Polycyclic aromatic hydrocarbons in atmospheric particulate depositions and urban soils of Moscow,Russia

Purpose

The study was conducted to quantify the polycyclic aromatic hydrocarbons (PAHs) accumulation in urban soils from different functional areas via atmospheric inputs with particulate matter.

Materials and methods

PAH concentration and pattern were measured in the particulate matter of snow depositions, in the upper layers of artificial soils from densely built-up areas and in the undisturbed natural soils (Umbric Retisols) from green park area. Samples were collected in 2011–2013 at 58 sites with different traffic activities located at the territory of the Eastern Administrative Okrug of Moscow. The soil samples and filters with particulate matter were extracted by pressurized liquid extraction using Dionex ASE200. Clean-up analyses were performed on SPE cartridges filled with silica gel. Concentrations of PAHs were determined by high-performance liquid chromatography using an Agilent 1100 System equipped with fluorescent detector.

Results and discussion

Mean values of PAH input with snow particles were 45–57 μg/m² for recreational and residential zones, and 140–264 μg/m² for traffic zones. The samples of depositions from different functional areas showed a similar PAH pattern and consisted primarily of 3–4-ring PAHs. Total PAH concentrations in upper layers of artificial soils showed similar mean values of 1.43–2.21 μg/g for all functional zones. The PAH content in soils from the park area was twofold lower than that from the built-up area (0.34–0.63 μg/g), despite equal levels of atmosphere contamination on these territories. The upper layers of natural soils from recreational and traffic zones showed slight differences in PAH content, though PAH input with snow was fivefold higher in the traffic zone. Compared with airborne depositions, soils contained significant amounts of 5–6-ring PAHs.

Conclusions

A high level of soil PAH contamination in urban areas of Moscow, several orders of magnitude higher than the current PAH input to them from the atmosphere, indicates a lack of direct connection of the PAH pool in soils with this source. The high PAH content in the upper layer of constructed soils can be the result of repeated use of materials subjected to a constant technogenic impact for the production of artificial soils.

     

Polycyclic aromatic hydrocarbons in green space soils in Shanghai: source,distribution, and risk assessment

Purpose

The purpose of this study is to study the major sources, concentrations, and distributions of polycyclic aromatic hydrocarbons (PAHs) in three different types of green space in Shanghai. In addition, we will quantitatively assess the burden of PAHs in the soil, as well as the potential carcinogenic risk of PAHs in humans. These results will provide valuable information for soil remediation and human health risk management.

Materials and methods

A total of 166 surface soil samples were collected in parks, greenbelts, and woodlands. Soils were extracted using accelerated solvent extraction (ASE). PAHs were analyzed by gas chromatography-mass spectrometry (GC-MS). The positive matrix factorization (PMF) model was used to identify major PAH emission sources and quantitatively assess their contributions to PAHs. The incremental lifetime cancer risk (ILCR) was used to quantify the potential health risk of PAHs.

Results and discussion

The average concentrations of ∑15 PAHs are 227?±?95 ng g^?1, 1632?±?251 ng g^?1, and 1888?±?552 ng g^?1 in the woodland, park, and greenbelt soils, respectively. The PMF results show that biomass (33%), coal (21%), vehicles (17%), natural gas (14%), oil (9%), and coke (7%) are the dominant sources of PAHs in the park soils. Diesel (40%), tire debris (30%), biomass (15%), gasoline (9%), and oil (5%) are the main sources in the greenbelt soils. Biomass (48%), vehicles (37%), and coal (15%) are the main sources in the woodland soils. The ILCRs of adults and children who are exposed to PAHs in soils range from 9.53?×?10^?8~1.42?×?10^?5.

Conclusion

In three types of green space in Shanghai, the dominant PAHs are high–molecular weight (HMW) compounds (≥?4 rings). This may be due to the proximity of the sampling site to emission sources. In addition, low–molecular weight (LMW) PAHs (with 2–3 rings) are relatively unstable, and these compounds are prone to volatilization and degradation. Source identification indicates that biomass combustion is the most dominant PAH source in the park and woodland soils, while vehicles are the dominant PAH source in the greenbelt soils. The ILCRs of adults and children indicate potential health risks, and children have a greater health risk than adults.

     

Characteristics,sources, and in situ phytoremediation of polycyclic aromatic hydrocarbon in rural dumpsites

Purpose

Without precaution to deal with gas emissions and leachate generation, dumpsites have become a severe environmental problem in many developing countries. The objectives of this study were to investigate the pollution status of polycyclic aromatic hydrocarbons (PAHs) in dumpsite soil in rural areas of China and to verify phytoremediation effectiveness with Sedum alfredii Hance and alfalfa (Medicago sativa L.) under complex pollution conditions in PAH-contaminated soil.

Materials and methods

In this study, we collected soil cores from four dumpsites in rural areas of North China (Hebei Province) for analysis, and correspondingly conducted an in situ phytoremediation experiment using Sedum alfredii Hance and alfalfa (Medicago sativa L.) at one of these sites, monitoring the total PAH concentration in soil.

