Appendix B
- Radionuclides in Sewage Sludge and Ash at POTW Test Sites and
Comparison With Other Sources of Radioactivity
The purpose of this Appendix is to compare published data on
typical concentrations of radionuclides in soil, fertilizer, and
building materials to the concentrations of radionuclides found
in the sludge and ash samples of a pilot study of nine Publicly
Owned Treatment Works (POTWs). The pilot study was conducted by
a federal interagency working group (Interagency Steering Committee
on Radiation Standards (ISCORS)) to develop sampling and analysis
procedures for a nationwide survey of radionuclide concentrations
in municipal sewage sludge and incinerator ash, to be conducted
in 1999.
Over the last several decades, the U.S. Environmental
Protection Agency (EPA) has conducted surveys of sewage sludge,
ash, compost, and the other products produced by POTWs, to determine
whether concentrations of pollutants that may pose a danger to
members of the public or POTW workers are present. Recently, the
U.S. Nuclear Regulatory Commission (NRC), the U.S. Department
of Energy (DOE), and the U.S. Department of Defense (DOD) have
begun a collaborative effort with EPA to conduct a survey of POTWs
nationwide to determine potential concentrations of naturally-occurring
and commercially utilized sources of radioactive materials in
the sludge or ash. The results of this survey will be available
in about 2 years.
A pilot study of nine POTWs was conducted to assist
the agencies in developing sampling and analysis procedures. It
is important to note that the purpose of this pilot study was
not to assess the relative safety or hazard of radioactive materials
in sewage sludge and incinerator ash, but rather to assess the
sampling and analysis procedures. As such, no conclusions were
drawn as to the relevance of radioactive material concentrations
detected in these samples. This document is intended to help put
these raw data in perspective.
Radiation in the environment from natural sources is the major
source of radiation exposure to man. Radiation exposure results
from the naturally-occurring radionuclides in the environment
(terrestrial radiation) and direct cosmic (extra-terrestrial)
radiation. Naturally-occurring radionuclides are present in some
plants and animals. In the human body, for example, radioactive
potassium (K-40) is present in bones and soft tissues and is the
principal naturally-occurring source of internal radiation exposure.
Some sources of natural radiation have been enhanced (concentrated)
by human technological activities and include wastes from mineral
ores and the petroleum industry, sludge and scale from drinking
water treatment, and articles made from naturally-occurring radioactive
materials such as thorium in lantern mantles. Together, this radiation
is often referred to as "natural" or "background"
radiation. It is all around us and cannot be completely avoided.
In addition to natural or background radiation, radiation from
man-made sources, such as X-ray machines and nuclear reactors
and fallout from nuclear weapons testing in the past, also results
in a relatively small source of radiation exposure to man.
Naturally-occurring radioactive materials are found in soil and
water as well as in materials used to build our homes, such as
bricks and stones. Geological formations and soils may contain
isotopes of uranium, thorium, radium, radon, and other radioactive
elements. The public is generally aware of the radioactive gas,
radon (radon-222), which is one of the decay products of the uranium
isotope uranium-238 that is found naturally in soil. Radon is
often found in the air we breathe and the water we drink. Radon-222
and its decay products contribute most of the radiation exposure
received by members of the public.
Radioactive Materials in Sewage
Sludge, Ash and Other Products
Sewage sludge and ash at POTWs may contain both naturally-occurring
and man-made radioactive materials. Water that originates in or
moves through geologic deposits containing naturally-occurring
radionuclides could result in radioactivity being carried to the
treatment facility with storm water runoff or infiltration entering
the sewer system, and water treatment plant residuals discharged
to the sewer system. Industrial, medical or research facilities
may also discharge radioactive materials to the sanitary sewer
system in accordance with prescribed State and Federal regulations.
In addition, radioactive materials administered to patients for
the diagnosis or treatment of illnesses are excreted into the
sewer system. Other industrial or residential discharges (such
as fertilizer residues) can contain naturally-occurring radioactive
materials that are not subject to licensing or regulation.
