Source Attribution of Polycyclic Aromatic Hydrocarbons and Dioxins in Soil and Dust Following Compound Climate Events in Legacy-Contaminated Environmental Justice Areas
Abstract
Communities with histories of industrial contamination may face heightened exposures when compound climate events interact with persistent organic pollutants. Limited multi-matrix data exist are available to evaluate how sequential wildfire and flood disturbances may influence contaminant distribution in environmental justice (EJ) communities. This study characterized polycyclic aromatic hydrocarbons (PAHs) in nonresidential soil/sediment (n = 75), residential surface soil (n = 35), control soil (n = 24), and residential indoor dust (n = 35), and polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) in selected 2–15 cm nonresidential and control soils, in the Globe-Miami area of Arizona, USA following the 2021 Telegraph and Mescal wildfires and subsequent flash floods. PAH diagnostic ratios classified 91–100% of samples across matrices as pyrogenic, while residential soils showed strong correlations among high molecular weight PAH co-correlations (r = 0.87–0.97) consistent with co-deposition/redistribution of combustion-derived particles. Residential soil ΣPAH16 ranged from 0.017 to 15,860 μg kg−1 and benzo[a]anthracene and benzo[a]pyrene exceeded USEPA soil-to-groundwater soil screening levels (SSL) in 40% and 20%, respectively. Indoor dust ΣPAH16 ranged from 1.667 to 167.5 μg m−2, with greater lower-molecular-weight contributions than outdoor soil, suggesting indoor-specific sources and partitioning processes in addition to possible outdoor-to-indoor transport. For PCDD/Fs, 16 of 17 congeners detected in flooded, nonresidential soils compared with 13 in controls; however, total PCDD/F concentrations and overall congener composition did not differ significantly (p = 0.22). Nonresidential soil toxic equivalency quotient (TEQ) values ranged from 0.192 to 29.6 ng kg−1, with the highest value observed at Icehouse Canyon, consistent with localized legacy dioxin contamination, including historical Agent Orange-related herbicide application as one plausible contributor. All samples exceeded the 2,3,7,8-Tetrachlorodibenzo-p-dioxin USEPA soil-to-groundwater SSL of 0.059 ng kg−1. Overall, findings support a layered-source interpretation in which combustion-derived PAHs and persistent legacy PCDD/Fs may coexist and be redistributed through post-fire runoff and flooding in these climate-vulnerable EJ communities.