INTRODUCTION:

Physical blockers like titanium (IV) oxide (TiO₂)present inmost skincare products have been shown to photo induce degradation of organic sunscreens, enzymes, and DNA^1,2. Studies on the acute toxicity of TiO₂ nanoparticles in mammals indicate intra-tracheal instillation, intraperitoneal injection or oral instillation of TiO₂ particles to animals evoke inflammatory response and histopathological changes³. In cultured macrophages, TiO₂ nanoparticles change the integrity of cell membrane and phagocytic activity⁴.

The reduction in cell viability, morphological alterations, compromises antioxidant system, intracellular ROS production, and significant DNA damage in cells exposed to TiO₂ nanoparticles signifying the potential of nanoparticles to induce cytotoxicity and genotoxicity in cultured human amnion epithelial (WISH) cells⁵.

TiO₂ absorbs about 70 % of incident UV, and in viable aqueous environments this may lead to generation of hydroxyl radicals. These free radicals may initiate oxidative reactions presenting possible undesirable mutagenic effects.⁶ demonstrated that, if the sunscreen agent TiO₂ illuminated with appropriate UV light it interacts with DNA or RNA and is, can cause serious damage. A recent study showed that even some modified TiO₂ particles specifically developed and marketed for sun-care, skin-care, and colour cosmetic formulations, still retain photocatalytic activity⁷. Mild cytotoxic response of TiO₂ nanoparticles has been reported and linked to induction of DNA damage.⁸ observed significant induction in micronucleus formation, reduction in glutathione, concomitant increase in lipid hydroperoxide and reactive oxygen species (ROS) generation demonstrating mild cytotoxic potential. Though induced ROS and oxidative stress may lead to oxidative DNA damage, micronucleus formation may form the basic mechanism of TiO₂ nanoparticle genotoxicity⁸.

Oxidative and nitrative stress causes nitration of the protein tyrosine, a post-translational modification linked to the onset or progression of diseases, such as cardiovascular diseases neurodegenerative diseases, and inflammation. The presence of tyrosine nitration in diseased conditions is an indication of the generation of peroxynitrite (ONOO⁻) in vivo produced from the very fast reaction of nitric oxide (NO) and superoxide (O₂^•¯) radical.⁹ recently demonstrated the physiological potential of nano-TiO₂to photocatalyse protein nitration in mouse skin homogenate. Tyrosine nitration is reported in several cutaneous pathological effects: contact hypersensitivity, systemic sclerosis, cutaneous inflammation, and thermal injury⁹. The anatase form of TiO₂ can greatly increase the formation of free radicals when exposed to sunlight and water in sunscreens. Studies indicate nano-anatase TiO₂ (1-100 nm) is highly photo-reactive, and thus hazardous. Nano-anatase TiO₂ in sunscreens was shown to react with sunlight and break down coatings on steel roofs at a rate 100-fold more than normal sunlight¹⁰. With the same effectiveness, nano-anatase is likely to attack viable tissues if it comes in contact.

The nano-particulate range of TiO₂in cosmetics possess a danger to infants and children with thinner, developing skin and people having broken skin. Nanoparticulate TiO₂ is widely used in sunscreen products to boost the SPF. Another area of application is in skin-lightening preparations. Skin-lighteners are designed to reduce the formation of melanin in the skin and thus the skin is left without adequate protection from the deleterious effects of UV radiation. Consequently, these products contain TiO₂ to afford broad-spectrum protection. From the foregoing it is apparent that the amount, particle size, and form of TiO₂ in a formulation needs to be controlled; European cosmetic, toiletry and perfumery association (COLIPA) set the maximum allowable concentration of TiO₂ in sunscreens as 25% (m/m)¹¹. However, most health regulatory bodies worldwide to date do not specify particle size limits. In the present work isolates, quantitate, and characterize the phases of titanium (IV) oxide present in skin-lightening products in the South African market.

MATERIALS AND METHODS:

Reagents:

Titanium (IV) oxide (TiO₂) (99.8% – Analytical Reagent Grade) from Riedel-de Haën A.G., Seelze-Hannover, was used for the preparation of standard solutions. Analytical grade sulphuric acid (H₂SO₄) (98.0%) was supplied by Associated Chemical Enterprises (Pty) Ltd, Johannesburg, South Africa, and BDH Chemicals Ltd, Poole, England. Potassium hydrogen sulphate (KHSO₄) was supplied by BDH Chemicals Ltd, Poole, England. A total of eight skin-lightening products containing TiO₂ were purchased from retail outlets in Durban, South Africa.

