EPA/600/R-13/156 | May 2014 | www.epa.gov/ord
United States
Environmental Protection
Agency
Decontamination of Drinking
Water Infrastructure
A Literature Review and Summary
Office of Research and Development
National Homeland Security Research Center
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EPA/600/R-13/156
May 2014
Decontamination of Drinking Water Infrastructure
A Literature Review and Summary
U. S. Environmental Protection Agency
Office of Research and Development
National Homeland Security Research Center
Cincinnati, OH 45268
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Disclaimer
The United States Environmental Protection Agency (EPA) through its Office of Research and
Development authored this report. It has been subjected to technical and administrative review
by the Agency but does not necessarily reflect the views of the Agency. Funding for this report
was received from Environment Canada through interagency agreement RW-C-922019-01-C.
EPA does not endorse the purchase or sale of any commercial products or services.
Questions concerning this document or its application should be addressed to:
Jeffrey Szabo, Ph.D., P.E.
National Homeland Security Research Center (NG-16)
Office of Research and Development
United States Environmental Protection Agency
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
(513)487-2823
szabo.jeff@epa.gov
Scott Minamyer
National Homeland Security Research Center (NG-16)
Office of Research and Development
United States Environmental Protection Agency
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
(513)569-7175
minamyer.scott@epa.gov
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Abbreviations and Acronyms
BAR Biofilm Annual Reactor
CBR Chemical, Biological, Radiological
CDC Centers for Disease Control
CPU Colony Forming Unit
cPVC Chlorinated polyvinyl chloride
Ct Concentration of Disinfectant Multiplied by Contact Time
CWA Chemical Warfare Agent
DCB Dichlorobenzene
DSS Distribution System Simulator
EC Environment Canada
EPA United States Environmental Protection Agency
HFO Hydrated Ferric Oxide
ICP-AES Inductively Coupled Plasma-Atomic Emission Spectroscopy
ICP-MS Inductively Coupled Plasma-Mass Spectrometer
ICP-OES Inductively Coupled Plasma-Optical Emission Spectroscopy
KOW Octanol-Water Coefficient
NSF National Sanitation Foundation
p-DCB />-Dichlorobenzene
PVC Polyvinyl Chloride
SFA Sodium Fluoroacetate
TCR Total Coliform Rule
XRD X-Ray Diffraction
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Table of Contents
Disclaimer ii
Abbreviations and Acronyms iii
Acknowledgements vi
Executive Summary 1
Chemical Agents 2
Introduction 2
Inorganics 2
Arsenic 2
Mercury 3
Petroleum Products 4
Toxins 4
Chemical Warfare Agents 4
Pharmaceuticals 4
Organic Chemicals 4
Chlordane 4
P-dichlorobenzene 5
Parathion 5
Chloropyrifos 6
Sodium Fluoroacetate 6
Chemical Research Discussion and Conclusions 6
Future Chemical Research 7
Biological Agents 9
Introduction 9
Spore-Forming Bacteria 9
Vegetative Bacteria 11
Viruses 12
Biological Agent Research Discussion and Conclusions 13
Future Biological Agent Research 14
Radiological Agents 14
IV
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Introduction 14
Cobalt 15
Strontium 15
Cesium 17
Radiological Contaminant Research Discussion and Conclusions 18
Future Radiological Contaminant Research 20
Overall Concluding Remarks 20
Reference List 22
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Acknowledgements
This report was developed in collaboration with Environment Canada, Emergencies Science and
Technology Section, Ottawa, Ontario, Canada, and was supported by the Chemical, Biological,
Radiological, Nuclear, and Explosives (CBRNE) Research and Technology Initiative (CRTI)
Program of Defense Research and Development Canada.
Contributions of the following individuals and organization to the development of this document
are gratefully acknowledged:
Environment Canada (EC)
. Emergencies Science and Technology Section
Vladimir Blinov, Ph.D.
Konstantin Volchek, Ph.D.
The authors also acknowledge Dr. Paul Randall (EPA's National Risk Management Research
Lab), Greg Welter, BCEE (O'Brien and Gere) and Frank Blaha, PE (Water Research
Foundation) for their comprehensive review of this report.
VI
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VII
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Executive Summary
Chemical, biological, or radiological (CBR)
contamination events or attacks on drinking
water infrastructure could have significant
public health, economic, and social impacts.
The intentional introduction of harmful
contaminants into drinking water
distribution systems, for example, has the
potential to contaminate the water along
with pipes and pumps used to convey the
water, storage tanks, service connections to
buildings, and water-consuming appliances,
such as water heaters. Complicating the
situation is the propensity of some
contaminants to adhere to corroded pipes or
biofilms on the pipe walls, potentially
prolonging the impact of the contamination
by desorption, leaching, or otherwise
detaching from the surface and into the
water over time after the incident.
Contamination incidents could also impact
drinking water treatment plants, wastewater
treatment facilities, and storm and sewer
systems.
Treatment and decontamination strategy
involves determining what the contaminants
are, the extent and location of
contamination, whether to clean or replace
contaminated infrastructure, techniques for
remediating the contaminants and associated
hazardous degradation by-products, how
long it will take, how much it will cost, and
how to verify that cleanup is completed.
The United States Environmental Protection
Agency (EPA) and the water sector have
extensive experience in treatment and
cleanup, but must prepare for significant
new challenges posed by intentional attacks
using potent and difficult to decontaminate
non-traditional or unregulated contaminants.
Factors influencing the approach and
effectiveness of treatment and
decontamination are often complex and
multifaceted. For example, for some
contaminants that could be used in an attack,
fate and transport in the water environment
is not well understood. Contaminants may
react with or adhere to various pipe
materials differently under various water
flow patterns, or they may produce
degradation products that are as dangerous
as or more dangerous than the original
substance. There is a need for knowledge
and research on new or enhanced treatment
and decontamination technologies and
protocols. There are many data gaps that
must be filled through research.
This literature review summarizes available
data on the propensity of select
representative target CBR contaminants to
adhere to wetted drinking water
infrastructure surfaces, such as pipes, and
techniques for decontamination should
adherence occur. Persistence and
decontamination data included in this report
pertain to the most common types of water
pipes used in North America, including
cast/ductile iron, cementitious material like
cement-mortar lined ductile iron, and
plastics like PVC1'2. Each section of this
report includes a discussion of the current
literature regarding persistence and
decontamination data for a range of CBR
agents on drinking water infrastructure.
This is followed by an analysis of
decontamination data from the literature on
drinking water infrastructure, or similar
materials and environments if no directly
applicable data was found. Conclusions
about techniques or methodologies for
drinking water infrastructure
l.Buried No Longer: Confronting America's Water Infrastructure Challenge, 2012: American Waterworks Association, Denver, CO.
2.Folkman, S., et al., Survey ofwater main failures in the United States and Canada. Journal of the American Water Works Association, 2012.
104(10): p. 70-79.
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decontamination that can be drawn from the suggestions for future research are
literature review are presented. Finally, discussed.
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Chemical Agents
Introduction
Research on chemical persistence on
drinking water infrastructure has often
focused on the adherence of inorganic
contaminants [1-4]. There are, however,
many other chemical classes of concern,
including organics, pharmaceuticals,
chemical warfare agents, and toxins.
Historically, research into drinking water
treatment of chemicals has focused on
regulated inorganic contaminants such as
heavy metals, disinfection byproducts, and
organics such as pesticides, herbicides, and
chemical discharges from industrial
processes. Many of these chemical agents
make their way into water distribution
systems through accidental releases,
discharge or agricultural runoff into ground
or surface water. Drinking water treatment
plants are typically designed to remove
many of these contaminants from water
before they enter the distribution system.
