Limitations of colloidal silver disinfection's raise serious questions about the ability colloidal silver solutions to produce safe, potable drinking water:

This article describes the limitations of relying on colloidal silver disinfection to make drinking water safe and potable. The article cites research on the use of colloidal silver and it cites health authority warnings about colloidal silver in various applicaitons including in water solution, in water disinfection, in drinking water, and in water filters. We explain that some biological or pathogenic drinking water contaminants are either resistant to standard disinfection approaches such as chlorination while other water contaminants such as hazardous chemicals or particulates are simply not addressed by disinfection.

Colloidal Silver Water Filters for Drinking Water Purification

Colloidal silver water filters for water disinfection & purification

Silver ceramic water filters are ceramic water filters which have been treated with colloidal silver - a step which might increase water filter effectiveness by killing bacteria in water passing through the system. Silver ceramic water filters are discussed separately in detail at CERAMIC FILTERS for WATER DISINFECTION.

But even a casual review of colloidal silver research indicates that while this substance may be safe for humans and other animals in topically applied uses (burns for example) (Maneewattanapinyo 2011), colloidal silver, including in newer nanoparticle forms (Panyala 2008) presents serious health risks when ingested such as by drinking water containing colloidal silver. And Ruparelia (2008) adds the interesting observation that bacterial susceptability to colloidal silver varies by species/strain.

Besides argyria and argyrosis, exposure to soluble silver compounds may produce other toxic effects, including liver and kidney damage, irritation of the eyes, skin, respiratory, and intestinal tract, and changes in blood cells. Metallic silver appears to pose minimal risk to health. The current occupational exposure limits do not reflect the apparent difference in toxicities between soluble and metallic silver; thus, many researchers have recommended that separate PELs be established. - Drake 2005

Watch out: while there is research supporting the use of colloidal-silver-impregnated water filters (Oyanedel-Craver 2007, Bielefeldt 2009) not all colloidal silver impregnated filters are effective.

A ceramic water filtration system coated with silver particles was created by Ron Rivera of Potters for Peace and used in developing countries for water disinfection. - Wikipedia. An investigation [PDF] into the effectiveness of this silver-coated ceramic water filter was completed in 2001.

That study showed that the silver-treated ceramic filter removed 98-100% of the indicator bacteria present in the source water. The filter does not remove arsenic (and probably not other similar chemicals), and the filter is unreliable for removal of pesticides or VOCs. - See "Investigation of the Potters for Peace Colloidal Silver Impregnated Ceramic Filter, Report 1: Intrinsic Ineffectiveness" [PDF]

Effectiveness of colloidal silver as a water disinfectant

Electrolytically dissolved silver has been used as a water disinfecting agent including in drinking water supplies of the Russian Mir orbital space station and the International Space Station.

The World Health Organization includes silver in a colloidal state produced by electrolysis of silver electrodes in water, and colloidal silver in water filters as two of a number of water disinfection methods specified to provide safe drinking water in developing countries.

However, simply using colloidal silver as a direct addition to drinking water can be an unreliable and unsanitary "... water treatment method according to Quackwatch (seeReferences or Citations ) and its use can lead to argyria. Colloidal silver is a suspension of submicroscopic metallic silver particles in a colloidal base.

Watch out: Ceramic water filters [which can be effective if properly used - (Tien 2008, Petros 2011)] should not be confused with attempts to "purify" water by simply adding unreliably formulated colloidal silver products to drinking water. The use of colloidal silver as a bacteriocide is well established (citations below) but its safety and effectiveness as an add-in water disinfectant does not appear supported by research we could find through 2014.

Watch out: a review of more than 400 articles of scholarly research conducted (Google Scholar August 2014) by the editor could not find a single research claim supporting the effectiveness of the direct use of home-made home-mixed colloidal silver in water solutions as a disinfectant - an approach we have observed taken by some homeowners in Mexico.

Watch out: Long-term use of silver preparations can lead to argyria, a condition in which silver salts deposit in the skin, eyes, and internal organs, and the skin turns ashen-gray. ... The official drug guidebooks (United States Pharmacopeia and National Formulary) have not listed colloidal silver products since 1975.

In August 1999, the U.S. Food and Drug Administration (FDA) banned colloidal silver sellers from claiming any therapeutic or preventive value for the product, noting that colloidal silver was being marketed for numerous diseases without evidence of safety or effectiveness.

The product now has the status of a dietary supplement in the US; it can be promoted with general "structure-function" claims, but cannot be marketed as preventing or treating any illness. Following this ruling, the FDA has issued numerous warnings to Internet sites which have continued to promote colloidal silver as an antibiotic or for other medical purposes. Original source, Wikipedia, includes citations in support of these statements.

