The use of jacaranda leaves to determine the distribution of trace elements in Pretoria
The spatial distribution of trace elements in Pretoria is investigated by reference to the concentrations of lead, iron, manganese, zinc and copper in Jacaranda leaf samples. Different methods of sample preparation and analysis are examined. The variation in the trace element concentrations on a leaf and within a tree; temporal variations (daily and monthly); spatial variations (along a road, in different land-use zones); and the effect of meteorological variables (rain and wind) are investigated. Differences between the results from two annual surveys, the distributions and anomalies for each of the examined elements are discussed. The relationship between results from leaf and adjacent air-filter and/or deposit gauges is examined. The linear regression equations for lead, iron, manganese and zinc are used to simulate the atmospheric concentrations of these elements. The application of leaf sampling to augment and clarify the results from the existing Pretoria atmospheric monitoring network is discussed. It is concluded that the technique can be successfully applied to determine the distributions of trace elements in Pretoria. There is little variation in the concentrations of zinc and copper. The high leaf lead concentrations are found in the City centre and at points of traffic convergence. Anomalies of manganese occur in the southern suburbs, probably derived from the soil, and for iron to the west of the City centre, the possible source of which is industrial activity. The influence of Iscor, the iron and steel works, to the west of Pretoria is clearly shown by the distribution of iron in Pretoria. The comparison with the results from the deposit gauges is poor. The correlation between the air-filter and leaf results is particularly good for lead and iron. The simulated distributions of lead and zinc are very similar, suggesting that traffic is the source of both. Of the existing atmospheric monitoring stations in Pretoria the site at Munitoria is located in a position well within the overall central area exhibiting the highest lead, iron and zinc concentrations. It is concluded that additional atmospheric monitoring sites are required to determine the sources of the anomalies for iron and manganese, the existence of which were unknown prior to this study.
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Department of Environmental and Geographical Science