Sedimentary records of polycyclic aromatic hydrocarbons (PAHs) in remote lakes across the Tibetan Plateau

Evidence of economic development revealed in centennial scale sedimentary records of organic pollutants in Huguangyan Marr Lake

Sedimentary records of polycyclic aromatic hydrocarbons (PAHs) and phthalates could reflect energy consumption and industrial production adjustment. However, there is limited knowledge about their effects on variations of PAH and phthalate compositions in the sediment core. The PAH and phthalate sedimentary records in Huguangyan Maar Lake in Guangdong, China were constructed, and random forest models were adopted to quantify the associated impact factors. Sums of sixteen PAH (∑16 PAH) and seven phthalate (∑7 PAE) concentrations in the sediment ranged from 28.8 to 1110 and 246-4290 μg/kg dry weight in 1900-2020. Proportions of 5-6 ring PAHs to the ∑16 PAHs increased from 32.0 %-40.7 % in 1900-2020 with increased coal and petroleum consumption, especially after 1980. However, those of 2-3 ring PAHs decreased from 30.7 % to 23.6 % due to the biomass substitution with natural gas. The proportions of bis (2-ethylhexyl) phthalate to the ∑7 PAEs decreased from 52.3 %-29.1 % in 1900-2020, while those of di-isobutyl phthalate increased (13.7 % to 42.3 %). The shift from traditional plasticizers to non-phthalates drove this transformation, though the primary plastic production is increasing. Our findings underscore the effectiveness of optimizing energy structures and updating chemical products in reducing organic pollution in aquatic environments.

Exploring organic and inorganic contaminant histories in sediment cores across the anthropocene: Accounting for site/area dependent factors

Sedimentary records help chronologically identify anthropogenic contamination in environmental systems. This study analysed dated sediment cores from L'Albufera Lake (Valencia, Spain), to assess the occurrence of heavy metals (HMs), polycyclic aromatic hydrocarbons (PAHs), perfluoroalkyl substances (PFASs), organophosphorus flame retardants (OPFRs), pesticides and pharmaceuticals and personal care products (PPCPs). The results evidence the continuing vertical presence of all types of contaminants in this location. The sediment age was difficult to establish. However, the presence of shells together with an historical estimation and the knowledge of sedimentary rates could help. HMs contents are higher in the upper layer reflecting the most recent increase of the industrial and agricultural practices in the area since the middle 20th century. Higher availability index of these HMs in the upper sediment layers is associated with point and diffuse contamination sources in the area. PAHs and OPFRs were homogeneous distributed through the sediments with few exceptions such as phenanthrene in the North and fluoranthene in the South. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) were detected throughout the sediment core while short-chain PFASs (except perfluoropentanoic acid (PFPeA)) were detected only in the top layer. Pesticides and PPCPs showed appreciable down-core mobility. The vertical concentration profiles of organic contaminants did not exhibit a clear trend with depth, then, it is difficult to develop a direct relationship between sediment age and contaminant concentrations, and to elucidate the historical trend of contamination based on dated sediment core. Consequently, linking contaminant occurrence in sediments directly to their historical use is somewhat speculative at least in the conditions of L'Albufera Lake.

Distribution and sources of polycyclic aromatic hydrocarbons in surface sediments of the East China marginal seas: Significance of the terrestrial input and shelf mud deposition

To investigate the distribution, sources, influencing factors, and ecological risk of polycyclic aromatic hydrocarbons (PAHs) in East China Marginal Seas (ECMSs) sediments, we measured the concentrations of 16 PAHs in 104 surface sediment samples collected from the ECMSs in 2014 and 2016. Total PAH concentration (∑PAHs) ranged from 4.49 to 163.66 ng/g dry weight (dry w), with 65.98 ± 33.00 (mean ± SD) ng/g dry w. The highest PAH concentrations and total organic carbon were observed in areas with fine-grained sediments in the Bohai Sea (BS), Yellow Sea (YS), and coastal East China Sea (ECS), indicating the prominent influence of regional hydrodynamics and sediment properties. The dominant PAH congener in BS and YS was BbF, whereas coastal ECS was Phe. The heterogeneity of PAH sources implies that terrestrial PAH input and shelf mud deposition have crucial roles in the source-sink processes of PAHs in a strongly human-influenced marginal sea.

Four Years of Active Sampling and Measurement of Atmospheric Polycyclic Aromatic Hydrocarbons and Oxygenated Polycyclic Aromatic Hydrocarbons in Dronning Maud Land, East Antarctica

Antarctica, protected by its strong polar vortex and sheer distance from anthropogenic activity, was always thought of as pristine. However, as more data on the occurrence of persistent organic pollutants on Antarctica emerge, the question arises of how fast the long-range atmospheric transport takes place. Therefore, polycyclic aromatic hydrocarbons (PAHs) and oxygenated (oxy-)PAHs were sampled from the atmosphere and measured during 4 austral summers from 2017 to 2021 at the Princess Elisabeth station in East Antarctica. The location is suited for this research as it is isolated from other stations and activities, and the local pollution of the station itself is limited. A high-volume sampler was used to collect the gas and particle phase (PM10) separately. Fifteen PAHs and 12 oxy-PAHs were quantified, and concentrations ranging between 6.34 and 131 pg m3 (Σ15PAHs-excluding naphthalene) and between 18.8 and 114 pg m3 (Σ13oxy-PAHs) were found. Phenanthrene, pyrene, and fluoranthene were the most abundant PAHs. The gas-particle partitioning coefficient log(Kp) was determined for 6 compounds and was found to lie between 0.5 and -2.5. Positive matrix factorization modeling was applied to the data set to determine the contribution of different sources to the observed concentrations. A 6-factor model proved a good fit to the data set and showed strong variations in the contribution of different air masses. During the sampling campaign, a number of volcanic eruptions occurred in the southern hemisphere from which the emission plume was detected. The FLEXPART dispersion model was used to confirm that the recorded signal is indeed influenced by volcanic eruptions. The data was used to derive a transport time of between 11 and 33 days from release to arrival at the measurement site on Antarctica.

Aged polycyclic aromatic hydrocarbons as stratigraphic marker in the Anthropocene: Evidence from Tibetan Lake sediments

Polycyclic aromatic hydrocarbons (PAHs) were supposed to serve as combustion marker reflecting the past energy use, but it was unclear whether their sediment records in the Anthropocene were "weathered" due to aging-induced formation of bound residues. In this study, the total concentration of PAHs (the sum of rapid desorption, slow desorption, and bound residue fractions) were determined in four dated sediment cores from eastern to central Tibet using multi-step sequential extraction method. The total 16 PAH concentrations were 11.8, 13.5, 18.9, and 29.4 ng/g dw (in average) in the Co Ngoin, Pung Co, Ahung Co, and Putok lakes, respectively. The stratigraphic records and estimated source contributions of PAHs in different areas of Tibet exhibited a coherent change in the mid-20th century in response to the Holocene-Anthropocene transition. The sediment PAHs also displayed a comparable pattern when the bound residue fraction was not accounted for, suggesting their effective retainability under natural aging conditions. This may be elucidated by the enduring forward and back conversions between slow desorption and bound residue fractions, which manifested similar time-dependent variations across PAH congeners. The distinct conversion tendencies of different congeners were predicted by the binding affinity of congeners to surface/inner regions of organic matter using molecular docking simulations. Our findings demonstrate the persistence of sediment PAH records under natural aging and validate the use of PAH documentary evidence for investigating the Anthropocene.

