Wildfire Burn Intensity Affects the Quantity and Speciation of Polycyclic Aromatic Hydrocarbons in Soils

Abstract

Wildfire-altered soil may be an important source of polycyclic aromatic hydrocarbons (PAHs) in the environment. With projected increase of wildfire frequency and intensity due to changing global climate, understanding the quantity and speciation of PAHs, including halogenated PAHs (XPAHs), resulting from different burn intensities has important ramifications for environmental quality concerns and global soil carbon dynamics. Here, we quantified levels of 16 U.S. Environmental Protection Agency regulated PAHs, 3 chlorinated PAHs, and 6 brominated PAHs in nonburned forest soils and burned ash/soil samples covered with black ash (B-Ash; moderate burn intensity) or white ash (W-Ash; severe burn intensity) from the 2013 Rim Fire (1,041 km 2 ) in California. The ∑ 16 PAH concentrations follow (mean ± standard deviation; μg/kg) B-Ash (893 ± 285) > W-Ash (515 ± 333) ≈ nonburned soils (247 ± 58). Moreover, the ∑ 16 PAH profiles were altered by both moderate and severe burn conditions with the size of aromatic structures following B-Ash > W-Ash > nonburned soils. Neither chlorinated nor brominated PAH concentration was significantly elevated by moderate or severe wildfire. Overall, fire intensity is critical in regulating soil PAH concentrations and profiles. Given the high erodibility of wildfire ash, these PAHs can be easily transported to rivers and reservoirs where they could impact the aquatic food web and drinking source water.

Chemical composition of wildfire ash produced in contrasting ecosystems and its toxicity to Daphnia magna

“…Fire dynamics (e.g. burn temperature) and soil properties are also important features in the composition of elements within ash (Pitman 2006;Bodí et al 2014;Chen et al 2018). In general, oxides and hydroxides of Ca, Mg, Si and P particularly tend to be abundant in wildfire ash (Pereira and Ú beda 2010;Silva et al 2015) as found in the ash tested here (Supplementary material Table S1).…”

“…The type of fuel and variations in combustion temperatures and oxygen availability are thought to strongly affect the concentration and type of PAHs in ash (Enell et al 2008;Rey-Salgueiro et al 2018). Chen et al (2018) found that PAHs concentrations were significantly higher in black wildfire ash (moderate burn severity) in comparison with white wildfire ash (high burn severity). This was also true of the ash types tested here with the darker (dark grey-black) ash samples (UK, URIA, CAN) containing a much higher concentration of PAHs than the lighter (light grey-white) samples (AUS, USA, SPA) (Table 4).…”

“…The organic fraction of ash may also contain organic contaminants of biological concern (Vila-Escalé et al 2007;Chen et al 2018). The data available on PAHs release following a fire, however, are quite limited (Vila-Escalé et al 2007;Kim et al 2011;Campos et al 2012;Rey-Salgueiro et al 2018).…”

“…Fires are a natural process in many habitat types worldwide (Bixby et al 2015), but they can be a social and environmental concern, potentially impacting public health, safety, infrastructure, biodiversity, land-use, water and air pollution (Bladon et al 2014;Brito et al 2017). Fire activity is projected to increase in many locations and ecotypes as a result of climate and societal changes, making the full understanding of their impacts crucial (Scholze et al 2006;Chen et al 2018).…”

“…Vila-Escalé et al 2007;Campos et al 2012;Oliveira-Filho et al 2018). Both present major biological concern owing to their carcinogenic potential, persistence within ecosystems and tendency to bio-accumulate (Smith et al 2011;Chen et al 2018). These contaminants are thought to have complex impacts on water quality and the biological effects of these in aquatic systems have been observed to persist across long spatial and temporal scales (Earl and Blinn 2003;Costa et al 2014).…”