Polycyclic Aromatic Hydrocarbons In Contaminated Soil Research Articles

Remediation of Polycyclic Aromatic Hydrocarbon-Contaminated Soil by Using Activated Persulfate with Carbonylated Activated Carbon Supported Nanoscale Zero-Valent Iron

Soil contamination by polycyclic aromatic hydrocarbons (PAHs) has been an environmental issue worldwide, which aggravates the ecological risks faced by animals, plants, and humans. In this work, the composites of nanoscale zero-valent iron supported on carbonylated activated carbon (nZVI-CAC) were prepared and applied to activate persulfate (PS) for the degradation of PAHs in contaminated soil. The prepared nZVI-CAC catalyst was characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). It was found that the PS/nZVI-CAC system was superior for phenanthrene (PHE) oxidation than other processes using different oxidants (PS/nZVI-CAC > PMS/nZVI-CAC > H2O2/nZVI-CAC) and it was also efficient for the degradation of other six PAHs with different structures and molar weights. Under optimal conditions, the lowest and highest degradation efficiencies for the selected PAHs were 60.8% and 90.7%, respectively. Active SO4−• and HO• were found to be generated on the surface of the catalysts, and SO4−• was dominant for PHE oxidation through quenching experiments. The results demonstrated that the heterogeneous process using activated PS with nZVI-CAC was effective for PAH degradation, which could provide a theoretical basis for the remediation of PAH-polluted soil.

Polycyclic aromatic hydrocarbons (PAHs) pollution and risk assessment of soils at contaminated sites in China over the past two decades

With rapid urbanization in China, soil pollution at contaminated sites has emerged as a significant concern in the environmental protection plan. Moreover, extensive research has focused on the analysis of other major contaminants. However, over the past two decades, only a few studies have systematically analyzed polycyclic aromatic hydrocarbons (PAHs) in contaminated soils, particularly their source identification, contamination level assessment, and risk evaluation. This study addressed these research gaps by comprehensively evaluating soil PAHs contamination at these sites through the collection and screening of relevant literature data from the past 20 years using a “front page filtering” approach. The results suggested that the most contaminated sites in China were associated with petrochemical plants, steel mills, and coking plants. Coal/biomass burning emerged as the predominant source of PAHs pollution in the soils of contaminated sites across China. Overall, the soils of contaminated sites exhibited relatively low levels of PAHs contamination. The single-factor index method showed that benzo(a)pyrene (BaP) was the PAH monomer with the highest contamination level. Geographically, Northeast and North China exhibited relatively higher contamination levels and ecological risks. Moreover, PAHs posed significant health hazards, as they exhibited significantly high toxic effects on the respiratory system, carcinogenicity, aromatic hydrocarbon receptors, estrogen receptors, and antioxidant response elements. Additionally, children and youths faced higher health risks than adults. The findings from this study provide a solid basis for developing strategies to manage PAHs at contaminated sites in China.

ECOLOGICAL AND HUMAN HEALTH RISKS ASSOCIATED WITH SOIL POLLUTION BY PAHS AND HEAVY METALS IN THE NIGER DELTA

Despite the prevalence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) in Niger Delta's crude oil regions, comprehensive research on their concentrations and combined risks in crude oil-contaminated soils is lacking. Our study focused on examining the concentration, source, spatial distribution, and health risk of 16 PAHs and 9different HMs in soils across a gradient of Niger Delta area Nigeria. The objective was to gain a comprehensive understanding of the HMs and PAHs' behavior in the environment and their potential impact on human health. The mean total concentrations of 16 PAHs (Σ16PAHs) were 779.58 ng/g for upland area, 749.46 ng/g for mid-slope area, and 679.37 ng g-1 for Low-land. The concentration of the HMs followed the order of Cu > Cd > Ni > Pb > Cr > Fe > Mn > Zn > Co, with Cu, Cd, Ni, and Pb exceeding the permissible levels. The study areas displayed varying concentrations of NO3-, PO42-, SO42- Ca, Na, and K, with some levels exceeding acceptable values, possibly influenced by crude oil contamination and the use of fertilizers. In the Niger Delta regions, the primary sources of soil PAH contamination include crude oil spills, natural crude oil seepage, and coal combustion. With this, the government of Nigeria should strengthen soil contamination monitoring, enforce spill regulations and promote eco-friendly farming.

