Transport of polycyclic aromatic hydrocarbons in highly vulnerable karst systems

Impact of land-use on PAH transfer in sub-surface water as recorded by CaCO3 concretions in urban underground structures (Paris, France)

In densely populated urban areas, the pressure on water resources is considerable and will tend to intensify over the next decades. Preserving water resources therefore seems fundamental, but many questions remain as to the transfer of contaminants to subsurface waters in these largely sealed areas. Because of their toxicity and persistence in the environment, this work focused on the study of polycyclic aromatic hydrocarbons (PAHs), ubiquitous pollutants mainly produced by human activities. To better understand the main factors leading to the retention or transport of these pollutants in urban environments, vertical transects, from the surface to several meters down, were established on three study sites in or near Paris (France), selected according to an urbanization gradient. Soil samples collected at the surface and urban secondary carbonate deposits (USCD), similar to cave speleothems, sampled underground in quarries and aqueducts were analyzed. As the hydrophobic properties of PAHs favor their sorption onto organic matter, the latter was also studied using organic carbon analysis and UV fluorescence spectroscopy. The USCD located closest to the urbanized surface contained high concentrations of PAHs (76.8 ± 5.3 ng g-1), while the USCD located at greater depth with organic soil on the surface contained the lowest amount of PAHs (2.9 ± 0.4 ng g-1), and no PAHs with log KOC > 5. The results highlight the predominant role played by the presence of organic topsoil at the surface in retaining and storing large amounts of PAHs (1914-2595 ng. gsoil-1), particularly the most hydrophobic ones (i.e. 60% of the 15 PAHs are characterized by a Log KOC >5), which are also the most toxic. The lithology and thickness of the bedrock (between the surface and the USCD) also play an important role in the retention of PAHs, particularly those adsorbed on the particulate phase.

In situ incubation of iron(II)-bearing minerals and Fe(0) reveals insights into metabolic flexibility of chemolithotrophic bacteria in a nitrate polluted karst aquifer

Groundwater nitrate pollution is a major reason for deteriorating water quality and threatens human and animal health. Yet, mitigating groundwater contamination naturally is often complicated since most aquifers are limited in bioavailable carbon. Since metabolically flexible microbes might have advantages for survival, this study presents a detailed description and first results on our modification of the BacTrap© method, aiming to determine the prevailing microbial community's potential to utilize chemolithotrophic pathways. Our microbial trapping devices (MTDs) were amended with four different iron sources and incubated in seven groundwater monitoring wells for ∼3 months to promote growth of nitrate-reducing Fe(II)-oxidizing bacteria (NRFeOxB) in a nitrate-contaminated karst aquifer. Phylogenetic analysis based on 16S rRNA gene sequences implies that the identity of the iron source influenced the microbial community's composition. In addition, high throughput amplicon sequencing revealed increased relative 16S rRNA gene abundances of OTUs affiliated to genera such as Thiobacillus, Rhodobacter, Pseudomonas, Albidiferax, and Sideroxydans. MTD-derived enrichments set up with Fe(II)/nitrate/acetate to isolate potential NRFeOxB, were dominated by e.g., Acidovorax spp., Paracoccus spp. and Propionivibrio spp. MTDs are a cost-effective approach for investigating microorganisms in groundwater and our data not only solidifies the MTD's capacity to provide insights into the metabolic flexibility of the aquifer's microbial community, but also substantiates its metabolic potential for anaerobic Fe(II) oxidation.

Transport and retention of n-hexadecane in cadmium-/naphthalene-contaminated calcareous soil sampled in a karst area

Studying the transport of petroleum hydrocarbons in cadmium-/naphthalene-contaminated calcareous soils is crucial to comprehensive assessment of environmental risks and developing appropriate strategies to remediate petroleum hydrocarbons pollution in karst areas. In this study, n-hexadecane was selected as a model petroleum hydrocarbon. Batch experiments were conducted to explore the adsorption behavior of n-hexadecane on cadmium-/naphthalene-contaminated calcareous soils at various pH, and column experiments were performed to investigate the transport and retention of n-hexadecane under various flow velocity. The results showed that Freundlich model better described the adsorption behavior of n-hexadecane in all cases (R2 > 0.9). Under the condition of pH = 5, it was advantageous for soil samples to adsorb more n-hexadecane, and the maximum adsorption content followed the order of: cadmium/naphthalene-contaminated > uncontaminated soils. The transport of n-hexadecane in cadmium/naphthalene-contaminated soils at various flow velocity was well described by two kinetic sites model of Hydrus-1D with R2 > 0.9. Due to the increased electrostatic repulsion between n-hexadecane and soil particles, n-hexadecane was more easily able to breakthrough cadmium/naphthalene-contaminated soils. Compared to low flow velocity (1 mL/min), a higher concentration of n-hexadecane was determined at high flow velocity, with 67, 63, and 45% n-hexadecane in effluent from cadmium-contaminated soils, naphthalene-contaminated soils, and uncontaminated soils, respectively. These findings have important implications for the government of groundwater in calcareous soils from karst areas.

