Plant Uptake Of Heavy Metals Research Articles

Effect of EDDS Application on Soil Cu/Cd Availability and Uptake/transport by Castor

To investigate the effect of chelating agents on plant uptake of heavy metals, castor (Ricinus communis L.) was used as the test plant. Soil culture and pot experiments were conducted to study the effects of different concentrations of ethylenediamine disuccinic acid (EDDS) on the forms of Cu and Cd in soil and their absorption and transport by castor. The results showed that the application of EDDS significantly increased the content of available Cu and Cd. After 15 days of cultivation, the available Cu and Cd concentrations in the soil increased by 43.01%-103.55% and 51.78%-69.43%, respectively. EDDS promoted the conversion of reducible Cu to weak acid extractable and increased the mobility of Cu. Meanwhile, the application of EDDS promoted the absorption, transport, and enrichment of Cu in castor. Under the application of 2.5 mmol·kg-1 EDDS and 5.0 mmol·kg-1 EDDS, the Cu concentrations in the shoots were 4.88 times and 16.65 times higher than that of the control (P< 0.05), and the Cu concentrations in the roots were 2.89 times and 3.60 times higher than that of the control (P< 0.05), respectively. The Cu transport coefficient significantly increased by 72.73% and 381.82% when treated with EDDS 2.5 and EDDS 5.0. Simultaneously, the phytoextraction of Cu in shoots, roots, and their sum were 14.08, 2.16, and 4.70 times higher than that of the control (P<0.05), respectively, when treated with EDDS 5.0. Furthermore, EDDS significantly increased the Cd concentrations in castor. When treated with EDDS 2.5 the shoots and roots increased by 15.15% and 57.42%, respectively, and the phytoextraction of total Cd significantly increased by 13.44%. Generally, the EDDS treatment could increase the available Cu and Cd in soil, promote the uptake of Cu and Cd, and improve the phytoremediation efficiency of castor. Among them, the addition of 5.0 mmol·kg-1 EDDS had the best effect for Cu, whereas the addition of 2.5 mmol kg-1 EDDS had a higher increase in the phytoextraction of Cd.

Increasing phosphorus plant availability from P-rich ashes and biochars by acidification with sulfuric acid

Biochars and ashes derived from thermal treatment of P-rich wastes could be used as bio-based fertilizers to improve P recycling. However, thermal treatments often result in low plant P availability. Acidification of these materials before soil application could potentially increase plant P availability. Based on the water-extractable P levels obtained in titration experiments, sulfuric acid concentrations between 2.5 M and 10 M were applied to digestate solids char and ash (DS-C, DS-A), poultry litter ash (PL-A), insect frass char (IF-C), sewage sludge char and ash (SS-C, SS-A) and meat and bone char (MB-C). Acidified and untreated materials were applied in a pot experiment with maize in 33P labeled soil to determine fertilizer P uptake. The acidification resulted in a significant increase in P solubility. The amount of acid required depended on the materials’ buffer capacity and P speciation. Based on XRD analysis, we assume that mainly Ca-associated P was solubilized. In the pot experiment, acidified materials outperformed untreated materials and the unfertilized control in terms of biomass and P uptake. The P recovery from the acidified materials ranked in the order DS-C > SS-A > PL-A > IF-C > DS-A > SS-C > MB-C. The acidification did not significantly decrease soil pH, nor was there an effect on plant heavy metal availability. In conclusion, acidification increased plant growth and P uptake without affecting plant heavy metal uptake and soil pH. Therefore, acidification to increase the P fertilizer value of ashes and chars is a promising approach to facilitate P recycling.