Drivers distinguishing of PAHs heterogeneity in surface soil of China using deep learning coupled with geo-statistical approach

Although numerous studies have reported the influencing factors of polycyclic aromatic hydrocarbons (PAHs) in surface soil from source, process or soil perspectives, the mechanism of PAHs heterogeneity in surface soil are still not well understood. In this study, the effects of 16 PAHs in surface soil of China sampled between 2003 and 2020 with their 17 “source-process-sink” factors at 1 km resolution (N = 660)) were explored using deep learning (eXtreme Gradient Boosting) to mine key information from complex dataset under the optimized parameters (i.e., learning rate = 0.05, maximum depth = 5, sub-sample = 0.8). It was observed that top five factors of 16 PAH had the largest cumulative contribution (i.e., from 84.8% to 98.1%) on their soil concentrations. PAH emission was the predominant driver, and its effect on soil PAH increases with increasing logKow. Soil was the second driver, in which clay can promote the partition of PAHs with low or middle logKow. However, sand can accumulate those congeners with high logKow. Moreover, the deep learning plus geo-statistical models (with low deviation for testing dataset (N = 283)) were capable of predicting soil PAH concentrations using their drivers with high accuracy. This study improved the understanding of the environmental fate and spatial variability of soil PAHs, as well as provided a novel technique (i.e., deep learning coupled with geo-statistics) for accurate prediction of soil pollutants.

Relationships among protozoa, bacteria and fungi in polycyclic aromatic hydrocarbon-contaminated soils

Soil bacterial and fungal communities play key roles in the degradation of organic contaminants, and their structure and function are regulated by bottom-up and top-down factors. Microbial ecological effects of polycyclic aromatic hydrocarbons (PAHs) and trophic interactions among protozoa and bacteria/fungi in PAH-polluted soils have yet to be determined. We investigated the trophic interactions and structure of the microbiome in PAH-contaminated wasteland and farmland soils. The results indicated that the total concentration of the 16 PAHs (∑PAHs) was significantly correlated with the Shannon index, NMDS1 and the relative abundances of bacteria, fungi and protozoa (e.g., Pseudofungi) in the microbiome. Structural equation modelling and linear fitting demonstrated cascading relationships among PAHs, protozoan and bacterial/fungal communities in terms of abundance and diversity. Notably, individual PAHs were significantly correlated with microbe-grazing protozoa at the genus level, and the abundances of these organisms were significantly correlated with those of PAH-degrading bacteria and fungi. Bipartite networks and linear fitting indicated that protozoa indirectly modulate PAH degradation by regulating PAH-degrading bacterial and fungal communities. Therefore, protozoa might be involved in regulating the microbial degradation of PAHs by predation in contaminated soil.

Low-temperature thermally enhanced bioremediation of polycyclic aromatic hydrocarbon-contaminated soil: Effects on fate, toxicity and bacterial communities

Remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil using thermal desorption technology typically requires very high temperatures, necessitating coupled microbial treatment for energy and cost reduction. This study investigated the fate and toxicity of PAHs as well as the responses of microbial communities following thermal treatment within a low temperature range. The optimal temperature for PAH mineralization was 20–28 °C, within the growth range of most mesophilic microorganisms. By contrast, 50 °C treatment almost completely inhibited PAH mineralization but resulted in the greatest detoxification effect particularly for cardiotoxicity and nephrotoxicity. A potential increase in toxicity was observed at 28 °C. Co-metabolism and non-extractable residue formation may play an interdependent role in thermally enhanced bioremediation. Moreover, alterations in bacterial communities were strongly associated with PAH mineralization and zebrafish toxicity, revealing that soil microorganisms play a direct role in PAH mineralization and served as ecological receptors reflecting changes in toxicity. Network analysis revealed that Firmicutes formed specific ecological communities at high temperature, whereas Acidobacteria and Proteobacteria act as primary PAH degraders at moderate temperature. These findings will enable better integration of strategies for thermal and microbial treatments in soil remediation.

