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 Home > UN World Health Organization Colloidal Report (extracts) 
 BELOW IS AN EDITED VERSION OF EXTRACTS TAKEN FROM THE FOLLOWING HEADED TITLED REPORT  edited by Alchemists Shop
UNITED NATIONS - WORLD HEALTH ORGANIZATION REPORT RELATING TO THE USE OF COLLOIDAL SILVER IN CERAMIC WATER FILTERS.

Submitted to Jubilee House
November 18, 2001
USAID Purchase Order Number:
     524-0-00-01-00014-5362

Extracts from Investigation
Colloidal Silver Impregnated Ceramic Filter

Report 2:  Field Investigations

Daniele S. Lantagne
Alethia Environmental

1    Project Background
1.1    Hurricane Mitch, USAID, and CACEDRF

In October 1998, Hurricane Mitch devastated Central America, causing over 3,000 deaths in Nicaragua alone (USAID 2001, 2001a).  An estimated 18 percent of the population of Nicaragua was affected by Mitch, and water and wastewater systems serving 804,000 people suffered over US$560 million in damage.  The Unites States provided US$22 million in immediate humanitarian and food aid, and an additional US$8 million to start reconstruction activities in health, agriculture, and micro-finance.

In May 1999, the United States Congress authorized US$621 million in aid under the Emergency Supplemental Appropriations Act (USAID, 2001).  These funds were authorized to support reconstruction in countries affected by Hurricanes George and Mitch, and were later authorized to cover Hurricanes Floyd and Lenny, as well as the earthquake of January 1999.  This appropriation created an account named the Central American and Caribbean Emergency Disaster Recovery Funds (CACEDRF).

USAID is responsible for administering US$586.8 million of the US$621 million allocated under CACEDRF (USAID, 2001a).  Of the total funds, US$94.1 million was allocated for economic reactivation, public health, school rehabilitation, disaster mitigation, and municipal restoration in Nicaragua.  As of June 30, 2001, a significant amount of progress on projects relating to water supply and sanitation had already occurred (Table 1-1).
Table 11:  CACEDRF Successes Relating to Water Supply and Sanitation in Nicaragua

USAID is responsible for administering US$586.8 million of the US$621 million allocated under CACEDRF (USAID, 2001a).  Of the total funds, US$94.1 million was allocated for economic reactivation, public health, school rehabilitation, disaster mitigation, and municipal restoration in Nicaragua.  As of June 30, 2001, a significant amount of progress on projects relating to water supply and sanitation had already occurred (Table 1-1).
Table 11:  CACEDRF Successes Relating to Water Supply and Sanitation in Nicaragua

Category    Success
Economic Reactivation 57,000 households incorporated environmentally sustainable practices on their farms 8,000 hectares of watershed area protected Public Health 2,440 wells rehabilitated or built 5,740 latrines constructed 600 seepage pits constructed 175 deep wells drilled in rural areas 10,000 training visits held to improve health behavior related to new water and sanitation infrastructure 6 health clinics constructed School Rehabilitation 196 schools scheduled for rehabilitation of wells and latrines Disaster Mitigation Cleaning and stabilizing stream channels Construction of drainage channels Municipal Restoration Projects with local governments on storm drain systems, flood control, river deck construction
 An additional goal of the rehabilitation program in Nicaragua is to investigate point-of-use household water filtration systems (USAID, 2001b).  To this end, USAID worked to install 40,000 sand filtration units, supervised by Maria Alejandra Bosche.  Ms. Bosche found that follow-up education was critical to the correct and continued use of the filter system (Bosche, personal conversation).

Secondly, USAID contracted with Jubilee House Community (JHC) to study the Potters for Peace (PFP) ceramic water filtration system.  JHC, an intentional Christian community, is a 501(c)3 organization in North Carolina (JHC-CDCA, 2001).  From 1979 – 1994, members of the community worked on shelters for homeless and battered women, as well as other social and justice issues, in North Carolina.  In 1994, the community moved to Nicaragua, established the Center for Development in Central America (CDCA), and began working with communities in Nicaragua.  After Hurricane Mitch, JHC-CDCA began to work on reconstruction projects in Nueva Vida, a nearby community swelled with displaced persons.  USAID provided funding and supplies to build housing, a medical clinic, and latrines (USAID, 2001c).  JHC and a group of volunteers worked with the community to build these facilities, in addition to a number of other projects.  One of these other projects is the promotion of the Potters for Peace water filtration system to provide safe drinking water for families in Nueva Vida.