Results and discussion

Results showed generally moderate pollution by PAHs in soil samples from dumpsites with pockets of heavy pollution. PAH concentrations in dumpsite soil ranged from 827 to 1101 ng/g (dry weight). High-molecular-weight PAHs were present in higher proportions at oldest dumpsite in operation. Certain molecular ratios of PAHs can be used to diagnose the source of PAHs in soil, and it indicated that the main sources were combustion of domestic coal and biomass, as well as the automobile exhaust and kitchen exhaust. A 17-month in situ phytoremediation experiment resulted in the effective removal of PAHs in the Sedum alfredii and alfalfa plots, with total PAH concentrations decreasing by 82.4% and 81.3%, respectively. Furthermore, PAH concentrations in plants correlated to plant growth conditions.

Conclusions

This study indicated that the soils of the dumpsites were generally moderately polluted by PAHs, and some parts of the area were heavily polluted. Both Sedum alfredii and alfalfa absorbed PAHs from soil, and PAH concentrations in these two plants correlated to the growth conditions of the plants. Phytoremediation can effectively be used for PAH removal in open dumpsites.

     

Source relationships between streambank soils and streambed sediments in a mercury-contaminated stream

Purpose

In contaminated streams, understanding the role of streambank and streambed source contributions is essential to developing robust remedial solutions. However, identifying relationships can be difficult because of the lack of identifying signatures in source and receptor pools. East Fork Poplar Creek (EFPC) in Oak Ridge, TN, USA received historical industrial releases of mercury that contaminated streambank soils and sediments. Here, we determined relationships between the contaminated streambank soils and sand-sized streambed sediments.

Materials and methods

Field surveys revealed the spatial trends of the concentrations of inorganic total mercury (Hg) and methyl mercury (MeHg), Hg lability as inferred by sequential extraction, particle size distribution, and total organic carbon. Statistical tests were applied to determine relationships between streambank soil and streambed sediment properties.

Results and discussion

Concentrations of Hg in streambank soils in the upper reaches averaged 206 mg kg^?1 (all as dry weight) (n?=?457), and 13 mg kg^?1 in lower reaches (n?=?321), while sand-sized streambed sediments were approximately 16 mg kg^?1 (n?=?57). Two areas of much higher Hg and MeHg concentrations in streambank soils were identified and related to localized higher Hg concentrations in the streambed sediments; however, most of the streambank soils have similar Hg concentrations to the streambed sediments. The molar ratio of Hg to organic carbon, correlation between MeHg and Hg, and particle size distributions suggested similarity between the streambank soils and the fine sand-sized fraction (125–250 μm) collected from the streambed sediments. Mercury in the fine sand-sized streambed sediments, however, was more labile than Hg in the streambank soils, suggesting an in-stream environment that altered the geochemistry of sediment-bound Hg.

Conclusions

This study revealed major source areas of Hg in streambank soils, identified possible depositional locations in streambed sediments, and highlighted potential differences in the stability of Hg bound to streambank soils and sediments. This work will guide future remedial decision making in EFPC and will aid other researchers in identifying source–sink linkages in contaminated fluvial systems.

     

Dissipation and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to organic matter in soils amended by exogenous rich-carbon material

Purpose

The aim of the research was to assess the effect of biochar addition on aging, degradation, and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to soil organic matter. The study was carried out as a sorption experiment in strictly controlled water and air conditions, which allowed for the accurate observation and prediction of PAH behavior in soils.

Materials and methods

Four soils were fortified with a PAH mixture (Fluorene-Flu, Anthracene-Ant, Phenanthrene-Phe, Pyrene-Pyr, Chrysene-Chry) at 20 mg kg^?1 of single-compound concentration level. The experiment was carried out in two trials: soils?+?5PAHs amended with biochar and soil?+?5PAHs without biochar addition with incubation times of 0, 1, 3, 6, and 9 months. After each interval time, the extractable (E-SOM) and stable organic matter (S-SOM) were measured as well as PAHs determined in two forms: total concentration (PAH-tot) and residual concentration (PAH-rest) after E-SOM extraction. The PAH loss and half-life times were estimated according to pseudo first-order kinetics equation.

Results and discussion

The amounts of PAH-tot in the soils without biochar decreased by an average of 92%, while in soil with biochar, this was 41% after 9 months of aging. The amount of PAHs-rest bounded with S-SOM after 9 months of incubation varied from 0.9 to 3.5% and 0.2 to 1.3% of the initial PAH concentration, respectively, for soils non-induced and induced by biochar. In soils without biochar, Flu, Ant, Phe, and Pyr exhibited similar T_1/2 (43–59 days), but Chry was characterized by a much higher and broader T_1/2 than other hydrocarbons (67–280 days). Biochar addition to the soils significantly influenced the half-life changes for all PAHs. The highest changes were noted for Phe (14-fold increase), and the lowest was for Flu (7-fold increase).

Conclusions

The addition of exogenous-rich carbon material such as biochar to the soil significantly changes the behavior and sorption potential of PAHs in the soil. Soils enriched with biochar are characterized by a higher persistence of PAHs, longer aging time, and lower affinity for sorption by native organic matter structures. Soils freshly polluted by PAH are mainly sorbed by E-SOM, which significantly increases their accessibility and reduces formation of bound-residues in the soil.

