Trends and patterns of polycyclic aromatic hydrocarbons (PAHs) in forest fire-affected soils and water mediums with implications on human health risk assessment

Pollution and toxicity of heavy metals in wildfires-affected soil and surface water: A review and meta-analysis

Wildfires, both natural and man-made, release and mobilize hazardous substances such as heavy metal(loids) (HM), which are known carcinogens. Following intense rainfall events, HM bound to soil organic matter are transported from the soil to surface water, resulting in water quality degradation. This study reviews the pollution status of HM in wildfire-affected soil and surface water, as well as their toxic effects on aquatic organisms and humans. The rate of HM release during wildfires depends on factors such as the type of tree burned and fire severity. The mobility of HM from soil to surface water is influenced by soil pH, organic matter content, rainfall intensity, and duration. The risk priority number (RPN) analysis indicates that both wildfire-affected soil and surface water require remediation to address HM contamination. HM concentrations in both soil and surface water decrease over time due to soil erosion, wind, storm events, and the depletion of burnt residues. The greatest percentage changes in HM concentrations in burned soils compared to unburned soils were observed for vanadium (340%), nickel (260%), and arsenic (110%). In surface water, the highest increases were seen for iron (740%), vanadium (530%), and aluminium (510%). Wildfire-affected water has been shown to cause toxic effects in aquatic organisms, including DNA damage, oxidative stress, and lipid peroxidation. The consumption of HM-contaminated water and fish poses significant health risks to humans. Therefore, post-fire monitoring of wildfire-affected areas is essential for designing treatment plants, assessing risks, and establishing maximum allowable HM concentrations in water.

Heavy metal(loid) contamination in forest fire affected soil and surface water: pollution indices and human health risk assessment

Forest fires, whether natural or anthropogenic, release and mobilize heavy metal(loids) (HM). Following intense rainfall events, soil-bound HM are transported from soil to surface water through surface runoff, leading to water quality deterioration. Pollution and ecological risk indices are effective tools for assessing HM contamination. Most forest fire-affected soils and surface water exhibited a degree of contamination greater than 3 and 8 (high and moderate pollution), with associated high and extremely high ecological risks (165 and 2389, respectively). Pollution indices revealed that soils were highly contaminated with Ni, Cu, Cr, and Pb, while Ni, Cu, Hg, Cd, and As posed significant ecological risks. Surface water was heavily contaminated with Pb, Mn, Al, and Fe, with Ni and V contributing to extremely high ecological risks. This study highlights that trace HM also requires substantial removal efforts to make water potable, with removal efficiencies needed for Sb (94.49%), Be (85.83%), Ba (70.75%), V (68.19%), and Se (65.51%). Fire-affected surface water poses an elevated cancer risk to both children (0.18 and 4.5 × 10-3) and adults (0.39 and 1.53 × 10-3) through oral and dermal exposure, respectively. Children are more vulnerable to dermal cancer and noncancer risks compared to adults. Low-cost treatment methods, such as the application of immobilizing agents combined with compost, straw mulching, and seeding, can be implemented to control soil erosion in forest areas, thereby reducing the transport of soil-bound HM to surface water. These findings can aid government agencies in developing new soil and water quality standards and implementing effective treatment measures.

Abiotic and biotic dissipation in natural attenuation of phenanthrene and benzo[a]pyrene: A systematic quantification study in contrasting soils

Natural attenuation represents a significant ecosystem function for mitigating the quantity and toxicity of polycyclic aromatic hydrocarbons (PAHs) through both abiotic and biotic dissipation processes. This study systematically investigated abiotic and biotic dissipation of phenanthrene (Phe) and benzo[a]pyrene (BaP) in four soils over 360 days, using CSIA to quantitatively analyze δ1³C changes and demonstrate biodegradation. The results indicated that extractable Phe was primarily attenuated via biodegradation (65%-81%), as revealed by CSIA, with the δ1³C changes ranging from 2.06‰ to 4.20‰ across the four soil types. Only 17%-27% of Phe dissipated by forming Type II non-extractable residues (NERs), while its Type I NERs remained available for microbial utilization. Notably, the microbial genera Gemmatimonas and Sphingomonas emerged as key contributors to the biotic dissipation of Phe. Conversely, extractable BaP was predominantly attenuated through abiotic process (35%-52%), particularly via the formation of Type I and Type II NERs, with a smaller fraction (6%-17%) undergoing biotic dissipation. Although the changes in δ1³C values for BaP were only 0.76‰-1.06‰, the significant changes (p < 0.05) supported the microbial degradation of BaP. Additionally, soil organic matter and pH influenced the extractable and residual Phe, whereas soil electrical conductivity and texture primarily affected BaP rather than Phe. These findings underscore the multiple dissipation mechanisms involved in the natural attenuation of PAHs in soils and offer valuable quantitative data for remediation strategies of PAHs-contaminated soils.