JHC worked with PFP to contract Daniele Lantagne, Principal of Alethia Environmental and Lecturer in Civil and Environmental Engineering at the Massachusetts Institute of Technology, to complete the project.  The project was divided into two deliverables, one addressing the intrinsic effectiveness of the filter, and the other addressing the performance of the filters under field conditions.  Specifically the reports are to address the following:

Report 1:  Intrinsic Effectiveness of the Potters for Peace
Ceramic Filter

·    Best practices for colloidal silver application.
·    Expected filter flow rates with and without colloidal silver.
·    Expected lifetime per application of colloidal silver.
·    Concentration of silver in filtered water.
·    Effects of ingestion of the silver.
·    Inactivation of microbes as a function of the concentration of silver.
·    Effectiveness of silver in removing other pollutants commonly found in the area of interest.

Completion Deadline:  December 21, 2001

The PFP Filter
Initial Filter Design

In 1981 the InterAmerican Bank financed a comparative study designed to determine which of 10 appropriate technology filters could be best adapted to the objectives of the project, which were (ICAITI, 1994):

1.    to produce a domestic filter of suitable capacity;
2.    in a self-supporting manner;
3.    whose production would foster economic activity at low income levels; and
4.    foster artisan activity.

ICAITI, an industrial research institute in Guatemala supported by the Organization for American States, was contracted to complete the research and to choose a model.  Ten models were evaluated based on filtration flow, bacteriological efficiency, ease of manufacture, availability of materials, final cost, contribution to artisan activity, and ease of distribution.  All but two models were discarded after initial review because they did not meet basic criteria.  The two models not discarded were:

1.     Lathed clay filter with feldspar, sawdust, and colloidal silver impregnation; and
2.     Lathed clay filter with sand, sawdust, and colloidal silver impregnation.

None of the ten models investigated utilized chlorine as a disinfectant.

Further research was then conducted on the two models that met the basic criteria.  This research, led by Fernando Mazareigos, did extensive bacteriological testing over a 3 to 10 month period.  Results of this research include:

1.    Of 302 filtered samples analyzed, only 6.3 percent were above 1.0 coliforms per 100 mL of water.  The method used for analysis was most probable number.    
2.    Application of silver was determined to be more uniform when applied by brush as opposed to filtering water containing colloidal silver through the filtering element.
3.    Frequent contamination was found both in the first few runs of the filter (41 percent contaminated) and after handling the element during sampling.  This was attributed to handling the filter and ICAITI recommended that users refrain from touching the element during its useful life.  Due to the omnipresent bacteria in the environment “usage of the filter must be accompanied by sanitary and hygienic practices in order to maximize the potential benefits to health.”
4.    Flow in the filters gradually declined from 3.5 liters per hour on Day 1 to 1.97 liters per hour on Day 365.  The report contained no information on turbidity of the raw water supply.
5.    ICAITI recommended not using the filter with chlorinated water.  No reason was given.

Based on these results, ICAITI concluded that a colloidal silver impregnated ceramic filter was the only design that met all established criteria of the study.  The United Nations then included this filter in their Appropriate Technology Resource Material Manual.  ICAITI concluded its study by producing a 'Manual Para La Fabricacion De Filtros Artesanales De Agua Potable.'

Table 01:  Worldwide Public Health Impact of Waterborne Disease (WHO, undated)

Disease    Morbidity       (per year)    Mortality (deaths / year)    Population at risk
Waterborne & water-washed          
Cholera          
Diarrheal disease    1,500 million episodes in children under 5    4 million in children under 5    over 2,000 million
Enteric fevers    500,000 cases    25,000  
Poliomyelitis    204,000    25,000  
Ascariasis (roundworm)    1,000,000    20,000  
Leptospirosis          
Trichuriasis          
          
Water-washed          
Trachoma    6 – 9 million blind        500 million
Leishmaniasis    400,000 new infections / year        350 million
Relapsing fever          
Typhus fever          
          
Water-based          
Schistosomiasis    200 million    200,000    500 – 600 million
Dracunculiasis    over 10 million        over 100 million
The microorganisms that cause these waterborne diseases are classified as bacteria, protozoa, viruses, and helminths (Levinson, 1996).  These four organisms belong to different kingdoms and are eukaryotic (containing DNA with a nuclear membrane), prokaryotic (without a defined membrane), and noncellular (Table 3-2).

