Evaluating the phytoremediation potential of Phragmites australis grown in pentachlorophenol and cadmium co-contaminated soils

Cr(III) and Cr(VI) removal in floating treatment wetlands (FTWs) using Typha domingensis

Floating treatment wetlands (FTWs) are a cost-effective ecological engineering tool for the restoration of polluted water bodies. The aims of this work were to evaluate the removal of Cr(III) and Cr(VI) by FTWs using Typha domingensis, and to assess Cr accumulation and distribution in plant tissues and sediment. Treatments were 5 and 10 mg L-1 of Cr(III), and 5 and 10 mg L-1 of Cr(VI), with and without FTWs, and biological control (BC) with FTW without Cr addition. Both Cr species were efficiently removed from water in all treatments (Cr removal > 80%). Cr concentration in sediments of treatment without FTWs was significantly higher than in sediments of treatments with FTWs, indicating that T. domingensis was directly involved in Cr removal. In sediment, Cr was mainly bound to the organic matter in all treatments with a low risk of future release under FTW conditions. T. domingensis demonstrated tolerance to both Cr species at 5 and 10 mg L-1 with Cr accumulated mainly in the roots in all treatments. The use of FTWs planted with T. domingensis is a suitable tool to remediate water bodies contaminated with Cr.

Biogas from aquatic plants: A bioenergetics incentive for constructed wetlands usage

Our study demonstrated the energy gains when using biomass from three macrophyte, used commonly in constructed wetlands for wastewater treatment, the water hyacinth, cattail, and dwarf papyrus, as a substrate for biogas generation. The biochemical methane potential for the three biomass was evaluated in batch and at bench at 37 °C. A kinetic analysis of anaerobic digestion was also conducted for these substrates, evaluating the biogas composition and energy potential. Anaerobic digestion resulted in 94.27, and 25 mL_CH4/gVS_substrate of dry mass; and 19,569.65, 5617.88, and 6068.45 kJ/t of cattail, water hyacinth, and dwarf papyrus, respectively. Biomass from water hyacinth did sustain the fastest degradation, indicating that models considering the lag phase are more adequate to evaluate the anaerobic digestion of this type of substrate. Higher digestion speed resulted in the generation of 2901.88 kJ/t more energy with biomass from water hyacinth versus cattail, highlighting its value for use in constructed wetlands.

The potential of saltmarsh halophytes for phytoremediation of metals and persistent organic pollutants: An Australian perspective

Persistent organic and inorganic pollutants are among the most concerning pollutants in Australian estuaries due to their persistent, ubiquitous, and potentially toxic nature. Traditional methods of soil remediation often fall short of practical implementation due to high monetary investment, environmental disturbance, and potential for re-contamination. Phytoremediation is gaining traction as an alternative, or synergistic mechanism of contaminated soil remediation. Phytoremediation utilises plants and associated rhizospheric microorganisms to stabilise, degrade, transform, or remove xenobiotics from contaminated mediums. Due to their apparent cross-tolerance to salt, metals, and organic contaminants, halophytes have shown promise as phytoremediation species. This review examines the potential of 93 species of Australian saltmarsh halophytes for xenobiotic phytoremediation. Considerations for the practical application of phytoremediation in Australia are discussed, including mechanisms of enhancement, and methods of harvesting and disposal. Knowledge gaps for the implementation of phytoremediation in Australian saline environments are identified, and areas for future research are suggested.

Micro- and Macroelements Content of Plants Used for Landfill Leachate Treatment Based on Phragmites australis and Ceratophyllum demersum

One of the key problems associated with the functioning of landfills is the generation of leachate. In order to reduce their negative impact on the environment, various treatment technologies are applied. Among them, solutions based on the use of phytotechnology deserve special attention. The aim of this study was to evaluate the impact of landfill leachate on the content of micro- and macroelements in plant material. The research was carried out in four municipal waste landfills located in Poland. Emergent macrophytes (P. australis) and submergent macrophytes (C. demersum) were used in this research. The migration and distribution of pollutants reaching the roots and shoots of P. australis from water solutions were also studied. The concentrations of heavy metals in the studied plants were low in all analysed cases. Higher metal contents could often be observed in roots rather than in shoots, but these differences were insignificant. The chemical composition of the studied plant samples was primarily related to the source of origin of the treated leachate (landfill), as clearly demonstrated by cluster analysis. In the conducted studies, no important differences were noted in the accumulation of the studied components between submergent plants (C. demersum) and emergent macrophytes (P. australis).

Assessment of Reed Grasses (Phragmites australis) Performance in PFAS Removal from Water: A Phytoremediation Pilot Plant Study

Per- and polyfluoroalkyl substances (PFASs) have multiple emission sources, from industrial to domestic, and their high persistence and mobility help them to spread in all the networks of watercourses. Diffuse pollution of these compounds can be potentially mitigated by the application of green infrastructures, which are a pillar of the EU Green Deal. In this context, a phytoremediation pilot plant was realised and supplied by a contaminated well-located in Lonigo (Veneto Region, Italy) where surface and groundwaters were significantly impacted by perfluoroalkyl acids (PFAAs) discharges from a fluorochemical factory. The investigation involved the detection of perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), perfluorobutanesulfonic acid (PFBS) and perfluorooctanesulfonic acid (PFOS) inside the inlet and outlet waters of the phytoremediation pilot plant as well as in reed grasses grown into its main tank. The obtained results demonstrate that the pilot plant is able to reduce up to 50% of considered PFAAs in terms of mass flow without an evident dependence on physico-chemical characteristics of these contaminants. Moreover, PFAAs were found in the exposed reed grasses at concentrations up to 13 ng g−1 ww. A positive correlation between PFAA concentration in plants and exposure time was also observed. In conclusion, this paper highlights the potential efficiency of phytodepuration in PFAS removal and recommends improving the knowledge about its application in constructed wetlands as a highly sustainable choice in wastewater remediation.

