SOILS, CLAYS AND CLAY MINERALS

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THESIS OVERVIEW

CHAPTER 1: BACKGROUND TO THE STUDY This is an introductory chapter giving a general description of cosmetics. The evolution of cosmetics using clays and/or minerals as cosmetics from ancient days to the current status is highlighted. The regulations controlling the composition and/or ingredients of cosmetics are also discussed. The global role of clays is outlined and contrasted with the Southern African position involving letsoku and related substances. A brief approach on how to explore letsoku is presented. CHAPTER 2: LITERATURE REVIEW OF COSMETICS This chapter describes cosmetics and introduces the role of the cosmetics regulatory bodies. It provides a review of clays and clay minerals as ingredients in cosmetics in ancient and current times, both globally and locally. It further elaborates on the physicochemical and chemical properties of cosmetic ingredients, their nature and the regulations controlling their inclusion in products. Adverse effects such as toxicity are also accentuated. A comprehensive critique of the techniques that have enabled knowledge about cosmetics and their ingredients to be gained is presented. CHAPTER 3: RESEARCH DESIGN AND METHODOLOGY This chapter covers the practical experimental design for assessing the concepts mentioned in Chapter 2. The techniques used are briefly described and presented, together with the methods used for the analyses. The analyses covered chemical composition, physicochemical and structural properties. CHAPTER 4: RESULTS This is a detailed presentation of the results of the various analyses undertaken. The results for physicochemical properties are particle size distribution, specific surface area, pH, colour, water content and loss on ignition. The results for the chemical assessments are clay mineral content, metal oxide and trace metal contents. SEM morphological micrographs of the clayey soils are also presented. The results for structural properties are reflected in the thermograms and in the FTIR spectra. CHAPTER 5: DISCUSSION AND ANALYSIS Chapter 5 is a critique of the results from Chapter 4 and the key findings. The study contributions and possibilities for future research are also outlined.