Table 02:  Biologic Relationships of Pathogenic Microorganisms (Levinson, 1996)

Kingdom    Pathogenic Microorganism    Type of Cell
Animal    Helminths    Eukaryotic
Protist    Protozoa
Fungi    Eukaryotic
Eukaryotic
Prokaryote    Bacteria    Prokaryotic
    Viruses    Noncellular


 
Bacteria are single-celled prokaryotic (without nucleus) members of the eubacteria group (MEI, 1991).  Although they are not eukaryotes (with a defined nucleus), they have similar cell chemistry to eukaryotes.  Their size varies from 0.3 to 100 μm in length, depending on their shape (Table 3-3).   E. coli is a rod shaped bacteria that is 0.5 μm in width and 2 μm in length.  Most of the bacteria are larger than the 1μm pore size that Potters for Peace aims to maintain in their filter.

Table 03:  Bacteria Types and Size (adapted from MEI, 1991)

Shape    Name    Size
Spherical    cocci, coccus    1 – 3 μm in diameter
Rod    bacilli, bacillus    0.3 – 1.5 μm in width
1.0 – 10 μm in length
Curved rod    vibrios    0.6 – 1.0 μm in width
2 – 6 μm in length
Spiral    spirilla    up to 50 μm
Filamentous        up to 100 μm and longer

 

Protozoa are single-celled eukaryotic (with a nucleus) organisms.  They feed on bacteria and other microscopic organisms.  Giardia lamblia and cryptosporidium are common disease-causing protozoa.  Protozoa range in size from 8 – 100 μm.

Viruses are parasitic particles consisting of a strand of genetic material.  They do not have the ability to synthesize new compounds, and instead invade the host cell and redirect the host genetic material to produce viral particles.  Because they do not have the structure to reproduce themselves, viruses are the smallest of the disease-causing organisms, at 0.02 – 0.2 μm.

Helminths are worms that are part of the animal kingdom.  Platyhelminthes (flatworms) and Aschelminthes (flukes, tapeworms) are present in water bodies throughout the world, and enter the human body to cause diseases such as trichinosis, hookworm, and roundworm infestation.

Infectious agents commonly found in drinking water include members of the bacteria, virus, protozoa, and helminth groups and cause diseases ranging from diarrhea to jaundice to acute respiratory illnesses (Table 3-4).



Table 04:  Waterborne Disease-Causing Organisms (MEI, 1991)

Organism    Disease    Remarks
Bacteria      
   Escherichia coli    Gastroenteritis    Diarrhea
   Legionella pneumophila    Legionellosis    Acute respiratory illness
   Leptospira    Leptospriosis    Jaundice, fever
   Salmonella typhi    Typhoid fever    Fever, diarrhea
   Salmonella       Salmonellosis    Food poisoning
   Shigella    Shigelloisis    Bacillary dysentery
   Vibrio cholerae    Cholera    Heavy diarrhea, dehydration
   Yersinia enterolitica    Yersinosis    Diarrhea
      
Viruses      
   Adenovirus    Respiratory disease  
   Enteroviruses (67 types, including polio, echo, etc.)    Gastroenteritis, heart anomalies, meningitis  
   Hepatitis A    Infectious hepatitis    Jaundice, fever
   Norwalk agent    Gastroenteritis    Vomiting
   Reovirus    Gastroenteritis  
   Rotavirus    Gastroenteritis  
      
Protozoa      
   Balantidium coli    Balantidiasis    Diarrhea, dysentery
   Cryptosporidium    Cryptosporidiosis    Diarrhea
   Entamoeba histolytica    Amebiasis    Diarrhea, bleeding
   Giardia lamblia    Giardiasis    Diarrhea, nausea, indigestion
      
