Hongwen Sun

Enzyme activities during degradation of polycyclic aromatic hydrocarbons by white rot fungus Phanerochaete chrysosporium in soils

The degradation of three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, pyrene and benzo[a]pyrene in soils by Phanerochaete chrysosporium, and the enzyme activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) produced during degradation, were analyzed. The results showed that the 19-d percentage degradation ranged from 72.77+/-1.39% to 25.50+/-3.41% for the three compounds, and the maximum LiP and MnP activities ranged from 0.16+/-0.005 to 0.05+/-0.002 U g(-1) and from 1.92+/-0.03 to 0.54+/-0.03 U g(-1), respectively. Degradation percentage and enzyme activities both exhibited inverse relationships with the octanol/water partition coefficient (K(ow)) of the compounds, indicating that LiP and MnP from P. chrysosporium may be the primary enzymes responsible for PAH degradation in soil. As the soil organic matter (SOM) content increased from 0.3% for Soil 1 to 19% for Soil 4, the 19-d degradation percentage of pyrene decreased from 66.20+/-2.72% to 32.42+/-1.05%, and correspondingly, the maximum of LiP and MnP activities increased from 0.05+/-0.002 to 1.78+/-0.15 U g(-1) and from 0.34+/-0.03 to 1.78+/-0.15 U g(-1), respectively. Hence, it is plausible to conclude that the P. chrysosporium appeared to degrade not only the PAHs with small molecular size but also the macromolecular SOM. When SOM differences are large, as in this study, SOM has greater influence on enzyme activity than low-level exotic pollutants.

Impacts of charcoal characteristics on sorption of polycyclic aromatic hydrocarbons

Sorption of three polycyclic aromatic hydrocarbons (PAHs, phenanthrene, anthracene and pyrene) on three charcoals and their precursor substance (sawdust) was studied. The charcoals obtained by heating at 400 degrees C for different periods were different in chemical composition and structure. Sorption characteristics were described by a Polanyi-Dubinin-Manes model combined with poly-parameter linear free energy relationships. The results revealed that though partition could not be neglected for sawdust and charcoal containing large sawdust residue, adsorption controlled the sorption of PAHs on matured charcoals, where pi-pi electron donor-acceptor (EDA) exerted as the main molecular-scale interactions. Charring elevated partition coefficients (K(oc)) of the three PAHs more than one order of magnitude, which ranged from 10(5.74) to 10(6.58) on charcoals (for PAHs at equilibrium concentration C(e)=0.005S(w)). Adsorption increased with the aromaticity of the charcoals, however, polar aromatic structure may stimulate sorption of PAHs due to the presence of pi-pi EDA interactions.

Plant uptake of aldicarb from contaminated soil and its enhanced degradation in the rhizosphere

Experiments were conducted to investigate the degradation of aldicarb, an oxime carbamate insecticide, in sterile, non-sterile and plant-grown soils, and the capability of different plant species to accumulate the pesticide. The degradation of aldicarb in soil followed first-order kinetics. Half lives (t1/2) of aldicarb in sterile and non-sterile soil were 12.0 and 2.7 days, respectively, which indicated that microorganisms played an important part in the degradation of aldicarb in soil. Aldicarb disappeared more quickly (p< or =0.05) in the soil with the presence of plants, and t1/2 of the pesticide were 1.6, 1.4 and 1.7 days in the soil grown with corn, mung bean and cowpea, respectively. Comparison of plant-promoted degradation and plant uptake showed that the enhanced removal of aldicarb in plant-grown soil was mainly due to plant-promoted degradation in the rhizosphere.

6:2 Fluorotelomer alcohol biotransformation in an aerobic river sediment system

The 6:2 FTOH [F(CF(2))(6)CH(2)CH(2)OH] is a major raw material being used to replace 8:2 FTOH [F(CF(2))(8)CH(2)CH(2)OH] to make FTOH-based products for industrial and consumer applications. A novel aerobic sediment experimental system containing 20 g wet sediment and 30 mL aqueous solution was developed to study 6:2 FTOH biotransformation in river sediment. 6:2 FTOH was dosed into the sediment to follow its biotransformation and to analyze transformation products over 100 d. The primary 6:2 FTOH biotransformation in the aerobic sediment system was rapid (T(1/2)<2d). 5:3 acid [F(CF(2))(5)CH(2)CH(2)COOH] was observed as the predominant polyfluorinated acid on day 100 (22.4 mol%), higher than the sum of perfluoropentanoic acid (10.4 mol%), perfluorohexanoic acid (8.4 mol%), and perfluorobutanoic acid (1.5 mol%). Perfluoroheptanoic acid was not observed during 6:2 FTOH biotransformation. The 5:3 acid can be further degraded to 4:3 acid [F(CF(2))(4)CH(2)CH(2)COOH, 2.7 mol%]. This suggests that microbes in the river sediment selectively degraded 6:2 FTOH more toward 5:3 and 4:3 acids compared with soil. Most of the observed 5:3 acid formed bound residues with sediment organic components and can only be quantitatively recovered by post-treatment with NaOH and ENVI-Carb™ carbon. The 6:2 FTCA [F(CF(2))(6)CH(2)COOH], 6:2 FTUCA [F(CF(2))(5)CF=CHCOOH], 5:2 ketone [F(CF(2))(5)C(O)CH(3)], and 5:2 sFTOH [F(CF(2))(5)CH(OH)CH(3)] were major transient intermediates during 6:2 FTOH biotransformation in the sediment system. These results suggest that if 6:2 FTOH or 6:2 FTOH-based materials were released to the river or marine sediment, poly- and per-fluorinated carboxylates could be produced.

