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Though the photocatalytic properties of Titanium Dioxide has been known for many years, it wasn't until NASA helped develop it for use on the International Space Station as an air purification system that it became somewhat viable, though expensive.  Pure-Light Technologies has taken the NASA technology and improved upon it in several ways, and in the process reduced it's cost to consumers.  
 

THE SCIENCE

The unique action of the PURE-LIGHT TECHNOLOGIES light bulb is that it uses light in a photocatalytic action to continuously create two special types of super oxygen molecules called Superoxide (0-2) and Hydroxyl ion radical (HO) that kill bacteria, viruses, mold, and also break down toxic VOC pollutants. The air that we breathe is full of these bacteria, viruses, mold, toxic pollutants (called VOC--Volatile Organic Compounds like Carbon Monoxide, Benzine, Formaldahyde...)  especially in enclosed areas like hospitals, schools, businesses, and homes looking for a place to land and grow.  As air comes near the PURE-LIGHT coated light bulbs it gets cleansed of these bacteria, viruses, mold, and pollutants. The air also gets deoderized as well.  There is also a secondary PURE-LIGHT effect on the surfaces of items near the light bulb, such as kitchen/bathroom counters, dishes, stoves, cutting boards, door knobs, etc.

  • The unique photocatalytic phenomenon or action was discovered in 1967.
  • The well known PHOTOCATALYTIC ACTION of TiO2 is such that when light hits it, it produces a special type of excited electron. This excited electron, when it comes into contact with a water molecule, changes the water molecule (H20) into a couple of types of special super oxygen molecules called SUPEROXIDE (O-2) and HYDROXYL ION (HO). These two super oxygen molecules provide a triple "action"... two actions against viruses and bacterias, and another "action" against VOCs.
  • SUPEROXIDE (O-2), or super oxygen (also called hyperoxide), is actually produced in the human body in large quantities by Phagocytes (White blood cells)  and is used by the immune system to kill invading microorganisms.

    Superoxide (O-2) inside the body, or in the air, combines with a microorganism giving it essentially a boost of oxygen. Good cells thrive with the extra oxygen while viruses and bacteria are killed by the extra oxygen.

    Superoxides are also used in firefighterers' oxygen tanks and divers rebreather systems in order to provide a readily available source of oxygen.

    The HYDROXYL ION radical (HO) is often referred to as the "detergent" of the atmosphere because it reacts with many pollutants called VOCs (Volatile Organic Compounds), often acting as the first step to their removal.

    Hydroxyl radicals also attack the porous cell walls of bacteria and viruses which destroys them through the process known as cell lysing. Human, animal and plant cells are “designed” to be in the sunlight and have cell walls that are less porous and are not harmed by atmospheric hydroxyl radicals.

WHAT MAKES PURE-LIGHT BULBS UNIQUE

Though the properties of TiO2 are well documented, there have been problems in the past with applications:

* The first problem is that the photocatalytic process of TiO2 works well with sunlight or high power UV lights but not with ordinary light. PURE-LIGHT overcomes this by using a newly developed proprietary enhanced TiO2 formulation (Z-TiO2) that works extremely well with ordinary light. PURE-LIGHT TECHNOLOGIES has the exclusive rights to use this new formulation on light bulbs.

* The second problem is getting the TiO2 to "stick" to a surface longer than a few weeks or months. That is why other companies have tried to do it, but it has not worked very well for them. PURE-LIGHT has developed a new patent pending process that can "seal" the TiO2 to the surface of a light for up to 10 years. Since PURE-LIGHT developed it, no one else has it.

THE STUDIES

Below are a number of studies that delve into the properties and uses of titanium dioxide nanoparticles.

International Journal of Photoenergy Volume 2010 (2010), Article ID 764870, 11 pages

Develop Methods To Assess And Improve Poultry And Egg Quality

Studies of photokilling of bacteria using titanium dioxide nanoparticles

Technology For Growing Plants In Space Leads To Device That Destroys Pathogens, Like Anthrax

UCL scientists develop novel approaches for killing MRSA and E.coli

Titanium Dioxide: Toxic or Safe?

 

International Journal of Photoenergy Volume 2010 (2010), Article ID 764870, 11 pages http://dx.doi.org/10.1155/2010/764870
Applications of Photocatalytic Disinfection Using Titanium Dioxide

Department of Chemical and Biological Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, ON, K1N6N5, Canada

28 June 2010; Accepted 11 August 2010

Academic Editor: Detlef W. Bahnemann
This is an open access article distributed under theCreative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Due to the superior ability of photocatalysis to inactivate a wide range of harmful microorganisms, it is being examined as a viable alternative to traditional disinfection methods such as chlorination, which can produce harmful byproducts. Photocatalysis is a versatile and effective process that can be adapted for use in many applications for disinfection in both air and water matrices. Additionally, photocatalytic surfaces are being developed and tested for use in the context of “self-disinfecting” materials. Studies on the photocatalytic technique for disinfection demonstrate this process to have potential for widespread applications in indoor air and environmental health, biological, and medical applications, laboratory and hospital applications, pharmaceutical and food industry, plant protection applications, wastewater and effluents treatment, and drinking water disinfection. Studies on photocatalytic disinfection using a variety of techniques and test organisms are reviewed, with an emphasis on the end-use application of developed technologies and methods.

1. Introduction

Applications of photocatalytic processes are widely recognized as viable solutions to environmental problems [13]. Disinfection of bacteria is of particular importance, because traditional methods such as chlorination are chemical intensive and have many associated disadvantages. For example, in water treatment applications, chlorine used for disinfection can react with organic material to generate chloro-organic compounds that are highly carcinogenic [45]. Furthermore, some pathogens such as viruses, certain bacteria such as Legionella, and protozoans such as Cryptosporidium and Giardia lamblia cysts have been known to be resistant to chlorine disinfection [67]. Other treatment alternatives such as ozonation and irradiation using germicidal lamps (254 nm) have their own problems and limitations, such as the lack of residual effect [8] and generation of small colony variants [9] for the latter and production of toxic disinfection byproducts for the former [10].

In comparison, the  semiconductor commonly used in photocatalytic processes is nontoxic, chemically stable, available at a reasonable cost, and capable of repeated use without substantial loss of catalytic ability [11]. Heterogeneous photocatalysis using titanium dioxide is a safe, nonhazardous, and ecofriendly process which does not produce any harmful byproducts. Extensive research in this field has been done in the area of photocatalytic removal of organic, inorganic, and microbial pollutants [1213].

The mechanism of bactericidal action of  photocatalysis, as reported by Sunada et al. is attributed to the combination of cell membrane damage and further oxidative attack of internal cellular components, ultimately resulting in cell death [14].

Since the breakthrough work of Matsunaga et al. in 1985 reporting the application of  photocatalysis for the destruction of Lactobacillus acidophilus, Saccharomyces cerevisiae, and Escherichia coli using platinum-loaded  [15], there has been much interest in the biological applications of this process. A very comprehensive review of the application of  photocatalysis for disinfection of water is given by Mccullagh et al. [16], with many others available in the literature [1721].