Improved remediation of co-contaminated soils by heavy metals and PAHs with biosurfactant-enhanced soil washing

Due to the huge toxicity of co-contaminated soil with PAHs and heavy metals and the complexity of their remediation, it is thus critical to take effective remediation actions to remove heavy metals and PAHs simultaneously from the co-contaminated soil. Biosurfactant-enhanced soil washing (BESW) were investigated in this study for remediation of soil co-contaminated with phenanthrene (PHE) and cadmium (Cd). The co-existence of PHE and Cd caused the change of the structure of soil and rhamnolipid micelle, which lead to different removal rate of PHE and Cd from co-contaminated soil compared with single contaminated soil. The results of FT-IR and NMR showed that PHE entered micelles of rhamnolipid and Cd formed the complexation with the external carboxyl groups of rhamnolipid micelle. We also found that pH, concentration of rhamnolipid solution, temperature and ionic strength had influence on co-contaminated soil remediation. The effects of above mentioned four factors on co-contaminated soil remediation in BESW processes were analyzed by using Taguchi design of experiment method. Taguchi based Grey Relational Analysis was conducted to identify the optimal remediation conditions, which included pH = 9, concentration of rhamnolipid = 5 g/L, temperature = 15 °C and ionic strength = 0.01 M. Under the optimal conditions for BESW, removal rates of cadmium and phenanthrene reached 72.4% and 87.8%, respectively in co-contaminated soil.

Heavy Metals Assimilation by Native and Non-Native Aquatic Macrophyte Species: A Case Study of a River in the Eastern Cape Province of South Africa

There is continuous deterioration of freshwater systems globally due to excessive anthropogenic inputs, which severely affect important socio-economic and ecological services. We investigated the water and sediment quality at 10 sites along the severely modified Swartkops River system in the Eastern Cape Province of South Africa and then quantified the phytoremediation potential by native and non-native macrophyte species over a period of 6 months. We hypothesized that the presence of semi and permanent native and non-native macrophytes mats would reduce water and sediment contamination through assimilation downriver. Our results were variable and, thus, inconsistent with our hypotheses; there were no clear trends in water and sediment quality improvement along the Swartkops River. Although variable, the free-floating non-native macrophyte, Pontederia (=Eichhornia) crassipes recorded the highest assimilation potential of heavy metals in water (e.g., Fe and Cu) and sediments (e.g., Fe and Zn), followed by a submerged native macrophyte, Stuckenia pectinatus, and three native emergent species, Typha capensis, Cyperus sexangularis, and Phragmites australis. Pollution indices clearly showed the promising assimilation by native and non-native macrophytes species; however, the Swartkops River was heavily influenced by multiple non-point sources along the system, compromising the assimilation effect. Furthermore, we emphasise that excessive anthropogenic inputs compromise the system's ability to assimilate heavy metals inputs leading to water quality deterioration.

Persistent organic pollutants (POPs) in coastal wetlands: A review of their occurrences, toxic effects, and biogeochemical cycling

Coastal wetlands, such as mangroves, seagrass beds, and salt marshes, are highly threatened by increasing anthropic pressures, including chemical pollution. Persistent organic pollutants (POPs) have attracted attention in these particularly vulnerable ecosystems, due to their bioaccumulative, pervasive, and ecotoxic behavior. This article reviews and summarizes available information regarding current levels, biogeochemical cycling, and effects of POPs on coastal wetlands. Sediment POP levels were compared with international quality guidelines, revealing many areas where compounds could cause damage to biota. Despite this, toxicological studies on some coastal wetland plants and microorganisms showed a high tolerance to those levels. These taxonomic groups are likely to play a key role in the cycling of the POPs, with an active role in their accumulation, immobilization, and degradation. Toxicity and biogeochemical processes varied markedly along three main axes; namely species, environmental conditions, and type of pollutant. While more focused research on newly and unintentionally produced POPs is needed, mainly in salt marshes and seagrass beds, with the information available so far, the environmental behavior, spatial distribution, and toxicity level of the studied POPs showed similar patterns across the three studied ecosystems.

Removal of pentachlorophenol from contaminated wastewater using phytoremediation and bioaugmentation processes

The phytoremediation procedure was conducted by Lemna gibba (L) and Typha angustifolia (T) and the bioaugmentation procedure used P. putida HM627618. The ability of the selected P. putida HM627618 to tolerate and remove PCP (200 mg L^-1) was measured by high performance liquid chromatography analysis and optical density at 600 nm. Five different experiments were conducted in secondary treated wastewater for PCP testing removal (100 mg L^-1) including two phytoremediation assays (T + PCP; L + PCP), three bioaugmentation-phytoremediation assays (T + B + PCP; L + B + PCP; L + T + B + PCP) and a negative control assay with PCP. Various analytical parameters were determined in this study such as bacterial count, chlorophylls a and b, COD, pH and PCP content. The main results showed that the average PCP removal by P. putida HM627618 was around 87.5% after 7 days of incubation, and 88% of PCP removal was achieved by treatment (T + B) after 9 days. During these experiments, pH, COD and chloride content showed a net increase in all treatments. The chlorophylls a and b in case of (T) and (L) Chlorophylls a and b for T and L phytoremediation showed a decrease with a value less than 10 μg/mg of fresh material after 20 days of cultivation.

Assessment of the Streptomyces-plant system to mitigate the impact of Cr(VI) and lindane in experimental soils

Phytoremediation techniques have been proposed as ecological methods to clean up contaminated sites. This study is aimed to evaluate the effect of the Streptomyces sp. Waksman & Henrici and Zea mays L. plant system on the dissipation of Cr(VI) and/or lindane from a co-contaminated soil, being 2 mg kg^-1 of lindane and 150 mg kg^-1 of chromium used. Lindane dissipation was improved in the presence of plant-microorganism association; however, Cr(VI) removal was higher when plants or the microorganism were separately. In co-contaminated systems, chromium content in plant tissues was lower than metal content in plants grown only with Cr(VI), suggesting that lindane could interfere with metal accumulation in the plant. The high malondialdehyde (MDA) concentration detected in non-inoculated plants grown with chromium could be consequence of high metal concentration in plant tissues. Interestingly, plants inoculated with Streptomyces sp. Z38 growing with Cr(VI) showed decrease in MDA concentration, indicating that the bacterium could activate defense mechanisms in the plant. Also, inoculated plants showed the highest value of superoxide dismutase activity. Lettuce plants used as bioindicators grew better in biologically treated soils compared with lettuce grown on non-treated soil. The results presented in this work provide the basis that will allow the optimization of future trials on a larger scale.