Linking PAHs concentration, risk to PAHs source shift in soil and water in epikarst spring systems, Southwest China

A systematic assessment of the variations in the ecological risk of PAHs and the key emission sources controlling the variations is of great importance to human health and aquatic organisms. PAH concentrations, composition, source, and ecological risk in soils and water in two different periods (2010-2011 and 2019) of three typical epikarst springs in Southwest China were investigated. Results showed that PAH concentrations in soil and water have an overall downward trend (a reduction of 57 % and 93 %, respectively) in the past 10 years, which is consistent with the downward trend in the relative contribution rate of raw coal production (a 66 % reduction). In terms of composition, the proportion of low-ring PAHs decreased, medium-ring and high-ring PAHs increased in the soil profile. The proportion of low-ring PAHs did not change obviously, the proportion of medium-ring PAHs increased, and the proportion of high-ring PAHs decreased in epikarst springs. The source of PAHs changed remarkably over time, the relative contribution of coal combustion to PAHs decreased from 38 % to 20 %, and the vehicle contribution of PAHs increased from 31 % to 44 % in soils. The relative contribution rate of unburned oil and coke oven and biomass combustion change is less. Furthermore, the ecological risk of PAHs in the soils was reduced from moderate risk 2 to moderate risk 1, the risk in epikarst spring was reduced from high risk to moderate risk 2 after 10 years. This study demonstrates that substituting petroleum and coal with green energies can reduce PAH concentrations and risk.

Seasonal trends and retention of polycyclic aromatic compounds (PACs) in a remote sub-Arctic catchment

Atmospheric deposition is the most dominant source of polycyclic aromatic hydrocarbons (PAHs) in remote and pristine areas. Despite low bioaccumulation potential, PAHs and their persistent transformation products (PAH-derivatives) are chemicals of concern as they can harm human and animal health through chronic low dose exposure. In this study, atmospheric deposition fluxes of polycyclic aromatic compounds (PACs) were measured on a seasonal basis (3-month periods) from 2012 to 2016 in a remote subarctic forest catchment in northern Europe. The target PACs included 19 PAHs and 15 PAH-derivatives (oxygenated, nitrogenated, and methylated PAHs). The deposition fluxes of ƩPAHs and ƩPAH-derivatives were in the same range and averaged 530 and 500 ng m2 day-1, respectively. The fluxes were found to be higher with a factor of 2.5 for ƩPAHs and a factor of 3 for ƩPAH-derivatives during cold (<0 °C) in comparison to warm (>10 °C) periods. PAHs and PAH-derivatives showed similar seasonal patterns, which suggests that these two compound classes have similar sources and deposition mechanisms, and that the source strength of the PAH-derivatives in air follows that of the PAHs. The terrestrial export of PACs via the outlet of the catchment stream was estimated to be 1.1% for ƩPAHs and 1.7% for ƩPAH-derivatives in relation to the annual amounts deposited to the catchment, which suggests that boreal forests are sinks for PACs derived from the atmosphere. Some individual PACs showed higher export than others (i.e. chrysene, cyclopenta(c,d)pyrene, carbazole, quinoline, and benzo(f)quinoline), with high export PACs mostly characterized by low molecular weight and low hydrophobicity (2-3 benzene rings; log Kow<6.0).

Dilution of concentrations of PAHs from atmospheric particles, bulk deposition to soil: a review

Polycyclic aromatic hydrocarbons (PAHs) are emitted to the atmosphere by various anthropogenic activities as well as natural sources, they undergo long-range transport, are degraded (e.g., by photolysis) and finally they are deposited onto the surface and potentially accumulate in topsoil. The dry deposition of particle-bound PAHs dominates the accumulation of PAHs in soil and their further fate in soil is governed by sorption/desorption from these airborne particles. This paper offers an overview on concentrations of particle-bound PAHs, the dry deposition fluxes and finally concentrations of PAHs in soil. In addition, spatial and temporal variations of PAHs are considered. The results show that concentrations of particle-bound PAHs typically range from 1 mg g^-1 up to 10 mg g^-1 in cities with coal-based heating in winter and in countries with coal-based industry incl. electrical power production. These values are very high and exceed the legal limits set in soils by orders of magnitude. Atmospheric deposition rates typically reach several mg m^-2 a^-1, but in winter, especially in countries with heating, deposition rates are up to 10 times higher. PAHs concentrations in soils show a very wide variation from less than 1 µg g^-1 in rural areas up to 10 µg g^-1 in urban space, which is about 1000 times lower than the concentration of PAHs on particles in the atmosphere. This demonstrates the relevance of high concentrations of PAHs on airborne particles deposited on soils, which also highlights the importance of considering incremental lifetime cancer risk models for both air and soil and assessing the total health risk of PAHs to humans.

Spatial and seasonal variation and sources of deposition fluxes of polycyclic aromatic hydrocarbons (PAHs) in Shanghai

Spatial and temporal variations of polycyclic aromatic hydrocarbons (PAHs) deposition fluxes and sources may significantly facilitate risk evaluation and pollution control of super megacity in China. A study on PAHs of wet and dry deposition in Shanghai was conducted from January to December of 2019. Seventeen sampling sites located in four functional areas were set, including the Baoshan iron and steel industry area (BS), Jinshan petrochemical industry area (JS), city center (CC), and Chongming agricultural area (CM). A total of 15 PAHs were determined by gas chromatography-mass spectrometry (GC-MS, Agilent 7890A/5975C). PAHs atmospheric deposition flux in winter was highest (3.12 ± 1.98 μg/(m²·day), mostly attributed to local emissions accumulation under adverse meteorological diffusion conditions, as well as pollutants transport from northern China during heating season. PAHs deposition fluxes in industrial area (BS and JS) were 3.75 ± 4.08 μg/(m²·day) and 3.18 ± 3.62 μg/(m²·day) respectively, which were greater than those in CC and CM, accounting for 1.91 ± 1.06 μg/(m²·day) and 1.41 ± 0.61 μg/(m²·day) respectively. Proportional composition and isomer ratios of PAHs indicated that the PAHs deposition in winter and spring samples were more homogeneous, whereas those of summer and autumn seemed to be more variable and dispersed. Positive matrix factorization model were employed to identify the potential sources of PAHs in specific functional areas. A dominance of contribution was attributed to coal combustion (46%) at BS, petroleum volatilization (48%) at JS, biomass burning (55%) at CM, and vehicle emission (49%) at CC. This study highlighted that local urbanization and industrialization have a significant contribution to PAHs deposition to specific functional regions in Shanghai.

