Tuesday, 4 April 2017

Evaluating the health risks presented by clays traditionally used as cosmetics in South Africa.

Forms of clay have been used as cosmetics since at least the Mesolithic, and the practise is still widespread in many cultures today. In South Africa such clays are gathered and sold by traditional healers in many areas, both for daily use and for specific rituals and ceremonies, with some clays being sold as sunscreens or for other medicinal purposes. The composition of such clays has been extensively studied in Eastern Cape Province, but almost no work has been carried out on cosmetic clays from other parts of South Africa.

In a paper published in the South African Journal of Science on 29 March 2017, Refilwe Morekhure-Mphahlele of the Department of Chemistry at Tshwane University of Technology and the Department of Chemical Engineering at the University of Pretoria, Walter Focke of the Institute of Applied Materials at the University of Pretoria, and Wiebke Grote of the Department of Geology at the University of Pretoria, describe the results of the chemical analysis of samples of cosmetic clays obtained from traditional healers at three locations in South Africa.

Three of these samples came from a river pool near Mtubatuba in KwaZulu-Natal, where they were sold under the isiZulu name ubumba. Two came from Nongoma, also in KwaZulu-Natal, and were again marketed as ubumba. The final sample came from the Mbaleni wetlands of Limpopo Province, where it was sold under the Tshivenda name vumba. All were sold in clear polythene bags. 

The clays were found to be quite variable in composition, even when obtained from the same source, suggesting that the collectors were choosing them for their colour and texture rather than other qualities. All the clays were creamy in texture and yellowish grey in colour.

One of the samples from Mtubatuba plus the sample from the Mbaleni wetlands were comprised mainly of smectite, with significant amounts of quartz and lower amounts of kaolin and plagioclase, while the other samples were comprised chiefly of quartz, also with and lower amounts of kaolin and plagioclase. All also contained minor amounts of the titanium dioxide minerals rutile and anatase. The high levels of quartz in the clays is a potential concern, as quartz is harmful when ingested, not so much because it is directly toxic, but because the body cannot expel it, so that over time it can build up within tissues. However moderate external use of quartz-based cosmetics should not be a problem. 

 Scanning electron micrographs showing the morphology of powder particles. V1, U2 and U3: smectite platelets; U3: kaolin flakes; W1: a titanium dioxide crystal on top of quartz agglomerates; W2: quartz agglomerate. Morekhure-Mphahlele et al. (2017).

The samples did not contain any obviously harmful elements, such as arsenic, lead or uranium, though they did contain trace amounts of chromium, copper, zinc and nickel, which are potentially harmful, as well as strontium, which is not directly harmful but which has naturally occurring radioactive isotopes, and zirconium and yttrium, which are also radioactive. Morekhure-Mphahlele et al. suggest that future work is needed to ascertain if these elements present a health risk, which will depend on the extent to which they are bound to the clay minerals or readily exchangeable and therefore bioavailable (i.e. can be absorbed into the body).

The sample from the Mbaleni wetlands was slightly acidic, whereas all of the others were slightly basic. None of the samples was likely to cause immediate harm due to its pH, but healthy Human skin is usually slightly acidic, and potentially long-term use of basic cosmetics could disrupt the natural flora of the skin (Bacteria and other micro-organisms), potentially leading to dry, sensitive, skin or even eczema. 

See also...

http://sciencythoughts.blogspot.co.uk/2016/12/three-killed-colecting-coloured-soils.htmlhttp://sciencythoughts.blogspot.co.uk/2016/11/evidence-of-heat-treatment-during.html

http://sciencythoughts.blogspot.co.uk/2015/01/the-pigment-binding-agent-in-tang.htmlhttp://sciencythoughts.blogspot.co.uk/2012/07/ceramic-figurines-from-pleistocene-of.html

http://sciencythoughts.blogspot.co.uk/2012/05/dating-chauvet-cave-art.htmlhttp://sciencythoughts.blogspot.co.uk/2012/02/neanderthals-using-red-ochre-at-least.html
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