FOREWORD

The evolution of cosmetics over centuries is a captivating story. Their composition has undergone drastic transformation from 10000 BCE to date. The obsession with having a pale, angelic white complexion resulted in the flourishing of dangerous products. White lead, a mixture of PbCO3 and Pb(OH)2, known as ceruse, or Venetian ceruse, or spirits of Saturn, was the predominant skin whitener among the English, Greeks and Romans. Mixtures such as ceruse were found to cause lead poisoning, skin damage, hair loss, facial tremors, muscle paralysis and death. Queen Elizabeth I is reported to have lost so much hair that her forehead appeared enlarged. Pearl powder (BiCl3) and French chalk (Mg3Si4O10(OH)2) were also used as skin whiteners. On the other hand, the Egyptian Cleopatra used milk baths, oils and the dead- sea salts to enhance her beauty in a fairly safe way. Unfortunately, this was counteracted by the toxic eye paints of her time. These were mixtures of PbO4, HgS, antimony (Sb) and cinnabar (α-HgS). The poisonous products were purchased from the pharmacy and deliberately hidden among medicines in the marble chests. Crème celeste was an innovative mixture of white wax, spermaceti, sweet almond oil and rose water which emerged during these times. It was a moisturizer, skin lightener, emollient and could hide blemishes. It later became known as cold cream. This study will review mainly developments concerning clays and minerals, even though other materials were involved, as mentioned before. Kohl was made from galena (PbS), malachite pigment (CuCO3⋅Cu(OH)2 and ochre (iron oxides with clay). The Egyptians used it on eyelashes, eyelids and eyebrows around 4000 BCE. Around 1000 BCE the Greeks were whitening their complexions with chalk (CaCO3) and lead. Red ochre (Fe2O3 in clay) laced with iron oxide was used for their lipstick. During the period from 1400 to 1500 AD arsenic sometimes replaced lead in face powder. Mud baths emerged on the scene among the Romans in 100 AD. White lead paint gained popularity with European women, especially Queen Elizabeth I with her blond hair and pale skin, giving the “the mask of youth” look. The blond “angelic” hair was achieved by applying a mixture of sulphur, alum (KAl(SO4)2.12H2O) and honey. This was allowed to stand in the sun prior to use. The Queen had labelled colourful make-up as “vulgar and improper” and suitable for actors only. Around 1800 AD ZnO2 appeared on the scene as a face powder to replace the toxic lead and copper mixtures. Around 1900 AD make-up became popular again. The French shifted from their perception of “Jezebels” to acceptance of make-up. Men were even using pastes to hide scars and blemishes. Ancient history revealed the numerous pigments generated by the ancient Egyptians (Scott, 2016). Several shades of reds, pinks and yellows were obtained by mixing ochres of different colours. Red (anhydrous iron oxide Fe2O3), yellow (hydrated iron hydroxide FeO(OH).nH2O or limonite) and brown ochres (hydrated iron oxide FeO(OH) or goethite) were mixed with minerals such as calcite (CaCO3), orpiment (As2S3) and gypsum (repeating unit of CaSO4.2H2O). There is emphasis on the distinction between red ochre (a natural substance containing Fe2O3) and haematite (Fe2O3, a pure version of red ochre). Scott (2016) also mentioned mixtures such as calcite, carbon black (an iron-titanium compound mixed with calcium carbonate) and MnO2 for eye make-up. The ancient communities had the freedom to expose their skins to danger because of lack of control, knowledge and regulatory organizations. The current consumers enjoy the benefits of the emergence of various cosmetic regulatory bodies. Cosmetic ingredients are subject to regulations. Aspects covered by these regulations include the terminology used and formulation procedures, with the ultimate aim of ensuring safety for humans. The regulations unambiguously prescribe restrictions on the definition of cosmetics, their properties, the ingredients that may be used, their positive and negative impact on users and the environment. They include aspects such as cosmetic composition as well as the chemical structures, functions and toxicity of the ingredients. The European Parliament and European Council regulate cosmetics via Regulation (EC) No. 1223/2009, (dated 30 November 2009 and the subsequent amendments thereto) of the European Parliament and of the Council on cosmetic products. The FDA defines cosmetics as “articles intended to be rubbed or poured”. Most of these are emulsions containing surfactants such as creams, lotions, gels, make-up and products for removing make-up, products intended for application to the lips, products for nail care and make-up, sunbathing products, products for tanning without sun, skin-whitening products and anti-wrinkle products. The variety of products invariably involves a broad spectrum of ingredients, but the focus of this study is on minerals, clays and clay minerals. The individual chemical ingredients in cosmetics are subject to a review by the Cosmetic Ingredient Review (CIR). The latter operates in association with the Personal Care Products Council (previously the Cosmetic, Toiletry and Fragrance Association, CTFA). It is supported by the FDA and the Consumer Federation of America. The FDA is a non-voting member but observes the CIR activities as it may use their findings in its own safety reviews of cosmetic ingredients. Recommendations are made on the safety and use of the compounds based on the available scientific literature encompassing data. The nine-member steering committee, made up of three dermatologists, two chemists and four pharmacologists or toxicologists, is involved in the general policy and direction of the CIR. The composition of the cosmetics is further subject to the International Cosmetic Ingredient Nomenclature Committee (INC), which is sponsored by the Personal Care Products Council. This is responsible for designating a uniform system, known as INCI names, for cosmetic ingredients that are used globally for consistency in ingredient names. Approved names are published in the International Cosmetic Ingredient Dictionary and Handbook. (http://www.cosmeticsinfo.org/Ingredient-dictionary). Globally, several researchers have reported on the use of some clays and clay minerals as cosmetic ingredients, including their functions (Konta, 1995);(Carretero, 2002);(Carretero and Pozo, 2010);(CIR, 2014 ), Heckroodt (1991) described clay as the finest fraction, < 2 μm, in the clay, silt and sand triangle based on particle size and structure. Cosmetic physicochemical properties and thermodynamic stability are strongly influenced by the afore-mentioned attributes. The physicochemical properties of clay minerals, e.g. kaolinite, smectites, talc and muscovite, are important attributes in therapeutic applications (Carretero, 2002; Schoonheydt and Johnston, 2006). These authors discussed in detail the oral and topical therapeutic activity, as well as the cosmetic action, of clays in creams, sunscreens, dermatological protectors, anti- inflammatories and gastro-intestinal medications. Soils and clays also play important cultural and medicinal roles in the life of humankind (Certini and Ugolini, 2013; Hartemink, 2015b; Hartemink and McBratney, 2008). Two approaches, namely the ethno-pedological and ethno-pharmacological, help to capture spiritual, cognitive and practical aspects of the use of clay (Adderley et al., 2004; Barrera- Bassols and Zinck, 2003; De Smet, 1998; Krasilnikov and Tabor, 2003). Soil-derived minerals such as ochre have featured in various cultural products for almost 100 000 years (Carretero, 2002; Hodgskiss and Wadley, 2017; Konta, 1993a; López-Galindo et al., 2007; Viseras et al., 2007). In essence, ochre is a natural soil-based pigment that ranges in colour from yellow to deep orange or brown. It is essentially a mixture of oxides of iron with varying amounts of sand and clay. Locally, the Matike et al. (2011) study on the Eastern Cape clayey soils highlighted the effect of pH of cosmetics on the acid mantle of skin. The latter study mainly focused on physicochemical properties. Their mineralogical and chemical composition hence their possible cosmetic role, were recommended for future studies. On the other hand the Dlova et al. (2013) study identified two traditional types of clays from the Inanda district in Durban, South Africa as low degree UVA protectors. The authors did not examine their safety profile nor their composition. The Jumbam (2014) research on ten clayey soil samples from the Isinuka springs in the Eastern Cape revealed the presence of several clay minerals. Some of them were kaolinite, smectite, plagioclase and halite. The main cosmetic role emphasized was protection against UV radiation and for their effect on pH. The Sotho clans of Southern Africa have described a number of clayey soils as letsoku. These are named differently elsewhere, such as chomane in Shangani, imbola in Xhosa, ilibovu in Swati and luvhundi in Venda. There are several other names given by other ethnic groups (Matike et al., 2014). Letsoku has also been associated with other materials, e.g. a black manganese oxide (Pahl, 1974b), white clays (probably kaolin) (Bishop, 1984) and the black sekama (ilmenite) (Ambrose et al., 2001). The aim of this study was to explore the clayey soils as potential cosmetic ingredients. Comparison of the clayey soils with well-known topical clay minerals (Carretero, 2002; Carretero and Pozo, 2010; Ekosse, 2000; Favero et al., 2016; Konta, 1995) would aid in confirming the suitability of these soils as ingredients of or as modern cosmetics. The main custodians of the knowledge of the letsoku sampling sites are traditional healers. This added intrigue to the original objective of the research. Subsequently, other functions of and more detailed background information about these clays were investigated. Therefore an interdisciplinary exploratory approach was adopted, resulting in a two-pronged epistemological and a characterization study.