However, data on persistence of many
chemical agents that could potentially be
used to contaminate a drinking water
distribution system are very limited. This
section summarizes available adherence and
decontamination data for specific target
chemical contaminants in regard to water
distribution system infrastructure, identifies
contaminant classes for which little data
currently exists, and discusses which of
these may be suitable for future research.
Inorganics
Arsenic
In drinking water, arsenic will be found in
its oxidized forms as arsenic(III) (arsenite)
or arsenic(V) (arsenate). In a drinking water
contamination scenario, arsenate would be
more pertinent since arsenite will be
oxidized in drinking water when it reacts
with disinfectant residuals (free chlorine or
chloramines or oxidants in the drinking
water process). Common arsenate and
arsenite compounds are soluble in water, but
solubility depends on the compound.
Sodium arsenate, for example, has a
solubility of 61g/100 ml water @ 15 °C [5].
Association of arsenic with infrastructure
surfaces, especially in drinking water, is
well documented. Numerous studies have
directly collected corrosion/scale samples
from drinking water distribution systems,
analyzed those samples for sorbed arsenic
through inductively coupled plasma mass-
spectrometer (ICP-MS), and included
inductively coupled plasma-atomic emission
spectroscopy (ICP-AES) and X-ray
diffraction (XRD). All have shown the
presence of sorbed arsenic [4, 6-8]. In
general, arsenite (As(III)) is considered
more soluble and mobile, and arsenate
(As(V)) is considered more likely to
associate with solid surfaces . One study
found that arsenic can incorporate into
calcite [9]. Calcite can be present on iron or
cement-mortar pipe interiors, depending on
water quality conditions.
Decontamination information is limited, but
useful information has been presented by
two studies. One study showed that sodium
arsenite injected into chlorinated water does
adhere and persist on cement-lined iron
coupons cut from pipe sections [10]. The
coupons were conditioned in Cincinnati,
Ohio tap water and had an established
biofilm. Persistence of arsenic was not
influenced by flow rate. Decontamination
with flushing did not consistently remove As
from the coupons, and flushing with low pH
(pH=4) did not increase the removal of
sorbed As. Maximum removal observed
with flushing (using normal tap water pH
[8.5] and low pH water) was 51%. Flushing
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with a phosphate buffer did not result in the
removal of any additional arsenic. Acidified
potassium permanganate consistently
removed 54-61% of adhered As.
Implementation of NSF Standard 60 Pipe
Cleaning Aid Products Flushing (NW-
310/NW-400 flushing, Floran Biogrowth
Remover™/Floran Catalyst™ liquid
activator, and Floran Top Ultra™/Catalyst,
Blue Earth Labs, Lenexa, KS) resulted in
46-67% removal. Copeland et al. (2007)
show that As desorbs from iron scale over
time with increasing pH (testing between pH
6-9) [11]. Increasing pH above 9 may be an
effective way of removing adsorbed As [12].
Mercury
Mercuric compounds (Hg(II)) are soluble in
ambient and drinking water matrices and are
better studied than mercurous compounds.
Oxidized mercury compounds of interest are
mercuric chloride, mercuric sulfate, and
mercuric nitrate. Mercuric chloride (HgCb)
is more soluble than other compounds, with
a solubility of 7.4 g/100 ml at 20 °C (3.6
g/100 ml at 0 °C) [5]. It is often assumed
that mercury in drinking water would
effectively be in an oxidized, soluble
compound due to the oxic nature of drinking
water with disinfectant. In some aquatic
systems, mercury can be transformed by
microorganisms to methylmercury, which is
highly toxic [13].
Mercury persistence on drinking water
infrastructure has not been studied in detail,
but persistence on biofilm has been
observed. One study showed that mercury
(Hg(II), introduced as HgCb) sorbed to
biofilms, but found that planktonic cells
were more susceptible to the toxic effects of
Hg than biofilm organisms [13]. This was
explained by the fact that diffusion may
prevent all of the dissolved Hg from
reaching the biofilm, but also that
extracellular polymeric substances material
in the biofilm may sequester Hg and prevent
it from impacting the biofilm organisms.
Other work observed that the biofilms
grown on glass slides did sorb Hg(II) and
methylmercury [14]. After an initial spike,
the amount of Hg detected in the biofilms
decreased. This could be due to desorption,
but the authors of that reference attributed
the decrease to de-methylation of the
mercury followed by volatilization of
elemental mercury. Finally, a study focused
on wastewater showed that an Hg-resistant
strain of bacteria does uptake and reduce
soluble mercury in wastewater [15]. A
bench-scale study found less than 1%
attachment of mercury when introduced at
100 mg/L on pipes made of iron, galvanized
iron, PVC, cement-mortar and polyethylene,
epoxy and copper, some with biofilm [16].
Like persistence data, little information on
techniques for decontamination should
adherence occur was found. One study that
focused on drinking water found that
mercury injected as mercuric chloride did
persist on cement-lined iron with an
established biofilm [10]. Decontamination
results were mixed. Flushing results were
variable with more adhered mercury found
post-flushing in some experiments and 19-
51% removal in others. Low pH (pH 4)
consistently showed 21-23% removal.
Acidified permanganate removed 72-96% of
the adhered mercury. Mercury was injected
as Hg(II) which is the fully oxidized state,
so oxidation was not the mechanism for
removal. It was speculated that the low pH
of the permanganate solution dissolved
adhered mercury and removed it from the
pipe surface.
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Petroleum Products
One study examined petroleum product
persistence on drinking water infrastructure
and techniques for decontamination should
adherence to infrastructure occur. The study
focused on diesel fuel and cement-mortar
drinking water pipe that was extracted from
a water distribution system [10]. Diesel fuel
was found to be persistent on the cement-
mortar coupons, with 21-23 mg of diesel
adhering to each coupon (19 in2). Flushing
removed 36-38% of the adhered diesel, but
Surfonic® TDA-6 surfactant (Huntsman
Corporation, The Woodlands, TX) removed
more than 96%. Surfonic TDA-6 is an
ethoxylate dispersant that is also effective
for chlordane and may be an effective
decontaminant for other petroleum products.
However, a case study of an accidental
diesel fuel contamination event in drinking
water showed that flushing and continual
use of water for household sanitation over
two days was enough to bring the amount
of fuel below the taste and odor threshold
[16].
Toxins
No data were found in the open literature on
plant, bacterial, fungal or algal toxin
persistence on drinking water infrastructure
material or techniques for decontamination
should adherence to infrastructure occur.
However, it is known that botulinum toxin
concentration is reduced by 99.90% to
99.99% in the presence of 0.5 mg/L free
chlorine at 25° C [17]. Ricin is also
sensitive to free chlorine, with 99.7+%
destroyed within 20 min [18]. Free chlorine
destroys cyanotoxin below pH 8, but free
chlorine is ineffective against anatoxin-a.
Ozone can destroy anatoxin-a as well as
microcystin and cylindrospermopsin [19].
Unless the water was dechlorinated or toxins
were introduced in large enough quantities
to eliminate the disinfectant residual, these
toxins would likely be destroyed by free
chlorine upon introduction into a drinking
water distribution system. Sensitivity to free
chlorine may limit persistence in drinking
water systems.
Chemical Warfare Agents
No data were found in the open literature on
CWA (chemical warfare agent) persistence
on drinking water infrastructure material or
techniques for decontamination should
adherence occur. However, since many
CWA are organophosphates, data on the
persistence and decontamination of the
organophosphate class may be used to
inform CWA class information (see the
Organic Chemicals section below).
