Development of a Test Method for Leaching of Lead From Lead-Based Paints Through Encapsulants.
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899