Phytoremediation Effect and Soil Microbial Community Characteristics of Jiulong Iron Tailings Area, Jiangxi

The aim of this paper was to explore the remediation effect and mechanism of Wetland pine (Pinus elliottii), Chinese fir (Cunninghamia lanceolata (Lamb.) Hook), and Alder (Alnus cremastogyne Burkill) on heavy metal contaminated soil in the iron tailings of Jiulong Iron Tailings Area. At the same time, the specificity of plant rhizosphere and non-rhizosphere soil microbial community structure and ecological function were analyzed based on macrogenomic sequencing. The results showed that the dominant microbial genera in J1 (control) was Acidobacteria, followed by Proteobacteria and Actinobacteria. The microbial genera with the highest percentage of relative abundance in J2, J3, J4, J5, and J6 (J2, Wetland Pine rhizosphere; J3, Wetland Pine non-rhizosphere; J4, Chinese fir rhizosphere; J5, Alder rhizosphere; J6, Alder non-rhizosphere) were Proteobacteria, followed by Acidobacteria, and Actinobacteria. It was found that Proteobacteria promoted heavy metal solubilization, activated heavy metals, and converted their forms to improve plant uptake of heavy metals. This proves that the microorganisms of Proteobacteria are the key microbial genera in the study of regional heavy metal remediation. The antibiotic resistance genes (ARGs) in microorganisms can respond to the inducement of heavy metals. Here, we investigated the relationship between the abundance of soil microorganisms ARGs and heavy metal pollution in Jiulong Iron Tailings Area. There are significant differences in the quantity and category of ARGs in the rhizosphere and non-rhizosphere soil samples of the three tree species. The results of this study provide the foundation for the theory and practice of remediation of heavy metal contamination in soils of iron tailing areas in Jiulong Iron Tailings Area in similar stand conditions.

Sepiolite, Palygorskite, and Triple Super Phosphate on the Uptake of Heavy Metals by Two Iranian Wheat Cultivars Inoculated With Piriformospora indica Fungus

Background and Purpose: Soil remediation in contaminated soils is an important factor of environmental research. This research evaluated the effect of sepiolite, palygorskite, and triple super phosphate (TSP) on decreasing the heavy metals uptake by wheat cultivars inoculated with Piriformospora indica (P. indica). Materials and Methods: Treatments included applying sepiolite, palygorskite (at the rate of 0% and 5% (W/W), and TSP (0% and 0.5% W/W) in the Pb- and Zn-polluted soil under cultivation of 2 wheat cultivars (Mihan and Pishgam cultivars) that inoculated with P. indica fungus. Plants were harvested after 90 days, and Pb and Zn concentrations in soils and plants were measured using atomic absorption spectroscopy. Furthermore, the catalase (CAT) enzyme activity was also measured. Results: With applying 5% (W/W) sepiolite and palygorskite, the plant Pb concentration was significantly reduced by 11.8%, while the plant Zn concentration increased by 13.9%. Plant Zn and Pb concentrations considerably increased and decreased following plant inoculation. However, plant cultivars showed different results. Our results showed that the Pb and Zn concentrations were lower in Mihan than in the Pishgam wheat cultivar. In addition, increasing soil Pb availability caused a significant increase in CAT enzyme activity. Soil contamination with heavy metals had a negative impact on plant root colonization. Conclusion: The interaction of plant cultivars and P. indica significantly affected plant heavy metal uptake by plants. However, environmental studies have found that applying organic amendments like nan-clays or TSP can reduce the absorption of Pb by plants.

Selected rhizobacteria facilitated phytoremediation of barren and heavy metal contaminated gold mine tailings by Festuca arundinacea