Quantitation of TiO₂:

Preparation of standard solutions:

A mass of 0.05g of TiO₂ (> 99%) was weighed and dissolved in 100mL of hot concentrated H₂SO₄ (> 98%), with constant stirring for 12 h to make a standard stock solution of 300mg mL^–1 of Ti⁴⁺. The stock solution was used to make working standards in the range 2 mg dm^-3– 10mg dm^-3. All Standards were purchased from Capital Labs, South Africa).

Preparation of samples:

Different masses of the skin-lightening samples in the range of 0.4 - 0.6g were weighed into a fused silica crucible and placed into an electrical furnace (Natalab supplies, South Africa) with the temperature set at 600 ºC for three hours to give carbon-free ash. The ash was allowed to cool in a desiccator for 10 min, and then about 0.5g of KHSO₄was added to it. The crucible containing the ash residue and KHSO₄was heated over a Bunsen burner for 15 min to fuse the mixture. The molten product was then dissolved in hot, concentrated H₂SO₄ and the solution transferred to a beaker. This solution was strongly heated to ensure complete solubilization of the TiO₂. The sample solutions were then diluted with deionised water to 100mL. A ten-fold dilution was done for samples that did not fall within the range of the calibration standards. All samples were analysed in triplicate.

Inductively coupled plasma-optical emission spectroscopy analysis:

Analysis of TiO₂ in sunscreens was as prescribed by¹². An inductively coupled plasma optical emission spectrometer Perkin Elmer (Optima 5300 DV) fitted with an auto-sampler was used for the quantitation of TiO₂ and the data was processed by Perkin Elmer Win Lab 32 software. The instrument was programmed to sample each standard and sample five times in radial view mode. Other operating conditions were: argon gas flow rate of 1.5 L min^-1, auxiliary and nebulizer gas flows at 0.2 L min^-1 and 0.8 L min^-1 respectively. The pump flow rate was set at 1.5mL min^-1 with the plasma radiofrequency working at 1300W. The data were acquired at a wavelength of 337.279nm.

Method validation:

The method validation was done by spiking a TiO₂-free sample with about 10mg of TiO₂. A mass of ~ 0.150g of the spiked sample was accurately weighed into a fused silica crucible. The crucible was then put in an electrical furnace at 600°C for three hours after which it was placed in a desiccator for 10 min to cool. To the cooled carbon-free ash residue a mass of 0.50g of KHSO₄ was added and fused over a Bunsen burner for 15 min. The molten product was dissolved in hot, concentrated H₂SO₄ and made up to 100mL with deionized water it was then subjected to a ten-fold dilution. The diluted sample was subjected to ICP-OES analysis. The standards were analyzed in between sample runs to check on instrument signal response and precision. An intra- and inter-day analysis were performed based on the precision of the standards analysis within the day of analysis and between days of analysis.

Data analysis:

The calibration data was analyzed with Microsoft Excel^© 2007 tool pack. The limit of detection (LOD) and limit of quantitation (LOQ) was calculated from the results of the linear calibration curve of the standards. The results were expressed as mean ± SD.

Characterization of TiO₂:

Extraction of TiO₂:

Samples containing TiO₂ were washed with solvents of varying polarity indices to isolate crystalline particles. A mass of ~ 0.2g of the sample was weighed into a beaker and washed firstly in 200mL dimethylformamide with ultrasonication for 2 h. The solvent with the dissolved organics was filtered through Whatman 1 filter paper and the remaining solid residue was then re-washed with fresh solvent in the order: methanol, acetone, and chloroform. The order varied depending on the sample matrix. Each wash was similarly filtered until crystalline TiO₂could be observed. The isolated crystals were then dried in an electric oven at 100°C for one hour.

Characterization by PXRD:

PXRD analyses were done by using a Bruker D8 Advance diffractometer equipped with an Anton Paar XRK 900 reaction chamber, a TCU 750 temperature control unit, with CuK_α radiation at 40 mA; 40 kV and 1.5405 Å. The diffractograms were collected over a 2θ of 10.000° - 89.893° range at a goniometric velocity of 0.034° min^-1 at 25°C. The spectral data was accumulated and processed by using Diffrac^plus basic XRD Wizard2.8 software. The diffraction peaks of crystalline phases were compared with standard anatase and rutile reported in the JCPDS database. The particle size of TiO₂ extracted by the sequential solvent system was estimated from the width, of diffraction peaks, calculated by using Scherrer's equation:

where K is Scherrer's constant (0.89): shape factor, λ is the X-ray wavelength used (1.5405 Å), β is the width at half maximum intensity (FWHM) in radians of the diffraction peak measured at 2θ, θ is the Bragg angle, and τ is mean size of the crystalline particles.