Research in the field of photocatalytic disinfection has been very diverse, with the /UV process being shown to successfully inactivate many microorganisms including bacteria such as E. coli [2224], L. acidophilus [15], Serratia domonas stutzeri [25], Bacillus pumilus [26], Streptococcus mutans [1], yeasts such asS. cerevisiae [15], algae such as Chlorella vulgaris [15], and viruses such as phage MS2 [152728], B. fragilis bacteriophage [1527], Poliovirus I [28], Cryptosporidium parvum [29], and Giardia intestinalis [30].

Research efforts are being made to improve the efficiency of the  catalyst by means of doping with various metals [3133] and nonmetals [3435]. Other parameters which can be varied in a photocatalytic process, such as the source of ultraviolet irradiation [18] and factors affecting process efficiency [36] have also been under investigation. Additionally, there are countless reactor designs and configurations [3738] used to exploit photocatalytic disinfection for a wide range of applications, as this process can be used in both water and air matrices [39]. The current review will focus on developments in photocatalytic disinfection for application in the following contexts: indoor air and environmental health, biological and medical applications, laboratory and hospital applications, pharmaceutical and food industry, plant protection applications, wastewater and effluents treatment, and finally, drinking water disinfection.

2. Indoor Air and Environmental Health

The photocatalytic process is well recognized for the removal of organic pollutants in the gaseous phase such as volatile organic compounds (VOCs), having great potential applications to contaminant control in indoor environments such as residences, office buildings, factories, aircrafts, and spacecrafts [4041].

To increase the scope of the photocatalytic process in application to indoor air, the disinfection capabilities of this technique are under investigation [39]. Disinfection is of importance in indoor air applications because of the risk of exposure to harmful airborne contaminants. Bioaerosols are a major contributor to indoor air pollution, and more than 60 bacteria, viruses, and fungi are documented as infectious airborne pathogens. Diseases transmitted via bioaerosols include tuberculosis, Legionaries, influenza, colds, mumps, measles, rubella, small pox, aspergillosis, pneumonia, meningitis, diphtheria, and scarlet fever [42]. Traditional technologies to clean indoor air include the use of activated charcoal filters, HEPA filters, ozonation, air ionization, and bioguard filters. None of these technologies is completely effective [20].

In the pioneering work by Goswami et al. [4344] investigating the disinfection of indoor air by photocatalysis, a recirculating duct facility was developed to inactivate biological contaminants in air with photocatalytic techniques. Experiments using Serratia Marcescens in air achieved a 100% destruction of microorganisms in a recirculating loop in 600 minutes [43]. This time was reduced to less than 3 minutes in later experiments [45].

Photocatalytic oxidation can also inactivate infectious microorganisms which can be airborne bioterrorism weapons, such as Bacillus anthracis (Anthrax) [4648]. A photocatalytic system was investigated by Knight in 2003 to reduce the spread of severe acute respiratory syndrome (SARS) on flights [49], following the outbreak of the disease. Similarly, in 2007 the avian influenza virus A/H5N2 was shown to be inactivated from the gaseous phase using a photocatalytic prototype system [39].

Inactivation of various gram-positive and gram-negative bacteria using visible light and a doped catalyst [50] and fluorescent light irradiation similar to that used in indoor environments was studied [51] and shows great promise for widespread applications.

It was also shown that E. coli could be completely mineralized on a  coated surface in air [42]. Carbon mass balance and kinetic data for complete oxidation of E. coli, A. niger, Micrococcus luteus, and B. subtilluscells and spores were subsequently presented [52]. A comprehensive mechanism and detailed description of the  photokilling of E. coli on coated surfaces in air has been extensively studied in order understand to a considerable degree and in a quantitative way the kinetics of E. coli immobilization and abatement using photocatalysis, using FTIR, AFM, and CFU as a function of time and peroxidation of the membrane cell walls [5357].

Novel photoreactors and photo-assisted catalytic systems for air disinfection applications such as those using polyester supports for the catalyst [58], carbon nanotubes [59], combination with other disinfection systems [60], membrane systems [61], use of silver bactericidal agents in cotton textiles [6264] for the abatement of E. coli in air, high surface area CuO catalysts [65], and structure silica surfaces [66] have also been reported.

In terms of environmental health, the antifungal capability of  photocatalysis against mold fungi on coated wood boards used in buildings was confirmed [67] using A. nigeras a test microbe, and UVA irradiation.

3. Biological and Medical Applications

Due to the disinfection abilities of photocatalytic processes, they are being explored for use in medical applications. Studies have been done using  coatings on bioimplants to implement photocatalysis for antibacterial purposes [476869]. Shiraishi et al. explored the photocatalytic activity of S. aureus, a common pathogenic bacterium in implant-related infection, using  film on stainless steel and titanium substrates [70]. The bactericidal effect of the coating was confirmed upon UV irradiation, and the use of these coated photocatalytic substrates present a useful strategy for the control of such infections associated with biomedical implants.

Photocatalysis is also able to kill animal cells, such as in the antitumor activity shown using subcutaneous titania injection onto skin tumours followed by 40 minutes of UV illumination [71]. This procedure produced a tenfold tumour volume reduction after three weeks, where the catalyst and light alone control runs showed tumor increases in volume by factors of 30–50. The use of photocatalysis for cancer cell treatment has also been documented elsewhere [172].

As previously alluded to in air-disinfection strategies, photocatalysis can be employed to remove harmful airborne biological threats such as Anthrax [4873]. In this sense, it can be an effective technique for combating bioterror and preventing the spread of airborne biological threats.

4. Laboratory and Hospital Applications

Particularly in microbiological laboratories and in areas in intensive medical use, frequent and thorough disinfection of surfaces is needed in order to reduce the concentration of bacteria and to prevent bacterial transmission. Conventional methods of disinfection with wiping are not long-term effective, and are staff and time intensive. These methods also involve the use of harsh and aggressive chemicals. Disinfection with hard ultraviolet light (UVC) is usually unsatisfactory, since the depth of penetration is inadequate and there are occupational health risks [74].

Photocatalytic oxidation on surfaces coated with titanium dioxide offers an alternative to traditional methods of surface disinfection. Research has examined the biocidal activity of thin films of titania anchored to solid surfaces [7476]. The effectiveness of this process was demonstrated using bacteria relevant to hygiene such asE. coli, p. aeruginosa, S. aureus, and E. faecium [74]. The inactivation of E. coli (ATCC8739) cells deposited on membrane filters during irradiation with fluorescent light was also shown as an application of self-disinfecting surfaces [77].

 thin films deposited on stainless steel using a novel flame-assisted CVD technique were also tested for antimicrobial activity on E. coli [69]. There is a wider range of applications for this self-disinfecting material because of the desirable mechanical properties and resistance to corrosion of stainless steel. Transparent films on this substrate have also been shown to be effective for sterilization of B. pumilus [78]. In this study, the-coated stainless steel was shown to have a higher photocatalytic activity than the same coating on glass substrates.