Helminths      
   Ascaris lumbricoides    Ascariasis    Roundworm infestation
   Enterobius vericularis    Enterobiasis    Pinworm
   Fasciola hepatica    Fascioliasis    Sheep liver fluke
   Hymenolepis nana    Hymenolepiasis    Dwarf tapeworm
   Taenia saginata    Taeniasis    Beef tapeworm
   T. solium    Taeniasis    Pork tapeworm
   Trichuris trichiura    Trichuriasis    Whipworm



Thus, a number of different organisms of varying size and pathology contribute to waterborne disease throughout the world.  Two mechanisms in the PFP filter contribute to reduction of these organisms.  The first mechanism is filtration.  The PFP filter will trap any particle or organism that is larger than the pore size of the filter.  PFP aims to have a pore size of 1 μm (1 micron).  This would trap a significant portion of bacteria, and all protozoa and helminths.  However, viruses are smaller than 1 micron, and thus would not be trapped.

To date, no studies have been completed analyzing the pore size of the PFP filter.  For Report 1 of this study (December 2001), analysis of the pore size of the PFP filter and retention rates of selected viruses and protozoa will be completed.

The second inactivation mechanism for organisms contributing to waterborne disease utilized in the PFP filter is COLLOIDAL SILVER.  

Colloidal Silver as a Disinfectant
Silver is a soft, malleable metal, which is stable in water and oxygen but attacked by sulfur compounds in air to form a black sulfide layer (CRC, 1997).  The atomic number of silver is 47, its atomic weight is 107.868, and it exists in its common valence states of Ag+, Ag2+, and the mineral form of argentite, Ag2S.  Typical ambient concentrations of silver are presented in Table 4-1.  Silver is present throughout the environment in small concentration (milligram to nanogram), but is not essential for animal or plant life.

Table 01:  Typical Ambient Concentrations of Silver (adapted from CRC, 1997)

Content    Concentration
Total Content in Soils    0.03 – 0.9 mg/kg
Soluble Content in Soils    0.01 – 0.05 mg/kg in 1 N NH4AOC
Content in Sea Water    0.04 μg/kg
Content in Fresh Water    0.13 μg/kg
Content in Marine Animals    3 – 10 mg/kg
Content in Humans    Blood:    < 2.7 μg/L
Bone:     1.1 mg/kg
Liver:     <5 – 32 ng/g
Content in Animals    6 μg/kg
Content in Plants    0.01 – 0.5 mg/kg
Content in Common Foods    0.07 – 20 mg/kg
Essentiality    Plants:      no
Animals:   no


The daily dietary intake by humans is estimated at 0.0014 to 0.08 mg (CRC, 1997).  When the maximum CRC intake per day (0.08 mg) is calculated over a 70-year lifetime, a total of 2.0 grams of silver are ingested per person per lifetime.

0.08 mg / day   365 days / year  70 years = 2.0 grams / lifetime
  
Toxic intake for humans is 60 milligrams, while a lethal intake is 1.3 to 6.2 grams (CRC, 1997).



Silver Human Health Standards and Regulations
World Health Organization (WHO)

In their Guidelines for Drinking-Water Quality, 2nd Edition (1993), the WHO addressed human health effects of silver and guidelines values to prevent those effects.

WHO determined that:

1.    The retention rate of silver in humans and animals is only 0 – 10 percent.  The retained silver is mainly stored in the liver and skin.  The half-life of silver in the liver is 50 days.
2.    Silver is occasionally found naturally in ground and surface water at 5 μg/L.
3.    Average human intake of silver is 7.1 μg/day.
4.    The acute lethal dose of silver nitrate is a minimum of 10 grams.
5.    Argyria is the only known human health effect of silver, and “is a condition in which silver is deposed on skin and hair.”

Based on their research, the WHO recommended a guideline value for silver of 10 grams per lifetime.  This is a NOAEL (no observed adverse exposure limit) standard.   WHO concludes by stating “as the contribution of drinking-water to this NOAEL will normally be negligible, the establishment of a health-based guideline value is not deemed necessary.”   In 1996, the WHO reiterated this determination by designating silver as a “U” compound.   “It is unnecessary to recommend a health-based guideline value for these compounds [U compounds] because they are not hazardous to human health at concentrations normally found in drinking-water.”