Characterisation by high resolution transmission electron microscopy:

Samples for high resolution transmission electron microscopy (HR-TEM) observation were prepared by dispersing the extracted TiO₂ powders in an absolute ethanol solution under ultrasonic irradiation. The dispersed TiO₂ was then deposited on carbon-copper grids. The crystallite sizes and shapes were observed by HR-TEM on a JEOL JEM-2100 microscope at 200 kV. The structure resolution of the microscope was set at 0.2 nm.

RESULTS AND DISCUSSION:

The TiO₂ content of the eight skin-lightening products investigated in this work was determined by ICP-OES. The analytical method had a linear working from 0.48 to 2.5 mmol dm^-3 as observed from the calibration curve of the standards. The correlation coefficient of the calibration curve (determined in triplicate) was 0.999.

Table 1 shows the amounts, particle size, and phases of the TiO₂ analyzed in this work. The LOD was calculated by using equation 1:

where S_y/x is the standard error of the slope and b is the slope of the calibration curve ¹³. The limit of detection was 0.06518 mg dm^-3. The LOQ from this data was calculated using equation 2:

Table 1: Average percentage concentration, particle size and phase of TiO₂in the skin-lightening samples.

Sample	٭TiO₂ % (m/m)	Particle size/nm	Phase of TiO₂
B	6.90 ± 0.01	16.23 ± 0.31	Rutile/anatase
E	7.47 ± 1.24	26.39 ± 1.79	Rutile
G	5.65 ± 0.01	45.03 ± 1.27	Rutile
L	3.04 ± 0.01	22.86 ± 4.14	Rutile
C	2.83 ± 0.01	44.42 ± 2.00	Anatase
I	3.35 ± 0.00	58.70 ± 0.38	Anatase
J	2.86 ± 0.01	42.59 ± 5.35	Anatase
K	3.73 ± 0.01	51.67 ± 6.56	Anatase

* Each value is an average of three replicates (mean ± SD).

The limit of detection at this wavelength was 0.2151mg dm^-3. The recovery test using spiked samples gave a mean recovery of 98.8% and the signal stability was determined by the intra- and inter-day analysis. The intra-day analysis using an authentic standard gave an RSD% of 0.10% and an inter-day value of 0.10% thereby indicating very high precision.

The percentage composition of titanium (IV) oxide in these samples was in the range of 2.83% to 7.47% (Table 1). These were all well below the COLIPA allowable 25% (m/m) maximum concentration of titanium (IV) oxide in a cosmetic formulation¹¹. Most of the samples contained approximately 3% (m/m) TiO₂, which when compared with the maximum allowed limit is low.

The PXRD characterization of the samples gave signals at 2θ values: 25.22, 37.73, 38. 45, 47.82 and 54.95° characteristic of anatase, at 27.33 37.73, 41.10, 54.10 and 68.69° characteristic of the rutile phase of TiO₂ (see Figure 1).

Figure 1: X-ray diffactogram for sample E (anatase) and sample G (rutile) superimposed on library difractograms of anatase and rutile.

The crystallite size estimation was based on the Scherrer equation. The Scherrer formula can provide a good estimate of the particle size but a variety of factors can contribute to the width of a diffraction peak. Besides crystallite size, the most important of these are usually inhomogeneous strain and instrumental effects. If all of these other contributions to the peak width were zero, then the peak width would be determined solely by the crystallite size and the Scherrer formula would apply. If the other contributions to the width are non-zero, then the crystallite size can be larger than that predicted by the Scherrer formula, with the peak broadening coming from the other factors. The eight samples gave crystallite sizes in the range of 16.23nm to 58.38 nm (see Table 1). These all fall within the nano-dimension.

Analysis of the high-resolution transmission electron microscopy images also revealed grain sizes in the nano range (see Figures 2 and 3).

Figure 2: HRTEM images of samples E and showing well-defined crystalline TiO2.

