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.

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.

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.

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.

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.

Using a high biomass plant Pennisetum hydridum to phyto-treat fresh municipal sewage sludge.

The study was carried out to investigate the use of a high biomass plant, Pennisetum hydridum, to treat municipal sewage sludge (MSS). An experiment composed of plots with four treatments, soil, fresh sludge, soil-sludge mixture and phyto-treated sludge, was conducted. It showed that the plant could not survive directly in fresh MSS when cultivated from stem cuttings. The experiment transplanting the incubated cutting with nurse medium of P. hydridum in soil and fresh MSS, showed that the plants grew normally in fresh MSS. The pilot experiment of P. hydridum and Alocasia macrorrhiza showed that the total yield and nutrient amount of P. hydridum were 9.2 times and 3.6 times more than that of A. macrorrhiza. After plant treatment, MSS was dried, stabilized and suitable to be landfilled or incinerated, with a calorific value of about 5.6MJ/kg (compared to the initial value of 1.9MJ/kg fresh sludge).

[Enhanced Phytoextraction of Heavy Metals from Contaminated Soils Using Sedum alfredii Hance with Biodegradable Chelate GLDA].

Chemically enhanced phytoextraction by hyperaccumulator has been proposed as an effective approach to remove heavy metals from contaminated soil. Pot experiment was conducted to investigate the effect of application of the biodegradable chelate GLDA (L glutamic acid N,N-diacetic acid) at different doses or the combination of GLDA with EDTA (ethylenediamine tetraacetic acid) or CIT (citric acid) on the uptake of Cd, Zn and Pb by Sedum alfredii Hance (a Zn and Cd hyperaccumulator). Experimental results showed that GLDA addition to soil significantly increased the concentrations of Cd and Zn in Sedum alfredii Hance and its Cd and Zn phytoextraction compared to the control. Additionally, GLDA at 2.5 mmol · kg(-1) resulted in the highest phytoextraction, being 2.5 and 2.6 folds of the control for Cd and Zn, respectively. However, the combined application of GLDA + EDTA (1:1) and GLDA + CIT (1 :1 and 1:3) at a total dose of 5 mmol · kg(-1) did not increase the phytoextraction of Zn and Cd, compared to the GLDA only treatment. Therefore, the biodegradable chelate GLDA could be regarded as a good chelate candidate for the phytoextraction of heavy metals of heavy metals from contaminated soils, particularly for Cd and Zn contaminated soils.

Phytoremediation of sewage sludge and use of its leachate for crop production.

The land application of sewage sludge has the potential risk of transferring heavy metals to soil or groundwater. The agricultural reuse of sludge leachate could be a cost-effective way to decrease metal contamination. Sludge leachate collected during the phytoremediation of sludge by co-cropping with Sedum alfredii and Zea mays was used for irrigating vegetables in a field experiment. Results indicate that the concentrations of Cu, Zn, Pb, and Cd in sludge leachates complied with the National Standards for agricultural irrigation water in China. For the vegetable crop Ipomoea aquatica, nutrients obtained only from the sludge leachate were not sufficient to support growth. For the second crop, Brassica parachinensis, no differences in biomass were observed between the treatment with leachate plus a half dose of inorganic fertilizer and the treatment with a full dose of inorganic fertilizers. The concentrations of heavy metals in I. aquatica and B. parachinensis were not significantly affected by the application of sludge leachates. Compared with initial values, there were no significant differences in Zn, Cd, Cu, and Pb concentrations in soil following treatment with sludge leachate. This study indicates that on range lands, sludge phytoremediation can be conducted at the upper level, and the generated sludge leachate can be safely and easily used in crop production at the lower level.

Cadmium sorption characteristics of soil amendments and its relationship with the cadmium uptake by hyperaccumulator and normal plants in amended soils.

