Mineralogical And Geochemical Aspects Of Clayey Soils Biology Essay

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Clay from Isinuka springs in Port St Johns area of the Eastern Cape of South Africa is used by local people for cosmetic purposes and for treatment of an array of ailments and diseases. This study relates the acclaimed cosmetic and therapeutic properties of the clay to its mineralogical and geochemical composition and properties. The clay samples were dried and subjected to pH measurement and found to be all alkaline, particle size distribution, X-ray Fluorescence (XRF) analyses leading to the detection of As, Co, Cr, Cu, Ni, Pb, Sr, U and Zn concentrations in the samples. The highest mean concentration of element recorded was strontium with a mean value of 2550 ppm. X-ray and FTIR analyses gave insight on the mineralogical content of the samples. Based on the results obtained, it became clear that the clay though useful for therapy and cosmetics purposes, may effectively constitute a health risk especially on repeated exposure. The acclaimed dermatological properties of the clays may be ascribed to the presence of sulfur and arsenic in the samples. A microbiological analysis of the samples may further shed some light on the alleged medicinal properties of the clays.

Keywords: Clay, chemicals, mineralogy, Isinuka traditional spar, healing

Introduction

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Clay refers to soil particles that are generally less than 2 µm in diameter and occur widely in many parts of the world especially in Africa. Their use by humans and animals for various purposes dates back many centuries, evident from data traced back to 60 BC . Clays form an integral part of African cultural wellbeing and are used in varied forms of traditional rituals, cosmetics and medical practices to treat an array of ailments and diseases. The concept of spa treatment (curortology), now popular in industrialized countries, is not new to Africa. Guthrie (1951) reported on the regular use of medicated baths and mud baths by Africans, while Thompson (1965) noted that the use of vapor or steam baths to treat fevers and rheumatoid arthritis was a common feature amongst native Africans. In open African markets, clays of various shades and colors are sold for use in cosmetic, medicinal and dermatological applications.

In the Transkei region of South Africa, it is not uncommon to see women faces covered with white, yellow or black clays, as a cosmetic and/or to protect their faces from damaging sun rays. The same is true of traditional initiates, who cover their entire bodies with clays. It is believed that clays originating from the Isinuka (310 35' 0"S, 290 28' 0"E) in the Port St. Johns area are unique to South Africa and they are widely used for cosmetic and therapeutic purposes. Accounts of the healing qualities of the spring water and clays from this area abound. Reports of the smell of hydrogen sulfide from the spring and/or clay mine date back hundreds of years. The spa is frequented primarily by local people in search of spiritual and physical healing. However, the treatment environment there differs considerably from services offered by high-profile luxury destination spas, day spas and hotel spas. The World Health Organization has recognized traditional medicine as an invaluable means of satisfying the basic health care needs of about 80% of the world's population. Calls are being made for the systematic evaluation of traditional remedies by scientific methods, to ascertain their efficacies and to maintain strict observation of safety standards. More and more, Western countries are discussing and legislating the integration of traditional medicines in their health care systems. Appreciation of indigenous knowledge and traditional medicine and healthcare by governments and medical associations is increasing. Behind the reemergence of curortology lies the current popular revolt against synthetic products and the demand for more natural ways of treatment, especially for rheumatoid arthritis, for which there is no effective synthetic treatment. The comeback of curortology is greatly aided by advances in science, which shed much light on the healing properties of clays.

We conducted a scant analysis of Isinuka healing clays (Jumbam, 2011). Later on we embarked on a much broader study of the clays to encompass their mineralogy and geochemical aspects in order to have an in depth insight of the possible elements responsible for the acclaimed healing properties. The results of such findings are hereby presented.

Materials and Methods

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Ten samples of clayey materials used for cosmetic and therapeutic purposes were collected from Isinuka village in the Eastern Cape Province, South Africa. Four of the samples (Samples 1, 2, 3 and 4) were collected from a cave beneath a rock outcrop where water drips constantly from the roof of the cave onto a marshy slippery white clayey sedimentary material claimed to be used for the treatment of skin diseases and skin care . These samples were whitish in colour. Four other samples (Samples 5, 6, 7 and 8) were collected from the most popular pond-like spring located on top of the rock outcrop. The popular bathing spring is about 3 m2 wide. It spring emits a sulfur dioxide-like odour, and the water is turbid and dark grayish in colour and used by visitors for curing acne and other skin diseases . The last two samples (Samples 9 and 10) were collected from a much less frequented man-made pond about 50 m below the village hidden in the woods.