Bacterial consortium biotransformation of pentachlorophenol contaminated wastewater

The aims of this study were (i) to compare PCP removal (100 mg L^-1) by two bacterial consortia B₁ and B₂ in sterile wastewater (STWW) and liquid mineral medium (MSM), (ii) PCP effect in biofilm formation and antimicrobial susceptibility. PCP removal was measured by high-performance liquid chromatography (HPLC) during 168 h at 30 °C. Biofilm formation was assessed with two approaches: Congo Red Agar and Microtiter-plate. Antimicrobial susceptibility was determined by the agar disc diffusion technique. The results showed that the PCP removal for consortium B₁ and B₂ after 168 h was 70 and 97.5% in STWW; 62.2 and 85.5% in MSM, respectively. In addition, PCP addition showed an increase in biofilm development especially for B₂ consortium around 3.5 nm in 100 mg L^-1 PCP. PCP added in the Muller Hinton (MH) medium and Gentamicin disc showed a clear increase in diameter of cell lysis around 2 to 4.5 cm.

Microbial Spectra, Physiological Response and Bioremediation Potential of Phragmites australis for Agricultural Production

Common reed (Phragmites australis) can invade and dominate in its natural habitat which is mainly wetlands. It can tolerate harsh environments as well as remediate polluted and environmental degraded sites such as mine dumps and other polluted wastelands. For this reason, this can be a very critical reed to reclaim wastelands for agricultural use to ensure sustainability. The present review manuscript examined the microbial spectra of P. australis as recorded in various recent studies, its physiological response when growing under stress as well as complementation between rhizosphere microbes and physiological responses which result in plant growth promotion in the process of phytoremediation. Microbes associated with P. australis include Proteobacteria, Bacteriodetes, and Firmicutes, Fusobacteria, Actinobacteria, and Planctomycetes families of bacteria among others. Some of these microbes and arbuscular mycorrhizal fungi have facilitated plant growth and phytoremediation by P. australis. This is worthwhile considering that there are vast areas of polluted and wasted land which require reclamation for agricultural use. Common reed with its associated rhizosphere microbes can be utilized in these land reclamation efforts. This present study suggests further work to identify microbes which when administered to P. australis can stimulate its growth in polluted environments and help in land reclamation efforts for agricultural use.

Macrophyte and indigenous bacterial co-remediation process for pentachlorophenol removal from wastewater

This study has contributed in the description of bioaugmentation-phytoremediation efficiency process using Typha angustifolia concerning PCP tolerance and removal from wastewater. Samples of wastewater were collected from industrial wastewater plants, namely row wastewater effluent "E.WW", primary wastewater "P.WW", secondary wastewater "S.WW", clarified wastewater "AC.WW". These effluents were spiked with PCP at different rate (100, 500, and 1000 mg.L^-1), physical, chemical and biological properties were monitored. A second experiment was set up in order to check the efficiency of phytoremediation treatments of the different effluents artificially contaminated with 200 mg.L^-1 PCP after 20 days lab scale experiment. An important PCP removal by indigenous bacteria was showed in S. WW with values from 1000 to 72.2 mg.L^-1 from T0 (start of the experiment) to TF (end of the experiment), respectively. Phytoremediation process allowed a decrease of PCP rate from 200 to 6.4 mg.L^-1, a decrease of chloride content from 14.0 to 4.0 mg.L^-1 in S.WW samples was observed. Furthermore, a significant increase of bacterial number in S.WW and AC.WW to 1.700 × 10⁶ and 1.450 × 10⁶ CFU.mL^-1, respectively was observed. In addition, the DGGE analysis showed that after bioaugmentation-phytoremediation treatments, the highest species richness and relative abundance in wastewater effluent was observed. Novelty statement Pentachlorophenol (PCP) is one of highly toxic of polychlorophenols and required to continuously monitor in environment. This paper presenting a sensitive method phytoremediation and bioaugmentation for PCP biotransformation in wastewater. The novelty is the choice of a macrophyte Typha angustifolia, which is still used for the elimination of heavy metals but it not used for pesticide and pollutant removal in wastewater. Also, there are different analysis that was performed in order to check phyto-technique process (DGGE and HPLC). On the other side, in this study, the phyto-techniques with Typha angustifolia positively affected intrinsic microorganisms in order to promote pollutant remediation. So, the intrinsic microorganisms in wastewater with the macrophyte presence have a great capacity to reduce this pollutant and improve the bioremediation process.

Alkylphenols and Chlorophenols Remediation in Vertical Flow Constructed Wetlands: Removal Efficiency and Microbial Community Response

This study aims to investigate the effect of two different groups of phenolic compounds (the alkylphenols nonylphenol (NP) and octylphenol (OP), and the chlorophenol pentachlorophenol (PCP)) on constructed wetlands (CWs) performance, including on organic matter, nutrients and contaminants removal efficiency, and on microbial community structure in the plant bed substrate. CWs were assembled at lab scale simulating a vertical flow configuration and irrigated along eight weeks with Ribeira de Joane (an urban stream) water not doped (control) or doped with a mixture of NP and OP or with PCP (at a 100 μg·L−1 concentration each). The presence of the phenolic contaminants did not interfere in the removal of organic matter or nutrients in CWs in the long term. Removals of NP and OP were >99%, whereas PCP removals varied between 87% and 98%, mainly due to biodegradation. Microbial richness, diversity and dominance in CWs substrate were generally not affected by phenolic compounds, with only PCP decreasing diversity. Microbial community structure, however, showed that there was an adaptation of the microbial community to the presence of each contaminant, with several specialist genera being enriched following exposure. The three more abundant specialist genera were Methylotenera and Methylophilus (methylophilaceae family) and Hyphomicrobium (hyphomicrobiaceae family) when the systems were exposed to a mixture of NP and OP. When exposed to PCP, the three more abundant genera were Denitromonas (Rhodocyclaceae family), Xenococcus_PCC_7305 (Xenococcaceae family) and Rhodocyclaceae_uncultured (Rhodocyclaceae family). To increase CWs efficiency in the elimination of phenolic compounds, namely PCP which was not totally removed, strategies to stimulate (namely biostimulation) or increase (namely bioaugmentation) the presence of these bacteria should be explore. This study clearly shows the potential of vertical flow CWs for the removal of phenolic compounds, a still little explored subject, contributing to promote the use of CWs as nature-based solutions to remediate water contaminated with different families of persistent and/or emergent contaminants.