Sediment core records and impact factors of polycyclic aromatic hydrocarbons in Chinese lakes

Lake sediment is a natural sink for polycyclic aromatic hydrocarbons (PAHs). PAH sedimentation characteristics and their impact factors of Chinese lakes have mainly been qualitative assessed. However, quantitative impacts of PAH sedimentation from different factors have not been well analyzed. To fill this gap, we screened PAH sedimentation records from the literature, for 51 lakes in China and other regions of the world, to identify historical concentration variation and the impact factors of PAHs in different regions, in lake sediment. The results show that PAH concentrations in the sediment core in the selected Chinese lakes (478 ± 812 ng/g dry weight (dw)) were significantly lower than those in North America (5518 ± 6572 ng/g dw) and Europe (3817 ± 4033 ng/g dw). From 1900 to 2015, most of the lakes in China showed an increasing trend of PAH sedimentation concentrations, with the lakes in Southeastern China showed a decreasing trend of PAH concentration in the period of 2001-2015, which was later than the peak times shown in Western countries (1941-1970). The 2-3-ring PAHs were the main components in the sediment core of Chinese lakes, but the proportion to the total PAHs decreased from 72% in 1900-1940 to 55% in 2001-2015. Generalized additive modeling (GAM) was adopted to simulate the associations between PAH sedimentation records and the impact factors. There are large regional variations of economic and industrial development in China. The impact factors of PAH accumulation in the lake sediments differ in different regions. However, population and the consumption of coal, pesticides, and fertilizer were identified to be the most important impact factors influencing PAH sedimentation. The Chinese government needs to strengthen control measures on pollutant discharge to reduce the anthropogenic impact of PAH sedimentation in lakes.

Effects of organic carbon burial on biomarker component changes in contamination in northeast Dianchi watershed

The upper reaches of the Yangtze River have experienced increasing anthropogenic stress. Quantitative tracing of carbon (C) sources and ecological risks through biomarkers i.e., polycyclic aromatic hydrocarbons (PAHs) and n-alkanes is significant for C neutrality and sequestration. Here, source and sink patterns, and factors influencing C burial and biomarker components in a small catchment of Dianchi Lake were explored. The sediment core covered the period 1855-2019. Before 1945, the organic C accumulation rate (OCAR) ranged from 0.71 to 5.12 mg cm^-2 yr^-1, and the PAHs and n-alkanes fluxes were 106.99-616.09 ng cm^-2 yr^-1 and 5.56-31.37 μg cm^-2 yr^-1. During 1945-2005, the OCAR, PAH, and n-alkane burial rapidly increased from 3.19 to 16.17 mg cm^-2 yr^-1, 230.40 to 2538.81 ng cm^-2 yr^-1, and 11.63 to 61.90 μg cm^-2 yr^-1. During 1855-2019, deposition fluxes of PAHs and n-alkanes increased 13.01 and 9.14 times, resulting in increased C burial, driven by environmental changes. A PMF model and the diagnostic ratio indicated that PAHs from coal combustion and traffic emission increased from 22.32% to 65.20% during 1855-2019. The PAH concentrations reflected normal-moderate contamination and potential risks to the aquatic environment. The results facilitate a comprehensive understanding of anthropogenic-driven interactions between increasing OC burial and ecological risks.

An evaluation of the impact of traffic on the distribution of PAHs and oxygenated PAHs in the soils and moss of the southeast Tibetan Plateau

Contaminants in high-altitude mountains such as the Tibetan Plateau (TP) have attracted extensive attention due to their potential impact on fragile ecosystems. Rapid development of the economy and society has promoted pollution caused by local traffic emissions in the TP. Among the pollutants emitted by traffic, polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) are of particular concern due to their high toxicity. The TP provides an environment to explore the degree and range of contribution for traffic-induced PAHs and OPAHs. In this study, soils and moss were collected at different altitudes and distances from the G318 highway in the southeast TP. The total concentrations of PAHs (∑₁₆PAHs) and OPAHs (∑₆OPAHs) in soils were in the range of 3.29-119 ng/g dry weight (dw) and 0.54-9.65 ng/g dw, respectively. ∑₁₆PAH and ∑₆OPAH concentrations decreased logarithmically with increasing distance from traffic. A significantly positive correlation between ∑₁₆PAHs and altitude was found at sampling points closest to traffic. Dominant PAHs constituents in soil and moss included chrysene (CHR), benzo[g,h,i]perylene (BghiP), and benzo[b]fluoranthene (BbF); prevalent OPAH compounds were 9-fluorenone (9-FO) and 9,10-anthraquinone (ATQ). These compounds were related to characteristics of traffic emissions. The multiple diagnosis ratio and correlation analysis showed that exhaust emissions were the main source of the PAHs and OPAHs in the studied environment. PMF modeling quantification of the relative contribution of traffic emissions to PAHs in roadside soils was 45 % on average. The present study characterized the extent and range of traffic-induced PAH and OPAH emissions, providing valuable information for understanding the environmental behaviors and potential risks of traffic-related contaminants in high-altitude areas.

Source apportionment of polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Lake Dagze Co, Tibetan Plateau, China: Comparison of three receptor models

Receptor models are a useful tool for identifying sources of polycyclic aromatic hydrocarbons (PAHs) in multiple environmental media. In this study, three different receptor models (including the principal component analysis-multiple linear regression (PCA-MLR), positive matrix factorization (PMF), and Unmix models) were used to apportion the sources of 16 priority PAHs in a sediment core of Lake Dagze Co. The ∑PAHs (sum of all 16 measured PAHs) concentrations ranged from 51.89 to 132.82 ng/g with an average of 80.39 ng/g. The ∑PAHs were dominated by 2-3 ring PAHs, accounting for 80.12% on average, thereby indicating that they mainly originated from biomass and coal combustion and/or from long-range atmospheric transportation. The three models produced consistent source apportionment results. The greatest contributor to ∑PAHs was biomass combustion, followed by coal combustion, vehicle emissions, and petrogenic sources. Moreover, the temporal variation of the common sources was well-correlated among models. The multi-method comparison and evaluation results showed that all three models were useful tools for source apportionment of PAHs, with the PMF model providing better results than the PCA-MLR and Unmix models. The temporal trends of factor contributions were verified by PAHs with different ring numbers. Significant correlations were found between the simulated concentrations of each source factor and the PAHs with different ring numbers (P<0.01), except for the petrogenic source identified by the Unmix model (P>0.05). This study can provide useful information for further investigation of source apportionment of PAHs in the sediment cores.

Polycyclic aromatic hydrocarbons in remote lakes from the Tibetan Plateau: Concentrations, source, ecological risk, and influencing factors

Polycyclic aromatic hydrocarbons (PAHs) have received worldwide attention due to their potential teratogenic, persistent, and carcinogenic characteristics. In this study, the PAHs concentrations in two dated sediment cores taken from central Tibetan Plateau (TP) were analyzed to study the deposition history, potential sources, ecological risks, and influencing factors. Total concentration of PAHs (∑PAHs) ranged from 50.0 to 195 ng g^-1 and 51.9-133 ng g^-1 in sediments of Pung Co (PC) and Dagze Co (DZC), respectively. 2-3-ring PAHs were dominant in the two lake sediments, accounting for an average of 77.5% and 80.1%, respectively. The historical trends of ∑PAHs in the two lakes allowed to distinguish three periods, namely, relative stability before the 1950s, a gradual increase between the 1950s and the 1990s, and then a decline to the present-day. In addition, the trend in the concentration level of each PAH composition was consistent with ∑PAHs before the 1990s, while they exhibited different trends since the 1990s, which may be the result of a combination of anthropogenic activities and climate change in recent years, whereas before the 1990s the PAH profile was mainly influenced by atmospheric deposition. The results of source apportionment examined according to diagnostic ratios and positive matrix factorization were consistent and revealed that PAHs were primarily derived from biomass and coal combustion. Significant correlations between PAHs and organic carbon (OC) indicate that OC might be a key factor influencing the concentration of PAHs in sediments. The ecological risk assessment demonstrated that PAHs in TP sediments occurred at a low risk level. Results of this study could be helpful to develop a deeper insight into the deposition history of PAHs in remote lakes of the TP region and explore the response of these variations to climate change and human activities.