Pharmaceuticals
No data were found in the open literature on
pharmaceutical persistence on drinking
water infrastructure material or on
techniques for decontamination should
adherence occur.
Organic Chemicals
Chlordane
A pilot-scale pipe loop study showed that
flushing with Surfonic TDA-6 effectively
removed chlordane from both cement-lined
ductile iron and clear PVC pipe surfaces.
The decontamination efficiency ranged
between 89% and 91% for the cement-lined
ductile iron pipe material and was 99% for
the clear PVC pipe material. Chlordane
showed strong adherence to both cement-
lined ductile iron pipe and clear PVC pipe
surfaces [10]. Another study also tested the
adhesion of chlordane applied to surfaces
that simulate cement-lined and PVC pipes.
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Chlordane was shown to adsorb onto the
pipe material coupons. Flushing evaluations
suggested effective decontamination with
flowing water for chlordane on concrete and
PVC. Hyperchlorination with no flow was
not effective at decontaminating chlordane
on concrete or PVC [20].
Static bench-scale experiments using
sections of various types of iron, galvanized
iron, plastic and cementitious pipe showed
that chlordane adsorbed to all pipe surfaces,
although cement-lined ductile iron and
polyethylene results were inconclusive. The
insecticide demonstrated strong attachment
and a relationship between duration of
contaminant exposure and mass of material
attaching to the pipe wall. Chlordane was
selected as a high log Kow chemical
surrogate with a log Kow value of 6.2.
Surfactants were found to be effective in
removing organic contaminants from pipe
surfaces. The recovery of chlordane was
relatively consistent by pipe material,
ranging from 68% for used galvanized pipe
to 120% for epoxy-coated steel pipe [16].
Chlordane was used by an unknown
perpetrator to contaminate a drinking water
system in Pittsburgh in 1980. A detailed
firsthand account of the response to the
incident is documented by an author of the
report titled "Guidance for Decontamination
of Water System Infrastructure" [16].
Investigations by the water utility and law
enforcement confirmed that the
contamination was intentional, but the
perpetrator was never found. Contaminated
water was contained in the distribution
system and a systematic campaign of
flushing was undertaken as a
decontamination method. Flushing was an
effective way to reduce the amount of
contamination in the water over the course
of days, but chlordane was still detected up
to nine months after the incident. Hot water
tanks in consumers' homes were particularly
difficult to decontaminate. The research
studies cited in this section and this case
study show that more effective
decontaminants should be identified for
chlordane since it has been used as a
drinking water system contaminant.
P-dichlorobenzene
Static bench-scale experiments using
sections of various types of pipe showed that
p-dichlorobenzene (p-DCB) attached at rates
greater than 5% to iron pipe with biofilm;
new galvanized, used galvanized, cement-
lined ductile iron (with seal coat); and
epoxy-coated steel pipe under non-flow
conditions. There was relatively low
adsorption of p-DCB to chlorinated
polyvinyl chloride (cPVC) pipe surfaces.
Surfactants were found to be moderately
effective in removing p-DCB from pipe
surfaces, with a recovery efficiency that
ranged from 13% for cPVC to 60% for
epoxy-coated steel pipe [16].
Parathion
There is only limited data on persistence on
soils and river sediments, and no data on
interactions with pipes or techniques for
decontamination of infrastructure should
adherence occur. In surface water, parathion
will usually disappear within a week, mainly
by adsorption to suspended particles and
bottom sediments. Adsorbed parathion is
subject to degradation by microorganisms
and chemical hydrolysis. For typical
drinking water treatment techniques, one
article reported the following degradation
results: chlorine, 100%; chlorine plus
aluminum sulfate, 100%; ozone, 80%; ozone
plus aluminum sulfate, 80-90%; and
chlorine plus activated carbon plus
aluminum sulfate, 100% [21].
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The chemical transformation process
involves the substitution of the sulfur atom
in the P-S bond of the pesticide with an
oxygen atom into its oxon (oxygen
analogues). This transformation is a
concern because chlorination is the most
commonly used disinfection technique in
many US drinking water treatment plants
and the product oxon of parathion is
generally considered to be more toxic than
the parent compound. Based on research on
the rates of sorption and partitioning of
contaminants in river biofilm, sorption to
pipe walls is possible [22-25].
Chloropyrifos
This review found no adequate information
on the adhesion of chloropyrifos on drinking
water system infrastructure or on techniques
for decontamination should adhesion occur.
Studies pertaining to water treatment or
persistence in the environment indicate that
chloropyrifos adsorbs strongly to soil
particles, adheres to sediments and
suspended organic matter in water sources,
and is persistent [26]. As with most
pesticides, chloropyrifos is not well removed
by typical physical treatment processes.
Removal from water improves with
oxidation using free chlorine or ozone
followed by conventional treatment [21, 27,
28]. However, rapid reaction with chlorine
in water treatment yields its oxon as a
primary by-product that is more stable in
chlorine and more toxic than the parent
compound [22, 25, 29]. Reaction with
monochloramine is substantially slower
[30]. There is no information about the
interaction with biofilm.
Sodium Fluoroacetate
Sodium fluoroacetate (SFA) is a long-
lasting, toxic, and miscible-to-highly-soluble
rodenticide. One bench-scale study tested
the adhesion of sodium fluoroacetate applied
to simulated cement-lined pipe and
decontamination by flushing and
hyperchlorination. SFA was shown to
adsorb onto the pipe material coupons.
Persistence and flushing evaluation
suggested that decontamination with flowing
water (1.5-2.0 fps) for SFA on concrete was
not effective. Hyperchlorination (25-50
mg/L) with no flow was not effective in
decontaminating SFA on concrete [20].
Chemical Research Discussion and
Conclusions
Arsenic adsorption to pipe material,
particularly corroded iron, is well
characterized. Decontamination options
have been explored, and some data suggests
that higher pH may be a decontamination
option for arsenic. NSF-60 pipe cleaning
agents removed arsenic, but results were
similar to simple flushing. Mercury was
shown to adhere to cement-mortar
infrastructure, but little data on iron
persistence were found. Decontamination
of mercury with acidified potassium
permanganate was effective and future
research should further examine
decontamination on other common
infrastructure materials such as unlined iron.
Diesel fuel has been studied in a model
drinking water system and an effective
decontaminant was used (Surfonic TDA-6).
Gasoline is similar in nature to diesel in that
they are both composed of hydrocarbons,
except that the hydrocarbon chains in
gasoline are shorter than in diesel. Since
gasoline is at least as prevalent as diesel,
determining its persistence on cement-
mortar, iron and PVC may be worthwhile.
No data was found on CWA or
pharmaceutical persistence on drinking
water infrastructure, nor was data found on
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toxin persistence. However, it is known that
ricin and botulinum toxins are oxidized by
free chlorine, which may limit their ability
to persist on infrastructure in a drinking
water distribution system.
Little direct information on organic
contaminant persistence exists beyond
sodium fluoroacetate, p-dichlorobenzene
and chlordane. However, these three
contaminants represent a wide range of
octanol water partition coefficient with log
KOW values of-0.061, 3.4 and 6.2 for sodium
fluoroacetate, p-dichlorobenzene and
chlordane, respectively. As Kow increases,
the propensity for a chemical to associate
with octanol (and not with water) increases,
which can be used as a proxy for the
tendency of a chemical to associate with a
solid surface, like drinking water
infrastructure, and not dissolve in water.
