A two-compartment exposure device for foliar uptake study

Nitrogen addition facilitates phytoremediation of PAH-Cd cocontaminated dumpsite soil by altering alfalfa growth and rhizosphere communities

Thousands of unlined landfills and open dumpsites seriously threatened the safety of soil and groundwater due to leachate leakage with a mass of pollutants, particularly heavy metals, organic contaminants and ammonia. Phytoremediation is widely used in the treatment of cocontaminated soils because it is cost-effective and environmentally friendly. However, the extent to which phytoremediation efficiency and plant physiological responses are affected by the high nitrogen (N) content in such cocontaminated soil is still uncertain. Here, pot experiments were conducted to investigate the effects of N addition on the applicability of legume alfalfa remediation for polycyclic aromatic hydrocarbon‑cadmium (PAHCd) co-/contaminated soil and the corresponding microbial regulation mechanism. The results showed that the PAH dissipation rates and Cd removal rates in the high-contamination groups increased with the external N supply, among which the pyrene dissipation rates in the cocontaminated soil was elevated most significantly, from 78.10% to 87.25%. However, the phytoremediation efficiency weakened in low cocontaminated soil, possibly because the excessive N content had inhibitory effects on the rhizobium Ensifer and restrained alfalfa growth. Furthermore, the relative abundance of PAH-degrading bacteria in the rhizosphere dominated PAH dissipation. As reflected by principal coordinate analysis (PCoA) analysis and hierarchical dendrograms, the microbial community composition changed with N addition, and a more pronounced shift was found in the rhizosphere relative to the endosphere or shoots of alfalfa. This study will provide a theoretical basis for legume plant remediation of dumpsites as well as soil contaminated with multiple pollutants.

Prediction of organic contaminant uptake by plants: Modified partition-limited model based on a sequential ultrasonic extraction procedure

Predicting the translocation of organic contaminants to plants is crucial to ensure the quality of agricultural goods and assess the risk of human exposure through the food web. In this study, the performance of a modified plant uptake model was evaluated considering a number of chemicals, such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs), with a range of physicochemical properties; different plant species (Ipomoea aquatica Forsk (swamp morning glory), Chrysanthemum coronarium L. (crown daisy), Zea mays L. (corn), Brassica rapa pekinensis (Chinese cabbage), Cucurbita moschata (pumpkin), Raphanus sativus L. (radish), Spinacia oleracea L. (spinach) and Capsicum annuum L. (pepper)); and different types of soil (paddy soil, laterite soil and black soil). The biases of predictions from a previously used partition-limited model were -76.4% to -99.9% relative to the measured concentrations. An overall transmission factor (α_tf=0.39), calculated from a linear regression of the measured bioavailable fraction (C_bio) and the total concentration in plants, was considered a crucial modification and was included in the modified model. C_bio was found to better represent the chemical content available in soil for root uptake. The results from this study improve the accuracy of predictions for vegetation-uptake assessments by modifying the partition-limited model and then validating the modified model using comparisons between predicted data and measured values. The accuracy of the concentrations of organic contaminants in plants improved: when using the modified model, 89.5% of the predictions were within 40% of the actual value. The average bias was limited to 1.5%-30.5%. The model showed great potential to predict plant uptake using the bioavailable fraction concentration in soil.

Partition uptake of a brominated diphenyl ether by the edible plant root of white radish (Raphanus sativus L.)

Polybrominated diphenyl ethers (PBDEs) are of a class of emerging contaminants. In this study, the accumulation of 4-bromodiphenyl ether (BDE-3) by different parts of a live white radish was investigated. Different cultural media (hydroponics, silica sand, and soil) were used to sustain the radish plant during its uptake and in-plant translocation of BDE-3. The results showed that BDE-3 can be translocated from the roots to the aboveground organs and the accumulated levels of BDE-3 in different parts of the white radish followed the order for the three types of cultivation: fibrous roots > peels > main roots > leaves. The results were analyzed by the aid of the partition-limited model for the plant uptake. The relevant partition coefficients (K_OC and K_d) and uptake parameters of BDE-3 with plant components (K_pt and K_lip) were obtained for analyzing the BDE-3 distribution. The partition-limited model offers a significant insight into the uptakes of BDE-3 by the various components of live white radishes. The types of cultivation affected the total sorption level, translocation factors (TFs), extent to equilibrium (α_pt), and root concentration factors (RCFs).