One-century sedimentary record, sources, and ecological risk of polycyclic aromatic hydrocarbons in Dianchi Lake, China

In this study, the sedimentary records, sources, and ecological risks of polycyclic aromatic hydrocarbons (PAHs) in Dianchi Lake were analyzed. The concentrations of ΣPAH₁₆ in the sediments of Dianchi Lake ranged from 368 to 990 ng/g, with an average value of 572 ng/g, peaking in 1988. Economic development, rapid population growth, and rapid growth of coal consumption have a greater impact on the HMW (high molecular weight) PAHs than on the LMW (low molecular weight) PAHs in the sedimentary environment. The results of the diagnostic ratios and PCA (principal component analysis) model show that the main sources of PAHs were coal and biomass combustion, as well as the fossil fuel combustion in individual years. The risk assessment results showed that the PAH concentrations in the sediment were within a safe range. In the past 100 years of sediment pore water, other 2-3 ring LMW PAHs were within a safe range (except for Phe, which reached chronic toxic pollution levels in some years). With an increase in industrialization and urbanization, the burning of fossil fuels such as coal and petroleum has increased, and some of the 4-6 ring HMW PAHs have reached chronic toxicity or even acute toxicity in the sediment pore water.

Occurrence characteristics and source appointment of polycyclic aromatic hydrocarbons and n-alkanes over the past 100 years in southwest China

The extensive anthropogenic activities and their potential impacts during the Anthropocene have led to a research focus on the sedimentary record. In the present study, the occurrence and temporal variations in the fluxes and compositions of n-alkanes and polycyclic aromatic hydrocarbon (PAHs) were investigated in ²¹⁰Pb-dated sediment cores from a small catchment near the outflow Tanglangchuan in the western Dianchi Lake, China. The continuing organic contamination (i.e. PAHs and n-alkanes) from inputs to outputs has been of concern. To trace the sources and driving forces, multi indicators were applied. Results showed that the total organic carbon (TOC) contents and C/N ratios varied in the range of 4.20-12.30 mg g^-1 dw and 8.64-15.65, respectively, indicating algae- and terrestrial plant-derived organic matter (OM). The flux of Σn-alkanes ranged from 0.67 to 38.86 μg cm^-2 a^-1 with a peak in 2013. The long-chain n-alkanes (Σn-alk_26-35) and short-chain n-alkanes (Σn-alk_12-20) accounted for 44.02%-49.38% and 35.32%-41.49% of the Σn-alkanes, respectively. A bimodal distribution of n-alkanes was displayed in the sediments implying the sedimentary OM may be derived from a mixed source of endogenous and exogenous origin. The posterior peak (≥n-C₂₆) compounds in the highest abundance were n-C₃₁ or n-C₃₃ with a significant odd-numbered C predominance, representing terrestrial plant-derived OM. Whereas n-C₁₆ was rich in all sediment profiles reflecting crude oil or incompletely combusted fossil fuel-derived source. The indicators analysis showed an increasing trend of the contribution from terrestrial plants and wet to drought climate during 1873-2019. The sedimentary flux of ΣPAHs ranged between 11.71 and 1231.54 ng cm^-2 a^-1 and the percent of high-ring PAHs rose annually indicating enhanced anthropogenic activities. In the past 147 years, the results of present study highlight the influence of the agricultural and industrial economy on the catchment outlets.

Spatiotemporal distribution of polycyclic aromatic hydrocarbons in sediments of a typical river located in the Loess Plateau, China: Influence of human activities and land-use changes

The Loess Plateau, as the key energy base of China, has sensitive responses to the global changes, and receives polycyclic aromatic hydrocarbons (PAHs) from anthropogenic activities. However, understanding how anthropogenic and climate factors affect synergistically the PAHs distribution in this vulnerable ecological environment is deficient. Here the spatiotemporal distribution of PAHs in sediments from a typical river of the Loess Plateau were investigated. The PAHs were mainly from coal combustion in the range of 194-514 ng g^-1, and their concentrations were generally higher in normal season than wet season as the dilution effect of high river discharge and strong precipitation. The interactive effects of land-use and precipitation showed PAHs enriched in forest-grass land were transferred into rivers through surface and subsurface runoff during light rainfall, resulting in the increase of the PAHs concentrations in river sediments. In contrast, large precipitation in wet season would obscure any spatial variations. In addition, human activities, especially energy production, directly enhanced PAHs accumulation in river sediments due to the emission from the production processing of oil and coal, and indirectly influenced the PAHs by impacting the per capita GDP. These findings had important implications for the management and prediction of PAH accumulation.

Century-long record of polycyclic aromatic hydrocarbons from tree rings in the southeastern Tibetan Plateau

Limited studies have been carried out on the historical variations of atmospheric polycyclic aromatic hydrocarbons (PAHs), especially in remote regions of the world. In this study, century-long record of PAHs (1916-2018) were reconstructed from tree rings in the remote southeastern Tibetan Plateau (TP). The total concentrations of 15 PAHs varied from 27.5 to 6.05 × 10² ng/g dry weight (dw), with a mean value of 1.40 × 10² ng/g dw. Higher levels of PAHs were observed during World War Ⅱ and the Peaceful Liberation of Tibet, and increasing trends were observed starting from rapid industrialization in India. Both the isomer ratios and the positive matrix factorization model results indicated biomass and coal combustion were the dominant sources of PAHs. The carcinogenic risk of PAHs to local residents was assessed, which might have been negligible in most past periods and lower than in other regions of the world. Nevertheless, since the beginning of the 21st century, the cancer risk has been increasing year by year, indicating more actions are needed to reduce emissions of PAHs. This study provides an idea for reconstructing the pollution history of PAHs at the global scale.

Polycyclic aromatic hydrocarbons in sedimentary cores of Tibetan Plateau: Influence of global warming on cold trapping

Cold condensation is an important pathway for polycyclic aromatic hydrocarbons (PAHs) depositing at remote alpine lakes after long-range atmospheric transportation. However, in the context of global warming, the obvious temperature rise in the Tibetan Plateau (TP) might have an impact on the air deposition of PAHs by controlling the extent of cold condensation. To investigate the influence of rising temperatures on the atmospheric deposition of PAHs, two dated sedimentary cores from Pumoyum Co Lake (PC) and Selin Co Lake (SC) were collected, respectively and concentrations of 16 individual PAHs were measured. In both PC and SC, the total concentration of 16 PAHs presented relatively lower levels in four historical periods of "hot anomaly" including 1973-1975, 1988-1989, 1998-1999, and 2006-2007. This indicated that the hot temperatures might restrict the atmospheric deposition of PAHs. Besides, the results of the principal component analysis did discriminate those "hot anomalies". As the temperature kept increasing in TP, for low molecular weight PAHs and high molecular weight PAHs, the influence of rising temperatures on the cold condensation was different. Therefore, it was identified that the effect of global warming on the environmental fate of POPs cannot be neglected, especially in alpine regions like TP.

Fate of polycyclic aromatic hydrocarbons in the Pacific sector of the Arctic Ocean based on a level III fugacity environmental multimedia model

The sink-source controversy for global polycyclic aromatic hydrocarbons (PAHs) in high-latitude seas is extremely concerning. A level III fugacity model was developed for the southern Chukchi Sea to estimate the fate of 16 priority PAHs. The model results indicate large losses were due to seawater advection outflow, followed by degradation in seawater. The Chukchi Sea serves as a source of 4 PAHs (i.e., Nap, Ace, Acp and Fl) in the atmosphere and sediment but acts as a final sink for the other 12 PAHs. The water-air diffusion flux and wet deposition flux play dominant roles in the total transfer flux of the 4 PAHs and the other 12 PAHs, respectively. The source/sink role that high-latitude seas play in PAH distribution has changed under the influence of global climate change. The model proposed in this study provides an approach to support further study of the fate of PAHs in high-latitude seas.

Use of comprehensive target analysis for determination of contaminants of emerging concern in a sediment core collected from Beppu Bay, Japan

In recent years, concern about the release of anthropogenic organic micropollutants referred to as contaminants of emerging concern (CECs) has been growing. The objective of this study was to find potential CECs by means of an analytical screening method referred to as comprehensive target analysis with an automated identification and quantification system (CTA-AIQS), which uses gas and liquid chromatography combined with mass spectrometry (GC-MS and LC-QTOF-MS). We used CTA-AIQS to analyze samples from a sediment core collected in Beppu Bay, Japan. With this method, we detected 80 compounds in the samples and CTA-AIQA could work to useful tool to find CECs in environmental media. Among the detected chemicals, three PAHs (anthracene, chrysene, and fluoranthene) and tris(isopropylphenyl)phosphate (TIPPP) isomers were found to increase in concentration with decreasing sediment depth. We quantified TIPPP isomers in the samples by means of targeted analysis using LC-MS/MS for confirmation. The concentration profiles, combined with previous reports indicating persistent, bioaccumulative, and toxic properties, suggest that these chemicals can be categorized as potential CECs in marine environments.