Data are available on chlordane and p-
dichlorobenzene on cement-mortar and iron
surfaces, and with cement-mortar for sodium
fluoroacetate. Future research could focus
on these three chemicals, and the resulting
data could be extrapolated to other
chemicals with similar Kow values.
The existing data show that surfactants are
effective at removing chemical agents from
pipe materials. Surfonic TDA-6 removed
90% of the chlordane attached to cement
mortar infrastructure, and it was also
effective against p-dichlorobenzene.
Surfonic N-60 also achieved 90% removal
of p-dichlorobenzene adhered to cement-
mortar. Flushing and chlorination were not
effective at decontamination of sodium
fluoroacetate.
Future Chemical Research
Inorganics: Decontamination of adhered
arsenic with high pH flushing should be
explored on iron and cement-mortar
infrastructure. Mercury persistence on iron
infrastructure should be explored, and
decontamination with acidified potassium
permanganate should be attempted.
Petroleum Products: Diesel and/or gasoline
persistence on corroded iron should be
studied, and if they are persistent, the
effectiveness of Surfonic TDA-6 should be
assessed. Gasoline and diesel are both
widely used and available hydrocarbons and
are good candidates for future study.
Toxins: Further characterizing toxin
degredation in chlorinated and
chloraminated water may help determine if
toxins will persist in water long enough to
become attached to infrastructure surfaces.
Clearly, experiments directly examining
persistence on infrastructure materials
should also be conducted.
Organics: Further examination of
persistence on infrastructure materials and
techniques for decontamination of
infrastructure materials could be collected
with sodium fluoracetate, p-
dichlorobenzene, and chlordane since these
chemicals represent a wide range of Kow.
Specifically, sodium fluoroacetate should be
examined on corroded iron, and
decontamination with surfactants (like
Surfonic TDA-6) should be attempted.
Alternatively, a representative contaminant
from classes such as organophosphorous and
carbamate pesticides could be chosen and its
persistence on infrastructure materials could
be examined. No data on persistence of
Pharmaceuticals or CWA were found, so
these may be priority areas of future
research. Organic contaminants often react
with chlorine or chloramines, so a summary
of their chlorine reactivity may indicate how
likely they are to persist in disinfected water
and reach drinking water infrastructure.
Chlordane decontaminants should be
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researched further since this chemical has a
history of contamination in drinking water
systems.
General: A future research goal that crosses
all chemical classes would be the
development of methods for sampling and
analysis. Validated methods for extraction
of contaminant from coupons (iron, cement-
mortar, PVC) would be helpful in any future
research endeavor and lend increased
credibility to the data generated from the
study.
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Biological Agents
Introduction
Compared to chemical and radiological
contaminants, substantial data for
persistence of biological agents (mainly
bacteria) are readily available. This is
primarily due to the fact that coliform
persistence and regrowth in drinking water
biofilm has been researched in conjunction
with the promulgation of the Total Coliform
Rule by the United States Environmental
Protection Agency. Much of this research
was conducted in the 1980s, prior to the
publication of the first Total Coliform Rule
in 1989, and the 1990s
(http://water, epa. gov/lawsregs/rulesregs/sdw
a/tcr/basicinformation.cfm) [31-40]. This
data set is a rich source of information on
persistence and, in some papers,
decontaminati on.
While vegetative coliform bacteria has been
the focus of a significant amount of
research, additional studies are needed on
spore-forming bacteria, such as Bacillus
anthracis (the causative agent of anthrax),
which are hardier and more persistent than
vegetative cells. If decontamination of
spore-forming bacteria from drinking water
infrastructure is successful, the same method
should also be effective for vegetative cells.
This chapter is divided into analyses of
literature about spore-forming bacteria and
vegetative bacteria persistence on drinking
water infrastructure and decontamination.
Data on virus such as bacteriophage are
more limited, but it is discussed where
applicable.
Spore-Forming Bacteria
Research on Bacillus spore adhesion in
drinking water systems has occurred on
copper, PVC, and galvanized iron coupons,
which are representative of new and old
household plumbing materials [41]. Results
showed that 1 mg/L free chlorine has little
effect on the number of spores in the bulk
water phase after 1 hour of contact, but 5
and 10 mg/L achieved 97% and 99.99%
removal, respectively. These inactivation
data are similar to results from other studies
in the literature [42-45]. Between 20 to 95%
of the spores inoculated into the model
system adhered to the pipe with the fewest
on PVC and the most on galvanized iron.
Although experimental conditions such as
temperature, pH, and flow were not reported
[41], the data confirm that spores injected
into a drinking water distribution system can
survive typical disinfectant residuals and
adhere to and persist on household plumbing
materials.
Bacillus spore persistence was examined in
a study funded by the Water Research
Foundation, formerly known as the
American Water Works Association
Research Foundation [16]. In this study,
pipe sections of various infrastructure
materials (iron, cement mortar, galvanized
iron, copper, PVC) were filled with water,
contaminated with a target contaminant, and
allowed to incubate under stagnant
conditions for seven days. Stagnant
incubation was used to mimic a scenario
where contaminated water is isolated in a
drinking water system, allowed to sit
stagnant until its disposition is decided, and
then flushed out.
Exposing spores that had been adhered to
galvanized iron pipe to 50 mg/L free
chlorine for 6, 60, and 1,200 min (Ct
[concentration x contact time] of 300, 3,000,
and 30,000 mg/L-min, respectively) resulted
in 65-84% removal when the initial number
of attached spores was 7x 104 cfu. One
hundred percent removal was reported with
heavily tuberculated iron under the same
-------
chlorination conditions. However, the
authors point out that few spores were
initially recovered from the iron surface
(500 cfu) and the results may not be reliable.
Poor recovery may have been due to
inadequate sampling. Initial chlorine
residual quickly decreased from 50 mg/L in
galvanized and tuberculated iron pipes to
nearly zero at 60 minutes and was
undetectable thereafter.
A series of experiments were conducted
using EPA bench-scale systems, which
include biofilm annular reactors (BAR), and
reactors developed by the US Center for
Disease Control and Prevention (CDC). In
one study, B. cereus spores were added to a
BAR that had biofilm of Pseudomonas
fluorescens grown on polycarbonate
coupons [46]. The authors estimated that up
to 3% of the 105 cfu/ml spores introduced
were adhered to the biofilm. Chlorination
with 2 to 3 mg/L for 7 to 8 days resulted in 2
to 3-log removal. Numerous spores still
remained in the single species biofilm.
Other BAR studies used iron, cement-
mortar, and PVC coupons that are
representative of water distribution mains
currently in service [47]. Free chlorine
concentration up to 70 mg/L resulted in 3-
log removal of B. globigii spores, but
persistence was still observed [48].
Application of chlorine dioxide to the same
reactor/coupon set-up resulted in 4-log
inactivation of adhered B. globigii over the
course of 4 days [49]. Application of 5
mg/L free chlorine resulted in 2 to 4-log
removal of B. globigii attached to cement-
mortar coupons, with no detectable spores
remaining [50].
CDC reactors were operated with PVC and
copper coupons, which simulate household
plumbing materials. Spores persisted on the
coupons and contact with 103 mg/L free
chlorine and with 49 mg/L monochloramine
produced 2-log removal in 60 minutes of
contact [51]. An extension of this study
examined germination of spores with L-
alanine and inosine before disinfection [52].
Application of germinant reduced the
number of attached spores by 1.5 to 3.0-log,
with up to 4.6-log reduction after application
of free chlorine at 100 mg/L. Log
reductions of 0.4 to 0.6 were observed with
chlorination alone. The results show that
germination can enhance the
decontamination potential of free chlorine.