In 2002, the Australian Therapeutic Goods Administration (TGA) found that there were no legitimate medical uses for colloidal silver and no evidence to support its marketing claims. Given the associated safety risks, the TGA concluded that "efforts should be made to curb the illegal availability of colloidal silver products, which is a significant public health issue."[26].

Water disinfectant effectiveness, particularly using bleach, is also limited by water pH

We explain in this separate but important article that WELL DISINFECTANT pH ADJUSTMENT may also be necessary for effective water disinfection.

Research on the Effectiveness & Safety of Colloidal Silver in Various Applications

• See this article's full list of citations atReferences or Citations
• Benn, Troy M., and Paul Westerhoff. "Nanoparticle silver released into water from commercially available sock fabrics." Environmental science & technology 42, no. 11 (2008): 4133-4139.
• Bielefeldt, Angela R., Kate Kowalski, and R. Scott Summers. "Bacterial treatment effectiveness of point-of-use ceramic water filters." Water research 43, no. 14 (2009): 3559-3565. Abstract
  
  Laboratory experiments were conducted on six point-of-use (POU) ceramic water filters that were manufactured in Nicaragua; two filters were used by families for ca. 4 years and the other filters had limited prior use in our lab. Water spiked with ca. 106 CFU/mL of Escherichia coli was dosed to the filters. Initial disinfection efficiencies ranged from 3 – 4.5 log, but the treatment efficiency decreased with subsequent batches of spiked water.
  
  Silver concentrations in the effluent water ranged from 0.04 – 1.75 ppb. Subsequent experiments that utilized feed water without a bacterial spike yielded 103–105 CFU/mL bacteria in the effluent. Immediately after recoating four of the filters with a colloidal silver solution, the effluent silver concentrations increased to 36 – 45 ppb and bacterial disinfection efficiencies were 3.8–4.5 log.
  
  The treatment effectiveness decreased to 0.2 – 2.5 log after loading multiple batches of highly contaminated water. In subsequent loading of clean water, the effluent water contained < 20–41 CFU/mL in two of the filters. This indicates that the silver had some benefit to reducing bacterial contamination by the filter. In general these POU filters were found to be effective, but showed loss of effectiveness with time and indicated a release of microbes into subsequent volumes of water passed through the system.
• Brown, Joe, and M. Sobsey. "Microbiological effectiveness of locally produced ceramic filters for drinking water treatment in Cambodia." Journal of water and health 8, no. 1 (2010): 1-10. Abstract:
  
  Low-cost options for the treatment of drinking water at the household level are being explored by the Cambodian government and non-governmental organizations (NGOs) working in Cambodia, where many lack access to improved drinking water sources and diarrhoeal diseases are the most prevalent cause of death in children under 5 years of age. The ceramic water purifier (CWP), a locally produced, low-cost ceramic filter, is now being implemented by several NGOs, and an estimated 100,000 + households in the country now use them for drinking water treatment.
  
  Two candidate filters were tested for the reduction of bacterial and viral surrogates for waterborne pathogens using representative Cambodian drinking water sources (rainwater and surface water) spiked with Escherichia coli and bacteriophage MS2. Results indicate that filters were capable of reducing key microbes in the laboratory with mean reductions of E. coli of approximately 99% and mean reduction of bacteriophages of 90–99% over >600 litres throughput. Increased effectiveness was not observed in filters with an AgNO3 amendment.
  
  At under US$10 per filter, locally produced ceramic filters may be a promising option for drinking water treatment and safe storage at the household level.
• Christensen, Frans M., Helinor J. Johnston, Vicki Stone, Robert J. Aitken, Steve Hankin, Sheona Peters, and Karin Aschberger. "Nano-silver–feasibility and challenges for human health risk assessment based on open literature." Nanotoxicology 4, no. 3 (2010): 284-295.
  Abstract:
  
  This study aims at investigating feasibility and challenges associated with conducting a human health risk assessment for nano-silver based on the open literature by following an approach similar to a classical regulatory risk assessment. Gaps in the available data set, both in relation to exposures and hazard, do not allow reaching any definite conclusions that could be used for regulatory decision making.
  
