Cadmium phytoremediation potential of Houttuynia cordata: Insights from growth, uptake, and rhizosphere mechanisms.

Cadmium (Cd) pollutes 7.0 % of China's land area. This study examined the potential of Houttuynia cordata for Cd phytoremediation because of its ability to accumulate Cd in its growth matrix. H. cordata were planted in plastic pots filled with paddy field soils having low (LCd), medium (MCd), and high (HCd) Cd levels of 0.19, 0.69, and 2.91 mg/kg, respectively. After six months of growth, harvested plant parts were evaluated for Cd uptake and tolerance mechanisms. Metabolomics and metagenomics approaches were employed to investigate the soil rhizosphere mechanism. Results showed that the average plant biomass increased as soil Cd increased. The biomass Cd contents surpassed the allowable Cd limits for food (≤ 0.2 mg/kg) and medicinal uses (≤ 0.3 mg/kg). Cd contents were higher in H. cordata roots (30.59-86.27 mg/kg) than in other plant parts (0.63-2.90 mg/kg), with significantly increasing values as Cd soil level increased. Phenolic acids, lipids, amino acids and derivatives, organic acids, and alkaloids comprised the majority (69 in MCd vs HCd and 73 % in LCd vs HCd) of the shared upregulated metabolites. In addition, 13 metabolites specific to H. cordata root exudates were significantly increased. The top two principal metabolic pathways were arginine and proline metabolism, and beta-alanine metabolism. H. cordata increased the abundance of Firmicutes and Glomeromycota across all three Cd levels, and also stimulated the growth of Patescibacteria, Rozellomycota, and Claroideoglomus in HCd. Accordingly, H. cordata demonstrated potential for remediation of Cd-contaminated soils, and safety measures for its production and food use must be highly considered.

Combining potassium chloride leaching with vertical electrokinetics to remediate cadmium-contaminated soils.

This study evaluated the feasibility of combining potassium chloride (KCl) leaching and electrokinetic (EK) treatment for the remediation of cadmium (Cd) and other metals from contaminated soils. KCl leaching was compared at three concentrations (0.2%, 0.5%, and 1% KCl). EK treatment was conducted separately to migrate the metals in the topsoil to the subsoil. The combined approach using KCl leaching before or after EK treatment was compared. For the single vertical EK treatment, the removal of Cd, lead (Pb), copper (Cu) and zinc (Zn) from the topsoil (0-20 cm) was 9.38%, 4.80%, 0.95%, and 10.81%, respectively. KCl leaching at 1% KCl removed 84.06% Cd, 9.95% Pb, 4.34% Cu, and 19.93% Zn from the topsoil, with higher removal efficiency than that of the 0.2% and 0.5% KCl leaching treatments. By combining the KCl leaching and EK treatment, the removal efficiency of heavy metals improved, in particular for the 1% KCl + EK treatment, where the removal rate of Cd, Pb, Cu, and Zn from the upper surface soil reached 97.79%, 17.69%, 14.37%, and 41.96%, respectively. Correspondingly, the soil Cd content decreased from 4 to 0.21 mg/kg, and was below the Chinese standard limit of 0.3 mg/kg soil. These results indicate that 1% KCl + EK treatment is a good combination technique to mitigate Cd pollution from contaminated soils used for growing rice and leafy vegetables.

Degradation and humification of steroidal estrogens in the soil environment: A review.

Emerging pollutants are toxic and harmful chemical substances characterized by environmental persistence, bioaccumulation and biotoxicity, which can harm the ecological environment and even threaten human health. There are four categories of emerging pollutants that are causing widespread concern, namely, persistent organic pollutants, endocrine disruptors, antibiotics, and microplastics. The distribution of emerging pollutants has spatial and temporal heterogeneity, which is influenced by factors such as geographical location, climatic conditions, population density, emission amount, etc. Steroidal estrogens (SEs) discussed in this paper belong to the category of endocrine disruptors. There are generally three types of fate for SEs in the soil environment: sorption, degradation and humification. Humification is a promising pathway for the removal of SEs, especially for those that are difficult to degrade. Through humification, these difficult-to-degrade SEs can be effectively transferred or fixed, thus reducing their impact on the environment and organisms. Contrary to the well-studied process of sorption and degradation, the role and promise of the humification process for the removal of SEs has been underestimated. Based on the existing research, this paper reviews the sources, classification, properties, hazards and environmental behaviors of SEs in soil, and focuses on the degradation and humification processes of SEs and the environmental factors affecting their processes, such as temperature, pH, etc. It aims to provide references for the follow-up research of SEs, and advocates further research on the humification of organic pollutants in future studies.