The idea of germinant-enhanced
decontamination of spores was further
extended to a pilot-scale drinking water
distribution system simulator (DSS) [53].
Cement-mortar and corroded iron coupons
were inserted into a six-inch diameter pipe
with tap water flowing through it. After a
one-month conditioning period, the DSS
was contaminated with B. globigii spores.
Adhered spores were exposed to germinant,
then free chlorine at 5 and 25 mg/L,
followed by exposure to flowing water at a
mean velocity of 1 ft/sec. Germination
enhanced the effect of chlorination of
cement-mortar, while flushing was enhanced
on spores adhered to corroded iron.
Chlorination and flushing left viable spores
on each coupon type when used alone
(except cement-mortar at 25 mg/L free
chlorine), but adding a germinant enhanced
decontamination to the extent that no viable
spores could be detected on the coupons.
Other pilot-scale studies have supported the
previously mentioned research. B. globigii
spores were shown to persist on a 15 year
old pipe that carried drinking water in a
pilot-scale experimental system [54]. In
another pilot-scale study, sections of aged
cement-mortar lined pipe removed from a
drinking water distribution system were
placed into the DSS mentioned in the
germination study and contaminated with
10
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spores at a concentration of 10 cfu/ml [10].
Flushing at a mean velocity of 2.5 ft/sec
resulted in no removal of adhered spores.
Disinfection with 200 mg/L free chlorine
and flushing (2.5 ft/sec) for two hours
decreased adhered spores by 95% (1.3-log),
with many viable spores remaining on the
coupons.
Vegetative Bacteria
Much of the research related to vegetative
bacteria persistence in biofilm has focused
on coliforms such as Escherichia coli and
Klebsiellapneumoniae [32-34, 39, 55-58].
The general trend of these studies is that
coliforms can adhere to biofilm and persist
or grow when exposed to simulated drinking
water conditions. The authors cite the
protection from disinfectants that biofilms
offer, but many of these studies used
dechlorinated conditions during injections of
coliforms. Beyond PVC, many of these
studies use glass or carbonaceous materials
that are not representative of water
distribution system infrastructure. One
study did examine coliform persistence on
mild steel with biofilm and found that 10
times more coliforms accumulated than on
PVC with biofilm [32].
Another study examined E. coli persistence
on PVC coupons colonized by drinking
water biofilm in a 4-inch diameter pipe [35].
Injected E. coli was detectable on the PVC
coupons up to 18 days in unchlorinated
water in the presence of flow. Another
study used corroded iron as a coupon
material and assessed Klebsiella
pneumoniae persistence in the presence of
flow [59]. Experiments were conducted in
chlorinated and unchlorinated water.
Persistence on iron was observed up to 17
days in unchlorinated water and up to 12
days with chlorine residual less than 1 mg/L.
Interestingly, K. pneumoniae cultured under
low nutrient conditions persisted longer than
those cultured under rich conditions,
indicating that environmental isolates may
persist longer in drinking water systems.
However, both were not detectable on the
coupons after 17 days with constant flow of
1 ft/sec.
Legionellapneumophila persistence on
biofilm has been studied by multiple
researchers. Like much of the research into
coliforms, substratum materials used to
grow biofilm are not representative of
drinking water distribution systems
infrastructure. However, persistence was
observed for limited periods of time, usually
in unchlorinated conditions. One researcher
grew a drinking water biofilm on glass and
PVC slides and observed persistence
between 20 to 40 days [60]. Persistence was
observed for 15 days under similar
conditions using stainless steel slides [61].
A study on the persistence of L.
pneumophila on biofilm found that chlorine
and monochloramine were effective at
decontamination. However,
monochloramine worked faster than
chlorine, likely due to its lower reactivity
with various biofilm components [62].
Finally, two complementary studies found
that L. pneumophila persisted on coupons up
to 12 days in the presence of a free chlorine
residual of 0.2 mg/L [63]. However,
fluorescent in-situ hybridization found DNA
signatures on the coupons up to 38 days
after contamination, although it was not
determined if viable cells were present [64].
Data has been published on contamination
of drinking water supplies with vegetative
bacterial pathogens. E. coli 0157:H7 was
the cause of the contamination of the
Cabool, Missouri water supply, which likely
originated from a series of water main
breaks and meter replacements [65, 66].
The water supply was unchlorinated at the
11
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time of the outbreak, which allowed the E.
coli to persist in the water column. A
program of chlorination (up to 3 mg/L) and
flushing to adequately spread the
disinfectant was used to decontaminate the
system. After decontamination (and a "Boil
Water" advisory) the number of cases of E.
coli infection dropped precipitously.
E. coli 0157:H7 was also the cause of a large
water supply outbreak in Walkerton,
Ontario, Canada [67, 68]. The cause of the
outbreak was attributed to infiltration of
runoff contaminated with animal waste, and
the susceptibility of the old corroded cast
iron pipes to harboring E. coli. Remediation
included distribution system flushing,
disinfection of building plumbing with
chlorine, as well as implementation of a
program to replace the old cast iron water
mains. These actions ended the outbreak,
indicating that flushing and chlorination can
be effective against E. coli.
Salmonella typhimurium was attributed to an
outbreak of illness that originated in the
water supply in Gideon, Missouri [69, 70].
Past research has shown the potential for
Salmonella spp. persistence on biofilm [60].
Contamination occurred from bird droppings
and feathers entering a water storage tank.
The water system did not contain a
disinfectant residual, and a flushing event
before the outbreak helped spread
contamination through the distribution
system. In addition to a boil water advisory,
the water tank was chlorinated, which
stopped the outbreak. However, a
systematic program of chlorination in the
distribution system was not undertaken. In
2008, Salmonella contamination occurred in
Alamosa, Colorado [71]. Prior to the
outbreak, the water supply was not
chlorinated. Chlorine was added to the
distribution system at 25 mg/L, with a goal
of maintaining at least 10 mg/L for 24 hours.
An extensive flushing program was also
implemented. This strategy was successful,
and the water supply was chlorinated
thereafter.
Viruses
Data on virus persistence in drinking water
biofilm is more limited than for other
microorganisms, but some studies exist.
Virus persistence was studied in a pilot-scale
unit using biofilm formed on PVC coupons.
Poliovirus 1 persisted for less than 6 hours
on the coupons, and a chlorine residual of
0.04 mg/L inhibits live virus persistence in
the bulk water and biofilm [72]. Limited
poliovirus persistence (6 days) was observed
in another study on polycarbonate with
drinking water biofilm [73]. However, the
viral RNA was observed up to 35 days with
no chlorine present.
Alternatively, calicivirus persisted on PVC
coupons with drinking water biofilm in the
presence of 0.15 mg/L free chlorine for 3
weeks [74]. Bacteroides fragilis phage B40-
8 and coliphage MS-2 persisted up to 30
days at low levels on PVC and stainless steel
[75, 76]. Interestingly, a consistent 0.5
mg/L free chlorine residual was present,
indicating that some viruses were unaffected
by the residual. A recent review article on
viral persistence in biofilms cites numerous
conference proceedings that support the idea
that viruses persist in drinking water
biofilms in the presence of free chlorine,
although the proceedings may not be readily
available [77].
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Biological Agent Research
Discussion and Conclusions
A common theme that occurs in many of the
cited studies is that decontamination with
free chlorine leaves viable Bacillus spores
adhered to the coupons of drinking water
infrastructure. This is an important finding
since chlorine is commonly used in drinking
water treatment and is known to be a strong
oxidant. Numerous studies have shown that
Bacillus spores suspended in water with free
chlorine are resistant to inactivation, but
given enough contact time they are
undetectable by culture [42-45].