  Results show that repeated inhalation in the workplace and possibly consumer inhalation may cause risks. Also (uncontrolled) nano-silver drug intake and burn treatment of large parts of the body with wound dressings may cause risks. Main future work should focus on generating occupational and consumer exposure data, as well as toxicity data on absorption (are particles or only ions absorbed?), information on genetoxicity, and further information on the toxicity following inhalation exposure to sizes and agglomeration states as uncounted in the workplace.
• Drake, Pamela L., and Kyle J. Hazelwood. "Exposure-related health effects of silver and silver compounds: a review." Annals of Occupational Hygiene 49, no. 7 (2005): 575-585.
  Abstract:
  
  A critical review of studies examining exposures to the various forms of silver was conducted to determine if some silver species are more toxic than others. The impetus behind conducting this review is that several occupational exposure limits and guidelines exist for silver, but the values for each depend on the form of silver as well as the individual agency making the recommendations. For instance, the American Conference of Governmental Industrial Hygienists has established separate threshold limit values for metallic silver (0.1 mg/m3) and soluble compounds of silver (0.01 mg/m3).
  
  On the other hand, the permissible exposure limit (PEL) recommended by the Occupational Safety and Health Administration and the Mine Safety and Health Administration and the recommended exposure limit set by the National Institute for Occupational Safety and Health is 0.01 mg/m3 for all forms of silver. The adverse effects of chronic exposure to silver are a permanent bluish-gray discoloration of the skin (argyria) or eyes (argyrosis).
  
  Most studies discuss cases of argyria and argyrosis that have resulted primarily from exposure to the soluble forms of silver.
  
  Besides argyria and argyrosis, exposure to soluble silver compounds may produce other toxic effects, including liver and kidney damage, irritation of the eyes, skin, respiratory, and intestinal tract, and changes in blood cells. Metallic silver appears to pose minimal risk to health. The current occupational exposure limits do not reflect the apparent difference in toxicities between soluble and metallic silver; thus, many researchers have recommended that separate PELs be established.
• Fung, Man C., and Debra L. Bowen. "Silver products for medical indications: risk-benefit assessment." Clinical Toxicology 34, no. 1 (1996): 119-126.
  Abstract:
  
  Background: Legitimate medicinal use of silver-containing products has dramatically diminished over the last several decades. Recently, however, some manufacturers have begun to enthusiastically promote oral colloidal silver proteins as mineral supplements and for prevention and treatment of many diseases. Indiscriminate use of silver products can lead to toxicity such as argyria.
  
  Objective: To assist health care professionals in a risk versus benefit assessment of over-the-counter silver-containing products, we herein examine the following issues: historical uses, chemistry, pharmacology, clinical toxicology, case reports of adverse events in the literature, and the recent promotion of over-the-counter silver products. Other sources of silver exposure (including environmental and dietary) and EPA exposure staruiards are discussed.
  
  A list of currently available silver products is provided for easy reference and screening. Conclusions: We emphasize the lack of established effectiveness and potential toxicity of these products.
• Gaul, L. Edward, and A. H. Staud. "Clinical spectroscopy: seventy cases of generalized argyrosis following organic and colloidal silver medication, including a biospectrometric analysis of ten cases." Journal of the American Medical Association 104, no. 16 (1935): 1387-1390. Excerpt from Abstract
  
  The alarming increase of argyrosis leaves little doubt as to our purpose in this report. There has been an accumulation of indubitable clinical evidence which makes it imperative to present before those who prescribe, dispense or use these drugs the danger entailed therein.
  
  It must be emphasized that within the past year, following intranasal applications with Argyrol and Neo-Silvol in fifteen children under 10 years of age, an argyrosis developed. Ten of these fifteen children were girls. All these children will present throughout their lives a conspicuous and permanent bluish or slate-gray discoloration that will select them as objects of whispered comments by friends and strangers.
  
  At present there is no treatment for argyria.
  The obvious responsibility for this injudicious medication rests with the circularized advertisements by the various manufacturers to the physicians; for example, they say: Argyrol solution, in any strength, may be used in the throat, nose and ...
• Gulbranson, Scott H., Joseph A. Hud, and Ronald C. Hansen. "Argyria following the use of dietary supplements containing colloidal silver protein." CUTIS-NEW YORK- 66, no. 5 (2000): 373-378.
• Gupta, Amit. "Silver as a biocide: will resistance become a problem?." Nature Biotechnology 16 (1998): 888-888. Abstract:
  
  Human encounters with silver-containing products are surprisingly numerous worldwide1­3, primarily as a biocide or antimicrobial agent. In water usage, silver- and copper-based disinfectants are used in hospital and hotel distribution systems to control infectious agents (for example, Legionella).
  
  Silver, together with copper, is commonly used to inhibit bacterial and fungal growth in chicken farms and in postharvest cleaning of oysters. Silver is used to sterilize recycled water aboard the MIR space station and on the NASA space shuttle4. Popular home water purification units in the United States contain silverized activated carbon filters along with ion-exchange resins. In Mexico, Microdyn (colloidal silver in gelatin) is sold in supermarkets to disinfect salad vegetables and drinking water.
  