PROBLEM STATEMENT

The study was inspired by the transition of the cosmetic industry towards more natural ingredients and the quest to reclaim the vanishing cultural practices of Southern African peoples. Clayey soils have been used for eras among Southern African indigenous people. Topical application is their commonly known function. Several names such as letsoku (Sotho clans), libovu (Swazi), imbola (Xhosa) and chomane (Shona) have been used to describe these clayey soils. The challenge is to establish a link between the function, nature and composition of the clays. The relevance of mineral composition to the manifold claimed traditional uses of letsoku are to be discussed in the context of the known functions that clays and minerals impart to modern formulations, in particular topical cosmetics. Furthermore, to give a scientific account for commonality in function and the differences in the names. 1.2.1 Research questions The background provided in Section 1.2 raises questions that create a need for some logical or scientific explanation that may justify the continued topical use of letsoku by humans. Therefore there is a need to provide answers to the following questions: • What do people use letsoku for? • What is the nature of letsoku and is there a link between its nature and its function(s)? • Is there justification in the claims made, including the common use of the name letsoku for various clayey soils? • Can letsoku compare satisfactorily with the cosmetic ingredients or products currently used? 1.2.2 Objectives The study could not proceed without actual samples of letsoku, hence it was imperative to locate the sourcing sites. Therefore it was essential to do the following: 1. Obtain representative samples. 2. Establish the location of each sourcing site as this was crucial to the research. 3. Seek reliable informants on the use of letsoku and the sourcing sites or suppliers of the clayey soil. 4. Determine the physicochemical properties, chemical and mineral compositions of the samples collected to determine commonality amongst the various clayey soils that could substantiate or refute the claims made about these clayey soils. 5. Establish whether there is a correlation between the functions attributable to letsoku and the composition and properties of the samples.

