A total of 106 24-h PM₂.₅ aerosol samples were collected in an urban area (Shijiazhuang, SJZ) and a suburban area (Liulihe, LLH, Fangshan County, Beijing) in the Beijing-Tianjin-Hebei (BTH) region in 2 periods: the first is from 10 July to 10 August, which is before Sept. Third Parade (Period I); the second is from 20 Aug. to 6 Sept. 2015, which is during Sept. Third Parade (Period II). Polar organic tracers, including isoprene, α-pinene, β-caryophyllene and toluene oxidation products, as well as sugars and carboxylic acids were measured. In Period II, rigorous emission-reduction measures were taken in the BTH region. With the anthropogenic emission being cut down significantly, the average concentrations of isoprene, α-pinene, β-caryophyllene and toluene oxidation products and all carboxylic acids (except tetradecanoic, palmitic, and stearic acids), were lower in Period II than those in Period I in LLH, indicating that the SOA tracers were decreased with precursor emission volumes and yields in the atmosphere. Moreover, sugar compounds were shown with comparable levels during the two periods in LLH, suggesting that no measures were taken to reduce the intensities of the biogenic sources. On the contrary, tetradecanoic, palmitic, and stearic acids were shown with obviously higher concentrations in Period II than those in Period I, demonstrating that cooking fumes increased during Sept. Third Parade period.The positive matrix factorization (PMF) model combining with tracer-based method was applied to explore the sources of secondary organic carbon (SOC). It reveals that the sources of SOC include isoprene, α-pinene, β-caryophyllene and toluene oxidation products, fossil fuel combustion, cooking fumes and regionally transferred aged aerosols. These sources accounted for 11.3%, 9.0%, 15.5%, 10.9%, 29.2%, 2.9%, 21.1% of SOC for SJZ, and 12.7%, 11.2%, 9.7%, 14.4%, 25.3%, 0%, 26.7% of SOC for LLH, during the whole sampling periods respectively.

We examined polycyclic aromatic compounds (PACs) and petroleum biomarkers (steranes, hopanes, and terpanes) in radiometrically-dated lake sediment cores from the Athabasca oil sands region (AOSR) and the Peace-Athabasca Delta (PAD) region in Alberta (Canada) to determine whether contributions from petroleum hydrocarbons have changed over time. Two floodplain lakes in the PAD (PAD 30, PAD 31) recorded increased flux of alkylated PACs and increased petrogenic (petroleum-derived) hydrocarbons after ∼1980, coincident with a decline of sediment organic carbon content and a rise of bulk sedimentation rate, likely due to increased Athabasca River flow. A large expansion of upstream oilsands mining, upgrading, and refining may also have contributed to the observed shift to more petrogenic hydrocarbons to sediments since the 1980s. Alkylated PAC flux increased in the floodplain lake analyzed within the AOSR (Saline Lake) since the 1970s–1980s, coincident with a sharp rise in sediment organic carbon content and increased contributions of petrogenic hydrocarbons. These changes identify increased supply of petrogenic PACs occurred as Athabasca River floodwaters waned, and may implicate aerial contributions of petrogenic hydrocarbons from oilsands activity. PACs and petroleum biomarkers (steranes, hopanes, and terpanes) in sediment cores from Saline Lake, PAD 30 and PAD 31 revealed a predominance of petrogenic hydrocarbons in these lakes. In contrast, we recorded minimal petrogenic hydrocarbons in the reference lakes outside the surface minable area of the AOSR and PAD (Mariana Lake and BM11), though we noted slight increases in petrogenic contributions to modern (2010–2016) sediments. We show how a combined analysis of PACs and petroleum biomarkers in sediments is useful to quantify petrogenic contributions to lakes with added confidence and highlight the potential for petroleum biomarkers in lake sediment cores as a novel and effective method to track petroleum hydrocarbons in lake sediment.

The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.