The samples were air-dried, and analysed for selected physicochemical, geochemical and mineral identification at Council for Geoscience in Pretoria, South Africa. Whereas the pH of the samples was determined in a clay water suspension, the particle size distribution of the samples were determined using a Malvern Masterizer 2000 Laser Particle size analyzer fitted with a Hydro 2000G dispersion unit. The concentrations of selected trace elements were determined using a PAN Analytical Axios, sequential WDXRF spectrometer equipped with a 4 kW Rh tube. Concentrations of trace elements were determined in pressed powder pellets each comprising of a sample mixed with Hoechst wax. An amphibolite reference material was used for quality control of the data generated. Methods used for X-ray and XRF analyses are described in Council for Geosciences (2011), and .

Results and Discussions

pH of samples

The pH range of the samples was 7.94 - 10.05 indicating that they were all alkaline. Samples 1 to 4 from the cave exhibited an average pH of 9.9 (strongly alkaline) compared to the average pH of 8.0 (moderately alkaline) for samples 5 -10 collected from the open springs. The strong alkaline pH value range of the samples brings to question the possibility of using these clays as possible cure against acne as reported (Faniran et al. 2001). The pH of normal human skin ranges between 5.4 - 5.9 . Such high alkalinity may have an adverse effect on the skin if the clay is applied directly without any pretreatment or neutralization. The skin's pH according to is the major factor influencing acne and other skin diseases. Propionibacterium acnes which causes acne thrives more on alkaline skin. Continuous application of alkaline clays on the skin may cause skin pH to increase promoting rather than preventing the development of acne. However, native Africans generally possess knowledge of clay preparations for cosmetic and/or medicinal purposes suitable for the nature of their skin.

Particle size distribution of clayey samples (PSD)

The samples had varied particle sizes with majority of them having silt as the dominant particle size. Two groups of PSD were observed (Figure 1). Samples 7, 8, 9 and 10 had finer particles than the others. The samples were therefore classified as either as silt, silt loam or loam (Figure 2). Particle size plays an important role in the application of clays for cosmetic or medicinal purposes. If the material comprises of coarse particles, it may cause abrasion and damage the skin. The particle size distribution of the material may also influence its healing properties through its influence on cation exchange properties. High clay content may be indicative of cation exchange and absorption/adsorption properties which may play a role in the cleansing properties of the material. In addition, particle size has been reported to play a significant role in the use of soils and clays as skin protectors because of their influence on refractive index (Hewitt, 1992; Hoang-Minh et al., 2010). The smaller the particle size, the greater the surface area of the material and the greater its potential as a cleanser.

Figure 1. Particle size distribution of clayey samples 1-10

Figure 2. Particle size distribution of samples

Minerals contents of the clayey soils

Seventeen minerals were identified in the clayey samples from Isinuka spa: quartz (SiO2), mica, calcite (CaCO3), interstratified illite (K0.6(H3O)0.4Al1.3Mg0.3Fe2+0.1Si3.5O10(OH)2·(H2O)), aragonite (CaCO3), gypsum CaSO4.2(H2O), rozenite Fe2+SO4.4(H2O), K-feldspart (KAlSi3O8), plagioclase (Na,Ca)(Si,Al)4O8), kaolinite (Al2Si2O5(OH)4), chlorite (ClO2−), halite (NaCl), pyrite (FeS2), pyrophylite (Al2Si4O10(OH)2), spinel (MgAl2O4) and smectite (Na0.3(Al,Mg)2Si4O10(OH)2.XH2O). Table 1 gives a summary of results of the semi quantitative analysis of identified minerals in the clayey soil samples. Quart, mica and calcite were the three dominant mineral phases in the samples followed by interstratified illite/smectite. Figure 3 is a representative diffractogram of analyzed sample 1. The results of FTIR of the clayey soil samples are shown on table 2. Here as expected the FTIR results are a complement of the XRD results shown on table 1. The presence of quartz, smectite and possibly muscovite is indicated.

