The effects of aging time on the fraction distribution and bioavailability of PAH

Understanding the effects of aging time on the fraction distribution and bioavailability of PAH, such as phenanthrene (PHE) and pyrene (PYR), has considerable benefits for risk assessment, food security and remediation strategies for contaminated soil. The results of the present study show that the proportion of the desorbed PHE decreased from ca. 82% at day 0 to ca. 65% at day 150. In addition, non-desorbed PHE increased from ca. 18% at day 0 to ca. 31% at day 150, whereas the changes of desorbed and non-desorbed PYR showed no significant trend during this aging period. The proportion of desorbed PYR was lower than that of PHE, whereas the opposite occurred with the non-desorbed fraction. After 150 d of aging, the proportion of bound residues (PHE and PYR) increased significantly with the cultivating time from ca. 0.2% to ca. 4.7% and ca. 0.1% to ca. 1.2% for PHE and PYR, respectively. In addition, the bioavailability of PAH (PHE and PYR) to earthworms was also assessed over 0-150 d. The results showed that the uptake rate and bioconcentration factor (BCF) of pollutants by earthworms displayed the following biphasic character: a rapid decrease over the first 15 d followed by a slow decrease over the next 135 d. Moreover, the earthworm uptake rate of PHE was greater than that of PYR throughout the incubation period, indicating that PHE has a higher bioavailability than PYR. In addition, the positive correlation between the uptake rate of earthworms and PAH extractability suggested that a three-step extraction is a reliable approach to predict PHE bioavailability in soil. However, a limit was observed for PYR.     

Nonlinear binding of phenanthrene to the extracted fulvic acid fraction in soil in comparison with other organic matter fractions and to the whole soil sample

Fractions of soil organic matter in a natural soil were extracted and sorption (or binding) characteristics of phenanthrene on each fraction and to the whole sample were investigated. The organic carbon normalized single point sorption (or binding) coefficient followed lipid > humin (HM) > humic acid (HA) > fulvic acid (FA) > whole soil sample, while the nonlinear exponent exhibited lipid > FA > HA > whole soil sample > HM. FA showed nonlinear binding of phenanthrene as it often does with other fractions. HM and HA contributed the majority of organic carbon in the soil. The calculated sorption coefficients of the whole soil were about two times greater than the measured values at different equilibrium phenanthrene concentrations. As for phenanthrene, the sorption capacity and nonlinearity of the physically mixed HA-HM mixtures were stronger as compared to the chemically reconstituted HA-HM composite. This was attributed to (besides the conditioning effect of the organic solvents) interactions between HA and HM and acid-base additions during fractionation.     

Antagonism of phenanthrene cytotoxicity for human embryo lung fibroblast cell line HFL-I by green tea polyphenols

Polycyclic aromatic hydrocarbons (PAHs) have been detected in some commercial teas around the world and pose a threat to tea consumers. However, green tea polyphenols (GTP) possess remarkable antioxidant and anticancer effects. In this study, the potential of GTP to block the toxicity of the model PAH phenanthrene was examined in human embryo lung fibroblast cell line HFL-I. Both GTP and phenanthrene treatment individually caused dose-dependent inhibition of cell growth. A full factorial design experiment demonstrated that the interaction of phenanthrene and GTP significantly reduced growth inhibition. Using the median effect method showed that phenanthrene and GTP were antagonistic when the inhibitory levels were less than about 50%. Apoptosis and cell cycle detection suggested that only phenanthrene affected cell cycle significantly and caused cell death; GTP lowered the mortality of HFL-I cells exposed to phenanthrene; However, GTP did not affect modulation of the cell cycle by phenanthrene.     