A one-century sedimentary record of N- and S-polycyclic aromatic compounds in the Athabasca oil sands region in Canada

The atmospheric deposition of polycyclic aromatic compounds (PACs) is considered a major pathway to isolated lakes and bogs in the Athabasca oil sands region (AOSR), Canada. However, the suite of PACs measured has been limited. We report the detailed depositional history of nitrogen and sulphur heterocyclic PACs using a ²¹⁰Pb dated sediment core (1914-2015) near major developments in the AOSR. We observed (1) an exponential growth in the deposition of heterocyclic PACs to recent times with an average doubling time of 12 years, (2) significant breakpoints in PAC fluxes in the mid to late 1980s, and (3) a synchronous increase of PACs with crude oil production (r² = 0.82, p = 0.001). NPACs were not detected prior to the 1960s in the sediment core studied, suggesting they may hold promise in serving as indicators for atmospheric PAC deposition of industrial origin. Furthermore, a change in heterocyclic PAC distribution profiles beginning in the 1970-1980s, after the onset of mining, resembling a petcoke signature, was also observed. Significant positive correlations (p < 0.05) were observed between heterocyclic PACs, and several metal(loid)s, including priority pollutant elements, chromium and beryllium, and rare earth elements, cerium, lanthanum and yttrium (r² > 0.75), suggesting the potential of a common source or similar transport and fate mechanisms. Significant negative or no correlations were observed between heterocyclic PACs and other metal(loid)s, including vanadium, total mercury and lead, possibly reflecting the impact of broader regulatory controls introduced in the mid-1970s on some metal(loids) but not on PACs, including the installation of electrostatic precipitators in major upgrader stacks.

Historical trends of PCBs and PBDEs as reconstructed in a lake sediment from southern Tibetan Plateau

High-altitude lake sediment can be used as a natural archive to reconstruct the history of pollutants. In this work, the temporal distribution of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were determined using a high-resolution gas chromatography coupled with high-resolution mass spectrometer (HRGC/HRMS) in an alpine lake sediment core collected from the southern Tibetan Plateau (TP) to examine whether the expected decreasing trends due to the implementation of the international Conventions could be observed. The concentrations of PCBs and PBDEs in the sediment core were in the range of 11.8-142 pg/g dw and ND-457 pg/g dw, and their fluxes were in the range of 2.51-31.7 ng/(m²·yr) and ND-43.2 ng/(m²·yr), respectively. The prevalence of low-chlorinated (tri-CB) PCBs and low-brominated (tri- to tetra-) PBDEs in most sections of the sediment profiles was observed, suggesting that the light molecular weight PCBs and PBDEs have most likely reached lake sediments by long-range atmospheric transport from distant sources. Despite the restrictions on their applications, the sediment records for the concentrations and fluxes showed no corresponding decreasing trend with restrictions for PCBs, which suggested that these POPs (e.g., PCBs) were still emitted to the environment owing to the influence of primary or secondary emissions. To our knowledge, this is the first report on input history of atmospheric PCBs and PBDEs recorded in TP Lake sediment.

Urban stormwater and crude oil injury pathways converge on the developing heart of a shore-spawning marine forage fish

Understanding how aquatic organisms respond to complex chemical mixtures remains one of the foremost challenges in modern ecotoxicology. Although oil spills are typically high-profile disasters that release hundreds or thousands of chemicals into the environment, there is growing evidence for a common adverse outcome pathway (AOP) for the vulnerable embryos and larvae of fish species that spawn in oiled habitats. Molecular initiating events involve the disruption of excitation-contraction coupling in individual cardiomyocytes, which then dysregulate the form and function of the embryonic heart. Phenanthrenes and other three-ring (tricyclic) polycyclic aromatic hydrocarbons (PAHs) are key drivers for this developmental cardiotoxicity and are also relatively enriched in land-based urban runoff. Similar to oil spills, stormwater discharged from roadways and other high-traffic impervious surfaces contains myriad contaminants, many of which are uncharacterized in terms of their chemical identity and toxicity to aquatic organisms. Nevertheless, given the exceptional sensitivity of the developing heart to tricyclic PAHs and the ubiquitous presence of these compounds in road runoff, cardiotoxicity may also be a dominant aspect of the stormwater-induced injury phenotype in fish early life stages. Here we assessed the effects of traffic-related runoff on the embryos and early larvae of Pacific herring (Clupea pallasii), a marine forage fish that spawns along the coastline of western North America. We used the well-characterized central features of the oil toxicity AOP for herring embryos as benchmarks for a detailed analysis of embryolarval cardiotoxicity across a dilution gradient ranging from 12 to 50% stormwater diluted in clean seawater. These injury indicators included measures of circulatory function, ventricular area, heart chamber looping, and the contractility of both the atrium and the ventricle. We also determined tissue concentrations of phenanthrenes and other PAHs in herring embryos. We find that tricyclic PAHs are readily bioavailable during cardiogenesis, and that stormwater-induced toxicity is in many respects indistinguishable from canonical crude oil toxicity. Given the chemical complexity of urban runoff, non-tricyclic PAH-mediated mechanisms of developmental toxicity in fish remain likely. However, from the standpoint of managing wild herring populations, our results suggest that stormwater-driven threats to individual survival (both near-term and delayed mortality) can be understood from decades of past research on crude oil toxicity. Moreover, Pacific herring embryos are promising sentinels for water quality monitoring in nearshore marine habitats, as in situand sensitive indicators of both toxic runoff and the effectiveness of pollution reduction efforts such as green stormwater infrastructure.

Distribution, source, and ecological risks of polycyclic aromatic hydrocarbons in Lake Qinghai, China

Contamination by polycyclic aromatic hydrocarbons (PAHs) has been observed at high elevation environments; however, the occurrence and spatial variation of PAHs in alpine lakes of China is not well understood. We measured 15 priority PAHs in the sediments of Lake Qinghai in the Qinghai-Tibet Plateau, and assessed their distribution, source, and ecological risks. The total PAH concentration ranged from 30.4 to 125.2 ng g^-1. Low molecular weight PAHs were dominant in the sediments, suggesting a local source for the emissions. Sediment sites closer to local settlements and rivers had higher concentration of PAHs. The concentration of PAHs was significantly correlated with pH, probably as a result of the high salinity of the lake, while it was not significantly correlated with organic matter content. Molecular diagnostic ratio analysis indicated that PAHs were derived mainly from coal and biomass combustion. Specifically, the positive matrix factorization model showed that petrogenic sources, vehicular emissions, biomass combustion, and coal combustion contributed for 11.6, 16.3, 23.6, and 48.5% of the PAHs, respectively. The risk quotient method was used to assess ecological risk of PAHs individually. The results indicate that indeno[1,2,3-cd]pyrene, benzo[b]fluoranthene, benzo[a]pyrene, phenanthrene, and anthracene would produce moderate ecological risks in 5, 20, 65, 100, and 100% of the sediment sites, respectively, while the other 10 PAH homologues would scarcely produce any serious ecological risk. We used the hierarchical Archimedean copula integral assessment model to evaluate the integral risk of PAHs. The result showed that 10, 40, and 50% of the sediment sites belong to mid-high, low, and mid-low risk levels, respectively. The current concentration and risk levels of PAHs in this study might be used as a baseline to assess the influence of future anthropogenic activities.

