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Development of a Test Method for Leaching of Lead From Lead-Based Paints Through Encapsulants.


pdf icon Development of a Test Method for Leaching of Lead From Lead-Based Paints Through Encapsulants. (4257 K)
Nguyen, T.; McKnight, M. E.; Byrd, W. E.

NISTIR 5783; 39 p. February 1996.

Sponsor:

Department of Housing and Urban Development, Washington, DC

Available from:

National Technical Information Service
Order number: PB96-154984

Keywords:

coatings; encapsulant; diffusion; lead; leaching; paints; test methods; induction period

Abstract:

Lead in paint has been associated with lead poisoning in children. The use of polymeric encapsulants is a potential abatement method for controlling the exposure to lead from lead-based paints. The objective of this study was to provide a technical basis for a standard test method to measure the transport of lead through polymeric encapsulants. In developing this method, the following variables were investigated: lead pigment type and concentration in the lead-based film, chemical type and pH of leaching solutions, and encapsulant resins. The lead-containing films were prepared using a linseed oil binder. The encapsulants were water-borne epoxy and acrylic products and an oil-based alkyd paint. An experimental setup consisting of a cylinder attached to lead-based film, with and without an encapsulant, applied to a poly(methyl methacrylate) (PMMA) substrate was found suitable for a lead leaching test. A pH controlled system was required and found convenient for controlling the pH of the leaching solutions. Little (<5%) lead was leached from a linseed-oil film containing either lead chromate or lead carbonate pigment immersed in inoganic acids or bases in the pH range between 2 and 12, suggesting that little lead would be expected to leach from a lead-based painted wll when the wall comes into contact with weak inorganic acids, or ammonia-based cleaning solutions. Because sufficient lead must be leached from the paint to measure the transport properties of encapsulants, additional leaching agents were investigated. Among the chemical compounds studied, acetic acid was the most efficient lead leaching agent. A pH 2, 3.5 mol/L acetic acid in water leached nearly 70% lead from a lead carbonate-containing film within 5 hours; this is about 70 times greater than amount of lead leached after 100 hours in a nitric solution of the same pH. Consequently, a leaching solution containing 3.5 moles acetic acid in 1 liter of water was chosen. For lead-based films under an encapsulant, an induction period exists before lead begins to leach out of the films. After the induction time, a substantial amount of lead leached from the lead-based films under epoxy and acrylic encapsulants and the alkyd paint. The rate in the water-born encapsulants were higher than that of the oil-based alkyd paint. FTIR in the internal reflection mode provided a good method to follow the conversion of acetic acid to lead acetate, and these data were used for determining the diffusion coefficient of lead acetate in a lead-based film. The diffusion coefficient of lead acetate formed from a vinegar solution in a lead-based film was found to be in the same range as other organic acetates, 10-10 cm2/s. The diffusion coefficients of 100% acetic acid in lead-based linseed-oil films, encapsulants, and alkyd paint were measured using a video/computer image analysis procedure; the values are in the 10-9 cm2/s to 10-11 cm2/s range. Acetic acid was found to be a good candidate for leaching lead from a lead-based film with and without an encapsulant covering it.