Titania photocatalysts doped with CuO were coated on surfaces and evaluated for biocidal activity [79]. This investigation also explored the synergistic effect of photocatalysis and toxicity of copper to inactivate bacteriophage T4 and E. coli.

Enhanced photocatalysis using nitrogen-doped  was also reported for its visible light-induced bactericidal activity against human pathogens [80]. It was proposed in this study that photocatalytic disinfection using visible light can offer a means of continuous disinfection for surfaces constantly in contact with humans, such as door handles and push buttons. Visible light-induced inactivation of E. coli was also studied using titania codoped with nitrogen and sulfur [8184]. This introduces new disinfectant opportunities in public environments, such as public toilets, schools, hospitals, stations, airports, hotels, or public transportation, which are ideal places for the transmission of pathogens [8586].

Photocatalysis has also been investigated for the inactivation of prions, the infectious agents of a family of transmissible, fatal, neurodegenerative disorders affecting both humans and animals [87]. These prions may be transmitted via ingestion of contaminated food or during medical treatments with contaminated biological materials or surgical tools. The effectiveness of photocatalytic oxidation for inactivating these prions can help to reduce the risk of spread and demonstrates the practical applications of this technology for disinfection of contaminated surfaces and inanimate objects.

Another application of photocatalysis in a hospital setting is for the control of Legionnaire’s disease, which is associated to hot water distribution systems containing bacteria of the Legionella species [88]. In laboratory scale studies, it was shown that photocatalytic oxidation using /UV was able to mineralize the cells of four strains of L. pneumophilia serogroup 1 (strain 977, strain 1009, strain 1004, and ATCC 33153) upon prolonged treatment. This implies that the process used might be a viable alternative to the traditional disinfection processes used for the control of Legionella bacteria in hospital hot water systems, such as thermal eradication and hyperchlorination [89].

5. Pharmaceutical and Food Industry

Due to the antibacterial applications of -mediated photooxidation, this process shows promise for the elimination of microorganisms in areas where the use of chemical cleaning agents or biocides is ineffective or is restricted by regulations, for example in the pharmaceutical and food industries [33].  is nontoxic and has been approved by the American Food and Drug Administration for use in human food, drugs, cosmetics, and food contact materials [90].

 powder-coated packaging film was shown to inactivate E. coli (ATCC 11775) in vitro when irradiated with UVA light [90]. Actual tests on cut lettuce stored in a -coated film bag under such irradiation also showed this method to be effective for the reduction of E. coli colonies, indicating that the  coated film could reduce microbial contamination on the surfaces of solid food products and hence reduce the risk of microbial growth in food packaging.  photocatalysis has also shown to be effective for the inactivation of other foodborne bacteria such as Salmonella chloraesuis subsp., Vibrio parahaemolyticus, and Listeria monocytogenes [69].

Surface disinfection is also of importance to food processing, as foodborne infections can be caused by the proliferation and resistance to cleaning procedures of pathogenic germs on surfaces of the production equipment in such industries. Studies with E. coli strains (PHL 1273) [91] synthesizing curli, a type of appendage that allows the bacteria to stick to surfaces and form biofilms, were able to inactivate this organism using titania and various types of UV irradiation. In dark events studies, following the bacterial inactivation, no bacterial cultivability was recovered after 48 hours, indicating that the durability of the disinfection was adequate. Nitrogen doping of the titania photocatalyst was also reported in a separate study [92] with the use of visible light to inactivate E. coli and biofilm bacteria. Disinfection of E. coli using -containing paper and UV fluorescent irradiation has also been shown [93].

6. Plant Protection Applications

Photocatalytic disinfection is potentially very important in the control and inactivation of pathogenic species present in the nutritive solution in circulating hydroponic agricultures [94]. Many plant pathogens can be transmitted by irrigation and recycled waters used in hydroponic agriculture. Conventional bactericidal methods often apply chemical pesticides to disinfect these pathogens, but these are often harmful to animals, humans, and the environment due to their residual toxicity [95]. Photocatalytic disinfection of these plant pathogens using  may be used as a new tool for plant protection and an alternative to the use of harsh chemicals.

Using  thin film on a glass substrate and UVA irradiation, Enterobacter cloacae SM1 and Erwinia carotovora subsp. Caratovora ZL1, phytopathogenic enterobacteria that cause basal rot and soft rot in a variety of vegetable crops, were efficiently inactivated [95]. Subsequent studies investigated the effects of doping the titania catalyst with various photosensitive dyes using visible light irradiation [96]. It was shown that the disinfection of the phytopathogenic bacteria causing basal and soft rot could be efficiently carried out under visible light using these doped catalysts.

Solar photocatalytic disinfection using batch process reactors and titania photocatalysts was also shown to be effective for the disinfection of five wild strains of the Fusarium genus (F. equiseti, F. oxysporum, F. anthophilum, F. verticilloides, and F. solani), a common plant pathogen [97]. In this case, natural solar radiation was used and the photocatalytic solar disinfection was compared to solar-only disinfection for these fungi. The photocatalytic process was found to be faster than the solar-only disinfection in all trials.

The disinfecting ability of titania photocatalyst films was also tested on pathogens of mushroom diseases:Trichoderma harzianum, Cladobotryum varium, Spicellum roseum, and P. tolaasii. The disinfection of these species was confirmed by experiments conducted in mushroom growing rooms under black light irradiation, and subsequently, white light irradiation [98].

7. Wastewater and Effluents

The use of photocatalysis for water and wastewater treatment is a topic well documented in the literature, especially with respect to solar photocatalysis [172199102]. Due to the ability of photocatalysis to mineralize many organic pollutants, it has been used for remediation of contaminated groundwaters through the use of parabolic solar concentrating type reactors. Photocatalysis has been used in engineering scale for solar photocatalytic treatment of industrial nonbiodegradable persistent chlorinated water contaminants [21], and in field scale for treatment of effluents from a resins factory [103]. This process has also shown to be effective for treatment of wastewaters from a 5-fluororacil (a cancer drug) manufacturing plant [104], distillery wastewater [105], pulp and paper mill wastewater [106], dyehouse wastewater [17], and oilfield produced water [35].

However, the disinfection capabilities of photocatalytic processes have not thoroughly been exploited for treatment of wastewaters. Wastewater reclamation and reuse is of growing importance, especially in areas where the freshwater supply is limited, and so effective disinfection of wastewaters is necessary. Any technical means of sewage reuse is limited by persistent organic pollutants and microorganisms which are not removed by the conventional mechanical and biological treatment train [107]. Additional treatment is therefore necessary before any reuse can take place.

