Substitutes
Paint manufacturers replaced white lead with a less toxic substitute, titanium white (based on the pigment titanium dioxide) which was first used in paints in the 19th century. (In fact, titanium dioxide is considered safe enough to use as a food coloring and in toothpaste, and is a common ingredient in sunscreen.) The titanium white used in most paints today is often coated with silicon or aluminum oxides for better durability. Titanium white has been criticized for leading to "chalkiness" when mixed with colors, and the possibility of decreased permanence of organic pigments mixed with it due to its high refractive index.
Zinc white is less opaque than titanium white, and is often seen as a superior white for lightening other pigments in mixtures. Although zinc white is the standard white for the watercolor medium it has long been of debatable permanence in oils. Critics of the pigment argue that its use leads to excessive cracking and delamination, even when very sparingly mixed with other pigments such as lead white.[9]
Some art-supply manufacturers supply a "lead white hue," a mixture, usually of titanium and zinc white, which attempts to imitate the hue of genuine lead paint without the toxicity. It does not, however, have the desirable structural (physical) properties of lead white.
Source: Wikipedia