Phenanthrene degradation in Arthrobacter sp. P1-1: initial 1,2-, 3,4- and 9,10-dioxygenation, and meta- and ortho-cleavages of naphthalene-1,2-diol after its formation from naphthalene-1,2-dicarboxylic acid and hydroxyl naphthoic acids

Arthrobacter sp. P1-1, isolated from a polycyclic aromatic hydrocarbon (PAH)-contaminated site in Hilo, HI, USA, can decompose phenanthrene (40 mg l⁻¹) completely within 7 days. A detailed phenanthrene metabolism map was constructed based on metabolite analysis and replacement cultures. Initial dioxygenation occurs on 1,2-, 3,4-, and 9,10-C of phenanthrene, dominantly on 3,4-C positions. Rapid accumulation of 5,6- and 7,8-benzocoumarin suggests that phenanthrene-1,2- and -3,4-diols mainly undergo meta-cleavage. However, a trace amount of o-carboxyvinylnaphthoates and diphenic acid indicates a limited extent of ortho-cleavage of the diols. Naphthalene-1,2-diol, as a common and converged metabolite, was formed from 1-[(E)-2-carboxyvinyl]-2-naphthoic acid, naphthalene-1,2-dicarboxylic acid, and 1-hydroxy-2-naphthoic acid in separate culture tests. Naphthalene-1,2-diol is then degraded in a dominant phthalic acid pathway and a minor salicylic acid pathway. Several metabolites of phthalic acid were found, while no salicylic acid metabolites were detected. The strain P1-1 likely has a very diverse set of PAH-degrading enzymes or the enzymes having relaxed substrate-specificity.     

Equilibrium sorption of phenanthrene by soil humic acids

This study investigated the effect of chemical heterogeneity of humic acids (HAs) on the equilibrium sorption of phenanthrene by HA extracts. Six HA samples were extracted from three different soils with 0.5 M NaOH and 0.1 M Na₄P₂O₇ and were characterized with elemental analysis, infrared spectrometry, and solid-state ¹³C nuclear magnetic resonance (NMR) spectrometry. The equilibrium sorption measurements were carried out with a batch technique and using the six HA solids as the sorbents and phenanthrene as the sorbate. The measured sorption isotherm data were fitted to the Freundlich equation. The results showed that, for the same soil, (i) the total HA mass extracted with Na₄P₂O₇ was 13.7–22.6% less than that extracted with NaOH, (ii) the Na₄P₂O₇-extracted HA had higher O/C atomic ratio, greater content of polar organic carbons (POC), and lower aliphatic carbon content than the NaOH-extracted HA, and (iii) the Na₄P₂O₇-extracted HA exhibited greater sorption isotherm linearity and but not dramatic difference in sorption capacities than the NaOH extracted HA. The differences in the HA properties resulting from the two different extraction methods may be because NaOH can hydrolyze insoluble HA fractions such as fatty acid like macromolecules bound on soils whereas Na₄P₂O₇ could not. As a result, the HAs extracted with the two different methods had different polarity and functionality which affected their sorption property for phenanthrene.     

Acute toxic effects of phenanthrene on Chinese mitten crab Eriocheir sinensis北大核心CSCD

Phenanthrene is a persistent organic pollutant frequently found in aquatic environments. This paper aimed to assess the acute effects (96 h) of phenanthrene on Chinese mitten crab (Eriocheir sinensis), a key economic aquatic animal in China. An acute semi-static toxic test was carried out to expose E. sinensis to water-borne phenanthrene with different concentrations (1.00, 1.63, 2.65, 4.31 and 7.00 mg L-1) for 96 hours. Mortality and toxic reactions were used as effect criteria. Furthermore, the oxidative stress relative biomarkers (activities of CAT, SOD, GST and content of MDA in hepatopancreas and gills) were measured for E. sinensis exposed to four lower concentrations of phenanthrene (1.00, 1.63, 2.65 and 4.31 mg L-1). The median lethal concentration (LC50) for 24,48 and 96 hour phenanthrene exposure was 16.7, 2.96 and 2.14 mg L-1, respectively; and the safe concentration (SC) of phenanthrene on E. sinensis was 0.214 mg L-1. Phenanthrene significantly increased the activity of CAT in hepatopancreas and gills, and showed a significant dose-effect relationship in hepatopancreas. Bell-shape response patterns were found in the activities of GST and SOD in the hepatopancreas and gills, with significant increases of hepatopancreas GST at 1.00 and 1.63 mg L-1 (P < 0.05), and a significant decrease at 4.31mg L-1 (P < 0.05). Phenanthrene significantly increased the contents of gills MDA at 2.65mg L-1 and hepatopancreas MDA at all four concentrations of phenanthrene. Phenanthrene, especially of high concentration, is highly toxic on E. sinensis, causing lipid peroxidative damage and even acute mortality. Meanwhile, E. sinensis can adapt to lower concentrations of phenanthrene by increasing the activities of SOD, CAT and GST. Because the CAT and GST activities of the gill and hepatopancreas are very sensitive to the presence of high-concentration phenanthrene, they can be used as highly sensitive biomarkers for phenanthrene polluted water.     