Activation of persulfate by highly dispersed FeCo bimetallic alloy for in-situ remediation of polycyclic aromatic hydrocarbon-contaminated soil

Design of high-performance, environmentally friendly catalysts for remediation of contaminated soil is critical. Nano-zero-valent iron is widely used for this purpose and has high catalytic activity, but it readily agglomerates, which limits its use. To design efficient, environmentally friendly, and inexpensive soil remediation materials, we developed a Fe/Co-and nitrogen-doped carbon catalyst (FeCo/NC). The Fe and Co on the support were highly dispersed, many active sites were exposed, and the two metals exhibited synergistic catalytic effects. The ability to degrade anthracene in soil was evaluated through activating peroxodisulfate (PDS). The catalytic performance of the dual-doped catalyst was up to 24% more than that of catalysts doped with only Fe or Co. The FeCo/NC@PDS system efficiently removed 98.87% of anthracene from soil after 6 h. Moreover, the catalyst maintained excellent stability in both acidic and alkaline environments. The reaction mechanism was explored using radical quenching experiments combined with ESR spectra. In addition to a radical pathway involving OH, SO4−, and O2−, there was a non-radical pathway involving 1O2. The optimum conditions for use of the catalyst were determined, and possible degradation pathways for anthracene were proposed. This study provides data for the development of in-situ soil remediation catalysts.

Synergic remediation of polycyclic aromatic hydrocarbon-contaminated soil by a combined system of persulfate oxidation activated by biochar and phytoremediation with basil: A compatible, robust, and sustainable approach

A new remediation strategy for polycyclic aromatic hydrocarbon (PAH)-contaminated soil was proposed using a combination of ammonium persulfate (APS) oxidation activated by iron-modified biochar (FBC) and phytoremediation with the aromatic plant, basil. After the 105-day pot experiment, the removal rates of soil total Σ16 PAHs by this combined system reached 61.6%–69.5%. In the combined system, basil grew the best among all treatment groups because the addition of FBC and APS increased the contents of available potassium and nitrogen in soil. The essential oils extracted from basil were deemed free of PAH contamination. High-throughput sequencing of soil bacteria and fungi after 105 days revealed that the advanced oxidation process substantially reduced the richness and diversity of soil microbes, which were restored to the original state by basil. Results indicate that the combined system can remediate the contaminated soil in a synergy by pronouncing the degradative capacity of FBC-APS while mitigating its adverse effects, which is suggested to be an effective, robust, and sustainable approach that holds promise for future site applications.

Heterologous spatial distribution of soil polycyclic aromatic hydrocarbons and the primary influencing factors in three industrial parks

Soil polycyclic aromatic hydrocarbons (PAHs) generated from industrial processes are highly spatially heterologous, with limited quantitative studies on their main influencing factors. The present study evaluated the soil PAHs in three types of industrial parks (a petrochemical industrial park, a brominated flame retardant manufacturing park, and an e-waste dismantling park) and their surroundings. The total concentrations of 16 PAHs in the parks were 340–2.43 × 103, 26.2–2.63 × 103, and 394–2.01 × 104 ng/g, which were significantly higher than those in the surrounding areas by 1–2 orders of magnitude, respectively. The highest soil PAH contamination was observed in the e-waste dismantling park. Nap can be considered as characteristic pollutant in the petrochemical industrial park, while Phe in the flame retardant manufacturing park and e-waste dismantling park. Low molecular weight PAHs (2–3 rings) predominated in the petrochemical industrial park (73.0%) and the surrounding area of brominated flame retardant manufacturing park (80.3%). However, high molecular weight PAHs (4–6 rings) were enriched in the other sampling sites, indicating distinct sources and determinants of soil PAHs. Source apportionment results suggested that PAHs in the parks were mainly derived from the leakage of petroleum products in the petroleum manufacturing process and pyrolysis or combustion of fossil fuels. Contrarily, the PAHs in the surrounding areas could have been derived from the historical coal combustion and traffic emissions. Source emissions, wind direction, and local topography influenced the PAH spatial distributions.