Fate of heavy metals and major nutrients in a sludge-soil-plant-leachate system during the sludge phyto-treatment process.

Land application of sewage sludge usually leads to increased levels of heavy metals in soil, plants and groundwater. Pre-treatment using plants has been proposed to reduce the contents of heavy metals and water in sludge prior to land application. This study quantified the transfer of Zn, Cd, Pb and major nutrients in a sludge-soil-plant-leachate system during the treatment of sewage sludge. To accomplish this, a two year pot experiment was carried out to collect leachate, mono- and co-cropping of Sedum alfredii and feed crops was conducted in sludge with an under-layer soil support. Sludge phyto-treatment increased Zn and Cd concentrations in the under-layer soil, but not Pb. Specifically, 70%, 70% and 80% of the original Zn, Cd and Pb, respectively, remained in the sludge, while about 40%, 70% and 60% of the original N, P and K remained. Only 3% to 5% of Cd and Zn and < 1% of Pb were transferred into the under-layer soils or leachates, while more than 12% of the N and P were transferred. Co-planting S. alfredii and feed crops led to a significant reduction of heavy metals in leachates when compared with sludge without planting. Overall, sludge leachate is more appropriate than whole sludge for recycling in agriculture since it reduces the chance of heavy metal contamination in the agro-ecosystem; therefore, co-cropping phytotreatment of sludge can be coupled with sludge leachate recycling for crop production and re-collection of the sludge residue for landfilling.

Dissolution of different zinc salts and zn uptake by Sedum alfredii and maize in mono- and co-cropping under hydroponic culture.

Previous soil pot and field experiments demonstrated that co-cropping the hyperaccumulator Sedum alfredii with maize increased Zn phytoextraction by S. alfredii and decreased Zn uptake by maize shoots. This hydroponic experiment was conducted to investigate whether the facilitation of Zn phytoextraction by S. alfredii resulted from improved dissolution in this co-cropping system and its relation to root exudates. S. alfredii and maize were mono- and co-cropped (without a root barrier) in nutrient solution spiked with four Zn compounds, ZnS, ZnO, Zn3(PO4)2 and 5ZnO x 2CO3-4H2O (represented as ZnCO3) at 1000 mg/L Zn for 15 days without renewal of nutrient solution after pre-culture. The root exudates were collected under incomplete sterilization and analyzed. The results indicated that the difference in Zn salts had a greater influence on the Zn concentration in maize than for S. alfredii, varying from 210-2603 mg/kg for maize shoots and 6445-12476 mg/kg for S. alfredii in the same order: ZnCO3 > ZnO > Zn3(PO4)2 > ZnS. For the four kinds of Zn sources in this experiment, co-cropping with maize did not improve Zn phytoextraction by S. alfredii. In most cases, compared to co-cropped and mono-cropped maize, mono-cropped S. alfredii resulted in the highest Zn2+ concentration in the remaining nutrient solution, and also had a higher total concentration of low molecular weight organic acids (LMWOA) and lower pH of root exudation. Root exudates did partly influence Zn hyperaccumulation in S. alfredii.

Field experiments to assess the remediation efficiency of metal-contaminated soil by flushing with ferric chloride followed by applying amendments.

