Ecological effects of combined pollution associated with e-waste recycling on the composition and diversity of soil microbial communities.

The crude processing of electronic waste (e-waste) has led to serious contamination in soils. While microorganisms may play a key role in remediation of the contaminated soils, the ecological effects of combined pollution (heavy metals, polychlorinated biphenyls, and polybrominated diphenyl ethers) on the composition and diversity of microbial communities remain unknown. In this study, a suite of e-waste contaminated soils were collected from Guiyu, China, and the indigenous microbial assemblages were profiled by 16S rRNA high-throughput sequencing and clone library analysis. Our data revealed significant differences in microbial taxonomic composition between the contaminated and the reference soils, with Proteobacteria, Acidobacteria, Bacteroidetes, and Firmicutes dominating the e-waste-affected communities. Genera previously identified as organic pollutants-degrading bacteria, such as Acinetobacter, Pseudomonas, and Alcanivorax, were frequently detected. Canonical correspondence analysis revealed that approximately 70% of the observed variation in microbial assemblages in the contaminated soils was explained by eight environmental variables (including soil physiochemical parameters and organic pollutants) together, among which moisture content, decabromodiphenyl ether (BDE-209), and copper were the major factors. These results provide the first detailed phylogenetic look at the microbial communities in e-waste contaminated soils, demonstrating that the complex combined pollution resulting from improper e-waste recycling may significantly alter soil microbiota.

Biochar: an effective amendment for remediating contaminated soil.

Biochar is a carbon-rich material derived from incomplete combustion of biomass.Applying biochar as an amendment to treat contaminated soils is receiving increasing attention, and is a promising way to improve soil quality. Heavy metals are persistent and are not environmentally biodegradable. However, they can be stabilized in soil by adding biochar. Moreover, biochar is considered to be a predominant sorptive agent for organic pollutants, having a removal efficiency of about 1 order of magnitude higher than does soil/sediment organic matter or their precursor substances alone.When trying to stabilize organic and inorganic pollutants in soil, several features of biochar' s sorption capacity should be considered, viz., the nature of the pollutants to be remediated, how the biochar is prepared, and the complexity of the soil systemin which biochar may be used. In addition, a significant portion of the biochar or some of its components that are used to remediate soils do change over time through abiotic oxidation and microbial decomposition. This change process is commonly referred to as "aging:" Biochar "aging" in nature is inevitable, and aged biochar exhibits an effect that is totally different than non-aged biochar on stabilizing heavy metals and organic contaminants in soils.Studies that have been performed to date on the use of biochar to remediate contaminated soil are insufficient to allow its use for wide-scale field application.Therefore, considerable new data are necessary to expand both our understanding of how biochar performs in the field, and where it can be best used in the future for soil remediation. For example, how biochar and soil biota (microbial and faunal communities)interact in soils is still poorly understood. Moreover, studies are needed on how to best remove new species of heavy metals, and on how biochar aging affects sorption capacity are also needed.

[Research Progress in Reducing Pollution and Sequestration of Carbon by Carbon Neutral Plants].

Under the dual constraints of economic development and ecological carrying capacity, it is necessary to explore more technical means to achieve carbon neutrality and peak in China. Plants are important carriers of terrestrial and marine carbon sink systems, whereas phytoremediation is also a scientific method to remedy environmental pollution. However, the current studies mostly focus on the single aspect of plant carbon sequestration (including both the reduction of pollutant concentrations in environmental media and degradation of pollutants) or plant pollution reduction, without considering the dual benefits of plant pollution reduction and carbon sequestration. In order to explore the carbon neutral effect of plants, we focused on the pollution reduction and carbon sequestration effect of carbon neutral plants and its progress and evaluated the pollution reduction and carbon sequestration potential of carbon neutral plants and other organisms (such as animals and soil microorganisms) and environmental functional materials. The mechanisms underlying the synergistic coupling of carbon neutral plants and animals, microorganisms, and environmental functional materials and ecosystems in reducing pollution and carbon sequestration were also explored. Finally, we proposed constructive prospects for future research on the effects of carbon neutral plants on pollution reduction and carbon sink.

