Hydrochem
Systems Corp.
129 S. Eldridge Way
Golden, Colorado 80401
| Date: |
September 1, 1995 |
| To: |
Marble Institute of America |
| From: |
Donald Langmuir, PhD, Professor Emeritus of
Geochemistry,
Colorado School of Mines, & President, Hydrochem Systems
Corp. |
| Subject: |
The article 'Granite and Radon' published in
Solid Surface |
I am appalled and dismayed
that any journal would accept a pseudo-science article such
as this for publication. If this article had been submitted
to a reputable scientific journal, the editors and reviewers
would have demanded that the author supply scientific evidence
to support his/her many unfounded and unsupported assertions
and conclusions. Lacking such evidence they would have rejected
it for publication. As a separate point, I am very suspicious
of a paper that has no named author. Who is responsible for
this attack on granite countertops? Is it someone who stands
to benefit economically?
Two of the scientific
experts who the author (or authors?) cites repeatedly in the
bibliography as sources of the arguments have become aware
of the 'Granite and Radon' paper. They agree with me that
the author's conclusion that a granite countertop could emit
a high and dangerous concentration of radon to a home is both
totally fallacious and ludicrous. In fact, as you will see
below, the amount of radon released from a typical granite
countertop is certain to be completely negligible and well
below detection by any known method of radioactive analysis.
I would be delighted to have a granite countertop in my home!
As to my credentials
to evaluate and refute 'Granite and Radon', I have been conducting
funded university research and publishing in peer reviewed
journals on the geochemistry of radioactive elements for nearly
20 years at Penn State University and the Colorado School
of Mines. In recognition of this expertise, I was nominated
by the National Academy of Sciences and appointed to serve
as a member of the U.S. Nuclear Waste Technical Review Board
by President Reagan in 1989, and reappointed to that position
for a second four-year term by President Bush in 1992.
It is worth noting
that the stone industry, whether advertising countertops,
building materials or monuments, terms many stones 'granites'
that are not true granites to a geologist. A true granite,
which is often grey or pink, is chiefly comprised of a potassium
aluminum silicate mineral (K-feldspar or potassium feldspar)
and quartz (silica or SiO2). Rocks called granites by the
industry also include magnesium silicates (e.g. peridotites
and serpentines) and a host of other chemically different
rock-types, most of which contain much less uranium than does
true granite.
As admitted by the
author of 'Granite and Radon', there have been no direct measurements
of radon release from granite countertops. Model calculations
suggested by Dr. Richard Wanty, using a standard, scientifically
accepted approach and conservative assumptions, indicate that
the radon release from a granite countertop is orders of magnitude
below detection by any known analytical method. Incidentally,
Dr. Wanty, who is a geochemist with the U.S. Geological Survey,
co-authored or co-edited four of the expert references cited
in the author's bibliography. He has performed research and
published on the geochemistry of radioactive elements for
sixteen years, and studied radon as a public health issue
since 1986. Dr. Wanty's worksheet reproduced below may be
used to calculate the concentration of radon that would be
released from a granite countertop. The worksheet is shown
with an example calculation, assuming a ten-foot by seven-foot
granite countertop.
The EPA standard, which
is not to be exceeded in indoor air, is 4 picoCuries per liter
of air (4 pCi/L). Eisenbud 1 indicates that the average contributions
of radon from various sources to indoor air are 1.5 pCi/L
from the soil (under and around the house), 0.01 pCi/L from
public water supplies (0.4 pCi/L) from private wells), 0.05
pCi/L from building materials, and 0.2 pCi/L from outdoor
air. These values are for the average house which is ventilated
such that over one hour the air is changed 0.5 to 1.5 times.
The vanishingly small amount of radon in household air that
might be released from a granite countertop (0.00000074 pCi/L)
as computed below, has been calculated assuming no exchange
of indoor and outdoor air, which would further trivialize
its significance. Note also that the radon content of outside
air is 270,000 times greater than that released by the countertop.
There are certain properties
of rocks that can increase their radon emanation efficiency,
or in other words increase the release of radon from a given
weight of rock. These are rock properties that maximize the
exposure of internal or external rock surfaces to water or
air, allowing any radon gas to escape. The author of 'Granite
and Radon' argues that such properties, which include rock
porosity, fissuring and mylonitization, will increase radon
releases. This is probably true, however, a granite with such
properties would be too brittle to make into a countertop,
and too open to take a polish, and so would not be marketable
as a countertop - unless the rock pores were first filled
with a chemical sealant. Such sealing would also eliminate
any possible radon release problems.
In summary, to show
how laughable are the concerns expressed in 'Granite and Radon',
the typical granite countertop in our example will release
7.4 x 10 -7 pCi/L of air. This corresponds to 2.7 x 10 -8
atom decays per second (dps). This represents 0.85 decays
per year. In other words, less than one atom of radon is produced
by the countertop in one year. This is hardly worth getting
excited about. I would suggest that a good way to reduce our
exposure to the radon present in outdoor air, would be to
build an air-tight house out of granite countertops!
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