Use of potentially toxic elements in sedimentable industrial dust to trace their input in soils (Northern France)

PurposeAt the vicinity of metallurgical and steel activities, notable contamination of Potentially Toxic Elements (PTE) is measured in discrete environmental compartments (soils, biosphere, atmosphere). The main question addressed in this study pertains to the influence of industrial dust fallout on PTE concentrations in soils. The study was conducted near the seaport of Dunkerque, belonging to one of the most industrialised and dust-emitting sites of France.Materials and methodsA composite sample of dust fallout was collected over a 4-month-period in urban areas downwind of nearby industries. SEM-EDS and ICP-AES/MS analyses were conducted on this sample to identify metallurgical particles and highlight the main tracer elements of industrial activities. Then, a comprehensive characterization of soils was conducted to map the spatial distribution of metallic pollution levels in the study area. Nearby soil parameters analysis (grain-size distribution, pH, CEC, SOM, calcium carbonates and water contents), the soil chemical composition was identified using XRF and ICP-AES/MS analyses.Results and discussionWe quantified the proportion of particles of industrial origin in the composite dust sample at 88% of the total fraction, stressing the importance of metallurgical activities near the seaport of Dunkerque. This dust sample shows particularly high enrichment factors (EF) for Cd, Cr, Ni, and Mo with values of 235, 108, 78 and 169 respectively. The use of different pollution assessment indexes evidences that Mo-Cr-Ni associations appear particularly interesting to trace the incorporation of metallurgical sedimentable dusts into soils. Thus, we identified the presence of distinct high-PTE patches related to industrial dust deposition in the studied soils, with a parallel decrease in their quality index (i.e. Mo Geo Accumulation Index indicating moderate to heavy contamination).ConclusionsOur study revealed that the soils located close to the industrial area are the most affected by industrial dust deposition. Several factors explaining the spatial distribution of the soil contamination levels are examined, and it seems that distance from emission sources is not necessarily the most relevant. The study suggests that distribution of plant cover or buildings may act as barriers preventing soils from being exposed to dust deposits.