However, the WHO addresses the fact that silver is often used as a disinfectant, and in such cases, “the daily intake of silver from drinking-water can constitute the major route of oral exposure.”    Thus, WHO has established an additional guideline value for when silver is “used to maintain the bacteriological quality of drinking-water.”  This guideline states “higher levels of silver, up to 0.1 mg/L (this concentration gives a total dose over 70 years of half the human NOAEL of 10 g) could be tolerated in such cases without risk to health.”

Thus, the guideline value appropriate for use in analyzing the PFP filter is 0.1 mg/L (or 100 μg/L) in the finished, filtered water.
 
United States Environmental Protection Agency (USEPA)

The USEPA has also investigated silver to determine appropriate drinking water standards.  The USEPA recommends a maximum intake of 5 μg/kg/day (1996).  In the average 70 kilogram adult, this is equivalent to 350 μg/day.  This recommendation was established to prevent argyria, “a medically benign but permanent bluish-gray discoloration of the skin.  Argyria results from the deposition of silver in the dermis and also from silver-induced production of melanin.”   Argyria is “more pronounced in areas exposed to sunlight due to photoactivated reduction of the metal”, and “although the deposition of silver is permanent, it is not associated with any adverse health effects.”  
(Editorial Comment: Argyria is the result in ingesting silver powder however fine it is pulverized, can never be as tiny as moder day  colloidal silver produced electrically. Furthermore there has never been any recorded cases of Argyria derived from any ultrafine colloidal silver, which has been assessed as safe even it taken at the rate of 100ml bottle 12ppm everyday for a year.  Consequently Silver salts or pulverized silver powder MUST never be confused with Colloidal Silver)

In addition, “no evidence of cancer in humans has been reported despite frequent therapeutic use of the compound over the years.”  Silver was used for centuries to treat syphilis, and as an astringent in topical preparations. 

The 2001 National Secondary Drinking Water Regulations recommends a maximum silver concentration of 0.10 mg/L (or 100 μg/L), but specifically states that “EPA recommends secondary standards to water systems but does not require systems to comply.  However, states may choose to adopt them as enforceable standards.”  These secondary non-enforceable guidelines regulate “contaminants that may cause cosmetic effects or aesthetic effects in drinking water.”  The USEPA does not address separate standards for use of silver as a disinfectant.   It is of note that the USEPA secondary standard is the same as the WHO guideline value for use of silver as a disinfectant:  0.1 mg/L or 100 μg/L.
The USEPA has also investigated silver to determine appropriate drinking water standards.  The USEPA recommends a maximum intake of 5 μg/kg/day (1996). In the average 70 kilogram adult, this is equivalent to 350 μg/day. This recommendation was established to prevent argyria, a medically benign but permanent bluish-gray discoloration of the skin. Argyria results from the deposition of silver in the dermis and also from silver-induced production of melanin. Argyria is more pronounced in areas exposed to sunlight due to photoactivated reduction of the metal”, and “although the deposition of silver is permanent, it is not associated with any adverse health effects.
(Editorial Comment: Argyria is the result in ingesting silver powder however fine it is pulverized, can never be as tiny as moder day  colloidal silver produced electrically. Furthermore there has never been any recorded cases of Argyria derived from any ultrafine colloidal silver, which has been assessed as safe even it taken at the rate of 100ml bottle 12ppm everyday for a year.  Consequently Silver salts or pulverized silver powder MUST never be confused with Colloidal Silver)


In addition, no evidence of cancer in humans has been reported despite frequent therapeutic use of the compound over the years. Silver was used for centuries to treat syphilis, and as an astringent in topical preparations.

The 2001 National Secondary Drinking Water Regulations recommends a maximum silver concentration of 0.10 mg/L (or 100 μg/L), but specifically states that “EPA recommends secondary standards to water systems but does not require systems to comply. However, states may choose to adopt them as enforceable standards.”  These secondary non-enforceable guidelines regulate contaminants that may cause cosmetic effects or aesthetic effects in drinking water. The USEPA does not address separate standards for use of silver as a disinfectant.   It is of note that the USEPA secondary standard is the same as the WHO guideline value for use of silver as a disinfectant: 0.1 mg/L or 100 μg/L.