Degradation of organic pollutants by intimately coupling photocatalytic materials with microbes: a review

With the rapid development of industry and agriculture, large amounts of organic pollutants have been released into the environment. Consequently, the degradation of refractory organic pollutants has become one of the toughest challenges in remediation. To solve this problem, intimate coupling of photocatalysis and biodegradation (ICPB) technology, which allows the simultaneous action of photocatalysis and biodegradation and thus integrates the advantages of photocatalytic reactions and biological treatments, was developed recently. ICPB consists mainly of porous carriers, photocatalysts, biofilms, and an illuminated reactor. Under illumination, photocatalysts on the surface of the carriers convert refractory pollutants into biodegradable products through photocatalytic reactions, after which these products are completely degraded by the biofilms cultivated in the carriers. Additionally, the biofilms are protected by the carriers from the harmful light and free radicals generated by the photocatalyst. Compared with traditional technologies, ICPB remarkably improves the degradation efficiency and reduces the cost of bioremediation. In this review, we introduce the origin and mechanisms of ICPB, discuss the development of reactors, carriers, photocatalysts, and biofilms used in ICPB, and summarize the applications of ICPB to treat organic pollutants. Finally, gaps in this research as well as future perspectives are discussed.

Quantifying the influencing factors and multi-factor interactions affecting cadmium accumulation in limestone-derived agricultural soil using random forest (RF) approach

Cadmium (Cd) is a highly toxic heavy metal that occurs widely in the environment and poses extensive threats to human health, animals, and plants. This study aims to identify and apportion multi-source and multi-phase Cd pollution from natural and anthropogenic inputs using ensemble models that include random forest (RF) in agricultural soils on Karst areas. The contributions of natural and anthropogenic factors to Cd accumulation were quantitatively assessed using the RF machine learning method. The results revealed that the main influencing factors were pH, organic carbon (C_org), and elevation. Moreover, the interaction effects of pH and C_org on distance and elevation were also quantified and visualised. It is observed that pH and C_org had stronger effects on soil Cd concentration than that of distance when pH > 7.02 and C_org > 1.53. In other words, higher Cd content in the soil along roadways may be caused by the interaction of distance, pH and C_org, with pH and C_org playing the dominant role in our case. Moreover, the maximum contribution of a single factor, elevation, to Cd concentration was about 0.13 mg/kg, and its interactions reached 1.082 mg/kg and 0.83 mg/kg, respectively, when combined with pH and C_org at 194.0 m. However, with increasing elevation, pH and C_org gradually took over the leading roles. This result not only gives us a quantitative understanding of the relationship between the factors that affect soil cadmium accumulation, but also provides an accurate method for source apportionment of heavy metals in soil.

Macrophyte Potential to Treat Leachate Contaminated with Wood Preservatives: Plant Tolerance and Bioaccumulation Capacity

Pentachlorophenol and chromated copper arsenate (CCA) have been used worldwide as wood preservatives, but these compounds can toxify ecosystems when they leach into the soil and water. This study aimed to evaluate the capacity of four treatment wetland macrophytes, Phalaris arundinacea, Typha angustifolia, and two subspecies of Phragmites australis, to tolerate and treat leachates containing wood preservatives. The experiment was conducted using 96 plant pots in 12 tanks filled with three leachate concentrations compared to uncontaminated water. Biomass production and bioaccumulation were measured after 35 and 70 days of exposure. There were no significant effects of leachate contamination concentration on plant biomass for any species. No contaminants were detected in aboveground parts of the macrophytes, precluding their use for phytoextraction within the tested contamination levels. However, all species accumulated As and chlorinated phenols in belowground parts, and this accumulation was more prevalent under a more concentrated leachate. Up to 0.5 mg pentachlorophenol/kg (from 81 µg/L in the leachate) and 50 mg As/kg (from 330 µg/L in the leachate) were accumulated in the belowground biomass. Given their high productivity and tolerance to the contaminants, the tested macrophytes showed phytostabilization potential and could enhance the degradation of phenols from leachates contaminated with wood preservatives in treatment wetlands.

An overview on heavy metal resistant microorganisms for simultaneous treatment of multiple chemical pollutants at co-contaminated sites, and their multipurpose application

Anthropogenic imbalance of chemical pollutants in environment raises serious threat to all life forms. Contaminated sites often possess multiple heavy metals and other types of pollutants. Elimination of chemical pollutants at co-contaminated sites is imperative for the safe ecosystem functions, and simultaneous removal approach is an attractive scheme for their remediation. Different conventional techniques have been applied as concomitant treatment solution but fall short at various parameters. In parallel, use of microorganisms offers an innovative, cost effective and ecofriendly approach for simultaneous treatment of various chemical pollutants. However, microbiostasis due to harmful effects of heavy metals or other contaminants is a serious bottleneck facing remediation practices in co-contaminated sites. But certain microorganisms have unique mechanisms to resist heavy metals, and can act on different noxious wastes. Considering this significant, my review provides information on different heavy metal resistant microorganisms for bioremediation of different chemical pollutants, and other assistance. In this favour, the integrated approach of simultaneous treatment of multiple heavy metals and other environmental contaminants using different heavy metal resistant microorganisms is summarized. Further, the discussion also intends toward the use of heavy metal resistant microorganisms associated with industrial and environmental applications, and healthcare. PREFACE: Simultaneous treatment of multiple chemical pollutants using microorganisms is relatively a new approach. Therefore, this subject was not well received for review before. Also, multipurpose application of heavy metal microorganisms has certainly not considered for review. In this regard, this review attempts to gather information on recent progress on studies on different heavy metal resistant microorganisms for their potential of treatment of co-contaminated sites, and multipurpose application.

Phytoremediation for co-contaminated soils of cadmium and pyrene using Phragmites australis (common reed)

Soil contamination is currently the most severe problem as it poses a toxicological impact on human health and ecosystems. A greenhouse experiment was carried out to investigate the effect of 20 and 40 mg kg^-1 of cadmium (Cd) or 50 and 100 mg kg^-1 of pyrene (PYR) and the combined effect of Cd-PYR on the growth of Phragmites australis together with the uptake and accumulation of Cd as well as removal of PYR. Results demonstrated that the single or co- contaminants of Cd and PYR did not affect plant growth relative to control treatments, except low Cd and high PYR treatment, which showed a significant increase in 91% biomass compared to the control. However, under the joint effect of Cd-PYR, P. australis was unwilling to uptake and translocate Cd, and bioconcentration factor (BCF) and translocation factor (TrF) values were less than one. The removal rate of PYR in the soils and soil enzymes was negatively impacted at the elevated Cd level in the soil. Our study shows that P. australis may have the potential for phytostabilization but cannot be useful for phytoextraction.