Occurrence and sources of polycyclic aromatic hydrocarbons in atmosphere and soil from 2013 to 2019 in the Fildes Peninsula, Antarctica

Long-term monitoring is essential for revealing pollution trends, but relevant studies in the Antarctic remain limited. In this study, a seven-year continuous monitoring of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere and soil was carried out at the Fildes Peninsula, Antarctica. Average concentrations of Σ₁₅PAHs were 7134.491 pg/m³ and 61.093 ng/g in air and soil, respectively. A declining trend was observed for Σ₁₅PAHs in air during the 2013-2019 summer, but this was not found in soil. Potential sources of PAHs in the Fildes Peninsula were identified by PMF modeling, correlation analysis, air mass back-trajectories and component analysis. The results showed that PAHs in the gas phase were more easily influenced by long-range atmospheric transport (LRAT) than in the particle phase. Moreover, temperature played a key role in the PAHs concentration in particle phase. Occurrence of Σ₁₅PAHs in soil was mainly attributed to local sources including fossil fuel combustion and spilling.

Source apportionment of priority PAHs in 11 lake sediment cores from Songnen Plain, Northeast China

Elevated concentrations of polycyclic aromatic hydrocarbons (PAHs) have been observed with rapid agricultural and industrial development in the Songnen Plain, Northeast China, but the prospective sources have not been yet apportioned. The concentration of PAHs was measured in 31 sediment samples from 11 Songnen Plain lakes in 2015. The background flux of PAHs in these lake sediments is < 463 μg m^-2 year^-1. The maximal concentration of 16 U.S. EPA priority PAHs (599 ng g^-1) recorded in this study is lower or similar to that found in most of the lake sediments across China, but higher than remote areas, such as North America Rocky Mountains. Both concentration and flux of PAHs increased after the 1950s, which correspond to the industrial development in this area and would probably mark the beginning of the Anthropocene in this region. A chemical mass balance model estimated that straw burning was a major source of Σ₁₃PAH (3-6 rings) during the past 200 years, with an average contribution of 22.1%, followed by forest fire (21.2%), burning of gasoline (19.1%), coal (12.2%), coke (4.8%) and diesel (3.9%), whereas the contribution from crude oil and natural gas was negligible (<1%). Straw burning (20.2-25.2%) and forest fire (16.7-30.6%) were major sources of PAHs and contributed increasing flux in the past 200 years. The elevated level of PAH recorded after 1950s in this region are also from burning of gasoline (26.1-26.4%), coal (15.3-15.8%), and coke (5.1-9.0%). The contribution of petrogenic sources (e.g., direct oil spill) to the concentration of Σ₁₃PAH seemed to be ignorable, at least in these lakes.

Mercury isotopes in frozen soils reveal transboundary atmospheric mercury deposition over the Himalayas and Tibetan Plateau

The concentration and isotopic composition of mercury (Hg) were studied in frozen soils along a southwest-northeast transect over the Himalaya-Tibet. Soil total Hg (Hg_T) concentrations were significantly higher in the southern slopes (72 ± 54 ng g^-1, 2SD, n = 21) than those in the northern slopes (43 ± 26 ng g^-1, 2SD, n = 10) of Himalaya-Tibet. No significant relationship was observed between Hg_T concentrations and soil organic carbon (SOC), indicating that the Hg_T variation was not governed by SOC. Soil from the southern slopes showed significantly negative mean δ²⁰²Hg (-0.53 ± 0.50‰, 2SD, n = 21) relative to those from the northern slopes (-0.12 ± 0.40‰, 2SD, n = 10). The δ²⁰²Hg values of the southern slopes are more similar to South Asian anthropogenic Hg emissions. A significant correlation between 1/Hg_T and δ²⁰²Hg was observed in all the soil samples, further suggesting a mixing of Hg from South Asian anthropogenic emissions and natural geochemical background. Large ranges of Δ¹⁹⁹Hg (-0.45 and 0.24‰) were observed in frozen soils. Most of soil samples displayed negative Δ¹⁹⁹Hg values, implying they mainly received Hg from gaseous Hg(0) deposition. A few samples had slightly positive odd-MIF, indicating precipitation-sourced Hg was more prevalent than gaseous Hg(0) in certain areas. The spatial distribution patterns of Hg_T concentrations and Hg isotopes indicated that Himalaya-Tibet, even its northern part, may have been influenced by transboundary atmospheric Hg pollution from South Asia.

Historical variation of black carbon and PAHs over the last ~200 years in central North China: Evidence from lake sediment records

As the largest coal-producing province in China, the coal production of Shanxi Province accounts for one third of the country's total. Thus it is of great importance to study the pollution history of typical pollutants in Shanxi Province and their links with energy usage in North China. Sediment cores from two relatively remote lakes in central North China were retrieved to investigate historical evolutions of black carbon (BC) and polycyclic aromatic hydrocarbons (PAHs) in the last ~200 years. The two records show several-fold increases in both concentrations and depositional fluxes of BC, char, soot, and PAHs in recent five decades, which were associated with the influence of anthropogenic activities resulting from socio-economic development in Shanxi Province. However, after ~2000 their fluxes decreased sharply due to China's effort on environmental protection. These changes indicate that atmospheric BC and PAHs loads in the region were affected significantly by recent anthropogenic activities and environmental policies. Ratios of individual PAHs and char/soot indicate pyrogenic sources of these increased pollutants in recent decades, with coking industry and coal combustion as the two major sources. Significant positive correlations between BC and PAHs were observed in both cores of Lake Gonghai and Lake Mayinghai, indicating that they were likely co-transported by BC particles from similar sources. This study provides new and important understanding of the atmospheric pollution history of BC and PAHs in North China.

The sedimentary record of polycyclic aromatic hydrocarbons in Yamzho Yumco Lake: evolution of local sources and adsorption dynamic in the Tibetan Plateau

With the rapid increase in anthropogenic activities, the local emissions of polycyclic aromatic hydrocarbons (PAHs) in background regions, such as the Tibetan Plateau (TP), have attracted great attention. The deposition of PAHs in lake sediments provides a historical evolutionary record of such compounds in these regions. To investigate the evolution of PAHs in the TP, two sedimentary cores from Yamzho Yumco Lake were collected and dated at high resolution, and the concentrations of 16 PAHs and sediment properties were also analyzed. The total concentrations of the 16 PAHs ranged from 6.52 to 57.97 ng/g (dry weight) in YC1 and from 0.91 to 4.57 ng/g (dry weight) in YC2. According to the methods of principal component analysis (PCA) followed by multilinear regression analysis (MLRA), four sources of PAHs in the sediments were qualitatively and quantitatively identified, such as petroleum combustion, petrogenic, coal combustion, and biomass burning. Thus, the historical evolution of PAHs was summarized. In addition, the transported distance from local PAH emission sources was found to greatly affect the composition and concentration of PAHs in sites YC1 and YC2. Specifically, local sources contributed a greater proportion of heavy molecular weight (HMW) PAHs in YC1 and a higher proportion of light-molecular-weight (LMW) PAHs in YC2. Moreover, fine particles (size < 20 μm) were found to play a significant role in adsorbing PAHs in sediments. Furthermore, ∑₁₆PAHs in sediments were linearly correlated with the percentage of fine particles (size < 20 μm). This study provides a first example to investigate the historical evolution of PAH local emission in background regions by using lake sedimentary records, especially in the TP. Specifically, different local sources were identified using the methods of PCA followed by MLRA, and PAHs in TP sediments were predominantly adsorbed by fine particles rather than by total organic carbon (TOC) because the amount of TOC was limited.

Persistent organic pollutants in the polar regions and the Tibetan Plateau: A review of current knowledge and future prospects

Due to their low temperatures, the Arctic, Antarctic and Tibetan Plateau are known as the three polar regions of the Earth. As the most remote regions of the globe, the occurrence of persistent organic pollutants (POPs) in these polar regions arouses global concern. In this paper, we review the literatures on POPs involving these three polar regions. Overall, concentrations of POPs in the environment (air, water, soil and biota) have been extensively reported, with higher levels of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) detected on the Tibetan Plateau. The spatial distribution of POPs in air, water and soil in the three polar regions broadly reflects their distances away from source regions. Based on long-term data, decreasing trends have been observed for most "legacy POPs". Observations of transport processes of POPs among multiple media have also been carried out, including air-water gas exchange, air-soil gas exchange, emissions from melting glaciers, bioaccumulations along food chains, and exposure risks. The impact of climate change on these processes possibly enhances the re-emission processes of POPs out of water, soil and glaciers, and reduces the bioaccumulation of POPs in food chains. Global POPs transport model have shown the Arctic receives a relatively small fraction of POPs, but that climate change will likely increase the total mass of all compounds in this polar region. Considering the impact of climate change on POPs is still unclear, long-term monitoring data and global/regional models are required, especially in the Antarctic and on the Tibetan Plateau, and the fate of POPs in all three polar regions needs to be comprehensively studied and compared to yield a better understanding of the mechanisms involved in the global cycling of POPs.