  A quick surf on the Internet shows that silver is offered by several companies in different forms, and marketed as a health food additive--"Nature's alternative to antibiotics"--although the US Food and Drug Administration (FDA; Rockville, MD) has proposed that over-the-counter drug products containing colloidal silver or silver salts are not generally recognized as safe or effective for internal or external use and are frequently misbranded.
• Hoburg, Albrecht, Heinz Hungerbach, and Werner Struzina. "Oral hygiene agent containing hydrogen peroxide stabilized by colloidal silver." U.S. Patent 5,437,858, issued August 1, 1995.
• Okan, Denis, Kevin Woo, and R. Gary Sibbald. "So what if you are blue? Oral colloidal silver and argyria are out: safe dressings are in." Advances in skin & wound care 20, no. 6 (2007): 326-330.
• Quackwatch comments on colloidal sliver: - This website offers authoritative references, government publications, studies, and more information about use of colloidal silver to treat drinking water.
  
  Colloidal silver is a suspension of submicroscopic metallic silver particles in a colloidal base. Long-term use of silver preparations can lead to argyria, a condition in which silver salts deposit in the skin, eyes, and internal organs, and the skin turns ashen-gray. Many cases of argyria occurred during the pre-antibiotic era when silver was a common ingredient in nosedrops.
  
  When the cause became apparent, doctors stopped recommending their use, and reputable manufacturers stopped producing them. The official drug guidebooks (United States Pharmacopeia and National Formulary) have not listed colloidal silver products since 1975. - Website: quackwatch.com/01QuackeryRelatedTopics/PhonyAds/silverad.html
• Ji, Jun Ho, Jae Hee Jung, Sang Soo Kim, Jin-Uk Yoon, Jung Duck Park, Byung Sun Choi, Yong Hyun Chung et al. "Twenty-eight-day inhalation toxicity study of silver nanoparticles in Sprague-Dawley rats." Inhalation toxicology 19, no. 10 (2007): 857-871. Abstract:
  
  The antibacterial effect of silver nanoparticles has resulted in their extensive application in health, electronic, and home products. Thus, the exposed population continues to increase as the applications expand. Although previous studies on silver dust, fumes, and silver compounds have revealed some insights, little is yet known about the toxicity of nano-sized silver particles, where the size and surface area are recognized as important determinants for toxicity. T
  
  hus, the inhalation toxicity of silver nanoparticles is of particular concern to ensure the health of workers and consumers. However, the dispersion of inhalable ambient nano-sized particles has been an obstacle in evaluating the effect of the inhalation of nano-sized particles on the respiratory system.
  
  Accordingly, the present study used a device that generates silver nanoparticles by evaporation/condensation using a small ceramic heater. As such, the generator was able to distribute the desired concentrations of silver nanoparticles to chambers containing experimental animals. The concentrations and distribution of the nanoparticles with respect to size were also measured directly using a differential mobility analyzer and ultrafine condensation particle counter.
• Kim, Jin Sik, Kyung Seuk Song, Jae Hyuck Sung, Hyun Ryol Ryu, Byung Gil Choi, Hyun Sun Cho, Jin Kyu Lee, and Il Je Yu. "Genotoxicity, acute oral and dermal toxicity, eye and dermal irritation and corrosion and skin sensitisation evaluation of silver nanoparticles." Nanotoxicology 7, no. 5 (2013): 953-960.
  Abstract:
  
  To clarify the health risks related to silver nanoparticles (Ag-NPs), we evaluated the genotoxicity, acute oral and dermal toxicity, eye irritation, dermal irritation and corrosion and skin sensitisation of commercially manufactured Ag-NPs according to the OECD test guidelines and GLP. The Ag-NPs were not found to induce genotoxicity in a bacterial reverse mutation test and chromosomal aberration test, although some cytotoxicity was observed.
  
  In acute oral and dermal toxicity tests using rats, none of the rats showed any abnormal signs or mortality at a dose level of ∼ 2000 mg/kg. Similarly, acute eye and dermal irritation and corrosion tests using rabbits revealed no significant clinical signs or mortality and no acute irritation or corrosion reaction for the eyes and skin. In a skin sensitisation test using guinea pigs, one animal (1/20) showed discrete or patchy erythema, thus Ag-NPs can be classified as a weak skin sensitiser.
• Silver, Simon. "Bacterial silver resistance: molecular biology and uses and misuses of silver compounds." FEMS microbiology reviews 27, no. 2‐3 (2003): 341-353.
  Abstract:
  
  Resistance to silver compounds as determined by bacterial plasmids and genes has been defined by molecular genetics. Silver resistance conferred by the Salmonella plasmid pMGH100 involves nine genes in three transcription units. A sensor/responder (SilRS) two-component transcriptional regulatory system governs synthesis of a periplasmic Ag(I)-binding protein (SilE) and two efflux pumps (a P-type ATPase (SilP) plus a three-protein chemiosmotic RND Ag(I)/H+ exchange system (SilCBA)). The same genes were identified on five of 19 additional IncH incompatibility class plasmids but thus far not on other plasmids.
  