Status of copper accumulation in agricultural soils across China (1985-2016)

The first national-scale assessment of Cu contamination of agricultural soils covering 1731 sites in China was performed based on 1837 published papers. The temporal and spatial variations from 1985 to 2016 in the Cu concentrations and the ecological and health risks associated with Cu exposure were analyzed. Approximately, 21.02% of the sampling sites revealed Cu concentrations that exceeded the screening value (50.00 mg/kg; GB15618-2018). The Cu concentrations differed among five geographical regions in the decreasing order of South China > West China > East China > Northeast China > North China. Notably, concentration of Cu in agricultural soils have begun to diminish since 2011 due to reduced heavy metal inputs. Cu mainly originated from anthropogenic activities such as mining and agricultural activities. Linear correlations were observed between the amounts of fungicides and fertilizers applied and the Cu concentrations in the soils, which suggested that the application of fungicides and fertilizers is an important contributor to the accumulation of Cu in soils. Additionally, the geoaccumulation index (I_geo) and ecological risk index (E_fⁱ) values implied that pollution and ecological risk resulting from soil Cu concentration were in low levels. The hazard index (HI) values were higher for children than for adults. Therefore, children should be prioritized for protection from heavy metal pollution. Overall, this study details the status of Cu contamination of agricultural soils in China, and thus provides insights for policymakers regarding the preventive measures.

Phragmites australis in combination with hydrocarbons degrading bacteria is a suitable option for remediation of diesel-contaminated water in floating wetlands

The presence of diesel in the water could reduce the growth of plant and thus phytoremediation efficacy. The toxicity of diesel to plant is commonly explained; because of hydrocarbons in diesel accumulate in various parts of plants, where they disrupt the plant cell especially, the epidemis, leaves, stem and roots of the plant. This study investigated the effect of bacterial augmentation in floating treatment wetlands (FTWs) on remediation of diesel oil contaminated water. A helophytic plant, Phragmites australis (P. australis), was vegetated on a floating mat to establish FTWs for the remediation of diesel (1%, w/v) contaminated water. The FTWs was inoculated with three bacterial strains (Acinetobacter sp. BRRH61, Bacillus megaterium RGR14 and Acinetobacter iwoffii AKR1), possessing hydrocarbon degradation and plant growth-enhancing capabilities. It was observed that the FTWs efficiently removed hydrocarbons from water, and bacterial inoculation further enhanced its hydrocarbons degradation efficacy. Diesel contaminated water samples collected after fifteen days of time interval for three months and were analyzed for pollution parameters. The maximum reduction in hydrocarbons (95.8%), chemical oxygen demand (98.6%), biochemical oxygen demand (97.7%), total organic carbon (95.2%), phenol (98.9%) and toxicity was examined when both plant and bacteria were employed in combination. Likewise, an increase in plant growth was seen in the presence of bacteria. The inoculated bacteria showed persistence in the water, root and shoot of P. australis. The study concluded that the augmentation of hydrocarbons degrading bacteria in FTWs is a better option for treatment of diesel polluted water.

Bioremediation of cadmium-trichlorfon co-contaminated soil by Indian mustard (Brassica juncea) associated with the trichlorfon-degrading microbe Aspergillus sydowii: Related physiological responses and soil enzyme activities

Soil co-contaminated with heavy metals and organics is often difficult to remediate. In this study, pot experiments were conducted to investigate the concurrent removal of cadmium (Cd, two levels: Cd_L [10 mg kg^-1] and Cd_H [50 mg kg^-1]) and trichlorfon (TCF, 100 mg kg^-1) from co-contaminated soil by comparing the following remediation methods: natural remediation (NR), soil inoculated with Aspergillus sydowii (AS), soil planted with Brassica juncea (BJ), and soil planted with B. juncea and inoculated with A. sydowii (BJ-AS). The physiological responses of B. juncea and soil enzyme activities after remediation were also studied. B. juncea grew well in co-contaminated soil at both Cd levels. The biomass and chlorophyll content of B. juncea in Cd_H soil were lower than those in Cd_L soil, whereas the malondialdehyde content and activities of catalase, peroxidase and superoxide dismutase of B. juncea in Cd_H soil were higher than those in Cd_L soil. Cd accumulation in B. juncea was high in Cd_H soil, whereas high Cd removal efficiency was observed in Cd_L soil. TCF could be thoroughly degraded within 35 days in NR at both Cd-level soils. AS, BJ and BJ-AS promoted TCF degradation and enhanced the activities of catalase, urease, sucrase and alkaline phosphatase in soil compared with the NR. BJ-AS showed the highest phytoextraction ratio (3.32% in Cd_L and 1.34% in Cd_H soil) and TCF degradation rate (half-life of 2.18 and 2.37 days in Cd_L and Cd_H soil, respectively). These results demonstrate that BJ-AS could effectively remove Cd and TCF from soil and is thus a feasible technology for the bioremediation of these co-contaminated soil.

The effect of two different biochars on remediation of Cd-contaminated soil and Cd uptake by Lolium perenne

Biochar can be widely used to reduce the bioavailability of heavy metals in contaminated soil because of its adsorption capacity. But there are few studies about the effects of biochar on cadmium uptake by plants in soil contaminated with cadmium (Cd). Therefore, an incubation experiment was used to investigate the effects of rice straw biochar (RSBC) and coconut shell biochar (CSBC) on Cd immobilization in contaminated soil and, subsequently, Cd uptake by Lolium perenne. The results showed that the microbial counts and soil enzyme activities were significantly increased by biochar in Cd-contaminated soil, which were consistent with the decrease of the bioavailability of Cd by biochar. HOAc-extractable Cd in soil decreased by 11.3-22.6% in treatments with 5% RSBC and by 7.2-17.1% in treatments with 5% CSBC, respectively, compared to controls. The content of available Cd in biochar treatments was significantly lower than in controls, and these differences were more obvious in treatment groups with 5% biochar. The Cd concentration in L. perenne reduced by 4.47-26.13% with biochar. However, the biomass of L. perenne increased by 1.35-2.38 times after adding biochar amendments. So, Cd uptake by whole L. perenne was augmented by RSBC and CSBC. Accordingly, this work suggests that RSBC and CSBC have the potential to be used as a useful aided phytoremediation technology in Cd-contaminated soil.