Figure 3: Particle size measurement for sample A observed using high-resolution transmission electron microscopy

This range is useful for the attenuation of UV radiation. Attenuation is the combined effect of absorbing and scattering of the incident light. Because nano-TiO₂ absorbs more UV light than it scatters compared with pigmentary grade TiO_2, itis preferred in most sunscreen preparations. Also, in this size range, it does not produce a whitening effect on the skin and thus it is more aesthetically appealing. The two methods of characterization thus proved helped useful in crystallite size approximation. However, the measurement from the HR-TEM depends on the particle dispersion and it is not apparent on the form of TiO₂ being measured. Whereas with the PXRD both particle size and form of TiO₂ could be obtained by library match. In this work, three samples displayed pure anatase signals indicating that the samples contained majorly anatase and four displayed rutile signals. One sample, however, showed mixed signals of anatase and rutile thereby showing a mixture of the two in the samples (Table 1).

DISCUSSION:

Samples investigated in this work contained TiO₂ acting as a sunscreen. The high refractive index of TiO₂ makes it useful for this purpose. The refractive indices of the rutile and anatase forms of TiO₂ are 2.75 and 2.54 respectively¹⁴. In this study, the crystallite size range was from 16.23 – 58.70nm (Table 1) as determined by PXRD. The particles of TiO₂ in the size range < 100nm are referred to as nano-TiO₂ and those > 100nm are known as pigmentary-TiO₂. The nano-TiO₂ have shown to be excellent UV filters or blockers because they have strong UV light absorbing capabilities and resistance to discolouration under UV irradiation. This advantage enhances its stability and ability to protect the skin from UV light¹⁵. Hence, nano-TiO₂ particles are frequently used in cosmetics because they scatter visible light less than pigmentary-TiO₂ while still providing UV protection. The majority of sunscreens intended for infants or people with delicate skin use are often based on TiO₂ and/or ZnO, because these physical UV filters are believed to cause less skin irritation than other UV absorbing agents.

However, nano-TiO₂ is naturally photocatalytic because when they absorb UV light electrons are excited and promoted for anatase to the conduction band across the 3.2 eV bandgap. This excitation is induced by UV light of wavelengths below 385 nm. The excited electrons promoted from the valence band (v_b) to the conduction band (c_b) generate Ts1wo mobile charged species; negatively charged single electrons (e^–) and positively charged spaces called holes (h⁺) (chemical equation 1). The electron and hole pair (e^–/h⁺) (equation 2) may recombine or migrate rapidly to the particle surface. At the surface, the electrons and holes may participate in chemical reactions with adsorbed chemical species. Two possible reactions may take place at the surface. The e^– may react with dissolved oxygen gas (O₂) and h⁺ with hydroxyl (OHˉ) ions or water (H₂O), to form superoxide (O₂ˉ) or hydroxyl (˙OH) radicals:

TiO₂ + hν → TiO₂ (e^–/h⁺) (1)

TiO₂ (e^–/h⁺) → e^– (c_b) + h⁺ (v_b) (2)

e^¯ (c_b) + O₂→ O₂˙ˉ (3)

h⁺ (v_b) + OH^– → ^˙OH (4)

h⁺ (v_b) + H₂O → ^˙OH + H⁺ (5)

The O₂¯ and, in particular, the ˙OH radicals formed are the active agents for the degradation of organic compounds:

^˙OH or O₂˙ˉ + substrate → photo-oxidized products¹⁶. (6)

Also, the excited electrons may return to their ground state, emitting energy, or escape from the particle (chemical equation 2). Escaped electrons may initiate oxidative reactions in nearby molecules, generating free radicals (chemical equation 3 - 5). Free radicals may cause further damage to skin cells or interact with other sunscreen components producing chemical species with undesirable effects (equation 6). The fear is that this could lead to cancer in the skin.

