Y.L Yu

The role of citric acid on the phytoremediation of heavy metal contaminated soil.

Adsorption and hydroponics experiments were conducted to study the role of citric acid on the phytoremediation of heavy metal contaminated soil. The results show that addition of citric acid decreased the adsorption of both lead and cadmium, such an effect was bigger for cadmium than for lead. The decrease in the adsorption of Pb and Cd was mainly due to a decrease of pH in the presence of citric acid. The presence of citric acid could alleviate the toxicity of Pb and Cd to radish, and stimulate their transportation from root to shoot. The studies of heavy metal forms using sequential extraction demonstrated that lead was mainly existed as FHAC (a lower bioavailable form) in the root, while F(HCl) was the dominant form in the leaf. The addition of citric acid to the soil changed the concentration and relative abundance of all the forms. The detoxifying effect of citric acid to Pb in shoots might result from the transformation of higher toxic forms into lower toxic forms. Cadmium was mainly present as F(NaCl), therefore, it had higher toxicity than lead. The addition of citric acid increased the abundance of F(H2O) + F(NaCl), indicating that citric acid treatment could transform cadmium into more transportable forms.

Rapid degradation of butachlor in wheat rhizosphere soil

The degradative characteristics of butachlor in non-rhizosphere, wheat rhizosphere, and inoculated rhizosphere soils were measured. The rate constants for the degradation of butachlor in non-rhizosphere, rhizosphere, and inoculated rhizosphere soils were measured to be 0.0385, 0.0902, 0.1091 at 1 mg/kg, 0.0348, 0.0629, 0.2355 at 10 mg/kg, and 0.0299, 0.0386, 0.0642 at 100 mg/kg, respectively. The corresponding half-lives for butachlor in the soils were calculated to be 18.0, 7.7, 6.3 days at 1 mg/kg, 19.9, 11.0, 2.9 days at 10 mg/kg, and 23.2, 18.0, 10.8 days at 100 mg/kg, respectively. The experimental results show that the degradation of butachlor can be enhanced greatly in wheat rhizosphere, and especially in the rhizosphere inoculated with the bacterial community designated HD which is capable of degrading butachlor. It could be concluded that rhizosphere soil inoculated with microorganisms-degrading target herbicides is a useful pathway to achieve rapid degradation of the herbicides in soil.

Physiological mechanism of plant roots exposed to cadmium

Physiological experiments on plant roots exposed to cadmium were conducted on carrot and radish using a liquid culture and a pot experiment with a series of cadmium applications. Activities of four enzymes (catalase, peroxidase, polyphenol oxidase, superoxide dismutase), and concentrations of free proline and malonaldehyde in the roots of both plants were investigated. Results showed that the germination rate and growth of roots of both plants were inhibited at the concentration of 20 mg Cd/l, and the inhibition was increased with the increasing concentrations of cadmium, both in the liquid culture and in the pot experiment; activities of the four enzymes declined similarly in both species. The concentration of proline in roots reached the maximum when the application of cadmium was at the level of 20 mg/l in the liquid culture (or 20 mg/kg in soil), and then it declined slowly with the increasing concentration of cadmium. However, the reverse trend was observed for the concentration of malonaldehyde. All of bio-indicators measured here was quite sensitive to the addition of cadmium.

Effect of cadmium on nodulation and N2-fixation of soybean in contaminated soils

The effects of cadmium stress on nodulation, N2-fixation capabilities of the root nodule, the change in ultrastructure of the root nodule, soybean growth, and the distribution of cadmium in plants were studied. The results obtained show that the nodulation of soybean roots was greatly inhibited by the addition of Cd, especially at the addition level of 10 and 20 mg kg(-1) soil. The inhibition of plant growth, especially the root growth, increased as the cadmium concentration increased, with deleterious effects observed for the roots. The weight ratio of soybean root/leaf decreased as the Cd concentration increased, which might explain the reason for nodulation decreases. The results also indicate that N2-fixation of root nodule was stimulated to some extent at the low levels of Cd addition, but decreased sharply with further increase of the Cd concentration. High Cd levels were also associated with changes in the ultrastructure of root nodule, in which the effective N2-fixing area was reduced and the N2-fixing cells in the area also reduced. In addition, the results also reveal that the content of Cd in different parts of the plants was as follows: roots >> stems > seeds, indicating that the accumulation of Cd by roots is much larger than that by any other part of the soybean plant, and might cause deleterious effects to root systems.