Remediation of polycyclic aromatic hydrocarbon-contaminated soils using microbes and nanoparticles: A review

Polycyclic aromatic hydrocarbon (PAH) pollution is a global concern because of their toxicity to environment and ecosystem, which induces adverse effects on plants, animals, and humans. Hydrocarbons are mainly released from natural and anthropogenic activities, such as incomplete fuel combustion, leakages in oil pipelines, and the extensive use of pesticides; PAH contaminants include petroleum hydrocarbons (PHCs), halogenated hydrocarbons, chlorophenols, and pesticides. Bioremediation using microorganisms such as bacteria and fungi is developing as an effective and promising technique to remediate PAHs from the environment. Owing to their remediation efficiency, this method is environmentally friendly and represents a novel approach for reducing the risk of PAHs to human health and the ecosystem. Nanoparticles may be applied in bioremediation, and will not only induce fewer toxic effects but also reduce the effective overall time and costs involved. This article provides a summary of the application of nanomaterials, bacteria, and fungi to PAH remediation; we review and briefly discuss the structure, properties, sources, fate, toxicity, and remediation approaches involved in the remediation of PAH-polluted sites.

Distribution, risk assessment, and source apportionment of polycyclic aromatic hydrocarbons (PAHs) using positive matrix factorization (PMF) in urban soils of East India.

This study investigated 16 United States environmental protection agency priority PAHs profiles and their sources in 40 urban soils collected from two industrialised cities, Jamshedpur and Bokaro, in east India and assessed their health risk to humans. The results showed the predominance of high molecular weight (HMW) PAHs (4-5 rings). The total PAHs concentration in surface soils ranged from 2223 to 11,266ng/g and 729 to 5359ng/g (dw), respectively, for Jamshedpur and Bokaro. Higher concentrations of PAHs were recorded at the selected industrial areas and heavy traffic zones of both cities. In JSR city 4-ring PAHs contributed 43% of total PAHs trailed by 5-ring PAHs 27.2%. Similarly, in BKR city 4-ring PAHs contributed 34% of the total PAHs, followed by 3-ring PAHs 28.9% and 5-ring PAHs 22.9%. Total organic carbon in surface soils exhibited moderate correlation with the low molecular weight (ΣLMW) PAHs (R2 = 0.69) and a comparatively strong correlation with the ΣHMW PAHs (R2 = 0.89), suggesting strong adsorption of HMW PAHs to urban soils. The Diagnostic and PMF modelling analysis indicated that the major sources of PAHs contamination in soils were petroleum combustion, vehicular emissions, biomass, and coal combustion. The health risk assessment shows that the cumulative probability of carcinogenic risks was under the acceptable limits of 10-4 to 10-6. At some sampling areas in both cities, the maximum value of total exposure cancer risk slightly exceeded the acceptable limits indicating some carcinogenic risk for adults.