The probability of photo-electron promotion and generation of e^–/h⁺ pairs is the phase of the nano-TiO₂ crystal. In this work, both phases of TiO₂, namely, anatase and rutile were identified in the skin-lightening products. It is known that rutile is more photostable than anatase. This arises from the size dependence on the orbital character of the conduction band of anatase TiO₂ nanocrystals. It is known that the appearance and predominance of unoccupied states derived from the hybridization of the antibonding Ti 4s and O 2p band are observed when the nanoparticle size approaches the exciton radius (ca. 1nm). Such extended hybridization of O 2p with Ti 4s compared to narrow directional 3d in rutile demonstrates a confinement effect in anatase TiO₂ nanocrystals, a factor in electron excitation upon UV irradiation. The presence of s-hybridized band gap states controls the interfacial electron transfers and reduces the back reaction¹⁴. This may create an avalanche of escaped electrons that may attack viable skin cells via the generation of free radicals as illustrated above. On this account, rutile should be the preferred phase of TiO₂ for use in cosmetic preparations. In this study samples C, D E and H showed characteristic peaks of the anatase in the XRD diffractograms (see Figure 1) an evidence that anatase is still used in some skin-lightening preparations. The forms of TiO₂ present in these samples were not indicated on the packet labels. This is a major concern because anatase TiO₂ is a very active photocatalyst and should not be used in cosmetic preparations. Secondly, as shown by⁷ even surface-modified TiO₂ still retains photocatalytic activity.

The question of the percutaneous penetration of TiO₂ has drawn a lot of attention, especially after topical application. Table 2 shows the relationship between particle size and possible viable tissue penetration by the nano-range particles. In the worst-case scenario the particle range of TiO₂ found in this work (16 – 59nm, Table 1) are likely to enter viable tissue should they be in contact with any of these body tissues.

Table 2: Particle size and entry into the human body

Nanoparticle Size/nm	Entry Point
70	Alveolar surface of lung
50	Cells
30	Central nervous system
20	No data yet

(http://www.organicmakeup.ca/titaniumdioxide.asp (accessed on 14/10/2020)

Animal studies indicate that subjects who routinely apply sunscreens with micronized TiO₂ show that the skin can absorb microfine particles^9,17. The samples investigated in this work all have TiO₂ in the nano-range (< 100 nm) (Table 1). The penetration of nano-TiO₂ into the cells may lead to photocatalysis within the cell, causing DNA damage after exposure to sunlight.

¹⁸and¹⁹ have shown that a Ti⁺⁴ solution stimulates neutrophils and increases the quantity of released O₂¯ anions. The authors showed that the cytotoxic effect of Ti particles is size-dependent and that they must be smaller than that of cells. Animal model studies have shown the ingested titanium accumulates in the liver DNA leading to histopathological changes and hepatocyte apoptosis^5,20.

However, some studies show that there is no deeper penetration of topically applied TiO₂ into viable skin tissue²¹. The same study indicated that there is possible penetration of TiO₂ into the open skin parts around the follicles. This is a pointer that compromised skin surface may be susceptible to TiO₂ penetration. The effects of viable tissue incorporated TiO₂ include induction of ROS reactions that can lead to DNA mutations and cell death²². There are reports that TiO₂ particles isolated from commercial sunscreen products induced DNA strand breaks and other lesions in DNA plasmids and human cells²⁰. It can therefore be inferred that the presence of TiO₂ in sunscreen formulations can initiate or lead to photo-oxidative damage of the skin. Though, other investigations have shown that coarse or fine particles of TiO₂ to be safe and effective at deflecting and absorbing UV light, protecting the skin^23,24. But consumers should avoid using products with nano-pigments, either in sunscreens or colour cosmetics if they have any wounds or broken skin. Such preparations should be used with caution on the children where the skin is thinner and more permeable.

Most of the investigated products in this work contained a combination of TiO₂ with organic UV-filters tert-butylmethoxy dibeznoylmethane, 2-ethylhexy-p-methoxy cinnamate, and benzophenone-3. There is the possibility that TiO₂ may photocatalyse the photodegradation of these UV filters. Several reports indicate loss of photo-absorption efficacy of these UV filters in the presence of TiO₂²⁵. The photoproducts resulting from the TiO₂ photocatalyzed reactions of the organic UV filters lead to a loss of photoprotection and a potential risk to the skin. Besides, the toxicities of the resulting photoproducts are not known.

To inhibit the effects of TiO₂ on the organic macromolecules and other substrates the surface of the TiO₂ may require deactivation. The surface deactivation of nano-TiO₂ like the one found in this work may afford thin-film uniform surface coating on the particles. However, such surface modifications have been found ineffective in photo-oxidative reactions⁷. The structural modification of the TiO₂crystalline lattice by the introduction of impurities has been shown to reduce the photo-activity of TiO₂. The choice of the transition metal (dopant) determines the photo-response of the doped TiO₂. Recently, it was demonstrated that manganese-doped TiO₂ had enhanced UVA absorption, less degradation of other organic constituents of the formulation and a reduction in a free radical generation ²⁶. However, there is no guarantee that surface coating or doping completely deactivates TiO₂.