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Table 1. The results in wt% of semi quantitative XRD analysis of minerals identified in clayey soil samples from Isinuka spa.

Sample

Calcite

Aragonite

Gypsum

Rozenite

K-feldspar

Plagioclase

Quartz

Mica

Kaolinite

Chlorite

Halite

Pyrite

Pyrophyllite

Spinel

Smectite

Illite/ Smectite/ Interstratification

1

27

6

1

2

-

2

31

9

-

-

6

3

3

-

-

10

2

14

-

-

-

3

2

40

25

-

-

-

-

-

4

-

12

3

2

-

-

-

6

2

45

37

2

-

-

-

-

-

-

6

4

-

-

-

-

-

2

42

42

2

-

-

-

-

-

3

7

5

16

4

2

1

-

2

49

15

-

-

1

2

-

-

-

8

6

27

4

1

1

-

2

40

12

-

-

4

3

-

-

-

6

7

4

-

-

-

-

2

49

36

2

-

-

-

-

-

-

7

8

29

4

4

1

-

2

32

9

1

-

4

2

2

-

-

10

9

28

-

3

-

-

3

40

14

-

6

1

-

-

-

-

5

10

28

-

1

-

-

2

44

12

2

-

3

-

1

-

-

5

Figure 3. Representative diffractogram of clayey soils (sample 1) with identified peaks.

Table 2 Infrared band positions and pure kaolinite for clayey soils from Isinuka Springs near Port St Johns

Samples

1

2

3

4

5

6

7

8

9

10

Remarks

Pure kaolinite

3694

3650

3620

3618

3618

3618

3617

3619

3617

3618

3628

Smectite occurrence (weak peak around 1636)

3470

3408

3370

3397

3408

3398

3398

3443

3373

3118

2971

2971

2971

2037

2037

2149

1114

1737

1962

1737

1738

1738

1738

1738

Quartz and possible muscovite occurrence at 1115 and 1025

1423

1415

1412

1423

1417

1423

1434

1559

1435

1365

1365

1365

1365

1302

1302

1265

1255

1265

1285

1285

1265

1228

1217

1217

1216

1216

1216

1216

1212

1212

1203

1202

1204

1204

1189

1189

1188

1010

1003

999

996

999

1002

1000

979

982

987

987

Al2OH bending bands

936

924

922

925

912

887

886

886

882

884

885

909

910

910

910

873

872

872

873

872

872

842

845

841

830

829

830

830

815

816

814

840

815

815

814

814

815

790

798

797

797

797

797

797

796

796

796

797

Interference for quartz at 785-820 and muscovite at 799. (Al-O-Si vibrations of micas)

786

787

786

786

786

786

786

778

778

777

777

777

777

777

777

777

777

752

729

728

723

720

728

729

714

715

715

715

693

694

694

694

694

694

694

693

694

693

694

Quartz interference could occur

657

537

468

430

Geochemistry of clayey soils

Sulfur content

Since the spring water and clays are claimed to have medicinal properties and a pungent sulfur dioxide-like smell oozing out of the springs, it was important to test for the sulfur content of the samples collected. All samples had sulfur content < 1.5%. Samples 1 -4 collected from inside the cave where there is no noticeable pungent gaseous smell, had lower concentrations of sulfur compared to those from the open springs. Despite lower concentrations of sulfur in samples from the cave, visitors nevertheless collect the material and use it for topical applications. Continual saturation of the whitish clay with saline water dripping from the roof of the cave might result in improving its medicinal properties. The use of bath salts for therapeutic purposes is well known. The sulfur content in samples collected from the open springs was above 0.8%, rising to 1.3 % in sample 9 (Fig. 4). The use of sulfur in dermatological applications is well established due to its antifungal, antibacterial and keratolytic activities .The sulfur content in the samples may add value to the healing properties claimed.