The Cd, Cu, Pb, and Zn removal efficiencies achieved by flushing with FeCl3 were determined in a field experiment using soil contaminated with multiple metals. Soil was first flushed with FeCl3 and then with FeCl3 or a mixture of chelators. Flushed soil was amended with lime and organic matter to revitalize the soil, then the soil was used to grow Zea mays and Brassica juncea. The heavy metal concentrations in groundwater were determined to assess the risks of leaching caused by soil flushing. The Cd, Cu, Pb, and Zn removal efficiencies were 70%, 40%, 33%, and 17%, respectively, when FeCl3 (25 mmol (kg topsoil)-1) was applied. The second washing generally did not significantly decrease the heavy metal contents of the soil but the second FeCl3 washing did decrease the Pb content. Pb leached from topsoil was partly retained by the subsoil 20-40 cm deep. The Zea mays yields were significantly lower but the Brassica juncea yields were significantly higher after the combined soil flushing and amendment treatment than after only the amendment treatment. This indicated that soil flushing only negatively affected growth of deep-rooted Z. mays. The Cd, Cu, Pb, and Zn concentrations in Z. mays grains and the edible parts of B. juncea grown in remediated soil were below the Chinese tolerable limits for contaminants in food. Washing with FeCl3 did not increase groundwater contamination during the study. The results indicated that flushing soil with FeCl3 and subsequent amendments is a technically feasible method for remediating agricultural soil contaminated with Cd.

Phytoextraction and Migration Patterns of Cadmium in Contaminated Soils by Pennisetum hybridum.

This study was conducted to identify soil cadmium (Cd) removal pathways and their contribution rates during phytoremediation by Pennisetum hybridum, as well as to comprehensively assess its phytoremediation potential. Multilayered soil column tests and farmland-simulating lysimeter tests were conducted to investigate the Cd phytoextraction and migration patterns in topsoil and subsoil simultaneously. The aboveground annual yield of P. hybridum grown in the lysimeter was 206 ton·ha-1. The total amount of Cd extracted in P. hybridum shoots was 234 g·ha-1, which was similar to that of other typical Cd-hyperaccumulating plants such as Sedum alfredii. After the test, the topsoil Cd removal rate was 21.50-35.81%, whereas the extraction efficiency in P. hybridum shoots was only 4.17-8.53%. These findings indicate that extraction by plant shoots is not the most important contributor to the decrease of Cd in the topsoil. The proportion of Cd retained by the root cell wall was approximately 50% of the total Cd in the root. Based on column test results, P. hybridum treatment led to a significant decrease in soil pH and considerably enhanced Cd migration to subsoil and groundwater. P. hybridum decreases Cd in the topsoil through multiple pathways and provides a relatively ideal material for phytoremediation of Cd-contaminated acid soils.

[Effectiveness and Mechanisms of Chemical Leaching Combined with Electrokinetic Technology on the Remediation of Heavy Metal Contaminated Soil].

In this study, chemical leaching and electrokinetic technology were used to remediate heavy metal contaminated soil to elucidate its effectiveness and mechanisms. Chemical leaching agents of FeCl3, Fe(NO3)3, KCl, KNO3, and HCl solutions were selected, and the effects of Fe3+, K+, H+, and Cl- on four heavy metal (Cd, Pb, Cu, and Zn) removals were compared and analyzed. Then, the influence of the speciation of heavy metals in soil after chemical leaching on the electrokinetic remediation efficiency was studied. The results showed that Fe3+, K+, H+, and Cl- had different effects on the four heavy metal removals; for Cd and Zn, the removal effect of H+was the most effective, but for Pb and Cu, the effect of Fe3+ was the most obvious. On the whole, FeCl3 and Fe(NO3)3 showed the best removal effect for Cd, Pb, and Cu. For the removal of Zn from the soil, the difference in the removal effect of the five leaching agents was not obvious. In comparison with that of FeCl3 and Fe(NO3)3, the HCl solution had a moderate removal effect on the four heavy metals in the soil, and the neutral salts KCl and KNO3 had little removal effect on the four heavy metals. Especially for Cd and Cu, KCl and KNO3 addition significantly increased the removal of heavy metals through the subsequent electrokinetic remediation. After the chemical leaching, electrokinetic remediation could make heavy metals in the topsoil (0-10 cm) migrate downward and enrich the 10-20 cm and 20-30 cm soil layers, which requires further studies to resolve.