Disturbed phospholipid metabolism by three polycyclic aromatic hydrocarbons in Oryza sativa

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants in soils that can be readily absorbed by crops, affecting growth and development. Phospholipids (PLs) are essential components of cell membrane and can indicate cellular responses to various organic pollutants. However, the detailed molecular mechanism of phospholipid metabolism based regulation employed by crops in response to PAHs stresses remains elusive. This study characterized the accumulation patterns of representative PAHs, namely phenanthrene (PHEN), pyrene (PY), and benzo[a]pyrene (BaP) in rice (Oryza sativa). Crop’s responses to PAHs via the regulation of phospholipid metabolism were also explored. PHEN exhibited the highest accumulation in both roots and shoots, followed by PY and BaP, despite PY exhibited much greater phytotoxicity than the other two PAHs. The exposure to 10–500 μg/L PY resulted in downregulations of the phospholipase A2 genes PLA2-3, PLA2-4, and PLA2-6 (to 19% of the control without exposure) and phospholipase C genes PLC-1, PLC-2, and PLC-4 (to 50% of the control), consistent with the changes in phospholipase activity. The contents of typical PLs, including phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidic acid also decreased to a greater extent than those in the PHEN- and BaP-exposed groups. These were the major reasons for the relatively high phytotoxicity of PY, in terms of growth inhibition and cell membrane damage. These findings provide a more comprehensive understanding of crop responses to PAHs and provide insights into risk assessment of soil PAH contamination, which hold potentials in improving food safety and quality worldwide.

Ingestion and Dermal Cancer Risk via Exposure to Polycyclic Aromatic Hydrocarbon-Contaminated Soils in an Oil-Producing Community, Niger Delta, Nigeria.

There is an intrinsic link between polycyclic aromatic hydrocarbons (PAHs) accumulated in soils and increased health risk to humans after exposure to contaminated soil via ingestion, inhalation of particulates carrying PAHs, and direct contact with polluted soils. However, the assessment of PAH contamination in most developing countries fails to consider health risk assessment. Therefore, a comprehensive study was conducted to determine the concentration, source, toxicity, and human health risks of 16 PAHs in an urban area in Warri, Delta State, in the Niger Delta region of Nigeria. The results showed varying contamination levels for PAH in soil samples from all sampling points, with benzo[a]anthracene (BaP; at 338.81 μg/kg) being the most abundant at all 9 sampling stations. The highest total concentration of PAH was observed at station 5 (1230.98 μg/kg), which was closest to a flow station. Further comparison with PAH contamination standards showed that soils from stations 1 and 2 were weakly contaminated (<600 μg/kg), and soil samples from stations 3, 4, 6, 7, and 9 were moderately contaminated (<1000 μg/kg). Soil samples from stations 5 and 8 were observed to be heavily contaminated (>1000 μg/kg). The BaP estimates for soil samples obtained for stations 3 to 9 were higher than the BaP soil screening value (15 μg/kg), indicating a carcinogenic potential of soil samples. The results also showed that the incremental lifetime cancer risk estimates for PAH in the soil for adults and children were above the recommended threshold (10-4 ) for ingestion and dermal contact, implying that exposure to contaminated soil could lead to cancers in adults and children. Currently, there are no regional or national standards for PAHs in soil that would indicate an increased likelihood for human exposure and subsequent health issues. Environ Toxicol Chem 2021;40:261-271. © 2020 SETAC.

Nitric oxide-dependent biodegradation of phenanthrene and fluoranthene: The co-occurrence of anaerobic and intra-aerobic pathways

