1. SILVER HYDROGEN PEROXIDE:
what the guidelines say
26
S U M M E R 2 0 1 5 feature article
However, despite the HSE’s acceptance, SHP’s
efficacy and safety have not always been well
understood and there has been some wariness
about its use.The waters have also been muddied
by some confusion over the published wording
of the HSG274 paragraph relating to SHP. Any
misunderstanding has now been rectified by the
HSE’s COSHH and Chemicals Carcinogens Unit, and the current online version
confirms the clarified wording for Section 2.116 (an addendum will also be included
in any hard copy publications):
In fact this focus on SHP’s inclusion in HSG274 has been a useful opportunity for
improved clarity over its usage.
As HSG274 makes clear, SHP already has a history of usage in the UK. In fact it has
been used since 2002 as a water disinfection treatment to remove biofilm in both
domestic water systems and other contexts such as cooling towers, with systems
well flushed to remove any nutrients and disinfectant released by the process.
Some of the confusion over SHP relates to uncertainty over
what levels of SHP are acceptable in domestic water systems.
In the UK, SHP is accepted in England and Wales by the
Drinking Water Inspectorate (DWI) for disinfection of potable
water reservoirs, tanks and pipelines, with the proviso that the
chemical must be completely removed from the system at the
end of the process.2
In potable water for public supply, the DWI
specifies that levels of hydrogen peroxide should be below 1ppm,
with silver levels below 1ppb for silver. The Drinking Water
Quality Regulator for Scotland (DWQR) and the Drinking Water
Inspectorate for Northern Ireland (a unit within the Northern
Ireland Environment Agency) follow the same guidelines as the
DWI in England and Wales.
Elsewhere, however, levels considered ‘safe’ are significantly higher. In the United
States, the highly respected and independent US based certification organisation the
National Sanitation Foundation (NSF) has certified use of one SHP product, Huwa-
San™ TR50 (EndoSan in the UK), for use at levels of up to 8ppm in water distribution
systems, following a rigorous oral risk assessment of the carcinogenic effects of
hydrogen peroxide in 2010.3
As a result of these NSF’s guidelines, SHP (Huwa-San) is also now being used in
Canada, as a secondary disinfectant for water treatment at Killaloe and other
townships in Ontario,4,5,6
while in Europe, hydrogen peroxide has been approved for
treatment of drinking water at levels up to 17ppm under European Standard- EN 902
(2009).
One of the reasons for the DW’s cautiously low limits of SHP in potable water is due
to on-going concern over an incident in 2008 when SHP was implicated in morbidity
and one death in several dialysis patients.7,8
However, it is well documented that
this incident was the result of failure to meet guidelines and follow manufacturers’
instructions properly, which illustrates the need for rigorous pre-use risk assessment
before it is used.
The DWI is concerned about the toxicity of silver - yet it is now generally accepted
that silver is not toxic at the very low levels likely to be present in water.The EU
and WHO, as of April 2014 and noted in HSG274, do not declare any established
standards for silver.WHO guidelines state “there is no adequate data with which to
derive a health based guideline value for silver in drinking water.” WHO also states
that “special situations exist where silver may be used to maintain the bacteriological
quality of drinking water. Higher levels of up to 0.1 mg/litre (this concentration gives a
total dose over 70 years of half the human NOAEL [No Observed Adverse effect level]of
10 g), could be tolerated in such cases without risk to health”.
The DWI is currently awaiting the imminent registration of certain SHP products
under the EU Biocidal Products Regulations. However, Bob Wilson (Bsc, MWMSoc) of
the Meadowhead Consultancy notes that in fact in certain SHPs “hydrogen peroxide
is the only active biocidal substance in SHP and [it] is approved under the BPR.”
He goes on to say:
“I’m very clear about using SHP where silver is not an active biocide, as long as it
doesn’t go into water that’s going to be drunk. Most buildings should have outlets
labelled as ‘not potable water’ ....[because] in a building there are very few places
in reality where you could actually call the water ‘potable’... For instance if it goes
through a cold water storage tank... [where] it can pick up contamination. Most
buildings have mains water separated, e.g., in kitchens. It’s fine to use this within a
building water system, but only the part of the system where it wouldn’t be in the
sections feeding to a potable water outlet.... you would dose the water system after
the mains water supply to the drinking water outlets.”
Safety of H2O2 and silver
Hydrogen peroxide has been
widely used as a bleaching
agent, disinfectant and
medicine for over 100 years
and its many uses considered
safe today include teeth
whitening, acne treatment
and hair dyes. It is used in
wine and liquors for ageing
and as an approved food
additive, in minute amounts
in Japan and Canada and the
US, where it also has GRAS
status, ie generally recognised
as safe by the US FDA, for a
use in certain food processing.
