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Zinc removal efficiencies derived from an analysis of natural soil dosed with zinc solids and flushed with deionized water and solutions should be considered liberal rather than conservative owing to the procedure for manufacturing the zinc-contaminated soil. This is because ZnSO4*7H2O is a highly unlikely soluble mineral, and consequently, the unusually high Zn removal is unlikely to be representative of site-contaminated soils. However, while the authors concede that the high solubility of ZnSO4 makes results likely nonconservative, the claim that the characteristics of natural contaminated soils can be truly matched remains lacking in support.

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds that can be captured and accumulate in the bioretention cell media, which may lead to secondary pollution and ecological risks. This research aimed to understand the spatial distribution of 16 priority PAHs in bioretention media, identify their sources, evaluate their ecological impact, and assess the potential for their aerobic biodegradation. The highest total PAH concentration (25.5 ± 1.7 μg/g) was observed 1.83 m from the inlet and 10–15 cm deep. The individual PAHs with the highest concentrations were benzo [g,h,i]perylene in February (1.8 ± 0.8 μg/g) and pyrene in June (1.8 ± 0.8 μg/g). Data indicated that primary sources of PAHs were fossil fuel combustion and petroleum. The ecological impact and toxicity of the media were assessed by probable effect concentrations (PECs) and benzo [a]pyrene total toxicity equivalent (BaP-TEQ). The results showed that the concentrations of pyrene and chrysene exceeded the PECs, and the average BaP-TEQ was 1.64 μg/g, primarily caused by benzo [a]pyrene. The functional gene (C12O) of PAH-ring cleaving dioxygenases (PAH-RCD) was present in the surface media, which indicated that aerobic biodegradation of PAHs was possible. Overall, this study revealed the PAHs accumulated most at medium distance and depth, where biodegradation may be limited. Thus, the accumulation of PAHs below the surface of the bioretention cell may need to be considered during long-term operation and maintenance. [Display omitted] • PAHs accumulate faster in depth than surface. • Petroleum and fossil fuel combustion are major sources of PAHs in bioretention cell. • Toxicity of PAHs may impact bacteria activity. • PAHs in surface media may be biodegradable. • The distribution of PAHs may be affected by both adsorption and biodegradation. [ABSTRACT FROM AUTHOR]