Gold mine tailings pose a significant challenge for phytoremediation due to their poor nutrition and heavy metal pollution. Rhizobacteria-assisted phytoremediation is a promising method, yet limited research has been conducted on its application in gold mine tailings. In this study, rhizobacteria R1 (Bacillus paramycoides) and R2 (Klebsiella michiganensisW14T) were isolated from the rhizosphere of Festuca arundinacea (F. arundinacea) to enhance the phytoremediation of gold mine tailings. Our results showed that inoculation of R1 and R2 led to a significant increase in the average germination rates of F. arundinacea by 36.9% and 16.5%, respectively. Furthermore, the average plant height increased by 68.3% and 53.4%, respectively. Importantly, after inoculation with rhizobacteria, the contents of Mn, Pb, and As in F. arundinacea increased by 13.2–33.9%, 40.1–41.0%, and 98.1%–124.5%, respectively, indicating that the rhizobacteria enhanced the plant uptake of heavy metals. The improved nutrient content and enzyme activity in the tailings after inoculation with rhizobacteria were positively correlated with the heavy metal content in F. arundinacea. In addition, inoculation of rhizobacteria significantly altered the microbial community structure of the tailings, with Bacillus becoming the dominant genus in the rhizosphere tailings of F. arundinacea after R1 inoculation. Overall, our findings demonstrated that rhizobacteria R1 was better to enhance the phytoremediation of gold mine tailings. These results offer valuable insights into the mechanism of rhizobacteria-assisted phytoremediation and provide a practical method to enhance remediation of gold mine tailings.

Coal gangue modified bioretention system for runoff pollutants removal and the biological characteristics

In this study, coal gangue (CG) was applied as media in bioretention system to remove runoff pollutant. CG modified bioretention systems show good removal efficiency towards runoff pollutant due to the high adsorption capacity of CG. The removal of total phosphorus (TP), total nitrogen (TN), ammonia (NH4+-N) and chemical oxygen demand (COD) by CG modified bioretention systems was influenced by diverse rainfall conditions including rainfall concentration, recurrence period and drying period, and their removal rate ranged 94–99%, 30–70%, 83–97% and 33–86%, respectively. The effluent concentration of Zn, Pb and Cu was as low as 3.14–10.99 μg/L, 0.66–2.56 μg/L and 0.60–3.15 μg/L, respectively. In addition, CG could promote the plant heavy metal uptake and thus decrease their accumulation in soil to a certain extent. Meanwhile, Malondialdehyde (MDA) content and peroxidases (POD) activities of plants in CG modified bioretention were lower than that in tradition bioretention, indicating that CG could help plants recovery and lessened the oxidative stress for the negative impact of high heavy metals accumulation. CG-based media alleviated the inhibitory effect of rainwater runoff pollutant accumulation (especially heavy metals) on microbial diversity and the enhancement of the dominant bacteria (such as Proteobacteria and Bacteroidota) could conduce the nutrients removal in the bioretention systems. In overall, this study demonstrated that the CG modified bioretention systems show an excellent removal performance combine with biological effects.

Effects of biochar on soil properties, heavy metal availability and uptake, and growth of summer squash grown in metal-contaminated soil

• Biochar types had high variability in physical and chemical properties. • Biochar application helped in modifying the physio-chemical properties of soil. • Biochar types and rates played a vital role in the immobilization of heavy metals. • Casuarina biochar was more suitable for plant growth in metal-polluted soils. • Both BCF and TF varied significantly for different types and rates of biochars. Pollution of agricultural soil with heavy metals is a serious hazard to the environment and human health. The application of biochar can be a cost-effective and environmentally friendly way to reduce heavy metal bioavailability in contaminated soils and thus their uptake by plants. A pot experiment was conducted to evaluate the effect of three types of biochar (mango, Casuarina and Salix as feedstocks) at two application rates (2% and 4% w/w) on soil characteristics, heavy metal availability in soil and bioaccumulation in plants, as well as the growth of summer squash grown in highly polluted soil. The results indicated that the highest dry weight of root and shoot was recorded at the lowest application rate of Casuarina biochar followed by mango and Salix biochars. Compared to untreated soil, the adding of Casuarina biochar at 4% decreased the concentrations of Cd, Co, Cr, Cu, Ni, Pb and Zn by 25.7%, 52.1%, 12.1%, 32.3%, 31.0%, 85.0% and 25.2% in the root, and by 37.2%, 66.9%, 24.3%, 40.2%, 42.0%, 89.2% and 35.5% in the shoot, respectively. Casuarina biochar at 4% treatment was found to be the most effective in reducing the uptake of heavy metals by roots and shoots. Also, this treatment had the highest significant reductions in the availability of heavy metals over the untreated soil. The reductions in bioconcentration factor and translocation factor achieved with biochar application varied significantly for different types and rates of biochars. All biochar applications increased significantly soil pH, organic matter and electrical conductivity compared to untreated soil. It can be concluded that Casuarina biochar has great potential as a soil amendment for increasing the heavy metal immobilization, reducing the availability and plant uptake of heavy metals, and enhancing the growth of summer squash plants. :