Early work on photocatalytic disinfection of municipal secondary wastewater effluents showed an inactivation of coliform bacteria and Poliovirus I using suspensions of titanium dioxide and fluorescent and sunlight irradiation, respectively [28].

Photocatalysis is also useful for disinfection of sewage containing organisms which are highly resistant to traditional disinfection methods, such as Cryptosporidium parvum [108] and noroviruses [109].

Municipal wastewater effluents from a sewage disposal plant in Hannover, Germany were treated in a slurry  reactor under UVA irradiation to simultaneously detoxify and disinfect the samples [110]. The photocatalytic treatment was able to diminish the concentration of dissolved organic pollutants (indicated by TOC and COD), and as well inactivate pathogenic microorganisms (indicated by E. coli). A similar result was obtained from studies monitoring Faecal streptococci and total coliforms using slurry  systems with UVA lamps and solar irradiation, respectively [111].

The investigation of bacterial consortia of E. coli and Enterococcus species present in real wastewaters from a biological wastewater treatment plant in Lausanne (Switzerland) [112] indicated that the Enterococcus species are less sensitive to photocatalytic treatment than coliforms and other gram-negative bacteria. Additionally, the effects of temperature, turbidity, and various other physical parameters of the samples on the photocatalytic inactivation of E. coli were investigated [113].

Further research investigates enhanced photocatalysis to improve the efficiency of disinfection of wastewaters for reuse, for example, by the use of titania-activated carbon catalyst mixtures [114], and through the development of nanocrystalline photocatalytic  membranes [115]. The latter is of particular importance in aeronautical applications, as it combines membrane separation technologies with advanced oxidation technologies to create photocatalytic composite membranes designed for the treatment and reuse of water on long-duration space missions [116].

An inexpensive approach to synthesizing a novel nitrogen-doped  photocatalyst has also been developed [117], improving the efficiency of visible light-induced disinfection of wastewaters, and introducing a new generation of catalysts for this application.

8. Drinking Water Disinfection

Titania photocatalysis has been proven to be effective in the removal of chemical compounds and microbiological pathogens from water. A thorough review by Mccullagh et al. [16] of the application of photocatalysis for the removal of biological species in this context examines studies on the disinfection effect of suspensions, effect of additives and pH, respectively, on the photocatalytic abilities and disinfection effect of  thin films, and the effect of electrochemically applied potential on the photobactericidal effect of thin films. The current discussion will focus on the various applications of photocatalytic drinking water disinfection.

8.1. Drinking Water Production in Developing Countries

In 2004, it was estimated that about 15% of the world’s population, mostly living in the less-favored regions of the planet, did not have access to enough fresh water to satisfy their daily needs, and this number was expected to double by 2015 [118]. This represents a serious public health issue since waterborne, water-washed, and water-based diseases are associated with lack of improvement in domestic water supply and adequate sanitation [119]. Development of low cost-effective methods for removal of pollutants from water supplies can help alleviate this problem. Especially in rural communities, water disinfection must have sufficiently low operational costs. Alternative technologies to traditional chlorination are now being considered for household use [120].

Solar disinfection (SODIS) is a simple technology that is capable of inactivating many waterborne pathogenic bacteria using the combined effect of solar UVA radiation and temperature [121124]. This method is low cost and does not produce toxic byproducts, however, limits the volume of water subject to treatment (typically 2L per exposed water bottle) and has a disadvantageous long time of process (typically 2 day exposure for complete inactivation) [119].

The combination of sunlight and photocatalyst is a promising option for water treatment in areas with insufficient infrastructure but high yearly sunshine. The use of compound parabolic reactors as an efficient technology to collect and focus diffuse and direct solar radiation onto a transparent pipe containing contaminated water has demonstrated feasibility to disinfect water using  suspensions [125127].

The European Union International Cooperation program (INCO) has sponsored initiatives for developing a solar photocatalysis-based cost-effective technology for water decontamination and disinfection in rural areas of developing countries, the SOLWATER and AQUACAT projects, respectively [94]. These projects are aimed at developing a solar reactor to decontaminate and disinfect small volumes of water, and field tests with the final prototypes were carried out to validate operation under real conditions [127].

The final SOLWATER prototype was composed of two tubes containing Alstrohm paper impregnated with titanium dioxide, and two tubes containing a supported photosensitizer [94]. These tubes are placed on a compound parabolic concentrating collector and run in series, where the electricity is provided by a solar panel (Figure 1).

Field tests using the SOLWATER prototype placed the reactor in the yard of a shanty house in Los Pereya, Tucuman, Argentina and studied the removal of bacterial contamination during three months of testing using natural water contaminated with coliforms, E. Faecalis, and P. aeruginosa, as well as high levels of natural organic matter and variable inorganic pollutants [127]. The SOLWATER reactor was shown to be effective for this application. Similar tests have been performed in photoreactors installed in various geographic regions, including Egypt, France, Greece, Mexico, Morocco, Peru, Spain, Switzerland, and Tunisia [94].

Other research in the field of potable water production in developing countries includes the development of affordable and efficient technology in the form of batch borosilicate glass and PET plastic SODIS reactors fitter with flexible plastic inserts coated with  powder [128]. These were shown to be 20 and 25% more effective, respectively, than SODIS alone for the inactivation of E. coli K12. This novel system was also able to reduce the concentration of Cryptosporidium parvum oocysts present [129]. It should be also noted that there has also been significant research done in the advance of solar disinfection of this highly resistant organism using SODIS alone [123130131].

8.2. Surface Water Treatment

While the majority of photocatalytic disinfection studies reported are carried out with distilled water or buffer solutions [16], there have been attempts to quantify the effects of the chemical constituents of natural surface waters on  photocatalysis [132133]. It has been shown, using surface water samples, that the presence of inorganic ions and humic acids decrease the photocatalytic disinfection rate of E. coli [133].

Other efforts have been made to evaluate photocatalysis applications using real waters [134138]. For example, the integration of  photocatalysis into traditional water treatment processes for the removal of organic matter, which has variable levels during the year, was studied in the UK using three surface water samples [136].

Natural water samples from the Cauca River in Cali, Columbia showed drastic E. coli culturable cell concentration increase 24 hours after stopping irradiation [135]. This was not observed for the control experiment using an E. coli suspension in distilled water. It was concluded that caution should be taken when making predictions based on simple models as they are not necessarily representative of natural crude water samples.

The effect of pH, inorganic ions, organic matter, and  on E. coli photocatalytic inactivation by  was studied by simulating natural and environmental conditions of these parameters using distilled and tap water samples [132]. The results of this study and others [133] confirmed that laboratory results using ultrapure water samples are not representative of the real application in natural waters.

In studies done on surface water samples by Ireland et al. [134], it was concluded that inorganic-radical scavengers can have a major negative impact on the efficacy of the photocatalytic process, and the presence of organic matter in the water samples also degrades the E. coli inactivation kinetics.