Polycyclic aromatic hydrocarbons (PAHs) pollution as well as the emissions of nitric oxide (NO) and greenhouse gas nitrous oxide (N2O) in denitrification processes are currently two environmental issues of great concern. Although bioremediation of PAHs under denitrification is considered a promising approach, denitrification was an important contributor to N2O and NO emissions. This long-term study confirmed for the first time that microorganisms could utilize NO to efficiently degrade phenanthrene and fluoranthene. When the two systems of NO-dependent phenanthrene and fluoranthene degradation were stable, the first-order rate constants of phenanthrene and fluoranthene in the two systems (0.1940 and 0.0825 day−1, respectively) were close to those values (0.2290 and 0.1085 day−1, respectively) observed at nitrate-reducing conditions. Further analysis of functional genes revealed that phenanthrene and fluoranthene might be degraded under the combined action of the anaerobic pathway mediated by NO reduction and intra-aerobic pathway mediated by NO dismutation. The genomic analysis showed that Nod genes had high diversity and most of them were similar to aquifer cluster group in the two systems. Microbial community structure analysis indicated that Pseudomonas and Ochrobactrum might be key participants in NO-dependent phenanthrene degradation system, and Azoarcus, Alicycliphilus and Moheibacter might play vital roles in NO-dependent fluoranthene degradation system. This study provides new perspective for anaerobic remediation of PAH pollution and simultaneously reducing NO and N2O emissions during bioprocesses, which has important ecological significance for amending sediment and soil PAHs contamination and potential application for the removal of PAHs in flue gas.

Remediation of Anthracene-Contaminated Soil with Sophorolipids-SDBS-Na2SiO3 and Treatment of Eluting Wastewater

The soil pollution of polycyclic aromatic hydrocarbons (PAHs) is serious in China, which not only affects the living and growing environment of plants and animals but also has a great impact on people’s health. The use of hydrophobic organic compounds to make use of surfactant ectopic elution processing is more convenient and cheaper as a repair scheme and can effectively wash out the polycyclic aromatic hydrocarbons in the soil. Therefore, we mixed sophorolipids:sodium dodecylbenzene sulfonate (SDBS):Na2SiO3 according to the mass ratio of 1:15:150. We explored the influencing factors of high and low concentrations of PAH-contaminated soil using a single factor test and four factors at a two-level factorial design. Then, the elution wastewater was treated by ultrasonic oxidation technology and the alkali-activated sodium persulfate technology. The results showed that: (1) In the single factor test, when the elution time is 8 h, the concentration of the compounded surfactant is 1200 mg/L, the particle size is 60 mesh, the concentration of NaCl is 100 mmol/L, and the concentration of KCl is 50 mmol/L, and the effect of the PAH-contaminated soil eluted by the composite surfactant is the best. Externally added NaCl and KCl salt ions have a more obvious promotion effect on the polycyclic aromatic hydrocarbon-contaminated soil; (2) in the interaction experiment, single factor B (elution time) and D (NaCl concentration) have a significant main effect. There is also a certain interaction between factor A (concentration agent concentration) and factor D, factor B, and factor C (KCl concentration); (3) the treatment of anthracene in the eluate by ultrasonic completely mineralizes the organic pollutants by the thermal and chemical effects produced by the ultrasonic cavitation phenomenon, so that the organic pollutants in the eluate are oxidized and degraded into simple environmentally friendly small molecular substances. When the optimal ultrasonic time is 60 min and the ratio of oxidant to activator is 1:2, the removal rate of contaminants in the eluent can reach 63.7%. At the same time, the turbidity of the eluent is significantly lower than that of the liquid after centrifugal separation, indicating that oxidants can not only remove the pollutants in elution water but also remove the residual soil particulate matter; and (4) by comparing the infrared spectrum of the eluted waste liquid before and after oxidation, it can be seen that during the oxidation process, the inner part of eluent waste liquid underwent a ring-opening reaction, and the ring-opening reaction also occurred in the part of the cyclic ester group of the surfactant, which changed from a ring to non-ring.

Enhancing Salix viminalis L.-mediated phytoremediation of polycyclic aromatic hydrocarbon-contaminated soil by inoculation with Crucibulum laeve (white-rot fungus).