Migration Behavior and Influencing Factors of Petroleum Hydrocarbon Phenanthrene in Soil around Typical Oilfields of China

Petroleum spills and land contamination are becoming increasingly common around the world. Polycyclic aromatic hydrocarbons (PAHs) and other pollutants found in petroleum are constantly migrating underground, making their migration in soil a hot research topic. Therefore, it is of great significance to evaluate the migratory process of petroleum hydrocarbons in petroleum-polluted soil to clarify its ecological and environmental risks. In this study, Phenanthrene (PHE) was used as a typical pollutant of PAHs. The soil was gathered from three typical oilfields in China, and a soil column apparatus was built to simulate the vertical migration of PHE in the soil. The migration law and penetration effect of PHE in various environmental conditions of soil were investigated by varying the ionic strength (IS), pH, particle size, and type of soil. According to the literature, pH has no discernible effect on the migration of PHE. The migration of PHE was adversely and positively linked with changes in IS and soil particle size, respectively. The influence of soil type was mainly manifested in the difference of organic matter and clay content. In the Yanchang Oilfield (YC) soil with the largest soil particle size and the least clay content, the mobility of PHE was the highest. This study may reveal the migration law of PAHs in soils around typical oilfields, establish a new foundation for PAH migration in the soil, and also provide new ideas for the management and control of petroleum pollution in the soil and groundwater.

Distribution, sources and transport of polycyclic aromatic hydrocarbons (PAHs) in karst spring systems from Western Hubei, Central China

Karst groundwater is an important water resource but it is vulnerable to contaminants, due to the distinctive geological features of abundant transmissive fractures and conduits in the karst area which connect the surface to the underground systems. Anthropogenic activity-derived polycyclic aromatic hydrocarbons (PAHs) on the surface environment could enter groundwater easily and rapidly and threaten water security in karst areas. Samples in the multimedia environment from 10 specific karst spring systems from Western Hubei of Central China were collected to analyze 16 priority PAHs and to investigate their transport in these karst spring systems. The total concentrations of PAHs in the soil, river water, river sediments, spring water, and spring sediments ranged between 6.04 and 67.7 ng g^-1, 4.56 and 11.4 ng L^-1, 29.9 and 1041 ng g^-1, 4.09 and 222 ng L^-1, and 5.88 and 83.0 ng g^-1, respectively. Levels of PAHs in this area were relatively low when compared to other karst areas. Proportions of low-molecular-weight (LMW)-PAHs in the water, sediments and soil (average 58.2-78.8%) were much higher than those of high-molecular-weight (HMW)-PAHs. The proportion of LMW-PAHs in the sediments (especially in river sediments) was higher than that in the soil. Characteristic ratio analysis and principal component analysis showed that PAHs were from high-temperature combustion of the mixture of coal and biomass, and vehicle emission, where coal and biomass combustion were the dominant sources. Significant correlations of PAH compositions in different media of karst spring systems were observed, especially in the Yuquangdong (YQD)-Migongquan (MGQ), Jiuzhenziquan (JZZQ), Xianyudong (XYD) and Fengdong (FD) karst spring systems, indicating the rapid PAH transport from the recharge area soil to the discharge area of spring water and sediments.

Convolutional Neural Network for Measurement of Suspended Solids and Turbidity

The great potential of the convolutional neural networks (CNNs) provides novel and alternative ways to monitor important parameters with high accuracy. In this study, we developed a soft sensor model for dynamic processes based on a CNN for the measurement of suspended solids and turbidity from a single image of the liquid sample to be measured by using a commercial smartphone camera (Android or IOS system) and light-emitting diode (LED) illumination. For this, an image dataset of liquid samples illuminated with white, red, green, and blue LED light was taken and used to train a CNN and fit a multiple linear regression (MLR) by using different color lighting, we evaluated which color gives more accurate information about the concentration of suspended particles in the sample. We implemented a pre-trained AlexNet model, and an MLR to estimate total suspended solids (TSS), and turbidity values in liquid samples based on suspended particles. The proposed technique obtained high goodness of fit (R2 = 0.99). The best performance was achieved using white light, with an accuracy of 98.24% and 97.20% for TSS and turbidity, respectively, with an operational range of 0–800 mgL−1, and 0–306 NTU. This system was designed for aquaculture environments and tested with both commercial fish feed and paprika. This motivates further research with different aquatic environments such as river water, domestic and industrial wastewater, and potable water, among others.