Copyrolysis of food waste and rice husk to biochar to create a sustainable resource for soil amendment: A pilot-scale case study in Jinhua, China

Worldwide, massive amounts of food waste have been generated at increasingly accelerated rates, posing potentially great risks to the environment. Shifting traditional waste treatment to a sustainable bioeconomy thus challenges food chain management worldwide. In this study, food waste was copyrolyzed with rice husk to produce biochar with a pilot-scale industrialized system. The efficiency of the material conversion and the properties and functions of the produced biochars as well as the potential environmental impacts of pyrolysis were evaluated using in situ measurements, physico-chemical characterization and in vitro (pot) experiments with biochar. The results showed that the emissions of potential toxic compounds and metals from the pyrolysis system were within the guideline limits under the legislation of China or the EU commission. On average, biochar yielded approximately 20% of feedstock and contained a total organic carbon content of 433 g kg−1. In the pot experiment, Chinese cabbage yield and quality were significantly improved, and the plant uptake of heavy metals was significantly reduced in soil amended with food waste biochar compared to no biochar amendment. Furthermore, the food waste biochar was blended with mineral nutrients to create a biochar based compounded N-P-K fertilizer. Application of the biochar based compound fertilizer exerted a significant positive effect on cabbage growth and nutrient use efficiency relative to a conventional mineral compound fertilizer. For per tonne of dry mass of food waste, copyrolysis costed less than 60 USD but gained a gross profit of more than 30 USD. Therefore, the copyrolysis of food waste with crop residues could be applicable to the safe recycling of food waste into value added products to raise agricultural production.

Presence and Plant Uptake of Heavy Metals in Tidal Marsh Wetland Soils.

Marsh grasses have been used as efficient tools for phytoremediation and are known to play key roles in maintaining ecosystem functions by reducing the contamination of coastlines. This study was initiated to understand how human activities in wetlands can impact ion-heavy metal concentrations in relation to native and invasive marsh grasses. The study site, Blackbird Creek (BBC) is a tidal wetland that experiences agricultural, fishing, recreational, residential and other anthropogenic activities throughout the year. Heavy metals cadmium, arsenic, and lead in the soils and marsh grasses were monitored along with the ion compositions of soils. The main objective of this study was to understand if the marsh soils containing monotypic stands of native (Spartina) and non-native (Phragmites) vegetation display similar levels of heavy metals. Differences were observed in the concentrations of heavy metals at study sites with varying marsh vegetation types, and in soils containing vegetation and no vegetation. The soils with dense Spartina and Phragmites stands were anaerobic whereas soil at the boat ramp site was comparatively less anaerobic and also had increased levels of cadmium. Heavy metal concentrations in soil and Phragmites leaves were inversely correlated whereas they were positively correlated in Spartina sites. Electrical conductivity and pH levels in soil also showed increased cadmium and arsenic concentrations. These findings collectively infer that human activities and seasonal changes can increase soil complexities affecting the bioavailability of metals.