Effects of soil polycyclic musk and cadmium on pollutant uptake and biochemical responses of wheat (Triticum aestivum).

The single and joint toxicological effects of AHTN and cadmium (Cd) on early developmental stages of wheat, including AHTN and Cd uptake, chlorophyll (CHL), malondialdehyde (MDA), superoxide dismutase (SOD), and peroxidase (POD) contents in the seedlings, were investigated. Uptake of AHTN or Cd by seedlings increased with an increase in the concentrations of AHTN and Cd in soil. The presence of Cd inhibited the uptake of AHTN in wheat seedlings, while the low concentration of AHTN could induce the uptake of Cd. The biosynthesis of CHL was significantly inhibited by single AHTN and joint stress with AHTN and Cd. The MDA contents in wheat leaves and roots were significantly affected by single and joint stress with AHTN and Cd. SOD and POD activities in leaves was significantly induced by AHTN and Cd. However, the effect of AHTN and Cd on SOD and POD activities in roots was insignificant. This might indicate that wheat leaves were more sensitive to the binary mixture than wheat roots.

Terrestrial ecotoxicological effects of the antimicrobial agent triclosan.

Triclosan is an antimicrobial agent widely used in many contemporary consumer and health care products. This study assayed phytotoxicity of triclosan using plant growth tests, soil microbial activity using soil respiration and phosphatase activity tests and soil microbial functional diversity using the Biolog ECO plates. The results showed that triclosan inhibited plant growth in soil, with rice seeds being more sensitive than cucumber seeds with EC50 values of 57 and 108 mg/kg. Soil respiration was significantly inhibited in the treatments with triclosan at concentrations more than 10mg/kg (dry soil) during the first 4 days of incubation, but recovered later on after longer incubation. Phosphatase activity was also inhibited for all the soils treated with triclosan (from 0.1 to 50mg/kg dry soil), but a declining inhibition was observed after 2 days of incubation. Biolog analysis found that triclosan treatment increased the utilization of carbon sources and exerted no adverse effects on the functional diversity of soil microbial community.

Cadmium tolerance and accumulation of Althaea rosea Cav. and its potential as a hyperaccumulator under chemical enhancement.

The role of ornamental plants has drawn much attention as the urban pollution levels exacerbate. Althaea rosea Cav. had showed its strong tolerance and accumulation ability of Cd in our previous work, thus, the effects of ethylenediamine triacetic acid (EDTA), ethylenegluatarotriacetic acid (EGTA) and sodium dodecyl sulfate (SDS) on its Cd phytoremediation capacity were further investigated in this work. It reconfirmed that the species had strong tolerance and accumulation ability of Cd. Particularly, the species can be regarded as a potential Cd-hyperaccumulator through applying chemical agents. However, different chelators and surfactants had great differences in affecting hyperaccumulating characteristics of the species. EGTA and SDS could not only increase the dry biomass of the plants, but also promote Cd accumulation in shoots and roots. On the contrary, EDTA was toxic to the species by restraining the growth of plants, although it could promote Cd accumulation in shoots and roots of the plants to a certain extent. Thus, EGTA and SDS were effective in enhancing phytoremediation with Althaea rosea Cav. for Cd contaminated soils, while EDTA is ineffective in this regard.

Seasonal dynamics of phytoplankton in relation to key aquatic habitat factors in a polluted urban small water body in Tianjin, China.

To evaluate the seasonal dynamics of phytoplankton and its relationships with aquatic habitat factors in polluted urban landscape lakes, annual investigations have been carried out in the West zone of Xinkai Lake. The results showed that the lake belongs to the eutrophic-supertrophic type in terms of key habitat factors measurement. The seasonal succession of phytoplankton community was determined. The dominant cyanobacterial species Oscillatoria tenuis Ag. bloomed in autumn, although the other species with higher degrees of dominance never bloomed in the year investigated. Significant correlations between some habitat factors and phytoplankton biomass were observed.