Using a field-scale compound parabolic collector at the Swiss Federal Institute of Technology (EPFL), in Lausanne, natural water from the Leman Lake was used to suspend E. coli in the presence of  and irradiation under solar conditions [126]. From studies on the postirradiation period, the effective disinfection time (EDT) was defined as the time necessary to avoid bacterial regrowth after 24 h (or 48 h) in the dark after stopping phototreatment. It was suggested that the EDT necessary be used as an indicator of the impact of the solar photocatalytic process on bacteria instead of the UV dose required to achieve a certain level of disinfection.

8.3. Eutrophic Water Treatment

Another application of photocatalytic disinfection is in the treatment of eutrophic water. Control of algal blooms in eutrophic water is important because toxic cyanobacterial blooms in drinking water supplies may cause human health problems [137]. Copper-based algaecides can be used to control these blooms, however this method introduces secondary environmental problems [138].

Photocatalytic inactivation of three species of algae: Anabaena, microcystis, and Melosira, was studied using  coated glass beads and UV-light irradiation [138]. Complete photocatalytic inactivation of Anabaena, microcystis, and Melosira was obtained in about 30 minutes, while the inactivation efficiency for Melosira was somewhat lower due to the inorganic siliceous wall surrounding the cells.

The floating -coated hollow glass beads were introduced into a mesocosm installed at the Nakdong River, Kimhae, Korea [138]. This mesocosm was a 25 m2 and 2 m deep semipermeable membrane. The concentrations of chlorophyll-a were measured for one month, and it was shown that more than 50% of the chlorophyll-a concentration could be reduced using photocatalysts and natural solar radiation. A picture of the experimental mesocosm is depicted in Figure 2.

764870.fig.002
Figure 2: Experimental mesocosm used in Nakdong River, Korea [138].
8.4. Groundwater Treatment

The ability of photocatalysis to break down and detoxify harmful organic chemicals has been exploited for groundwater treatment, as shown by engineering scale demonstrations using solar photocatalysis to remediate groundwater contaminated from leaking underground storage tanks [139].

The disinfecting abilities of photocatalytic processes for application to treating groundwater contaminated with microorganisms such as F. Solani [140] was also investigated and shown to be effective for the removal of such microorganisms. Natural well water containing the F. Solani species and solar illumination and employing CPCs was also explored as a process configuration for this application [141].

9. Conclusion

The photocatalytic technique is a versatile and efficient disinfection process capable of inactivating a wide range of harmful microorganisms in various media. It is a safe, nontoxic, and relatively inexpensive disinfection method whose adaptability allows it to be used for many purposes. Research in the field of photocatalytic disinfection is very diverse, covering a broad range of applications.

Particularly, the use of photocatalysis was shown to be effective for various air-cleaning applications to inactivate harmful airborne microbial pathogens, or to combat airborne bioterror threats, such as Anthrax. Photocatalytic thin films on various substrates were also shown to have potential application for “self-disinfecting” surfaces and materials, which can be used for medical implants, “self-disinfecting” surgical tools and surfaces in laboratory and hospital settings, and equipment in the pharmaceutical and food industries. Photocatalytic food packaging was shown to be a potential way to reduce the risk of foodborne illnesses in cut lettuce and other packaged foods. In terms of plant protection, photocatalysis is being investigated for use in hydroponic agricultures as an alternative to harsh pesticides. For water treatment applications, photocatalytic disinfection has been studied and implemented for drinking water production using novel reactors and solar irradiation. Eutrophic waters containing algal blooms were also shown to be effectively treated using -coated hollow beads and solar irradiation.

The effectiveness of photocatalytic disinfection for inactivating microorganisms of concern for each of these applications was presented, highlighting key studies and research efforts conducted. While the performance of this technology is still to be optimized for the specific applications, based on the literature presented, it is abundantly evident that photocatalysis should be considered as a viable alternative to traditional disinfection methods in some cases.

In a move towards a more environmentally friendly world, traditional solutions to classic problems, such as the production of safe drinking water, must shift towards more sustainable alternatives. Photocatalytic disinfection is not only a replacement technology for traditional methods in traditional applications, but also a novel approach for solving other disinfection problems, such as the control of bioterror threats. In this sense, the strength of photocatalytic disinfection lies in its versatility for use in many different applications.

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Location: Quality and Safety Assessment Research Unit

Title: Performance and mechanism of standard nano-TiO2(P-25) in photocatalytic disinfection of foodborne microorganisms - salmonella typhimurium and listeria monocytogenes

 

Authors 
item Long, Men -
item Wang, Jiamei -
item Zhuang, Hong
item Zhang, Yingyang -
item Wu, Haizhou -
item Zhang, Jianhao -

 

Submitted to: Food Control 
Publication Type: Peer Reviewed Journal 
Publication Acceptance Date: October 22, 2013 
Publication Date: November 17, 2013 
Citation: Long, M., Wang, J., Zhuang, H., Zhang, Y., Wu, H., Zhang, J. 2013. Performance and mechanism of standard nano-TiO2(P-25) in photocatalytic disinfection of foodborne microorganisms - salmonella typhimurium and listeria monocytogenes. Food Control. 39(2014):68-74.

 

Interpretive Summary: Salmonella and Listeria are commonly detected in both raw and ready-to-eat meat products, and are responsible for many outbreaks of foodborne diseases in the USA. Nano-TiO2 has been demonstrate to be very effective to inhibit microbial growth under UV light, and is considered as a novel material that can be used for eliminating microbial pathogens from food. The objective of this study was to investigate the antimicrobial effects of nano-TiO2 particles on bacterial pathogens, Salmonella typhimurium and Listeria Monocytogenes, which are commonly found on raw and/or cooked poultry meat products. Our results show that nano-TiO2 effectively reduced the populations of either of the pathogens under UV light. Its effectiveness could be affected by nano-TiO2 concentrations and the initial microbial populations. L. monocytogenes was more resistant to nano-TiO2 treatment than Salmonella. Electronic microscopic images showed that under UV light, nano-TiO2 resulted in damage of bacterial cell walls, release of cell components, and subsequently the cell death. These results demonstrate that we can use nano-TiO2 to treat food products and reduce the risk of foodborne diseases by reducing pathogen populations and/or inhibiting pathogen growth.