Status of cadmium accumulation in agricultural soils across China (1975-2016): From temporal and spatial variations to risk assessment

Based on 1186 published studies, the first national-scale assessment of cadmium (Cd) contamination in agricultural soils across China was conducted. Cd concentrations, temporal and spatial variations, and ecological and health risks resulted from Cd exposure were analyzed. A small part of sampling sites with Cd concentration surpass the screening value and the control value (GB15618-2018), respectively. Soil Cd concentrations in South China were higher than other regions. Ecological risks resulting from Cd contamination were low. Soil Cd concentrations accumulated gradually from 1981 to 2016. Cd mainly came from anthropogenic activities, such as mining, smelting, sewage irrigation, and fertilization. Linear correlations were observed between application amounts of fertilizers and Cd concentrations in soil, indicating that the application of nitrogen, phosphorus, potassium, and compound fertilizers is an important contributor of Cd in soils. This study details the overall Cd contamination status of agricultural soils in China, thus can provide insights for policymakers regarding contamination prevention measures.

Phragmites australis - a helophytic grass - can establish successful partnership with phenol-degrading bacteria in a floating treatment wetland

Helophytic plants contribute significantly in phytoremediation of a variety of pollutants due to their physiological or biochemical mechanisms. Phenol, which is reported to have negative/deleterious effects on plant metabolism at concentrations higher than 500 mg/L, remains hard to be removed from the environmental compartments using conventional phytoremediation procedures. The present study aims to investigate the feasibility of using P. australis (a helophytic grass) in combination with three bacterial strains namely Acinetobacter lwofii ACRH76, Bacillus cereus LORH97, and Pseudomonas sp. LCRH90, in a floating treatment wetland (FTW) for the removal of phenol from contaminated water. The strains were screened based on their phenol degrading and plant growth promoting activities. We found that inoculated bacteria were able to colonize in the roots and shoots of P. australis, suggesting their potential role in the successful removal of phenol from the contaminated water. Pseudomonas sp. LCRH90 dominated the bacterial community structure followed by A. lowfii ACRH76 and B. cereus LORH97. The removal rate was significantly high when compared with the individual partners, i.e., plants and bacteria separately. The plant biomass, which was drastically reduced in the presence of phenol, recovered significantly with the inoculation of bacterial consortia. Likewise, highest reduction in chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total organic carbon (TOC) is achieved when both plants and bacteria were employed. The study, therefore, suggests that P. australis in combination with efficient bacteria can be a suitable choice to FTWs for phenol-degradation in water.

Phytoremediation potential and control of Phragmites australis as a green phytomass: an overview

Phragmites australis (common reed) is one of the most extensively distributed emergent plant species in the world. This plant has been used for phytoremediation of different types of wastewater, soil, and sediments since the 1970s. Published research confirms that P. australis is a great accumulator for different types of nutrients and heavy metals than other aquatic plants. Therefore, a comprehensive review is needed to have a better understanding of the suitability of this plant for removal of different types of nutrients and heavy metals. This review investigates the existing literature on the removal of nutrients and heavy metals from wastewater, soil, and sediment using P. australis. In addition, after phytoremediation, P. australis has the potential to be used for additional benefits such as the production of bioenergy and animal feedstock due to its specific characteristics. Determination of adaptive strategies is vital to reduce the invasive growth of P. australis in the environment and its economic effects. Future research is suggested to better understand the plant's physiology and biochemistry for increasing its pollutant removal efficiency.

Bioaccumulation in Miscanthus sacchariflorus grown on cadmium-contaminated sediments: a comparative study between submerged and non-submerged environments

Bioaccumulation of heavy metals in aquatic plants is significantly affected by hydrological regime and therefore the accumulation and translocation of cadmium in five organs-panicle, leaf, stem, root, and bud-of an emergent plant (Miscanthus sacchariflorus) were compared between the submerged environment and non-submerged environment. In the submerged condition, the cadmium concentration was higher in the panicle and leaf than in the stem, root, and bud. Cadmium concentration in the root exhibited a positive regression with cadmium concentration in the sediment. However, cadmium concentration in the panicle, leaf, stem, and bud exhibited no significant regression with cadmium concentration in the sediment. In the non-submerged environment, the cadmium concentration was higher in the below-ground organs than in the aboveground organs. The mean bioaccumulation coefficient in the 24 investigated plots in the submerged environment was higher than that in the 20 and 40 mg kg^-1 cadmium treatments in the non-submerged environment. The mean translocation factor in the submerged environment was nine times higher than that in non-submerged environment. These results indicate that submergence enhanced cadmium bioaccumulation in the aboveground organs and that this plant can be used to remove heavy metals from polluted rivers and lakes.

Concentration effects of the UV filter oxybenzone in Cyperus alternifolius: assessment of tolerance by stress-related response

Phytoremediation has been proposed to reduce the load of the sunscreen oxybenzone (OBZ) in the aquatic environment. Despite the proven removal efficiency of this compound, little is known about its influence, particularly oxidative stress on plants. In this study, a short-term incubation of macrophytic Cyperus alternifolius was performed to prove the plant's ability to withstand the stress. Detached shoots were immersed in medium spiked with different concentrations of OBZ (50, 100, and 500 μM) for 2, 4, and 7 days, respectively. Increased formation of O₂^- and H₂O₂ in Cyperus treated with OBZ was characterized by intense colorization following histochemical staining. Alterations of enzyme activities involved in the antioxidative defense system indicate an adaptive response of C. alternifolius to this xenobiotic stress. Quantification of lipid peroxidation reveals that no significant membrane damage occurred during incubation with OBZ. Overall, 50 μM OBZ (tenfold higher than the amount frequently detected in the environment) exhibited low toxic effects. Accordingly, this pilot study provides information on the potential use of Cyperus to remove emerging sunscreen contaminants from water bodies.