Oxidative stress biomarkers of the polychaete Nereis diversicolor exposed to cadmium and petroleum hydrocarbons.

Changes in the activity of antioxidant enzymes including superoxide dismutase (SOD) and peroxidase (POD) and in the content of soluble protein (SP) in Nereis diversicolor exposed to cadmium (Cd) and petroleum hydrocarbons (PHCs) were investigated under a laboratory condition. The results indicated that SOD activity in N. diversicolor exposed to Cd and PHCs significantly (P<0.05) increased with exposure time. This increase of SOD activity can be considered a sensitive biomarker of oxidative stress by Cd and PHCs. The decrease in POD activity and SP content in N. diversicolor could also sensitively reflect oxidative stress induced by Cd and PHCs. Concentration combination of Cd and PHCs had significant (P<0.05) influences on the activity of SOD and POD, as called double-dose dependent effects. There were highly significant (P<0.01) effects of exposure time on SOD activity in N. diversicolor at single or joint exposure of Cd and PHCs. Exposure time also resulted in significant differences in POD activity (P<0.05) and SP content (P<0.01) in N. diversicolor which was simultaneously exposed to Cd and PHCs, as called time-dependent effects. Compared with day 0, SOD activity in non-exposed N. diversicolor increased, possibly due to the effects of temperature. Therefore, the effects of pollutants with emphasis on abiotic parameters on the antioxidant defense system should be considered in future studies.

Growth responses of three ornamental plants to Cd and Cd-Pb stress and their metal accumulation characteristics.

Up to now, there was no document on ornamental plants that had been applied to phytoremediation, which can remedy contaminated environment and beautify it at the same time. Thus, the growth responses and possible phytoremediation ability of three ornamental plants selected from the previous preliminary experiments were further examined under single Cd or combined Cd-Pb stress. The results showed that these tested plants had higher tolerance to Cd and Pb contamination and could effectively accumulate the metals, especially for Calendula officinalis and Althaea rosea. For C. officinalis, it grew normally in soils containing 100 mg kg(-1) Cd without suffering phytotoxicity, and the Cd concentration in the roots was up to 1084 mg kg(-1) while the Cd concentration in the shoots was 284 mg kg(-1). For A. rosea, the Cd accumulation in the shoots was higher than that in the roots when the Cd concentration in soils was <100 mg kg(-1), and reached 100 mg kg(-1) as the criteria of a Cd hyperaccumulator when the Cd concentration in soils was 100 mg kg(-1). Their accumulation and tolerance to Cd and Pb were further demonstrated through the hydroponic-culture method. And A. rosea had a great potential as a possible Cd hyperaccumulator under favorable or induced conditions. Furthermore, the interactive effects of Cd and Pb in the three ornamentals were complicated, not only additive, antagonistic or synergistic, but also related to many factors including concentration combinations of heavy metals, plant species and various parts of plants. Thus, it can be forecasted that this work will provide a new way for phytoremediation of contaminated soils.

Microbial community structure and function in sediments from e-waste contaminated rivers at Guiyu area of China.

The release of toxic organic pollutants and heavy metals by primitive electronic waste (e-waste) processing to waterways has raised significant concerns, but little is known about their potential ecological effects on aquatic biota especially microorganisms. We characterized the microbial community composition and diversity in sediments sampled along two rivers consistently polluted by e-waste, and explored how community functions may respond to the complex combined pollution. High-throughput 16S rRNA gene sequencing showed that Proteobacteria (particularly Deltaproteobacteria) dominated the sediment microbial assemblages followed by Bacteroidetes, Acidobacteria, Chloroflexi and Firmicutes. PICRUSt metagenome inference provided an initial insight into the metabolic potentials of these e-waste affected communities, speculating that organic pollutants degradation in the sediment might be mainly performed by some of the dominant genera (such as Sulfuricurvum, Thiobacillus and Burkholderia) detected in situ. Statistical analyses revealed that toxic organic compounds contributed more to the observed variations in sediment microbial community structure and predicted functions (24.68% and 8.89%, respectively) than heavy metals (12.18% and 4.68%), and Benzo(a)pyrene, bioavailable lead and electrical conductivity were the key contributors. These results have shed light on the microbial assemblages in e-waste contaminated river sediments, indicating a potential influence of e-waste pollution on the microbial community structure and function in aquatic ecosystems.

