Environmental fate of combustion-derived organic compounds in arid, urban soils in central Arizona-Phoenix

In this research we wanted to ask, what is the magnitude, distribution, and fate
of non-point carbon pollution in a low-density, urban area? To answer this question,
the goal of the project is to: 1) characterize and quantify combustion-derived
carbon compounds in soils near roadways across the Phoenix valley, 2) explore the
dynamic fate of Polycyclic Aromatic Hydrocarbons (PAHs) in soils, and 3) assess the
importance of microbial community structure in PAH storage and dynamics. We
collected 63 soil samples near highways across the Phoenix valley to characterize
and quantify PAH compounds using extraction methods with Ultrasound Sonication and
analyses by Gas Chromatography-Mass Spectrometry (GC-MS). Additionally, we measured
a suite of soil properties and processes to explore the role of abiotic and biotic
factors on the retention of PAHs in urban soil. PAH concentrations in arid Phoenix soils ranged from 52 ug/kg dry soil to 8,296
ug/kg (mean 926 ug/kg), nearly an order of magnitude lower on average than expected
based on data from other cities (Figure 1, Table 1). The project findings show the
extent of these pollutants, an EPA-priority group of hazardous compounds, in urban
soils. Although the most likely sources for PAH content in roadway soils are vehicle
emissions, they were not correlated with traffic density (r2 = 0.024; p = 0.26) or
highway age (r2 = 0.044; p = 0.13) across all sites. However, PAH concentrations
were significantly correlated to soil organic matter (r2 = 0.36; p less than 0.001).
These results suggest that PAH concentrations in roadway soils of desert cities may
be controlled by factors associated with carbon retention, such as soil organic
matter, rather than source or rate of deposition

本研究旨在探究低密度城区中非点源碳污染的量级、分布特征与归趋。为解答该科学问题，本项目的研究目标为：1）表征并定量菲尼克斯河谷沿线道路周边土壤中燃烧源碳类化合物；2）探究土壤中多环芳烃（Polycyclic Aromatic Hydrocarbons, PAHs）的动态归趋；3）评估微生物群落结构在多环芳烃赋存与动态变化中的重要性。本研究于菲尼克斯河谷沿线高速公路周边采集了63份土壤样品，采用超声萃取法对多环芳烃类化合物进行表征与定量，并通过气相色谱-质谱联用仪（Gas Chromatography-Mass Spectrometry, GC-MS）完成分析。此外，本研究还测定了一系列土壤理化性质与过程，以探究非生物与生物因子对城市土壤中多环芳烃保留行为的影响。菲尼克斯干旱区土壤中的多环芳烃浓度范围为52 μg/kg干土至8296 μg/kg干土（平均值为926 μg/kg），平均浓度较其他城市的已有研究结果低近一个数量级（见图1、表1）。本研究结果明确了这类属于美国环境保护署（Environmental Protection Agency, EPA）优先管控的危险化合物在城市土壤中的污染范围。尽管道路周边土壤中多环芳烃的最主要来源为机动车尾气，但在所有采样点中，其浓度与交通密度（决定系数r²=0.024，p=0.26）及高速公路建成年限（r²=0.044，p=0.13）均无显著相关性。但多环芳烃浓度与土壤有机质含量呈显著正相关（r²=0.36，p<0.001）。上述结果表明，荒漠城市道路周边土壤中的多环芳烃浓度，可能由与碳固持相关的因子（如土壤有机质）所调控，而非污染来源或沉降速率。