Evidence for persistent organic pollutants released from melting glacier in the central Tibetan Plateau, China

The occurrence and sources of PAHs, oxygenated PAHs (OPAHs), and nitrated PAHs (NPAHs) in soil and vegetation from the Antarctic, Arctic, and Tibetan Plateau

Although the fate of PAHs in the three polar regions (Antarctic, Arctic, and Tibetan Plateau) has been investigated, the occurrence and contamination profiles of PAH derivatives such as oxygenated PAHs (OPAHs) and nitrated PAHs (NPAHs) remain unclear. Some of them are more toxic and can be transformed from PAHs in environment. This study explored and compared the concentrations composition profiles and potential sources of PAHs, OPAHs, and NPAHs in soil and vegetation samples from the three polar regions. The total PAH, OPAH, and NPAH concentrations were 3.55-519, n.d.-101, and n.d.-1.10 ng/g dry weight (dw), respectively. The compounds were dominated by three-ring PAHs, and the most abundant individual PAH and OPAH were phenanthrene (PHE) and 9-fluorenone (9-FO), respectively. The sources of PAHs and their derivatives were qualitatively analyzed by the diagnostic ratios and quantified using the positive matrix factorization (PMF) model. The ratios of PAH derivatives to parent PAHs (9-FO/fluorene and 9,10-anthraquinone/anthracene) were significantly higher in the Antarctic samples than in the Arctic and TP samples, implying a higher occurrence of secondary OPAH and NPAH formation in the Antarctic region. To our knowledge, this is the first comparative study that simultaneously investigated the contamination profiles of PAHs and their derivatives in the three polar regions. The findings of this study provide a scientific basis for the development of risk assessment and pollution control strategies in these fragile regions.

Polycyclic aromatic hydrocarbon dynamics in soils along proglacial chronosequences in the Alps

Polycyclic aromatic hydrocarbons (PAHs) were studied in the soils of three proglacial areas in France (Noir and Chardon Glaciers) and Italy (Miage Glacier). PAH contents, PAH stocks and PAH contents normalized to the total organic carbon contents (PAHs/TOC ratio) were investigated along proglacial soil chronosequences to infer their evolutions with soil age (from 3 to 4200 years), where the PAH contamination was only related to long-range atmospheric transport. Evolutions of PAH and TOC contents, PAHs/TOC ratio and PAH stock were fitted with exponential and logarithmic relations. For the three proglacial areas, PAH contents increased rapidly during the first 150 years of soil development, ranged from 4 to 152 ng·g-1, and showed a strong relationship with total organic carbon (TOC) contents (r = 0.83, p < 0.05). The joint increase of PAH and TOC contents suggested that PAH accumulation in soils were not only driven by PAH inputs but also by the capacity of soils to store these contaminants. PAH contents in the oldest soils (from 1200 BCE and 2200 BCE) were similar than for soils from 1850 CE. The period 1850-2019 CE corresponded to a decrease in the PAHs/TOC ratio suggesting both a faster accumulation of TOC than PAHs and a dilution effect of PAHs already present in soils. For the oldest soils, the PAHs/TOC ratio appeared similar to those for soils from 1850 CE, with values ranging from 0.48 to 2.06 ng·mg-1, suggesting an equilibrium between both parameters for soils older than 170 years. Finally, PAH stocks ranged from 0.41 mg·m-2 to 6.80 mg·m-2 in the youngest and oldest soils, respectively. These results do not allow us to identify the same period of greatest emission as other studies (estimated ~1960), but they revealed changes in the capacity of soils to store these pollutants.

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.

Primary emissions or environmental persistence contribute to the present DDTs: Evidence from sediment records in Tibetan lakes

Dichlorodiphenyltrichloroethane (DDT) compounds are still circulating the global environment even though the technical DDT has been restricted in agriculture since the last century. The persistent presence of DDTs worldwide remains uncertain, as it is unclear whether their existence is primarily due to ongoing use or the prolonged persistence in soils and sediments that result in continuous reemission into the atmosphere. The present study applied a sequential extraction procedure to determine the DDT concentrations in rapid desorption, slow desorption, and bound residue fractions in the dated sediment cores from distinct regions of Tibet. The temporal variation of total DDTs (sum of three fractions) in sediments from southern and eastern Tibet respectively revealed the different DDT usage histories in India and China mainland. Nevertheless, the current application volumes of DDT-containing products in these regions were found to decrease significantly. The reversible transformations among three fractions of DDTs with aging time was observed along sediment profile, including the back conversion from bound residue. This process may be the key driver to prolong the half-life of sediment p,p'-DDT, resulting in the persistence of secondary sources of this persistent organic pollutant in the global environment for a longer duration than previously expected.