Metal accumulation in the polychaete Hediste japonica with emphasis on interaction between heavy metals and petroleum hydrocarbons.

The accumulation of cadmium (Cd) and copper (Cu) in the polychaete Hediste japonica exposed to the mixture of Cd (or Cu) and petroleum hydrocarbons (PHCs) was investigated and compared with that exposed to single Cd (or Cu). The increased bioavailability of Cd or Cu with exposure concentrations resulted in an increase in the accumulation and net accumulation rate of Cd or Cu during single metal exposure. The net accumulation rate of Cd increased, but the net accumulation rate of Cu decreased with exposure time during single metal exposure, suggesting that H. japonica could actively regulate Cu burden in their body by inhibition of absolute uptake or promotion of excretion. The interactions between Cd (or Cu) and PHCs had complicated influences on the net accumulation rate of Cd and Cu in H. japonica under the condition of the binary mixture, which are dependent on their concentration combinations and exposure time.

Effects of exogenous chelators on phytoavailability and toxicity of Pb in Zinnia elegans Jacq.

Chelate-enhanced phytoremediation is considered as an effective method for the extraction of lead (Pb) by plants. However, more detailed studies are needed to evaluate the effect of exogenous chelators on phytoavailability and toxicity of Pb in plants, then to find out the proper applied concentration of chelators to minimize the combined toxicity to the plants and maximize phytoavailable Pb. To clarify these questions, the seed germination test of Zinnia elegans Jacq. exposed to solutions containing Pb and four types of chelators including sodium ethylenediamine tetra-acetic acid (Na2EDTA), oxalic acid, tartaric acid and citric acid was observed. The results showed that the roots and shoots treated with equimolar chelators and Pb were longer than those treated with half and two folds of the molar concentrations of Pb. The growth of seedlings was inhibited by surplus addition of chelators, and the toxicity of complexes was less than that of Pb and chelators. In particular, 2.4 mM EDTA and 1.2 mM oxalic acid significantly (P<0.05) increased Pb uptake when the seeds were treated with 2.4 mM Pb. In the 4.8 mM Pb solution, Pb accumulation in the seedlings was markedly (P<0.05) increased by 4.8 mM EDTA, 2.4 mM tartaric acid, 4.8 mM tartaric acid and 2.4 mM citric acid, and amounted to 6752.4, 6453.8, 6541.4 and 6598.3 microg g(-1), respectively. With the superfluous addition of chelators, Pb accumulation in the seedlings decreased in a concentration-dependent manner. When Pb was used at 2.4 mM, an equimolar concentration of EDTA not only increased Pb uptake but also stimulated the seedling growth. Thus, chelating agents in their appropriately concentrations could counteract Pb toxicity, but superfluous chelators resulted in less Pb uptake and growth inhibition of the seedlings.

Single and joint stress of acetochlor and Pb on three agricultural crops in northeast China.

