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Spot Test Kits for Detecting Lead in Household Paint: A Laboratory Evaluation.

pdf icon Spot Test Kits for Detecting Lead in Household Paint: A Laboratory Evaluation. (1559 K)
Rossiter, W. J., Jr.; Vangel, M. G.; McKnight, M. E.; Dewalt, G.

NISTIR 6398; 94 p. May 2000.


Department of Housing and Urban Development, Washington, DC

Available from:

National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161.
Telephone: 1-800-553-6847 or 703-605-6000;
Fax: 703-605-6900; Rush Service (Telephone Orders Only) 800-553-6847;
Order number: PB2000-100134


paints; detection; kit response; lead based paint; lead level; lead chromate; operator effect; spot test kits; testing; white lead


A laboratory study was conducted to determine the reliability of spot test kits for detecting the presence of lead in household paint when tests were conducted by certified lead inspectors or risk assessors. Reagent solutions were applied to paint specimens and, subsequently, the specimens were observed for characteristic color change. For the study, four test kits were based on the reaction of lead ion with sulfide ion to produce a gray or black color, whereas four others were based on the reaction of lead ion with rhodizonate ion to give a pink or red color. These eight kits were used in an experiment investigating the effect of lead level, lead pigment type, operator, paint-film substrate, overlayer paint type, and overlayer paint thickness. Test samples, prepared using either a white lead (i.e., basic lead carbonate) or a lead chromate pigment, had ten lead levels ranging from 0 mg/cm2 to 3.5 mg/cm2. Five operators were trained according to test protocols based on each kit manufacturer's instructions. The study showed that the spot test kits gave positive results at lead levels less than 1 mg/cm2. Consequently, a positive response could not be relied on to indicate the presence of lead-based paint, which is defined as paint having lead levels equal to, or greater than, 1 mg/cm2. This finding is consistent with the results of past field studies. A criterion against which a spot test kit may be considered as acceptable for use as a negative screen (i.e., a test for which a negative result indicates a low probability of lead > 1 mg/cm2) for the presence of lead-based paint was proposed. This criterion is: Upon evaluation of spot test kit response, the probability of a negative response (with 95% confidence) at a lead level of 1 mg/cm2 is < 5%. Equivalently, the lead level at which there is a 95% probability of a positive response (with 95% confidence) should be < 1 mg/cm2. The type of lead pigment had a significant effect on the spot test kit response. For white lead specimens, six kits--three sulfide-based and three rhodizonate-based--gave low percents of false negatives (< 2%) and met the proposed criterion for acceptance as a negative screen for lead-based paint. For lead chromate specimens, three of these six kits (two sulfide-based and one rhodizonate-based) also had low percents of false negatives (< 2%) and met the proposed acceptance criterion. The other factors--overlayer type, overlayer thickness, operator, and substrate--did not generally show significant effects in cases where the spot test kits appeared to be candidates for use as negative screens for lead-based paint. Finally, the study results lead to the suggestion that an evaluation of spot test kit response should afford a low percent of positive results at the 0 mg/cm2 lead level because, in practice, false-positives may needlessly spur test kit users into taking further, but unnecessary, investigative action for the presence of lead.