Atmospheric contamination of lutetium in Leicestershire (England) using tree bark biomonitoring

The presence/distribution of lutetium (Lu) in topsoils from Leicester city and surrounding areas (England) represents a low risk for the population (ingestion and dermal contact); meanwhile, its content in wild mushrooms could present some oral risks. To monitor the air quality, about 2-5 grams were collected from a sample of of bark with a length of 2-6 millimetres from 55 different trees across Leicester and 41 from surrounding rural/suburban areas; samples were taken at 1.50–1.80 metres from the ground to limit contamination from topsoil/dust. Lu was monitored by ICP-MS in cleaned/ground/homogenised samples mineralised with HNO₃/H₂O₂ [LoD=0.066 ng/g dry weight (dw)]. Results were compared with previous studies performed on 106 mushrooms and 850 topsoils collected in the same areas. Levels of Lu were similar in both main areas; data were presented as medians and ranges for urban and rural areas, respectively (in ng/g dw): 0.580 (0.182-2.118) and 0.584 (0.402-1.071). This results are in line with the distribution observed in topsoils, i.e., Lu did not show statistical differences between urban and rural areas (p-value = 0.602; 0.117 vs. 0.123 mg/kg). However, some bark samples collected in the city presented higher levels of this element. This pattern is similar to levels observed in wild mushrooms, in which the higher presence of Lu was detected in mushrooms collected in urban areas (0.347 vs. 0.196 ng/g dw). Results suggest similar sources of air contamination by Lu across the main areas monitored, in which topsoils might play a role that should be further assessed, although these made minor contributions to the levels monitored in wild mushrooms. Although preliminary, in general, levels of Lu found in the tree bark were lower than the natural background reference concentration of Lu reported in plant materials collected in a forest in northwest Germany (2.5-5 ng/g dw), suggesting a minor contamination by Lu in Leicestershire.