In order to evaluate ecological risk of agrochemicals in agricultural environment, single and joint toxic effects of an important herbicide and a typical heavy metal on root elongation of crops were investigated. Seeds of the three crops including wheat (Triticum aestivum), Chinese cabbage (Brassica pekimensis) and soybean (Glycine max) as the main crops in northeast China were exposed to acetochlor as a herbicide and lead (Pb) as a heavy metal using the pot-culture method, and meadow brown soil as one of the main soils distributed in northeast China was applied in the investigation. The results indicated that the interactive effects of the two pollutants on root elongation of the three crops were very complicated although they had markedly significant (P < 0.01) linear interrelationships based on the regression analyses. When the concentration of added Pb2+ reached 200 mg/kg, acetochlor and Pb had an antagonistic effect on the inhibition of root elongation of the three crops. However, acetochlor and Pb had significantly (P < 0.05) synergic effects on the inhibition of root elongation when concentration of added Pb2+ was up to 1000 mg/kg. At the low concentration of added Pb, joint toxicity of acetochlor and Pb was more dependent on the concentration of Pb. Among the three crops, wheat was the most sensitive to the toxicity of Pb and Chinese cabbage was the most sensitive to the toxicity of acetochlor.

Single and joint effects of pesticides and mercury on soil urease.

The influence of two pesticides including chlorimuron-ethyl and furadan and mercury (Hg) on urease activity in 4 soils (meadow burozem and phaeozem) was investigated. The soils were exposed to various concentrations of the two pesticides and Hg individually and simultaneously. Results showed that there was a close relationship between urease activity and organic matter content in soil. Chlorimuron-ethyl and furadan could both activate urease in the 4 soils. The maximum increment of urease activity by chlorimuronethyl was up to 14%-18%. There was almost an equal increase (up to 13%-21%) in the urease activity by furadan. On the contrary, Hg markedly inhibited soil urease activity. A logarithmic equation was used to describe the relationship (P<0.05) between the concentration of Hg and the activity of soil urease in the 4 tested soils. Semi-effect dose (ED50) values by the stress of Hg based on the inhibition of soil urease in the 4 soils were 88, 5.5, 24 and 20 mg/kg, respectively, according to the calculation of the corresponding equations. The interactive effect of chlorimuron-ethyl or furadan with metal Hg on soil urease was mainly synergic at the highest tested concentrations.

Joint stress of chlorimuron-ethyl and cadmium on wheat Triticum aestivum at biochemical levels.

Biochemical responses to joint stress of chlorimuron-ethyl and cadmium (Cd) in wheat Triticum aestivum were examined. The joint action of chlorimuron-ethyl and Cd weakened the inhibition of Cd or chlorimuron-ethyl on the formation of chlorophyll. It was deduced that wheat plants had the capability to protect themselves by increasing the activity of the antioxidant enzyme peroxidase (POD) with the exposure time. The joint effect of chlorimuron-ethyl and Cd on the superoxide dismutase (SOD) activity in leaves was additive, while the joint effect on the SOD activity in roots was determined by the interaction of chlorimuron-ethyl and Cd in wheat. It was also concluded that the change of malondialdehyde (MDA) content in wheat might not be a good biomarker in the oxidative damage by chlorimuron-ethyl, while a decrease in the soluble protein content and POD activity in roots could be considered as a biomarker in the damage of wheat by chlorimuron-ethyl and Cd.

Phytoremediation of cadmium-contaminated soils by Rorippa globosa using two-phase planting.