     

Influence of PAH contamination on soil ecological status

Purpose

The purpose of this paper is to study the responses of soil biological parameters as indicator of ecological status on PAH-contaminated soil.

Materials and methods

Studies are conducted on the soils and natural grassy vegetation of monitoring plots subjected to Novocherkassk power station (NPS) emissions. Monitoring plots were established at different distances from the NPS (1.0–20.0 km).

Results and discussion

The level of polycyclic aromatic hydrocarbons (PAHs) around NPS is the highest at the monitoring plot located at distance 1.6 km to the northwest through the prevailing wind direction. Gradually, decrease of PAHs was observed while increasing the distance from the NPS through the prevailing wind direction. Calculation of correlations between PAH level and biological activity parameters of soils showed lack of dependence with total and every PAH content in all 12 studied monitoring plots. The most significant correlations were found between PAH content and enzyme activity in the monitoring plots situated through the prevailing wind direction from NPS.

Conclusions

The main pollution source in the studied area is NPS. It was found that contamination of soil by PAHs has a direct dependence on the activity of all biological communities in chernozems, as well as the activities of dehydrogenase and the phytotoxicity of soils. Inverse correlations have been revealed between the PAH contamination and abundance of soil bacteria.

     

Contamination of highly weathered urban soils in Uberlândia,Brazil

We determined heavy metal, polycyclic aromatic hydrocarbon (PAH), and polychlorinated biphenyl (PCB) concentrations in 18 topsoils of Uberlândia (420,000 inhabitants, Brazil) and in 3 rural topsoils. Concentrations of Al (11—124 g kg^—1) and Fe (13—109 g kg^—1) are large because of desilification. Concentrations of Cd (0.1—0.5 mg kg^—1), Cr (13—72), Cu (6—154), Mn (28—974), Ni (4—29), Pb (3—26), Zn (4—107), the sum of 20 PAHs (=Σ20PAHs:7—390 μg kg^—1), and the sum of 14 PCBs (=Σ14PCBs:0.05—1.25) are comparable to or below background concentrations in temperate soils except for Cu at two sites. More than 67% of the metals are strongly bound in Fe oxides and silicates; metals are more bioavailable in the urban than in the rural soils. The most abundant PAHs in the urban soils, on average, are naphthalene (19.0 ± 13.4% of Σ20PAHs) and the benzo(b+j+k)fluoranthenes (11.4 ± 6.7%); the most abundant PCBs are nos. 138 (23.3 ± 11.0% of Σ14PCBs) and 153 (14.3 ± 6.4%). The rural soils contain larger percentages of low molecular PAHs and up to tetra‒chlorinated PCBs than the urban soils. The different pollutant concentrations and patterns in the studied tropical compared with many temperate soils indicate different sources and fate.     

Trace elements and polycyclic aromatic hydrocarbons in road gully sediments from different land uses,Hong Kong

Purpose

This study investigated the concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), zinc (Zn), and polycyclic aromatic hydrocarbons (PAHs) in sediments collected from gully pots for road drainage in Hong Kong. The presence and intensity of anthropogenic contamination of road gully sediments were assessed. Identifications of potential sources of trace elements and PAHs were performed to help understand the situation for future control of pollution to the land and aquatic environments.

Materials and methods

Gully sediment samples were collected from gully pots of 18 roads that are potentially exposed to different pollution sources in Hong Kong. The selection of roads considered different road features, adjacent land uses, and traffic volumes. Composite samples were collected for the analysis of trace elements (Cd, Cr, Cu, Pb, Ni, and Zn) and PAHs by an accredited environmental testing laboratory. Geo-accumulation index (I_geo), contamination factor (C_f), modified degree of contamination (mC_d), ecological risk factor (Er), and pollution load index (PLI) were used to assess the level of ecological risk of trace element contamination. Positive matrix factorization (PMF) and PAH diagnostic ratios were applied to identify the sources of trace elements and PAHs.

Results and discussion

Elevated trace element concentrations were commonly found in gully sediments. The concentrations of Zn (267–3700 mg kg^?1) were the highest compared to the other trace elements. Noticeable high concentrations of Cu (27–1020 mg kg^?1), Pb (21–332 mg kg^?1), and Cr (14–439 mg kg^?1) were found in all samples. The PAH contents were moderate to high (0.6 to 24.7 mg kg^?1). Commercial/industrial emissions and road features that cause frequent acceleration-deceleration and turning events showed important influences on the contaminant levels. Strong correlations between the concentrations of Cd, Cr, Pb, and Zn were identified, implying that these trace elements are likely from common sources. The contamination assessment indices reflect significant sediment pollution. The ecological risk ranges from the considerable/moderate-risk class to over the high-risk class.

Conclusions

The collected gully sediments are identified as highly contaminated and need to be isolated from the environment upon final disposal. Through the comprehensive analysis of the collected data, this study provides a detailed insight into the contaminant levels of road gully sediments and potential sources of contamination. Disposal of gully sediments and potential impacts due to release of contaminants into the downstream aquatic environment during rainstorm events should receive attention and need further investigation.

     

Toxicity of imidacloprid to the earthworm Eisenia andrei and collembolan Folsomia candida in three contrasting tropical soils

Purpose

Imidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.

Materials and methods

Acute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.

