Aims: The aim was to biomonitor air quality for praseodymium (Pr) in Leicester city (England) after detecting slight contamination of this element in topsoils across the city and surrounding rural areas, when compared with other industrialised towns in Europe.

Methods: Thin layers of bark were collected from 96 trees from Leicester (n=55) and surrounding rural/suburban areas (41), at a consistent height of 1.50–1.80 metres from the ground. Pr was monitored by ICP-MS in cleaned/ground/homogenised samples mineralised with HNO₃/H₂O₂ [LoD=0.157 ng/g dry weight (dw)]. The data were compared with the levels of Pr described in 52 topsoil composite samples collected in the same year (2017-18).

Results: The levels of Pr were slightly higher in the samples collected from trees that grw in urban areas (median and ranges, in ng/g dw): 2.611 (0.714-47.603) and 2.450 (0.757-14.839). These results might be explained by the presence of Pr monitored in topsoils, in which no statistical differences were found between both main areas, detecting a wide distribution of this element across the city and in surrounding rural areas. Levels were much higher than the range reported in Pinus ponderosa bark samples (US; 1.85-2.69 ng/g dw) collected in an area in eastern Washington away from roads, to reduce the effect from traffic, suggesting some anthropic atmospheric contamination of Pr in Leicester city and surrounding areas, derived from different sources such as agricultural practices, waste disposal, metal recycling, vehicular/industrial emissions, and urbanisation. However, the toxic risks derived from the ingestion of and dermal contact with Pr present in topsoils in Leicester city is likely to be minimal.

Conclusions: The presence of Pr in air in Leicester could be affected by different anthropic sources that should be investigated to reduce its presence; studies should include the monitoring of the content of Pr in particulate matter in Leicester city.