Biochar Affects Heavy Metal Uptake in Plants through Interactions in the Rhizosphere

Heavy metals in soil pose a constant risk for animals and humans when entering their food chains, and limited means are available to reduce plant accumulation from more or less polluted soils. Biochar, which is made by pyrolysis of organic residues and sees increasing use as a soil amendment to mitigate anthropogenic C emissions and improve agronomic soil properties, has also been shown to reduce plant availability of heavy metals in soils. The cause for the reduction of metal uptake in plants when grown in soils enriched with biochar has generally been researched in terms of increased pH and alkalinity, while other potential mechanisms have been less studied. We conducted a pot experiment with barley using three soils differing in metal content and amended or not with 2% biochar made from Miscanthus x giganteus, and assessed plant contents and changes in bioavailability in bulk and rhizosphere soil by measuring extractability in acetic acid or ammonium nitrate. In spite of negligible pH changes upon biochar amendment, the results showed that biochar reduced extractability of Cu, Pb and Zn, but not of Cd. Rhizosphere soil contained more easily extractable Cu, Pb and Zn than bulk soil, while for Cd it did not. Generally, reduced plant uptake due to biochar was reflected in the amounts of metals extractable with ammonium nitrate, but not acetic acid.

Fate and transfer of heavy metals following repeated biogas slurry application in a rice-wheat crop rotation

The application of biogas slurry, from anaerobic digestion of livestock excreta, to cropland has proven to be an effective mechanism for recycling nutrients within farms. However, the potential pollution of heavy metals from repeated biogas slurry fertilization has not received much attention. Here we present the results of a field experiment under rice-wheat rotation demonstrating the accumulation, speciation distribution and plant uptake of heavy metals (Cu, Zn, Pb and Cd) in soil following biogas slurry application. The treatments were: zero biogas slurry application (BS0), and biogas slurry application for three (BS3) and five (BS5) years, at a rate of 450 m3 ha−1 y−1. Our findings show that biogas slurry fertilization resulted in accumulation of Cu and Zn in the soil. The concentrations of soil Cu and Zn under BS5 were, respectively, 38 and 29% greater in the wheat season and 35 and 35% greater in the rice season relative to BS0 (p < 0.05). The bioavailability of soil Cu and Zn increased following biogas slurry application. Plant uptake of Cu and Zn to all parts of wheat and rice plants (excluding Cu in wheat straw) increased with the years of biogas slurry application (p < 0.05), and the concentration of Cd in wheat grain was significantly greater in BS5 relative to BS0 (p < 0.05). After five years of biogas slurry fertilization, concentrations of Cu, Zn, Pb and Cd in wheat grains were 3.28, 25.19, 0.11 and 0.053 mg kg−1 and 4.24, 33.78, 0.12 and 0.035 mg kg−1 for rice grains, respectively, all within the safety limits. Our results demonstrate that repeated biogas slurry fertilization for five years has a relatively low pollution risk of heavy metals. However, long-term field monitoring and co-application with metal-immobilizing materials are required to ensure the safety of its application to cropland.

Effects of fillers combined with biosorbents on nutrient and heavy metal removal from biogas slurry in constructed wetlands

The performance of fillers (biochar and zeolite) and their combinations with biosorbents (compound microbial agent and chlorella) in nutrients and heavy metals removal from biogas slurry in constructed wetlands (CWs) planted water spinach (Ipomoea aquatica) and plant uptake of heavy metals was investigated. The results demonstrated that the removal rate of nutrients in CWs was all above 60%. COD removal efficiencies were not significantly affected by fillers and biosorbents, all above 80%. The removal rates of TN and NH4+-N were the highest when the two fillers and two biosorbents were added, and the combination of biochar and chlorella presented the optimal removal effect on TP. The efficiency of removing heavy metals from biogas slurry in CWs was As > Zn > Cu, and their removal rates were 35.38%–83.89%, 8.15%–23.69% and 0.32%–0.88%, respectively. The removal efficiency of As by the combination of biochar and composite microbial agent was high. The combination of the two fillers and two biosorbents had the best effect on reducing Cu and Zn enrichment in the aboveground part of water spinach in each treatment, while biochar alone had the best effect on reducing As enrichment in the aboveground and underground parts of water spinach. This study can provide a basis for the application of fillers and biosorbents in the treatment of biogas slurry in livestock and poultry farms in wetlands.

