Effects of fulvic acid concentration and origin on photodegradation of polycyclic aromatic hydrocarbons in aqueous solution: Importance of active oxygen

With an Xe arc lamp house as simulated sunlight, the influences of fulvic acid (FA) concentration and origins on photodegradation of acenaphthene, fluorine, phenanthrene, fluoranthene and pyrene in aqueous solution have been studied. Similar effects of FAs, collected from five places around China, on polycyclic aromatic hydrocarbon (PAH) photodegradation have been observed. Active oxygen was of significance in PAH photodegradation with the presence of FAs. For systems with 1.25 mg L⁻¹ FAs, the contributions of OH to PAH photodegradation rates were from 33% to 69%. FAs had two opposite effects, i.e., stimulating the generation of active oxygen and advancing PAH photodegradation; competing with PAHs for energy and photons and restraining PAH photodegradation. Generally, photodegradation rates of the 5 PAHs decreased with the increase of FAs concentration; except fluoranthene and pyrene were advanced in solutions with low FA concentration. The influences of FA concentration on PAH photodegradation were more significant than FA origin.     

Cell size dependence of additive versus synergetic effects of UV radiation and PAHs on oceanic phytoplankton

Polycyclic Aromatic Hydrocarbons’ (PAHs) toxicity is enhanced by the presence of ultraviolet radiation (UVR), which levels have arisen due to the thinning of the ozone layer. In this study, PAHs’ phototoxicity for natural marine phytoplankton was tested. Different concentrations of a mixture of 16 PAHs were added to natural phytoplankton communities from the Mediterranean Sea, Atlantic, Arctic and Southern Oceans and exposed to natural sunlight received in situ, including treatments where the UVR bands were removed. PAHs’ toxicity was observed for all the phytoplankton groups studied in all the waters and treatments tested, but only for the pico-sized group a synergetic effect of the mixture and UVR was observed (p = 0.009). When comparing phototoxicity in phytoplankton from oligotrophic and eutrophic waters, synergy was only observed at the oligotrophic communities (p = 0.02) where pico-sized phytoplankton dominated. The degree of sensitivity was related to the trophic degree, decreasing as Chlorophyll a concentration increased.     

Polycyclic aromatic hydrocarbons in lake sediments from the High Tatras

European alpine lake systems are used as indicators of air quality over the continent. Preliminary data showed high polycyclic aromatic hydrocarbons (PAH) loads in the High Tatras (Eastern Europe) in comparison to other mountain regions. Here, insight on the spatial distribution of PAH is provided from analysis of top-core sediments of 27 alpine lakes distributed along the High Tatras.Top-core sediment concentrations were higher than those in deep-cores, and they were higher than those observed in other European high mountain regions. The PAH profiles were uniform and comparable to those observed in aerosols and snow, indicating that atmospheric deposition was the predominant PAH input pathway to the lakes. Good agreement between estimated atmospheric deposition and sedimentation fluxes was observed. However, in several lakes in the western range higher sediment fluxes may correspond to higher PAH depositions levels. The higher concentrations may also reflect inputs from potential emission source areas.     

Variation in indoor levels of polycyclic aromatic hydrocarbons from burning various biomass types in the traditional grass-roofed households in Western Kenya

Biomass burning as fuel in the traditional grass-roofed rural households of Western Province of Kenya in open fire places, in poorly ventilated conditions, lead to accumulation of soot under the roofs. This study characterized and quantified the polycyclic aromatic hydrocarbons (PAHs) in accumulated soot in these households and determined the variation in PAHs concentrations with fuel biomass type. Soot samples collected from the households were extracted, cleaned and analysed by gas chromatography. The PAHs were identified using retention times, verified by gas chromatographic mass spectral analysis and quantified from peak area responses using the internal standard method. The PAHs levels significantly varied (P ≤ 0.05) with biomass type in the order: dung ≥ indigenous trees ≥ exotic trees ≥ shrubs and crop residues. Use of dung and wood from indigenous trees as fuel should be discouraged since they are higher emitters (P ≤ 0.05) of carcinogenic PAHs.     