CONCLUSIONS:

This study aimed to isolate, characterize and quantitate the amount of TiO₂ present in the eight skin-lightening preparations. The percentage composition of TiO₂ in these skin-lightening agents was found to be in the range of 2.83 % to 12.47 % (m/m). Both anatase and rutile forms of TiO₂ were found present in the nano range (16.23 nm to 51.67 nm). Since anatase TiO₂ is a potent photocatalyst it should not be used in such topical skin preparations. This is more so since it has been shown that surface modification does not eliminate this photocatalytic activity.

ACKNOWLEDGEMENT:

The authors are grateful to the University of Kwa Zulu-Natal, College of Agriculture, Engineering and Science for the award of a Doctoral Bursary and Dedan Kimathi University, Chemistry Department for facilities provided.

REFERENCES:

1. Egerton, A.; Everall, J. N.; Mattinson, A. J.; Kessell, M. L.; Tooley, R. I., Interaction of TiO2 nano-particles with organic UV absobers. Journal of Photochemistry and Photobiology A: Chemistry 2008, 193, 10 - 17.

2. Sayre, R. M.; Dowdy, J. C.; Ricci, A.; Chretien, M. N.; Scaiano, J. C., Mineralization of organic sunscreens: interesting, but relevant? Comment and response. Photochemical and Photobiological Sciences 2003, 2 (10), 1050-1051.

3. Chen, J.; Zhou, H.; Santulli, C. A.; Wong, S. S., Evaluating Cytotoxicity and Cell Uptake from the Presence of Variously Processed TiO2 Nanostructured morphologies. Chem. Res. Toxicol. 2010, 23, 871 - 879.

4. Zhang, R.; Niu, Y.; Li, Y.; Zhao, C.; Song, B.; Li, Y.; Zhou, Y., Acute toxicity study of the interaction between titanium dioxide nanoparticles and lead acetate in mice. Environmental Toxicology and Pharmacology 2010, 30 (1), 52-60.

5. Saquib, Q.; Al-Khedhairy, A. A.; Siddiqui, M. A.; Abou-Tarboush, F. M.; Azam, A.; Musarrat, J., Titanium dioxide nanoparticles induced cytotoxicity, oxidative stress and DNA damage in human amnion epithelial (WISH) cells. Toxicology In Vitro 2012, 26 (2), 351-61.

6. Hidaka, H.; Horikoshi, S.; Serpone, N.; Knowland, J., In vitro photochemical damage to DNA, RNA and their bases by an inorganic sunscreen agent on exposure to UVA and UVB radiation. Journal of Photochemistry and Photobiology A: Chemistry 1997, 111, 205-2013.

7. Tiano, L.; Armeni, T.; Venditti, E.; Barucca, G.; Mincarelli, L.; Damiani, E., Modified TiO2 particles differentially affect human skin fibroblasts exposed to UVA light. Free Radical Biology and Medicine. 2010, 49 (3), 408-15.

8. Shukla, R. K.; Sharma, V.; Pandey, A. K.; Singh, S.; Sultana, S.; Dhawan, A., ROS-mediated genotoxicity induced by titanium dioxide nanoparticles in human epidermal cells. Toxicology in Vitro 2011, 25 (1), 231-241.

9. Lu, N.; Zhu, Z.; Zhao, X.; Tao, R.; Yang, X.; Gao, Z., Nano titanium dioxide photocatalytic protein tyrosine nitration: A potential hazard of TiO2 on skin. Biochemical and Biophysical Research Communications. 2008, 370 (4), 675-680.

10. Barker, P. J.; Branch, A., The interaction of modern sunscreen formulations with surface coatings. Progress in Organic Coatings 2008, 62 (3), 313-320.

11. Atitaya, S.; Juwadee, S.; Atitaya, S., Particle size characterization of titanium dioxide in sunscreen products using sedimentation field-flow fractionation-inductively coupled plasma-mass spectrometry. Analytical and Bioanalytical Chemistry. 2011, 399 (2), 973-978.

12. de la Calle, I.; Menta, M.; Klein, M.; Séby, F., Screening of TiO2 and Au nanoparticles in cosmetics and determination of elemental impurities by multiple techniques (DLS, SP-ICP-MS, ICP-MS and ICP-OES). Talanta. 2017, 171, 291-306.

