Lichens as biomonitors for manganese and lead in pretoria, South Africa

Parmotrema austrosinense (Zahlbr.) Hale lichens were collected from the Pretoria central business district (CBD), as well as three sites to the east of Pretoria; the National Botanical Gardens, the CSIR campus and the suburb of Lynnwood, with the aim of utilising these lichens as bio-monitors of air quality to determine the effects of the phasing out of leaded petrol and the simultaneous introduction of manganese anti-knock additives to fuel in South Africa. In addition to lichens, roadside dust and soil samples were collected from the CBD and CSIR campus, and all samples were analysed by flame atomic absorption spectrometry after acid digestion. There was no significant difference (95 % confidence) between the Mn content of lichens from all sampling sites (overall average of 97.1 ± 39.1 μg.g^-1, n= 28), which was most likely due to an even suspension of Mn-containing particles arising from soil dust. Additional contributions to Mn loading as a result of vehicle emissions were currently not evident. For all non-CBD sites, higher Pb levels were found in lichens which were nearer to busy roads, suggesting an historical impact by vehicular emissions of Pb arising from leaded petrol usage. The Pb concentrations in lichens found in the CBD (average of 181.1 ± 98.0 μg.g^-1, n=10) were significantly higher (95 % confidence limits) than those of lichens growing outside of the CBD area (average of 41.5 ± 36.4 μg.g^-1, n=18), and the Pb levels were higher than those of Mn, which was contrary to that found in sites outside the CBD.