A review on occurrence and risk of polycyclic aromatic hydrocarbons (PAHs) in lakes of China

Polycyclic aromatic hydrocarbons (PAHs) residues have attracted attention worldwide. This study summarizes the current levels of PAH exposure in the water environments of lakes. In addition, the risk levels from individual PAHs and ΣPAHs in the water environments of lakes in China were evaluated by incremental lifetime cancer risk (ILCR) assessment, the toxic equivalent concentration (TEQ_BaP), the risk quotient (RQ), the effects range-low (ERL) and the effects range-median (ERM). The results showed that the concentrations of ∑PAHs in water and sediment ranged from 4.0 to 12,970.8 ng L^-1 and 6.52 to 7935.21 ng g^-1, respectively, and the highest concentrations of individual PAHs were of naphthalene (Nap) (6525 ng L^-1), followed by indeno(1,2,3‑cd)pyrene (IcdP) (3452.6 ng g^-1). Concentrations in the Great Lakes region in China showed spatial difference, with the Qinghai-Tibet Plateau Lakes District and Mongolia-Xinjiang Lakes District being less polluted. However, the pollution level of PAHs in lakes is relatively high at the global scale. The ecological risk assessment found a moderate level of ∑PAHs in water, but benz(a)anthracene (BaA) and phenanthrene (Phe) had high RQ values, which might pose a significant risk to aquatic organisms in lakes. Although the contents of ∑PAHs in sediments are low, most individual PAHs pose potential risks, especially acenaphthene (Ace), fluorene (Flu) and dibenz(a,h)anthracene (DahA). This study revealed the pollution levels of PAHs across China and provided a scientific basis for PAH pollution control and environmental protection.

Assessing the level and sources of Polycyclic Aromatic Hydrocarbons (PAHs) in soil and sediments along Jhelum riverine system of lesser Himalayan region of Pakistan

Lesser Himalayan Region (LHR) is an important mountain ecosystem which supports a wide range of biodiversity for native flora and fauna. Human population in this region is largely dependent upon local sources for their livelihood. Surface soil (n = 32) and sediment (n = 32) were collected from four different altitudinal ranges of LHR and analyzed for priority Polycyclic Aromatic Hydrocarbons (PAHs) recommended by USEPA. Level, sources and distribution pattern of PAHs were assessed in soil and sediments samples collected from four altitudinal zones in LHR. Total PAHs concentration level of PAHs in soil and sediments ranged from 62.79 to 1080 ng g^-1 and 14.54-437.43 ng g^-1, respectively. Compositional profile of PAHs in both soil and sediment were dominated by low and medium molecular weight PAHs, ranged from 18.02 to 402.18 ng g^-1in soil and 0.32-96.34 ng g^-1in sediments. In the context of spatial distribution trend, highest mean concentrations of PAHs in soil were recorded in zone D (sites from the rural region) and for sediments highest concentrations were detected at zone A, which includes dam sites. In all four zones, no altitudinal trend of PAHs in soil and sediments was observed. Source apportionment through receptor modelling by positive matrix factorization (PMF) revealed that local sources such as biomass combustion and vehicular emissions are important sources of PAHs in this region. The prevalence of monsoon atmospheric circulation system in LHR implicated that this region is also influenced by medium and long range atmospheric transportation of PAHs from neighboring countries where potential sources and high level of PAHs has been reported.

Sedimentary biogeochemical record in Lake Gonghai: Implications for recent lake changes in relatively remote areas of China

Owing to rapid socio-economic development and climate warming, lakes even in remote areas have experienced marked changes in the last century. However, there are few studies revealing the multi-faceted biogeochemical changes and disentangling impacts of human and climate in relatively remote lakes in China. In this study we reconstructed historical changes of geochemistry, nutrition, primary production, ecology, and pollution in an alpine lake (Gonghai) in central North China, and revealed coherent changes and drivers in relatively remote Chinese lakes by compiling other records. Results show that Lake Gonghai has experienced considerably biogeochemical changes since the 1980s induced mainly by increased regional human activities, with detected human-related changes occurring in the 1950s-70s. The most important change is a shift of diatom primary producers in the 1980s, caused mainly by an increase of regional atmospheric N and P deposition associated with rapid socio-economic development. Another remarkable change is the increase of pollution levels since the 1980s, represented by heavy metals, also caused by atmospheric deposition. Compiled sediment records demonstrate similar biogeochemical changes in most lakes from relatively remote areas of China since the 1970s-80s, associated closely with increased inputs of human-induced atmospheric N, P and pollutants, whereas the influence of climate warming is likely limited. This study highlights markedly human-related biogeochemical changes in relatively remote Chinese lakes during the Anthropocene epoch.

Comparing and modeling sedimentary profiles of elemental carbon and polycyclic aromatic hydrocarbons between early- and newly-urbanized areas in Shanghai

Rapid urbanization created unique urban environment with a characteristic of dramatic modification of land cover, consequently causing profound perturbations in the transport and fate of pollutants in urban ecosystem. Taking a hyper-urbanization city (Shanghai) as an example to reveal the influence of urbanization development on pollutant footprint, this study reconstructed and compared historical evolutions of elemental carbon (EC) and polycyclic aromatic hydrocarbons (PAHs) based on two lake sediment cores (DSL: Dianshan Lake; LXL: Luxun Lake) from early- and newly-urbanized areas, respectively. Historical fluxes of EC and total PAH (Σ₁₆PAHs) showed similar and sharply fluctuant increases occurring after the 1950s in the DSL core later than the LXL core after the 1900s. In modern times (after 2000), the mean fluxes of EC and Σ₁₆PAHs in the LXL core were 2.68- and 1.38-fold greater than those in the DSL core, respectively, indicating the stronger influence from more intensive human activities and longer industrial history in early urbanized area. Based on the significant correlations among socioeconomic factors with EC and Σ₁₆PAH fluxes, the extended STIRPAT (stochastic impacts by regression on population, affluence and technology) models were successfully constructed, revealing that significance of these driving factors were in the order of population > the proportion of heavy industry > coal consumption > gross domestic product (GDP) per capita > vehicle amount. In general, the obvious discrepancy in historical stage and intensity of sedimentary EC and PAH accumulations implied that some newly fast-developing cities still have a chance to adjust urban development strategy to avoid more serious pollution.

Natural attenuation of naphthalene along the river-bank infiltration zone of the Liao River, Shenyang, China

In this study, the natural attenuation of naphthalene during riverbank infiltration was examined using batch experiments. The results indicated that, as the grain size and the permeability coefficient decreased, the natural attenuation rate of naphthalene increased, and it was highest in loam (62%) and lowest in coarse sand (20%). The half-life of naphthalene was longest in coarse sand (700 d) and shortest in mild clay (250 d). Facultative anaerobes such as Methylophilaceae accounted for about 70% of the total bacteria and played a major role in naphthalene degradation. A high total organic carbon concentration and large specific surface area can promote natural attenuation of naphthalene. Moreover, the adsorption to riverbank sediment in the hyporheic zone and bioremediation by indigenous microorganisms can effectively eliminate naphthalene during river water infiltration to the riverbank aquifer.

