Xincai Chen

Subcellular distribution and chemical forms of cadmium in Phytolacca americana L.

Phytolacca americana L. (pokeweed) is a promising species for Cd phytoextraction with large biomass and fast growth rate. To further understand the mechanisms involved in Cd tolerance and detoxification, the present study investigated subcellular distribution and chemical forms of Cd in pokeweed. Subcellular fractionation of Cd-containing tissues indicated that both in root and leaves, the majority of the element was located in soluble fraction and cell walls. Meanwhile, Cd taken up by pokeweed existed in different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 80% ethanol in roots, followed by 1 M NaCl, d-H(2)O and 2% HAc, while in leaves and stems, most of the Cd was extracted by 1 M NaCl, and the subdominant amount of Cd was extracted by 80% ethanol. It could be suggested that Cd compartmentation with organo-ligands in vacuole or integrated with pectates and proteins in cell wall might be responsible for the adaptation of pokeweed to Cd stress.

Enhancement of phenanthrene and pyrene degradation in rhizosphere of tall fescue (Festuca arundinacea)

A greenhouse experiment was conducted with varying concentrations of phenanthrene (11-344 mg kg(-1)) and pyrene (15-335 mg kg(-1)) spiked in the soil to evaluate the phytoremediation of PAHs contaminated soil using tall fescue (Festuca arundinacea). After 65-day of tall fescue growth, plant biomass, microbial viable counts, dehydrogenase activity, water-soluble phenolic compounds, phenanthrene and pyrene residual concentrations and removal percentages were determined. The results showed that target PAHs (phenanthrene and pyrene) did not affect plant biomass at lower concentrations but a reduced biomass (only 53.5% of shoot and 29.7% of root compared to control) was observed at higher concentrations. Higher biological activities (microbial viable counts, water-soluble phenolic compounds, dehydrogenase activity) and PAHs degradation rates were detected in planted soils than unplanted controls. After harvest, 91.7-97.8% of phenanthrene and 70.8-90.0% of pyrene had been degraded in the planted soils, which were 1.88-3.19% and 8.85-20.69% larger than those in corresponding unplanted soils. This enhanced dissipation of target PAHs in planted soils might be derived from increased biological activity in the rhizosphere. The results of the present study suggest that the presence of tall fescue roots were effective in promoting the phytoremediation of PAHs contaminated soil.

Heavy metal availability and impact on activity of soil microorganisms along a Cu/Zn contamination gradient

All the regulations that define a maximum concentration of metals in the receiving soil are based on total soil metal concentration. However, the potential toxicity of a heavy metal in the soil depends on its speciation and availability. We studied the effects of heavy metal speciation and availability on soil microorganism activities along a Cu/Zn contamination gradient. Microbial biomass and enzyme activity of soil contaminated with both Cu and Zn were investigated. The results showed that microbial biomass was negatively affected by the elevated metal levels. The microbial biomass-C (C(mic))/organic C (C(org)) ratio was closely correlated to heavy metal stress. There were negative correlations between soil microbial biomass, phosphatase activity and NH4NO3 extractable heavy metals. The soil microorganism activity could be predicted using empirical models with the availability of Cu and Zn. We observed that 72% of the variation in phosphatase activity could be explained by the NH4NO3-extractable and total heavy metal concentration. By considering different monitoring approaches and different viewpoints, this set of methods applied in this study seemed sensitive to site differences and contributed to a better understanding of the effects of heavy metals on the size and activity of microorganisms in soils. The data presented demonstrate the relationship between heavy metals availability and heavy metal toxicity to soil microorganism along a contamination gradient.

Accumulation and detoxification of manganese in hyperaccumulator Phytolacca americana

Pokeweed (Phytolacca americana) has recently received much attention because of its ability to hyperaccumulate manganese (Mn). The internal mechanism of detoxification of Mn, however, is not fully understood. In the present study, we investigated Mn accumulation, subcellular distribution, chemical speciation and detoxification through oxalate in pokeweed. The plant accumulated excess Mn in the leaves, mainly in the water-soluble fraction, and over 80% of Mn was in a water-soluble form, while accumulation of excess Mn in the cellular organelle and membrane fraction caused phytotoxicity. In addition, pokeweed has an intrinsically high oxalate content. In all experiments, there was sufficient oxalate to chelate Mn in leaf water extracts at all different levels of Mn application. Phase analysis of X-ray diffraction detected oxalate-Mn chelate complexes, and gel chromatography further confirmed the chelation of Mn by oxalate. In conclusion, pokeweed accumulates excess Mn in the soluble fraction of leaf cells, most likely in vacuoles, in which detoxification of Mn could be achieved by chelation with oxalate.

Enhanced phytoremediation potential of polychlorinated biphenyl contaminated soil from e-waste recycling area in the presence of randomly methylated-β-cyclodextrins.

The crude recycling of electronic and electric waste (e-waste) is now creating soil pollution problems with organic compounds such as polychlorinated biphenyls (PCBs). The present study aimed to compare the phytoremediation potential of four plant species (rice, alfalfa, ryegrass and tall fescue) for PCBs contaminated soil from Taizhou city, one of the largest e-waste recycling centers in China. In addition, the enhanced effects of randomly methylated-beta-cyclodextrins (RAMEB) on PCBs phytoremediation potential were evaluated. Higher PCBs removal percentages of 25.6-28.5% in rhizosphere soil were observed after 120 days, compared with those of the non-rhizosphere (10.4-16.9%) and unplanted controls (7.3%). The average PCBs removal percentages of four plant species increased from 26.9% to 37.1% in the rhizosphere soil with addition of RAMEB. Meanwhile, relatively high microbial counts and dehydrogenase activity were detected in planted soils and a stimulatory effect by RAMEB addition was found. The present study indicated that all the plant candidates were feasible for phytoremediation of PCBs contaminated soil from the e-waste recycling area, and tall fescue with RAMEB amendment seemed as a promising remediation strategy. High PCBs removal percentage was due to the increased PCBs bioavailability as well as biostimulation of microbial communities after plantation and RAMEB addition.