Green remediation of cadmium-contaminated soil by cellulose nanocrystals.

Cellulose nanocrystals (CNC) were used as a novel, green eluent to remediate Cd-contaminated soil in this study. The influence of washing conditions on the removal of Cd, including CNC concentration, pH value, liquid/solid (L/S) ratio, contact time and temperature were investigated. The effect of CNC remediation of Cd-contaminated soil on soil health and the possible remediation mechanism were also explored. The results showed that CNC concentration, pH value and contact time had a significant effect on the removal efficiency of Cd. CNC rapidly removed heavy metals in soil within 30 min. When the pH value of the eluent was 9.0, the removal efficiency of Cd could reach 86.3 %. The eluent mainly removed exchangeable and reducible fractions of Cd, which could effectively reduce the bioavailability of heavy metals. CNC washing had no negative effects on seed growth, species abundance and Shannon index. C-O, -COO- groups on CNC played an important role in the reaction between CNC and soil Cd, and other oxygen-containing functional groups on CNC could also assist in adsorption, ion exchange and chemical complexation processes. Therefore, cellulose nanocrystals had the potential to remediate heavy metal-contaminated soils in a green and efficient manner.

Evaluation of manganese application after soil stabilization to effectively reduce cadmium in rice.

In order to produce safe rice from cadmium (Cd) contaminated soils, a special pot experiment in the field was proposed to facilitate the study of multiple remediation measures. In the field experiments, four treatments were selected for the first half of the year: rice without soil treatment (R); rice with zeolite stabilization (RZ); oilseed rape phytoremediation (OR); and inter-cropping Sedum alfredii and maize phytoremediation (IC). As the early rice with zeolite stabilization still contained elevated Cd, manganese (Mn) fertilizer was added in the late rice with a special pot experiment in the field. Results showed that, in the first crops, the grains of maize and oilseed rape contained Cd below the food standard limit, while Cd in rice grain exceeded the limit of 0.2 mg/kg. The RZ treatment did not reduce Cd in rice but decreased significantly Mn in rice straw. In the late rice, Mn fertilizer additionally reduced Cd in rice grain to 0.12 mg/kg in combination with the RZ treatment. Mn accumulation in rice straw was enhanced by Mn fertilizer. These results indicate that the pot experiment in the field provides a useful tool to further evaluate effective treatment combinations to reduce Cd in rice.

Cadmium adsorption behavior of porous and reduced graphene oxide and its potential for promoting cadmium migration during soil electrokinetic remediation.

In this study, a porous reduced graphene oxide (PRGO) carbon nanomaterial was successfully obtained by activation of natural graphite with KOH at high temperature and was applied as an auxiliary electrode in soil electrokinetic remediation to investigate the promoting effect on Cd migration. We found that PRGO contained a large amount of oxygen-containing groups (hydroxyl and carboxyl groups) and exhibited high Cd2+ adsorption efficiency at pH values above 4, achieving a maximum adsorption capacity of 434.78 mg/g for Cd. In addition, PRGO could selectively adsorb Cd, Pb, Cu, and Zn but not K, Na, or Mg from soil solution. The electrokinetic remediation experiment showed that the PRGO auxiliary electrode promoted the migration of Cd and effectively controlled the increase in soil pH near the cathode, possibly due to ion exchange between the surface functional groups on the auxiliary electrode and Cd2+. In addition, the location of the PRGO auxiliary electrode strongly influenced the migration of Cd. For instance, the soil Cd concentration of treatment H-5 was 57.86% lower than that of H-0 at a distance of 5-10 cm from the electrode; however, the soil Cd concentration measured at 0-5 cm for treatment H-5 was 34.84% higher than that of treatment H-0. Our study demonstrated that PRGO could be applied as an auxiliary electrode to promote Cd migration during electrokinetic remediation of Cd-contaminated soil.

Potential for phytoremediation of nonylphenol from sewage sludge.

