This is the second in a series of Tech Tips on lead-based paint. This Tech Tip describes the methods used to determine if lead exists in a paint.
Lead-based paint is defined as any paint, varnish, stain, or other applied coating that has at least 1 milligram of lead per square centimeter (mg/cm2) or 0.5% by dry weight (5,000 micrograms per gram dry weight, or 5,000 parts per million).
There are three methods of determining if paint has lead in it:
- Having a certified laboratory analyze a paint chip sample
- Hiring a certified contractor to use an x-ray fluorescence (XRF) instrument to measure the amount of lead on a painted surface
- Using a chemical test kit or using the swab method.
An Environmental Protection Agency (EPA) report, A Field Test of Lead-Based Paint Testing Technologies: Summary Report (EPA 747-R-95-002a), recommends only the laboratory analysis and XRF methods. The report concluded that chemical test kits cannot determine the extent of lead-based paint on a surface and users cannot be confident that test kits will discriminate accurately between lead-based paint and other paint.
Paint Chip Lab Analysis.
The paint chip lab analysis method is simple. Paint samples are taken from a painted surface. The samples are sent to a lab. The lab tests paint samples for lead by atomic absorption spectrophotometry (AAS) or inductively coupled plasma (ICP). The tests show how much lead is in the paint. The lab reports the results.
The Department of Housing and Urban Development (HUD) recommends that paint chip samples be taken from a 4-square-inch area of paint. The testing laboratory may have different requirements. The 4-square-inch sample guarantees that enough paint will be collected for labora-tory analysis. The 4-square-inch area may be of any shape (a 2- by 2-inch square or a 1- by 4-inch rectangle, for example). Areas from which paint chip samples are collected should be repaired to prevent exposure in the event the paint contains lead. Also, take representative samples of the paint from several areas. Record the location of each sample.
All layers of paint must be removed, since the lower layers are more likely to contain lead. Include as little as possible of the underlying material (wood, plaster, metal, or brick) in the sample. The test results are reported in percent of lead by sample weight. Adding substrate material in the sample would give erroneous results.
All laboratories analyzing lead paint must participate in the EPA's National Lead Laboratory Accreditation Program and be accredited by an organization recognized by the EPA. For more information, contact the National Lead Information Center Clearinghouse (1-800-424-LEAD) and ask for the most current list of EPA-recognized laboratories. Costs range from $12 to $25 per paint chip sample. The labs will give you complete instructions on taking paint samples and will give you shipping containers. Local and regional environmental labs may be available for lead testing. Mailing samples out-of-state is also a reasonable approach and may yield lower lab costs and faster results.
Advantages--Paint chip analysis is considered the most accurate method for measuring lead in paint as long as paint chip samples include all layers of paint and do not include substrate material. It is also the cheapest method if you are testing only a few paints.
Disadvantages--It can take for several days to several weeks to get the results, depending on the lab. The surface must be disturbed and repaired.
Results--Paint chip analysis measures the amount of lead in the paint by weight. The weight of lead in the sample is compared to the weight of the entire sample, and is reported as a percentage. If the sample has 0.5% lead or higher (5,000 parts per million), HUD considers this to be a lead paint. Lead levels may also be reported as mg/cm2 as long as the surface area of the paint removed was measured.
|Figure 1--X-ray flourescence instruments use radiation to measure the amount of lead on a painted surface.|
X-ray fluorescence (XRF) instruments measure the amount of lead on a painted surface by exposing the surface to high-energy radiation (gamma rays in this case). The radiation causes lead to emit x-rays at a characteristic frequency. The intensity of the rays is measured by the instrument's detector and converted to a number that represents the amount of lead per unit area (usually in milligrams per square centimeter). Operators of XRF machines require special training to prevent radiation exposure.
These instruments (Figure 1) are very expensive, ranging in price from $10,000 to $15,000. Operators must be trained and certified. In most cases, a certified contractor can be hired for a few hundred dollars an hour. Although the cost may appear high, a contractor using these instruments can inspect many surfaces in a short period of time. Call the National Lead Information Center Clearinghouse (1-800-424-LEAD) to locate certified XRF operators in your area.
Advantages--The XRF instrument can tell immediately if the paint has lead in it and how much lead is present. Testing does not damage the painted surface. It is the best method when many surfaces or buildings are being tested.
Disadvantages--XRF measurements have a larger margin of error than laboratory analysis of paint chips. XRF instruments should not be used to test highly curved or intricate surfaces because of safety concerns, poor reliability of the results, and the inability to determine the exact surface area. Laboratory analysis of paint chip samples is recommended when irregular surfaces are being examined or when an inconclusive measurement is taken. An inconclusive measurement is a reading within the tolerance zone of the XRF machine around the established lead limit of 1.0 milligram of lead per square centimeter of a painted surface. For example, if an XRF instrument had a tolerance zone of +/- 0.2 mg/cm2, the inconclusive range would be between 0.8 mg/cm2 and 1.2 mg/cm2. A reading of 0.9 mg/cm2 would require that a paint chip sample be analyzed to verify the results.
Results--XRF readings tell how much lead is in the tested surface area. Results are reported in milligrams per square centimeter. If the reading is greater than 1 milligram per square centimeter (1.0 mg/cm2), then the surface is considered a lead surface. Usually more than one XRF reading is taken for a surface. The average of those readings is the result.
Chemical Test Kits.
|Figure 2--Swab testing kits can detect lead.|
Chemical test kits detect lead by a chemical reaction that causes a color change if lead is present in concentrations of at least 0.5% lead by weight. Chemical test kits are inexpensive and easy to use. They are available from local hardware stores or distributors. Several types of test kits are available. One type uses a sodium sulfide or sodium rhodizonate solution that is applied to a notched surface or a paint chip. Lead is indicated if the solution turns the appropriate color. Another type uses a swab (Figure 2) that is rubbed onto a painted surface. Lead is present if the swab turns the appropriate color.
Chemical test kits are not recommended by the EPA because of the possibility of false readings and because the tests do not tell how much lead is present in the paint. Sometimes the color change is difficult to interpret--especially if dark colors are being tested.
Advantages--The chemical spot testing method is quick, easy, and inexpensive. Test kits can be purchased directly from the manufacturer, distributor, or hardware store. Testing can be done at your convenience and you get the results right away.
Disadvantages--The chemical test does not tell you how much lead is present. Sometimes the test indicates lead is present when it is not (a false positive) and other times indicates lead is not present when it is (a false negative). The chemical tests only test the exposed layers, not the underlying layers that may be more likely to contain lead.
Results--Lead is present if the chemical test turns a specific color, usually red or brown.
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