  Of 70 random enteric isolates from a local hospital, isolates from catheters and other Ag-exposed sites, and total genomes of enteric bacteria, 10 have recognizable sil genes. The centrally located six genes are found and functional in the chromosome of Escherichia coli K-12, and also occur on the genome of E. coli O157:H7. The use of molecular epidemiological tools will establish the range and diversity of such resistance systems in clinical and non-clinical sources.
  
  Silver compounds are used widely as effective antimicrobial agents to combat pathogens (bacteria, viruses and eukaryotic microorganisms) in the clinic and for public health hygiene. Silver cations (Ag+) are microcidal at low concentrations and used to treat burns, wounds and ulcers. Ag is used to coat catheters to retard microbial biofilm development. Ag is used in hygiene products including face creams, ‘alternative medicine’ health supplements, supermarket products for washing vegetables, and water filtration cartridges.
  
  Ag is generally without adverse effects for humans, and argyria (irreversible discoloration of the skin resulting from subepithelial silver deposits) is rare and mostly of cosmetic concern.
  
  [Really? Perhaps the authors should take a look at and comment on some of the research that reaches a different conclusion (e.g. Gaul - 1935 and Drake 2005) - Ed. ]


• Lantagne, Daniele S., and Alethia Environmental. "Investigation of the potters for peace colloidal silver impregnated ceramic filter." Report 1 (2001): 79. details are at
  • Lantagne, Daniel S. et als, "Investigation of the Potters for Peace Colloidal Silver Impregnated Ceramic Filter - Report 1: Intrinsic Effectiveness", Daniele S. Lantagne, Alethia Environmental, Allston, MA, Submitted to Jubilee House Community, December 21, 2001, USAID Purchase Order Number: 524-0-00-01-00014-5362 . Quoting from one of the conclusion in that study, p. 58:
    Based on the results of the microbiological challenges detailed above, the following conclusions are presented:
    
    1. Some small bacteria, which are potentially a human health concern, pass through the filter when tested in the laboratory at CIRA-UNAN.
    
    2. This summary of the historical data clearly shows that many different filter designs over the years remove 98-100 percent of the indicator bacteria present in the source water.
    
    3. Studies of filters that are two and seven years old indicate that the filters still effectively remove microbiological contaminants. This indicates that the colloidal silver does not ‘wear out’, and that with proper maintenance, there seems to be no need to reapply silver to the filter. Currently, the PFP recommendation is to reapply the colloidal silver once per year to the filter. This does not seem to be necessary based on the laboratory data. However, reapplication of colloidal silver provides a safety factor in the field that should not be removed without more extensive testing.
• Lansdown, Alan. "Silver in health care: antimicrobial effects and safety in use." (2006): 17-34.
• Maneewattanapinyo, Pattwat, Wijit Banlunara, Chuchaat Thammacharoen, Sanong Ekgasit, and Theerayuth Kaewamatawong. "An evaluation of acute toxicity of colloidal silver nanoparticles." J Vet Med Sci 73, no. 11 (2011): 1417-23. Abstract:
  
  Tests for acute oral toxicity, eye irrita tion, corrosion and dermal toxicity of co lloidal silver nanoparticles (AgNPs) were c on- ducted in laboratory animals following OECD guidelines. Oral administration of AgNP s at a limited dose of 5,000 mg/kg produced nei- ther mortality nor acute toxic signs throughout the observation period. Percentage of body weight gain of the mice showed no s ignificant difference between control and treatment groups. In the hemato logical analysis, there was no significant difference between mi ce treated with AgNPs and controls. Blood chemistry an alysis also showed no differences in any of the parameter examined.
  
  There was neither any gross lesion nor histopat hological change observed in various organs.
  
  The results indicated that the LD 50 of colloidal AgNPs is greater than 5,000 mg/kg body weight. In acute eye irritation and corrosion study, no mortality and toxic signs were observed when various doses of colloidal AgNPs were instilled in guinea pig eyes during 72 hr observation peri od. However, the instillation of AgNPs at 5,000 ppm produced transient eye irrita tion during early 24 hr observa tion time. No any gross abnormality was noted in the skins of the guinea pigs exposed to various doses of colloidal AgNPs. In addition, no signifi cant AgNPs exposure relating to dermal tis sue changes was observed microscopically.
  