As mentioned above, the main concern for product regulation of SHPs relates to
its silver content.The European Biocidal Products Directive in relation to nanosilver
consumer products approves certain silver salts, but its list does not include silver
nitrate. Silver nitrate salts are not present in all SHPs.As already discussed above,
silver in certain SHPs has no active biocidal role.
According to WHO’s Guidelines for Drinking Water Quality, most foods contain
traces of silver in the 10–100 μg/kg range.The background document for
development for this document notes that average silver concentrations in natural
waters are 0.2–0.3 μg/litre.9
In the UK, if used according to manufacturers’ instructions, the recommended
dosing for certain SHP products appear to introduce silver into a water supply at
significantly below that allowed by the WHO.
When the Health and Safety Executive (HSE) last year published HSG274 (Part 2), the most recent guidelines
on the control of Legionella in hot and cold water systems, they for the first time recognised the use of silver
hydrogen peroxide (SHP) as an alternative biocide to more traditional chlorinated water treatments.1
Since the
control of Legionella and other bacteria in hot and cold water systems is rarely straightforward, and more often
than not requires a combination of measures, the inclusion of another alternative to the arsenal of options is to
be welcomed.
“Silver stabilised hydrogen peroxide has a history of use in the control of
legionella in water systems.A silver hydrogen peroxide solution is injected
directly into the water system and if applied and maintained according to the
manufacturers’ instructions, can be an effective means of control. However, this
should not be used in water systems supplying dialysis units.”
by Susan Pearson
2. 27
How SHP works
Silver hydrogen peroxide is a silver-catalysed compound which contains 50%
hydrogen peroxide combined with minute amounts (320-500ppm) of silver.The
hydrogen peroxide, a powerful oxidiser, is the active disinfection agent. SHP works as
a microbial killer by producing destructive free hydroxyl radicals that attack bacterial
membrane lipids, DNA and other essential microbial cell components to cause rapid
cell death.
However, hydrogen peroxide on its own is thermodynamically unstable and quickly
decomposes to form water and hydrogen, making its disinfection properties short-
lived. Many microorganisms produce the enzyme catalase, which can protect cells
from their own metabolically produced hydrogen peroxide by initiating a split into
water and oxygen.The addition of ionic silver to hydrogen peroxide ‘stabilises’ it,
protecting it from this catalase-mediated degradation and allowing it to penetrate
cell walls to destroy potentially pathogenic microorganisms.
There are a number of silver stabilised hydrogen peroxide based chemicals available;
these utilise different stabilising systems, giving them different degrees of stability
and efficacy.
Efficacy
Hydrogen peroxide has been shown to have a biocidal action against a broad
range of microorganisms, including bacteria, yeasts, fungi, viruses, and spores.10,11
For example, 0.5% (5000 ppm) accelerated hydrogen peroxide has demonstrated
bactericidal and virucidal activity within one minute and mycobactericidal and
fungicidal activity within five minutes.12
Organisms with high cellular catalase
activity, such as Staphylococcus aureus, require 30–60 minutes of exposure to
0.6% hydrogen peroxide for a 108
reduction in cell counts, while certain waterborne
organisms with lower catalase activity, such as Pseudomonas spp, require only 15
minutes’ exposure.13
Test work on biofilm removal conducted by VITO /
PIDPA14
in Belgium confirms that SHP fulfils all three
of the criteria required of an effective Legionella
bactericide: that the treatment should be effective
against planktonic Legionella and kill Legionella
quickly; should remove and treat biofilm; and should
also destroy amoebae and their cysts, which can act
as host to Legionella bacteria.
At the Killaloe Water Treatment Plant in Ontario, which services 1800 homes and
was the first site in North America to utilise SHP for the secondary disinfection
of potable water, research undertaken to confirm the efficacy of SHP (specifically
Huwa-San TR50) as an alternative biocide to chlorine demonstrated that this product
contributes to the reduction of trihalomethanes in the drinking water system by
80%.
Trihalomethanes are potentially carcinogenic products formed when chlorine reacts
with organic materials in water, such as decaying plant material, and are of particular
concern in North America. SHP has now been used at Killaloe since the end of
November 201215
and has been rolled out as a secondary treatment in several further
communities to replace the previous chlorine treatment.