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.

Climate change influence on the levels and trends of persistent organic pollutants (POPs) and chemicals of emerging Arctic concern (CEACs) in the Arctic physical environment - a review

Climate change brings about significant changes in the physical environment in the Arctic. Increasing temperatures, sea ice retreat, slumping permafrost, changing sea ice regimes, glacial loss and changes in precipitation patterns can all affect how contaminants distribute within the Arctic environment and subsequently impact the Arctic ecosystems. In this review, we summarized observed evidence of the influence of climate change on contaminant circulation and transport among various Arctic environment media, including air, ice, snow, permafrost, fresh water and the marine environment. We have also drawn on parallel examples observed in Antarctica and the Tibetan Plateau, to broaden the discussion on how climate change may influence contaminant fate in similar cold-climate ecosystems. Significant knowledge gaps on indirect effects of climate change on contaminants in the Arctic environment, including those of extreme weather events, increase in forests fires, and enhanced human activities leading to new local contaminant emissions, have been identified. Enhanced mobilization of contaminants to marine and freshwater ecosystems has been observed as a result of climate change, but better linkages need to be made between these observed effects with subsequent exposure and accumulation of contaminants in biota. Emerging issues include those of Arctic contamination by microplastics and higher molecular weight halogenated natural products (hHNPs) and the implications of such contamination in a changing Arctic environment is explored.

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.

Occurrence, sources and potential risks of polycyclic aromatic hydrocarbons in a permafrost soil core, northeast China

Polycyclic aromatic hydrocarbons (PAHs) in an AMS ¹⁴C-dated permafrost soil core extracted from continuous permafrost zone were measured to reconstruct the pollution history from the early Holocene (ca. 15480 a BP) and its potential risks under climate changes were evaluated in northeast China. Total PAH concentrations varied from 209 to 2161 ng/g through the core, which were moderately contaminated in the surface but heavily contaminated historically. Factor analysis indicated that volcanic activity, diagenesis from biological precursors and palaeo forest fires were dominant PAH sources, while petroleum emission was identified in the active layer due to the construction of China-Russia oil pipeline. Significant increases in 5-ring, 6-ring and 7 carcinogenic PAHs (p < 0.05) were observed from surface to the interface of the active layer and ice-rich permafrost layer, showing a selective downward migration in the active layer which might be effected by the repetitive cycles of freezing and thawing. Results implied that PAHs in the ice-rich permafrost layer could lead to an unpredictably serious consequence under the further climate warming.

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.

Modelling Watershed and River Basin Processes in Cold Climate Regions: A Review

Watersheds in cold regions provide water, food, biodiversity and ecosystem service. However, the increasing demand for water resources and climate change challenge our ability to provide clean freshwater. Particularly, watersheds in cold regions are more sensitive to changing climate due to their glaciers’ retreat and permafrost. This review revisits watershed system and processes. We analyze principles of watershed modelling and characteristics of watersheds in cold regions. Then, we show observed evidence of their impacts of cold processes on hydrological and biogeochemical processes and ecosystems, and review the watershed modeling and their applications in cold regions. Finally, we identify the knowledge gaps in modeling river basins according to model structures and representations of processes and point out research priorities in future model development.

Precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans in Arctic and Antarctic marine sediments: Environmental concern in the face of climate change

Polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/F) and their precursors - pentachlorophenol (PCP) and triclosan (TCS), constitute a group of persistent, highly toxic multimedia pollutants, being easily transported via atmosphere over long distances, thus particularly threatening to the polar areas. The global fate of PCDD/Fs is temperature-dependent, and their transfer and immobilization at the Poles are described by the grasshopper effect and the cold trap phenomenon. The aim of this interdisciplinary study was to perform a preliminary assessment of the present state of pollution of Arctic and Antarctic marine sediments by PCP and TCS along with determination of PCDD/Fs contamination by immunoassay. Sediments from 20 stations were collected during two polar expeditions (2013-2016). The study area covered Hornsund Fjord and the southwest coast of Wedel-Jarlsberg Land (Arctic) - Skodde Bay, Nottingham Bay, Isbjørnhamna Bay and Admiralty Bay (Antarctica) - Suszczewski Cove, Halfmoon Cove and Herve Cove. The studied contaminants were quantified in 60% of the collected sediments, with almost half exceeding the environmentally safe levels according European regulations and worldwide literature. The determined levels of PCP, TCS and PCDD/F in Arctic and Antarctic sediments were to be comparable to those reported in the southern Baltic Sea located in the intense industrialized mid-latitudes. Maximum concentrations were observed in the vicinity of retreating, marine terminating glaciers. This observation confirms reemission of POPs into the global cycle with respect to the worldwide ocean warming. The results of this study should gain attention of the international and regional environmental agencies as well as the main chlorine production decision makers.

