Using geostatistics and local Moran's I to identify pollution hotspots of rare earth elements in urban soils of London

Rare earth elements (REEs) in urban soils are receiving more attention because of their potential toxicity and long-term effects on human health. Up to now, there is little information about the spatial patterns of REEs and... [ view full abstract ]

Rare earth elements (REEs) in urban soils are receiving more attention because of their potential toxicity and long-term effects on human health. Up to now, there is little information about the spatial patterns of REEs and their influencing factors in urban soils. In this study, based on data from the British Geological Survey “London Earth” geochemical survey containing a total of 6468 soil samples collected from the urban area of London, the spatial distribution of Y, Yb, Sc, La, Ce, Sm and Nd, and the influencing factors were investigated. Spatial clusters and spatial outliers were classified using the index of local Moran’s I, showing elevated concentrations of REEs in the northwest, northeast and south parts of the study areas while all the 7 REEs exhibited generally similar spatial patterns: high values were mainly located in soil over Alluvium, Glacial till and Clay-with-flints deposit, demonstrating close relationships between REEs and the lithology. Meanwhile, hotspot analysis identified high values of REEs in public parks, private golf clubs, school playing fields and domestic gardens especially in Brent, Harrow, Croydon and Bromley. These areas are likely to arise from anthropogenic activities including the application of phosphate fertilisers. The hotspots of REEs revealed in urban soils may imply potential contamination requiring further attention.

Key words: Hotpots, Rare earth elements, Local Moran’s I, Urban soil