Distribution and Potential Sources of OCPs and PAHs in Waters from the Danshui River Basin in Yichang, China

To investigate the concentrations, spatial distribution, potential sources and mass fluxes of organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in waters from the Danshui River Basin, a total of 20 water samples were collected and analyzed from a karstic river in Western Hubei of Central China. The average concentrations of total OCPs and PAHs in the river water were 4719 pg·L^-1 and 26.2 ng·L^-1, respectively. The characteristic ratios of different isomers and the composition analysis of individual OCPs and PAHs revealed that HCHs originated from a mixed input of technical HCHs and Lindane, DDTs were mainly from technical DDTs, and PAHs mainly originated from biomass and coal combustion. The mass flux analysis showed that PAHs had a higher emission and heavier burden than OCPs in the Danshui River Basin. OCPs and PAHs emitted from agricultural or other human activities could enter the groundwater and then be transported to the surface/river water in the karst area. The adsorption of OCPs and PAHs by particles and the sedimentation of particles could be the primary processes to intercept these pollutants in the water of the karstic river system.

Sources and pollution path identification of PAHs in karst aquifers: an example from Liulin karst water system, northern China

Karst water, with constituting major sources for water supply worldwide, is vulnerable and prone to be polluted. In this study, it is reported that karst water polycylic aromatic hydrocarbons (PAHs) pollution is caused by the infiltration of surface runoff in the bared carbonate areas, which is of universal significance for the protection of groundwater resources in karst region. Hydro-geochemistry, stable isotopes (δD, δ¹⁸O and ⁸⁷Sr/⁸⁶Sr) and characteristic ratio method were conducted together to illustrate the concentration, distribution, sources and pollution path of polycyclic aromatic hydrocarbons in groundwater in the Liulin karst water system of northern China. The results showed that total concentration of polycyclic aromatic hydrocarbons ranged from 39.25 to 16,830 ng/L in groundwater, with Naphthalene being the dominant component, and the median value increased gradually along the flow path. The highest polycyclic aromatic hydrocarbons concentrations in karst water were mainly observed in the coal mining and the discharge areas. Based on the characteristic ratios, the polycyclic aromatic hydrocarbons in the study area mainly come from local incomplete combustion of woods, fossil fuels, coal and liquid fuels. The slight shift of δD and δ¹⁸O and moderate ⁸⁷Sr/⁸⁶Sr ratios suggest that the polycyclic aromatic hydrocarbons in karst water is mainly polluted by surface runoff during rain events in the bared karst region. The leakage of river water may partly contribute to the polycyclic aromatic hydrocarbons in some karst water, which normally located close to the karst water - river water mixing line. This study provides a new technical method for tracing the sources and identifying the pollution paths of organic pollution in a karst water system.

High-frequency data reveal differential dissolved and suspended solids behavior from a mixed restored prairie and agricultural catchment

Quantifying temporal variability and fluxes within hydrologic catchments is critical to understanding the underlying chemical and physical processes leading to material transport. Measuring variability and fluxes requires sampling at time scales similar to the time scale of process occurrence. This demand has led to the development of automated sampling systems designed to sample at high frequencies, on the order of minutes. While widely deployed in a variety of systems, we installed two high-frequency sampling devices in a single drainage comprised of restored prairie and agricultural land uses in temperate Eastern Nebraska. The sampling systems determined flow rate, conductivity, and turbidity at 15-minute intervals for a twelve-month period. Conductivity was used as a proxy for total dissolved solids (TDS) concentrations and turbidity was used as a proxy for total suspended solids (TSS) concentrations. Using the high-frequency data, estimates of solids flux were calculated, error on the estimates was constrained, the effects of sample timing were considered, and conductivity and turbidity changes during precipitation events were examined. Overall, TDS fluxes were about three times higher than TSS fluxes from the catchment as a whole. However, the TSS fluxes were higher in the agricultural section of the catchment than from the restored prairie. Sheet and rill soil loss estimates from both the restored prairie and agricultural settings were low (<0.060 mm/yr). For TDS flux calculations, sampling at a monthly frequency gave a value that was only 11% lower than sampling every 15 min. For TSS flux calculations, sampling only during precipitation events (0.7% of the time) would capture 67% of the annual flux. Thus, minimizing error in sampling strategies depends on the constituent being analyzed.

Groundwater sampling in karst terranes: passive sampling in comparison to event-driven sampling strategy

Karst aquifers are very easily contaminated because of the surficial features that commonly exist in karst terranes. Pollutant releases into sinkholes, sinking streams, and/or losing streams commonly result in concentrated solutes rapidly infiltrating and migrating through the subsurface to eventually discharge at downgradient springs unless intercepted by production wells, but slow percolation through soils also may result in serious contamination of karst aquifers. The unique features of karst terranes tend to cause significant problems in the interpretation of results obtained from water-quality grab samples of karst groundwater. To obtain more representative samples, event-driven sampling was proposed some decades ago, but event-driven sampling can be difficult and expensive to implement. In this paper, application of passive-sampling strategies is advocated as a means for effectively obtaining representative water-quality samples from karst aquifers. A passive-sampling methodology may be particularly useful for karst aquifers that may be found in complexly folded and faulted terranes. For example, a groundwater tracing investigation of a contaminated site in a karst terrane confirmed that several offsite springs and wells are connected to the contaminated site. Tracer recoveries suggested transport rates that were relatively slow for flow in a karstic aquifer (~0.02 m/s). Breakthrough curves were erratic and spiky. To obtain representative groundwater samples, a passive-sampling methodology is recommended.