BACKGROUND: Phytoextraction of contaminated soils by heavy metals can provide a great promise of commercial development. Although there are more than 400 species of hyperaccumulators found in the world, phytoremediation technology is rarely applied in field practice for remedying contaminated soils, partially due to low biomass and long growth duration for most of discovered hyperaccumulating plants. In order to enhance the metal-removing efficiency in a year, the two-phase planting countermeasure of phytoextraction by harvesting anthesis biomass was investigated on the basis of the newly found Cd-hyperaccumulator Rorippa globosa (Turcz.) Thell. with 107.0 and 150.1 mg/kg of the Cd accumulation in stems and leaves, respectively, when soil Cd added was concentrated to 25.0 mg/kg. METHODS: The field pot-culture experiment was used to observe the distribution property of R. globosa aboveground biomass and to examine characteristics of accumulating Cd by the plant at different growth stages. The concentration of Cd in plants and soils was determined using atomic absorption spectrophotometry (AAS). RESULTS AND DISCUSSION: The results indicated that the total dry stem and leaf biomass of R. globosa harvested at the flowering phase was up to 92.3% of that at its full maturity and the concentration of Cd in stems and leaves harvested at the flowering phase was up to 73.8% and 87.7% of that at the mature phase, respectively. The Cd-removing ratio by shoots of R. globosa harvested at the flowering phase was up to 71.4% of that at the mature phase. It was also found, by observing the growth duration of R. globosa, that the frostless period at the experiment site was twice as long as the growth time from the seedling-transplanted phase to the flowering phase of the hyperaccumulator. CONCLUSION: R. globosa could be transplanted into contaminated soils twice in one year by harvesting the hyperaccumulator at its flowering phase based on climatic conditions of the site and traits of the plant growth. In this sense, the extraction efficiency of Cd in shoots of R. globosa increased 42.8% compared to that of at its single maturity when the plant was transplanted into contaminated soils after it had been harvested at its flowering phase and the plant accumulated Cd from soil at the same extraction ratio at its second flowering phase. Thus, the method of anthesis biomass regulation by the two-phase planting is very significant to increase the Cd-removing efficiency by phytoremediation used in practice over the course of a year. RECOMMENDATION AND OUTLOOK: As for some hyperaccumulators that the growth duration from the seedling-transplanted phase to the flowering phase are short and the concentrations of heavy metals accumulated in their shoots at the flowering phase are high, the efficiency of phytoremediation can greatly be improved using the method of the two-phase planting.

Influences of petroleum on accumulation of copper and cadmium in the polychaete Nereis diversicolor.

Using the exposure simulation experiment, the action of petroleum affecting the accumulation of the trace metals including copper (Cu) and cadmium (Cd) in littoral polychaete Nereis diversicolor collected from the Shuangtaizi Estuary in Liaoning Province, China was examined. The results showed that there was a markedly non-linear relationship between the accumulation of Cu in worms and the experimental concentration of Cu in exposure solutions when the concentration of petroleum remained at 0, 100, and 220 microl/L, respectively. However, significantly non-linear relationship for worms exposed to Cd was observed only when the concentration of added petroleum was 0 and 220 microl/L. The accumulation of Cu in worms did not differ significantly among the three different levels of petroleum concentrations combined with various concentrations of Cu. So was the accumulation of Cd in worms (p > 0.05). However, the addition of petroleum in exposure solutions brought about an increase in the accumulation of Cu in Nereis diversicolor, in comparison with single Cu pollution. On the other hand, when the concentration of added petroleum remained at 100 microl/L, the accumulation of Cd in worms was lower than that in worms exposed to various concentrations of only cadmium. However, the worms exposed to Cd and petroleum 220 microl/L did not show obvious and identical increase in the accumulation of Cd, compared with single Cd exposure. The accumulation of both Cu and Cd in worms did not increase significantly with the increases in concentrations of Cu or Cd in exposure solutions combined with petroleum (0, 100, and 220 microl/L) under the experimental conditions. Although Nereis diversicolor is exposed to very high Cu and Cd in exposure solutions, accumulation and detoxification mechanisms are sufficient to cope with the extra metal influx in order to survive.

Removal of heavy metals from a contaminated soil using tartaric acid.