Nonylphenol (NP) is considered a major contaminant that must be removed to enable safe and environmentally friendly land application of sewage sludge. Phytoremediation is a technology in which plants are used to remove and/or stabilize organic and inorganic contaminants present in the soil, municipal wastewater, and sewage sludge. In this study, a 391-d large pot experiment was conducted to remove NP from sewage sludge by phytoremediation using Zea mays L. 'Yunshi-5', Lolium perenne L., and co-cropping of the two plants. The fate of NP in the soil under the sewage sludge was assessed at the same time. At the end of the experiment, the NP levels in sludge from the various treatments were as follows: control (38.60%) > L. perenne (31.27%) > Z. mays (16.25%) > co-cropping (15.28%). Degradation followed an availability-adjusted first-order kinetics with a decreasing order of half-lives as follows: control (88.2 d) > L. perenne (87.3 d) > co-cropping (66.2 d) > Z. mays (59.1 d). The results indicated that Z. mays and co-cropping could both degrade NP. The concentrations of NP in tissues of different plants differed significantly. The mean bioconcentration factors for Z. mays and L. perenne were 0.16 and 3.69, respectively. Direct removal of NP from sewage sludge by plant uptake was negligible, as was downward movement of NP in the system. Moreover, NP was not detected in soils in any treatments at harvest.

Aggregation kinetics and mechanisms of silver nanoparticles in simulated pollution water under UV light irradiation.

This paper investigated the effect mechanism of complex components (fulvic acid [FA], sodium dodecylbenzene sulfonate [SDBS], and sodium nitrate [NaNO3 ]) on the aggregation kinetics of polyvinylpyrrolidone-modified silver nanoparticles (PVP-AgNPs) under UV irradiation. The results showed that FA and NaNO3 alone did not cause aggregation due to the high steric hindrance and/or electrostatic repulsive forces. In high concentration of SDBS solution (20-50 mM), the stability of PVP-AgNPs was reduced by adsorbing SDBS on nanoparticle surface and replacing their PVP coatings. A mixed system of two pollutants had a synergistic effect on PVP-AgNPs aggregation. In the mixed system of SDBS and FA, the interaction of SDBS and PVP-AgNPs dominated the aggregation of PVP-AgNPs. NaNO3 significantly improved the aggregation rate of PVP-AgNPs in SDBS solution due to the charge neutralization effect of electrolyte. In 20 mg/L FA solution, the aggregation rate increased slightly with increasing NaNO3 concentration from 50 to 200 mM due to the charge neutralization effect, while the hydrodynamic diameters of PVP-AgNPs increased linearly and rapidly to micrometer size because the spatial conformation of adsorbed FA became compact in high-salinity solution. The calculation results of eDLVO theory were basically consistent with most of the experimental results. PRACTITIONER POINTS: PVP-AgNPs was uniformly dispersed in NaNO3 or FA solution under UV irradiation. PVP-AgNPs formed aggregates in SDBS solutions under UV irradiation. A system with two mixed pollutants had a synergistic effect on promoting aggregation of PVP-AgNPs. eDLVO theory could explain the aggregation results in different chemical conditions except in NaNO3 solution.

Polycyclic aromatic hydrocarbons and phthalic acid esters in vegetables from nine farms of the Pearl River Delta, South China.

This study investigated the occurrence of 16 polycyclic aromatic hydrocarbons (PAHs) and 6 phthalic acid esters (PAEs) in 11 vegetable species collected from nine farms of the Pearl River Delta, South China. Twelve PAH compounds and all PAE compounds were detected by gas chromatography coupled with mass spectrometry (GC-MS) in vegetables. The total concentrations of PAHs (Sigma(PAHs)) and PAEs (Sigma(PAEs)) ranged from 7.0 to 5353 microg kg(-1) dry weight (d.w.), with a mean value of 1173 microg kg(-1) d.w., and from 0.073 to 11.2 mg kg(-1) d.w., with a mean value of 3.2 mg kg(-1) (d.w.), respectively. The highest levels of Sigma(PAHs) and Sigma(PAEs) were found in Brassica juncea and Brassica parachinensis, respectively. For the same vegetable, the bioconcentration factors (BCFs; the ratio of contaminant concentration in plant tissue to the soil concentration) of PAHs (between 0.0037 and 5.5) are generally higher than those of PAEs (between <0.0001 and 0.61). It was also noted that there were great variations of organic contaminant levels, BCFs, and benzo[a]pyrene equivalent concentrations, which depend on the various contaminants, sampling locations, and vegetable species. The occurrences of PAHs and PAEs in this study are compared with those in other studies and their sources are discussed.