Anthropogenic PAHs in lake sediments: a literature review (2002-2018)

Lake sediments are an important reservoir for toxic and hydrophobic polycyclic aromatic hydrocarbons (PAHs). Monitoring of PAHs in sediment is helpful to understand pollution mechanisms and anthropogenic activities. This study reviews studies of PAHs in lake sediments published during 2002-2018. The studies' findings are analyzed, distributions of PAHs in lake sediments are summarized, and the applicability of lake sediments for tracking changes in PAH emission sources is emphasized. Lake sediments heavily polluted with PAHs are distributed in China, Egypt, the USA, and some urban lakes in Africa. The high levels of PAHs are predominantly associated with human activities such as anthropogenic combustion, petroleum industries, road traffic, and socioeconomic factors. However, the concentrations of sedimentary PAHs in most lakes were below the international guideline values.

Lake sediment records of persistent organic pollutants and polycyclic aromatic hydrocarbons in southern Siberia mirror the changing fortunes of the Russian economy over the past 70 years

Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) have previously been detected in the surface sediments, water, and endemic organisms of Lake Baikal, a UNESCO World Heritage Site. The Selenga River is the primary source of freshwater to Lake Baikal, and transports pollutants accumulating in the Selenga River basin to the lake. Sources of POPs and PAHs in the Selenga River basin grew through the 20th century. In the present study, temporal changes in the concentrations of PAHs and POPs were reconstructed from two lakes in the Selenga River basin over the past 150 years using paleolimnological techniques. Increased concentrations in PAHs and PCBs were recorded initially in the 1930s. The 1940s-1980s was the period of greatest exposure to organic contamination, and concentrations of dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs) and many PAHs peaked between the 1960s and 1980s in the two lakes. Declines in concentrations and fluxes were recorded for most PAHs and POPs in the 1980s and 1990s. Temporal trends in concentrations of total and individual compounds/congeners of PAH, PCBs, and polybrominated diphenyl ethers (PBDEs) indicate the contribution of both local and regional sources of contamination in the 20th and 21st centuries. Temporal variations in contaminants can be linked to economic and industrial growth in the former USSR after World War II and the economic decline of Russia in the late-1980s and early-1990s, as well as global trends in industrialization and development during the mid-20th century.

Historical record of anthropogenic polycyclic aromatic hydrocarbons in a lake sediment from the southern Tibetan Plateau

High-altitude lake sediments can be used as natural archives to reconstruct the history of pollutants. In this work, the temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was determined in a sediment core collected from the southern Tibetan Plateau (TP), which was dated by using the ²¹⁰Pb dating method and validated with the ¹³⁷Cs fallout peak. The concentrations of the anthropogenic PAHs (Σ₈PAH) in the sediment core ranged from 0.83 to 12 ng/g dw, and the fluxes of the Σ₈PAH were in the range of 2.1-27 g/cm²/year. The temporal variations in the concentration and input flux of anthropogenic PAHs were low with little variability before the 1950s, and then gradually increased from the 1950s to the 1980s, and an accelerated increase was observed after the early 1980s. The content of total organic carbon played an insignificant role in affecting the time trends of PAHs in the sediment core. Diagnostic concentration fractions of PAH components indicate PAHs in the lake sediment of the southern TP which are mainly from biomass burning and/or from long-range atmospheric transport.

Spatial variation of polycyclic aromatic hydrocarbons (PAHs) in surface sediments from rivers in hilly regions of Southern China in the wet and dry seasons

Seasonal variations of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments from 13 rivers in hilly regions of southern China were studied. Concentrations of PAHs analyzed in the wet season were higher than those analyzed in the dry season, with residues ranging from 74.3 to 1930.9 ng g^-1 dw in the wet season and from 96.9 to 1388.9 ng g^-1 dw in the dry season. The primary contributors were 3- and 4-ringed congeners accounting for 59.8% ± 10.1% and 58.3% ± 9.3% of the identified PAHs in the wet and the dry seasons, respectively. Proximity to sources and locations susceptible to high atmospheric depositional inputs results in high concentrations of PAH. Diagnostic ratios have indicated that the sources of PAHs in different seasons make no apparent difference. Furthermore, a principal component analysis and multiple linear regression (PCA-MLR) studies indicate that combustion sources such as vehicle emissions and coal combustion are the primary sources of PAHs. Toxicological risk assessments based on TEQ^care suggested that Benzo[a]pyrene, benz[a]anthracene, dibenz[a,h]anthracene could pose high ecological risks in this area.

Insight into the local source of polybrominated diphenyl ethers in the developing Tibetan Plateau: The composition and transport around the Lhasa landfill

In the background region of the Tibetan Plateau (TP), the rapid urbanization probably results in the massive generation of persistent organic pollutants (POPs), which lacks monitoring and evaluation. Since landfill could serve as an important sink of the locally used POPs, the analysis of POPs in the Tibetan landfill area might help us to understand the source composition and their transport in the TP. In this study, the concentration variations of polybrominated diphenyl ethers (PBDEs) in five soil profiles and seven surficial sediments around the largest Tibetan landfill were investigated. The total concentrations of PBDEs ranged from 128 to 1219 ng/kg in soils, and from 447 to 7295 ng/kg in sediments. The dominance of nona- and deca-BDEs possibly indicated the wide usage of deca-BDE as flame retardant in the TP. The vertical and spatial distribution patterns of PBDEs within soils plausibly revealed their main transport pathways by atmospheric dispersion and leachate seepage from landfill. Based on principal components analysis and multiple linear regression, these two pathways were estimated to account for 61% and 39% of the total concentrations, respectively. Additionally, the spatial and vertical distributions of octa-to deca-BDEs within soils were significantly influenced by soil particle size. Although the PBDEs inventory in the study area was comparatively low, the rapid urbanization in the TP might dramatically accelerate the PBDE emissions in the future. This study firstly introduced the presence of local PBDEs in the TP, and the inventory already influenced the surrounding environment. Once involved in the regional cycle of the TP, the local source of PBDEs from waste might significantly serve to raise background level resulting otherwise primarily from long-range atmospheric transport.

Polycyclic aromatic hydrocarbons in soils and lichen from the western Tibetan Plateau: Concentration profiles, distribution and its influencing factors

The Tibetan Plateau (TP) is a huge area and rarely affected by human activity, and is regarded as one of the most remote regions on the earth. Many studies about the long-range atmospheric transport (LRAT) of semi-volatile organic compounds (SVOCs) were conducted in southern and central TP. However, there are very limited studies focused on PAHs in the western TP and the concentrations profiles, distribution and its controlling factors in this area remains unclear. Thus, to explore this knowledge gap, 37 surface soil samples and 23 lichen samples were collected and analyzed for PAHs. The total concentration of 16 US EPA's priority PAHs (∑₁₆PAHs) in western TP ranges 14.4-59.5ng/g and 38.0-133ng/g dry weight (dw) with a mean value of 30.8 and 84.6ng/g dw in soil and lichen, respectively, which is lower than the concentrations in most remote areas worldwide. In the western TP, low molecular weight PAHs (2-3 rings) are dominant (occupied 77.4% and 87.9% on average in soil and lichen, respectively), implying a significant contribution of LRAT in this area. The significant linear correlations (R² = 0.372-0.627, p < 0.05) between longitude and soil concentration suggest a strong impact of the westerly wind on the distribution of PAHs in soil. In addition, the concentration ratio of lichen/soil (L/S) was found to linearly increase with the increasing log K_OA of individual PAH, suggesting lichen has a strong ability in filtering more lipophilic airborne pollutants in western TP.

Source identification and ecological impact evaluation of PAHs in urban river sediments: A case study in Taiwan

The Love River and Ho-Jin River, two major urban rivers in Kaohsiung City, Taiwan, are moderately to heavily polluted because different types of improperly treated wastewaters are discharged into the rivers. In this study, sediment and river water samples were collected from two rivers to investigate the river water quality and accumulation of polycyclic aromatic hydrocarbons (PAHs) in sediments. The spatial distribution, composition, and source appointment of PAHs of the sediments were examined. The impacts of PAHs on ecological system were assessed using toxic equivalence quotient (TEQ) of potentially carcinogenic PAHs (TEQ^carc) and sediment quality guidelines. The average PAHs concentrations ranged from 2161 ng/g in Love River sediment to 160 ng/g in Ho-Jin River sediment. This could be due to the fact that Love River Basin had much higher population density and pyrolytic activities. High-ring PAHs (4-6 rings) contributed to 59-90% of the total PAHs concentrations. Benzo(a)pyrene (BaP) had the highest toxic equivalence quotient (up to 188 ng TEQ/g). Moreover, the downstream sediments contained higher TEQ of total TPHs than midstream and upstream sediment samples. The PAHs were adsorbed onto the fine particles with high organic content. Results from diagnostic ratio analyses indicate that the PAHs in two urban river sediments might originate from oil/coal combustion, traffic-related emissions, and waste combustion (pyrogenic activities). Future pollution prevention and management should target the various industries, incinerators, and transportation emission in this region to reduce the PAHs pollution.