Chemical behavior of Cd in rice rhizosphere.

Chemical behavior of Cd in rice rhizosphere as affected or not by Pb was investigated. The NH4OAc extractable Cd in the rhizosphere was distinctly lower than that in bulk soil. The depletion of Cd in the rhizosphere could not be simply attributed to Cd uptake by rice. The observed phenomena could be attributed to the decreasing pH in the rhizosphere and the complexing capabilities of soluble exudates for Cd. Extractable Cd increased in both the rhizosphere and bulk soil after the addition of Pb, which might be caused by the replacement of Pb for Cd. The extractable Cd in the non-rhizosphere varied with the distance from the root surface, especially within 0-1 mm, which was greatly affected by the combined effects of mass flow, activation and fixation, and had the lowest extractable Cd. Pb addition affected the distribution of extractable Cd in the non-rhizosphere, implying that the affinity of Pb for organic matter was greater than that of Cd. The difference of Cd species between rhizosphere and bulk soil demonstrated that the transformation of exchangeable Cd (EXC-Cd) to OM-Cd (bound to organic matter) and FMO-Cd (bound to iron and manganese oxide) occurred in the rice rhizosphere due to the exudations from the rice root, the activity of microorganisms on the root surface and the activation of Fe and Mn oxides. The interaction between Pb and Cd resulted in the content of EXC-Cd being higher in the presence of Pb, whereas the OM-Cd content was lower in the presence of Pb.

Effects of calcium cyanamide on soil microbial communities and Fusarium oxysporum f. sp. cucumberinum

Calcium cyanamide (CaCN(2)) has been one of the potential candidates as soil disinfectant since the restriction of methyl bromide in soil fumigation due to its ecological risk. However, little information is available on effects of CaCN(2) on soil microbial community. In this study, the soil microbial communities and the fate of pathogen Fusarium oxysporum (Schlechtend, Fr) f. sp. cucumberinum (Owen) Snyder and Hansen (F.O. f. sp. cucumberinum) in response to CaCN(2) treatment was evaluated. F.O. f. sp. cucumberinum population in soil treated with CaCN(2) at rates of 80 and 200 gm(-2) was suppressed by 88.7 and 92.2% after 15 d of CaCN(2) application. Bacterial, fungal, and actinomycete populations were also greatly decreased after 3 d of CaCN(2) application, but they recovered to the control level by 15 d. The variation in functional diversity of soil microbes characterized by principal component analysis, diversity and evenness indices based on Biolog data followed a similar trend. Meanwhile, the band number from the DGGE of soil 16S rDNA fragments increased from 9 for the non-CaCN(2)-treated soil to 10 or 12 after different rates of CaCN(2) application at 15 d, indicating the increase of abundant rDNA types in the community. The results suggest that CaCN(2) application had only a short-term and transitory impact on the indigenous soil microbial community in contrast to the long-term suppression of the F.O. f. sp. cucumberinum population. It is feasible to reduce Fusarium wilt without significant impact on microbial community by application of CaCN(2) at reasonable doses.

The different responses of glutathione-dependent detoxification pathway to fungicide chlorothalonil and carbendazim in tomato leaves.

Chlorothalonil (CHT) and carbendazim (CAR) are two widely used fungicides in agriculture. Despite their agronomic importance in pest control, little is known about their detoxification in the plant. In this study, we investigated the effects of these fungicides on glutathione (GSH) content, GSH-dependent enzyme activities and gene expression in tomato leaves. Results showed that exposure to CHT resulted in increases in GSH content, activities of glutathione S-transferases (GSTs) and glutathione reductase (GR), as well as the transcriptional levels of glutathione S-transferase genes (GST1, GST2 and GST3), glutathione synthetase gene (GSH), glutathione reductase gene (GR) and glutathione peroxidase gene (GPX) in tomato leaves, but such increases were not observed in leaves exposed to CAR. In addition, GSTs, GR, peroxidase (POD) activities and most of GSH-dependent gene expression were induced by CHT in a concentration- and time-dependent manner. These results suggest that GSH-dependent pathway plays an important role in the CHT detoxification but not in the CAR detoxification in tomato leaves.

