SILVER HYDROGEN PEROXIDE:what the guidelines say

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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 silverHydrogen 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

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How SHP worksSilver 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.

EfficacyHydrogen 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 CollegePositive 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 65oC and cold water in the building kept below 200C. 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

by Susan Pearson

www.exeterexpressandecho.co.uk

References

1 HSG274, Part 2, page 39 “Water treatment and control programmes for hot and cold water systems”: 2.116.2 http://dwi.defra.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdf, page 15.3 NSF International, Hydrogen Peroxide CAS 7722-84-1, Oral Risk Assessment, March 2010. 4 Killaloe Drinking Water System, THM Reduction Project, Second Summary Report to the Ministry of the Environment, Ontario Clean Water Agency(OCWA) Project No. 11 – 0094, Prepared by: Engineering Services OCWA, September 13, 2013.5 http://ese.dgtlpub.com/2013/2013-06-30/pdf/Innovative_disinfection_technology_cuts_high_THM_levels_in_drinking_water.pdf 6 www.lfpress.com/2013/05/16/community-will-become-only-the-second-in-north-america-to-use-hydrogen-peroxide-as-a-secondary-water-treatment7 http://www.dailymail.co.uk/health/article-1081353/The-deadly-threat-kidney-dialysis-patients-hospital-water-supply.html8 Newbigging, N. et al NDT Plus, 2: 158-160, 2009. 9 World Health Organization, “Guidelines for drinking-water quality,” 2nd ed. Vol. 2. 2003 (Health criteria and other supporting information, Geneva, 1996).10 Guiot P., Terraz A., van Oosterom P. and Wilson R. “Hydrogen and silver: their uses as disinfectants in United Kingdom domestic water systems,” Waterline (Water Management Society), Summer 2003: 21-26. 11 Block, S.S. Ed., “Disinfection, sterilization and preservation, 4th Edition”, Philadelphia: Lea and Febiger, 1991. 12 Omidbakhsh, N. and Sattar, S.A. “Broad-spectrum microbiocidal activity, toxicologic assessment, and materials compatability of a new generation of accelerated hydrogen peroxide-based environmental surface disinfectant,” Am J Infect Control 34: 251-7, 2006.13 Schaeffer, A.J., Jones, J.M. and Amundsen, S.K. “Bacterial effect of hydrogen peroxide on urinary tract pathogens,” Appl Environ Microbiol 40: 337-40, 1980. 14 Gommers, K. (VITO) and Huysman K. (PIPA) “Evaluation of Huwa-San TR-50 for the removal of biofilm” (paper written for limited distribution following commission from Roam Chemie to investigate the effect of Huwa-San on water system biofilms) Report no 2004/MPT/R/101. Contract number 031293), 2004.15 Killaloe Drinking Water System, THM Reduction Project, Second Summary Report to the Ministry of the Environment, Ontario Clean Water Agency(OCWA) Project No. 11 – 0094, Prepared by: Engineering Services OCWA, September 13, 2013.16 Martin, N., Bass, P. and Liss, S.N. “Application of a novel silver-stabilized hydrogen peroxide in secondary disinfection of potable water and proposed mechanism for enhanced antibacterial activity,” 16th Canadian National Drinking Water Conference, Gatineau, Quebec, (October) 2014.

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Susan Pearson BSc (susan@wordways.co.uk) is a freelance journalist and communications consultant specialising in medicine and the environment.

Brae High School, Shetland Continuous dosing with SHP was introduced in 2009 at Brae High School, an ‘eco’ school in Shetland to combat high temperatures in the mains water entering the building. Cold water temperatures were reaching as high as 350C because the incoming mains supply is situated adjacent to a heating pipe. This pipe work could not be relocated, which meant an alternative to temperature control for Legionella had to be introduced.

Constant dosing with SHP was introduced to control the cold system, with subsequent water testing indicating good microbiological control. The introduction of SHP to the system also allowed calorifier levels to be lowered from 60°C to 50°C in the hot water system. This in turn delivered an energy saving of 12%, equating to savings of around £9680 each year.

© Chris Downer (Creative Commons Licence).

Perth Royal Infirmary Silver hydrogen peroxide dosing was introduced in 2007 into a large geriatric ward that had a very persistent Legionella issue. Following the installation the hospital carried out weekly TVC and Legionella checks to confirm that the biofilm contamination had been cleared. Within a short time after initiation of SHP dosing, TVC tests were reduced to < 1 CFU/ml. Dosing of the system has continued and Legionella counts have remained at <1 CFU/litre with TVCs at < 1 CFU/ml.

SILVER HYDROGEN PEROXIDE: what the guidelines say