Organochlorine pesticides in the sedimentary core of the southern Tibetan Plateau: The missing pieces induced by lateral remobilization

The sedimentary core in remote alpine lakes has been recognized as an ideal proxy to reconstruct the emission and air deposition histories of persistent organic pollutants (POPs). Nevertheless, POPs formerly stored in a catchment might also contribute to the variation in the lake sediment by lateral remobilization. In this study, to reveal the relative importance of lateral remobilization, we measured the vertical profiles and isomeric ratios of dichlorodiphenyltrichloroethanes (DDTs), hexachlorocyclohexanes (HCHs) and endosulfan in a dated sedimentary core collected from Lake Yamzho Yumco in the southern Tibetan Plateau. In addition to the flux peaks in the 1970s corresponding to the heavy atmospheric deposition of DDTs and HCHs, these pollutants' fluxes displayed rebounds in the flood periods, with characteristic low ratios of DDT/DDE (α-/β-HCH). This might indicate a massive remobilization of "weathered" pesticides from catchment soil to the lake because of strong hydro-dynamics. Moreover, the relative contribution of lateral remobilization to the lake sediment in the past decades was recognized through the correlation between DDT/DDE (α-/β-HCH) ratios and ∑DDT (∑HCH) fluxes. The results showed that the lateral remobilization contributed to 20-42% of the total fluxes. This study discriminated the air deposition from the contribution of lateral remobilization, which improves current understanding of the vertical POPs profiles in the sedimentary core.

Temporal occurrence and sources of persistent organic pollutants in suspended particulate matter from the most heavily polluted river mouth of Lake Chaohu, China

The Nanfei River is by many measures the most heavily polluted tributary to Lake Chaohu. In this study, the temporal occurrence and sources of four classes of persistent organic pollutants (POPs), including polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs), in suspended particulate matter (SPM) from the river mouth were investigated monthly during 2014. Results show that concentrations of all four POPs in SPM were higher than those in the sediment of Lake Chaohu. PBDEs (26.7 ng g^-1 dry weight (dw)) were originated mainly from commercial deca-BDE mixtures. PCB concentrations (1.336 ng g^-1 dw) were lower than those of sediments in many other water bodies worldwide. PAHs (2597 ng g^-1 dw) and OCPs (57.38 ng g^-1 dw) were the most common POPs. PAHs mainly had high molecular weights and originated from pyrolytic sources, with a small proportion of petrogenic origin. The predominant OCPs were DDTs, heptachlorepoxides, dieldrin, hexachlorocyclohexanes, hexachlorobenzene, and chlordanes. Most OCPs originated from historical use, except lindane. Generally, of all the POPs studied, those of primary ecological concern should be acenaphthene, fluorene, DDTs, and chlordanes. Higher concentrations of POPs were detected during winter and spring than in summer and autumn, probably because of the high river flow during the rainy season. The high concentration of POPs in the riverine SPM and the fractionation of POPs in the water and SPM of the river should be a focal point in the future study of Lake Chaohu.

Historical records and sources of polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in sediment from a representative plateau lake, China

The PAH and OCP concentrations in sediment cores collected from a deep lake were measured and evaluated chronologically. The results indicated that the PAH and OCP concentrations significantly increased from the 1950s to the 1990s and subsequently decreased to recent years. Integrated molecular diagnostic ratios indicated that the predominant petrogenic sources occurred from the 1950s-1980s. Petroleum and fuel combustion dominated the source of contamination more recently as a result of energy structure changes in this region. Additionally, HCHs and DDTs were the dominant OCP compounds, making up a majority of the total OCPs present (>85%). HCHs accounted for a larger ratio of the OCPs between the 1950s and 1980s, suggesting that HCHs were the dominant POPs in this period. DDTs then became dominant in the 1980s and later. High α/γ-HCH ratios suggested that the emission and conversion of local technical HCHs were the predominant HCHs source. The ratios of (DDE + p,p'-DDD)/DDTs and p,p'-DDT/DDTs indicated that the DDTs mainly originated from historical input. In addition, the dramatic decrease since the 1980s may be the result of China's banning of DDTs. However, DDTs were still present in the 1990s, suggesting DDTs were still used in this region and beyond.

A review of current knowledge and future prospects regarding persistent organic pollutants over the Tibetan Plateau

Since the turn of the century, our understanding of the quantities, transport pathways, and fate of persistent organic pollutants (POPs) over the Tibetan Plateau (TP), the largest and highest plateau on Earth, has greatly enhanced. We begin in this article by reviewing the available literature on the levels of POPs over the TP. In general, the levels of most POPs are similar or lower than values reported for other background regions. However, dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) levels in air and soil far exceed those measured in other mountainous areas. The East Asian monsoon, Indian Monsoon and westerly winds are responsible for the long-range atmospheric transport (LRAT) and arrival of POPs over the TP. Surface soil and vegetation act as "final sinks" for DDTs and other high molecular weight POPs. Linked to the continuous use of POPs in surrounding counties, LRAT and "cold trapping" by the TP can happen following emission-transport-deposition events, leading to the enrichment of POPs in the TP environment. Bioaccumulation of DDTs and high chlorinated PCBs have been found in Tibetan terrestrial and aquatic food chains, and newly emerging compounds such as polyfluoroalkyl substances and hexabromocyclododecanes have been widely detected in wild fish species. The corresponding ecological risks should be of great concern. Climate change, such as increased temperatures and changing coverage of snow and glaciers, has the potential to affect the behavior and distribution of POPs. Therefore, long-term monitoring data are required. Ineffective regulation regarding POPs has been reported for countries in South Asia, emissions patterns, the outflow of POPs, and their seasonal and inter-annual variability should therefore be clarified. Estimating the loading of POPs, as well as how they move, within the TP, especially under the impact of glacial melt and global warming, should be a priority.

Concentrations and potential health hazards of polycyclic aromatic hydrocarbon in shallow groundwater of a metal smelting area in Southeastern China

A total of 20 shallow groundwater samples were collected from a metal smelting area in southeastern China to determine the concentrations of 16 priority polycyclic aromatic hydrocarbons (PAHs), calculate their toxic equivalents (TEQs) to benzo[a]pyrene (BaP), and estimate the carcinogenic risk of drinking the shallow groundwater. The total concentrations of the 16PAHs (∑PAHs) in the shallow groundwater ranged from 9.62 to 1663.93ngL(-1), with a mean value of 312.63ngL(-1), and the total concentrations of the 7 potentially carcinogenic PAHs (∑PAHC7) ranged from 3.11 to 33.60ngL(-1), with a mean value of 9.61ngL(-1). Naphthalene and BaP, were the dominant PAH species and potentially carcinogenic PAH species in the shallow groundwater of the study area, and they account for 89.97% of ∑PAHs and 82.62% of ∑PAHC7, respectively. High molecular weight-PAHs (HM-PAHs) accounted for a relatively high proportion in the majority of shallow groundwater samples with lower concentrations of ΣPAHs, indicated that HM-PAHs were mainly from historical residues. The TEQs to BaP of the 16PAHs in the 20 shallow groundwater samples varied greatly from 2.55 to 32.73ngL(-1), with a mean value of 8.61ngL(-1), and BaP was the dominant contributor. The total carcinogenic risk levels caused by the 16PAHs in the shallow groundwater in majority of the area were found to be higher than the limit set by the US EPA, posing a potentially serious health risk to those who depend on shallow groundwater for drinking water.