In order to select appropriate amendments for cropping hyperaccumulator or normal plants on contaminated soils and establish the relationship between Cd sorption characteristics of soil amendments and their capacity to reduce Cd uptake by plants, batch sorption experiments with 11 different clay minerals and organic materials and a pot experiment with the same amendments were carried out. The pot experiment was conducted with Sedum alfredii and maize (Zea mays) in a co-cropping system. The results showed that the highest sorption amount was by montmorillonite at 40.82 mg/g, while mica was the lowest at only 1.83 mg/g. There was a significant negative correlation between the n value of Freundlich equation and Cd uptake by plants, and between the logarithm of the stability constant K of the Langmuir equation and plant uptake. Humic acids (HAs) and mushroom manure increased Cd uptake by S. alfredii, but not maize, thus they are suitable as soil amendments for the co-cropping S. alfredii and maize. The stability constant K in these cases was 0.14-0.16 L/mg and n values were 1.51-2.19. The alkaline zeolite and mica had the best fixation abilities and significantly decreased Cd uptake by the both plants, with K > or = 1.49 L/mg and n > or = 3.59.

[Continuous remediation of heavy metal contaminated soil by co-cropping system enhanced with chelator].

In order to elucidate the continuous effectiveness of co-cropping system coupling with chelator enhancement in remediating heavy metal contaminated soils and its environmental risk towards underground water, soil lysimeter (0.9 m x 0.9 m x 0.9 m) experiments were conducted using a paddy soil affected by Pb and Zn mining in Lechang district of Guangdong Province, 7 successive crops were conducted for about 2.5 years. The treatments included mono-crop of Sedum alfredii Hance (Zn and Cd hyperaccumulator), mono-crop of corn (Zea mays, cv. Yunshi-5, a low-accumulating cultivar), co-crop of S. alfredii and corn, and co-crop + MC (Mixture of Chelators, comprised of citric acid, monosodium glutamate waste liquid, EDTA and KCI with molar ratio of 10: 1:2:3 at the concentration of 5 mmol x kg(-1) soil). The changes of heavy metal concentrations in plants, soil and underground water were monitored. Results showed that the co-cropping system was suitable only in spring-summer seasons and significantly increased Zn and Cd phytoextraction. In autumn-winter seasons, the growth of S. alfredii and its phytoextraction of Zn and Cd were reduced by co-cropping and MC application. In total, the mono-crops of S. alfredii recorded a highest phytoextraction of Zn and Cd. However, the greatest reduction of soil Zn, Cd and Pb was observed with the co-crop + MC treatment, the reduction rates were 28%, 50%, and 22%, respectively, relative to the initial soil metal content. The reduction of this treatment was mainly attributed to the downwards leaching of metals to the subsoil caused by MC application. The continuous monitoring of leachates during 2. 5 year's experiment also revealed that the addition of MC increased heavy metal concentrations in the leaching water, but they did not significantly exceed the III grade limits of the underground water standard of China.

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.

Effect of composting on the removal of semivolatile organic chemicals (SVOCs) from sewage sludge.

In order to investigate the occurrence and removal of semivolatile organic chemicals (SVOCs) in the compost of sewage sludge, three different composting treatments, including manual turned compost (MTC), intermittent aerated compost (IAC), and naturally aerated compost (NAC) were conducted. Thirty SVOCs in composts were Soxhlet-extracted and analyzed by GC/MS. After 56 days of composting, the total concentrations of 16 polycyclic aromatic hydrocarbons (∑PAHs) ranged from 0.55 to 8.20 mg kg(-1) dry weight, decreasing in order of IAC>MTC>NAC. The total concentrations of six phthalic acid esters (∑PAEs), five chlorobenzenes or three nitroaromatic compounds were less than 5.0 mg kg(-1). Compared with the initial concentrations in sewage sludge, a significant reduction of ∑PAHs, ∑PAEs and chlorobenzenes was observed. The removal rates of ∑PAHs and ∑PAEs ranged from 54.6% to 75.9% and from 58.3% to 90.6%, respectively. Compared with different composting processes, MTC showed the highest potential for removal of SVOCs.

[Effects of mixed chelators on the leaching of cadmium in contaminated soils under intercropping system].