Occurrence of polycyclic aromatic hydrocarbons in surface sediments of a highly urbanized river system with special reference to energy consumption patterns

Sediment samples collected from downstream of the Dongjiang River, a highly urbanized river network within the Pearl River Delta of South China, were analyzed for 28 polycyclic aromatic hydrocarbons (PAHs). Total concentrations of 28 PAHs, 16 priority PAHs designated by the United States Environmental Protection Agency (USEPA) and the seven carcinogenic PAHs classified by the USEPA ranged from 480 to 4600, 100 to 3400 and 10 to 1700 ng/g dry weight, respectively. Principal component analysis-based stepwise multivariate linear regression showed that sediment PAHs were predominantly derived from coal combustion, refined fossil fuel combustion and oil spills, accounting for 37%, 32% and 23%, respectively, of the total loading. The levels of sediment PAHs remained steady from 2002 to 2008, during which fossil fuel consumption had doubled, probably reflecting efforts to control PAH emissions from fossil fuel combustion. Finally, use of natural gas and liquefied petroleum gas in automobiles should be encouraged to improve environmental quality.     

Sorption of polycyclic aromatic hydrocarbons (PAHs) on glass surfaces

Sorption of polycyclic aromatic hydrocarbons (PAHs) to glass commonly used in laboratories was studied. Sorption coefficients (K_d) of five selected PAHs to borosilicate glass surfaces were measured using column chromatography. A linear relationship between log K_d and the corresponding water solubility of the subcooled liquid (log S_w) of the investigated PAHs was observed. Based on the determined sorption coefficients our data revealed that mass loss caused by sorption on glass walls strongly depends on the ratio of solution volume to contacted surface area (V/S). The influence of solution chemistry such as ionic strength, solution pH, presence of cosolvent, and the influence of temperature on the sorption process were investigated. In the presence of ionic strength, sorption coefficients concurrently increased but less than a factor of 2 up to 0.005 M calcium chloride concentration. However, further increasing ionic strength had no influence on K_d. The cosolvent reduced sorption at a concentration of methanol in water above 0.5% (v/v); however, for benzo[a]pyrene even with 10% (v/v) methanol the mass loss would be still higher than 10% (with a V/S ratio less than 0.25). Significant effects of the solution pH and temperature were not observed. These results suggest that van der Waal’s forces dominate the sorption process. In the analysis of highly hydrophobic PAHs in aqueous samples, mass loss due to sorption on glass walls should be accounted for in the final result if untreated glass is used. The presented relationship between log K_d and log S_w may help to decide if such a correction is necessary. Furthermore, the frequently used silanization of glass surfaces may not be sufficient to suppress sorption for large PAHs.     

Fenton based remediation of polycyclic aromatic hydrocarbons-contaminated soils

This paper aims to review the applications of Fenton based treatments specifically for polycyclic aromatic hydrocarbons-contaminated soils. An overview of the background and principles of Fenton treatment catalysed by both homogenous (conventional and modified Fenton) and heterogeneous (Fenton-like) catalysts is firstly presented. Laboratory and field soil remediation studies are then discussed in terms of efficiency, kinetics and associated factors. Four main scopes of integrated Fenton treatments, i.e. physical-Fenton, biological-Fenton, electro-Fenton and photo-Fenton are also reviewed in this paper. For each of these integrated remediation technologies, the theoretical background and mechanisms are detailed alongside with achievable removal efficiencies for polycyclic aromatic hydrocarbons in contaminated soils compared to sole Fenton treatment. Finally, the environmental impacts of Fenton based soil treatments are documented and discussed.     

Characterization of extractable and non-extractable polycyclic aromatic hydrocarbons in soils and sediments from the Pearl River Delta, China

Formation of bound residues of pollutants in soils and sediments is an important process to control the fate of pollutants in the environment. The most of bound residue is not solvent extractable. In this paper, we measured both extractable and non-extractable polycyclic aromatic hydrocarbons (PAHs) in different organic matter fractions of samples from the Pearl River Delta, China. Non-extractable PAHs concentration was 234.45-1424.57 μg/kg and accounted for 33.78-57.44% of total PAHs. 2-3 Ring PAHs were the dominant species and differed in concentration substantially between the samples. The atomic ratio of PAHs over organic-C in the fractions ordered as solvent soluble organic matter > humin > humic acids, matching the content of aliphatic moieties in the fractions of organic matter. The ratio of extractable and non-extractable PAHs may relate to the aging process of PAHs in soil and sediment.     