Data on spore inactivation in water would
support the conclusion that extending
decontaminant contact time should also
adequately decontaminate spores attached to
pipe material. This may be true for some
pipe materials, but common distribution
system materials such as corroded iron or
cement-mortar have been shown to be
difficult to decontaminate with free chlorine.
However, enhancing flushing or chlorination
with germination has proven to be more
effective than flushing or chlorination alone.
Alternative disinfectants such as chlorine
dioxide have also proven to be effective at
decontaminating adhered spores without
germination enhancement. Therefore,
germination with a chemical suited for the
Bacillus species followed by chlorination at
least 25 mg/L and introduction of clean
water moving at a velocity of at least 1 ft/sec
is more effective than chlorination or
flushing alone. Alternatively, application of
at least 25 mg/L chlorine dioxide is more
effective than chlorination at that level in
bench scale applications.
The amount of literature discussing
decontamination of vegetative bacteria
adhered to infrastructure surfaces in
experimental drinking water systems is
limited. Much of the literature focuses on
initial attachment or persistence, often under
conditions somewhat relevant to drinking
water, but in dechlorinated water. The
literature related to decontamination of
vegetative bacteria includes numerous
studies examining real-world
decontamination incidents. Specific data on
the number of pathogens associated with an
infrastructure material before and after
decontamination was not collected in these
studies. However, the large drops in
infection after decontamination measures
were taken indicate that the measures were
successful. In the studies that examined
decontamination of adhered vegetative
bacteria, free chlorine with flushing was
commonly used.
Ultimately, chlorination may be adequate for
decontamination of drinking water
distribution systems contaminated with
vegetative bacteria, with the addition of
flushing to ensure adequate transport of the
disinfectant. In the studies cited in this
report, free chlorine levels used for
decontamination ranged from undefined to 3
to 25 mg/L. However, since vegetative
bacteria are more sensitive to disinfection
than spore formers, methods that are
effective for spore formers should also
decontaminate vegetative bacteria.
However, if pathogenic vegetative bacteria
are harbored by amoebae in drinking water
biofilm, they may be more difficult to flush
or disinfect [78].
It is well documented in the literature that
viruses in water are sensitive to various
disinfectants such as chlorine, chlorine
dioxide, and ferrate [79-83]. Although the
literature presents a mixed picture on virus
persistence, there is some evidence that they
do persist, even in the presence of a
disinfectant. The highest chlorine residual
used in the cited studies was 0.5 mg/L, and
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high levels used for decontamination of
spores have not been studied. It is notable
that virus persistence was observed on glass,
PVC, and stainless steel coupons, which
should be easier to decontaminate relative to
iron or cement-mortar. In the absence of
any firm data on virus decontamination, the
techniques used for spore-forming bacteria
should be applied as suggested by the
Spaulding hierarchy [84].
Future Biological Agent Research
Spore-Forming Bacteria: Given the
effectiveness of chlorine dioxide on the
bench scale, this disinfectant and other
alternative disinfectants should be explored.
Ozone and peracetic acid are good
candidates for study as are peroxide,
acidified nitrite, monochloramine and mixed
oxidants.
Vegetative Bacteria: Additional data on the
adequacy of specific levels of free chlorine
to decontaminate infrastructure surfaces
(i.e., iron and cement-mortar) could confirm
or disprove what can be extrapolated from
the literature on disease outbreaks in water
supplies. It can also be assumed that if a
technique is effective at decontaminating
drinking water infrastructure surfaces with
adhered spore formers, then that technique
would also be effective against vegetative
bacteria. Research to confirm this
assumption would be of interest.
Viruses: Examine model virus persistence
on common drinking water infrastructure
materials such as iron and cement-mortar. If
persistence is observed, attempt
decontamination with disinfectants such as
chlorine (25+ mg/L), chlorine doxide, and
monochloramine.
Radiological Agents
Introduction
Historically, research related to
radionuclides in drinking water has focused
on two areas. The first is evaluating
treatment techniques to remove
radionuclides from source water [85-88].
The primary goal of treatment in the U.S. is
ensuring that alpha and beta emitters are
below regulatory limits. The second area of
research came from an observation that in
some communities, the amount of a
particular radionuclide (or alpha/beta
emitter) was sometimes observed to be
higher at a consumer's tap than it was in the
water leaving a treatment plant [89-91].
Results from these papers show that low
concentrations of radium originating in
groundwater was accumulating on pipe
surfaces over the course of years.
Desorption due to sloughing of pipe material
or treatment changes led to observed
concentrations above regulatory limits at the
consumer's tap. This research complements
other work focused on inorganics, such as
lead and arsenic, which accumulate on pipe
scales and later desorb [4, 92].
This section discusses similar research, but
in the context of contamination of drinking
water pipes with radionuclides of concern:
cesium, strontium, and cobalt. As
previously mentioned, radium and uranium
are found in groundwater and have a track
record of research in the peer-reviewed
literature. Cesium, cobalt, and strontium
have not previously been examined for their
persistence in drinking water systems.
Therefore, the literature review in this
section focuses on work from nuclear
cleanup sites where groundwater was
contaminated with these radioisotopes.
Information will be extrapolated to common
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drinking water infrastructure materials (iron
and cement-mortar lined iron).
Cobalt
Of the three radionuclides discussed in this
section, the fewest number of papers were
related to cobalt. When dissolved in
disinfectant free water, cobalt forms a
soluble salt that adsorbs to magnetite, which,
along with hematite and goethite, is a
common corrosion by-product in iron
drinking water pipes [93]. Nearly 100%
desorption was observed when pH was
decreased below 3. Magnetite adsorption
has been seen in another study, but hematite
adsorption was also observed [94]. Parallel
experiments with cesium and strontium did
not show adsorption on hematite. The
authors of that study speculate that cobalt
may form a Co-Fe matrix, or precipitate on
hematite surface. Cobalt adsorption to clay
has also been observed, which may share
some chemical species with cement-mortar
(cement and sand), but are generally far
more complex [95]
Cobalt was observed to adsorb to corroded
iron that had been conditioned in a drinking
water distribution system simulator for one
month [96]. Cobalt was introduced as
water-soluble cobalt, which is in the +2
oxidation state. Cobalt reacted with free
chlorine in the water and oxidized to Co(III),
which is insoluble in water. The Co(III)
precipitated on the iron surface and persisted
for 42 days. It likely would have persisted
longer, but 42 days was the duration of the
persistence experiment. Co(III) is only
soluble in acid, and contact with sulfuric
acid (0.36 M) removed over 90% of
precipitated cobalt. This treatment also
removed some of the corrosion layer, so,
while successful, it is uncertain whether this
decontamination method would be useful in
a real drinking water distribution system.
Strontium
One study has specifically focused on
strontium [97] adsorption to drinking water
infrastructure, but numerous other studies
have examined aqueous strontium
adsorption to various iron oxides, clays, and
silica compounds. The research study that
focused on drinking water used a model
distribution system and examined strontium
persistence on iron oxides that form on
unlined iron conditioned in potable water
[98]. The iron oxides contained background
strontium since stable strontium was present
in the tap water used in the study. Strontium
was spiked into the model system at 100
mg/L and allowed to contact the coupons for
1 hour before being flushed out. The
amount of strontium adhered to the coupons
increased six-fold immediately after
contamination, but returned to the baseline
concentration one day after contamination.