Relevance of dissolved organic matter generated from green manuring of Chinese milk vetch in relation to water-soluble cadmium.

Dissolved organic matter (DOM) can become a carrier of soil contaminants. Therefore, an understanding of the evolution and characteristics of DOM produced by Chinese milk vetch during green manuring is crucial. In this study, DOM solutions from 28 days' manuring with three different organic materials were characterized using three-dimensional fluorescence excitation-emission matrix (3D-EEM) with parallel factor (PARAFAC) analysis, and ultraviolet-visible spectroscopy. With the green manuring milk vetch at flowering period (MVFP), the DOC and water-soluble cadmium (WS-Cd) in soil solution reached 1875 mg/l and 2.64 µg/l, respectively, on day 6 after manuring. The PARAFAC analysis modeled three components: protein-like (tryptophan) and two humic-like components (humic acid and fulvic acid); DOM produced by MVFP was primarily protein-like during the early stage of decomposition. The aromaticity and molecular weight of DOM in the MVFP treatment was lower than in the other treatments, which could promote the release of soil particle-adsorbed Cd to soil solution. Principal components analysis showed that aromaticity was the main factor affecting Cd solubility, and the negative linear correlation of aromaticity with WS-Cd reached 0.4827. The results of this study supported the idea that manuring with MVFP might accelerate Cd infiltration to deep soil with water under gravity.

Polycyclic aromatic hydrocarbons and phthalic acid esters in the soil-radish (Raphanus sativus) system with sewage sludge and compost application.

We studied the accumulation of polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters (PAEs) in a latosolic red soil and radish (Raphanus sativus) with application of sewage sludge at rates of 10, 20 and 40 g kg(-1) soil or compost at rate of 10 g kg(-1) soil. In radish the concentrations of individual PAHs and PAEs varied from non-detectable to 803 microg kg(-1) dry weight (d.w.) and from non-detectable to 2048 microg kg(-1) d.w., respectively. Compared to the control, higher application rates of sewage sludge resulted in pronounced increases in shoot, root and soil concentrations of PAHs and PAEs. PAE concentrations in radish grown in soil spiked with sludge compost were higher while the PAH concentrations were comparable to those receiving 10 g kg(-1) of sewage sludge. However, the root biomass of radish in soil amended with compost was significantly higher and the shoot-to-root ratio was significantly lower than in the other treatments. The bioconcentration factors (BCFs, the ratio of contaminant concentration in plant tissue to the soil concentration) of di-n-butyl phthalate and di(2-ethylhexyl) phthalate in both shoots and roots and of total PAH concentrations in roots were less than 1.0, but some BCFs for individual PAHs were high with a maximum value of 80.

The status of soil contamination by semivolatile organic chemicals (SVOCs) in China: a review.

This paper summarizes the published scientific data on the soil contamination by semivolatile organic chemicals (SVOCs) in China. Data has been found for more than 150 organic compounds which were grouped into six classes, namely, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and phthalic acid esters (PAEs). An overview of data collected from the literature is presented in this paper. The Chinese regulation and/or other maximum acceptable values for SVOCs were used for the characterization of soils. In general, the compounds that are mostly studied in Chinese soils are OCPs, PAHs and PCBs. According to the studies reviewed here, the most abundant compounds were PAEs and PAHs (up to 46 and 28 mg kg(-1) dry weight, respectively); PCBs and OCPs occurred generally at concentrations lower than 100 microg kg(-1) dry weight. Nevertheless, quite high concentrations of PCDD/Fs, PCBs and PBDEs were observed in contaminated sites (e.g., the sites affected by electronic waste activities). The average concentrations of PAHs and OCPs in soils of North China were higher than those in South China. The principal component analysis demonstrated different distribution patterns for PAH, PCB and PCDD/F congeners and for the various sites/regions examined. The isomer ratios of DDTs and hexachlorocyclohexanes (HCHs) indicated different sources and residue levels in soils. Finally, this review has highlighted several areas where further research is considered necessary.

