Abstract

Samples of tree bark, collected over an area of 4 km² near a small non-ferrous metals smelter in Derbyshire, UK, were analysed for Pb and Al by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Analyte concentrations varied from 100 to over 25 000 mg kg⁻¹ and 5 to 1000 mg kg⁻¹, respectively. While an inverse relationship between the Pb content of bark and distance from the smelter was observed, concentrations fluctuated, indicating a variability in sample collection efficiency and problems in standardization. To overcome these effects, the Pb/Al ratio was calculated and subsequently normalized to the average Pb/Al ratio in continental crust (0.00015). On the assumption that the time-averaged concentration of airborne Al in this area is relatively constant and derived principally from wind-blown soil, the measurement represents an anthropogenic ‘enrichment factor’ (^PbEF). ^PbEF varied from 10 000 to over 1 000 000, and showed a consistent reduction with distance from the smelter. Isolines of equal ^PbEF were subsequently defined on a map of the sampled area. Pb contamination was greatest in the vicinity of the smelter, and preferential transport along the NW–SE axis of the valley (in which the smelter is situated) was observed. The use of enrichment factors thus proved valuable in defining the relative level of airborne-derived Pb pollution.