Nitrogen fertilizer enhances zinc and cadmium uptake by hyperaccumulator Sedum alfredii Hance

Nitrogen (N) fertilization is known to have a substantial effect on heavy metal uptake in plants. However, the impact of N fertilization on plant growth and heavy metal uptake of hyperaccumulator plants remains unclear. This study examined the effect of N fertilization on growth and uptake of zinc (Zn) and cadmium (Cd) in Zn/Cd-hyperaccumulating plants species, Sedum alfredii (S. alfredii) Hance (Crassulaceae). Plants of S. alfredii were grown for 60 days in nutrient solution with 100 μmol Cd L−1 and 0–10 mmol N L−1, and in a Cd-contaminated soil receiving N fertilizer and composted pig manure amendment. Biomass production, nutrient uptake, and concentrations and accumulation of Zn and Cd in plant parts were measured. In the hydroponic experiment, both low ( 5 mmol L−1) N supply decreased the growth and Zn and Cd accumulation in the whole plants. The 2.5 mmol N L−1 is an optimal N dosage for shoot biomass production and Zn accumulation in shoots, while the 1.0 mmol N L−1 is an optimal N dosage for Cd accumulation in shoots, which was 68.1% higher than the control. The N doses of 1 to 2.5 mmol L−1 N represented optimal conditions for Zn and Cd accumulation in the shoots of S. alfredii seedlings. In the soil pot experiment, shoot dry weight decreased with increasing N fertilization rate, while composted pig manure decreased biomass production. Both Zn and Cd accumulation in the shoots of S. alfredii decreased along with the addition of higher N fertilization rate. However, the composted pig manure amendment increased the accumulation of Zn, but not Cd in the shoots. The application of N at appropriate amount enhanced the phytoremediation efficiency by S. alfredii in Zn/Cd-polluted fields, but the effectiveness of phytoextraction technology needs to be validated in the field trials.

Optimization of plant hormonal balance by microorganisms prevents plant heavy metal accumulation.

Heavy metal contamination is a threat to global food safety. Reducing heavy metal uptake in plants is a promising way to make plants safer, yet breeding the right set of traits can be tedious. We test whether microorganisms are able to impact the plant's hormonal balance hereby helping to manage plant heavy metal uptake. We focus on ethylene, a plant hormone regulating plant stress tolerance and nutrition. We grew three phylogenetically distinct plants, Rumex palustris, Alcea aucheri and Arabidopsis thaliana, on a cadmium-spiked soil. Plants roots were coated with the bacterium Pseudomonas putida UW4, which degrades the precursor of ethylene, or an isogenic ACC deaminase-deficient mutant lacking this ability. We followed ethylene concentrations, plant growth and cadmium uptake. Wildtype bacteria reduced shoot cadmium concentration by up to 35% compared to the control, while the mutant increased cadmium concentration. This effect was linked to ethylene, which was consistently positively correlated with cadmium concentration. We therefore propose that bacteria modulating plant hormonal balance may offer new possibilities to improve specific aspects of plant phenotype, in the present context reducing heavy metal. They may thus pave the way for new strategies to improve food safety in a context of the widespread soil contamination.