Toxic effects of chlorate on three plant species inoculated with arbuscular mycorrhizal fungi.

Pot experiments were conducted to examine the toxic effects of chlorate on bermudagrass, bahiagrass, and longan seedling with a focus on arbuscular mycorrhizal fungi-plant associations. The results show that application of chlorate could cause slight soil acidification, but the resulting pH was still around 5.5, which is unlikely to adversely affect plant growth. Increase in the application rate of chlorate resulted in a decrease in colonization rate of arbuscular mycorrhizal fungi in plant roots, P uptake by the plants and plant biomass. This appears to suggest that the reduction in plant growth may be related to impeded uptake of P by the plants due to the failure of the plants to form sufficient mycorrhizal associations when chlorate is in sufficient amounts to cause toxicity to arbuscular mycorrhizal fungi. Under the experimental conditions set for this study, bermudagrass suffered from stronger chlorate stress than bahiagrass and longan seedling did in terms of plant-arbuscular mycorrhizal fungi (AMF) symbiosis development.

Effect of mixed chelators of EDTA, GLDA, and citric acid on bioavailability of residual heavy metals in soils and soil properties.

Soil washing is an effective technology for the remediation of multi-metal contaminated soils. However, bioavailability of residual heavy metals in soils and soil properties could be changed during washing processes. This study investigated the effects of EDTA, FeCl3 and mixed chelators (MC) on bioavailability of residual heavy metals in soils and soil biological properties after soil washing. The results showed that soil washing by chelators successfully decreased the total concentration of heavy metals in soils, while it did not effectively decrease the exchangeable fraction of heavy metals, especially for calcareous contaminated soil. The toxic effects of the washed soils seemed to exhibit higher correlations with the changes in the soil properties such as soil pH and nutrient concentrations. As compared with FeCl3 and EDTA, MC tended to moderately change soil properties (e.g., pH, total N, available N, available P, and exchangeable K, Ca, and Mg). Additionally, MC-washed soil had the least influence on the soil enzymes activities, and had the highest germination and growth of Chinese cabbage. Accordingly, MC is a moderate washing solution in the removal of heavy metals from multi-metal contaminated soils, and had minimal negative effects on soil qualities.

Quantitative determination of organic priority pollutants in the composts of sewage sludge with rice straw by gas chromatography coupled with mass spectrometry.

In order to investigate the occurrence and distribution of organic contaminants in the compost of sewage sludge with rice straw, four different composting treatments at a low carbon/nitrogen (C/N) ratio (13:1) were conducted. Thirty semi-volatile organic compounds (SVOCs) listed as priority pollutants by both China and the US Environmental Protection Agency (EPA) were Soxhlet-extracted, separated and analyzed by gas chromatography coupled with mass spectrometry (GC-MS). The results showed that after composting (56 days) most of SVOCs were detected in the final composts. The total concentrations of polycyclic aromatic hydrocarbons (PAHs) and phthalic acid esters ranged from 1.8 to 10 mg/kg dry weight (d.w.) and from 9.8 to 18 mg/kg d.w., respectively, being significantly higher than those of chlorobenzenes and nitroaromatic compounds which were generally less than 1.0 mg/kg d.w. The concentrations and predominant compounds of organic contaminants in the different composts varied, and were affected by their physico-chemical properties and the composting processes. Concentrations of SVOCs in the static aerated composting processes especially intermittently aerated composting treatment were considerably lower than those in the manual-turned composting treatments. Concentrations of organic contaminants especially PAHs and di(2-ethylhexyl) phthalate in the final composts were in agreement with the maximum permissible limits for agricultural purposes proposed by the European Union and by the EPA.