In order to elucidate the influence of chelators on Cd leaching in contaminated soil, outdoor soil column (100 cm) leaching experiments were conducted using two paddy soils irrigated with Pb-Zn mining wastewater. Soil samples which under intercropping systems were collected from Qingyuan City (acid soil with pH 4.63) and Lechang city (neutral soil with pH 6.51), Guangdong Province of China. The mixture of chelators (MC) comprised of citric acid, monosodium glutamate waste liquid, EDTA and KCl with molar ratio of 10 : 1 : 2 : 3 at the concentration of 5 mmol x kg(-1) soil. The intercropping system used in this study was a Zn- and Cd-hyperaccumulator (Sedum alfredii) and a low-accumulating crop (Zea mays). Results showed that at day 2 after the application of MC, the Cd concentrations in leachates from every layer of neutral and acid soils increased significantly in the treatment with intercropping and MC. At day 8 the concentrations of Cd in leachate from layers below 20 cm in the neutral soil and below 60 cm in the acid soil were still significantly higher than those of control. However, the mobility of Cd was decreased greatly compared with that at day 2. At day 2 and day 8 the Cd concentrations in leachates from every layer of neutral and acid soils in the Co-crop + MC treatments exceed the value of the Groundwater Quality Standards (GB/T 14848-93). Cd in all soil columns showed the trend to migrate downwards, especially in the acid soil. The total Cd in the soil layers of 20 cm and 40 cm was decreased by 40% -58% and 39%-49% respectively at the end of the experiments compared to the initial value. After leaching of 100 days,the total Cd in 0-40 cm soil layer of acid soil reached the limit of National Soil Environmental Quality Standards (GB 15618-1995). The results also implied that in Cd-contaminated soil MC addition might enhance the potential risks of Cd contamination in groundwater.

[Reducing nutrients loss by plastic film covering chemical fertilizers].

With the low utilization rate of fertilizers by crop and the growing amount of fertilizer usage,the agricultural non-point source pollution in China is becoming more and more serious. The field experiments planting corns were conducted, in which the applied chemical fertilizers were recovered with plastic film to realize the separation of fertilizers from rain water. In the experiments, the influences of different fertilizing treatments on the growing and production of sweet corn were observed. The fertilizer utilization rate and the nutrient contents in surface run-off water with and without the film covering were also determined. Results showed that, with only 70% of the normal amount of fertilizers,the sweet corn could already get high yield under the experimental soil conditions. Soil analysis after corn crops showed that the amounts of available N, P and K in the soil increased obviously with the film-covering, and the decreasing order was: 100% fertilizers with film-covering > 70% fertilizers with film-covering > 100% fertilizers, 70% fertilizers > no fertilizer. The average utilization coefficients of fertilizers by the crop were 42%-87%, 0%-3%, 5%-15% respectively for N, P and K. It was higher with film-covering than that without covering, especially for the high fertilization treatment. Analysis of water samples collected for eight run-off events showed that, without film-covering, N, P and K average concentrations in the runoff waters with fertilizations were 27.72, 2.70 and 7.07 mg x L(-1), respectively. And they were reduced respectively by 39.54%, 28.05%, 43.74% with the film-covering. This can give significant benefits to the decrease of agricultural non-point source pollution and water eutrophication.

[Metal removal from contaminated soil by co-planting phytoextraction and soil washing].

Combining the different soil remediation technologies can overcome the shortcoming of a single technique, for example, the combination of phyto-extraction with chemical washing can enhance the phytoextraction and build up an effective technology. In a pot experiment, the co-crop of Sedum alfredii and Zea mays was conducted, chemical washing was also applied with different mixtures of chelators (MC). Metals amounts washed by leaching, the uptake of metals by plants and the metals contents remained in soils were determined. Results showed that the co-crop combining with 10 mmol x L(-1) MC washing removed the highest amount of Zn and Cd,and after 2 crops, the removal rates reached 6.0% and 40.46% of the soil total metal respectively for Zn and Cd, which were higher than those for the only co-planting. Soil analysis showed that the two successive co-crops with MC washings decreased soil Cd,Zn and Pb by 27.8% - 44.6%,12.6% -16.5% and 3.6% - 5.7%, respectively. Chemical washing with 50 mmol x L(-1) MC affected the growth of S. alfredii and resulted in higher metal contents in thereafter leachate water than the other less concentrated washing agents. EDDS ([S, S]-ethylenediaminedisuccinic acid) enhanced the phytoextraction of Cd and Zn but did not effectively wash Pb. Zn and Cd removal mainly depended on phytoextraction while Pb removal relied on MC-washing in this combined technology, by which the multi-metals contamination problem could be resolved.

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.

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.