TABLE OF CONTENTS :

• DECLARATION
• ABSTRACT
• ACKNOWLEDGEMENTS
• TABLE OF CONTENTS
• LIST OF FIGURES
• THESIS OVERVIEW
• LIST OF ABBEVIATIONS
• GLOSSARY
• CHAPTER 1 : BACKGROUND TO THE STUDY
  • 1.2 PROBLEM STATEMENT
  • 1.2.1 Research questions
  • 1.2.2 Objectives
  • 1.3 OVERVIEW OF THE RESEARCH DESIGN
  • 1.4 DATA COLLECTION AND ANALYSIS
  • 1.4.1 Epistemology
  • 1.4.2 Characterization
  • 1.5 RESEARCH METHODOLOGY
  • 1.5.1 Ethical considerations
  • 1.5.2 Determination of clay properties and composition
  • 1.6 CONTRIBUTION
• CHAPTER 2 : LITERATURE REVIEW
  • 2.1 INTRODUCTION
  • 2.2 PROPERTIES OF COSMETICS
  • 2.2.1 Physicochemical properties
  • 2.2.2 Chemical properties
  • 2.3 SOILS, CLAYS AND CLAY MINERALS
  • 2.3.1 Soils
  • 2.3.2 Clays
  • 2.3.3 Clay minerals
  • 2.4 TOXICITY AND SAFETY
  • 2.4.1 Toxicity of raw materials and trace elements
  • 2.4.2 Product safety
  • 2.5 OTHER ASPECTS OF CLAYS OR CLAY MINERALS
  • 2.5.1 Medicinal applications
  • 2.5.2 Artwork
  • 2.5.3 Cultural symbolism
  • 2.5.4 Traditional beliefs
  • 2.5.5 Aesthesia
  • 2.6 PIGMENTS
  • 2.6.1 Minerals
  • 2.6.2 Micas
  • 2.6.3 Ochre
  • 2.7 CLAY MINERAL IDENTIFICATION AND QUANTIFICATION
  • 2.7.1 Particle size
  • 2.7.2 BET (Brunauer Emmet Teller) surface area analysis
  • 2.7.3 Colour test
  • 2.7.4 pH measurement
  • 2.7.5 X-ray analysis
  • 2.7.6 Scanning electron microscopy (SEM)
  • 2.7.7 Thermal analysis
  • 2.7.8 Infrared spectroscopy
• CHAPTER 3 : RESEARCH DESIGN AND METHODOLOGY
  • 3.1 ETHICAL APPROVAL AND THE EPISTEMOLOGICAL STUDY
  • 3.2 MATERIALS AND METHODS
  • 3.2.1 Sample collection
  • 3.2.2 Sample processing
  • 3.3.1 Particle size distribution
  • 3.3.2 BET surface analysis
  • 3.3.3 Colour test
  • 3.3.4 pH measurement
  • 3.3.5 X-ray diffraction (XRD) analysis
  • 3.3.6 X-ray fluorescence spectroscopy (XRF) analysis
  • 3.3.7 Scanning electron microscopy (SEM)
  • 3.3.8 Thermogravimetric analysis (TGA)
  • 3.3.9 Infrared spectroscopic analysis
• CHAPTER 4 : RESULTS
  • 4.1 EPISTEMOLOGICAL STUDY
  • 4.1.1 Letsoku applications
  • 4.2 CHARACTERIZATION
  • 4.2.1 Particle size distribution (PSD)
  • 4.2.2 Physicochemical properties
  • 4.2.3 X-ray analyses
  • 4.2.4 SEM morphological analysis
  • 4.2.5 Thermogravimetric analysis (TGA)
  • 4.2.6 Infrared spectroscopic analysis
• CHAPTER 5 : DISCUSSION AND ANALYSIS
  • 5.1 ANALYSIS OF RESULTS
  • 5.2 KEY FINDINGS OF THE RESEARCH
  • 5.3 CONCLUSIONS AND RECOMMENDATIONS
  • 5.4 CONTRIBUTIONS
  • 5.5 FUTURE RESEARCH
  • REFERENCES

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