Technical Abstract: In this paper, effects of disinfection by nano-TiO2 were studied on the two typical foodborne microorganisms, Gram-negative bacterium Salmonella typhimurium and Gram-positive bacterium-Listeria monocytogenes, in meat products. The performance of nano-TiO2 against the foodborne pathogens was evaluated using a suspension system and the cellular mechanism was determined by images observed under an transmission electronic microscope. Results show that under UV light, nano-TiO2 disinfected both Gram-negative and Gram-positive pathogens very effectively in the suspension system under UV light. L. monocytogenes was more resistant to nano-TiO2 treatment than Salmonella under UV light. Nano-TiO2 concentrations and the initial bacteria populations in the suspensions had significant influences on the effectiveness of photocatalytic disinfection against the pathogen, S. typhimurium. The optimum concentration was between 0.2g/L and 1.5g/L. Increased initial S. typhimurium population (from 104 to 107 CFU/mL) resulted in reduced effectiveness of the photocatalytic disinfection by nano-TiO2. Electron microscope images revealed that nano-TiO2 photocatalytic disinfection started with damage of bacterial cell walls; then cell components released or defused out of the cells; and subsequently the cells completely lost their morphology (dissolved) and died. These results demonstrate that nano-TiO2 is very effective against pathogens that can grow well on meat products and the effectiveness can be significantly influenced by nano-TiO2 contents and pathogen populations. The findings in these experiments provide the essential information for further developing a nano-metal-based, antimicrobial packaging system to improve safety of meat products.


....
Studies of photokilling of bacteria using titanium dioxide nanoparticles.
Tsuang YH1, Sun JSHuang YCLu CHChang WHWang CC.
Author information
Abstract
Metal pins used to apply skeletal traction or external fixation devices protruding through skin are susceptible to the increased incidence of pin site infection. In this work, we tried to establish the photokilling effects of titanium dioxide (TiO2) nanoparticles on an orthopedic implant with an in vitro study. In these photocatalytic experiments, aqueous TiO2 was added to the tested microorganism. The time effect of TiO2 photoactivation was evaluated, and the loss of viability of five different bacteria suspensions (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus hirae, and Bacteroides fragilis) was examined by the viable count procedure. The bactericidal effect of TiO2 nanoparticle-coated metal plates was also tested. The ultraviolet (UV) dosage used in this experiment did not affect the viability of bacteria, and all bacteria survived well in the absence of TiO2 nanoparticles. The survival curve of microorganisms in the presence of TiO2 nanoparticles showed that nearly complete killing was achieved after 50 min of UV illumination. The formation of bacterial colonies above the TiO2 nanoparticle-coated metal plates also decreased significantly. In this study, we clearly demonstrated the bactericidal effects of titanium dioxide nanoparticles. In the presence of UV light, the titanium dioxide nanoparticles can be applicable to medical facilities where the potential for infection should be controlled.

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Technology For Growing Plants In Space Leads To Device Using TiO2 That Destroys Pathogens, Like Anthrax
 
April 5, 2002
 
NASA/Marshall Space Flight Center
 
Summary:
 
Building miniature greenhouses for experiments on the International Space Station has led to the invention of a device that annihilates anthrax -- a bacteria that can be deadly when inhaled.
"Space-based greenhouses may seem to have little to do with the war against terrorism," said Mark Nall, director of the Space Product Development Program at NASA's Marshall Space Flight Center in Huntsville, Ala. "Yet this invention shows how commercial space research can benefit people on Earth in unexpected ways."
The anthrax-killing air scrubber, AiroCide Ti02, is a tabletop-size metal box that bolts to office ceilings or walls. Its fans draw in airborne spores and airflow forces them through a maze of tubes. Inside, hydroxyl radicals (OH-) attack and kill pathogens. Most remaining spores are destroyed by high-energy ultraviolet photons.
"Spores that pass through the box aren't filtered -- they're fried," said John Hayman, president of KES Science & Technology Inc., the Kennesaw, Ga.-company that manufactures AiroCide Ti02. "That's appealing because you don't have to change an anthrax-laden air filter."
The technology to build the anthrax killer emerged from another product, Bio-KES, which is used by grocers and florists to remove ethylene and thus extend the life of vegetables, fruits and flowers. Ethylene (C2H4) is a gas released by the leaves of growing plants -- but too much of it can build up in an enclosed plant growth chamber or produce storage facility.
Too much ethylene causes plants to mature too quickly, fruit to ripen prematurely, and it even accelerates decay. This hinders researchers' efforts to harvest healthy plants grown in space and would also be undesirable when space travelers build larger space-based greenhouses for growing fresh food.
The research that led to the invention of Bio-KES started with a crucial discovery made in the early 90's by scientists at the Wisconsin Center for Space Automation and Robotics - a NASA Commercial Space Center at the University of Wisconsin-Madison. These scientists collaborated on the discovery with Dr. Marc Anderson, a professor and chemist who also works at the university.
The research team found that ultra-thin layers of titanium dioxide (TiO2) exposed to ultraviolet light converted ethylene into carbon dioxide (CO2) and water (H2O) -- substances that are good for plants. Subsequently, they developed a coating technology that applies TiO2 layers to the surfaces of many materials.
The Wisconsin Center for Space Automation and Robotics, which specializes in developing robotics/automation technologies for agriculture and biotechnology research in space, used the TiO2 coating technology to design an ethylene scrubber. This first-generation ethylene scrubber was used effectively inside the ASTROCULTURE™ plant growth unit, which grew potato plants during Space Shuttle mission STS-73 in 1995. Over the years, scientists refined the ethylene scrubber, and currently, the third-generation scrubber is being used successfully inside the ADVANCED ASTROCULTURE™ for plant experiments on the International Space Station.
This Space Station experiment and the Wisconsin Center for Space Automation and Robotics are part of NASA's Space Product Development Program, which encourages the commercialization of space by industry. There are 17 Commercial Space Centers across America, each specializing in a variety of areas such as agriculture, materials and biotechnology.
"Through our program, companies invest resources to do experiments in space that can benefit their businesses," said Nall. "This results in new and improved products and services for the American public."
Commercial Space Centers and their industry partners also explore how technologies, like the ethylene scrubber, created to conduct space-based research can be used for a variety of purposes, like killing anthrax, on Earth.
The first product the company developed for Earth-use was the Bio-KES -- used to remove ethylene in the air of produce and floral storage rooms and warehouses, thus increasing the shelf life of flowers, fruits and vegetables. The device, nominated as Discover Magazine's Product of the Year in 1998, is used across the globe by grocers, warehouse owners, and florists.
"Our tests showed that Bio-KES not only removed ethylene, but also killed airborne dust mites," said Hayman.
When the ultraviolet light strikes the TiO2 tubes inside Bio-KES, it creates positive and negative electrical charges. These charges tear apart nearby water molecules (H2O) and produce hydroxyl radicals (OH-).
"This hydroxyl by-product disrupts organic molecules and is thus deadly to dust mites, anthrax and many other pathogens," said Hayman. "We put higher-powered ultraviolet lamps in the AiroCide TiO2, so more hydroxyl radicals are produced, giving it an extra kick."
Scientists at the University of Wisconsin tested the AiroCide TiO2 with a non-virulent cousin of anthrax. During a typical experiment, a cloud of approximately 1,000 spores was sucked into the chamber and only 100 or so spores emerged. Spores spend at least 5 to 10 seconds traveling through the device's jumbled tubes and often(More)become trapped by turbulent airflow. They linger and are attacked by the hydroxyl radicals, or are zapped by the germ-killing ultraviolet light.
"The longer pathogens stay inside, the more likely they are to die," said Hayman. "Tests showed that as many as 93 percent of anthrax spores that enter the device are destroyed. Survivors are usually drawn back in on later passes through the reactor bed and are killed."
NASA has scheduled several more commercial experiments for upcoming Space Station expeditions. To learn more about Space Station experiments and science operations, visit:
Story Source:
The above story is based on materials provided by NASA/Marshall Space Flight CenterNote: Materials may be edited for content and length.