13. Thomsen, V.; Schatzlein, D.; Mercuro, D., Limits of detection in spectroscopy. Spectroscopy. 2003, 18, 112-114.

14. Vayssieres, L.; Persson, C.; Guo, J. H., Size effect on the conduction band orbital character of anatase TiO2 nanocrystals. Applied Physics Letters. 2011, 99 (18), 183101.

15. Morganti, P., Use and potential of nanotechnology in cosmetic dermatology. Clinical, Cosmetic and Investigational Dermatology. 2010, 3, 5-13.

16. Bunhu, T.; Kindness, A.; Martincigh, B. S., Determination of titanium dioxide in commercial sunscreens by inductively coupled plasma-optical emission spectroscopy. South African Journal of Chemistry. 2011, 64, 139-143.

17. Naya, M.; Kobayashi, N.; Ema, M.; Kasamoto, S.; Fukumuro, M.; Takami, S.; Nakajima, M.; Hayashi, M.; Nakanishi, J., In vivo genotoxicity study of titanium dioxide nanoparticles using comet assay following intratracheal instillation in rats. Regulatory Toxicology and Pharmacology. 2012, 62 (1), 1-6.

18. Kumazawa, R.; Watari, F.; Takashi, N.; Tanimura, Y.; Uo, M.; Totsuka, Y., Effects of Ti ions and particles on neutrophil function and morphology. Biomaterials. 2002, 23 (17), 3757-3764.

19. Tamura, K.; Takashi, N.; Kumazawa, R.; Watari, F.; Totsuka, Y., Effects of particle size on cell function and morphology in titanium and nickel. Materials Transactions. 2002, 43 (12), 3052-3057.

20. Dunford, R.; Salinaro, A.; Cai, L.; Serpone, N.; Horikoshi, S.; Hidaka, H.; Knowland, J., Chemical oxidation and DNA damage catalysed by inorganic sunscreen ingredients. FEBS Letters. 1997, 418 (1–2), 87-90.

21. Lademann, J.; Weigmann, H. J.; Rickmeyer, C.; Barthelmes, H.; Schaefer, H.; Mueller, G.; Sterry, W., Penetration of titanium dioxide microparticles in a sunscreen formulation into the horny layer and the follicular orifice. Skin Pharmacology and Applied Skin Physiology. 1999, 12 (5), 247-256.

22. Rahman, Q.; Lohani, M.; Dopp, E.; Pemsel, H.; Jonas, L.; Weiss, D. G.; Schiffmann, D., Evidence that ultrafine titanium dioxide induces micronuclei and apoptosis in Syrian hamster embryo fibroblasts. Environmental Health Perspectives. 2002, 110 (8), 797-800.

23. Donathan, G. B.; Thomas, A. M., Characterisation of the UVA protection Provided by Avobenzone, Zinc Oxide and Titanium Dioxide in Broad-Spectrum sunscreen Products. American Journal of Clinical Dermatology. 2011, 11 (6), 413-421.

24. Sadrieh, N.; Wokovich, A. M.; Gopee, N. V.; Zheng, J. W.; Haines, D.; Parmiter, D.; Siitonen, P. H.; Cozart, C. R.; Patri, A. K.; McNeil, S. E.; Howard, P. C.; Doub, W. H.; Buhse, L. F., Lack of Significant Dermal Penetration of Titanium Dioxide from Sunscreen Formulations Containing Nano- and Submicron-Size TiO2 Particles. Toxicological Sciences. 2010, 115 (1), 156-166.

25. Ricci, A.; Chretien, M. N.; Maretti, L.; Scaiano, J. C., TiO2-promoted mineralization of organic sunscreens in water suspension and sodium dodecyl sulfate micelles. Photochemical and Photobiological Sciences. 2003, 2 (5), 487-492.

26. Wakefield, G.; Lipscomb, S.; Holland, E.; Knowland, J., The effects of manganese doping on UVA absorption and free radical generation of micronised titanium dioxide and its consequences for the photostability of UVA absorbing organic sunscreen components. Photochemical and Photobiological Sciences. 2004, 3 (7), 648-652.

Received on 21.03.2021 Modified on 16.05.2021

Asian J. Research Chem. 2021; 14(5):324-330.

DOI: 10.52711/0974-4150.2021.00055