The Overlooked Occurrence of Environmentally Persistent Free Radicals in an Area with Low-Rank Coal Burning, Xuanwei, China

Abstract

The mining and burning of low-rank coal in Xuanwei, China have attracted a great deal of research attention because of the generated polyaromatic hydrocarbons (PAHs) and the high incidence of lung cancer in this region. Given the abundant transition metals in the allitic soil, we hypothesized that environmentally persistent free radicals (EPFRs) are formed in this region and the potential risk had not been addressed. Strong electron paramagnetic resonance (EPR) signals of 3.20 × 10 - 3.10 × 10 spins/g were detected in environmental samples, including chimney soot, coal, soil and total suspended particles (TSP). These EPR signals did not significantly change after 18-months storage and had g-values in the range of 2.0039-2.0046, suggesting typical organic free radicals. Similar strong EPR signals were observed in PAH (anthracene and pyrene as model compounds) degradation on simulated soil particles and lasted over one month even when the applied PAHs were 100% degraded. Based on g-value and bond width, we propose that EPR signals detected in TSP and soot originated from both coal combustion and PAH photodegradation. Further research is thus urgently required to investigate EPFR generation, exposure and risk in Xuanwei to better understand the cause of high lung cancer incidence.

Environmentally persistent free radicals in PM2.5: a review

“…Thus far, we have reported data of EPFRs in airborne PM in six countries, i.e., China, Germany, Greece, India, Saudi Arabia and the USA. As listed in Table 1, there are various forms of sampling media for airborne PM, including a glass fiber filter (GFF) [21,31], quartz fiber filter (QFF) [32][33][34][35], Teflon membrane filter (TMF) [24,36,37], polytetrafluoroethylene (PTFE) [35,38,39], polycarbonate filter (PCF) [40], and even a leaf [41].…”

“…If the aim is to obtain the overall content of EPFRs in the PM sample, it is advisable to use the QTB or QSB method. Studies have shown that most of the EPFRs in airborne PM are derived from solvent-resistant organic matter [21,45,46]. For instance, the direct measurement using the QSB method yielded an average EPFR concentration of 3.97 × 10 14 spins/m 3 for 12 samples collected in December 2017 in Xi'an, China.…”

“…For instance, the halflife of the ortho-semiquinone radical formed in the matrix of Zn(II)O/silica ranged from 46 to 73 days [14], which is 14 orders of magnitude longer than that of the hydroxyl radical (10 −9 s) [15]. EPFRs are ubiquitous in the environment and can either occur naturally in the biomass [16], coal [17], and soil [18] or be present in biochar [19], fly ash [20], and soot [21] as a consequence of various anthropogenic combustion and thermal processes.…”

Environmentally persistent free radicals mediated removal of Cr(VI) from highly saline water by corn straw biochars

“…In recent years, environmentally persistent free radicals (EPFRs) have attracted increasing attentions in respect of their adverse impacts on health (Lomnicki et al, 2008;Wang et al, 2018). EPFRs are formed during the pyrolysis of biomass in the presence of metal oxides via a mechanism of chemisorption followed by electron transfer (Lomnicki et al, 2008).…”

Physicochemical properties and oxidative potential of fine particles produced from coal combustion

“…Coal with higher volatile matter contributed to higher toxicity (cytotoxicity and global DNA methylation) in coal combustion particles produced by residential stoves (Wang et al 2016a). Hydroxyl radical generation of coal combustion particles collected from the chimney of coal power plant was much higher than total suspended particles in the ambient atmosphere (Wang et al 2018). However, the effects of coal burning temperature on both the chemistry and toxicity of coal combustion particles have not been adequately reported.…”