United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-018 August 1982
Project Summary
Seattle Distribution System
Corrosion Control Study:
Volume III. Potential for
Drinking Water Contamination
from Tin/Antimony Solder
Carlos E. Herrera, Gregory J. Kirmeyer, and Brian P. Hoyt
This study was conducted to evalu-
ate the potential leaching of metals
into drinking water from tin/antimony
solder. The study consisted of five
research steps: (1) An investigation of
the theory of corrosion products that
formed from the solder was con-
ducted using pe-pH diagrams and gal-
vanic coupling relationships, (2) static
laboratory metal leaching tests were
performed to determine the extent of
antimony leaching from the solder, (3)
field water samples were taken from
buildings that contained tin/antimony
soldered plumbing, (4) continuous-
flow metal leaching tests were used to
compare metal leaching from tin/an-
timony solder with lead/tin solder
under three water treatments (lime
plus sodium carbonate, lime plus
sodium bicarbonate, and lime plus
sodium bicarbonate plus silicate), and
(5) corrosion films that formed on
both tin/antimony and lead/tin solder
were analyzed by scanning electron
microscopy and X-ray diffraction.
The results indicate that increases in
metal concentrations resulting from
the corrosion of tin/antimony solder
are minimal. Metal leaching from the
solder is inhibited by the sacrificial
corrosion of tin and the formation of a
stable, double-layer tin passivation
film (SnO and SnO2). Side-by-side
tests comparing metal leaching from
tin/antimony with that from lead/tin
solders show substantial reductions in
standing water lead concentrations
when tin/antimony solder is used.
The use of tin/antimony solder in
place of lead-based solders should
result in reduced human exposure to
lead from drinking water with only
minimal increases in antimony
exposure.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory,
Cincinnati, OH, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The Seattle Water Department (SWD)
serves an average of 161 mgd of high
quality water to a population of more
than 1 million in the Greater Seattle
area. The water originates in the Cas-
cades from two mountain sources— the
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Cedar and Toll Rivers. The watersheds
are well protected and the water
requires only disinfection with gaseous
chlorine to meet state requirements
These mountain waters, which are pre-
dominantly rainfall and snowmelt
runoff, are very soft and tend to be
highly corrosive to the unlined, metallic
pipes in home plumbing systems.
The corrosiveness of Cedar and Tolt
water results from several related fac-
tors, including:
• Acidity, as indicated by low pH
(after chlorination andfluoridation,
pH is reduced to a range of 6.8 to
7.2 for the Cedar supply and 5.8 to
6.2 for the Tolt supply);
• Dissolved oxygen concentration at
saturated conditions;
• Insufficient calcium and bicarbo-
nate alkalinity in the water to form
protective calcium carbonate films
on pipe surfaces; and
• A relatively high [halogen + suit a -
te]/'alkalinity ratio that indicates
conditions favorable to pitting
corrosion.
In 1970, three factors combined to
intensify the corrosiveness of the water
supplies. First, the chlorine dosage at
the open distribution reservoir outlets
was increased to decrease the occur-
rence of positive bacteriological sam-
ples within the distribution system.
Second, ammoniation of the water
supply was stopped at the request of the
U.S. Public Health Service to enable a
free chlorine residual to be maintained
throughout the distribution system. This
change from combined chlorination to
free chlorination was implemented to
provide quicker, more effective disinfec-
tion of the unfiltered water supply. The
third factor that increased corrosive-
ness was the initiation of flouridation
with hydrofluorosilicic acid in 1970.
Corrosion of the plumbing systems
and the associated water quality degra-
dation has been a major concern of the
SWD for many years. Studies performed
from 1972 to 1976 demonstrate that the
levels of lead, copper, and iron in over-
night standing tap water often exceed
the maximum contaminant levels
defined by the National Interim Primary
and Secondary Drinking Water Regula-
tions. Cadmium and zinc were also
found to increase after overnight stand-
ing in home plumbing, but they rarely
exceeded their maximum levels. These
metals originate from the copper and
galvanized pipes and the solders used in
home plumbing systems. Although the
health impact of metal levels from over-
night standing water is not an accute
problem, it is certainly desirable to re-
duce exposure where possible.
The use of lead-based solders to join
copper pipe can create a problem with
regard to lead leaching. To reduce the
potential for lead contributions from this
source, the maximum allowable lead in
solder was limited to 0.20% by amend-
ment of the Seattle plumbing code. The
effect of this amendment was to require
contractors to use 95/5 tin/antimony
solder
Purpose and Scope of Work
This study was undertaken to evalu-
ate the potential leaching of metals into
drinking water from the tin/antimony
solder now being used in Seattle plumb-
ing. The study consisted of five research
steps: (1) An investigation of the theory
of corrosion products that formed from
the solder was conducted using pe-pH
diagrams and galvanic coupling rela-
tionships, (2) static laboratory metal
leaching tests were performed to deter-
mine the extent of antimony leaching
from the solder, (3) field water samples
were taken from the buildings that con-
tained tin/antimony soldered plumbing,
(4) continuous flow metal leaching tests
were used to compare metal leaching
from tin/antimony solder with that from
lead/tin solder under three water treat-
ments (lime plus sodium carbonate,
lime plus sodium bicarbonate, and lime
plus sodium bicarbonate plus silicate),
and (5) corrosion films that formed on
both tin/antimony and lead/tin solder
were analyzed by scanning electron
microscopy and X-ray diffraction.