  In summary, these findings of all toxicity test s in this study suggest that colloidal Ag NPs could be relatively safe when administered to oral, eye and skin of the animal models for short periods of time. KEY WORDS : acute toxicity, colloidal silver nanoparticles, dermal, eye, oral
• Mirsattari, S. M., R. R. Hammond, M. D. Sharpe, F. Y. Leung, and G. B. Young. "Myoclonic status epilepticus following repeated oral ingestion of colloidal silver." Neurology 62, no. 8 (2004): 1408-1410. Abstract
  The authors report a case of a 71-year-old man who developed myoclonic status epilepticus and coma after daily ingestion of colloidal silver for 4 months resulting in high levels of silver in plasma, erythrocytes, and CSF. Despite plasmapheresis, he remained in a persistent vegetative state until his death 5.5 months later. Silver products can cause irreversible neurologic toxicity associated with poor outcome.
• Oyanedel-Craver, Vinka A., and James A. Smith. "Sustainable colloidal-silver-impregnated ceramic filter for point-of-use water treatment." Environmental science & technology 42, no. 3 (2007): 927-933. Abstract:
  
  Cylindrical colloidal-silver-impregnated ceramic filters for household (point-of-use) water treatment were manufactured and tested for performance in the laboratory with respect to flow rate and bacteria transport. Filters were manufactured by combining clay-rich soil with water, grog (previously fired clay), and flour, pressing them into cylinders, and firing them at 900 °C for 8 h.
  
  The pore-size distribution of the resulting ceramic filters was quantified by mercury porosimetry. Colloidal silver was applied to filters in different quantities and ways (dipping and painting). Filters were also tested without any colloidal-silver application. Hydraulic conductivity of the filters was quantified using changing-head permeability tests. [3H]H2O water was used as a conservative tracer to quantify advection velocities and the coefficient of hydrodynamic dispersion. Escherichia coli (E. coli) was used to quantify bacterial transport through the filters.
  
  Hydraulic conductivity and pore-size distribution varied with filter composition; hydraulic conductivities were on the order of 10−5 cm/s and more than 50% of the pores for each filter had diameters ranging from 0.02 to 15 µm. The filters removed between 97.8% and 100% of the applied bacteria; colloidal-silver treatments improved filter performance, presumably by deactivation of bacteria.
  
  The quantity of colloidal silver applied per filter was more important to bacteria removal than the method of application. Silver concentrations in effluent filter water were initially greater than 0.1 mg/L, but dropped below this value after 200 min of continuous operation.
  
  These results indicate that colloidal-silver-impregnated ceramic filters, which can be made using primarily local materials and labor, show promise as an effective and sustainable point-of-use water treatment technology for the world’s poorest communities.
• Panyala, Nagender Reddy, Eladia María Peña-Méndez, and Josef Havel. "Silver or silver nanoparticles: a hazardous threat to the environment and human health." J Appl Biomed 6, no. 3 (2008): 117-29. Abstract:
  
  Nanotechnology is a rapidly growing science of produci ng and utilizing nano-sized particles that measure in nanometers. These nanomaterials are already having an impact on health care. Now-a-days we are using nanoproducts in various fields. Of these, silver na noparticles are playing a major role in the field of nanotechnology and nanomedicine. Their unique size-dependent properties make these ma terials superior and indispensable as they show unusual physical, chemical and biological properties.
  
  Silver nanoparticles have potential antimicrobial activity towards many pathogenic microbes. Along with th is antimicrobial activity, silver nanoparticles are showing unacceptable toxic effects on human health and the environment. The chronic exposure to silver causes adverse effects such as permanent bluish-grey disc oloration of the skin (argyria) and eyes (argyrosis).
  
  Besides argyria and argyrosis, exposure to soluble silver compounds may produce other toxic effects like liver and kidney damage, irritation of the eyes, skin, respiratory and intestinal tract and changes to blood cells. This review summarizes the hazardous effects of silver nanoparticles in the environment and theirs toxic effects on human health.
• Petrus, E. M., S. Tinakumari, L. C. Chai, A. Ubong, R. Tunung, N. Elexson, L. F. Chai, and R. Son. "A study on the minimum inhibitory concentration and minimum bactericidal concentration of nano colloidal silver on food-borne pathogens." Int Food Res J 18, no. 1 (2011): 55-66.
  Abstract:
  
  In the emerging issue of increased multi-resistant properties in foodborne pathogens, silver nano particles are being used increasingly as antimicrobial agents. Thus, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Nano Colloidal Silver towards food-borne pathogens such as Escherichia coli O157:H7, Listeria monocytogenes , Salmonella enterica Serovar Typhi, Vibrio cholerae , Vibrio parahaemolyticus , Bacillus cereus and Staphylococcus aureus were examined in this study.
  