Effects of adsorption on degradation and bioavailability of metolachlor in soil.

The ability of soil to adsorb metolachlor strongly influences its environmental fate, but little information is available on the correlation of its soil adsorption with degradation and bioavailability. The present study was conducted to characterize adsorption, degradation and bioavailability of metolachlor in five soils with different properties, and to investigate the effect of soil adsorption on degradation and bioavailability. Metolachlor was weakly adsorbed to the tested soils with adsorption coefficients ranging from 0.36 to1.18 μg 1-n mL n g -1 , suggesting its potential to move downward with percolating water. Adsorption followed a Freundlich isotherm and was positively correlated with soil organic matter (OM) content (p < 0.01). Degradation of metolachlor in soils obeyed the first-order kinetics, yielding the half-life varying from 37.9 to 49.5 days, which was significantly influenced by soil OM content (p < 0.01). The prolonged half-life by sterilization indicated that biodegradation was the dominant pathway for metolachlor degradation in soils. Uptake and bioaccumulation of metolachlor in soils by Eisenia foetida was also mainly controlled by soil properties, especially OM. Adsorption coefficients were negatively related to half-lives (p < 0.01) and bioaccumulation factors (p < 0.05), indicating that adsorption coefficients might be useful for predicting degradation and bioavailability of metolachlor in soils.

PREDICTION OF BIOAVAILABILITY OF CHLORPYRIFOS RESIDUES IN SOIL TO EARTHWORMS

An incubation test was conducted to investigate the effect of aging on bioavailability of chlorpyrifos in soil and to assess the feasibility of chemical extraction techniques for predicting bioavailability of chlorpyrifos in soil. Chlorpyrifos was spiked into sterilized soil and aged in microcosms for up to 120 days. The earthworms were incubated in the spiked soils, at 0, 7, 14, 30, 60, and 120 days after spiking, for a period of 7 days. After exposure, chlorpyrifos concentrations in the earthworm tissues were determined. Change in chemical extractability of soil-chlorpyrifos was measured using a several solvent systems including methanol, methanol-water (9:1), acetone-water (5:3), and water. The results show that chemical extractability and earthworm bioavailability of chlorpyrifos in soil decreased with aging. The amount of aged and unaged chlorpyrifos recovered from soil varied with the individual chemical extractant and extraction method. Concentrations of chlorpyrifos in Eisenia foetida were significantly higher than in Allolobophora caliginosa, suggesting that the bioavailability of chlorpyrifos was a species-dependent process. The extractability of chlorpyrifos by chemical solvents was significantly correlated with bioavailability fraction of E. foetida and A. caliginosa, showing that these extraction techniques may be efficient for predicting bioavailability of chlorpyrifos in soil.

Characterization of Chinese liquor aroma components during aging process and liquor age discrimination using gas chromatography combined with multivariable statistics

Chinese liquor aroma components were characterized during the aging process using gas chromatography (GC). Principal component and cluster analysis (PCA, CA) were used to discriminate the Chinese liquor age which has a great economic value. Of a total of 21 major aroma components identified and quantified, 13 components which included several acids, alcohols, esters, aldehydes and furans decreased significantly in the first year of aging, maintained the same levels (p > 0.05) for next three years and decreased again (p < 0.05) in the fifth year. On the contrary, a significant increase was observed in propionic acid, furfural and phenylethanol. Ethyl lactate was found to be the most stable aroma component during aging process. Results of PCA and CA demonstrated that young liquor (fresh) and aged liquors were well separated from each other, which is in consistent with the evolution of aroma components along with the aging process. These findings provide a quantitative basis for discriminating the Chinese liquor age and a scientific basis for further research on elucidating the liquor aging process, and a possible tool to guard against counterfeit and defective products.