Rapid and On-Site Approaches for Determination of Polycyclic Aromatic Hydrocarbons in Water and Air by Surface-Enhanced Raman Spectroscopy

Polycyclic aromatic hydrocarbons (PAHs) represent a class of carcinogenic, teratogenic, and mutagenic aromatic organic pollutants that are ubiquitous in the environment. The rapid and on-site detection of PAHs remains a challenge. This study proposes point-of-use (POU) surface-enhanced Raman spectroscopy (SERS)-based strategies for the qualitative and quantitative analyses of PAHs in environmental water and air. The results demonstrate clear correlations between the signal intensity and the logarithmic concentration of PAHs in water (ranging from 2.5 to 100 ppb), with satisfactory recovery and reproducibility. A similar trend was observed for PAHs on glass fiber filters modified with silver nanoparticles (AgNPs@GF filter). Specifically, the limits of detection (LOD) for fluoranthene, phenanthrene, and pyrene in water were 0.7, 1.0, and 0.1 ppb, respectively, while the LOD for fluoranthene, phenanthrene, and pyrene on the AgNPs@GF filter were 9.11, 18.18, and 14.59 ppb. Recovery rates in spiked real water and filters ranged from 83% to 126%, and the entire detection process was completed within 1 min. These findings highlight the significant potential of this method as a powerful tool for rapid on-site analysis of PAHs in various environmental matrices.

Long-term effects of petroleum mulch on concentration, health, and ecological risks of polycyclic aromatic hydrocarbons in sand dune soils of Khuzestan province, Iran

Environmental consequences of petroleum mulch application are crucial in regions prone to wind erosion and desertification. This study aimed to assess the long-term effects of petroleum mulching on soil polycyclic aromatic hydrocarbon (PAH) concentrations and the associated human and ecological risk indices. These indices include incremental lifetime cancer risk (ILCR), hazard index (HI), toxic equivalent concentration (TEQBaP), toxic unit (TU), and risk quotient (RQ) in soil samples from Khuzestan province, Iran. Soil samples were collected from two depths: surface soil (0-10 cm) and deep soil (10-50 cm) across four regions with varying durations of petroleum mulch application: less than 5 years (T5), 5-20 years (T20), 20-30 years (T30), and 30-40 years (T40), and a control sample without mulching. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the concentrations of 19 PAHs and 23 groups of alkylated PAHs (alkyl PAHs) in the soil. Petroleum mulching significantly impacted heavily contaminated soil samples (T5 and T20) with PAH levels ranging from 2.03 to 2.08 mg kg-1. Older samples (T30 and T40) showed lower contamination levels (0.29 and 0.41 mg kg-1), primarily due to the alkylated compounds. ILCR, HI, TEQBaP, TU, and RQ indices were highest in T5 and T20 surface samples, indicating high risk in T5 surface soil from RQ and moderate risk in the others, despite low cancer and non-carcinogenic risks. Although the risk from the compounds, particularly alkyl PAHs, has decreased over time, they could still adversely affect the ecosystem, emphasizing the use of environmentally friendly alternative mulches in such areas.

Spatiotemporal variation of polycyclic aromatic hydrocarbons in Tibetan lake sediment cores reveals the influence of forest fires