  The results obtained suggested that Nano Colloidal Silver exhibit a good bacteriostatic effect but poor bactericidal effect towards all food-borne pathogens tested. Nano Colloidal Silver can be a potential antimicrobial agent due to its low cost of production and high effectiveness in antimicrobial properties, which may find wide applications in various food industries to address food safety issues.
• Quadros, Marina E., and Linsey C. Marr. "Environmental and human health risks of aerosolized silver nanoparticles." Journal of the Air & Waste Management Association 60, no. 7 (2010): 770-781.
  Abstract:
  
  Silver nanoparticles (AgNPs) are gaining attention from the academic and regulatory communities, not only because of their antimicrobial effects and subsequent product applications, but also because of their potential health and environmental risks. Whereas AgNPs in the aqueous phase are under intensive study, those in the atmosphere have been largely overlooked, although it is well established that inhalation of nanoparticles is associated with adverse health effects.
  
  This review summarizes the present state of knowledge concerning airborne AgNPs to shed light on the possible environmental exposure scenarios that may accompany the production and popularization of silver nanotechnology consumer products. The current understanding of the toxicity of AgNPs points toward a potential threat via the inhalation exposure route.
  
  Nano-particle size, chemical composition, crystal structure, surface area, and the rate of silver ion release are expected to be important variables in determining toxicity. Possible routes of aerosolization of AgNPs from the production, use, and disposal of existing consumer products are presented. It is estimated that approximately 14% of silver nanotechnology products that have been inventoried could potentially release silver particles into the air during use, whether through spraying, dry powder dispersion, or other methods. In laboratory and industrial settings, six methods of aerosolization have been used to produce airborne AgNPs: spray atomization, liquid-flame spray, thermal evaporation-condensation, chemical vaporization, dry powder dispersion, and manual handling.
  
  Fundamental uncertainties remain about the fate of AgNPs in the environment, their short- and long-term health effects, and the specific physical and chemical properties of airborne particles that are responsible for health effects. Thus, to better understand the risks associated with silver nanotechnology, it is vital to understand the conditions under which AgNPs could become airborne.
• Ruparelia, Jayesh P., Arup Kumar Chatterjee, Siddhartha P. Duttagupta, and Suparna Mukherji. "Strain specificity in antimicrobial activity of silver and copper nanoparticles." Acta Biomaterialia 4, no. 3 (2008): 707-716., Abstract:
  
  The antimicrobial properties of silver and copper nanoparticles were investigated using Escherichia coli (four strains), Bacillus subtilis and Staphylococcus aureus (three strains). The average sizes of the silver and copper nanoparticles were 3 nm and 9 nm, respectively, as determined through transmission electron microscopy.
  
  Energy-dispersive X-ray spectra of silver and copper nanoparticles revealed that while silver was in its pure form, an oxide layer existed on the copper nanoparticles. The bactericidal effect of silver and copper nanoparticles were compared based on diameter of inhibition zone in disk diffusion tests and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of nanoparticles dispersed in batch cultures.
  
  Bacterial sensitivity to nanoparticles was found to vary depending on the microbial species. Disk diffusion studies with E. coli and S. aureus revealed greater effectiveness of the silver nanoparticles compared to the copper nanoparticles. B. subtilis depicted the highest sensitivity to nanoparticles compared to the other strains and was more adversely affected by the copper nanoparticles. Good correlation was observed between MIC and MBC (r2 = 0.98) measured in liquid cultures.
  
  For copper nanoparticles a good negative correlation was observed between the inhibition zone observed in disk diffusion test and MIC/MBC determined based on liquid cultures with the various strains (r2 = −0.75). Although strain-specific variation in MIC/MBC was negligible for S. aureus, some strain-specific variation was observed for E. coli.
• Sutherland, W. S., J. J. Laserna, M. J. Angebranndt, and J. D. Winefordner. "Surface-enhanced Raman analysis of sulfa drugs on colloidal silver dispersion." Analytical chemistry 62, no. 7 (1990): 689-693.
• Tien, Der-Chi, Kuo-Hsiung Tseng, Chih-Yu Liao, and Tsing-Tshih Tsung. "Colloidal silver fabrication using the spark discharge system and its antimicrobial effect on Staphylococcus aureus." Medical engineering & physics 30, no. 8 (2008): 948-952.
  Abstract:
  
  Nanoscale techniques for silver production may assist the resurgence of the medical use of silver, especially given that pathogens are showing increasing resistance to antibiotics. Traditional chemical synthesis methods for colloidal silver (CS) may lead to the presence of toxic chemical species or chemical residues, which may inhibit the effectiveness of CS as an antibacterial agent.
  