Silver is known historically for its medicinal properties, however recent research from
Queen’s University in Ontario has shown that the silver content specifically in the
SHP Huwa-San, has no independent anti-microbial effect.16
SHP compared with chlorine dioxide
• Higher dose levels of chlorine dioxide can result in smells, taint and taste in
the water;
• Levels of chlorine dioxide that can be used in drinking water are restricted to 0.5
ppm (including chlorite and chlorate breakdown products), a concentration that is
not always high enough to eradicate Legionella;
• Good temperature stability up to 95°C means that higher doses of certain SHPs
can be very suitable for use in hot water systems.This avoids the need to switch
off calorifiers to prevent ‘gassing off’ at high temperatures;
• Treatment with SHP can be significantly less aggressive to certain materials of
construction than chlorine dioxide. SHP is compatible with a wide variety of metal
and non-metal materials used in water systems, however, it can oxidise/pacify the
zinc used to galvanise steel.
Case Studies
There is very little peer-reviewed research available for the action of SHP products,
however the following examples illustrate how continuous dosing with a SHP can be
used successfully to resolve Legionella problems in water systems.These particular
cases all utilised EndoSan, a product that employs an ionic silver stabilisation
system in which a silver nitrate complex is used in the formulation of the stabiliser/
catalyst to provide a convenient source of soluble silver.The stabiliser that is added
to hydrogen peroxide in EndoSan is not silver nitrate itself, but a complex mixture
containing silver and nitrate registered under REACH.The silver in this product has no
biocidal action that can be separated from that of hydrogen peroxide.
West Exeter College
Positive counts for Legionella were found in both the hot and cold water systems at
West Exeter College, a PFI project built in 2007 by Carillion in Exeter, Devon.
The water systems in the main building were already managed in accordance with
L8, with hot water leaving the calorifiers maintained at 65o
C and cold water in
the building kept below 200
C.The regime had been successful in reducing overall
bacterial counts, but had never completely eradicated Legionella.The presence of
Legionella suggested persistent biofilm in the system.
A chlorine dioxide constant dosing pump was installed In March 2013, as was a 5m3
water meter to ensure the correct amount of chemical was dosed into the system.
Most of the College’s 338 water outlets were isolated to contain the problem, with
those remaining in use fitted with HEPA filters.
Mains water supplies a six tonne capacity cold water storage tank from where it is
pumped to the school’s four floors.A 230 litre break tank situated above the first
floor supplies water to the science block.There are two pumps situated in the first
floor subsidiary plant room next to the science department.
However, issues with water pressure and flow rates were observed and there also
appeared to be problems with the water system’s pipe work.This had not have been
constructed to the original design and late changes had introduced dead legs. Most
of these have now been removed.
A treatment with SHP, split between a series of shock disinfections outside of
operating hours (evenings and weekends) and a constant dosing pump operating
during the day was initiated in June 2013.
Results indicated that any microbiological contamination present prior to treatment
with SHP were removed by the shock disinfection and dosing. Samples following
SHP treatment were demonstrated as being clear of Legionella, indicating that the
persistent problem had been resolved. A low level maintenance dose of around 8-12
ppm SHP is now used to keep the hot and cold water system free of biofilm and
Legionella.
waterline | THE JOURNAL OF THE WATER MANAGEMENT SOCIETYfeature article
www.exeterexpressandecho.co.uk
![SILVER HYDROGEN PEROXIDE:
what the guidelines say
26
S U M M E R 2 0 1 5 feature article
However, despite the HSE’s acceptance, SHP’s
efficacy and safety have not always been well
understood and there has been some wariness
about its use.The waters have also been muddied
by some confusion over the published wording
of the HSG274 paragraph relating to SHP. Any
misunderstanding has now been rectified by the
HSE’s COSHH and Chemicals Carcinogens Unit, and the current online version
confirms the clarified wording for Section 2.116 (an addendum will also be included
in any hard copy publications):
In fact this focus on SHP’s inclusion in HSG274 has been a useful opportunity for
improved clarity over its usage.
As HSG274 makes clear, SHP already has a history of usage in the UK. In fact it has
been used since 2002 as a water disinfection treatment to remove biofilm in both
domestic water systems and other contexts such as cooling towers, with systems
well flushed to remove any nutrients and disinfectant released by the process.
Some of the confusion over SHP relates to uncertainty over
what levels of SHP are acceptable in domestic water systems.
In the UK, SHP is accepted in England and Wales by the
Drinking Water Inspectorate (DWI) for disinfection of potable
water reservoirs, tanks and pipelines, with the proviso that the
chemical must be completely removed from the system at the
end of the process.2
In potable water for public supply, the DWI
specifies that levels of hydrogen peroxide should be below 1ppm,
with silver levels below 1ppb for silver. The Drinking Water
Quality Regulator for Scotland (DWQR) and the Drinking Water
Inspectorate for Northern Ireland (a unit within the Northern
Ireland Environment Agency) follow the same guidelines as the
DWI in England and Wales.