Colloidal Silver and USFDA/USEPA Regulation

A colloidal solution is a true solution that consists of colloidal macromolecules and solvent and that is thermodynamically stable and readily reconstituted after separation of the macromolecules from the solvent (Stenesh, 1996).”  Furthermore, a colloid is a macromolecule or a particle in which at least one dimension has a length of 10-9 to 10-6 meters. Thus, colloidal silver is a stable solution of very small silver particles suspended in distilled water or proteins. Higher concentrations of colloidal silver (such as used by PFP) are suspended in proteins because they would not be stable in water (Quinto, personal conversation).

In 1999, the United States Food and Drug Administration (USFDA) issued a ruling that all over-the-counter (OTC) drug products containing colloidal silver ingredients or silver salts for internal or external use are not generally recognized as safe and effective and are misbranded. FDA is issuing this final rule because many OTC drug products containing colloidal silver
ingredients or silver salts are being marketed for numerous serious disease conditions and FDA is not aware of any substantial scientific evidence that supports the use of OTC colloidal silver ingredients or silver salts for these disease conditions (Federal Register, August 17, 1999).

(Editorial Comment: It is our opinion that the multinational drug companies have continued to lobby and influence the FDA over the past decades to remove their confirmation of colloidal silver despite thousands of documented clinical tests carried out within the USA by leading health and educational institutions.)



The burgeoning naturopathic market for colloidal silver in the United States prompted this ruling. In a cease-and-desist letter issued to Mr. Randy Winters, the USFDA quoted Mr. Winters’ web site as stating, colloidal silver has been proven to be useful against over 650 diseases, including cancer, without any known harmful side effects. It has been found to cause rapid regeneration of damaged cells and tissues, subdue inflammation and promote faster healing (FDA, 2000). A simple web search for “colloidal silver leads to numerous sites advertising unsubstantiated healing properties, and another set of sites selling home-based colloidal silver generation machines.

On August 8, 2001, I spoke with Ms. Roma Egli, the colloidal silver contact person at the USFDA, about the PFP filter and the use of colloidal silver for disinfection. Ms. Egli said that the USFDA does not deal with disinfection agents, and that the USEPA would regulate the use of colloidal silver in this manner. As long as PFP does not state that the filters are treating animals or humans for disease, and does not state that the colloidal silver is an antibiotic, the product is not regulated under the USFDA. She also mentioned that colloidal silver is used for water disinfection on transportation systems such as airplanes, trains, and boats. When asked, Ms. Egli did state that she has seen argyria cases in people only using naturopathic colloidal silver. No case she has seen is as severe as Rosemary Jacobs, but she has seen permanently blue fingertips. Overall, Ms. Egli expressed the viewpoint that the USFDA is concerned about labeling of colloidal silver as a medical drug when there is no research to support such claims. They are not concerned with colloidal silver as a disinfectant, and in fact Ms. Egli recommended that I talk with the Silver Institute (a promoter of colloidal silver as an antibiotic) about purchasing a generator to make colloidal silver in Nicaragua rather than importing it from Mexico. Because the generators are only capable of producing colloidal silver in the ppm range, as opposed to the 3.2 percent solution that PFP uses, this idea was determined to be not appropriate for PFP
.
XXXXXXXXXXXXXX

I then spoke with Wade Travathan, of the USEPA, about colloidal silver as a disinfectant. The EPA Office of the Pesticide Program regulates disinfectants because microorganisms in the United States are legally classified as pests. Thus, any product that kills microorganisms is classified under federal law as a pesticide. Mr. Travathan said that there are current, active products that are registered with EPA that use colloidal silver as a disinfectant. To become registered as a pesticide, you submit data that details toxicity and efficacy. You can refer to data that has already been submitted by another company, by offering that company appropriate compensation. The submission forms are available on the web site and submission is free of charge. However, there is a maintenance fee of US$1,000 dollars per year on your permit. The Office of the Pesticide Program can be reached at www.epa.gov/pesticides.

Thus, with the appropriate permitting from the USEPA Office of the Pesticide Program, and data supporting that the finished water concentration of silver is less than the USEPA secondary standard of 100 μg/L, a colloidal silver impregnated filter is a legal product to distribute and use in the United States and meets all USA regulations.

