The concentration and loading distribution of trace metals (Cu, Zn, Pb, Co, Ni, Cr, and Mn) and major elements (Al, Ca, Fe, and Mg) in different particle size fractions (2000–280, 280–100, 100–50, 50–10, 10–2, and <2μm) of surface soils from highly urbanized areas in Hong Kong were studied. The enrichment of Pb, Cu, and Zn in the urban soils was strongly influenced by anthropogenic activities, and Pb accumulated in fine particles was mainly derived from past vehicular emissions as shown by Pb isotopic signatures. Trace metals primarily accumulated in clay, fine silt, and very fine sand fractions, and might pose potential health risks via the inhalation of resuspended soil particles in the air (PM₁₀ or PM₂.₅), and ingestion of adhered soils through the hand-to-mouth pathway. The mobility, bioavailability, and human bioaccessibility of Pb and Zn in bulk soils correlated significantly with metal concentrations in fine silt and/or very fine sand fractions.

Scallop dredging grounds in the Firth of Lorn, western Scotland, are juxtaposed with rocky reef habitats raising concerns that reef communities may be impacted by sediment disturbed by nearby scallop dredging. A particle-tracking model of sediment transport and settling is applied at two scales. In the near-field, a suspension of typical sand/gravel-dominated bed sediment is subjected to a steady current across the dredge track. In the far-field, silt particles, which may persist in suspension for multiple tidal cycles, are tracked in the context of a regional model of tidally-driven flow. The principal sedimentary risk to reef habitats is predicted to come from settling sand particles when dredge tracks approach within tens of metres of a reef. The cumulative effect of dredging at the relatively low intensities recorded in this region is not expected to have a significant long-term impact on suspended silt concentrations and settlement in this highly dispersive environment.

In this study, using high-power low-frequency ultrasound, heated slurries with anionic surfactant sodium dodecyl sulfate (SDS) were treated to enhance desorption of DDT from soils with high clay, silt, and organic matter content and different pH (5.6–8.4). The results were compared with DDT extracted using a strong solvent combination as reference. Slurry ranges from 5 to 20 wt.% were studied. For a soil slurry (10 wt.%) at pH 6.9 with 0.1% v/v SDS surfactant heated to 40°C for 30 min, desorption was above 80% in 30 s using 20 kHz, 932 W/L ultrasonic intensity without solvent extraction. Other soils gave lower desorption efficiency in the range 40–60% after 30 s ultrasonic treatment. The percentage of organic matter, dissolved organic carbon, soil surface area, clay and silt percentage, and soil pH level were the key parameters influencing variations in desorption of DDT in the three soils in similar experimental conditions. DDT dissolution in SDS and soil organic matter removal employing the ultrasonic-enhanced organic matter roll-up mechanism emerged as the two best possible methods of DDT desorption. The method offers a practical, potentially low-cost alternative to high volume, costly, hazardous solvent extraction of DDT.

Instrumented column tests are often used to assess the effectiveness of methods to prevent acid mine drainage (AMD). These tests are seldom duplicated, and this lack of duplicate can cast some doubt about their repeatability and reliability. This paper provides an analysis of column test studies (with duplicates) performed with a commonly used methodology. The paper presents the analysis of two multi-layer covers with capillary barrier effects in which the water retention layer was made of a non-plastic silt and of two cover scenarios involving a single-layer low sulphide cover. The first study compared the cover performance to limit AMD when different cover materials are used, while the second study compared the thickness of covers on cover performance. Statistical comparison between duplicates was made using available geochemical data, hydro-geotechnical data, and gas concentrations. Student’s t-test statistical tools and analysis of variances were used to determine the repeatability of the data. The results indicate that a good reproducibility of the column tests can be achieved with a good set-up methodology and rigorous control of the boundary conditions.

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by incomplete combustion sources such as home heating, biomass burning, and vehicle emissions. PAH concentrations in soils are influenced by source inputs and environmental factors that control loss processes and soil retention. Many studies have found higher concentrations of these pollutants in soils within cities of temperate climates that have a centralized urban core. Less is known about the factors regulating PAH abundance in warm, arid urban ecosystems with low population densities but high traffic volumes. The relative importance of sources such as motor vehicle traffic load and aridland ecosystem characteristics, including temperature, silt, and soil organic matter (SOM) were explored as factors regulating PAH concentrations in soils near highways across the metropolitan area of Phoenix, AZ (USA). Highway traffic is high compared with other cities, with an average of 155,000 vehicles/day. Soils contained low but variable amounts of SOM (median 2.8 ±â€‰1.8% standard deviation). Across the city, median PAH concentrations in soil were low relative to other cities, 523 ±â€‰1,886 μg/kg, ranging from 67 to 10,117 μg/kg. Diagnostic ratio analyses confirmed that the source of PAHs is predominantly fuel combustion (i.e., vehicle emissions) rather than petrogenic, biogenic, or other combustion sources (coal, wood burning). However, in a multiple regression analysis including traffic characteristics and soil properties, SOM content was the variable most strongly related to PAH concentrations. Our research suggests that dryland soil characteristics play an important role in the retention of PAH compounds in soils of arid cities.