Historical Pollution and Source Contributions of PAHs in Sediment Cores from the Middle Reach of Huai River, China

Aliphatic and polycyclic aromatic compounds in coal and coal-based solid wastes: Relationship with coal-forming paleoenvironment and implications for environmental pollution

In this study, coal and coal-based solid wastes (coal gangue, fly ash, bottom ash, desulfurized gypsum and tar residue) were collected from major coal mines, power plants and coking plants in Lianghuai mining area (LH), China, and were analyzed for 76 polycyclic aromatic compounds (PACs), 27 n-alkanes and 2 isoprenoids (phytane and pristane). The total n-alkanes concentrations and ∑76 PACs in raw coals (640 ± 600 and 180 ± 87 μg/g) were higher than those in coal-based solid wastes (47 ± 40 and 24 ± 25 μg/g), but were lower than those in tar residue (3700 and 63,000 μg/g). It was discovered that the depositional paleoenvironment in LH was mostly a lacustrine and freshwater environment with oxidizing conditions and mixed organic matter input, but the Huainan coalfield had stronger oxidizing conditions and more input of terrestrial organic matter than that of the Huaibei coalfield. Alkylated PACs made up 56 ± 12 % of the ∑76PACs in raw coals, whereas solid wastes mainly consisted of 16 EPA PAHs (66 ± 16 %). Coal combustion and gangue weathering altered the structural properties of n-alkanes and PACs, resulting in a significant loss of n-alkanes and PACs, a higher proportion of parent PACs, and an increased abundance of short n-alkanes in the products (No apparent change of n-alkanes composition was observed through gangue weathering). The toxicity of PACs in raw coal and its solid wastes in LH from high to low was tar residue, raw coal, coal gangue, and coal-fired products. This investigation further confirmed that traditional diagnostic ratios may distort source information, and that they should not be used to assess PACs sources from raw coal particles or coal gangues, but rather to identify combustion sources near the point source. In addition, Retene/(Retene + Chrysene) < 0.03 may indicate direct contamination of raw coal particles.

Application of tree cores to investigate the historical pollution trends of atmospheric polycyclic aromatic compounds: A case study in a typical coal-contaminated region of China

In this study, 76 polycyclic aromatic compounds (PACs) were detected in air, soil, and tree core samples from Huainan, a typical coal-contaminated region of China. Concentrations of ΣPACs in soil and air samples were 2400 ± 5100 ng/g and 150 ± 63 ng/m3, respectively. Priority PAHs were predominant in both air and soil samples, contributing over 50 % of ΣPACs. Source analysis indicated that PAC contamination in Huainan primarily originated from local coal-related activities. The benzo[a]pyrene (BaP)-toxic equivalent concentrations (TEQBaP) of PACs in the air samples (5.6 ± 5.3 ng/m3) exceeded the threshold of 1 ng/m3. Some PACs, such as benzo[e]pyrene (BeP) and Alk-BaPs, demonstrated significant toxicity and are recommended for consideration as priority pollutants. The historical pollution trends of atmospheric PACs were obtained based on the tree core samples. PAC concentrations in tree core segments showed a strong correlation with atmospheric PM10 levels in Huainan. As air quality has improved in recent years, the PACs concentrations in tree core segments have also decreased. Historical fluctuations of atmospheric PACs were largely attributed to the changes in the gas treatment systems of a nearby coal-fired power plant and adjustments in environmental policies. By integrating trends observed in tree core segments with air concentrations, the historical atmospheric PAC concentrations were extrapolated. The extrapolated results showed similar concentration levels and trends when compared with historical data from other studies in China. Thus, tree cores can not only reflect the historical trends of atmospheric PACs with high temporal precision but also are feasible for extrapolating historical concentrations of airborne PACs.

Historical sedimentary and evolutionary characteristics of POPs and EDCs in typical regions of the three Gorges reservoir, China

The historical sedimentary and evolutionary characteristics of persistent organic pollutants and endocrine disruptors in typical regions of the Three Gorges Reservoir are scarcely studied. Herein, the 96-year data on contaminated sediment history were reconstructed using Caesium 137 isotope dating. Polychlorinated biphenyl concentrations in the involved sediment cores ranged from non-detected (ND) to 11.39 ng/g. The concentrations of polycyclic aromatic hydrocarbons ranged from ND to 2075.20 ng/g and peaked in the 1970s owing to natural, agricultural and human activities. Further, phthalate esters (PAEs) and heavy metals (HMs) were detected at concentrations ranging from ND to 589.2 ng/g and 12.10-93.67 μg/g, respectively, with highest values recorded in the 1980s owing to rapid industrialisation and insufficient management during China's early reform and development stages. PAE and HM concentrations have increased in recent years, suggesting the need to focus on industrial and agricultural activities that have caused this impact. Although current pollutant concentrations in sediments do not pose a risk to the aquatic ecosystem, they should be continuously monitored.