Figure 4. weight % content of sulfur in clayey samples

Substances applied to the skin can penetrate the skin and be able to cause local and systemic effects . The bromine concentration though comparatively small in samples 1-4, ranges from about 20 -100 ppm in samples 5-10 with a mean value of 66 ppm. This may be ascribed to the saline nature of the water in which the clay is imbedded. The concentrations of major and trace elements are summarized in Table3.. Arsenic was found in all the samples tested although the concentrations are low ranging from 6-15ppm with a mean value of 9.6 ppm. Although arsenic has a history of medicinal applications (Antman, 2001, Roy and Saha, 2002), it is nevertheless an extremely toxic element and can cause severe damage to human health even at low concentrations especially on repeated contact exposure. The concentrations of cobalt range from 4 to about 17 ppm while chromium has concentrations that are fairly evenly distributed across all samples ranging from about 55-90 ppm with a mean value of about 70 ppm. Copper and nickel have an almost equal distribution pattern in all samples but exhibit mean concentrations 38 and 21 ppm, respectively. Higher lead concentrations are seen in white clay samples 1-4 with a mean of 30 ppm as compared to black clays samples 5-10 with a mean value of 17 ppm. The mean values of strontium in white samples 1-4 is about 225 ppm while that in black samples is 2550 ppm, a sharp difference in concentration between the white and black clays. The highest concentration of uranium in white clays is 2.8 ppm while black clays exhibit a maximum value of 8.5 ppm. Zinc exhibits a similar distribution pattern across all samples with a mean concentration value of about 88 ppm.

Table 3

Results of major (wt%) and trace (ppm) elements analysed by X-ray fluorescence spectrometry

Sample

1

2

3

4

5

6

7

8

9

10

SARM-4

SARM-4

SiO2

48.16

58.24

58.73

57.48

25.14

30.62

41.33

26.78

33.59

41.33

52.64

50.91

TiO2

0.53

0.64

0.63

0.62

0.35

0.44

0.67

0.38

0.52

0.58

0.20

0.20

Al2O3

15.41

18.74

20.18

17.38

8.00

9.35

11.59

8.23

9.35

12.34

16.50

16.34

Fe2O3(t)

5.43

6.65

7.35

6.41

1.91

1.97

5.10

1.94

1.77

5.46

8.97

9.23

MnO

0.042

0.045

0.100

0.034

0.369

0.435

0.232

0.391

0.237

0.248

0.18

0.186

MgO

1.27

1.15

1.35

0.99

0.82

0.87

1.22

0.87

0.74

1.38

7.50

8.07

CaO

11.24

2.67

0.61

4.49

16.43

14.86

13.49

17.69

10.78

13.56

11.50

12.28

Na2O

1.10

1.01

1.12

0.95

4.41

2.99

2.57

3.99

2.64

2.09

2.46

2.56

K2O

3.58

3.94

4.14

3.83

0.97

1.34

1.68

0.97

2.10

2.17

0.25

0.31

P2O5

0.056

0.068

0.148

0.041

0.227

0.244

0.118

0.224

0.137

0.114

0.03

0.020

Cr2O3

0.010

0.014

0.013

0.013

0.008

0.010

0.013

0.008

0.010

0.011

30.000

0.007

L.O.I.