  To counter these problems a spark discharge system (SDS) was used to fabricate a suspension of colloidal silver in deionized water with no added chemical surfactants. SDS-CS contains both metallic silver nanoparticles (Ag0) and ionic silver forms (Ag+). The antimicrobial affect of SDS-CS on Staphylococcus aureus was studied.
  
  The results show that CS solutions with an ionic silver concentration of 30 ppm or higher are strong enough to destroy S. aureus. In addition, it was found that a solution's antimicrobial potency is directly related to its level of silver ion concentration.
• Van Halem, D., H. Van der Laan, S. G. J. Heijman, J. C. Van Dijk, and G. L. Amy. "Assessing the sustainability of the silver-impregnated ceramic pot filter for low-cost household drinking water treatment." Physics and Chemistry of the Earth, Parts A/B/C 34, no. 1 (2009): 36-42. Abstract:
  A low-cost technology to treat water at the household level is the ceramic silver-impregnated pot filter (CSF). The CSF consists of a pot-shaped filter element that is placed in a plastic receptacle. The ceramic pot filter is a promising treatment system to supply safe drinking water especially to people living in rural areas. The focus of this study was to assess the sustainability of a household drinking water treatment system based on five criteria: (i) accessibility, (ii) water quality, (iii) water production, (iv) functionality, and (v) environmental footprint.
  
  The removal of Escherichia coli and protozoan (oo)cysts was found to be significant, which was supported by the reduction in diarrhoea cases observed by CSF users in a recent field study. The retention of MS2 bacteriophages as an indicator for virus removal was, however, found to be unsatisfactory. It is therefore recommended that research on virus removal by CSF continues, especially in relation to the colloidal silver application and other potential additives.
  
  The criterion of water production was shown to be the limiting factor, because it reduced substantially during treatment of surface water. The fast clogging of the CSF during the first hours of use was caused neither by inorganic nor organic fouling, but by colloidal particles. Two direct effects may be identified from the decreasing flow rate: frequent scrubbing and higher water prices.
  
  Frequent scrubbing results in a higher risk of recontamination and breakage. Based on this finding the authors recommend an optimization study to increase the initial flow rate without sacrificing the removal efficiency.
• Vlachou, Evangelia, Elizabeth Chipp, Elizabeth Shale, Yvonne T. Wilson, Remo Papini, and Naiem S. Moiemen. "The safety of nanocrystalline silver dressings on burns: A study of systemic silver absorption." Burns 33, no. 8 (2007): 979-985.
• Wikipedia on use of colloidal silver 07/24/2010: (quoting / paraphrasing) - see http://en.wikipedia.org/wiki/Colloidal_silver
  
  True colloidal silver is a liquid suspension of microscopic particles of silver. The commercial alternative medicine product, also referred to as "colloidal silver", includes solutions that contain various concentrations of ionic silver compounds, silver colloids or silver compounds bound to proteins in water. Such products with concentrations of 30 parts per million (ppm) or less are typically manufactured using an electrolysis process, whereas those with higher concentrations of 50 ppm or more are usually silver compounds that have been bound with a protein.
  
  These solutions are currently marketed for internal and external use as an alternative medical remedy though there is no scientific evidence to support its effectiveness in vivo.[1] Excessive ingestion of colloidal silver can result in argyria, a condition in which the skin irreversibly turns blue or grey.
• Zahariev, Nikolay, Velichka Andonova, Dimitar Penkov, and Margarita Kassarova. "SILVER NANOPARTICLES: MORPHOLOGY, ADMINISTRATION AND HEALTH RISKS."
  Abstract:
  
  In recent decades, the applying of nano- and micro- carriers in the pharmaceutical technology is growing rapidly. They are used to protect the drug from the harmful effects of the environment, to increase the rate and extent of dissolution and thus they improve its bioavailability or provide controlled release of the drug substance for a period of time, at the desired location. A number of metallic, polymeric or inorganic derivatives are used to obtain the nanocarriers.
  
  Silver nanoparticles (Ag-NPs), with their antifungal, antibacterial and antiseptic properties, are of particular interest to the pharmaceutical industry.
  
  Several studies show that in addition to their beneficial effects on the human body, they can also cause side and toxic effects. The severity of these conditions is most often associated with the path of introduction of the Ag-NPs, their morphology, the dose and duration of the treatment. It is also of great significance the effect of such a production on the environment. The aim of this review is to evaluate the benefit – risk ratio of the use of Ag-NPs in the pharmaceutical practice.

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