Incomplete combustion of solid fuels (animal dung and bituminous coal) is a common phenomenon during residential cooking and heating in the Qinghai-Tibetan Plateau (QTP), resulting in large amounts of pollutants emitted into the atmosphere. This study investigated the pollutant emissions from six burning scenarios (heating and cooking with each of the three different fuels: yak dung, sheep dung, and bitumite) in the QTP's pastoral dwellings. Target pollutants such as carbon monoxide (CO), gas-phase polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), fine particles (PM₂.₅, particulate matter with an aerodynamic diameter < 2.5 μm), carbonaceous aerosols, water-soluble ions, and particle-phase PAHs were investigated. Emission factors (EFs) (mean ± standard deviation) of PM₂.₅ from the six scenarios were in the range of 1.21 ± 0.47–7.03 ± 1.95 g kg⁻¹, of which over 60% mass fractions were carbonaceous aerosols. The ratio of organic carbon to elemental carbon ranged from 9.6 ± 2.7–33.4 ± 11.5 and 81.7 ± 30.4–91.9 ± 29.0 for dung and bitumite burning, respectively. These values were much larger than those reported in the literature, likely because of the region's high altitudes—where the oxygen level is approximately 65% of that at the sea level—thus providing a deficient air supply to stoves. However, the toxicity and carcinogenicity of PAHs emitted from solid fuel combustion in the QTP are significant, despite a slightly lower benzo(a)pyrene-equivalent carcinogenic potency (Bapₑq) in this study than in the literature. The gas-to-particle partitioning coefficient of PAHs and VOC emission profiles in the QTP differed significantly from those reported for other regions in the literature. More attention should be paid to the emissions of PAH derivatives (oxygenated PAHs and nitro-PAHs), considering their enhanced light-absorbing ability and high BaPₑq from solid fuel combustion in the QTP.

Fluorescence spectroscopy is a commonly used technique to analyze dissolved organic matter in aquatic environments. Given the high sensitivity and non-destructive analysis, fluorescence has recently been used to study water-soluble organic carbon (WSOC) in atmospheric aerosols, which have substantial abundance, various sources and play an important role in climate change. Yet, current research on WSOC characterization is rather sparse and limited to a few isolated sites, making it challenging to draw fundamental and mechanistic conclusions. Here we presented a review of the fluorescence properties of atmospheric WSOC reported in various field and laboratory studies, to discuss the current advances and limitations of fluorescence applications. We highlighted that photochemical reactions and relevant aging processes have profound impacts on fluorescence properties of atmospheric WSOC, which were previously unnoticed for organic matter in aquatic environments. Furthermore, we discussed the differences in sources and chemical compositions of fluorescent components between the atmosphere and hydrosphere. We concluded that the commonly used fluorescence characteristics derived from aquatic environments may not be applicable as references for atmospheric WSOC. We emphasized that there is a need for more systematic studies on the fluorescence properties of atmospheric WSOC and to establish a more robust reference and dataset for fluorescence studies in atmosphere based on extensive source-specific experiments.

The deposition of light absorbing impurities (LAIs) (e.g., black carbon (BC), organic carbon (OC), mineral dust (MD)) on snow is an important attribution to accelerate snowmelt across the northern Xinjiang, China. At present, there is still a lack of understanding of the LAIs concentration, elution and enrichment process in snow cover over Xinjiang. Based on these, continuously sampling during two years carried out to investigate the concentrations, impacts and potential sources of LAIs in snow at Kuwei Station in the southern Altai Mountains. The average concentrations of BC, OC and MD in the surface snow were 2787 ± 2334 ng g⁻¹, 6130 ± 6127 ng g⁻¹, and 70.03 ± 62.59 μg g⁻¹, respectively, which dramatically increased along with snowmelt intensified, reflecting a significant enrichment process of LAIs at the snow surface. Besides, high LAIs concentrations also found in the subsurface and melting layers of the snowpit, reflecting the elution and redistribution of LAIs. With the simulation of the SNow ICe Aerosol Radiative model, BC was the main dominant factor in reducing snow albedo and radiative forcing (RF), its impact was more remarkable in the snowmelt period. The average contribution rates of BC, MD and BC + MD to snow albedo reduction increased by 20.0 ± 1.9%, 13.0 ± 0.2%, and 20.5 ± 2.3% in spring compared with that in winter; meanwhile, the corresponding average RFs increased by 15.8 ± 3.4 W m⁻², 4.7 ± 0.3 W m⁻² and 16.4 ± 3.2 W m⁻², respectively. Changes in the number of snowmelt days caused by BC and MD decreased by 3.0 ± 0.4 d to 8.3 ± 1.3 d. It indicated that surface enrichment of LAIs during snow melting might accelerate snowmelt further. Weather Research and Forecasting Chemistry model showed that the resident emission was the main potential source of BC and OC in snow. This implied that the mitigation of intensive snowmelt needs to mainly reduce resident emission of LAIs in the future.