Long-term study of Cr, Ni, Zn, and P distribution in Typha domingensis growing in a constructed wetland

The aim of this work was to study Cr, Ni, Zn, and P bioaccumulation in different compartments of Typha domingensis plants and sediment in a free-water surface constructed wetland for the treatment of a metallurgical effluent for 5 years. Removal efficiencies were satisfactory. To increase metal tolerance, its transport from belowground to aboveground tissues is reduced, being metal concentrations in the roots and rhizomes significantly higher than in the aerial and submerged parts of leaves. Regarding belowground tissues, metals were retained in the roots, while P was mainly accumulated in rhizomes. Bioaccumulation factors (BAFs) of Cr and Ni showed values near 1, and BAF of Zn and P were above 1 in several samplings, indicating bioaccumulation in the roots. Translocation factors (TFs) of Cr, Ni, and Zn were below 1, showing a scarce translocation from the roots to the aerial parts of the leaves, while the TF of P were above 1 in many samplings, indicating that this element is necessary for plant metabolism. The study of plant tissues where contaminants are accumulated allows gaining insight into the constructed wetland operation. The high translocation of P in T. domingensis makes this species suitable for its phytoextraction, while the low metal translocation makes T. domingensis suitable for phytostabilization.

Resistance strategies of Phragmites australis (common reed) to Pb pollution in flood and drought conditions

Resistance strategies of clonal organs, and parent and offspring shoots of Phragmites australis (common reed) to heavy metal pollution in soils are not well known. To clarify the tolerance or resistance strategies in reeds, we conducted a pot experiment with five levels of Pb concentration (0∼4,500 mg kg⁻¹) in flood and drought conditions. Lead toxicity had no inhibitory effect on the number of offspring shoots in flood environment; however, biomass accumulation, and photosynthetic and clonal growth parameters were inhibited in both water environment. At each treatment of Pb concentration, offspring shoots had greater biomass and higher photosynthesis indicators than parent shoots. The lowest Pb allocation was found in rhizomes. More of the Pb transported to above-ground parts tended to accumulate in parent shoots rather than in offspring shoots. Biomass and photosynthesis of offspring shoots, rhizome length, and the number of buds, rhizomes and offspring shoots in the flooded treatment were significantly greater than those in the drought treatment. Our results indicated that the tolerance strategies used by reeds, including higher biomass accumulation and photosynthesis in offspring shoots, low allocation of Pb in rhizomes and offspring shoots, and stable clonal growth, maintained the stability of population propagation and productivity, improving the resistance of reeds to Pb pollution in flood environment. However, the resistance or tolerance was significantly reduced by the synergistic effect of Pb and drought, which significantly inhibited biomass accumulation, photosynthesis, and clonal growth of reeds.

Desodification from calcareous saline sodic soil through phytoremediation with Phragmites australis (Cav.) Trin. ex Steud. and gypsum

The reclamation of saline sodic soils requires sodium removal and the phytoremediation is one of the proven low-cost, low-risk technologies for reclaiming such soils. However, the role of Phragmites australis in reclaiming saline sodic soils has not been evaluated extensively. The comparative reclaiming role of P. australis and gypsum was evaluated in a column experiment on a sandy clay saline sodic soil with EC_e 74.7 dS m^-1, sodium adsorption ratio (SAR) 63.2, Na⁺ 361 g kg^-1, and pH 8.46. The gypsum at 100% soil requirement, planting common reed (P. australis) alone, P. australis + gypsum at 50% soil gypsum requirements, and leaching (control without plant and gypsum) were four treatments applied. After 11 weeks of incubation, the results showed that all treatments including the control significantly reduced pH, EC, exchangeable Na⁺, and SAR from the initial values, the control being with least results. The gypsum and P. australis + gypsum were highly effective in salinity (EC_e) reduction, while sodicity (SAR) and Na⁺ reductions were significantly higher in P. australis + gypsum treatment. The reclamation efficiency in terms of Na⁺ (83.4%) and SAR (86.8%) reduction was the highest in P. australis + gypsum. It is concluded that phytoremediation is an effective tool to reclaim saline sodic soil.

Clonal integration facilitates spread of Paspalum paspaloides from terrestrial to cadmium-contaminated aquatic habitats

Cadmium (Cd) is a hazardous environmental pollutant with high toxicity to plants, which has been detected in many wetlands. Clonal integration (resource translocation) between connected ramets of clonal plants can increase their tolerance to stress. We hypothesised that clonal integration facilitates spread of amphibious clonal plants from terrestrial to Cd-contaminated aquatic habitats. The spread of an amphibious grass Paspalum paspaloides was simulated by growing basal older ramets in uncontaminated soil connected (allowing integration) or not connected (preventing integration) to apical younger ramets of the same fragments in Cd-contaminated water. Cd contamination of apical ramets of P. paspaloides markedly decreased growth and photosynthetic capacity of the apical ramets without connection to the basal ramets, but did not decrease these properties with connection. Cd contamination did not affect growth of the basal ramets without connection to the apical ramets, but Cd contamination of 4 and 12 mg·l^-1 significantly increased growth with connection. Consequently, clonal integration increased growth of the apical ramets, basal ramets and whole clones when the apical ramets were grown in Cd-contaminated water of 4 and 12 mg·l^-1 . Cd was detected in the basal ramets with connection to the apical ramets, suggesting Cd could be translocated due to clonal integration. Clonal integration, most likely through translocation of photosynthates, can support P. paspaloides to spread from terrestrial to Cd-contaminated aquatic habitats. Amphibious clonal plants with a high ability for clonal integration are particularly useful for re-vegetation of degraded aquatic habitats caused by Cd contamination.

Effect of Cd⁺² on phosphate solubilizing abilities and hydrogen peroxide production of soil-borne micromycetes isolated from Phragmites australis-rhizosphere

The aims of this work were to evaluate the phosphate-solubilization and hydrogen peroxide (H2O2) production by the soil-borne micromycetes, Aspergillus japonicus, Penicillium italicum and Penicillium dipodomyicola, isolated from Phragmites australis rhizosphere and to study the effect of several concentrations of Cadmium (Cd(2+)) on both variables. Our results showed that P. italicum achieved a higher P-solubilization and H2O2 production than A. japonicus and P. dipodomyicola, as only P. italicum showed a positive correlation (R(2) = 0.71) between P-solubilization and H2O2 production. In dose-response assays, P. italicum was also more tolerant to Cd(2+) (0.31 mM) in comparison to A. japonicus (0.26 mM). Analysis of the 2(4) factorial experimental design showed that P-solubilization by P. italicum was negatively affected by increases in Cd(2+) (p = 0.04) and yeast extract (p = 0.02) in the culture medium. The production of H2O2 was positively affected only by glucose (p = 0.002). Fungal biomass production was reduced significantly (p = 0.0009) by Cd(2+) and increased (p = 0.0003) by high glucose concentration in the culture medium. The tolerance and correlation between P-solubilization and H2O2 production in the presence of Cd(2+) was strain and species dependent. The effects of Cd(2+), glucose, ammonium sulfate and yeast extract on those variables were evaluated through a two-level factorial design. P. italicum is promising for P-solubilization in soils contaminated with Cd(2+) and may be an alternative for manufacture of biofertilizers to replace chemical fertilizers.