Despite declining anthropogenic emissions of polycyclic aromatic hydrocarbons (PAHs) due to global control strategies, forest fire emissions have been increasing, significantly affecting PAH dynamics in global sinks. This study investigated the spatiotemporal variations of sedimentary PAHs in three Tibetan lakes-Yiong Tso, Yamdrok Yumtso, and Urru Tso-to determine the influence of forest fires on PAH levels and historical trends. Yiong Tso Lake, located in a fire-affected watershed, exhibited the highest PAH concentrations (average of 43.4 ± 25.7 ng/g) with significant fluctuations since the 1920s, peaking in the 1960s (46.3 ng/g) and 1980s (91.3 ng/g), corresponding to periods of intense forest fires. This pattern aligned with source contribution estimates using the modified Cohen's d (mcd), indicating the dominance of forest fires as a PAH source until the 1990s. PAH concentrations decreased with increasing distance from the southeastern Tibetan Forest, as observed in Yamdrok Yumtso (average of 36.1 ± 19.9 ng/g) and Urru Tso (average of 16.4 ± 6.9 ng/g). Temporal variations in PAH concentrations and mcd values from these lakes also reflected a response to forest fires during the 1960s, suggesting a widespread influence of forest-fire-derived PAHs across the plateau. The impact of forest fires on sedimentary PAHs was expected to persist for decades, with an estimated half-life of approximately 11-12 years. These findings highlight significant emissions of PAHs from forest fires in the Tibetan Plateau, potentially transforming regional PAH dynamics and influencing global cycling.

Constructing perfluorinated UiO-67 for enrichment of polycyclic aromatic hydrocarbons in seawater and seabed sediments

To investigate the ocean contamination caused by polycyclic aromatic hydrocarbons (PAHs), UiO-67/perfluorooctanoic acid (UiO-67/PFOA) was synthesized through solvent-assisted ligand incorporation method. The UiO-67/PFOA was then served as an adsorbent in headspace solid-phase microextraction (HS-SPME) technology for collecting and concentrating trace PAHs. The addition of the PFOA improved the hydrophobicity and stability of the UiO-67/PFOA coating, and the C-F functional group in UiO-67/PFOA could form the pseudo hydrogen bonding with the CH on the benzene ring of PAHs, which endowed the UiO-67/PFOA with 1.60-4.63 times enrichment performance for PAHs than UiO-67. Under optimal conditions, the wide linear ranges of PAHs (0.01-20 ng·mL-1) with good coefficients of determination (R2 ≥ 0.9950) and low limits of detection (LODs, 0.003-0.008 ng·mL-1) were obtained. The recoveries of five PAHs from spiked seawater and seabed sediment by the developed method ranged from 81.14 % to 116.0 % with satisfactory results. This work provided a good adsorbent for the enrichment of trace PAHs in complicated environments and a new approach for the subsequent synthesis of adsorbents with good enrichment performance.

Metagenomic analysis reveals the microbial response to petroleum contamination in oilfield soils

The response of the microbes to total petroleum hydrocarbons (TPHs) in three types of oilfield soils was researched using metagenomic analysis. The ranges of TPH concentrations in the grassland, abandoned well, working well soils were 1.16 × 102-3.50 × 102 mg/kg, 1.14 × 103-1.62 × 104 mg/kg, and 5.57 × 103-3.33 × 104 mg/kg, respectively. The highest concentration of n-alkanes and 16 PAHs were found in the working well soil of Shengli (SL) oilfield compared with those in Nanyang (NY) and Yanchang (YC) oilfields. The abandoned well soils showed a greater extent of petroleum biodegradation than the grassland and working well soils. Α-diversity indexes based on metagenomic taxonomy showed higher microbial diversity in grassland soils, whereas petroleum-degrading microbes Actinobacteria and Proteobacteria were more abundant in working and abandoned well soils. RDA demonstrated that low moisture content (MOI) in YC oilfield inhibited the accumulation of the petroleum-degrading microbes. Synergistic networks of functional genes and Spearman's correlation analysis showed that heavy petroleum contamination (over 2.10 × 104 mg/kg) negatively correlated with the abundance of the nitrogen fixation genes nifHK, however, in grassland soils, low petroleum content facilitated the accumulation of nitrogen fixation genes. A positive correlation was observed between the abundance of petroleum-degrading genes and denitrification genes (bphAa vs. nirD, todC vs. nirS, and nahB vs. nosZ), whereas a negative correlation was observed between alkB (alkane- degrading genes) and amo (ammonia oxidation), hao (nitrification). The ecotoxicity of petroleum contamination, coupled with petroleum hydrocarbons (PH) degradation competing with nitrifiers for ammonia inhibited ammonia oxidation and nitrification, whereas PH metabolism promoted the denitrification process. Moreover, positive correlations were observed between the abundance of amo gene and MOI, as well as between the abundance of the dissimilatory nitrate reduction gene nirA and clay content. Thus, improving the soil physicochemical properties is a promising approach for decreasing nitrogen loss and alleviating petroleum contamination in oilfield soils.