Fig. 4

Boxplots of the absolute concentrations of trace metals, which showed enrichment over their background concentrations. All concentrations are given in mg/kg. Blue lines indicate the upper and the lower limit of the trigger action values as collected by Kabata-Penidas [128] from several European legislative documents. The upper limit for Ni exceeds the range of the plot. The red line indicates the geometric mean of screening levels compiled by the US EPA [129] from legislative documents with a focus on North America