This indicates that the mechanism of
strontium adherence to the iron oxides was
weak and reversible when the exposure was
transient, even at a relatively high
concentration of 100 mg/L. The baseline
strontium adhered to the coupons came from
long-term exposure (likely years) to low
levels (0.2 to 0.3 mg/L) of strontium. This
suggests that the longer strontium is in
contact with iron oxides, the greater the
chance it will become irreversibly adhered
or incorporated into the iron oxide complex.
Strontium adsorption to iron oxides has been
observed in numerous studies, although not
all of them directly examine desorption. In
one paper, strontium saturated the hydrated
ferric oxide (HFO) adsorption sites within
minutes of contact, and adsorption was
successfully modeled with the Donnan
diffusion model [99]. In another, strontium
adsorbed to HFO after 4 hours of contact
[100]. It was concluded that strontium
physically adsorbed to HFO (not
15
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chemically), meaning that desorption was
possible. Later research showed that
strontium adsorbed to HFO but substantially
more was adhered when bacteria were
present [101]. This may indicate that
biofilm accumulation on iron oxides may
promote adhesion. A follow up to this study
showed that the mechanism of strontium
adsorption to HFO was inner sphere
complexation, or adsorption of strontium to
HFO with no intervening water molecules
[102]. Complexing of this nature means that
strontium could form a persistent bond with
HFO.
Research on strontium adsorption to iron
oxides does expand beyond HFO. Common
iron oxide/oxyhydroxide species in
corrosion by-products formed in drinking
water are Fe3O4 (magnetite), a-FeOOH
(goethite), and y-FeOOH (lepidocrocite).
Studies have reported strontium adsorption
to goethite [95, 103, 104] and magnetite
[94], but adsorption or bonding directly to
the goethite may not be the primary
mechanism at play. Data from one
manuscript is used to argue that strontium
adsorbs to goethite as a SrOH+ complex
when carbonate is not present [105].
However when carbonate is present,
strontium forms complexes with carbonate
that then adsorb to goethite. Dissolved
carbonate ions are present in distributed tap
water, and, depending on the water quality,
precipitated calcium carbonate can also be
present on iron scale. Strontium and
calcium are neighbors in the alkaline earth
metals column of the periodic table and
share many similar properties. Strontium
exchange with calcium in carbonate
compounds might also promote strontium
adhesion on goethite and other iron oxides.
Strontium-carbonate complexation and
exchange with calcium are also observed in
adsorption to cement or concrete-mortar.
Drinking water infrastructure is commonly
lined with cement-mortar, which is a
mixture of Portland cement and sand.
Portland cement is largely calcium oxide
and sand is silicon dioxide, which is a
component of many clays. Cement-mortar
can also have precipitated calcium carbonate
(calcite). As with iron oxides, data shows
that strontium combining with carbonate
will precipitate onto the surface of cement,
silica, and kaolinite clays, and adsorption
can be reversible [104, 106, 107]. However,
strontium carbonate precipitation was
observed to be dominant below pH 8.6,
while strontium complexation with the silica
or kaolinite surface occurred above pH 8.6.
Other researchers have observed that at
strontium concentrations above 0.3 mmol,
strontium precipitates onto the surface of
clay. At concentrations below 0.3 mmol,
strontium substitutes with calcium in calcite
[108], which has also been observed in other
studies [109].
Data from other studies show that while
strontium incorporates into calcite
structures, it can be removed. In one,
strontium was put into contact with calcite
containing Portland cement for three days
and desorption of adsorbed strontium was
observed when clean water replaced the
strontium solution. Contact of clean water
with the strontium-contaminated cement
occurred for two days [110]. Desorption
with clean water took place after six
separate but identical sequential desorption
steps. In two other studies, strontium in
contact with kaolinite was found to
irreversibly incorporate into the clay
structure over weeks to months of contact
[111, 112]. These studies show that
strontium contact time with drinking water
infrastructure may influence how it persists.
Strontium adsorption has also been
examined under a range of pH. When
adsorption to goethite was studied under pH
16
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ranging from 6 to 10, no strontium
adsorption was observed at pH 6, while
nearly all strontium spiked into a goethite
suspension adsorbed at pH 10 [105].
Similar results were observed with
magnetite [93]. This study was reinforced by
another paper that showed 95% of dissolved
strontium adhered to iron oxides above pH
7.6, but none adsorbed at pH less than 4.5
[113]. Increasing strontium adsorption
(uncomplexed) at higher pH is a general
trend shown in the peer-reviewed literature
[85, 114, 115]. When Sr sorbed to iron
oxide coated sand at alkaline pH was
washed at pH 3, nearly all adsorbed Sr was
released [116]. One review article discusses
how the high pH in the cement/cement-
mortar matrix influences strontium
adsorption and precipitation, which is
enhanced at high pH [117]. These studies
point to low pH flushing as a potentially
effective decontamination option for
adhered strontium.
Cesium
Two studies specifically focused on the
adsorption of cesium to drinking water
infrastructure, but other studies may offer
insight into how cesium interacts with
similar materials. In the first study, cesium
was spiked into a model drinking water
system at 100 mg/L and allowed to contact
the iron coupons for two hours [96]. After
this two-hour contact period, the cesium
solution was flushed out and clean tap water
was allowed to flow past the coupons for 42
days to assess persistence. The coupons
were then dissolved through microwave-
assisted digestions and analyzed through
ICP-OES. No cesium was detected on the
coupons one day after spiking or during the
42-day monitoring period. No change in the
100 mg/L bulk water cesium concentration
was observed during contamination. Unlike
similar experiments performed with
strontium, samples from the cesium-
drinking water infrastructure study were not
taken immediately after the cesium was
flushed from the reactor. Samples were only
taken one day after cesium was flushed from
the reactor. So, if short-term persistence on
the iron occurred, it was not captured in this
study.
In the other study focused on drinking water,
iron (with and without biofilm), galvanized
iron (new and used), PVC (with and without
biofilm), cement-lined iron, copper,
polyethylene, PVC and epoxy pipes were
exposed to a stagnant solutions of stable
cesium chloride [16]. Adsorption of cesium
to the pipe interior surfaces was observed
with cement lined ductile iron, iron with
biofilm, and used galvanize iron with
percent attachments of 12.4%, 4.6% and
1.3%, respectively. Decontamination was
undertaken with a free chlorine solution (25
mg/L with 20 hours of contact time) and 1%
and 10% solutions of Simple Green®
cleaner (Sunshine Makers, Inc., Huntington
Beach, California). Free chlorine removed
23% and 26% of the adhered cesium from
the used galvanized and cement-lined iron
pipes, respectively. Simple Green at 10%
solution removed 45% and 47% of the
cesium adhered to cement-lined and
galvanized pipe, but a 1% solution was
significantly less effective. These results
show that common cleaning agents and
disinfectants can remove sorbed cesium
when it is delivered to a bench-scale
experimental pipe surface under stagnant
conditions.
Other experiments designed to provide
adsorption data for cesium-magnetite
isotherms over pH 6 to 9 can be used to
assess persistence. Isotherms were
generated by equilibrating cesium with
magnetite for one hour [93]. Cesium
initially adsorbed, but desorbed from the
17
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magnetite as soon as pH was lowered to
below three. Another study found that
cesium equilibrium with magnetite and
hematite occurred after two hours of contact,
although very little cesium adhered to
hematite [94]. Taken together, these studies
point toward cesium adsorbing to iron
oxides, but not persisting if clean water
flows after the contamination slug.
Furthermore, low pH flushing may also be
effective at removing an adhered cesium.