Adsorption behaviour and qspr studies of organotin compounds on estuarine sediment

The adsorption behaviour of eight organotin species and Sn4+ (SnCl4) on estuarine sediments has been reported for the first time. It was found that the adsorption of organotins varies greatly with molecular structure. The order of adsorption coefficient k is Sn4+ > mono- > di-> tri-organotins. Corre lations of log k with eight different structural parameters show that the electronic properties of the Sn atom is the principal factor controlling the adsorption behaviour of organotins. The adsorption mechanism of organotins is mainly an ion-exchange process, with little lipophilic partitioning.

Bioaccumulation of Butyltins via an Estuarine Food Chain

An estuarine food chain of threetrophic levels–algae (Platymonas sp.), rotifers (Brachionus plicatilis) and mysids (Neomysis awatschensis Brandt) was setup in laboratory in order to investigate contributionsof water and food to the accumulation of butyltins inupper trophic organisms, as well as to evaluate thelikelihood of biomagnification of butyltins throughthe aquatic food chain. Kinetics of bioaccumulationand depuration of butyltins through the food chainwere studied. Bioconcentration factors of butyltins inthe three organisms were high (103–104).Butyltin burdens in the upper trophic organisms atsteady-state of bioaccumulation by the ingestion oftainted food exceeded those observed by exposure towater only. For total butyltins, food chain transfernumber was 1.44 for algae to rotifers and 0.59 forrotifers to mysids, respectively. Biomagnification wasnot confirmed. It is concluded that whether or notbiomagnification occurs depends not only on theproperty of compounds but also on the organisms involved.

Concentration- and time-dependent sorption and desorption behavior of phenanthrene to geosorbents with varying organic matter composition

Batch equilibration and the decant-refill methods were used to measure sorption and desorption of phenanthrene to four geosorbents with varying organic matter composition at different contact times to better understand the mechanisms underlying sorption and desorption processes. The sorbents were characterized by solid-state (13)C cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. Sorption and desorption isotherms were constructed and fitted to the Freundlich model and the site energy distribution model was used to measure the relative change of distributed sorption energies. Concentration- and time-dependence were observed for both sorption and desorption processes. The high energy sites become filled with increasing sorbate concentration, resulting in the non-linearity of sorption isotherms and the increase of the desorption percentages. The shape of the sorption isotherms changed with the contact time, which was characterized by the variation of Freundlich model parameters (K(F) and n). More favorable sorption sites could be accessed when the contact time was extended, leading to the decrease of the desorption percentages. As indicated by the value of n, partitioning appeared to contribute more to the sorption of phenanthrene for the soils with higher oxygen-substituted carbon content and less condensed soil organic matter (SOM). Sorption in adsorption domains is energetically more favorable and kinetically less accessible as compared to partitioning domains, and both the composition and conformation of SOM play important roles in the sorption and desorption processes by forming specific interactions with phenanthrene molecules and governing the accessibility of sorption domains.

Sorption of Pyrene on Different Constituents of Rice Straw in the Presence of Phenanthrene, Benzo[a]pyrene, and Phenols

Treated and untreated rice straw extensively exists in the soil. In order to elucidate its possible effect on the fate of organic pollutants, sorption of pyrene by rice straw and its main constituents (lignin, cellulose, and hemi-cellulose) were studied, as single solute and in the presence of other co-existing organic pollutants, phenanthrene (Phen), benzo[a]pyrene (BaP), phenol, and pentachlorophenol (PCP). Pyrene showed the greatest sorption on lignin with greater aromaticity and smaller polarity, and the sorption coefficient was almost two orders of magnitude greater than those on cellulose and hemi-cellulose. Bi-solute sorption results showed that Phen, BaP and PCP exhibited apparent competitive sorption with pyrene on the four sorbents; while the existence of phenol promoted the sorption of pyrene on rice straw and lignin but inhibited the sorption on cellulose and hemi-cellulose. For the two polycyclic aromatic hydrocarbon (PAH) co-solutes and PCP, hydrophobicity and molecular size played important roles in competition, suggesting the direct competition for hydrophobic sorption sites and pore blockage mechanisms. In contrast, the polar co-solute, phenol showed different effects on pyrene sorption onto the four sorbents, suggesting that multiple interactions between polar organic compounds and sorbents are involved in the sorption.