Identifying indigenous non-agricultural uses of soil in selected communities in KwaZulu-Natal, their safety for use and understanding the soil properties that govern these uses.

Abstract

South African communities, especially in rural areas still practise indigenous soil use e.g. applying soil paste as sunscreen and geophagia among others. This study aimed to document non-agricultural uses of soil in communities such as Elandskop, KwaNxamalala, Willowfontein and Pietermaritzburg central in uMgungundlovu district. Information on soil uses was collected through key informant interviews and a baseline survey. The baseline survey was conducted through administering 50 questionnaires in each area. Ten soil samples (used for geophagia and cosmetics) were then collected from each area to analyse for soil physicochemical and biological properties using standard analytical techniques. The safety of soils for use was also assessed through microbial (bacterial, fungal, and total coliform counts, then E.coli identification) and heavy metal determination. Results showed that the soil uses that were ranked as most common were cosmetics, geophagia, medicinal followed by construction as the least used. Cosmetic soil was mostly used as sunscreen or skin cleansers. While geophagia was practised for enjoyment, cravings, and as nutrient supplement. The main side effects of geophagic soil were observed to be constipation, appendix infection and development of gull stones, while side effects to cosmetic soil use were skin irritation, drying and blemishes. Chemical analysis showed that the cosmetic soils had pHs in the acidic range (4.7 - 6.07), which corresponded with normal skin pH. The CEC was however deemed too low (3.04-24.11 Cmolckg-1) for these soils to be effect as cleansers as they would not be able to adsorb impurities from the skin. Geophagic soils also had acidic pH ranges (3.73 – 5.84), which corresponded with pH of human saliva, whilst their CEC was also low (3.6 – 25.41 Cmolckg-1) and typified that of low adsorption kaolinitic clays. Cosmetic soil users preferred red coloured soil as effective sunscreens. This was confirmed by mineralogy analysis that revealed a high presence of haematite in these soils, which has low UV transmission. Both quartz (which was supported by course soil textures) and haematite featured regularly in the cosmetic and medicinal soils, but these soils however lacked metals like zinc oxide and titanium oxide found in commercial sunscreens, making them less effective as sunscreens. The high levels of quartz in cosmetic and medicinal soils can also potentially cause skin abrasion when applied regularly. Geophagic soil colours varied from white through pale yellow, reddish yellow, yellow brown to light grey; which typified a range of minerals from kaolinite, quartz, calcite, and haematite. High levels of quartz however pose a risk to dental enamel damage and intestinal wall abrasion if consumed in excess, while haematite is a beneficial source of nutritional iron. It was recommended that users select finer textures to consume or apply onto their body to avoid the negative effects of high quartz levels. The E.coli bacterium was found in samples from Elandskop, KwaNxamalala, and Willowfontein, but not in those from PMB central. This could be because vendors in PMB central heat-treated their soils before selling, which helped kill these harmful bacteria. Some geophagic samples also had coliform (381-741 CFU/ml) counts that were above the limit (<200 CFU/ml) set for fresh vegetables, indicating a risk of pathogenic diseases. It was recommended that soil users from other areas should also use heat-treatment to minimise pathogenic contamination in their samples. Cosmetic soils generally had lower concentrations of trace metal elements compared to similar studies in South Africa. Some of these elements e.g. Pb (0.13 - 6.67mg/kg), Zn (-0.14 - 0.87 mg/kg), Cd (-0.04 - 0.34 mg/kg) actually had concentrations below the recommended safety limits and were thus harmless in cosmetic soils making them safe for use. Geophagic soils mostly had low and safe levels of Cu (-0.88.-1.50 mg/kg), Zn (-0.31-1.15 mg/kg) as well as Cd (-0.0067-0.31), Fe (-3.58 to 15.85 mg/kg), Ni (-0.39-1.27mg/kg), making them essential sources of these nutrients as opposed to being toxic. However, Pb (0.27-5.93 mg/kg) and Mn (-0.19-9.56 mg/kg) levels in geophagic samples were above their safety limits set by WHO/FAO making them unsafe in this regard. Consumers must thus watch out for lead poisoning when consuming geophagic soils.