NASA/Marshall Space Flight Center. "Technology For Growing Plants In Space Leads To Device That Destroys Pathogens, Like Anthrax." ScienceDaily. ScienceDaily, 5 April 2002. .
 

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New research from the UCL Eastman Dental Institute and UCL Chemistry, presented at the spring conference of the Society for General Microbiology (SGM), has provided a potential drug for MRSA treatment and a new antibacterial coating using Titanium Dioxide which will help fight hospital-acquired infections.

Targeting MRSA

Research led by Dr Sean Nair and Professor Michael Wilson, and conducted by research technician Linda Dekker from the UCL Eastman Dental Institute has resulted in the development of a light-activated drug that could be used in the treatment of infections caused by the hospital bug MRSA.  
Researchers attached an antimicrobial drug, which is activated by light, to a peptide (a protein fragment) that binds onto a molecule on the surface of the superbug bacteria. Such light-activated antimicrobial agents produce free radicals and an unstable form of oxygen when they are exposed to light at the right wavelength. The release of these free radicals damages and ultimately kills bacteria.   
To improve the effectiveness of treatment and avoid damage to human cells, the drug was targeted to MRSA by attaching it to a peptide that binds to a molecular receptor on the bacterium's surface.
99.97% of 10 million MRSA cells were killed using this new combination, which was 1,000 times more effective at killing MRSA compared to the commercially available SnCe6 when the same quantity is used. 
Dr Sean Nair commented: “The new drug also has the potential to prevent bacteria from producing tissue-damaging toxins and given its mechanism of killing, it is also very unlikely that bacteria can develop resistance to this treatment.”
Linda Dekker said: “The results from laboratory studies are very encouraging and indicate that this technique might be effective at treating topical infections such as wound and burn infections. 
“This work will require in vivo trials (outside the laboratory) before it can be used. Due to the growing resistance of many organisms to antibiotics, this approach may be the only one available for use against microbes resistant to all known antibiotics.”

Light-activated antibacterial TiO2 coating against hospital-acquired infections
In addition, Professor Ivan Parkin and Dr Charles Dunnill of UCL Chemistry, and Professor Michael Wilson, Dr Jonathan Pratten and Zoie  Aiken from the UCL Eastman Dental Institute have  developed a Titanium Dioxide hard coating with antibacterial properties that has been shown to kill 99.9% of 10 million Escherichia coli (E.coli) bacteria when a white hospital light was shone on its surface.
The veneer-like surface is made of titanium dioxide with added nitrogen. When it is activated by white light, similar to those used in hospital wards and operating theatres, it produces a decrease in the number of bacteria surviving on the test surface.
The hospital environment acts as a reservoir for the microbes responsible for healthcare-associated infections (HCAI) and new ways of preventing the spread of these pathogens to patients are needed. Antibacterial coatings could be applied to frequently touched hospital surfaces to kill any bacteria present and help reduce the number of HCAI.
Titanium dioxide based coatings are known to kill bacteria after activation with UV light. The addition of nitrogen to these coatings enables photons (the basic unit of light) available in visible light to be utilized to activate the surface and kill bacteria.
Zoie Aiken commented: "The activity of the coating will be assessed against a range of different bacteria such as MRSA and other organisms which are known to cause infections in hospitals. At present we only know that the coating is active against E. coli. However, E. coli is more difficult to kill than bacteria from the Staphylococcus group which includes MRSA, so the results to date are encouraging.
"The coating has currently been applied onto glass using a method called APCVD (atmospheric pressure chemical vapour deposition). We are also experimenting with different materials such as plastic. As an example, the coating could be applied to a plastic sheet that could be used to cover a computer keyboard on a hospital ward. The lights in the ward will keep the coating activated, which will in turn continue to kill any bacteria that may be transferred onto the keyboard from the hands of healthcare workers."
Professor Peter Mullany and Dr Philip Warburton also presented their research at the SGM. 







SAFETY


Titanium Dioxide: Toxic or Safe?
By Lori Stryker, B.Sc., B.H.Ec., B.Ed.

Titanium dioxide is the subject of new controversy, yet it is a substance as old as the earth itself. It is one of the top fifty chemicals produced worldwide. It is a white, opaque and naturally- occurring mineral found in two main forms: rutile and anatase. Both forms contain pure titanium dioxide that is bound to impurities. Titanium dioxide is chemically processed to remove these impurities, leaving the pure, white pigment available for use. Titanium dioxide has a variety of uses, as it is odorless and absorbent. This mineral can be found in many products, ranging from paint to food to cosmetics. In cosmetics, it serves several purposes. It is a white pigment, an opacifier and a sunscreen. Concern has arisen from studies that have pointed to titanium dioxide as a carcinogen and photocatalyst, thus creating fear in consumers. But are these claims true? What does the research on these allegations bear out? Would we as consumers benefit from avoiding this mineral to preserve our long-term health?

A carcinogen is a substance that causes a cellular malfunction, causing the cell to become cancerous and thus potentially lethal to the surrounding tissue and ultimately the body as these rapidly growing mutated cells take over. With the surge in cancer rates among all segments of the population, many people are attempting to reduce or eliminate their exposure to carcinogens. Titanium dioxide is regarded as an inert, non-toxic substance according to its Material Safety Data Sheet (MSDS).

Potential adverse effects are also listed on its MSDS, readily available online. For example, the MSDS has stated that titanium dioxide can cause some lung fibrosis at fifty times the nuisance dust, defined by the US Department of Labor as 15 mg/m cubed (OSHA) or 10 mg/m cubed (ACGIH Threshold Limit Value). Recently, the International Agency for Research on Cancer (IARC) has classified titanium dioxide to be a possible human carcinogen, thus a group 2B carcinogen. In Canada, titanium dioxide is now listed under WHMIS class D2A (carcinogen)as a result of the IARC designation (ccohs.ca). The definition by the IARC for Group 2B possibly carcinogenic to humans is as follows:

"This category is used for agents for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals. It may also be used when there is inadequate evidence of carcinogenicity in humans but there is sufficient evidence of carcinogenicity in experimental animals. In some instances, an agent for which there is inadequate evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals together with supporting evidence from mechanistic and other relevant data may be placed in this group. An agent may be classified in this category solely on the basis of strong evidence from mechanistic and other relevant data." (monographs.iarc.fr)

The NIOSH declaration of carcinogenicity in rats is based on a study by Lee, Trochimowicz & Reinhardt, "Pulmonary Response of Rats Exposed to Titanium Dioxide by Inhalation for Two Years" (1985). The authors of this study found that rats chronically exposed to excessive dust loading of 250 mg/m cubed and impaired clearance mechanisms within the rat, for six hours per day, five days per week for two years, developed slight lung tumours. They also noted that the biological relevance of this data to lung tumours in humans is negligible. It is important to note that rats are known to be an extremely sensitive species for developing tumours in the lungs when overloaded with poorly soluble, low toxicity dust particles. Rat lungs process particles very differently compared to larger mammals such as dogs, primates or humans (Warheit, 2004). This sensitivity in the lungs has not been observed in other rodent species such as mice or hamsters (Warheit, 2004), therefore using the rat model to determine carcinogenicity of titanium dioxide in humans can be misleading, as extrapolation of species-specific data to humans is erroneous.