Results and discussion

Acute toxicity for collembolans and earthworms was higher in Entisol (LC₅₀?=?4.68 and 0.55 mg kg^?1, respectively) when compared with TAS (LC₅₀?=?10.8 and 9.18 mg kg^?1, respectively) and Oxisol (LC_{50collembolans}?=?25.1 mg kg^?1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC_{50 TAS}?=?0.80 mg kg^?1; EC_{50 OXISOL}?=?0.83 mg kg^?1), whereas higher toxicity was observed in Entisol (EC₅₀?=?0.09 mg kg^?1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC₅₀?=?0.21 mg kg^?1) when compared to TAS (EC₅₀?=?1.89 mg kg^?1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.

Conclusions

The toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.

     

Identifying sources of polycyclic aromatic hydrocarbons (PAHs) in soils: distinguishing point and non-point sources using an extended PAH spectrum and <Emphasis Type="Italic">n</Emphasis>-alkanes

Background, aim, and scope  Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants. They are formed during pyrogenic and diagenetic processes and are components of petrogenic materials such as oils and coals. To identify PAH sources, several studies have employed forensic methods, which may be costly to execute. Although a large number of possible forensic methods are available (e.g., total ion chromatograms, PAH ratios, PAH alkyl homologue series, isoalkanes and isoprenoids, steranes and terpanes, stable isotope ratios, n-alkanes), one has to decide which method is the appropriate cost effective screening approach. In this study, three approaches were tested and compared by measuring (1) an extended PAH spectrum (i.e., 45 instead of the common 16 EPA-PAHs), (2) PAH ratios and (3) n-alkanes to determine if point sources are distinguishable from non-point sources, and if an individual source can be distinguished from a multiple source contaminated site in the study area. In addition, the study evaluated whether these methods are sufficient for source identification of selected samples, and if they constitute a sound strategy for source identification prior to the selection of more cost intensive methods. Materials and methods  Eighteen samples with previously characterized PAH point sources (previously characterized point sources in the Mosel and Saar region) were analyzed. Additionally, three river bank soils of Mosel and Saar rivers with known non-point PAH sources were investigated. The point sources were two gasworks, a tar impregnation facility, a creosoted timber, an acid tar, a tank farm, and a diesel contaminated site. Non-point sources were hard coal particles and atmospheric inputs in river bank soils. All samples were extracted with hexane and acetone, analyzed with a gas chromatograph coupled to a mass spectrometer for PAH distribution patterns and ratios. n-Alkanes were measured by a gas chromatograph equipped with a flame ionization detector. Results  Samples collected from point sources and non-point sources were analyzed by the use of three forensic methods, i.e., PAH patterns of an extended PAH spectrum, PAH ratios and n-alkanes. Identification by PAH patterns alone was insufficient for the non-point sources and some point sources, since the n-alkanes must be measured, as well. The use of PAH ratios with only 16 EPA-PAHs is less indicative in determining multiple sources because source assignments (or categories) change depending on the ratio used. Discussion  This study showed that by employing an extended PAH spectrum it is possible to fingerprint and distinguish sources. The use of alkylated PAHs is essential for identifying petrogenic sources. It is insufficient to rely exclusively on either the common 16 EPA-PAHs or the ratios to the parent PAHs when identifying non-point sources. Source identification using PAH ratios is only reliable if both parent and alkylated PAHs are measured. n-Alkane analyses provide more detailed information about petrogenic sources by verifying the presence of oils, diesel, gasoline, or coal in non-point sources. Conclusions  The three methods tested were deemed sufficient to distinguish between point and non-point PAH sources in the samples investigated. The use of an extended PAH spectrum provides the first step toward identifying possible sources. It simplifies the decision whether additional forensic methods should be necessary for more detailed source identification. Recommendations and perspectives  The determination of PAH alkyl homologue series, biomarkers, and isotopes is often advised (Kaplan et al., Environ Forensics 2:231–248, 2001; Oros and Simoneit, Fuel 79:515–536, 2000; Wang and Fingas, Mar Pollut Bull 47:423–452, 2003). The methods involved are complex and often expensive. We recommend a relatively uncomplicated and cost-effective method (i.e., extended PAH spectrum) before further and more expensive forensic investigations are to be conducted. Additional research with an extended sample set should be carried out to validate these findings for other sources and sites. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

SYNOPSIS Polycyclic Aromatic Hydrocarbons (PAHs) in Soil — a Review

PAHs are mainly produced by combustion processes and consist of a number of toxic compounds. While the concentrations of individual PAHs in soil produced by natural processes (e.g., vegetation fires, volcanic exhalations) are estimated to be around 1—10 μg kg⁻¹, recently measured lowest concentrations are frequently 10 times higher. Organic horizons of forest soils and urban soils may even reach individual PAH concentrations of several 100 μg kg⁻¹. The PAH mixture in temperate soils is often dominated by benzofluoranthenes, chrysene, and fluoranthene. The few existing studies on tropical soils indicate that the PAH concentrations are relatively lower than in temperate soils for most compounds except for naphthalene, phenanthrene, and perylene suggesting the presence of unidentified PAH sources. PAHs accumulate in C‐rich topsoils, in the stemfoot area, at aggregate surfaces, and in the fine‐textured particle fractions, particularly the silt fraction. PAHs are mainly associated with soil organic matter (SOM) and soot‐like C. Although the water‐solubility of PAHs is low, they are encountered in the subsoil suggesting that they are transported in association with dissolved organic matter (DOM). The uptake of PAHs by plants is small. Most PAHs detected in plant tissue are from atmospheric deposition. However, earthworms bioaccumulate considerable amounts of PAHs in short periods. The reviewed work illustrates that there is a paucity of data on the global distribution of PAHs, particularly with respect to tropical and southern hemispheric regions. Reliable methods to characterize bioavailable PAH pools in soil still need to be developed.     