Release of polycyclic aromatic hydrocarbons from Yangtze River sediment cores during periods of simulated resuspension

The role of resuspension duration on release of 16 PAHs was measured experimentally using a particle entrainment simulator (PES). Three sediment cores were resuspended for 12h at 0.2 and 0.5N m(-2). PAHs in water column and total suspended solids (TSS) were monitored at intervals. After 0.25h of resuspension, PAH release was on average 42% of their concentrations after 12h of resuspension, indicating fast release of PAHs from sediments in an initial short time. Moreover, PAHs released faster at 0.5N m(-2) than at 0.2N m(-2); low molecular weight PAHs (2-3-ring) released faster than median molecular weight (4-ring) PAHs. PAH concentrations in TSS showed generally increase with time and differences in magnitudes based on sediment type and energy. Overall, the composition of sediments is the major factor in determining the amount of released PAHs, more so than the level of resuspension energy applied.     

Concentrations and bioaccessibility of polycyclic aromatic hydrocarbons in wastewater-irrigated soil using in vitro gastrointestinal test

BACKGROUND, AIM, AND SCOPE: Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants and contribute to the pollution of soil environment. Soil ingestion is of increasing concern for assessing health risk from PAH-contaminated soils because soil ingestion is one of the potentially important pathways of exposure to environmental pollutants, particularly relevant for children playing at contaminated sites due to their hand-to-mouth activities. In vitro gastro-intestinal tests imitate the human digestive tract, based on the physiology of humans, generally more simple, less time-consuming, and especially more reproducible than animal tests. This study was conducted to investigate the level of PAH contamination and oral bioaccessibility in surface soils, using physiologically based in vitro gastro-intestinal tests regarding both gastric and small intestinal conditions. MATERIALS AND METHODS: Wastewater-irrigated soils were sampled from the metropolitan areas of Beijing and Tianjin, China, which were highly contaminated with PAHs. Reference soil samples were also collected for comparisons. At each site, four soils were sampled in the upper horizon at the depth of 0-20 cm randomly and were bulked together to form one composite sample. PAH concentrations and origin were investigated and a physiologically based in vitro test was conducted using all analytical grade reagents. Linear regression model was used to assess the relationship between total PAH concentrations in soils and soil organic carbon (SOC). RESULTS: A wide range of total PAH concentrations ranging from 1,304 to 3,369 mug kg(-1) in soils collected from different wastewater-irrigated sites in Tianjin, while ranging from 2,687 to 4,916 mug kg(-1) in soils collected from different wastewater-irrigated sites in Beijing, was detected. In general, total PAH concentrations in soils from Beijing sites were significantly higher than those from Tianjin sites, indicating a dominant contribution from both pyrogenic and petrogenic sources. Results indicated that the oral bioaccessibility of PAHs in small intestinal was significantly higher (from P < 0.05 to P < 0.001) than gastric condition. Similarly, the oral bioaccessibility of PAHs in contaminated sites was significantly higher (from P < or = 0.05 to P < 0.001) than in reference sites. Individual PAH ratios (three to six rings), a more accurate and reliable estimation about the emission sources, were used to distinguish the natural and anthropogenic PAH inputs in the soils. Results indicated that PAHs were both pyrogenic and petrogenic in nature. DISCUSSION: The identification of PAH sources and importance of in vitro test for PAH bioaccessibility were emphasized in this study. The oral bioaccessibility of individual PAHs in soils generally decreased with increasing ring numbers of PAHs in both the gastric and small intestinal conditions. However, the ratio of bioaccessibility of individual PAHs in gastric conditions to that in the small intestinal condition generally increased with increasing ring numbers, indicating the relatively pronounced effect of bile extract on improving the bioaccessibility of PAHs with relatively high ring numbers characterized by their high K ( ow ) values. Similarly, total PAH concentrations in soils were strongly correlated with SOC, indicating that SOC was the key factor determining the retention of PAHs in soils. CONCLUSIONS: Soils were contaminated with PAHs due to long-term wastewater irrigation. PAHs with two to six rings showed high concentrations with a significant increase over reference soils. Based on the molecular indices, it was suggested that PAHs in soils had both pyrogenic and petrogenic sources. It was also concluded that the oral bioaccessibility of total PAHs in the small intestinal condition was significantly higher than that in the gastric condition. Furthermore, the bioaccessibility of individual PAHs in soils generally decreased with the increasing ring numbers in both the gastric and small intestinal conditions. RECOMMENDATIONS AND PERSPECTIVES: It is suggested that more care should be given while establishing reliable soil criteria for PAHs, especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-to-mouth activities.