Methylmercury (MeHg) produced by anaerobic bacteria in lakes and reservoirs, poses a threat to ecosystem and human health due to its ability to bioaccumulate in aquatic food webs. This study used 48-hr microcosm incubations of profundal sediment and bottom water from a sulfate-rich, hypereutrophic reservoir to assess seasonal patterns of MeHg cycling under various treatments. Treatments included addition of air, Hg(II), organic carbon, and microbial inhibitors. Both aeration and sodium molybdate, a sulfate-reducing bacteria (SRB) inhibitor, generally decreased MeHg concentration in microcosm water, likely by inhibiting SRB activity. The methanogenic inhibitor bromoethanesulfonate increased MeHg concentration 2- to 4- fold, suggesting that methanogens were potent demethylators. Pyruvate increased MeHg concentration under moderately reduced conditions, likely by stimulating SRB, but decreased it under highly reduced conditions, likely by stimulating methanogens. Acetate increased MeHg concentration, likely due to the stimulation of acetotrophic SRB. Results suggest that iron-reducing bacteria (IRB) were not especially prominent methylators and MeHg production at the sediment-water interface is elevated under moderately reduced conditions corresponding with SRB activity. In contrast, it is suppressed under oxic conditions due to low SRB activity, and under highly reduced conditions (<-100 mV) due to enhanced demethylation by methanogens.

Despite the importance of bioavailability for organic chemical bioaccumulation by terrestrial and benthic invertebrates, the principles of bioavailability for organic chemical bioaccumulation remain poorly understood. Here we use large-scale databases with contrasting geographic, compound and organism coverage (from 925 sites, 446 compounds and 184 invertebrate species), and report that bioavailability for organic chemical bioaccumulation follows the power law. It represents that the internal concentration of organic chemicals is the composite power function of the lipid fraction of invertebrates, bulk site concentration of compounds, and organic carbon content of soils/sediments. This law directly links environmental exposures and body burdens of organic chemicals in contaminated sites, and provides a method for enabling case-specific risk assessments of a vast number of organic chemicals and contaminated sites. Our findings may pave the way for translating bioavailability knowledge into risk-oriented regulation of organic chemicals and contaminated sites.

Surfactants, after use, enter the environment through diffuse and point sources such as irrigation with treated and non-treated waste water and urban and industrial wastewater discharges. For the group of non-ionic synthetic surfactant alcohol ethoxylates (AEOs), most of the available information is restricted to the levels and fate in aquatic systems, whereas current knowledge of their behavior in soils is very limited. Here we characterize the behavior of different homologs (C12–C18) and ethoxymers (EO3, EO6, and EO8) of the AEOs through batch experiments and under unsaturated flow conditions during infiltration experiments. Experiments used two different agricultural soils from a region irrigated with reclaimed water (Guadalete River basin, SW Spain). In parallel, water flow and chemical transport were modelled using the HYDRUS-1D software package, calibrated using the infiltration experimental data. Estimates of water flow and reactive transport of all surfactants were in good agreement between infiltration experiments and simulations. The sorption process followed a Freundlich isotherm for most of the target compounds. A systematic comparison between sorption data obtained from batch and infiltration experiments revealed that the sorption coefficient (Kd) was generally lower in infiltration experiments, performed under environmental flow conditions, than in batch experiments in the absence of flow, whereas the exponent (β) did not show significant differences. For the low clay and organic carbon content of the soils used, no clear dependence of Kd on them was observed. Our work thus highlights the need to use reactive transport parameterization inferred under realistic conditions to assess the risk associated with alcohol ethoxylates in subsurface environments.

This study reports on the sources of atmospheric particle-bound mercury (HgP) in less studied regions of Nepal based on the analysis of stable mercury (Hg) isotopes in aerosol samples from two neighboring areas with high and low anthropogenic emissions (Kathmandu and Dhulikhel, respectively) during 2018. Although the Indian monsoon and westerlies are generally regarded as the primary carriers of pollutants to this region via the heavily industrialized Indo-Gangetic Plain, the concentrations of total suspended particles (TSP) and HgP in Kathmandu were higher than those in Dhulikhel, thus suggesting a substantial contribution from local sources. Both isotopic (δ²⁰⁰Hg and Δ¹⁹⁹Hg) and non-isotopic evidence indicated that dust, waste burning, and industrial byproducts (without Hg amalgamation) were the major sources of Hg in Kathmandu during the study period. Mercury may have been transported via air masses from Kathmandu to Dhulikhel, as indicated by the similar organic carbon/elemental carbon ratios and seasonal trends of TSP and HgP in these two locations. Local anthropogenic sources were found to contribute significantly to atmospheric Hg pollution through dust resuspension. Therefore, dust resuspension should be considered when evaluating the long-range transport of air pollutants such as Hg, particularly in anthropogenically stressed areas.