Atmospheric reactions of 9,10-anthraquinone

Source apportionment of particle-bound polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs (OPAHs), and their associated long-term health risks in a major European city

Many studies have drawn attention to the associations of oxygenated polycyclic aromatic hydrocarbons (OPAHs) with harmful health effects, advocating for their systematic monitoring alongside simple PAHs to better understand the aerosol carcinogenic potential in urban areas. To address this need, this study conducted an extensive PM2.5 sampling campaign in Athens, Greece, at the Thissio Supersite of the National Observatory of Athens, from December 2018 to July 2021, aiming to characterize the levels and variability of polycyclic aromatic compounds (PACs), perform source apportionment, and assess health risk. Cumulative OPAH concentrations (Σ-OPAHs) were in the same range as Σ-PAHs (annual average 4.2 and 5.6 ng m-3, respectively). They exhibited a common seasonal profile with enhanced levels during the heating seasons, primarily attributed to residential wood burning (RWB). The episodic impact of biomass burning was also observed during a peri-urban wildfire event in May 2021, when PAH and OPAH concentrations increased by a factor of three compared to the monthly average. The study period also included the winter 2020-2021 COVID-19 lockdown, during which PAH and OPAH levels decreased by >50 % compared to past winters. Positive matrix factorization (PMF) source apportionment, based on a carbonaceous aerosol speciation dataset, identified PAC sources related to RWB, local traffic (gasoline vehicles) and urban traffic (including diesel emissions), as well as an impact of regional organic aerosol. Despite its seasonal character, RWB accounted for nearly half of Σ-PAH and over two-thirds of Σ-OPAH concentrations. Using the estimated source profiles and contributions, the source-specific carcinogenic potency of the studied PACs was calculated, revealing that almost 50 % was related to RWB. These findings underscore the urgent need to regulate domestic biomass burning at a European level, which can provide concrete benefits for improving urban air quality, towards the new stricter EU standards, and reducing long-term health effects.

Anthraquinone as emerging contaminant: technological, toxicological, regulatory and analytical aspects

Anthraquinone (anthracene-9,10-dione) is a multifaceted chemical used in the paper industry, in the production of synthetic dyes, in crop protection against birds and is released from fossil fuels. Additionally, the anthraquinone scaffold, when substituted with sugars and hydroxyl groups is found in plants as metabolites. Because of these multiple applications, it is produced on a large scale worldwide. However, its toxicological aspects have gained interest, due to the low limits in the foods defined by legislation. Worrying levels of anthracene-9,10-dione have been detected in wastewater, atmospheric air, soil, food packaging and more recently, in actual foodstuffs. Recent investigations aiming to identify the anthracene-9,10-dione contamination sources in teas highlighted the packaging, leaves processing, anthracene metabolism, reactions between tea constituents and deposition from the environment. In this context, this review seeks to highlight the uses, sources, biological effects, analytical and regulatory aspects of anthracene-9,10-dione.

Graphical Abstract

Formation of Environmentally Persistent Free Radicals from the Irradiation of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) provide a complex matrix for environmentally persistent free radicals (EPFRs) to stabilize in particulate matter, allowing them to be transported over long distances in the atmosphere while participating in light-driven reactions and causing various cardiopulmonary diseases. In this study, four PAHs ranging from three to five rings (anthracene, phenanthrene, pyrene, and benzo[e]pyrene) were investigated for EPFR formation upon photochemical and aqueous-phase aging. Through electron paramagnetic resonance (EPR) spectroscopy, it was found that approximately 10¹⁵ to 10¹⁶ spins g^-1 of EPFRs were formed from the PAH upon aging. EPR analysis also revealed that carbon-centered and monooxygen-centered radicals were predominantly formed by irradiation. However, oxidation and fused-ring matrices have added complexity to the chemical environment of these carbon-centered radicals, as observed by their g-values. This study showed that atmospheric aging results not only in the transformation of PAH-derived EPFR but also in an increase in EPFR concentrations of up to 10¹⁷ spins g^-1. Therefore, because of their stability and photosensitivity, PAH-derived EPFRs have a major impact on the environment.

A yearlong monitoring campaign of polycyclic aromatic compounds and other air pollutants at three sites in Sweden: Source identification, in vitro toxicity and human health risk assessment

Air pollution is a complex mixture of gases and particulate matter (PM) with local and non-local emission sources, resulting in spatiotemporal variability in concentrations and composition, and thus associated health risks. To study this in the greater Stockholm area, a yearlong monitoring campaign with in situ measurements of PM₁₀, PM₁, black carbon, NO_x, O₃, and PM₁₀-sampling was performed. The locations included an Urban and a Rural background site and a Highway site. Chemical analysis of PM₁₀ was performed to quantify monthly levels of polycyclic aromatic compounds (PACs), which together with other air pollution data were used for source apportionment and health risk assessment. Organic extracts from PM₁₀ were tested for oxidative potential in human bronchial epithelial cells. Strong seasonal patterns were found for most air pollutants including PACs, with higher levels during the winter months than summer e.g., highest levels of PM₁₀ were detected in March at the Highway site (33.2 μg/m³) and lowest in May at the Rural site (3.6 μg/m³). In general, air pollutant levels at the sites were in the order Highway > Urban > Rural. Multivariate analysis identified several polar PACs, including 6H-Benzo[cd]pyren-6-one, as possible discriminatory markers for these sites. The main sources of particulate pollution for all sites were vehicle exhaust and biomass burning emissions, although diesel exhaust was an important source at the Highway site. In vitro results agreed with air pollutant levels, with higher oxidative potential from the winter samples. Estimated lung cancer cases were in the order PM₁₀ > NO₂ > PACs for all sites, and with less evident seasonal differences than in vitro results. In conclusion, our study presents novel seasonal data for many PACs together with air pollutants more traditionally included in air quality monitoring. Moreover, seasonal differences in air pollutant levels correlated with differences in toxicity in vitro.

Chemistry and Isotope Fractionation of Divalent Mercury during Aqueous Reduction Mediated by Selected Oxygenated Organic Ligands

We have investigated the chemistry and Hg isotope fractionation during the aqueous reduction of Hg^II by oxalic acid, p-quinone, quinol, and anthraquinone-2,6-disulfonate (AQDS), a derivate of anthraquinone (AQ) that is found in secondary organic aerosols (SOA) and building blocks of natural organic matter (NOM). Each reaction was examined for the effects of light, pH, and dissolved O₂. Using an excess of ligand, UVB photolysis of Hg^II was seen to follow pseudo-first-order kinetics, with the highest rate of ∼10^-3 s^-1 observed for AQDS and oxalic acid. Mass-dependent fractionation (MDF) occurs by the normal kinetic isotope effect (KIE). Only the oxalate ion, rather than oxalic acid, is photoreactive when present in HgC₂O₄, which decomposes via two separate pathways distinguishable by isotope anomalies. Upon UVB photolysis, only the reduction mediated by AQDS results in a large odd number mass-independent fractionation (odd-MIF) signified by enrichment of odd isotopes in the reactant. Consistent with the rate, MDF, and odd-MIF reported for fulvic acid, our AQDS result confirms previous assumptions that quinones control Hg^II reduction in NOM-rich waters. Given the magnitude of odd-MIF triggered via a radical pair mechanism and the significant rate in the presence of air, reduction of Hg^II by photoproducts of AQDS may help explain the positive odd-MIF observed in ambient aerosols depleted of Hg^II.