Linking atmospheric pollution to cryospheric change in the Third Pole region: current progress and future prospects

The Tibetan Plateau and its surroundings are known as the Third Pole (TP). This region is noted for its high rates of glacier melt and the associated hydrological shifts that affect water supplies in Asia. Atmospheric pollutants contribute to climatic and cryospheric changes through their effects on solar radiation and the albedos of snow and ice surfaces; moreover, the behavior and fates within the cryosphere and environmental impacts of environmental pollutants are topics of increasing concern. In this review, we introduce a coordinated monitoring and research framework and network to link atmospheric pollution and cryospheric changes (APCC) within the TP region. We then provide an up-to-date summary of progress and achievements related to the APCC research framework, including aspects of atmospheric pollution's composition and concentration, spatial and temporal variations, trans-boundary transport pathways and mechanisms, and effects on the warming of atmosphere and changing in Indian monsoon, as well as melting of glacier and snow cover. We highlight that exogenous air pollutants can enter into the TP's environments and cause great impacts on regional climatic and environmental changes. At last, we propose future research priorities and map out an extended program at the global scale. The ongoing monitoring activities and research facilitate comprehensive studies of atmosphere-cryosphere interactions, represent one of China's key research expeditions to the TP and the polar regions and contribute to the global perspective of earth system science.

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.

Assessment of organochlorine pesticides in the Himalayan riverine ecosystems from Pakistan using passive sampling techniques

Organochlorine pesticides (OCPs) pose a considerable threat to human and environmental health. Despite most OCPs have been banned, they are still reported to be used in developing countries, including Pakistan. We aimed to identify the distribution, origin, mobility, and potential risks from OCPs in three major environmental compartments, i.e., air, water, and soil, across Azad Jammu and Kashmir valley, Pakistan. The sums of OCPs ranged between 66 and 530 pg/g in soil, 5 and 13 pg/L in surface water, and 14 and 191 pg/m3 in air, respectively. The highest sum of OCPs was observed in the downstream zone of a river that was predominantly influenced by peri-urban and urban areas. The OCP isomers ratios (α-HCH/γ-HCH and o,p'-DDT/p,p'-DDT) indicate use of lindane and technical DDTs mixture as a source of HCH and DDT in the riverine environment. Similarly, the ratios of DDE and DDD/the sum of DDTs, α-endosulfan/β-endosulfan, and cis-chlordane/trans-chlordane indicate recent use of DDTs, endosulfan, and chlordane in the region. The air-water exchange fugacity ratios indicate net volatilization (fw/fa > 1) of α-endosulfan and trans-chlordane, and net deposition (fw/fa < 1) of β-endosulfan, α-HCH, γ-HCH p,p'-DDD, p,p'-DDE, and p,p'-DDT. Based on the risk quotient (RQ) method, we consider the acute ecological risks for fish associated with the levels of OCPs as negligible. However, more studies are recommended to evaluate the chronic ecological risks to other riverine-associated aquatic and terrestrial species as well as human health risks to the POPs exposure through food chain transfer in forthcoming years.

Environmental conditions affecting re-release from particulate matter of 4-Nonylphenol into an aqueous medium

4-nonylphenol is a persistent organic pollutant with endocrine-disrupting properties. A nonpolar product of microbial degradation derived from the surfactant nonylphenol polyethoxylate, 4-nonylphenol is capable of long-range transport attached to particulates. Bioactive concentrations of 4-nonylphenol have been found in the surface water, soils, snow, and particulate matter of the Eastern Sierra Nevada Mountains (USA) hundreds of miles from their origins. As a result of particulate deposition, seasonal and glacial snow pack concentrations measured 20 to 100 times higher than in surface waters. Batch desorption assays were run on particulate matter dosed with 4-nonylphenol. Desorption was measured in 63 to 500 μm particles under 2 different temperature conditions with varying fractions of organic carbon in turbulent or undisturbed states. Lower temperatures (4 °C) decreased the mean percentage of 4-nonylphenol released from particulates in disturbed and undisturbed conditions, whereas the mean percentage of 4-nonylphenol released at 20 °C was reduced by agitation. The effect of agitation at 4 °C was not practically or statistically significant. Particulates with a higher percentage of organic carbon (75%) released very little of the bound 4-nonylphenol (0.53%) compared with particulates containing 4 to 5% of organic carbon that released up to 13%. Larger particles released the least amount of 4-nonylphenol, whereas smaller particles released the most amount. Water and sediment samples taken from below the Palisades Glacier in the Sierra Nevada Mountains showed the greatest 4-nonylphenol concentrations directly below the glacier, implying that glacial particulates will release adsorbed 4-nonylphenol. Environ Toxicol Chem 2019;38:350-360. © 2018 SETAC.