Uptake Pathway, Translocation, and Isomerization of Hexabromocyclododecane Diastereoisomers by Wheat in Closed Chambers

To study the uptake pathways of 3 main hexabromocyclododecane diastereoisomers (α-, β-, and γ-HBCDs) in wheat, four closed chambers were designed to expose wheat to HBCDs via air and/or soil for 4 weeks. The results showed that HBCDs could be absorbed by wheat both via root from soil and via leaf from air. The Rt values (ratio of HBCDs from root-to-leaf translocation to the total accumulation in leaves) ranging from 14.4 to 29.8% suggested that acropetal translocation within wheat was limited. A negative linear relationship was found between log Rt and log Kow of the HBCD diastereoisomers (p < 0.05). The bioconcentration factors (BCFs, (μg/g wheat tissues)/(μg/g soil)) were in the order α- > β- > γ-HBCD in wheat roots and stems, being negatively related to their Kow values. No such correlation was found in leaves, where the HBCDs came mainly from air distribution. The results of enantiomeric fractions indicated that the (-)-enantiomer of α- and γ-HBCDs and the (+)-β-enantiomer were selectively accumulated. Furthermore, β- and γ-HBCDs were transformed to α-HBCD in the wheat, with 0.309-4.80% and 0.920-8.40% bioisomerization efficiencies at the end of the experiment, respectively, being the highest in leaves. Additionally, no isomerization product from α-HBCD was found.

Effect of surfactant amendment to PAHs-contaminated soil for phytoremediation by maize (Zea mays L.)

Understanding the uptake of organic pollutants by plants is an important part of the assessment of risks from crops grown on contaminated soils. This study was an investigation of the effects of surfactants added to PAHs-contaminated soil on the uptake and accumulation of PAHs in maize tissues during phytoremediation. The accumulation of phenanthrene (PHE) and pyrene (PYR) by maize plant was not influenced significantly by the surfactant amendment to the soil. The distribution of PHE and PYR in maize tissues was not positively correlated with the corresponding lipid contents. Remarkably, the concentrations of PHE (20.9 ng g(-1)) and PYR (0.9 ng g(-1)) in maize grain were similar to or even much lower than those in some foods. Moreover, surfactants could enhance the removal of pollutants from contaminated soil during phytoremediation, which might be due to surfactant desorption ability and microbial activity in soil. The study suggests that use of maize plant with surfactant is an alternative technology for remediation of PAHs-contaminated soils.

Accumulation of Hydrocarbons by Maize (Zea mays L.) in Remediation of Soils Contaminated with Crude Oil

This study has investigated the use of screened maize for remediation of soil contaminated with crude oil. Pots experiment was carried out for 60 days by transplanting maize seedlings into spiked soils. The results showed that certain amount of crude oil in soil (≤2 147 mg·kg(-1)) could enhance the production of shoot biomass of maize. Higher concentration (6 373 mg·kg(-1)) did not significantly inhibit the growth of plant maize (including shoot and root). Analysis of plant shoot by GC-MS showed that low molecular weight polycyclic aromatic hydrocarbons (PAHs) were detected in maize tissues, but PAHs concentration in the plant did not increase with higher concentration of crude oil in soil. The reduction of total petroleum hydrocarbon in planted soil was up to 52.21-72.84%, while that of the corresponding controls was only 25.85-34.22% in two months. In addition, data from physiological and biochemical indexes demonstrated a favorable adaptability of maize to crude oil pollution stress. This study suggested that the use of maize (Zea mays L.) was a good choice for remediation of soil contaminated with petroleum within a certain range of concentrations.

Identifying potential sources of Sudan I contamination in Capsicum fruits over its growth period

Sudan dyes in spices are often assumed to arise from cross-contamination or malicious addition. Here, experiments were carried out to identify the potential source of Sudan I-IV in Capsicum fruits through investigation of their contents in native Capsicum tissues, soils and associated agronomic materials. Sudan II-IV was not detected in any of the tested samples. Sudan I was found in almost all samples except for the mulching film. Sudan I concentrations decreased from stems to leaves and then to fruits or roots. Sudan I levels in soils were significantly elevated by vegetation treatment. These results exclude the possibility of soil as the main source for Sudan I contamination in Capsicum fruits. Further study found out pesticide and fertilizer constitutes the major source of Sudan I contamination. This work represents a preliminary step for a detailed Sudan I assessment to support Capsicum management and protection in the studied region.

