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Lippia scaberrima Sond. is an aromatic shrub of semi-arid, summer-rainfall grassland and occurs in the
northern provinces of South Africa. The plant is a common natural coloniser of gold mine tailings and
contaminated soils, and is one of a number of similar species that has been tested for use in tailings
stabilisation. Mine rehabilitation strategies worldwide involve the use of native and locally tolerant plants.
Where such plants have commercially valuable attributes, their use to stabilise contaminated soils and
tailings also provides opportunities for local beneficiation and the development of new industries post-
mining. The production of aromatic plants is considered a particularly safe option for mine waste since they
are generally unpalatable to herbivores and the steam distillation methods used for essential oil isolation
yield products free from metal and radioactive contaminants.
In the initial part of this study the essential oil of bulk samples of L. scaberrima growing in a natural habitat
was found to exhibit strong in vitro antifungal activity against several commercially important fruit post-
harvest spoilage pathogens. Gas chromatography with flame ionisation detection (GC-FID) analysis of the
oil identified limonene, 1,8-cineole and R-carvone as the main constituents. The antifungal activity of the oil
was attributed to the presence of R-carvone. These results were confirmed by several semi-commercial and
commercial trials on mango, avocado and citrus fruit.
The potential application of L. scaberrima essential oil, rich in R-carvone, as a post-harvest fungicide of
fruit, may necessitate the large-scale production of the oil. However, essential oil profiles of Lippia spp. in
general have been shown to exhibit high intraspecific variability due to genetic differences. In this
investigation the essential oil profiles of L. scaberrima specimens from populations growing in mine-
contaminated substrata were compared to those of specimens growing in uncontaminated soils to identify a
R-carvone chemotype selected for the harsh growing conditions existing in and around mine tailings. The
findings indicate that L. scaberrima does not bioaccumulate metals present in contaminated soils, and
essential oils prepared using steam distillation were free of metals and uranium.
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Legacy issues from abandonment to asset
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