Relationship between Polycyclic Aromatic Hydrocarbons in Sediments and Invertebrates of Natural and Artificial Stormwater Retention Ponds

Sediments and invertebrates were sampled from 9 stormwater retention ponds (SWRPs) and 11 natural, shallow lakes in Denmark. Samples were analyzed for 13 polycyclic aromatic hydrocarbons (PAHs). The SWRPs received urban and highway runoff from various types of drainage areas and the lakes were located in areas of various land uses. Comparing PAHs in the sediments of the SWRPs and the lakes, it was found that levels of total PAH were similar in the two aquatic systems, with median values of 0.94 and 0.63 mg·(kg·DM)−1 in sediments of SWRPs and lakes, respectively. However, the SWRP sediments tended to have higher concentrations of high-molecular-weight PAHs than the lakes. A similar pattern was seen for PAHs accumulated in invertebrates where the median of total PAH was 2.8 and 2.1 mg·(kg·DM)−1 for SWRPs and lakes, respectively. Principal component analysis on the PAH distribution in the sediments and invertebrates showed that ponds receiving highway runoff clustered with lakes in forests and farmland. The same was the case for some of the ponds receiving runoff from residential areas. Overall, results showed that sediment PAH levels in all SWRPs receiving runoff from highways were similar to the levels found in some of the investigated natural, shallow lakes, as were the sediment PAH levels from some of the residential SWRPs. Furthermore, there was no systematic trend that one type of water body exceeded environmental quality standards (EQS) values more often than others. Together this indicates that at least some SWRPs can sustain an invertebrate ecosystem without the organisms experiencing higher bioaccumulation of PAHs then what is the case in shallow lakes of the same region.

Characteristics and ecological risk assessment of polycyclic aromatic hydrocarbons in soil seepage water in karst terrains, southwest China

Concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils and soil seepage waters were analyzed along with dissolved organic carbon (DOC) to investigate the ecological risks and factors controlling the subsurface transport of PAHs in karst terrain in southwest China. The concentrations of dissolved PAHs in soil seepage water increased with depth and the mean concentrations at a depth of 80 cm were relatively high (exceeding 1147 ng/L). PAH composition in soil seepage water was dominated by low molecular weight (LMW) PAHs, whereas those associated with soil matrix were dominated by high molecular weight (HMW) PAHs. The results revealed that HMW PAHs in soil seepage water were closer to the equilibrium of dissolution than LMW and medium molecular weight (MMW) PAHs. However, due to the carrier functions of dissolved organic matter (DOM) for HMW PAHs, all PAHs can be continuously dissolved in the soil seepage water from soil matrix as the water moved vertical downward through the profiles. During this process, dynamic sorption and desorption processes were occurring between constituents in the soil seepage water and the soil matrix. This study demonstrates soil seepage water has posed a high risk to the groundwater, and effective protection is urgently needed.

Transport of a PAH-degrading bacterium in saturated limestone media under various physicochemical conditions: Common and unexpected retention and remobilization behaviors

Laboratory saturated columns packed with granular limestone grains were used to explore the retention and remobilization of functional bacteria FA1 under various physicochemical conditions. The unique surface properties of limestone and FA1 caused some unexpected phenomena. Solution IS, cation type, temperature and surface biological property all affected FA1 retention in the columns. The IS effect was temperature dependent and initial solution pH showed little influence due to the strong buffering ability of limestone. Perturbations of solution IS caused slight release of previously retained bacteria in some columns with NaCl as the background electrolyte, while increase in flow rate caused no release at all. When CaCl₂ was the background, bacterial remobilization only occurred following both cation exchange and IS reduction. DLVO forces incorporating with surface roughness calculation were determined to assist with interpretation of interaction mechanisms. All the experimental evidences suggest the importance of cation bridging, cation exchange, surface roughness, and hydrophobic interaction in controlling bacterium transport in saturated limestone porous media.

Vertical migration from surface soils to groundwater and source appointment of polycyclic aromatic hydrocarbons in epikarst spring systems, southwest China

Understanding the transfer process of polycyclic aromatic hydrocarbons (PAHs) in the karst terrain is of great importance to their ecological risk assessments, however, the impact of the vertical transfer of the soil PAHs on the underground water is largely unknown in the karst system. Here, the vertical distribution and the seasonal variation of 16 PAHs in the soils and the water of 4 epikarst spring catchments in Southwest China were investigated. The total concentration of the PAHs ranged within 61-3285 ng g^-1 in the soils, and 341-4969 ng L^-1 in the spring water. The vertical distribution of the PAHs in soils varied with ring numbers and altitude of the catchment. PAHs concentrations were linearly related with the total organic carbon (TOC) at different depths in the catchments 563-783 m above the sea level (A.S.L.). However, no correlation with TOC was observed in the catchment of a high altitude (2090 m A.S.L.), because the large water flux led to the fast migration of the 2-3 rings PAHs in soils. The PAHs in soils and springs were mainly derived from the combustion of grass/wood/coal, closely related with the primary fossil fuels used in this area. This study demonstrate that the groundwater was heavily polluted by PAHs in the karst terrains of Southwest China, due to the vertical transfer of PAHs from the surface soils, and effective protection was urgently needed.