Roles of root cell wall components and root plaques in regulating elemental uptake in rice subjected to selenite and different speciation of antimony

Root plaques and cell wall components play important roles in regulating the uptake of heavy metals in rice plants. Proper doses of selenium (Se) can reduce heavy metal uptake in plants. Whether Se can influence both the formation of root plaques and the contents of root cell wall components to affect heavy metal uptake in plants is unknown. A hydroponic culture system was set up using rice plants (Yangdao No.6) to mainly investigate the roles of root plaques and cell wall components in regulating the uptake of antimony (Sb) and Se in rice plants subjected to Se and different speciation of antimony [antimonite (Sb(III)) and antimonate (Sb(V))]. Se alone or plus different speciation of Sb showed a negative effect on plant growth. Addition of Se did not counteract the toxic effect of inhibiting rice plant growth exerted by Sb, despite the addition of Se to the solution containing 20 mg L−1 Sb(III) or Sb(V) significantly reduced Sb concentration in the roots. Addition of Se stimulated the formation of Mn plaque and addition of 5 mg L−1 Sb(III) or Sb(V) increased the formation of Fe plaque. When compared to the 20 mg L−1 Sb(III) treatment, the addition of 0.8 mg L−1 Se significantly increased the Fe plaque, but did not result in more accumulation of Sb on the root plaques. Other levels of Se did not show positive effects on the formation of Fe plaque on the roots of this rice plant when exposed to Sb(III) or Sb(V). In many cases, the single addition of Se, Sb(III) or Sb(V), especially for Se, can significantly increase the production of pectin, hemicelluloses and lignin. Additional Se helped rice plants exposed to Sb(III) or Sb(V) generate more pectin, hemicelluloses and lignin, especially when exposed to Sb(V). In summary, we speculate that Se inhibits, in most cases, the uptake of Sb in rice plants by affecting the root cell components rather than the formation of root plaques.

Heavy metals distribution and their bioavailability in earthworm assistant sludge treatment wetland.

Sludge treatment wetlands (STWs) have been used for sludge treatment in recent years, however, heavy metals (HMs) are one of the limiting factors for the final sludge application, and the fate of HMs in STWs are still not well studied. Therefore, six STWs with two plant species and earthworm addition were investigated to evaluate their effects on HMs distribution and bioavailability. The results showed that plant uptake of HMs was insignificant with earthworm addition. Earthworm had the highest enrichment for Cd with bioaccumulation factors of 6.9-7.3. Moreover, earthworm had a positive effect to remove HMs in accumulated sludge. Meanwhile, the bioavailability of Cd in accumulated sludge was decreased by earthworm addition, with the acid-soluble fraction decreased from range 16.5-22.7% to range 7.2-10.1%. Furthermore, HMs mass balance in the STWs revealed that HMs were widely distributed in the accumulated sludge, leachate and others, while their (except Cd) accumulation in the plants and earthworm are less than 1%. The Cd toxicity in the accumulated sludge can be reduced by the addition of earthworm with enrichment of 3.6-8.2%. Overall, earthworm addition have positive effects on distribution and bioavailability of HMs in STWs.

Fate of heavy metals and polycyclic aromatic hydrocarbons (PAH) in sewage sludge carbonisates and ashes – A risk assessment to a thermochemical phosphorus-recycling process

In the near future, phosphorus (P) recycling will gain importance in terms of decreasing primary resources. Sewage sludge (SSL) is an adequate secondary P-resource for P-fertilizer production but it is also a sink for heavy metals and organic pollutants. The present study is an investigation on thermochemical P-recycling of SSL. Various temperatures and amendments were tested regarding their performance to remove heavy metals and polycyclic aromatic hydrocarbons (PAH) and simultaneous increase of the plant-availability of P. The investigations were carried out on two types of SSL originating from wastewater treatment plants with chemical P-precipitation and enhanced biological P-removal, respectively. The results show that thermochemical treatment with chlorine donors is suitable to remove the majority of heavy metals and that a combination of a gaseous chlorine donor (HCl) and sodium additives leads to both high heavy metal removal and high plant availability of P. Furthermore, plant experiments show that almost all investigated thermochemical treatments can significantly reduce the bioavailability and plant uptake of heavy metals. Furthermore, PAHs are secondarily formed during low-temperature treatments (400–500 °C), but can be significantly reduced by using sodium carbonate as an additive.