Distribution of polycyclic aromatic hydrocarbons (PAHs) in floodplain soils of the Mosel and Saar River

Background, Aim and Scope  Polycyclic aromatic hydrocarbons (PAHs) have gained serious attention in the scientific community due to their persistence and toxic potential in the environment. PAHs may pose a risk to ecosystem health. Along the Mosel River/Germany, a tributary of the river Rhine, PAHs were found at significantly high concentrations (> 20 mg kg⁻¹, German national guideline value Z2, LAGA 1998). These high concentrations were detected during the construction of a storm water retention basin, in which the contaminated soils had to be removed and treated as hazardous waste. This resulted in higher construction costs for implementing flood prevention measures, but did not address the origin of these PAHs and its distribution along Mosel River. Hence, for future flood prevention projects, it is necessary to estimate the extent of PAH contamination along the Mosel River. The aim of the study is to determine the extent of PAH contamination in soils collected along Mosel and Saar River, and to obtain a first insight into the origin of the PAH contamination in this region. Materials and Methods  In total twenty seven sample sites were investigated. Forty two single samples were collected along a 167 km distance of Mosel River and six samples were collected along a 20 km distance of Saar River. Soil samples were collected at a depth of 0 to 2 m with a stainless steel corer (▫ 8 cm). Each 2 m sample was further separated into two sub-samples (0–1 m and 1–2 m). The sixteen EPA PAHs and three additional PAHs (1methylnaphthalene, 2methylnaphthalene and perylene) were analysed with gas chromatography mass spectrometry (GC-MS). For soil characterisation, total organic carbon (TOC), grain size, microscope and X-ray diffraction (XRD) analysis were performed. Results  Grain size for all soil samples was classified as a mixture of sand and silt. XRD analysis showed that all samples were dominated by quartz. Some clay minerals, such as illite and montmorillonite and feldspars, i.e. anorthoclase and orthoclase, were found in minor quantities. TOC ranged from 0.1% to 13%. Microscope analysis showed black coal particles in the majority of the soils collected from the Saar River and part of the Mosel River (downstream of the confluence of Saar and Mosel River). The black particles were not found further upstream along Mosel River. The sum of nineteen PAHs in the soil samples was up to 81 mg kg⁻¹ dry weight (dw). Most soil samples showed a relationship between the presence of coal particles and PAH concentrations. Discussion  Elevated PAH concentrations were found in all soil samples collected from Saar River and downstream Mosel River. Due to former coal mining activities in the Saarland, Germany, there is a strong evidence that the majority of the PAH contamination in the soils downstream Mosel River are linked to these mining activities. Upstream Mosel River coal particles were hardly found although PAH concentrations were high. Therefore another PAH source has to be responsible for these concentrations. PAH distribution patterns indicate a pyrogenic PAH input upstream Mosel River and a mixed input (petrogenic and pyrogenic) downstream Mosel River. Conclusions  Due to PAH distribution patterns, the contamination along the upstream of the Mosel River is probably linked to atmospheric depositions and other sources not linked to coal mining activities. Downstream Mosel River the PAH distribution patterns reflect former coal mining activities. We could corroborate for the first time that coal mining resulted in a serious problem of an extensive PAH contamination at Saar and Mosel River floodplain soils. Recommendations and Perspectives  Coal mining activities have a strong impact on the neighbouring regions (Johnson and Bustin 2006, Short et al. 1999, Stout et al. 2002). It is known that coals exhibit relative high PAH concentrations, especially in the low molecular weight PAHs (Chapman et al. 1996, Radke et al. 1990). However, PAHs in coals are hardly bioavailable (Chapman et al. 1996) and hence may have less adverse effects on exposed biota. They can act as sink for other hydrophobic contaminants. For the assessment of the environmental impact, a detailed study of the sorption and desorption behaviour of PAHs linked to coal particles should be carried out. ESS-Submission Editor: Dr. Ralph Portier (rportie@lsu.edu)     

Optimization of portable X-ray fluorescence spectrometry for the assessment of soil total copper concentrations: application at an ancient smelting site

Purpose

Copper (Cu) is the earliest anthropogenic metal pollutant, but knowledge of Cu soil concentrations at ancient metalworking sites is limited. The objective of this work was to examine the ability of portable X-ray fluorescence to quantify Cu in soils at such sites.