Occurrence and levels of micropollutants across environmental and engineered compartments in Austria

Occurrence and concentration of a broad spectrum of micropollutants are investigated in Austrian river catchments, namely polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), organotin compounds, perfluoroalkyl acids (PFAAs) and metals. The parallel analysis across multiple environmental and engineered compartments sheds light on the ratio of dissolved and particulate transport and on differences in concentration levels between point and diffuse emission pathways. It is found that some PAHs and organotins are present in rivers, groundwater and bulk deposition at higher concentrations than in municipal wastewater effluents. Among PFAAs and metals, highest concentrations were recorded either in atmospheric deposition or in discharges from wastewater treatment plants. The relevance of the analysis across compartments is best shown by the case of perfluorooctanesulfonic acid (PFOS). Despite municipal wastewater effluents being the emission pathway with highest concentrations, this study reveals that not only rivers, but also atmospheric deposition and groundwater sometimes exceed the environmental quality standard for surface waters. Moreover, this work reveals partially counterintuitive patterns. In rivers with treated wastewater discharges, increasing levels of dissolved compounds were measured at rising flow conditions, whereas the opposite would be expected owing to the dilution effect. This might derive from the mobilisation from soil or suspended particulate matter or rather find its explanation in high concentrations in atmospheric deposition. These hypotheses require however being tested through targeted studies. Additional future research includes the analysis of how regional or catchment specific characteristics might alter the relative importance of different emission pathways, and the modelling of emission and river loads to assess their relative contribution to river pollution.

Particle bound pollutants in rivers: Results from suspended sediment sampling in Globaqua River Basins

Transport of hydrophobic pollutants in rivers such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and heavy metals is often facilitated by suspended sediment particles, which are typically mobilized during high discharge events. Suspended sediments thus represent a means of transport for particle related pollutants within river reaches and may represent a suitable proxy for average pollutant concentrations estimation in a river reach or catchment. In this study, multiple high discharge/turbidity events were sampled at high temporal resolution in the Globaqua River Basins Sava (Slovenia, Serbia), Adige (Italy), and Evrotas (Greece) and analysed for persistent organic pollutants such as PAHs (polycyclic aromatic hydrocarbons) or PCBs (polychlorinated biphenyls) and heavy metals. For comparison, river bed sediment samples were analysed as well. Further, results are compared to previous studies in contrasting catchments in Germany, Iran, Spain, and beyond. Overall results show that loadings of suspended sediments with pollutants are catchment-specific and relatively stable over time at a given location. For PAHs, loadings on suspended particles mainly correlate to urban pressures (potentially diluted by sediment mass fluxes) in the rivers, whereas metal concentrations mainly display a geogenic origin. By cross-comparison with known urban pressure/sediment yield relationships (e.g. for PAHs) or soil background values (for metals) anthropogenic impact - e.g. caused by industrial activities - may be identified. Sampling of suspended sediments gives much more reliable results compared to sediment grab samples which typically show a more heterogeneous contaminant distribution. Based on mean annual suspended sediment concentrations and distribution coefficients of pollutants the fraction of particle facilitated transport versus dissolved fluxes can be calculated.

Transport of polycyclic aromatic hydrocarbons in a highly vulnerable karst underground river system of southwest China

The concentration and fluxes of polycyclic aromatic hydrocarbons (PAHs) were investigated in a karst underground river system in southwest China. Groundwater, particles, and sediments from underground river, topsoil, and surface water were monitored, allowing establishment of a conceptual model of PAH transport at the watershed scale. The results showed that PAHs could be transported from the surface to the subsurface through two migration pathways, which were slow-flowing water in the karst fissure and fast-flowing water in conduits. During rainfall events, increasing PAH levels (concentrations and fluxes) at the underground river exit indicated that hydrodynamic force could facilitate PAH transport. The PAHs in water were dominated by dissolved PAHs, accounting for 58.7% of total, especially in the freely dissolved phase, in which SPM-associated PAHs accounted for 41.3% of the total PAHs. Low molecular weight PAHs dominated transport and were mainly transported in dissolved form, whereas high molecular weight PAHs were dominated by SPM-associated transport during the rainfall events. A significantly positive correlation was observed between two-ring and three-ring freely dissolved PAHs and dissolved organic carbon (p < 0.01), respectively. Moreover, PAHs with four to five rings were relatively more abundant in the dissolved organic matter (DOM) associated phase than in the freely dissolved phase, suggesting a major role of DOM in their transport during rainfall events. The trend of PAH fluxes suggested that particle-facilitated transport was another dominant cause of PAH mobilization.

Effect of solid waste landfill organic pollutants on groundwater in three areas of Sicily (Italy) characterized by different vulnerability

The aim of this study was to obtain information on the presence and levels of hazardous organic pollutants in groundwater located close to solid waste landfills. Eighty-two environmental contaminants, including 16 polycyclic aromatic hydrocarbons (PAHs), 20 volatile organic compounds (VOCs), 29 polychlorinated biphenyls (PCBs), 7 dioxins (polychlorinated dibenzo-p-dioxins, PCDDs) and 10 furans (polychlorinated dibenzofurans, PCDFs) were monitored in areas characterised by different geological environments surrounding three municipal solid waste landfills (Palermo, Siculiana and Ragusa) in Sicily (Italy) in three sampling campaigns. The total concentrations of the 16 PAHs were always below the legal threshold. Overall, the Fl/Fl + Py diagnostic ratio revealed that PAHs had a petrogenic origin. VOC levels, except for two notable exceptions near Palermo landfill, were always below the legal limit. As concerns PCB levels, several samples were found positive with levels exceeding the legal limits. It is worth noting that the % PCB distribution differs from that of commercial compositions. In parallel, some samples of groundwater containing PCDDs and PCDFs exceeding the legal threshold were also found. Among the 17 congeners monitored, the most abundant were the highest molecular weight ones.

