The Parallel Transformations of Polycyclic Aromatic Hydrocarbons in the Body and in the Atmosphere

Abstract

Background. Polycyclic aromatic hydrocarbons (PAHs) emitted from combustion sources are known to be mutagenic, with more potent species also being carcinogenic. Previous studies show that PAHs can undergo complex transformations both in the body and in the atmosphere, yet these transformation processes are generally investigated separately. Objectives. Drawing from the literature in atmospheric chemistry and toxicology, we highlight the parallel transformations of PAHs that occur in the atmosphere and the body and discuss implications for public health. We also examine key uncertainties related to the toxicity of atmospheric oxidation products of PAHs and explore critical areas for future research. Discussion. We focus on a key mode of toxicity for PAHs, in which metabolic processes (driven by cytochrome P450 enzymes), leads to the formation of oxidized PAHs that can damage DNA. Such species can also be formed abiotically in the atmosphere from natural oxidation processes, potentially augmenting PAH toxicity by skipping the necessary metabolic steps that activate their mutagenicity. Despite the large body of literature related to these two general pathways, the extent to which atmospheric oxidation affects a PAH’s overall toxicity remains highly uncertain. Combining knowledge and promoting collaboration across both fields can help identify key oxidation pathways and the resulting products that impact public health. Conclusions. Cross-disciplinary research, in which toxicology studies evaluate atmospheric oxidation products and their mixtures, and atmospheric measurements examine the formation of compounds that are known to be most toxic. Close collaboration between research communities can help narrow down which PAHs, and which PAH degradation products, should be targeted when assessing public health risks. https://doi.org/10.1289/EHP9984

Analysis of nitro- and oxy-PAH emissions from a pilot scale silicon process with flue gas recirculation

“…Nitrogen oxides must be present for nitro-PAHs to form and NO x forming reactions are a source of radicals and atmospheric oxidative reactions. Hrdina et al 8 described the necessity of radicals and radical-initiated reactions to create oxidants such as and OH˙, which function as activators of the substitution reaction. Katritzky et al 11 described the nature of an aromatic substitution reaction, where the initial reaction step produces a temporary positively charged arenium ion.…”

“…In the work by Hrdina et al, 8 parent PAH transformation through atmospheric oxidation is described, recognizing the key atmospheric oxidants of PAHs to include ozone (O 3 ), hydroxyl radicals (OHc), nitrogen dioxide (NO 2 ), and nitrate radicals ðNO 3 Þ. Nitrated PAHs (nitro-PAH) and oxygenated PAHs (oxy-PAH) are two groups of substituted PAHs containing at least one nitro group (NO 2 ) or carbonylic oxygen attached to an aromatic ring. 9 As a result, some of the physiochemical properties change, compared to the parent PAHs, which in turn alter their environmental and toxicological effects.…”

“…The initial reaction to create a PAH adduct is seen to form both oxy and nitro-PAH species, based on the continued reaction of the adduct with available reactants, independent on the initiation of the reaction (by nitrate or hydroxyl radicals). 8,15 Oxy-and nitro-PAH compounds are also detected in research on emissions from diesel engines, where NO x is known to be a considerable part of the exhaust. Heeb et al 16 investigated how diesel engine lters inuence PAH and nitro-PAH proles in diesel exhaust and found the lter to promote the formation of some nitro-PAHs, enhancing the degradation of others depending on the operating conditions of the engine.…”

Potential Impacts of Energy and Vehicle Transformation Through 2050 on Oxidative Stress‐Inducing PM2.5 Metals Concentration in Japan

“…PAH quinones, as well as transition metals, catalyze ROS production through the redox cycle (Charrier & Anastasio, 2012; Jiang et al., 2019; Kumagai et al., 2002; McWhinney et al., 2013). In addition, even if exposed as PAHs, they are converted to PAH quinones in the body by reductases such as cytochrome P‐450 (Hrdina et al., 2022; Jiang et al., 2019; Kumagai et al., 2012). Also, it is necessary to analyze considering future scenarios for heavy‐duty vehicles, which are one of the major sources of PAH. Consideration of the source‐dependent solubility of metals.…”

Catalyst-Free Oxidation Reactions in a Microwave Plasma Torch-Based Ion/Molecular Reactor: An Approach for Predicting the Atmospheric Oxidation of Pollutants

“…However, little is known about the behavior of these products and the harm they pose to both human health and the environment under conditions of prolonged exposure, making the advance prediction of such products extremely important. However, as long oxidation time-scales are often not accessible in the laboratory and highly functionalized species tend to be challenging to detect, the identities of these later-generation products are generally not currently well understood . Some researchers have studied the oxidative products of pollutants produced by dust ventilation, ozone addition, or thermal and photodegradation; however, these studies often involve complex pretreatments as well as long reaction times, and the inability to observe intermediate products online is a drawback for elucidating reaction pathways.…”