Materials and methods

Using a Bruker Tracer III-SD pXRF, we examine factory “scan” settings versus simple instrument parameter changes (a reduction in energy settings from 40 to 12 kV) to target analysis for Cu. We apply these to a set of uncontaminated samples (n?=?18, <?92 mg Cu kg^?1) from Central Thailand and compare results to standard wet chemistry analysis (aqua regia digestion and ICP-OES analysis). We then apply the optimized method to a set of highly contaminated samples (n?=?86, <?14,200 mg Cu kg^?1) from a known ancient smelting site.

Results and discussion

We demonstrate that simple changes to factory recommended “scan” settings can double the sensitivity of Cu determination via pXRF (“optimized limit of determination” of 19.3 mg kg^?1 versus an initial value of 39.4 mg kg^?1) and dramatically improve the accuracy of analysis. Changes to other results for other elements are variable and depend on concentration ranges, soil matrix effects, and pXRF response for the individual element. We demonstrate that pXRF can accurately determine Cu across a wide concentration range and identify grossly contaminated soil samples.

Conclusions

We conclude that pXRF is a useful tool to rapidly screen and analyse samples at remote sites and can be applied to ancient metalworking sites. Simple optimization of the pXRF settings greatly improves accuracy and is essential in determining comparative background concentrations and “unaffected” areas. Application to other elements requires further element and matrix specific optimization.

     

Rubidium measured by XRF as a predictor of soil particle size in limestone and siliceous parent materials

Purpose

Information about particle size distribution (PSD) and soil texture is essential for understanding soil drainage, porosity, nutrient availability, and trafficability. The sieve-pipette/gravimetric method traditionally used for particle size analysis is labour-intensive and resource-intensive. X-ray fluorescence (XRF) spectrometry may provide a rapid alternative. The study’s aim was to examine the use of XRF for rapid determination of PSD in Irish soils.

Methods

Soils (n?=?355) from existing archives in Ireland were analysed with a benchtop energy-dispersive XRF (EDXRF). Correlation and regression analyses were determined to compare Rb, Fe, Al, and Si concentrations to % clay, % silt, and % sand. Also, linear regression models were developed to compare % clay, % sand, and % silt measured by the gravimetric method to values predicted by EDXRF.

Results

The relationship between element concentration and PSD was dependent on parent material. Rb, Al, and Fe showed a significant (p?<?0.05) correlation (r?>?0.50) with % clay and % sand in soils derived from limestone and siliceous stone parent materials. Rb was the best predictor for % clay (R²?=?0.49, RMSE?=?10.20) in soils derived from limestone and siliceous stone-derived soils.

Conclusion

Geochemistry and clay mineralogy of the soils’ parent material strongly influenced the EDXRF’s ability to predict particle size. The EDXRF could predict % clay in soils from parent materials which weather easily, but the opposite was true for soils with parent material recalcitrant to weathering. In conclusion, this study has shown that the EDXRF can screen % clay in soils derived from limestone and siliceous stone parent materials.

     

Soil slaking sensitivity as influenced by soil properties in alluvial and residual humid tropical soils

Purpose

In the humid Caribbean region characterized by high-intensity tropical rainfall, soil aggregate breakdown and pore blocking due to slaking pressures are major land degradation mechanisms. In this research, we investigated the susceptibility of soils to slaking pressures under rapid wetting as influenced by soil properties and the depositional origin from which the soil is formed using water-stable aggregates (WSAr) and percolation stability (PSc) as indices of the strength of aggregate inter-particle cohesion.

Materials and methods

Wet sieving and percolation stability analyses were employed to investigate WSAr and pore blocking, respectively. The combined effect of soil properties of clay, organic matter (OM), cation exchange capacity (CEC), and exchangeable sodium percentage (ESP) was used to determine the slaking sensitivity score (SSc) of 14 physiogeographically important soils in Trinidad, comprising of nine alluvial and five residual soils.

Results and discussion

Results showed that irrespective of alluvial or residual depositional nature of the parent material, samples had high SSc with an average WSAr of 37.8% and PSc of 6.0 mm/10 min. The linear relationships between SSc with WSAr (r²?=???0.12) and SSc with PSc (r²?=???0.012) of all the 14 soils although negative were weak. Clay content accounted for 94.0% of the variation in CEC in alluvial soils and had strong negative relationships with WSAr (r²?=???0.74) and PSc (r²?=???0.79) in residual soils. Additionally, OM with WSAr (r²?=?0.52) and PSc (r²?=?0.24), and CEC with WSAr (r²?=?0.46) and PSc (r²?=?0.39) showed significant positive linear relationships in residual soil.

Conclusions

The predominantly micaceous and kaolinitic clay mineralogy of these soils, coupled with the low OM contents, increases the proneness of the soils to slaking. This suggests that clay mineralogy is responsible for the high slaking sensitivity rather than clay content or just the depositional origin of the soils. As CEC increases, an accompanying increase in OM is required to increase inter-particle cohesion and to impart partial hydrophobicity, which in turn decreases mineralogically induced susceptibility of individual aggregates to slaking.