12.58

7.01

5.87

8.08

40.13

36.30

21.91

37.57

37.21

20.33

-0.40

-0.53

Total

99.42

100.17

100.23

100.32

98.77

99.43

99.92

99.06

99.09

99.62

129.83

99.57

H2O-

1.20

1.52

1.49

1.38

4.66

4.66

1.91

4.14

4.75

1.75

259.66

0.21

As

10

11

15

7.8

9.5

6.5

13

6.5

6.7

13

33.5

39

Ba

745

761

723

751

302

359

469

322

411

484

590

609

Bi

<3

<3

<3

<3

<3

<3

<3

<3

<3

<3

1.17

<3

Br

5.6

4.3

6.4

4.4

100

77

43

98

64

24

2.9

2.1

Ce

43

48

52

38

35

35

66

37

41

51

70

67

Co

5.5

7.4

15

4.0

8.7

9.3

17

8.8

8.8

15

14.2

16

Cr

74

88

81

82

55

63

75

57

65

70

62

66

Cs

<5

<5

<5

<5

12

10

<5

8.4

<5

<5

9.0

<5

Cu

24

31

41

33

51

45

32

51

48

30

21

18

Ga

26

29

30

26

11

13

16

11

14

17

19.3

20

Ge

8.0

7.3

9.5

6.7

22

20

2.4

18

20

2.5

1.3

1.3

Hf

<3

<3

<3

<3

10

6.8

<3

9.6

12

<3

6.8

5.9

La

29

35

42

27

21

20

39

16

22

33

34

38

Mo

<2

<2

<2

<2

<2

<2

<2

<2

3.2

<2

1.4

<2

Nb

13

14

14

14

4.9

6.4

11

4.9

7.6

10

16.6

16

Nd

19

20

30

15

17

18

33

18

21

26

28

26

Ni

14

19

31

12

27

23

27

26

18

27

20.4

22

Pb

24

40

28

27

5.2

6.2

24

4.9

6.7

20

98

96

Rb

253

258

263

245

108

124

144

112

133

157

140

144

Sc

22

28

43

22

73

80

11

68

102

12

11.2

13

Se

<1

<1

<1

<1

<1

<1

<1

1.1

<1

<1

0.14

<1

Sm

<10

<10

<10

<10

<10

<10

<10

<10

<10

<10

5.2

<10

Sr

426

168

83

207

1,991

1,797

1,297

2,118

1,813

1,239

155

161

Ta

<2

2.7

<2

<2

<2

<2

<2

<2

<2

<2

1.4

<2

Th

16

18

17

17

3.3

4.6

10

3.9

5.8

12

11.6

11

Tl

<3

<3

<3

<3

<3

<3

<3

<3

<3

<3

1.0

<3

U

4.0

4.6

2.7

3.5

8.1

7.6

6.2

8.6

8.5

5.5

3.3

3.3

V

125

134

140

128

100

98

99

92

111

96

86

92

W

<3

3.2

<3

<3

<3

<3

<3

<3

<3

<3

3.1

3.4

Y

25

25

76

20

122

123

54

118

127

52

25

28

Yb

3.4

3.4

5.4

<3

13

13

5.1

12

11

4.3

2.66

<3

Zn

57

73

138

54

109

103

89

101

69

89

680

680

Zr

153

197

222

196

652

551

225

546

749

193

245

250

Conclusions

This paper has examined the mineralogy and geochemical properties of the clayey soil material from Isinuka springs used for cosmetic and dermatological applications by the inhabitants of Isinuka, Port St Johns, the surrounding villages and towns in Pondoland of the Eastern Cape of South Africa. From the analytical data, the healing properties of the clays may be ascribed in part to the presence of sulfur known for its antibacterial and antifungal properties and the alkaline pH of the samples. Furthermore, the presence of arsenic either alone or in combination with sulfur and other elements may be responsible for the healing properties as well. Arsenic has a history of medical applications dating back centuries prior to the arrival of penicillin as a cure against syphilis, yaws and other bacterial infections . It is a human carcinogen and extremely toxic. Although the concentrations in the Isinuka clays are considerably small with an average value of only 9.6 ppm, repeated exposure could pose a health risk and should be avoided. The presence of lead especially in the white clays is small but could be a problem on repeated topical application of the clays given the established toxicity of lead. The fall of the Roman Empire was ascribed to the use of lead vessels for storing wine and water that poisoned the entire population . Although the elements listed in this study have some degree of negative health implications , their low concentrations are a consoling factor inspite of the mean value of strontium being as high as 2550 ppm. Although radon was not detected in the analysis, the presence of strontium and uranium may well signal the possibility of radioactivity of the samples.

This study reveals that the clay from this area, though useful for therapy and cosmetics, may constitute a health risk on repeated exposure. However, the people from Isinuka and patients receiving treatment from this village are culturally brought up to revere the healing system as holistic and handed down to them by their ancestors. The socio-economic and cultural implications of advocating a stop to the use of water and clay from these springs are at present unthinkable. Therefore, studies on the toxicological profile of these clays are necessary with a view of identifying appropriate beneficiation methods and technologies that make the clays safer for use.

Acknowledgement

The author would like to thank the Directorate of Research Development, Walter Sisulu University for financial assistance.