Oxygenated polycyclic aromatic hydrocarbons and azaarenes in urban soils: A comparison of a tropical city (Bangkok) with two temperate cities (Bratislava and Gothenburg)

Environmental conditions in the tropics favor the formation of polar polycyclic aromatic compound (polar PACs, such as oxygenated PAHs [OPAHs] and azaarenes [AZAs]), but little is known about these hazardous compounds in tropical soils. The objectives of this work were to determine (i) the level of contamination of soils (0–5 and 5–10 cm layers) from the tropical metropolis of Bangkok (Thailand) with OPAHs and AZAs and (ii) the influence of urban emission sources and soil properties on the distribution of PACs. We hypothesized that the higher solar insolation and microbial activity in the tropics than in the temperate zone will lead to enhanced secondary formation of OPAHs. Hence, OPAH to related parent-PAH ratios will be higher in the tropical soils of Bangkok than in temperate soils of Bratislava and Gothenburg. The concentrations of ∑15OPAHs (range: 12–269 ng g−1) and ∑4AZAs (0.1–31 ng g−1) measured in soils of Bangkok were lower than those in several cities of the industrialized temperate zone. The ∑15OPAHs (r = 0.86, p < 0.01) and ∑4AZAs (r = 0.67, p < 0.01) correlated significantly with those of ∑20PAHs highlighting similar sources and related fate. The octanol–water partition coefficient did not explain the transport to the subsoil, indicating soil mixing as the reason for the polar PAC load of the lower soil layer. Data on PAC concentrations in soils of Bratislava and Gothenburg were taken from published literature. The individual OPAH to parent-PAH ratios in soils of Bangkok were mostly higher than those of Bratislava and Gothenburg (e.g. 9-fluorenone/fluorene concentration ratio was 12.2 ± 6.7, 5.6 ± 2.4, and 0.7 ± 02 in Bangkok, Bratislava and Gothenburg soils, respectively) supporting the view that tropical environmental conditions and higher microbial activity likely lead to higher OPAH to parent-PAH ratios in tropical than in temperate soils.

Saving soils at degradation frontlines: Sustainable land management in drylands

Healthy soils are fundamental to life. They grow the food we eat and the wood we use for shelter and fuel, purify the water we drink, and hold fast to the roots of the natural world we cherish. They are the ground beneath our feet and beneath our homes. But they are under threat, especially from human overuse and climate change. Nowhere is this more evident than in dryland areas, where soil degradation – or desertification – wears away at this essential resource, sometimes with sudden rapidity when a tipping point is crossed. Though it is a challenge, preserving and restoring healthy soils in drylands is possible, and it concerns all of us. Sustainable land management points the way.