Exposure chambers for studying the partitioning of atmospheric PAHs in environmental compartments: validation and calibration using experimental and computational approaches

The environmental partitioning of atmospheric polycyclic aromatic hydrocarbons (PAHs) conditions their entry into food chains and subsequent risks for human health. The need for new experimental exposure devices for elucidating the mechanisms governing ecosystemic PAH transfer motivated the elaboration of an original small-scale exposure chamber (EC). A dual approach pairing experimentation and computational fluid dynamics (CFD) was selected to provide comprehensive validation of this EC as a tool to study the transfer and biological effects of atmospheric PAH pollution in microsystems. Soil samples and passive air samplers (PASs) were exposed to atmospheric pollution by phenanthrene (PHE), a gaseous PAH, for 2 weeks in examples of the EC being tested, set up under different conditions. Dynamic concentrations of atmospheric PHE and its uptake by PASs were simulated with CFD, results showing homogeneous distribution and constant atmospheric PHE concentrations inside the ECs. This work provides insight into the setting of given concentrations and pollution levels when using such ECs. The combination of experimentation and CFD is a successful ECs calibration method that should be developed with other semivolatile organic pollutants, including those that tend to partition in the aerosol phase.

Challenges in tracing the fate and effects of atmospheric polycyclic aromatic hydrocarbon deposition in vascular plants

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous organic pollutants that raise environmental concerns because of their toxicity. Their accumulation in vascular plants conditions harmful consequences to human health because of their position in the food chain. Consequently, understanding how atmospheric PAHs are taken up in plant tissues is crucial for risk assessment. In this review we synthesize current knowledge about PAH atmospheric deposition, accumulation in both gymnosperms and angiosperms, mechanisms of transfer, and ecological and physiological effects. PAHs emitted in the atmosphere partition between gas and particulate phases and undergo atmospheric deposition on shoots and soil. Most PAH concentration data from vascular plant leaves suggest that contamination occurs by both direct (air-leaf) and indirect (air-soil-root) pathways. Experimental studies demonstrate that PAHs affect plant growth, interfering with plant carbon allocation and root symbioses. Photosynthesis remains the most studied physiological process affected by PAHs. Among scientific challenges, identifying specific physiological transfer mechanisms and improving the understanding of plant-symbiont interactions in relation to PAH pollution remain pivotal for both fundamental and applied environmental sciences.

Root response in Pisum sativum and Zea mays under fluoranthene stress: morphological and anatomical traits

Introduced organic pollutants in all ecosystem compartments can cause stress resulting in a wide range of responses including different root development. In this study, the effects of a polycyclic aromatic hydrocarbon-fluoranthene (FLT; 0.1, 1 and 7 mg L(-1)) on the growth, morphology and anatomical structure of roots of pea and maize was evaluated. In comparison with pea, significant stimulation of root system growth of maize caused by 0.1 mg L(-1) (total length longer by 25%, number of lateral roots by 35%) and its reduction (total length by 34%) already by 1 mg L(-1) FLT is the proof of different interspecies sensitivity to low and higher environmental loading. Nevertheless in both plant species a high loading 7 mg L(-1) FLT significantly reduced both growth (total length by 95% in pea, 94% in maize) and the number of lateral roots (by 78% in pea, 94% in maize). Significantly increased thickness of root of both maize and pea was caused by 7 mg L(-1) FLT and in maize already by 0.1 mg L(-1) FLT. It may be mainly connected with an enlargement of stele area (up to 50% in pea and 25% in maize). Increased xylem area in root tip (by up to 385% in pea, 167% in maize) and zone of maturation (up to 584% in pea, 70% in maize) and its higher portion in stele area of root tip (by 9% in pea, 21% in maize), mainly in roots exposed 7 mg L(-1) FLT, are a proof of an early differentiation of vascular tissue and a shortening of root elongation zone. Moreover in both plant species exposed to this treatment, the decline of rhizodermis cells and external layers of primary cortex was found and also significant deformation of primordia of lateral roots was recorded.

Uptake, translocation, and debromination of polybrominated diphenyl ethers in maize

Uptake, translocation and debromination of three polybrominated diphenyl ethers (PBDEs), BDE-28, -47 and -99, in maize were studied in a hydroponic experiment. Roots took up most of the PBDEs in the culture solutions and more highly brominated PBDEs had a stronger uptake capability. PBDEs were detected in the stems and leaves of maize after exposure but rarely detected in the blank control plants. Furthermore, PBDE concentrations decreased from roots to stems and then to leaves, and a very clear decreasing gradient was found in segments upwards along the stem. These altogether provide substantiating evidence for the acropetal translocation of PBDEs in maize. More highly brominated PBDEs were translocated with more difficulty. Radial translocation of PBDEs from nodes to sheath inside maize was also observed. Both acropetal and radial translocations were enhanced at higher transpiration rates, suggesting that PBDE transport was probably driven by the transpiration stream. Debromination of PBDEs occurred in all parts of the maize, and debromination patterns of different parent PBDEs and in different parts of a plant were similar but with some differences. This study for the first time provides direct evidence for the acropetal translocation of PBDEs within plants, elucidates the process of PBDE transport and clarifies the debromination products of PBDEs in maize.