     

Polycyclic Aromatic Hydrocarbons, Polychlorinated Biphenyls and Trace Metals in Sediments from a Coastal Lagoon (Northern Adriatic, Italy)

Surface sediments (0–5 cm) were analysed to provide information on levels, spatial trends and sources of the 16 USEPA polycyclic aromatic hydrocarbons (PAH), 15 polychlorinated biphenyls (PCBs) and trace metals (copper, chromium, mercury, nickel and zinc) in channel and wetland habitats of Pialassa Baiona lagoon (Italy). The highest levels of PAHs, PCBs and Hg (3,032–87,150, n.d.–3,908 and 1.3–191 mg kg⁻¹) were mainly found at channel habitats close to industrial sources. Pyrogenic PAH inputs were significant, with a predominance of four-ring PAHs and combustion-related PAHs in both channel and wetland habitats. Among PCB congeners, chlorination class profiles show that penta- and hexachlorinated PCBs are the most prevalent homologues accounting for approximately 33% and 47% of the total PCB concentrations in channel sediments. Total toxicity equivalent factors (TEQs) of potentially carcinogenic PAHs varied from 348 to 7,879 μg kg⁻¹ and from 4.3 to 235 μg kg⁻¹ in channel and wetland sediments; calculated TEQs for dioxin-like PCB congeners at channel habitats ranged from n.d. to 86.7 μg kg⁻¹. Comparison of PAHs, PCBs and metal levels with Sediment Quality Guidelines suggests that more concern should be given to the southern area of the lagoon for potential risks of carcinogenic PAHs, dioxin-like PCBs and mercury.     

Persistent organic pollutant concentrations in air‐ and freeze‐dried compared to field‐fresh extracted soil samples of an eastern Slovak deposition gradient

Sample preparation affects the results of the determination of persistent organic pollutant (POP) concentrations in soils. We compared the extraction results of POPs from air‐ and freeze‐dried with field‐fresh samples. We determined the concentrations of 21 polycyclic aromatic hydrocarbons (PAHs) and 14 polychlorinated biphenyls (PCBs) in 35 horizons of forest soils (Lithosols and Cambisols) along a deposition gradient caused by a chemical factory in Strá?ske (eastern Slovakia). The organic C (C_org) concentrations of the studied samples ranged 14‐477 g kg^‐1, the sum of 21 PAH (Σ 21PAHs) concentrations 53‐6870 μg kg^‐1, and that of 14 PCBs (Σ 14PCBs) 0.12 96 μg kg^‐1. The benzofluoranthenes were the most abundant PAHs, and the hexa‐chlorinated PCBs 138 and 153 were the most abundant PCBs. The deposition gradient was reflected by decreasing PAH and PCB storages in the organic layer with increasing distance from the chemical factory (Σ 21PAHs: 82‐238, Σ 14PCBs: 0.34‐2.3 g ha^‐1). The PAH concentrations in air‐ and freeze‐dried samples were consistently lower than those in field‐fresh extracted samples. For naphthalene, this was mainly attributable to volatilization losses during drying. Naphthalene losses decreased with increasing C_org concentrations. For all other PAHs, drying reduced the extractability; the latter was correlated with the water content of the samples. The differences in most PCB concentrations among the sample preparation methods were small (within the determination error of ±15 %) and inconsistent. However, PCBs 8, 28, 52, and 209 had markedly higher concentrations in dried than in fieldfresh extracted samples. The increased recovery of low‐chlorinated PCBs in dried samples may be explained by redistribution of PCBs from higher to lower contaminated samples via the drying room atmosphere because there were no PCBs in analytical blanks. This assumption is supported by a close correlation between the octanol‐air distribution coefficient and the up to hexa‐chlorinated PCB concentrations (normalized to those in field‐fresh extracted samples) in air‐ (r = ‐0.90) and freeze‐dried (r = ‐0.86) samples. Our study shows that each sample preparation method has its specific advantages and disadvantages. Sample drying results in a standardization to a well‐defined water content and facilitates homogenization; therefore it increases the reproducibility of POP determinations. Extraction of field‐fresh samples reduces volatilization losses and contamination risks.     

Fractionated extraction of polycyclic aromatic hydrocarbons (PAHs) from polluted soils: estimation of the PAH fraction degradable through bioremediation

Chemical extractions were tested to estimate the fraction of 15 polycyclic aromatic hydrocarbons (PAHs) in polluted soils degradable through bioremediation. Of 30 soil samples, differing in PAH concentrations, from 10 long‐term polluted sites, four were used in screening tests conducted with 14 different extractants. PAH extractability increased in the order salt solutions < surfactant solutions < organic solvents and organic solvent–water mixtures. Closest correlations (r = 0.73–0.91) and ratios of c. 1:1 of the extracted to the degradable PAH concentrations were found with aqueous solutions of two surfactants (Genapol UDD 88, Synperonic LF/RA 30). The PAH extractability by surfactant solutions increased with surfactant concentration (0–50 mg ml^?1) and with decreasing degree of PAH condensation (6–2 rings). Kinetic behaviour of PAH solubilization by surfactants resembled the kinetics of PAH degradation (r = 0.84–0.99). With repeated extractions, a finite fraction of PAHs was extracted, which is thought to be the mobile and mobilizable PAH fraction, the latter being controlled by back‐diffusion from intra‐ and inter‐particle sites. Experiments with all 30 soil samples and a priori testing with an additional 10 soil samples confirmed that single extractions with surfactant solutions (5 mg ml^?1; soil:solution ratio 1:20) were suitable for estimating the degradable fraction of PAHs in soil. With separate linear regression equations for PAHs grouped according to their degree of condensation, the extracted concentrations described the degradable concentrations with correlation coefficients (r) ranging from 0.62 to 0.80 (P < 0.001). PAH extractions with the surfactant solutions can be used to assess the prospects of bioremediation of PAH‐polluted sites.     