Although plant-white-rot fungi (WRF) remediation is considered efficient in improving polycyclic aromatic hydrocarbon (PAH)-contaminated soil, the prospects for using it remain poorly known. Therefore, we evaluated whether the WRF Crucibulum laeve could improve the phytoremediation of PAH-contaminated soil by Salix viminalis L. A 60-day pot experiment was conducted to investigate the effects of C. laeve inoculation (using two inoculation treatments and a non-inoculated control) on the phytoremediation potential, growth, and antioxidant metabolism of S. viminalis cultivated in PAH-contaminated soil. The S. viminalis-C. laeve association synergistically caused the highest PAH removal rate. Under the S. viminalis-C. laeve treatment, 80% of the biological concentration and translocation factors for all tissues of S. viminalis were > 1, whereas only 20% of these factors were > 1 when S. viminalis was used alone. C. laeve inoculation remarkably enhanced phytoremediation by promoting S. viminalis-based phytoextraction of PAHs from soils. Furthermore, although C. laeve inoculation altered the antioxidant metabolism of S. viminalis by inducing oxidative stress, thereby inhibiting plant growth, the plant's hardiness enabled it to survive and grow normally for 60days after treatment. Therefore, phytoremediation using S. viminalis inoculated with C. laeve can be considered a feasible approach for the phytoremediation of PAH-contaminated soil.

Endocrine disruption and commensal bacteria alteration associated with gaseous and soil PAH contamination among daycare children

Polycyclic aromatic hydrocarbons (PAHs) are priority environmental pollutants that cause adverse health effects. PAHs belong to endocrine signaling disruptors to which children are sensitive to. Recent evidence suggests that PAH pollution alters the abundance of environmental bacteria that is associated with health outcomes. The alteration of environmental and commensal microbiota by PAH pollution has never been connected to endocrine signaling pathways.To estimate the risk of endocrine disruption in daycare children, we measured PAHs from soil and air of eleven urban daycare centres in Finland. We analyzed daycare yards' soil and children's gut and skin bacterial communities with 16S rRNA gene metabarcoding and used Kyoto Encyclopaedia of Genes and Genomes database to categorize endocrine signaling pathways. We also assessed the PAH hazard to children's health based on the current risk assesments.We observed associations between signaling pathways in endocrine system and gaseous PAH levels in ambient air. Peroxisome proliferator-activated receptor and adipocytokine signaling pathway decreased with higher chrysene concentration in the air. Soil PAH contamination was associated with altered Actinobacteria, Bacteoridetes and Proteobacteria communities on children's skin and in daycare yard soil. However, adjusted genera were not the same in soil and on skin, with the exception of Mycobacterium that was associated with higher PAH concentrations both in soil and on the skin. Even though fluoranhtene levels were above the current threshold values, total PAHs were below safety threshold values and based on current risk assessments there is a minor risk for child health.Our findings indicate that PAH concentrations that are considered safe may interfere with endocrine signaling by commensal microbiota and alter both environmental and commensal bacterial communities. The imbalance in human microbiota and the decrease in signaling pathways may contribute to emerging public health problems, including inflammatory disorders, obesity and diabetes. Therefore, the optimal risk assessments of PAHs and theoretically also other contaminants shaping commensal microbiota may need to take into account the possibility of the disruption of endocrine signaling pathways.

Comparison of oxidoreductive enzyme activities in three coal tar creosote-contaminated soils

This study used laboratory experiments to compare the effects of coal tar creosote on the activity of oxidoreductive enzymes in sandy loam, loamy sand and sandy clay loam soils. Different amounts of coal tar creosote were added to soil samples as follows: 0 (control), 2, 10 or 50 g kg–1 dry matter. The activity of soil dehydrogenases (DHAs), o-diphenol oxidase (o-DPO), catalase (CAT), nitrate reductase (NR) and peroxidases (POX) was determined. Contamination of soil with coal tar creosote affected oxidoreductase activity. Oxidoreductive enzyme activity following soil contamination with coal tar creosote was in the following order: DHAs &amp;gt; CAT &amp;gt; NR &amp;gt; POX &amp;gt; o-DPO in loamy sand and in sandy loam; and DHAs &amp;gt; POX &amp;gt; CAT &amp;gt; NR &amp;gt; o-DPO in sandy clay loam. The index of soil oxidoreductive activity (IOx) introduced in this study confirms the negative effect of coal tar creosote on oxidoreductase activity in soil. DHAs were the most sensitive to the contamination of soil with coal tar creosote. Moreover, the greatest changes in oxidoreductase activities were observed in loamy sand. Knowledge of the mechanism underlying the effects of coal tar creosote on oxidoreductive processes may enable development of a method for the bioremediation of polycyclic aromatic hydrocarbon-contaminated soils.