Mycorrhizal symbiosis and phosphorus fertilization effects on Zea mays growth and heavy metals uptake

ABSTRACTArbuscular mycorrhizal fungi (AMF) can promote plant growth and reduce plant uptake of heavy metals. Phosphorus (P) fertilization can affect this relationship. We investigated maize (Zea mays L.) uptake of heavy metals after soil AMF inoculation and P fertilization. Maize biomass, glomaline and chlorophyll contents and uptake of Fe, Mn, Zn, Cu, Cd and Pb have been determined in a soil inoculated with AMF (Glomus aggregatum, or Glomus intraradices) and treated with 30 or 60 µg P-K2HPO4 g−1 soil. Consistent variations were found between the two mycorrhizal species with respect to the colonization and glomalin content. Shoot dry weight and chlorophyll content were higher with G. intraradices than with G. aggregatum inoculation. The biomass was highest with 30 µg P g−1 soil. Shoot concentrations of Cd, Pb and Zn decreased with G. aggregatum inoculation, but that of Cd and Pb increased with G. intraradices inoculation. Addition of P fertilizers decreased Cd and Zn concentrations in the shoot. AMF with P fertilization greatly reduced maize content of heavy metals. The results provide that native AMF with a moderate application rate of P fertilizers can be exploited in polluted soils to minimize the heavy metals uptake and to increase maize growth.

Effects of biochar on availability and plant uptake of heavy metals – A meta-analysis

Biochar can be an effective amendment for immobilizing heavy metals in contaminated soils but has variable effects depending on its chemical and physical properties and those of the treated soil. To investigate the range of biochar's effects on heavy metal accumulation in plants in responses to the variation of soil, biochar and plant, we carried out a meta-analysis of the literature that was published before March 2016. A total of 1298 independent observations were collected from 74 published papers. Results showed that across all studies, biochar addition to soils resulted in average decreases of 38, 39, 25 and 17%, respectively, in the accumulation of Cd, Pb, Cu and Zn in plant tissues. The effect of biochar on heavy metal concentrations in plants varied depending on soil properties, biochar type, plant species, and metal contaminants. The largest decreases in plant heavy metal concentrations occurred in coarse-textured soils amended with biochar. Biochar had a relatively small effect on plant tissue Pb concentrations, but a large effect on plant Cu concentrations when applied to alkaline soils. Plant uptake of Pb, Cu and Zn was less in soils with higher organic carbon contents. Manure-derived biochar was the most effective for reducing Cd and Pb concentrations in plants as compared to biochars derived from other feedstock. Biochar having a high pH and used at high application rates resulted in greater decreases in plant heavy metal uptake. The meta-analysis provides useful guidelines on the range of effects that can be anticipated for different biochar materials in different plant-soil systems.

Metal contamination in a riparian wetland: Distribution, fractionation and plant uptake

Heavy metal pollution in aquatic system is of concern due its ecologic risk. In this study, we investigated the distribution, fractionation and plant uptake of heavy metals (As, Cd, Cr, Co, Cu, Ni, Pb and Zn) in a riparian wetland impacted by mining activities in Yunnan, southwest China. The results showed that excluding Cr, metal contents in sediment were higher than the background values, especially for As, which was 100-fold higher. While Cd showed high levels in the acid-soluble fraction with high availability, As, Cr, Cu, Ni and Pb mainly existed in the residual fraction with low availability. Two native aquatic plants including Phragmites australis (common reed) and Typha orientalis (bullrush) showed different uptake ability. T. orientalis accumulated more As, while P. australis accumulated more other metals. Based on geoaccumulation index (Igeo), As, Cd and Zn were more contaminated (Igeo> 3), followed by Cu, Pb and Co (Igeo<3), with Cr and Ni being slightly polluted (Igeo<1). According to risk assessment code, Cd showed high availability, followed by Zn and Co, with As exhibiting the lowest. The data suggested that both total and bioavailable metals should be considered for risk assessment of metal pollution in a wetland.