Paints contain lead when the paint manufacturer intentionally adds one or more lead compounds to the paint for some purpose. A paint product may also contain some amount of lead when paint ingredients that are contaminated with lead are used or when there is cross contamination from other product lines in the same factory.
When a paint manufacturer does not intentionally add lead compounds in the formulation of its paints, the lead content of the paint will be very low – usually less than 90 parts per million (ppm) total lead by dry weight and frequently much lower. If a paint manufacturer takes care to avoid the use of paint ingredients that are significantly contaminated with lead, the lead content of the paint will often be as low as 10 parts per million or less. IPEN recommends 90 ppm as an achievable and protective goal for lead in paint worldwide. While WHO, the U.S. CDC and other health agencies have determined that no safe level of childhood lead exposure can be established, 90 ppm is the current standard for household paints in the U.S. and Canada and would ensure that a manufacturer could sell its paint anywhere in the world.
The lead compounds most commonly added to paints are pigments. Pigments are used to give the paint its color; make the paint opaque (so it covers well); and protect the paint and the underlying surface from degradation caused by exposure to sunlight. Lead compounds commonly used as paint pigments include: lead chromates, lead oxides, lead molybdates, lead sulfates and others. Lead-based pigments are sometimes used alone and sometimes used in combination with other pigments.
Lead compounds also may be added to enamel (oil-based) paints for use as driers (sometimes called drying agents or catalysts). Enamel paints dry to a hard and smooth surface through a process that involves chemical reactions in which paint ingredients called binders polymerize and crosslink. The driers serve as catalysts that speed up the polymerization and make paints dry faster and more evenly. Lead compounds commonly used as driers include lead octoate and lead naphthenate. These lead-based driers are generally not used alone, but are usually combined with other driers, including compounds of manganese, cobalt and others.
Lead compounds are also sometimes added to paints used on metal surfaces to inhibit rust or corrosion. The most common of these is lead tetroxide, sometimes called red lead or minium. Inorganic pigments, fillers and possibly some other ingredients used in the manufacture of paints may be derived from natural, earth-based materials and may be more or less contaminated with lead depending on geological characteristics at the location where they were mined. When lead-contaminated ingredients are used in the manufacture of paints, this will contribute to the lead content of the paint.
Finally, when a paint manufacturer uses added lead compounds in the manufacture of some of its paints (such as industrial paints), other paints produced in the same facility might become contaminated with lead when proper housekeeping and cleanup procedures are not followed.