Abstract

Samples of tree bark, which accumulate airborne material, were collected from seven locations in the UK to provide an indication of the magnitude and source of lead pollution. Measurement of the Pb content and ^206/207Pb stable isotope ratio by inductively coupled plasma mass spectrometry revealed significant differences between the sites. The concentration of Pb varied over almost four orders of magnitude from 7.2 to 9,600 µg g⁻¹, the maximum values being found near a ‘secondary’ Pb smelter. The ^206/207Pb isotope ratios varied from 1.108 ± 0.002 to 1.169 ± 0.001. The lowest Pb concentrations and highest isotope ratios were detected in bark samples from the Scilly Isles, reflecting the low-level of industry and road traffic. In contrast, samples obtained from a city centre (Sheffield) and near a motorway (M1) contained 25–46 µg g⁻¹ Pb and recorded the lowest ^206/207Pb ratios. Higher concentrations in the vicinity of a coal-fired power station recorded a ^206/207Pb ratio of 1.14, suggesting a significant contribution from fly-ash. The relative contribution of lead from petrol (^206/207Pb = 1.08) and other sources such as coal (^206/207Pb = 1.18) were thus estimated using mass balance equations. Tree bark near the lead smelter recorded an intermediate ^206/207Pb ratio of 1.13 reflecting the processing of material of mixed origin.