Atmospheric phenanthrene pollution modulates carbon allocation in red clover (Trifolium pratense L.)

The influence of atmospheric phenanthrene (PHE) exposure (160 μg m(-3)) during one month on carbon allocation in clover was investigated by integrative (plant growth analysis) and instantaneous (13)CO(2) pulse-labelling approaches. PHE exposure diminished plant growth parameters (relative growth rate and net assimilation rate) and disturbed photosynthesis (carbon assimilation rate and chlorophyll content), leading to a 25% decrease in clover biomass. The root-shoot ratio was significantly enhanced (from 0.32 to 0.44). Photosynthates were identically allocated to leaves while less allocated to stems and roots. PHE exposure had a significant overall effect on the (13)C partitioning among clover organs as more carbon was retained in leaves at the expense of roots and stems. The findings indicate that PHE decreases root exudation or transfer to symbionts and in leaves, retains carbon in a non-structural form diverting photosynthates away from growth and respiration (emergence of an additional C loss process).

Enhanced dissipation of PAHs from soil using mycorrhizal ryegrass and PAH-degrading bacteria

The major aim of this experiment was to test the effects of a multi-component bioremediation system consisting of ryegrass (Lolium multiflorum), polycyclic aromatic hydrocarbons (PAHs)-degrading bacteria (Acinetobacter sp.), and arbuscular mycorrhizal fungi (Glomus mosseae) for cleaning up PAHs contaminated soil. Higher dissipation rates were observed in combination treatments: i.e., bacteria+ryegrass (BR), mycorrhizae+ryegrass (MR), and bacteria+mycorrhizae+ryegrass (BMR); than bacteria (B) and ryegrass (R) alone. The growth of ryegrass significantly (p<0.05) increased soil peroxidase activities, leading to enhanced dissipation of phenanthrene (PHE) and pyrene (PYR) from soil. Interactions between ryegrass with the two microbes further enhanced the dissipation of PHE and PYR. Mycorrhizal ryegrass (MR) significantly enhanced the dissipation of PYR from soil, PYR accumulation by ryegrass roots and soil peroxidase activities under lower PHE and PYR levels (0 and 50+50 mg kg(-1)). The present results highlighted the contribution of mycorrhiza and PAH-degrading bacteria in phytoremediation of PAH contaminated soil, however more detailed studies are needed.

Interrelationship of Pyrogenic Polycyclic Aromatic Hydrocarbon (PAH) Contamination in Different Environmental Media

Interrelationships between pyrogenic polycyclic aromatic hydrocarbons (PAHs) were assessed in air, soil, water, sediment, and tree leaves by using multi-media monitoring data. Concurrent concentration measurements were taken bimonthly for a year for the multi-media at urban and suburban sites. PAH level correlations between air and other media were observed at the urban site but were less clear at the suburban site. Considering a closer PAHs distribution/fate characteristics to soil than suspended solids, contamination in sediment seemed to be governed primarily by that in soil. The partitioning of PAHs in waters could be better accounted for by sorption onto black carbon and dissolved organic carbon.

Uptake of polycyclic aromatic hydrocarbons by maize plants

Roots and above-ground parts (tops) of maize plants, comprising cuticles, leaves and stems, have been exposed separately to polycyclic aromatic hydrocarbons (PAHs) by means of air-tight bicameral exposure devices. Maize roots and tops of plants directly accumulate PAHs from aqueous solutions and from air in proportion to exposure levels. Root and leaf concentration factors (log RCF and log LCF) are log-linear functions of log-based octanol-water partition coefficient (log Kow) and log-based octanol-air partition coefficient (log Koa). The PAHs' concentrations among cuticles, leaves and stems display good correlations with each other. PAH concentrations in each part of the plant tested correlated positively with atmospheric PAHs' concentrations. Comparisons between PAHs' concentrations of root epidermis and root tissue showed similar correlations. Bulk concentrations of contaminants in various plant tissues differed greatly, but these differences disappeared after normalization to lipid contents suggesting lipid-based partitioning of PAHs among maize tissues.