Contaminant Elements in Roadside Dust and Soil

Dear Colleagues,

The intended Special Issue should cover a data compilation of roadside dusts and urban soils. Air quality monitoring often refers to concentrations in m³ of air, but atmospheric deposition data and concentrations in dust are not so often reported. Further, the sampling strategy is of great influence upon the data and their interpretation, whether the mere dust is taken with a brush or a vacuum cleaner, or roadside soil cores are taken.

1. Origin and sampling

Data can only be compared if the same sampling depth has been used, which is found in the Material and Methods section of the respective paper. Datasets of roadside dust only of 0–2, 0–10, or 0–20 cm exist in the literature, the data of which should not be mixed. Roadside dust gets diluted with the adjacent soil at various amounts. Mapping or at least description of the sampling sites is essential. Various sources of input have been assigned, often from principal component analysis, which is per definition limited to linear dependencies.

2. Physical properties and minerals

Sealing and compaction impose great changes to hydraulic properties and soil gas transport, which can be monitored by electrical conductivity. Combustion processes cause inputs of magnetic particles. Radioactivity measurements in urban soil are still scarce.

Some minerals are indicative of human settlements, like glasses and bricks.

Physical changes remain for a long time and are indicative for excavations of historic settlement sites.

Because nanoparticles largely act as catalytic surfaces or can more easily enter living cells, information about nanoparticles is also welcome.

3. Chemical properties

Metal pollution, particularly so-called “heavy metals”, semimetals (e.g., As, Sb), and platinum group metals, have been often the subject of health concerns. Apart from total element contents, mobile soil fractions and adsorption studies have to be considered as well. As most urban green plants are not directly used for human or animal consumption, soil to plant transfer pathways are less important than in agricultural or forest areas.

In addition to metals, nonmetals like P, S, and Cl have to be considered as well.

Contamination levels have been classified by comparison with threshold levels for individuals, and as a combination of several parameters as the geoaccumulation index, the pollution index, and the contamination index.

4. Input to roadside soils

Atmospheric deposition sources are traffic, combustion processes, and abrasion from buildings, together with long-range transport. Changing technologies in industrial countries have reduced Pb and carbon soot and increased platinum group metals and CeO₂ from automotive catalysts. Washout from industrial emissions has been reduced through the purification of flue gases. There is still the input of de-icing salts, ashes and slags, and wastes from building and construction sites.

5. Output from roadside soils

To achieve optimization of green energy, green plants grown in parks and residential areas can be used as compost if the collection sites have been thoroughly selected for low contaminations. Others have to go to waste incineration.

The run-off from sealed plots enters adjacent urban soils and may be hazardous to urban trees. Urban run-off can be easily detected in stream sediments nearby.

6. Transformations

The levels of contamination usually decrease from roadside soils and industrial soils to parks, residential soil, and riverside areas, wetlands, and forests nearby.

Fires, floodings, and former industrial sites can be detected by changes of soil composition, as well as historic roads and railways, and fireplaces back to prehistoric times.

Worldwide, increasing population and global warming will necessitate developing remediation strategies for contaminated sites, to increase the areas of agricultural production and recreational forests, which is currently in progress.

Dr. Manfred Sager
Guest Editor

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