Effect of Pinus radiata derived biochars on soil sorption and desorption of phenanthrene

Biochars are anthropogenic carbonaceous sorbent and their influences on the sorption of environmental contaminants need to be characterized. Here we evaluated the effect of Pinus radiata derived biochars on soil sorption and desorption of phenanthrene. Two biochars separately produced at 350 °C and 700 °C and three soils were tested. Biochar amendment generally enhanced the soil sorption of phenanthrene. The biochar produced at 700 °C generally showed a greater ability at enhancing a soil’s sorption ability than that prepared at 350 °C. The single-step desorption measurement showed an apparent hysteresis in biochar-amended soils. After 28 d equilibration, the sorptive capacity of biochar-amended soil (with an organic carbon content of 0.16%) significantly decreased. This study clearly suggested that biochar application enhanced soil sorption of hydrophobic organic compounds, but the magnitude of enhancement depended on the preparation of biochars, the indigenous soil organic carbon levels, and the contact time between soil and biochar.     

Phenanthrene exposure produces cardiac defects during embryo development of zebrafish (Danio rerio) through activation of MMP-9

Phenanthrene (Phe) is one of the most abundant polycyclic aromatic hydrocarbons in the aquatic environment as a result of human activities. It is widely accepted that Phe has cardiotoxic effects. Even so, knowledge concerning the mechanism(s) of cardiac development toxicity is still limited. In this study, we exposed zebrafish embryos to environmentally relevant concentrations of Phe and then investigated its cardiotoxic effects and the mechanism(s) involved. Some cardiac morphogenetic defects, which was characterized by an abnormally looped and enlarged heart, dilated and thinner ventricular wall, and increased interstitial fibrosis, were observed in the Phe treated groups. The mRNA and protein expression levels of matrix metalloproteinase-9 (MMP-9), as well as the MMP-9 activity, were induced. Moreover, during co-treatment of the zebrafish embryos with MMP-9 inhibitor, the cardiac defects caused by Phe were attenuated. In addition, Phe exposure led to an up-regulation of transforming growth factor β (TGF-β), which plays a crucial role in mediating cardiac fibrosis. Taken together, our data indicated that the exposure to Phe of zebrafish embryos disrupted normal cardiac development, and that the cardiac defects induced by Phe were mediated by the MMP-9, while TGF-β was also involved in these cardiac defects.     

Enchytraeus crypticus as model species in soil ecotoxicology

Enchytraeids are ecologically relevant soil organisms, due to their activity in decomposition and bioturbation in many soil types worldwide. The enchytraeid reproduction test (ERT) guidelines ISO 16387 and OECD 220 are exclusive to the genus Enchytraeus and recommend using the species E. albidus with a 6-week test period. The suggested alternative, E. crypticus has a shorter generation time which may enable the ERT to be twice as fast. To confirm the suitability of a 3-week test period for E. crypticus, the toxicity of five chemicals, with distinct properties and modes of action, was assessed in LUFA 2.2 soil. In all controls the validity criteria were met, as survival of E. crypticus was above 92% and more than 772 juveniles were produced. The good performance supports its appropriateness as model species. Reproduction was more sensitive than survival, with only cadmium and 3,5-dichloroaniline causing significant lethal effects in the tested concentration ranges. The effect concentration causing 50% reduction in the number of juveniles (EC50) was 35 mg kg⁻¹ for cadmium, <1.0 mg kg⁻¹ for carbendazim, 145 mg kg⁻¹ for phenanthrene, 275 mg kg⁻¹ for pentachloroaniline and 102 mg kg⁻¹ for 3,5-dichloroaniline. To evaluate the sensitivity of E. crypticus, the present results were compared to literature data for E. albidus. In conclusion, E. crypticus is a suitable model species in soil ecotoxicology, with advantages such as good control performance and speed, leading to a reliable and faster ERT.