Identification of Scirpus triqueter root exudates and the effects of organic acids on desorption and bioavailability of pyrene and lead in co-contaminated wetland soils

Root exudates (REs) of Scirpus triqueter were extracted from the rhizosphere soil in this study. The components in the REs were identified by GC-MS. Many organic acids, such as hexadecanoic acid, pentadecanoic acid, vanillic acid, octadecanoic acid, citric acid, succinic acid, glutaric acid, and so on, were found. Batch simulated experiments were conducted to evaluate the impacts of different organic acids, such as citric acid, artificial root exudates (ARE), succinic acid, and glutaric acid in REs of S. triqueter on desorption of pyrene (PYR) and lead (Pb) in co-contaminated wetland soils. The desorption amount of PYR and Pb increased with the rise in concentrations of organic acids in the range of 0-50 g·L(-1), within shaking time of 2-24 h. The desorption effects of PYR and Pb in soils with various organic acids treatments decreased in the following order: citric acid > ARE > succinic acid > glutaric acid. The desorption rate of PYR and Pb was higher in co-contaminated soil than in single pollution soil. The impacts of organic acids in REs of S. triqueter on bioavailability of PYR and Pb suggested that organic acids enhanced the bioavailability of PYR and Pb in wetland soil, and the bioavailability effects of organic acids generally followed the same order as that of desorption effects.

Bioremediation of soils co-contaminated with heavy metals and 2,4,5-trichlorophenol by fruiting body of Clitocybe maxima

Pot experiments were performed to investigate the single effect of 2,4,5-trichlorophenol (TCP) or heavy metals (Cu, Cd, Cu+Cd) and the combined effects of metals-TCP on the growth of Clitocybe maxima together with the accumulation of heavy metals as well as dissipation of TCP. Results showed a negative effect of contaminations on fruiting time and biomass of the mushroom. TCP decreased significantly in soils accounting for 70.66-96.24% of the initial extractable concentration in planted soil and 66.47-91.42% in unplanted soil, which showed that the dissipation of TCP was enhanced with mushroom planting. Higher biological activities (bacterial counts, soil respiration and laccase activity) were detected in planted soils relative to unplanted controls, and the enhanced dissipation of TCP in planted soils might be derived from the increased biological activities. The metals accumulation in mushroom increased with the augment of metal load, and the proportion of acetic acid (HOAc) extractable metal in soils with C. maxima was larger than that in unplanted soils, which may be an explanation of metal uptake by C. maxima. These results suggested that the presence of C. maxima was effective in promoting the bioremediation of soil contaminated with heavy metals and TCP.

Effects of lead contamination on the clonal propagative ability of Phragmites australis (common reed) grown in wet and dry environments

Clonal propagation is important for the survival and maintenance of the common reed Phragmites australis. Pot culture experiments were conducted to investigate the effects of lead (Pb) concentration (0, 500, 1500, 3000, 4500 mg·kg(-1) ) and water stress on the clonal reproductive ability of this species. The Pb concentration found in plant organs, in decreasing order, was roots >shoots >rhizomes. There was a negative relationship between the growth of clonal propagative modules (excluding axillary shoot buds) and Pb concentrations, which caused a decrease in biomass, rhizome growth and number of axillary and apical rhizome buds. Daughter axillary shoots exhibited a tolerance strategy, with no significant change in their number; the axillary and apical rhizome buds, daughter apical rhizome shoots and rhizomes exhibited compensatory growth during the late stage of Pb (excluding 4500 mg·kg(-1) ) treatment in a wet environment. Pb applications above 500 mg·kg(-1) reduced these parameters significantly in the drought treatment, except for the number of axillary shoot buds, which did not change. Our results indicate that clonal propagative resistance to Pb contamination can occur via tolerance strategies, compensatory growth and a Pb allocation strategy, enabling these reeds to maintain population stability in wet environments. However, clonal modular growth and reproductive ability were inhibited significantly by the interaction between drought and Pb, which would cause a decline in P. australis populations in a dry environment. Lead concentrations of 4500 and 500 mg·kg(-1) in soils might meet or exceed the Pb tolerance threshold of clonally propagated reeds in wet and dry environments, respectively.

The tolerance of growth and clonal propagation of Phragmites australis (common reeds) subjected to lead contamination under elevated CO2conditions

Elevated CO₂might improve growth and clonal propagation resistance to Pb contamination through increasing photosynthetic, phalanx growth and population expansion.

The ability of Typha domingensis to accumulate and tolerate high concentrations of Cr, Ni, and Zn

The tolerance and removal efficiency of Typha domingensis exposed to high concentrations of Cr, Ni, and Zn in single and combined treatments were studied. Sediment and two plants were disposed in each plastic reactor. The treatments were 100 and 500 mg L(-1) of Cr, Ni, and Zn (single solutions); 100 mg L(-1) Cr + Ni + Zn (multi-metal solutions) and 500 mg L(-1) Cr + Ni + Zn (multi-metal solutions); and a control. Even though the concentrations studied were extremely high, simulating an accidental metal dump, the three metals were efficiently removed from water. The highest removal was registered for Cr. The presence of other metals favored Cr and did not favor Ni and Zn removal from water. After 25 days, senescence and chlorosis of plants were observed in Ni and Comb500 treatments, while Cr and Zn only caused growth inhibition. T. domingensis accumulated high metal concentrations in tissues. The roots showed higher metal concentration than submerged parts of leaves. Cr translocation to aerial parts was enhanced by the presence of Ni and Zn. Our results demonstrate that in the case of an accidental dump of high Cr, Ni, and Zn concentrations, a wetland system dominated by T. domingensis is able to retain metals, and the macrophyte is able to tolerate them the time necessary to remove them from water. Thus, the environment will be preserved since the wetland would act as a cushion.