Polycyclic aromatic compounds (PACs) in tree barks and tree cores of a national large-scale coal-fired power base of China: Sources, atmospheric toxicities, and pollution histories

Polycyclic aromatic compounds (PACs) are important hazardous air pollutants in China due to the country's coal-dominant energy structure. In order to reveal the pollution characteristics, sources, toxicity, and pollution historical trends of PACs in the atmosphere of the middle reach of the Huaihe River (MRHR), a large-scale coal-fired power base of China, tree barks and tree cores were collected and employed as passive air samplers and historical trend recorders, and 76 PACs were identified for the first time. ΣPACs in tree barks ranged from 170 to 3800 ng g^-1 (mean = 700 ± 720 ng g^-1), with the high concentrations observed mainly in the coal-mining and coal-bearing area. 16 priority PAHs (PriPAHs) were the predominant substances and accounted for 59 ± 8.3 % of ΣPACs. The combustion of coal and fuel oil was the most significant source of PACs, accounting for 43 % of ΣPACs, followed by the combustion of biomass (30 %) and non-combustion sources (27 %). Based on a bark-air partitioning model, volumetric air concentrations for ΣPACs were calculated to be 450-11,000 ng m^-3 (mean = 1600 ± 2000 ng m^-3). The BaP-toxic equivalent concentrations (TEQ_BaP) of ΣPACs (mean = 9.7 ± 15 ng m^-3) were significantly higher than the Chinese guideline (1 ng m^-3) and were mostly caused by coal & fuel oil combustion (55 ± 13 %). High molecular weight PACs were detected in lower percentages in tree cores than in tree barks, indicating that PACs in the particle phase were difficult to enter the tree core. Major PACs decreased in tree core samples between 2000 and 2020 as pollution control efforts improved, however, some PACs showed different trends when influenced by point sources.

Temporal and spatial characteristics of PAHs in oysters from the Pearl River Estuary, China during 2015-2020

Estuary connects the inland freshwater and open seawater, which may become a sink for pollutants from land-derived outflows, especially for persistent organic pollutants (e.g., polycyclic aromatic hydrocarbons, PAHs). Due to complex fluctuation in estuary, it's difficult to achieve a comprehensive assessment of the pollution characteristics by grabbed environmental samples. Oysters serve as efficient biomonitors of pollution status in highly dynamic and anthropogenically impacted estuaries, like the Pearl River Estuary (PRE), South China. Here, we investigated the annual, seasonal, and spatial variations of PAHs in the soft tissues of oysters from the PRE over the last six years (2015-2020) and quantitatively analyzed the influence of environmental factors on PAH occurrence in the oysters. The concentrations of Σ₁₅PAH in oysters ranged from 74 to 1164 (337 ± 218) ng/g dry wt., with a peak occurrence in 2017. Highly seasonal and geographical variations in PAH pollution were documented in the PRE, with higher concentrations in oysters during the wet season than dry season, and in the eastern coast than western coast. Furthermore, geographical variation in PAH levels in the oysters was enhanced during the wet season, indicating a possible contribution of heavy rainfall flushing from the Pearl River. In addition to precipitation, water temperature and salinity also significantly influenced PAH levels in the oysters from the PRE by changing the bioavailability and biokinetics. Long-term biomonitoring using oysters in the current study reflected the pollution status and variation trends of PAHs in the highly dynamic PRE.

Concentrations, distribution and risk of polycyclic aromatic hydrocarbons in sediments from seven major river basins in China over the past 20 years

Polycyclic aromatic hydrocarbons (PAHs) in river sediments in China have been extensively investigated. However, most previous studies only reported information about specific locations. As a result, the distribution and changes of these chemicals in sediments nationwide remain unknown. Based on published data during 1997-2020, we conducted a systematic meta-analysis to understand the concentration, risk and the spatiotemporal variation of PAHs in river sediments from the seven major river systems in China. The report provides a national picture of PAHs in river sediments of China. Among the seven river systems, higher concentrations of sediment PAHs are found in the basins of Liaohe River and Haihe River. In the study sediments, high-molecular-mass (4-6-ring) PAHs were predominated, reflecting the widespread combustion of coal and fossil fuels across China. In addition, PAH source assessment also suggests that raw coal and crude oil are important contributors to PAH concentrations in the rivers in northeastern China. Over the past 20 years, there is no downward trend in the concentrations of Σ₁₆PAHs in sediments in the seven river basins; but the contribution of high-temperature combustion to the pollution has declined. In addition, our calculated risks from sediment PAHs seem to decline between 1997-2006 and 2007-2017 periods, although the differences were not statistically significant (p > 0.05). Of note, the data collection and the risk assessment methods used in this preliminary survey may result in some uncertainty. Our results suggest that the PAHs in river sediments in China still need to be paid attention to due to the complexity of their sources and harms to aquatic organisms.