Characterization and Sources of PAHs and Potentially Toxic Metals in Urban Environments of Sevilla (Southern Spain)

The purpose of this study was to determine the degree of PAH contamination and the association of PAHs with metals in urban soil samples from Sevilla (Spain). Fifteen polycyclic aromatic hydrocarbons-PAHs (naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene, indeno[1,2,3-c,d]pyrene) and seven metals (Cd, Cr, Cu, Mn, Ni, Pb, Zn) have been evaluated in representative urban soil samples. Forty-one top soils (0–10 cm) under different land use (garden, roadside, riverbank and agricultural allotment) were selected. PAHs from soil samples were extracted by sonication using dichloromethane. The simultaneous quantification of 15 different PAH compounds were carried out by HPLC using multiple wavelength shift in the fluorescence detector. For qualitative analysis a photo diode-array detector was used. Metal (pseudo-total) analysis was carried out by digestion of the soils with aqua regia in microwave oven. The mean concentration of each PAH in urban soils of Sevilla showed a wide range, they are not considered highly contaminated. The results of the sum of 15 PAHs in Sevilla soils are in the range 89.5–4004.2 μg kg^?1, but there seems not to be a correlation between the concentration of PAHs and the land use. Of the 15 PAHs examined, phenanthrene, fluoranthene and pyrene were present at the highest concentrations, being the sum of these PAHs about 40% of the total content. Although metal content were not especially high in most soils, there are significant hints of moderate pollution in some particular spots. Such spots are mainly related with some gardens within the historic quarters of the city. The associations among metals and PAHs content in the soil samples was checked by principal components analysis (PCA). The largest values both for ‘urban’ metals (Pb, Cu and Zn) and for PAHs were mainly found in sites close to the historic quarters of the city in which a heavy traffic of motor vehicles is suffered from years.     

Redistribution of organic pollutants in river sediments and alluvial soils related to major floods

Background, Aims, and Scope  More frequent occurrence of stronger floods in Europe as well as in other parts of the world in recent years raises major concern about the material damages, but also an important issue of contamination of the affected areas through flooding. The effects of major floods on levels and distribution of contamination with hydrophobic organic pollutants were examined from the continuous set of data for floodplain soils and sediments from a model industrial area in the Czech Republic where a 100-year flood occurred in 1997. The goal of this study was to evaluate the risk related to contamination associated with such extensive natural events and characterize the spatial and temporal distribution and dynamics of pollutants related to a major flooding shortly after the floods and also in the time period several years after floods. Methods  Sediments and alluvial soils from fourteen sites each were repeatedly sampled during the period from 1996 until 2005. The sampling sites represented five regions. Collected top-layer sediment and soil samples were characterized and analyzed for hydrophobic organic pollutants PCBs, OCPs and HCB using GC-ECD and PAHs using a GC-MS instrument. Spatial and temporal differences as well as the relative distribution of the pollutants were examined in detail by statistical analysis including multivariate methods with special emphases placed on the changes related to floods. Results  The organic pollutants levels in both alluvial soils and sediments exceeded the safe environmental limits at numerous sites. Pollutants concentrations and relative distribution as well as organic carbon content in both sediment and floodplain soils were significantly affected by the flooding, which resulted in a decrease of all studied contaminants in sediments and significant rise of the PAH pollution in the flooded soils. There was a unique and highly conserved PAH pattern in soils regardless of the floods and greater changes in PAH pattern in sediments related to floods. The relative distribution of individual PAHs reflected a combustion generated PAH profile. PAH levels in the river sediments rose again at the sites with continuous sources several years after floods. Discussion  The results showed different dynamics of PAHs and PCBs during the floods when PAHs were redistributed from the sediments to alluvial soils while PCBs have been washed out of the study regions. The data reveal longer contamination memory and consistent contamination pattern in soils, whereas sediments showed more dynamic changes responding strongly to the actual situation. The stable PAH pattern within the regions also indicates that a relative amount of all compounds is comparable across the samples and, thus, that the sources at different sites have similar character. Conclusions  Sediments have the potential to function as a secondary source of contamination for the aquatic ecosystem, but also for the floodplain soils and other flooded areas. The floods served as a vector of PAHs contamination from sediments to soils. The reloading of river sediments in time, namely with PAHs, due to present sources increases their risk as a potential source in the next bigger flood event both to the downstream river basin and affected alluvial soils. Recommendations and Perspectives  The results stress the importance of including the floodplain soil contamination in the risk assessment focused on flood effects. Floodplain soils have stable long-term environmental memory related to contamination levels, pattern and distribution, whereby they can provide relevant information on the overall contamination of the area. The sediments will continue to serve as a potential source of contaminants and alluvial soils as the catchment media reflecting the major flood events, especially until effective measures are taken to limit contamination sources. ESS-Submission Editor: Dr. Henner Hollert (Hollert@uni-heidelberg.de) This article is openly accessible!