Mapping of heavy metal pollution in river water at daily time-scale using spatio-temporal fusion of MODIS-aqua and Landsat satellite imageries

For river water quality monitoring at 30m × 1-day spatio-temporal scales, a spatial and temporal adaptive reflectance fusion model (STARFM) is developed for estimating turbidity (T_u), total suspended solid (TSS), and six heavy metals (HV) of iron, zinc, copper, chromium, lead and cadmium, by blending the Moderate-Resolution Imaging Spectroradiometer (MODIS) and Landsat (L_s) spectral bands. A combination of regression analysis and genetic algorithm (GA) techniques are applied to develop spectral relationships between T_u-L_s, TSS-T_u, and each HV-TSS. The STARFM algorithm and all the developed relationship models are evaluated satisfactorily by various performance evaluation measures to develop heavy metal pollution index-based vulnerability maps at 1-km resolution in the Brahmani River in eastern India. The Monte-Carlo simulation based analysis of the developed formulations reveals that the uncertainty in estimating Zn and Cd is the minimum (1.04%) and the maximum (5.05%), respectively. Hence, the remote sensing based approach developed herein can effectively be used in many world rivers for real-time monitoring of heavy metal pollution.

Persistent organic pollutants in shallow percolated water of the Alps Karst system (Zugspitze summit, Germany)

In the German Calcareous Alps at the Zugspitze, percolated water close to a permafrost bedrock in a tunnel system was monitored long-term for polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), and 28 organochlorine pesticides (OCP). Semi-permeable membrane devices (SPMD) were deployed in a temporary surface water system at the Zugspitze plateau and analysed for PCB, PAH, and OCP. The high-volume water sampling was successfully implemented and all compounds were identified in the water percolated through the Karst system. However, the percentage distribution of contaminants in the percolated water differed significantly from that found in surface waters. The highest chlorinated PCDD homologues were the predominant compounds of the PCDD/F family, whereas percentages of PCB #52 increased in percolated water. Toxic equivalent values (TEQ) of samples ranged from 2.0 to 4.2pgTEQ/m³ and from 0.017 to 0.069pgTEQ/m³ for PCDD/F and PCB, respectively. Low and intermediate molecular weight PAH were the prevailing compounds in the samples. Endosulfan sulfate, endrin, and cis-heptachlor epoxide were enhanced after water percolation through the Karst system in comparison with the surface waters (wet deposition). The relative enrichment on these pesticides was related to the environmental bedrock conditions and glacier melting sources. In summary, the Karst system highly influenced the fate of organic persistent pollutants generating different chemical patterns in their percolated waters than those found at the surface systems.

Using turbidity for designing water networks

Some methods to design water networks with minimum fresh water consumption are based on the selection of a key contaminant. In most of these "single contaminant methods", a maximum allowable concentration of contaminants must be established in water demands and water sources. Turbidity is not a contaminant concentration but is a property that represents the "sum" of other contaminants, with the advantage that it can be cheaper and easily measured than biological oxygen demand, chemical oxygen demand, suspended solids, dissolved solids, among others. The objective of this paper is to demonstrate that turbidity can be used directly in the design of water networks just like any other contaminant concentration. A mathematical demonstration is presented and in order to validate the mathematical results, the design of a water network for a guava fudge production process is performed. The material recovery pinch diagram and nearest neighbors algorithm were used for the design of the water network. Nevertheless, this water network could be designed using other single contaminant methodologies. The maximum error between the expected and the real turbidity values in the water network was 3.3%. These results corroborate the usefulness of turbidity in the design of water networks.

Removal of Polycyclic Aromatic Hydrocarbons from Precipitation in an Urban Forest of Guangzhou, South China

Polycyclic aromatic hydrocarbon (PAH) concentrations and fluxes were measured monthly in situ from rain events in an urban forest in the megapolitan city Guangzhou, China, to investigate impacts of forest canopy and soils on PAHs. Mean Σ9-PAH concentrations were 107.5, 101.6, 106.3, 107.1 and 42.4 ng L(-1) in precipitation, throughfall, seepage water at the 30 and 60 cm soil depth, and runoff, respectively, indicating a great decrease in the form of runoff. Meanwhile, annual fluxes of total PAHs decreased from precipitation (205.9 µg m(-2) year(-1)), to throughfall (156.3 µg m(-2) year(-1)), and to seepage water (65.3 µg m(-2) year(-1) at 30-cm soil depth and 7.5 µg m(-2) year(-1) at 60-cm soil depth), but increased in runoff (34.1 µg m(-2) year(-1)). When compared to precipitation, PAH fluxes decreased by 83.4% in runoff, with 29% contributed by forest canopy and 71% by soils. Soil biodegradation explained 18.2% of PAH reduction by the surface soil layer and 34.6% by the middle soil layer.