Bacterial community and climate change implication affected the diversity and abundance of antibiotic resistance genes in wetlands on the Qinghai-Tibetan Plateau

Antibiotic resistance genes (ARGs) have been identified as emerging pollutants in the environment. However, little information is available for ARGs in natural wetlands at high altitude. In this study, we investigated 32 wetlands across the Qinghai-Tibetan Plateau, with the variation of wetland types, altitude, and environmental factors, to assess the determinant factor of ARGs in this area. ARGs were detected in all the wetlands, ranged from 1.80 × 105 to 1.35 × 107 copies per gram of soils. The ARGs in wetland soils were diverse and abundant, and varied from each site, but the spatial geographical distance did not influence the ARG profile. The mobile genetic elements in wetlands ranged from 3.13 × 103 to 1.02 × 106 copies per gram of soil, indicating the low abundance of mobile genetic elements suggests a lower transfer rate of ARGs between bacteria in the Plateau. Bacterial community composition was the main driver in shaping the ARG diversity and geographic distribution. Soil moisture and temperature were positively correlated with ARG abundance in this region. These results not only provide a better understanding of the background levels of ARGs in the Qinghai-Tibetan Plateau, but also shed light on the influence of climate change and increased human activities on the distribution of ARGs.

Spatial gradients of polycyclic aromatic hydrocarbons (PAHs) in air, atmospheric deposition, and surface water of the Ganges River basin

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous semi-volatile organic pollutants. Their environmental occurrence is of global concern as some of them are carcinogens, mutagens, and teratogens. In this study, concentrations and distributions of 16 priority PAHs (∑PAHs) were measured in air, atmospheric deposition, and surface water at various locations in Himalayan, Middle, and Lower Reaches of the Ganges River, covering a spatial transect of 2500km, during two seasons (pre-monsoon and monsoon). The concentration of ∑PAHs ranged between 2.2 and 182.2ngm^-3 in air, between 186 and 8810ngm^-2day^-1 in atmospheric deposition, and between 0.05 and 65.9ngL^-1 in surface water. Air concentrations were strongly correlated with human population density. In the Middle and Lower Reaches of the Ganges River, atmospheric PAHs were mainly attributed to fossil fuel combustion sources. In the Himalayan Reach the influence of forest fire or biomass combustion was evident during the dry pre-monsoon season. Seasonality in concentrations of PAHs in river water was evident in the Himalayan Reach of the river, as a probable consequence of climate-modulated secondary source intensity (i.e. releases from glacier melting). Seasonality faded in the Middle and Lower Reaches of the Ganges where water contamination is expected to mainly reflect anthropogenic primary sources. Ambient air concentrations were used to calculate the probabilistic incremental lifetime cancer risk (ILCR). It was expectedly found to be higher in the Middle and Lower Reaches compared to the Himalayan Reach. The strong correlation between population density and air concentrations suggests population density may be used as a surrogate variable to assess human health risk in data-sparse regions such as the Ganges River basin.

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.

High-resolution sedimentary records of some organochlorine pesticides in Yamzho Yumco Lake of the Tibetan Plateau: Concentration and composition

Sediment cores from lakes have been used to reconstruct the historic deposition of persistent organic pollutants (POPs), especially in remote alpine areas. To reconstruct the deposition history of organochlorine pesticides (OCPs) in the Tibetan Plateau (TP), two sediment cores from Yamzho Yumco Lake were drilled and dated with high-resolution, from which 23 OCPs were analyzed in greater detail. Regarding several legacy compounds, concentration peaks in the cores were observed in the 1970s, corresponding to the heavy usage of these compounds around the world. In addition, another peak was found at the end of the 1990s, which was explained as the addition of OCPs released from melting glaciers or the cryosphere due to global warming. Furthermore, it was found that the transformation or degradation of OCPs after deposition in the lake was limited by comparing the values of isomeric ratios at different times, such as (DDD+DDE)/∑DDTs, o,p'-DDT/p,p'-DDT and β-HCH/∑HCHs. Such results ensure that the detected OCPs in the lake sediments really reflect their characteristics at the time of deposition. On the other hand, weak environmental self-purification of the OCPs made them last longer in the TP than in other regions. Reasonably, the fragile ecological environment of the TP would be threatened not only by legacy POPs that remain in the sediments and soils but also by POPs released from melting glaciers or the cryosphere in the next few decades under the influence of global warming. Our research provides an insight into the influence of global warming and glacial melting on the environment of the TP, and further work to gain a better understanding of the environmental processes of POPs in the TP is ongoing.

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.