Procedures, Results and
Discussion
Theoretical Analysis
An investigation of the theory of cor-
rosion products formed from the solder
was conducted using pe-pH diagrams
and galvanic coupling relationships.
Results indicated that the leaching of
antimony from the solder may be inhi-
bited by two mechanisms:
1. Sacrificial Corrosion. Though
antimony alone is quite soluble, the
galvanic coupling relationships
among the three metals that make
up a soldered joint (tin, antimony,
and copper) indicate that the corro-
sion of tin is theoretically more
favorable than the corrosion of
antimony. Tin, therefore, mayactas
a sacrificial anode.
2. Passivation. Since tin can be passi
vated by tin oxide, a passivation filrr
may cover the entire surface of tht
solder and therby inhibit meta
leaching from the solder.
Laboratory Experiments
Laboratory experiments were con-
ducted to verify the theoretical phase of
the study Twenty test specimens con-
structed from tin/antimony solder and
copper sheet were immersed in Cedar
water in a sealed 50-ml glass container.
The samples were held under static
conditions at 20°C for periods of 0.5 to
98 hr. In addition, two samples of anti-
mony metal equalling the weight of
antimony in the solder specimens were
tested as described above for a 70-hr
period.
The laboratory static coupon tests
demonstrated that antimony dissolution
from tin/antimony solder is substan-
tially less than the theoretical or
observed dissolution from pure anti-
mony metal. The highest antimony con-
centration observed in the tin/antimony
solder coupon test was 3.7 fjg/L,
whereas 18,000/ug/L and 22,000//g/L
of dissolved antimony were observed in
the pure antimony metal corrosion
tests.
These results support the theoretical
conclusions already put forward. In the
short term, the inhibition of antimony
leaching from tin/antimony solder is a
result of the galvanic coupling relation-
ship, namely the sacrificial corrosion of
tin.
Field Sampling
The University of Washington has
been using 95/5 tin/antimony solder
on building plumbing systems™Since
about 1968. The field study consisted of
taking 0.95-L samples of overnight tap
water that had stood overnight in eight
buildings on the University campus. The
plumbing systems of the buildings
tested ranged from 1 to 10 years in age
and supposedly consisted of copper pip-
ing bonded with 95/5 tin/antimony
solder.
Samples of running water (0.95 L)
were taken at the mechanical room
(where the building plumbing connects
with the distribution system) of each
building to obtain the characteristics of
the inflowwater The 0.95-L water sam-
ple that had stood overnight was then
taken from the potable water tap fur-
thest from the mechanical room of the
building.
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The samples were then analyzed for
temperature, conductivity, alkalinity,
total and dissolved antimony, and total
lead, copper, and zinc.
The field sampling showed that, in the
long term, antimony corrosion is inhi-
bited by the passivation of tin in the
solder. Of all the samples tested, a
detectable antimony concentration was
found in only one building water sam-
ple. In addition, scanning electron
microscopy showed that two distinct
passivation films were present on the
tin/antimony-soldered joints removed
from the buildings at the University of
Washington.
Metal Leaching Tests
Short pipe sections of copper, copper
plus 50/50 lead/tin solder, and copper
plus 95/5 tin/antimony solder were
attached to continuous flow test units
for comparison of copper, lead, tin, and
antimony leaching under three alterna-
tive treatments. Two velocities were
used in establishing corrosion films in
the metal leaching sections. The pipe
sections were periodically removed
from the continuous flow test unit and
dissolved metals were determined after
periodic 22- to 24-hr contact with test
water in the laboratory.
The side-by-side metal leaching tests
indicated that lead leaching is substan-
tially less from tin/antimony solder
than from lead/tin solder. Some lead
initially leaches from the tin/antimony
solder; but after approximately 6 weeks
of testing, lead leaching was reduced to
below the detection limit. Antimony
leaching from the 95/5 tin/antimony
solder was also consistently below the
detection limit of 1.4^g/L.
Conclusions
Lead leaching is substantially
reduced and the subsequent increase in
the antimony concentration of the
drinking water is minimal if tin/antimo-
ny solder is used in plumbing systems in
place of lead-based solder. The low
metal leaching levels from 95/5 tin/an-
timony solder are mainly because of the
sacrificial corrosion of tin and the for-
mation of a tin oxide passivation film
that protects the surface of the solder
from corrosion.
The theoretical and experimental
results obtained in this study therefore
indicate that 95/5 tin/antimony solder
would be an excellent replacement for
lead-based solders in private and com-
mercial plumbing systems where lead
leaching is a problem.
The full report was submitted in ful-
fillment of Grant No. R-806686-010 by
the Seattle Water Department under
the sponsorship of the U.S. Environ-
mental Protection Agency.
Carlos E. Herrera, Gregory J. Kirmeyer, and Brian P. Hoyt are with the Seattle
Water Department, Seattle, WA 98144.
Marvin C. Gardels is the EPA Project Officer (see below).
The complete report, entitled "Seattle Distribution System Corrosion Control
Study: Volume III. Potential for Drinking Water Contamination from Tin/
Antimony Solder," (Order No. PB 82-231 242; Cost: $10.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
t US. GOVERNMENT PRINTING OFFICE 1982-559-017/0768
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