Occurrence and source apportionment of PAHs in highly vulnerable karst system

The concentration and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in topsoil, groundwater and groundwater suspended solids (SS) at Guozhuang karst water system of northern China were investigated. The total concentration of PAHs ranged from 622 to 87,880 ng/g dry weight in topsoil, from 4739 to 59,314 ng/g dry weight in SS, and from 2137 to 9037 ng/L in groundwater, with mean values of 17,174 ng/g, 11,990 ng/g and 5020 ng/L, respectively. High concentrations of PAHs were mainly observed in the coal mining industrial area and the discharge area. The composition of PAHs indicated that low molecular weight PAHs were predominant in groundwater samples, the content of medium molecular weight PAHs was elevated in SS, and carcinogenic high molecular weight PAHs were frequently detected in topsoil. The high contents of low-medium molecular weight PAHs in groundwater and SS suggested relatively recent local sources of PAHs that were transported into the aquifer via leakage of contaminated surface water and/or infiltration of PAH-containing precipitation. The results of evaluating sources of PAHs using ratios of specific PAH compounds showed that PAHs mainly originated from coal and wood combustion. Furthermore, five sources were identified by positive matrix factorization (PMF) model, and the contribution to the total loadings of groundwater PAHs were: 2% for unburnt oil, 32% for coal combustion, 22% for vehicle emission, 27% for biomass combustion and 18% for coke production, respectively. Furthermore, strong correlations of total PAHs with total organic carbon (TOC) in topsoil indicated co-emission of PAHs and TOC. Poor correlations of PAHs with dissolved organic carbon (DOC) in groundwater indicated that other factors exert stronger influences. Therefore, PAHs might have posed a major threat to the quality of potable groundwater in Guozhuang karst water system.

Monitoring of event-based mobilization of hydrophobic pollutants in rivers: calibration of turbidity as a proxy for particle facilitated transport in field and laboratory

Transport of many pollutants in rivers is coupled to mobilization of suspended particles which typically occurs during floods. Since the amount of total suspended solids (TSS) in rivers can be monitored by turbidity measurements this may be used as a proxy for the total concentration of particle associated pollutants such as PAHs, PCBs, etc. and several heavy metals. Online turbidity measurements (e.g. by optical backscattering sensors) would then also allow for an assessment of particle and pollutant flux dynamics if once calibrated against TSS and total pollutant concentrations for a given catchment. In this study, distinct flood and thus turbidity events were sampled at high temporal resolution in three contrasting sub-catchments of the River Neckar in Southwest Germany (Ammer, Goldersbach, Steinlach) as well as in the River Neckar itself and investigated for the total amount of PAHs and TSS in water; turbidity (NTU) and grain size distributions of suspended solids were determined as well. Laboratory experiments were performed with natural river bed sediments from different locations (Ammer) to investigate PAH concentrations, TSS and turbidity during sedimentation of suspended particles under controlled conditions (yielding smaller and smaller suspended particles and TSS with time). Laboratory and field results agreed very well and showed that turbidity and TSS were linearly correlated over an extended turbidity range up to 2000 NTU for the field samples and up to 8000 NTU in lab experiments. This also holds for total PAH concentrations which can be reasonably well predicted based on turbidity measurements and TSS vs. PAHs relationships - even for high turbidity values observed during flood events (>2000 NTU). Total PAH concentrations on suspended solids were independent of grain size of suspended particles. This implies that for the rivers investigated the sorption capacity of particles did not change significantly during the observed events.

Comparison of sedimentary PAHs in the rivers of Ammer (Germany) and Liangtan (China): differences between early- and newly-industrialized countries

As a proxy to trace the impact of anthropogenic activity, sedimentary polycyclic aromatic hydrocarbons (PAHs) are compared between the early industrialized and newly industrialized countries of Germany and China, respectively. Surface sediment samples in the Ammer River of Germany and the Liangtan River of China were collected to compare concentration levels, distribution patterns, and diagnostic plots of sedimentary PAHs. Total concentrations of 16 PAHs in Ammer sediments were significantly higher by a factor of ~4.5 than those in Liangtan. This contrast agrees with an extensive literature survey of PAH levels found in Chinese versus European sediments. Distribution patterns of PAHs were similar across sites in the Ammer River, whereas they were highly varied in the Liangtan River. Pyrogenic sources dominated in both cases. Strong correlations of the sum of 16 PAHs and PAH groups with TOC contents in the Liangtan River may indicate coemission of PAHs and TOC. Poor correlations of PAHs with TOC in the Ammer River indicate that other factors exert stronger influences. Sedimentary PAHs in the Ammer River are primarily attributed to input of diffuse sources or legacy pollution, while sediments in the Liangtan River are probably affected by ongoing point source emissions. Providing further evidence of a more prolonged anthropogenic influence are the elevated black carbon fractions in sedimentary TOC in the Ammer compared to the Liangtan. This implies that the Liangtan River, like others in newly industrialized regions, still has a chance to avoid legacy pollution of sediment which is widespread in the Ammer River and other European waterways.

Integrated monitoring of particle associated transport of PAHs in contrasting catchments

Water quality of rivers depends often on the degree of urbanization and the population density in the catchment. This study shows results of a monitoring campaign of total concentration of polycyclic aromatic hydrocarbons (PAHs) and suspended particles in water samples in adjacent catchments in Southern Germany with similar geology and climate but different degrees of urbanization. Defined linear relationships between total concentrations of PAHs in water and the amount of suspended solids were obtained indicating predominance of particle-facilitated transport. The slopes of these regressions correspond to the average contamination of suspended particles (C(sus)) and thus comprise a very robust measure of sediment pollution in a river. For the first time, we can show that C(sus) is distinct in the different catchments and correlates to the degree of urbanization represented by the number of inhabitants per total flux of suspended particles.