Many organizations and businesses have perpetuated this assessment of the carcinogenicity of titanium dioxide (ewg.org). However, several studies and study reviews have been used to compile the safety disclaimers for the regulations on the permitted use of titanium dioxide. One such study review took place in Rome, 1969 between the World Health Organization and the Food & Agriculture Organization of the United Nations. Cross species analyses were performed and reviewed for possible toxicity of titanium dioxide. The conference concluded that among the following species: rats, dogs, guinea pigs, rabbits, cats and human males, ingestion of titanium dioxide at varying diet percentages and over long periods of time did not cause absorption of this mineral. Titanium dioxide particulates were not detected in the blood, liver, kidney or urine and no adverse effects were noted from its ingestion. The U.S. Food & Drug Administration (2002) allows for its ingestion, external application including the eye area, and considers it a safe substance for public health. Other epidemiological studies showed that workers exposed to titanium dioxide exhibited no statistically significant relationship between such exposure with lung cancer and respiratory disease, although some cases of pulmonary fibrosis did occur. These studies were conducted in industrial settings where the increased exposure puts these individuals more at risk than the average person.

Titanium dioxide is listed as a safe pigment, with no known adverse effects when used in cosmetics, and approved by the FDA when 99% pure. It is not listed as a carcinogen, mutagen, teratogen, comedogen, toxin or as a trigger for contact dermatitis in any other safety regulatory publications beside the NIOSH (Antczak, 2001; Physical & Theoretical Chemical Laboratory, Oxford University respectively), with the exception of the recent IARC designation. It is reasonable to conclude then, that titanium dioxide is not a cancer-causing substance unless exposure is beyond safe limits during manufacturing using this substance. It is considered safe for use in foods, drugs, paints and cosmetics. This does not end the debate, however, as controversy over the safety of one unique form of titanium dioxide still exists.

One form of mineral or mineral extract, including titanium dioxide, that we should be concerned about is ultrafine or nano particles. As technology has advanced, so has its ability to take normal sized particles of minerals and reduce them to sizes never before imagined. While many are praising this new technology, others are warning of its inherent dangers to our bodies. A study by Churg et. al. at the University of British Columbia in their paper "Induction of Fibrogenic Mediators by Fine and Ultrafine Titanium Dioxide in Rat Tracheal Explants" (1999) found that ultrafine particles of the anatase form of titanium dioxide, which are less than 0.1 microns, are pathogenic or disease causing (see Table 1).

Table 1: Measurements of Mineral Pigment Particles
Particle Size Measurement
Coarse Less than 10 microns
Fine Less than 2.5 microns
Ultrafine (nanoparticles) Less than 0.1 microns or 100 nanometres
etcgroup.org
 
Table 2: Particle Size and Entry into the Human Body
Nanoparticle Size Entry Point
70 nanometres Alveolar surface of lung
50 nanometres Cells
30 nanometres Central Nervous System
Less than 20 nanometres No data yet
etcgroup.org
 

Kumazawa, et. al. in their study, "Effects of Titanium Ions and Particles on Neutrophil Function and Morphology" concluded that cytotoxicity (danger to the cell) was dependent on the particle size of titanium dioxide. The smaller the particle size, the more toxic it is (see Table 2). This conclusion is relevant to the consumer because of the cosmetics industry's increasing use of micronized pigments in sunscreens and colour cosmetics. Nanoparticles of titanium dioxide are used in sunscreens because they are colourless at that size and still absorb ultraviolet light. Many cosmetic companies are capitalizing on metal oxide nanoparticles. We have seen, however, that if titanium dioxide particles used to act as a sunscreen are small enough, they can penetrate the cells, leading to photocatalysis within the cell, causing DNA damage after exposure to sunlight (Powell, et. al. 1996) The fear is that this could lead to cancer in the skin. Studies with subjects who applied sunscreens with micronized titanium dioxide daily for 2-4 weeks showed that the skin can absorb microfine particles. These particles were seen in the percutaneous layers of the skin under UV light. Coarse or fine particles of titanium dioxide are safe and effective at deflecting and absorbing UV light, protecting the skin, but consumers should avoid using products with micronized mineral pigments, either in sunscreens or colour cosmetics.

As with any health issue, relevant studies must be examined closely to reach balanced conclusions about its impact on our health and well-being. Often, risk determinations are made without considering actual hazards and real-life exposures (Warheit, 2004). The Organic Make-up Co. considers fine or coarse particle sized titanium dioxide and other mineral pigments to be safe according to the studies available and information discussed in this article. Despite repeated requests for micronized pigments in our colour cosmetics, we insist on using only coarse or fine particles of mineral pigments, balancing our need to look beautiful with our more pressing need to stay healthy. With the multitude of cosmetics and chemicals available to us, it is in our best interest to become informed as consumers and make pure, natural and simple choices to protect our health and longevity.

Updated April 30, 2013

References:
  • Antczak, Cosmetics Unmasked. Harper Collins; London:2001
  • Blake, et.al. "Application of the Photocatalytic Chemistry of TiO2 to Disinfection and the Killing of Cancer Cells", Separation and Purification Methods; Vol 28 (1) 1999 p.1-50
  • Churg, Gilks, Dai, UBC Dept. of Pathology. Am J Physiol Lung Cell Mol Physiol. Vol 277 Issue 5 L975-L982, 1999
  • Dunford, et. al. FEBS Letters 418, 87 1997
  • Etcgroup.org
  • Kamazawa, et.al. "Effects of Titanium Ions and Particles of Neutrophil Function and Morphology". Biomaterials 2002 Sep 23 (17): 3757-64
  • Powell, et. al. GUT 38, 390 1996
  • Warheit, David "Nanoparticles: Health Impacts?". Materials Today, Feb. 2004
  • Witt, Stephen. Director of Technological Support, N. American Refractories Co.
  • http://www.ccohs.ca/headlines/text186.html
  • http://monographs.iarc.fr/ENG/Preamble/CurrentPreamble.pdf
 
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