Elsewhere, however, levels considered ‘safe’ are significantly higher. In the United
States, the highly respected and independent US based certification organisation the
National Sanitation Foundation (NSF) has certified use of one SHP product, Huwa-
San™ TR50 (EndoSan in the UK), for use at levels of up to 8ppm in water distribution
systems, following a rigorous oral risk assessment of the carcinogenic effects of
hydrogen peroxide in 2010.3
As a result of these NSF’s guidelines, SHP (Huwa-San) is also now being used in
Canada, as a secondary disinfectant for water treatment at Killaloe and other
townships in Ontario,4,5,6
while in Europe, hydrogen peroxide has been approved for
treatment of drinking water at levels up to 17ppm under European Standard- EN 902
(2009).
One of the reasons for the DW’s cautiously low limits of SHP in potable water is due
to on-going concern over an incident in 2008 when SHP was implicated in morbidity
and one death in several dialysis patients.7,8
However, it is well documented that
this incident was the result of failure to meet guidelines and follow manufacturers’
instructions properly, which illustrates the need for rigorous pre-use risk assessment
before it is used.
The DWI is concerned about the toxicity of silver - yet it is now generally accepted
that silver is not toxic at the very low levels likely to be present in water.The EU
and WHO, as of April 2014 and noted in HSG274, do not declare any established
standards for silver.WHO guidelines state “there is no adequate data with which to
derive a health based guideline value for silver in drinking water.” WHO also states
that “special situations exist where silver may be used to maintain the bacteriological
quality of drinking water. Higher levels of up to 0.1 mg/litre (this concentration gives a
total dose over 70 years of half the human NOAEL [No Observed Adverse effect level]of
10 g), could be tolerated in such cases without risk to health”.
The DWI is currently awaiting the imminent registration of certain SHP products
under the EU Biocidal Products Regulations. However, Bob Wilson (Bsc, MWMSoc) of
the Meadowhead Consultancy notes that in fact in certain SHPs “hydrogen peroxide
is the only active biocidal substance in SHP and [it] is approved under the BPR.”
He goes on to say:
“I’m very clear about using SHP where silver is not an active biocide, as long as it
doesn’t go into water that’s going to be drunk. Most buildings should have outlets
labelled as ‘not potable water’ ....[because] in a building there are very few places
in reality where you could actually call the water ‘potable’... For instance if it goes
through a cold water storage tank... [where] it can pick up contamination. Most
buildings have mains water separated, e.g., in kitchens. It’s fine to use this within a
building water system, but only the part of the system where it wouldn’t be in the
sections feeding to a potable water outlet.... you would dose the water system after
the mains water supply to the drinking water outlets.”
Safety of H2O2 and silver
Hydrogen peroxide has been
widely used as a bleaching
agent, disinfectant and
medicine for over 100 years
and its many uses considered
safe today include teeth
whitening, acne treatment
and hair dyes. It is used in
wine and liquors for ageing
and as an approved food
additive, in minute amounts
in Japan and Canada and the
US, where it also has GRAS
status, ie generally recognised
as safe by the US FDA, for a
use in certain food processing.
As mentioned above, the main concern for product regulation of SHPs relates to
its silver content.The European Biocidal Products Directive in relation to nanosilver
consumer products approves certain silver salts, but its list does not include silver
nitrate. Silver nitrate salts are not present in all SHPs.As already discussed above,
silver in certain SHPs has no active biocidal role.
According to WHO’s Guidelines for Drinking Water Quality, most foods contain
traces of silver in the 10–100 μg/kg range.The background document for
development for this document notes that average silver concentrations in natural
waters are 0.2–0.3 μg/litre.9
In the UK, if used according to manufacturers’ instructions, the recommended
dosing for certain SHP products appear to introduce silver into a water supply at
significantly below that allowed by the WHO.
When the Health and Safety Executive (HSE) last year published HSG274 (Part 2), the most recent guidelines
on the control of Legionella in hot and cold water systems, they for the first time recognised the use of silver
hydrogen peroxide (SHP) as an alternative biocide to more traditional chlorinated water treatments.1
Since the
control of Legionella and other bacteria in hot and cold water systems is rarely straightforward, and more often
than not requires a combination of measures, the inclusion of another alternative to the arsenal of options is to
be welcomed.
“Silver stabilised hydrogen peroxide has a history of use in the control of
legionella in water systems.A silver hydrogen peroxide solution is injected
directly into the water system and if applied and maintained according to the
manufacturers’ instructions, can be an effective means of control. However, this
should not be used in water systems supplying dialysis units.”
by Susan Pearson](https://image.slidesharecdn.com/918fd607-bd48-4f8d-9a0d-d7ea01fc9c4a-150722152517-lva1-app6891/85/SHP_Waterline-Summer2015-1-320.jpg)
