Metals in urban soils of Europe: A systematic review

Metal contamination of soils is widespread across Europe and is of great concern as it may impact food production, the supply of drinking water and human health (European Environment Agency, 2014; Panagos et al., 2013). Most re-search to date on soil metal contamination has focussed on agricultural soils (Tith et al., 2016a). Current knowledge of the extent of urban soil metal contamination in Europe, however, is limited, especially for soils in recreational areas, which is particularly concerning as these areas may have a high footfall. Here, we conducted a systematic analysis of metal contamination in European urban soils based on 174 peer-reviewed studies spanning 143 urban sites and 29 European countries. The results show that reporting of data on urban soil metals is highly heterogeneous across the study area. Over half of all studies are from only five countries (Italy, Spain, UK, Poland and Serbia) and no data are available for 14 other European countries. The metals that most commonly exceed national safety thresholds are Pb, Zn, Cu, Cr and Ni. Elevated levels of these metals are usually attributed to anthropogenic sources, primarily traffic and industry. Some 22 % of urban sites studied show anthropogenic enrichment; this phenomenon is most common in Italy, Serbia and Finland. In contrast, 44 % of urban sites studied show geogenic metal enrichment; this is most com-mon in Italy, the UK and Serbia. The dataset is subject to a sample size bias, whereby soil metal enrichment is identified more frequently in regions with more data. Future studies should focus on key knowledge gaps, such as urban soils in locations with current or historical heavy industrialisation and locations in central and eastern Europe. Study methods should be standardised to facilitate comparison of soil metal data from different studies and European safety thresholds should be identified for key elements.

Automated summary

Metal contamination of soils in Europe is widespread and of great concern due to its potential impact on food production, drinking water supply, and human health. However, current knowledge of urban soil metal contamination in Europe, particularly in recreational areas, is limited. This study conducted a systematic analysis of metal contamination in European urban soils based on 174 peer-reviewed studies, revealing highly heterogeneous reporting of data across the study area. Anthropogenic sources, such as traffic and industry, contribute to elevated levels of metals like Pb, Zn, Cu, Cr, and Ni in urban soils, while geogenic factors also play a role. Future research should focus on key knowledge gaps, standardize study methods, and identify European safety thresholds for key elements.