Surface properties and solubility enhancement of Gemini/conventional surfactant mixtures based on sulfonate Gemini surfactant

The synergistic effect of sulfonate Gemini surfactant (SGS12) with different kinds of conventional surfactants on surface properties and solubility enhancement was investigated. Results indicated that the absolute values of βm were in the following order: SGS12/BQAS > SGS12/DTAB > SGS12/rhamnolipid > SGS12/SDS > SGS12/Triton X-100. The cationic/anionic surfactant mixtures formed micelles at a low concentration, which resulted from the strong attraction among different charged hydrophilic headgroups. Moreover, the molar solubilization ratio and lnKm values indicated that the solubility of SGS12/BQAS, SGS12/Triton X-100, and SGS12/DTAB mixtures toward pyrene was higher than that of either component. The micelle's hydrodynamic sizes of cationic/anionic surfactant mixtures were larger than that of either component, so the hydrophobic space to dissolve additional pyrene was large. Furthermore, dynamic surface tension determination suggested that cationic/anionic surfactant mixtures had a relatively short induction period, and the n values for SGS12/BQAS and SGS12/DTAB mixtures were slightly larger than those for either component. At the total surfactant concentration of 1 μmol·L−1, the plots of γt versus t1/2 for all surfactant mixtures were linear, indicating that the initial adsorption was controlled by diffusion. The values of Dt→0 for SGS12/BQAS, SGS12/DTAB, and SGS12/rhamnolipid mixtures were higher than those of either pure component. Therefore, the mixture of these surfactants accelerated the adsorption process and lowered the adsorption energy barrier, and the mixing of cationic and anionic surfactants was beneficial for dynamic surface activity. In conclusion, the cationic/anionic surfactant mixtures demonstrated good potential for the remediation of polycyclic aromatic hydrocarbon-contaminated soils from equilibrium and dynamic viewpoints.

Zero-valent iron activated persulfate remediation of polycyclic aromatic hydrocarbon-contaminated soils: An in situ pilot-scale study

Zero-valent iron activated persulfate (ZVI/PS) is widely used for the degradation of contaminants. However, the applicability of ZVI/PS has rarely been tested for the in situ pilot-scale remediation of organic-contaminated sites. In this study, different types of ZVI, including micro/nanostructured ZVI (nZVI), stearic-coated micro/nanostructured ZVI (C-nZVI) and commercial micron-sized ZVI (mZVI), were used to activate PS to remove polycyclic aromatic hydrocarbons (PAHs) from the contaminated site. Three reaction pits were excavated for testing the activation ability of different types of ZVI, each with an area of ∼30 m2 and a depth of 4 m. The chemicals (30 g/kg of PS and 3.5 g/kg of ZVI) were added in a soil slurry by in situ stirring. After treatment for 104 days, the PAHs (∼17 mg/kg) removal efficiencies were 82.21%, 62.78%, and 69.14% for PS activated by nZVI, C-nZVI and mZVI, respectively. It was found that the soil pH decreases due to the release of H+ from PS decomposition. The catalase activity was enhanced compared to before the chemical application, while soil bacterial communities, reflected by operational taxonomic unit values, decreased markedly from 250 to ∼100. In particular, the bacteria of the phylum Chloroflexi almost disappeared after remediation. However, the bacteria of the phylum Firmicutes still dominated after remediation and exhibited a tolerance to PS. The findings of this study provide a useful implementation case when PS activation is used in the remediation of PAH-contaminated soil and groundwater.