Tables 1 and 2
provide the concentrations of radionuclides detected during the
pilot survey of sludges and ash from nine POTWs, as well as typical
ranges of radionuclide concentrations commonly found in U.S. soils
and common items such as fertilizers and building materials. The
curie (Ci), or fractions of a curie (e.g. picocurie), is the unit
for expressing a quantity of radioactivity. The unit normally
used to describe the concentrations of radioactivity in the environment
is picocuries per gram (pCi/g). A picocurie is one one-trillionth
(1/1,000,000,000,000) of a curie. Radionuclide concentrations
in these tables have been rounded to the nearest decimal point.
Values in these tables do not show uncertainty calculations. Sludge
and ash samples from POTWs associated with facilities known to
discharge man-made radionuclides were included in the pilot survey.
Inclusion in these tables does not imply that the range of radionuclide
concentrations presented for the materials is protective of human
health.
The ISCORS agencies make no representation as to human or environmental
health and safety significance from exposure to radionuclides
in the concentrations described in the tables. Further information
may be obtained from Robert Bastian at EPA (email: bastian.robert@epa.gov
or phone 202-260-7378), Behram Shroff at EPA (email: shroff.behram@epa.gov
or phone 202-564-9707) or Mary Thomas at NRC (email: mlt1@nrc.gov
or phone 301-415-6230).
Table 1 - Pilot Survey Concentration Ranges
and Typical U.S. Background Concentrations of Radionuclides in Soil,
Fertilizer, and Cmmon Building Materials(All values are in pCi/g-dry
weight)
R. Tykva and J.
Sabol, "Low-Level Environmental Radioactivity - Sources
and Evaluation," Technomic Publishing Company, Inc.,
Lancaster, Pennsylvania (1995). This reference is the source
of data for concentrations of radionuclides in soil and building
materials except for the concentrations of U-238, U-235, and
Cs-137 which came from references 5 and 6, respectively. The
concentrations of the daughters or decay products of U-238,
such as Th-234, Ra-226, etc., those of U-235, such as Th-227
and Ra-223, and those of Th-232 are set equal to those of
their respective parent radionuclides by assuming that the
daughters are in secular radioactive equilibrium with the
parent radionuclides. [back to Table 1]
Source for data
on fertilizers: National Council on Radiation Protection and
Measurements, 1987, Radiation Exposure of the U.S. Population
from Consumer Products and Miscellaneous Sources; NCRP Report
No. 95, pp. 24-32. This is the source of data for the concentrations
of radionuclides in fertilizers except for the concentration
of K-40 in soil which came from the reference in note 7. [back
to Table 1]
ND - Not detected.
The radionuclide was not detected in some of the samples during
the pilot study. For detection limits for radionuclides, see
the tables in "Report to the ISCORS Subcommittee on the
Sewage Nuclide Concentration Test Samples," dated November
23, 1998. [back to Table 1]
M. Eisenbud and
T. Gesell, "Environmental Radioactivity," Fourth
Edition (1997), Academic Press, New York, New York.[back
to Table 1]
Cs-137 concentration
range in soil obtained from Figure 4-4, p. 94 of NCRP Report
No. 50, "Environmental Radiation Measurements,"
Recommendations of the National Council on Radiation Protection
and Measurements (1976).[back
to Table 1]
Source for data
on K-40 in fertilizer: S. Cohen and Associates, 1997, Final
Draft NORM Waste Characterization; EPA Contract No. 68D20155,
WA No.5-09, pp. B-3-1 to B-3-24. [back
to Table 1]
Values for U-235
in soil, fertilizer and building materials were based on the
concentrations of U-238 in the same materials and the natural
ratio of U-235 to U-238. [back
to Table 1]
The symbol "<"
which appears throughout the table is an abbreviation for
the words "less than".
Gross alpha
and Gross beta – These measurements are generally
used as indicators of the presence of alpha and beta emitting
radionuclides in a sample. Gross alpha and gross beta activity
analyses are used to screen samples to determine the need
for nuclide-specific analyses. They were included in the pilot
study, but have no corresponding background levels, and thus
are not included in Table 1.
[back to Table 2]
ND - Not detected. The nuclide
was not detected in some of the samples during the pilot study.
See the tables in the EPA National Air
and Radiation Environmental Laboratory "Report to the ISCORS
Subcommittee on the Sewage Nuclide Concentration Test Samples,"
November 13, 1998, for detection limits for nuclides.
[back to Table 2]