Cesium interaction has been studied with
cement and cement-mortar matrices, mostly
in the context of nuclear waste storage in
concrete vessels. Data has shown that
mixtures of calcium oxide and silicon (the
main components of cement-mortar) adsorb
cesium, with the most adsorption occurring
at neutral pH [85]. It was also observed that
cesium retention was poor when ionic
strength was increased by adding salts. This
suggests that other ions out-compete cesium
for adsorption sites and that adsorption is
reversible. Data supporting this point shows
that the presence of competing ions such as
sodium, magnesium, and aluminum
deceases the adsorption of cesium on
magnetite and ferrite [118].
Although cesium has been shown to adsorb
to and persist on cement-mortar, some
authors have found that the process is
reversible. In one study, cesium was in
contact with cement for 147 days [106].
Equilibrium was achieved in this time, but
over 90% removal of cesium was observed
when the cesium-loaded cement was placed
in clean water. Like iron oxides, when ionic
strength is high (competing ions are
present), cesium adsorption on cement is
inhibited [107] and competing ions could
outcompete cesium for adsorption sites.
An observation from multiple studies is that
cesium uptake onto cement and kaolinite is
slow compared to radionuclides such as
strontium. As previously mentioned,
equilibration with cement took 147 days in
one study [106]. Another study saw cesium
equilibration with kaolinite take 1 year
(compared to strontium, which equilibrated
in 1 day) [112]. An interesting observation
from this study is that not only did more
cesium adsorb to kaolinite with time, but
cesium also became more tightly bound to
the clay with time. This may be explained
by the fact that diffusion into the cement
pore space is concurrent with adsorption
[119].
Radiological Contaminant
Research Discussion and
Conclusions
The available results indicate that cobalt
interaction with drinking water
infrastructure is straightforward. Soluble
cobalt(II) salt introduced into drinking water
with a disinfectant residual will oxidize to
cobalt(III) and precipitate. Precipitation
occurs as soon as the cobalt is mixed with
the water, and it is known that cobalt(III) is
only soluble in acidic solution. Low pH
flushing with compatible acids is the only
known method of removing precipitated
cobalt in situ. The available literature
included data on drinking water with free
chlorine as a disinfectant, corroded iron as
an infrastructure material, and acid as a
decontaminant. It may be beneficial to
study cobalt persistence with other
disinfectants and infrastructure materials to
determine if the published results with free
chlorine and iron translate.
Strontium has been shown to adhere to both
iron and cement mortar infrastructure
materials, but time and pH influence its
persistence. Transient exposure to iron does
not appear to lead to long-term persistence,
but persistence increases the longer
strontium is in contact with infrastructure
18
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materials. Strontium does associate with
cement/cement-mortar. Strontium can
precipitate and substitute for calcium in
calcium carbonate, so the presence of
carbonate greatly influences strontium
persistence. Alkaline pH leads to greater
strontium persistence, and low pH removes
strontium from iron and cement materials.
This means that adsorbed strontium may be
removed with low pH flushing, but this
should be tested.
Cesium interaction with iron has been
studied, and although adsorption can occur,
cesium does not appear to persist on iron
when flow is present. Persistence was
observed under completely stagnant
conditions and decontamination with free
chlorine and Simple Green® was
moderately effective. Cesium adsorption to
iron oxides is also inhibited by competing
ions. Cesium adheres to cement, cement-
mortar, and clays, but adsorption is slow
(compared to strontium), taking months or
up to a year. Some data suggests that longer
cesium contact time with cement will lead to
stronger binding, which could make
decontamination difficult. Little data on
cesium adsorption to cement-mortar was
found in a drinking water environment, and
this should be researched further. However,
the best option for decontamination appears
to be flushing at low pH and with competing
ions such as sodium or magnesium present.
19
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Future Radiological Contaminant
Research
Cobalt: Precipitation on cement mortar in
the presence of free chlorine should be
examined. Soluble cobalt should also be
introduced into chloraminated water to
assess whether precipitation is similar to
chlorinated water. Chelating agents (like
EDTA) could be effective at sequestering
cobalt.
Strontium: Persistence on cement-mortar
drinking water infrastructures should be
assessed under alkaline conditions since this
may lead to the most persistence. Low pH
flushing should be tested as a
decontamination method if persistence is
observed.
Cesium: Persistence on cement mortar under
drinking water conditions should be
examined. If persistence is observed,
decontamination with flushing, low pH
flushing, and removal with competing ions
should be studied.
Overall Concluding Remarks
The analysis in this report shows that
decontamination options for drinking water
infrastructure have been explored, but
important data gaps remain. In general,
microbial persistence in drinking water has
been studied more extensively than chemical
agents and radionuclides. Several studies
have been published that focus specifically
on decontamination of spore-forming
bacteria from drinking water infrastructure.
The data show that increasing chlorine
levels in a drinking water distribution
system may not be effective at
decontaminating spores. Techniques such as
germinating spores before chlorination or
using an alternative disinfectant such as
chlorine dioxide have shown promise.
However, the feasibility of a technique such
as germination will depend on whether
sufficient quantities of an effective
germinant can be realistically added to a
distribution system. Decontamination of
vegetative bacteria has been successful
using free chlorine and flushing. However,
it is possible that methods successful at
decontamination of spores would also be
effective for vegetative bacteria. Little
information is available on virus persistence
and techniques for decontamination of water
infrastructure should adherence occur.
Future studies focused on virus persistence
in both disinfected water and on drinking
water infrastructure would be beneficial.
Past research on radionuclide persistence on
drinking water infrastructure has focused on
radium and uranium, which are found in
ground water. This study reviewed
literature on cesium, strontium, and cobalt,
which are fission products or are found in
commercially available items and medical
devices. Cobalt persistence was
straightforward since soluble cobalt chloride
was found to react with free chlorine and
precipitate onto iron coupons. The
precipitated cobalt solids were only soluble
in acids. Future research should confirm
precipitated cobalt persistence on other
common infrastructure materials like
cement-mortar, and examine
decontamination solutions beyond
acidification. Cesium was not found to
persist on iron infrastructure when flow was
present, but it did persist when in contact
with iron pipes under stagnant conditions.
Free chlorine and a common household
cleaner removed some adhered cesium, but
more effective decontamination methods
should be studied. Cesium persistence is
possible on cement-mortar, and this should
be studied further. Strontium persisted for
less than one day on iron coupons,
indicating that strontium adhesion to the iron
20
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matrix is weak and reversible. Further
research on strontium persistence on
cement-mortar should be undertaken.
Available data on chemical agent
persistence is piecemeal. This analysis
found that persistence and decontamination
data exists for chlordane, p-dichlorobenzene
and sodium fluoroacetate, which could be
characterized as having low, medium and
high affinity water based on their octanol-
water coefficient. Decontamination data
showed that chlordane, p-dichlorobenzene,
and diesel fuel were effectively removed
(greater than 90%) from drinking water with
a commercially available ethoxylate
dispersant (Surfonic TDA-6). This
dispersant can be used as a decontaminant
for other chemicals as well. Sodium
fluoroacetate was not as persistent as the
other compounds, but flushing and
chlorination were not effective
decontamination techniques. Future study
of organic agents could use one
representative contaminant from a
contaminant class (e.g., organophosphorous
pesticide, carbamate pesticides) or use a
measure of a chemical's affinity for water
like octanol-water coefficient. Data on
inorganics (arsenic and mercury)
demonstrates persistence, and
decontamination was observed with flushing
and application of commercially available
decontamination solutions. However, most
studies showed removal between 40-70%, so
other decontamination techniques should be
studied. No data on persistence, or
techniques for decontamination should
adherence to infrastructure occur, was found
for pharmaceuticals, CWAs, or toxins.
21
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