This study reports the feasibility of remediation of a heavy metal (HM) contaminated soil using tartaric acid, an environmentally-friendly extractant. Batch experiments were performed to test the factors influencing remediation of the HM contaminated soil. An empirical model was employed to describe the kinetics of HM dissolution/desorption and to predict equilibrium concentrations of HMs in soil leachate. The changes of HMs in different fractions before and after tartaric acid treatment were also investigated. Tartaric acid solution containing HMs was regenerated by chestnut shells. Results show that utilization of tartaric acid was effective for removal of HMs from the contaminated soil, attaining 50%-60% of Cd, 40%-50% of Pb, 40 %-50% of Cu and 20%-30% of Zn in the pH range of 3.5-4.0 within 24 h. Mass transfer coefficients for cadmium (Cd) and lead (Pb) were much higher than those for copper (Cu) and zinc (Zn). Sequential fractionations of treated and untreated soil samples showed that tartaric acid was effective in removing the exchangeable, carbonate fractions of Cd, Zn and Cu from the contaminated soil. The contents of Pb and Cu in Fe-Mn oxide fraciton were also significantly decreased by tartaric acid treatment. One hundred milliliters of tartaric acid solution containing HMs could be regenerated by 10 g chestnut shells in a batch reactor. Such a remediation procedure indicated that tartaric acid is a promising agent for remediation of HM contaminated soils. However, further research is needed before the method can be practically used for in situ remediation of contaminated sites.

Ecological effects of crude oil residues on the functional diversity of soil microorganisms in three weed rhizospheres.

Ecological effects of crude oil residues on weed rhizospheres are still vague. The quantitative and diversity changes and metabolic responses of soil-bacterial communities in common dandelion (Taraxacum officinale), jerusalem artichoke (Silphium perfoliatum L.) and evening primrose (Acalypha australis L.) rhizospheric soils were thus examined using the method of carbon source utilization. The results indicated that there were various toxic effects of crude oil residues on the growth and reproduction of soil bacteria, but the weed rhizospheres could mitigate the toxic effects. Total heterotrophic counting colony-forming units (CFUs) in the rhizospheric soils were significantly higher than those in the non-rhizospheric soils. The culturable soil-bacterial CFUs in the jerusalem artichoke (S. perfoliatum) rhizosphere polluted with 0.50 kg/pot of crude oil residues were almost twice as much as those with 0.25 kg/pot and without the addition of crude oil residues. The addition of crude oil residues increased the difference in substrate evenness, substrate richness, and substrate diversity between non-rhizospheric and rhizospheric soils of T. officinale and A. australis, but there was no significant (p>0.05) difference in the Shannon's diversity index between non-rhizospheric and rhizospheric soils of S. perfoliatum. The rhizospheric response of weed species to crude oil residues suggested that S. perfoliatum may be a potential weed species for the effective plant-microorganism bioremediation of contaminated soils by crude oil residues.

Influences of phosphate nutritional level on the phytoavailability and speciation distribution of cadmium and lead in soil.

A pot experiment was conducted to examine the influence of phosphate levels on the phytoavailability and speciation distribution of cadmium (Cd), lead (Pb) in soil. Spring wheat (Triticum aestivum L.) was selected as the tested plant. There were 5 phosphate fertilizer(Ca(H2PO4)2) levels including 0, 50, 100, 200, and 400 mg P2O5/kg soil, marked by PO, P1, P2, P3, and P4, respectively. CdCl2 x 2.5H2O and Pb(NO3)2 were added to soil as the following levels: Cd + Pb = 25+0, 0+1000, and 25+1000 mg/kg, marked by T1, T2, and T3, respectively. The results showed that the P fertilizer promoted the dry weight of wheat in all treatments and alleviated the contamination induced by Cd and Pb. With increasing levels of the additional P fertilizer, Cd concentration in different parts (root, haulm, chaffand grain) of wheat decreased at the P1 level at first and then increased. The soluble plus exchangeable (SE) fraction of Cd in soil decreased at the P1 level and then increased from P2 to P4 levels. The moderate P fertilizer reduced the phytoavailability of Cd. The application of P could obviously restrain the uptake of Pb by wheat and there were significantly negative correlations between the levels of P and the uptake of Pb. Phosphorus supply resulted in a decrease in the SE fraction of Pb and there was a significantly negative correlation between the levels of P and the SE fraction of Pb in soil. All the levels of the P fertilizer in this experiment could reduce the phytoavailability of Pb. Thus, it is feasible to apply the P fertilizer (Ca(H2PO4)2) to Pb contaminated soils. However, the levels of P application should be restricted in case that redundant P may increase the phytoavailability of Cd.