Comparison of structure-dependent hormetic cytotoxicity induced by coplanar and non-coplanar PCB congeners

The effect of polychlorinated biphenyls (PCBs) on Vero cell proliferation was investigated, with the attempts to assess the possible hormetic dose-response and to compare their structure-dependent toxicity. Both PCB congeners revealed low doses stimulation in our experiment. However, significant cytotoxicity was only observed in PCB 52 concentrations larger than 0.1 microg ml(-1), while there was no significant inhibition in PCB 77-treated cells at concentrations selected. Furthermore, the time-dependent cytotoxic trends were different. The comparison between PCB 52 and PCB 77 indicated that the cytotoxic mechanisms involved in coplanar or non-coplanar PCB congener exposure were different, and this difference might be associated with individual genotoxicity and the release of contact inhibition, respectively.

Removal of Pyrene from Contaminated Soils by White Clover

Abstract Phytoremediation has been used as an emerging technology for remediation of soil contamination with polycyclic aromatic hydrocarbons (PAHs), ubiquitous persistent environmental pollutants derived from natural and anthropogenic processes, in the last decade. In this study, a pot experiment was conducted to investigate the potential of phytoremediation of pyrene from spiked soils planted with white clover (Trifolium repens) in the greenhouse with a series of pyrene concentrations ranging from 4.22 to 365.38 mg kg−1. The results showed that growth of white clover on pyrenecontaminated soils was not affected. The removal of pyrene from the spiked soils planted with white clover was obviously higher than that from the unplanted soils. At the end of the experiment (60 d), the average removal ratio of pyrene in the spiked soils with white clover was 77%, which was 31% and 57% higher than those of the controls with or without micobes, respectively. Both roots and shoots of white clover took up pyrene from the spiked soils and pyrene uptake increased with the soil pyrene concentration. However, the plant-enhanced dissipation of soil pyrene may be the result of plant-promoted microbial degradation and direct uptake and accumulation of pyrene by white clover were only a small part of the pyrene dissipation. Bioconcentration factors of pyrene (BCFs, ratio of pyrene, on a dry weight basis, in the plant to that in the soil) tended to decrease with increase in the residual soil pyrene concentration. Therefore, removal of pyrene in the contaminated soils was feasible using white clove.

Effect of sulphur on soil Cu/Zn availability and microbial community composition.

Successful phytoremediation depends mainly on the bioavailability of copper (Cu) and zinc (Zn) in the soil. We studied the potential effects of sulphur (S) amendment on mobility of copper, zinc and microbial community composition in soil under laboratory conditions. The results showed that with S application at 20 g S kg(-1), soil pH decreased about 3 units and the solubility of the Cu and Zn significantly increased after 64 days of incubation. The concentration of Cu in Cu-accumulator Elsholtzia splendens shoots and roots increased with S treatment. Concentration of Cu in the shoots was 156.5 mg kg(-1) under S treatment. It was 2.5 times of without application of S. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprint analysis revealed that there were certain groups of acidophilic soil bacteria in the soil after addition of S. We found specific clones such as 1 (from biofilter-treating hydrogen sulfide and methanol) and 4 (from metal-rich and acidic River Tinto) in the soil with S treatment. The above results indicated that S facilitated the mobility of Cu and Zn by soil microorganism and provided a basis for further studies of S-assisted phytoremediation.

Hormesis response of marine and freshwater luminescent bacteria to metal exposure

The stimulatory effect of low concentrations of toxic chemicals on organismal metabolism, referred to as hormesis, has been found to be common in the widely used luminescence bioassay. This paper aims to study the hormesis phenomenon in both marine and freshwater luminescent bacteria, named Photobacterium phosphorem and Vibrio qinghaiensis. The effects of Cu (II), Zn (II), Cd (II) and Cr (VI) on luminescence of these two bacteria were studied for 0 to 75 minutes exposure by establishing dose- and time-response curves. A clear hormesis phenomenon was observed in all four testing metals at low concentrations under the condition of luminescence assays.

Determination of copper binding in Pseudomonas putida CZ1 by chemical modifications and X-ray absorption spectroscopy

Previously performed studies have shown that Pseudomonas putida CZ1 biomass can bind an appreciable amount of Cu(II) and Zn(II) ions from aqueous solutions. The mechanisms of Cu- and Zn-binding by P. putida CZ1 were ascertained by chemical modifications of the biomass followed by Fourier transform infrared and X-ray absorption spectroscopic analyses of the living or nonliving cells. A dramatic decrease in Cu(II)- and Zn(II)-binding resulted after acidic methanol esterification of the nonliving cells, indicating that carboxyl functional groups play an important role in the binding of metal to the biomaterial. X-ray absorption spectroscopy was used to determine the speciation of Cu ions bound by living and nonliving cells, as well as to elucidate which functional groups were involved in binding of the Cu ions. The X-ray absorption near-edge structure spectra analysis showed that the majority of the Cu was bound in both samples as Cu(II). The fitting results of Cu K-edge extended X-ray absorption fine structure spectra showed that N/O ligands dominated in living and nonliving cells. Therefore, by combining different techniques, our results indicate that carboxyl functional groups are the major ligands responsible for the metal binding in P. putida CZ1.