Silver in Ceramics

Potters for Peace is not the only organization to use silver as a disinfectant in ceramic filtration units. Basu (1982) in India soaked ceramic candle filters with a pore size of 6 – 31 microns, and a filtration rate of 3 - 4 liters per hour, in silver salts. Filtered water with this system was bacteria-free. Basu chose silver over gold as the bacteriocide, and also tested candle filters with finer pores that would capture the bacteria. The filtration rate was so slow with these finer pores, however, that the filters were “not of much practical value. Thus a larger pore size, combined with a disinfectant, is of more practical value because the flow rate is high enough to provide enough water for a family.

Mechanisms of Action of Silver

Russell (1994) details the historic uses of silver, beginning with Aristotle advising Alexander the Great to boil water and store it in silver or copper vessels to prevent waterborne disease on his campaigns. In 1869, Ravelin reported that silver exerted its antimicrobial effect at very low concentrations, an effect with was later termed "oligodynamic" or "active with few" (Russell, 1994). In 1881, Crede advocated silver to prevent eye infections in newborns, and silver drops were used to prevent gonorrhea of the eye in newborns until very recently. In 1920, the microbiological action of silver was determined to be due to the Ag+ ions formed by tarnishing, surface-oxidation, or electrical activation.

Today, silver is more commonly used as a drinking water and swimming pool disinfectant in Europe than in the United States (Russell, 1994). Studies have shown that silver can be used when chlorine is present for additional disinfection.  Argyria, first reported in 1647, is less common today but is still reported.




Three main mechanisms are responsible for bacterial inactivation with silver (Russell, 1994):

1. Silver reacts with thiol (sulphydryl, SH) groups in the bacterial cell
a.In structural groups  
b.In functional (enzymic) proteins
2.Silver produces structural changes in bacterial cell membranes
3.Silver interacts with nucleic acids

These three mechanisms are described in further detail in the following sections.  Although it is unknown at this time which of these mechanisms is predominant in the PFP filter, laboratory data clearly shows that PFP filters impregnated with colloidal silver remove 99 – 100 percent of bacteria (CIRA-UNAN, various dates). Further information on the mechanism of action of colloidal silver in the filter and data on laboratory tests on the filter are presented in Report 2 (December 2001).

Heinig's research on silver deposited on an inert surface is of special note in relation to the PFP filter. Heinig (1993) showed silver on a large inert surface area exhibited a strong catalytic reaction with oxygen, which resulted in strong bactericidal activity.  The factors controlling the rate of the catalytic reaction were:  the size and dispersion of the silver on the surface area of the bed, and the volume of oxygen in solution. Heinig found that bacteria and viruses were killed on contact without the need for the release of metals into the water.



Silver as an Enzyme Inhibitor

Living cells are characterized by a complex and beautifully organized pattern of chemical reactions mediated and directed by enzyme systems (Webb, 1963). Webb continues by describing the theory of inhibiting enzymes as a means to understanding the “energetics of the cell.

Directly distorting the pathways of enzymically directed reactions by the introduction of a chemical substance is one approach amongst others to alter metabolic activity. Other ways to alter metabolic activity including changing the temperature or the pH, by irradiation of high pressure, are nonspecific and seldom does one have any idea as to exactly what is occurring in the complex protoplasmic matrix. If one had to choose the most interesting and important characteristic of enzyme inhibitors, what it is that makes them one of the most powerful tools in so many fields of biological investigation, it would be their relative specificity. The more we know about the exact nature of the perturbation produced and the more selective this action can be made, the more likely it is that clear interrelationships will emerge and the goal of understanding the energetics of the cell be achieved.

A number of metals are known to inactivate the SH (sulfur-hydrogen, or sulfhydryl, or thiol) bond in enzymes. Silver is widely used in biochemistry applications to determine if an enzyme has a SH group as part of its functional structure.

Webb's summary of data collected on the action of silver on the SH bond shows extremely varied inactivation depending on specific enzyme and concentration (Table 4-2)These different reactivities could be attributed to an electric field surrounding the SH group, steric factors depending on where the SH group is in the protein structure, occurrence of disulfide linkages, complexes of the SH group with surrounding groups, and whether there is a single or double SH group. Other SH inhibitors studied include mercury, arsenite, cadmium, iodine, ferricyanide, and permanganate.

Although there exists a large variation, SILVER clearly inactivates certain enzymes in sources that are responsible for waterborne disease (Table 4-2).  Waterborne disease sources are boldfaced in Table 4-2.

END OF EXTRACTS



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