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Key Message: Transgenic Crambe abyssinica lines overexpressing γ-ECS significantly enhance tolerance to and accumulation of toxic metal(loid)s, improving phytoremediation potential and offering an effective solution for contaminated soil management. Phytoremediation is an attractive environmental-friendly technology to remove metal(loid)s from contaminated soils and water. However, tolerance to toxic metals in plants is a critical limiting factor. Transgenic Crambe abyssinica lines were developed that overexpress the bacterial γ-glutamylcysteine synthetase (γ-ECS) gene to increase the levels of non-protein thiol peptides such as γ-glutamylcysteine (γ-EC), glutathione (GSH), and phytochelatins (PCs) that mediate metal(loid)s detoxification. The present study investigated the effect of γ-ECS overexpression on the tolerance to and accumulation of toxic As, Cd, Pb, Hg, and Cr supplied individually or as a mixture of metals. Compared to wild-type plants, γ-ECS transgenics (γ-ECS1-8 and γ-ECS16-5) exhibited a significantly higher capacity to tolerate and accumulate these elements in aboveground tissues, i.e., 76-154% As, 200-254% Cd, 37-48% Hg, 26-69% Pb, and 39-46% Cr, when supplied individually. This is attributable to enhanced production of GSH (82-159% and 75-87%) and PC2 (27-33% and 37-65%) as compared to WT plants under AsV and Cd exposure, respectively. The levels of Cys and γ-EC were also increased by 56-67% and 450-794% in the overexpression lines compared to WT plants under non-stress conditions, respectively. This likely enhanced the metabolic pathway associated with GSH biosynthesis, leading to the ultimate synthesis of PCs, which detoxify toxic metal(loid)s through chelation. These findings demonstrate that γ-ECS overexpressing Crambe lines can be used for the enhanced phytoremediation of toxic metals and metalloids from contaminated soils., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Nanobiotechnology is a potentially safe and sustainable strategy for both agricultural production and soil remediation, yet the potential of nanomaterials (NMs) application to remediate heavy metal(loid)-contaminated soils is still unclear. A meta-analysis with approximately 6000 observations was conducted to quantify the effects of NMs on safe crop production in soils contaminated with heavy metal(loid) (HM), and a machine learning approach was used to identify the major contributing features. Applying NMs can elevate the crop shoot (18.2 %, 15.4-21.2 %) and grain biomass (30.7 %, 26.9-34.9 %), and decrease the shoot and grain HM concentration by 31.8 % (28.9-34.5 %) and 46.8 % (43.7-49.8 %), respectively. Iron-NMs showed a greater potential to inhibit crop HM uptake compared to other types of NMs. Our result further demonstrates that NMs application substantially reduces the potential health risk of HM in crop grains by human health risk assessment. The NMs-induced reduction in HM accumulation was associated with decreasing HM bioavailability, as well as increased soil pH and organic matter. A random forest model demonstrates that soil pH and total HM concentration are the two significant features affecting shoot HM accumulation. This analysis of the literature highlights the significant potential of NMs application in promoting safe agricultural production in HM-contaminated agricultural lands., Competing Interests: Declaration of competing interest The authors declare that they have no competing interests., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Cadmium (Cd) accumulation in rice, a global environmental issue, poses a significant threat to human health due to its widespread presence and potential transfer through the food chain. Selenium (Se), an essential micronutrient for humans and plants, can reduce Cd uptake in rice and alleviate Cd-induced toxicity. However, the effects and mechanisms of Se supplementation on rice performance in Cd-contaminated soil remain largely unknown. Here, a global meta-analysis was conducted to evaluate the existing knowledge on the effects and mechanisms by which Se supplementation impacts rice growth and Cd accumulation. The result showed that Se supplementation has a significant positive impact on rice growth in Cd-contaminated soil. Specifically, Se supplementation decreased Cd accumulation in rice roots by 16.3 % (11.8-20.6 %), shoots by 24.6 % (19.9-29.1 %), and grain by 37.3 % (33.4-40.9 %), respectively. The grain Cd reduction was associated with Se dose and soil Cd contamination level but not Se type or application method. Se influences Cd accumulation in rice by regulating the expression of Cd transporter genes (OSLCT1, OSHMA2, and OSHMA3), enhancing Cd sequestration in the cell walls, and reducing Cd bioavailability in the soil. Importantly, Se treatment promoted Se enrichment in rice and alleviated oxidative damage associated with Cd exposure by stimulating photosynthesis and activating antioxidant enzymes. Overall, Se treatment mitigated the health hazard associated with Cd in rice grains, particularly in lightly contaminated soil. These findings reveal that Se supplementation is a promising strategy for simultaneous Cd reduction and Se enrichment in rice., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Declarations of interest None., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Micro/nanoplastic (MNP) pollution in soil ecosystems has become a growing environmental concern globally. However, the comprehensive impacts of MNPs on soil health have not yet been explored. We conducted a hierarchical meta-analysis of over 5000 observations from 228 articles to assess the broad impacts of MNPs on soil health parameters (represented by 20 indicators relevant to crop growth, animal health, greenhouse gas emissions, microbial diversity, and pollutant transfer) and whether the impacts depended on MNP properties. We found that MNP exposure significantly inhibited crop biomass and germination, and reduced earthworm growth and survival rate. Under MNP exposure, the emissions of soil greenhouse gases (CO 2 , N 2 O, and CH 4 ) were significantly increased. MNP exposure caused a decrease in soil bacteria diversity. Importantly, the magnitude of impact of the soil-based parameters was dependent on MNP dose and size; however, there is no significant difference in MNP type (biodegradable and conventional MNPs). Moreover, MNPs significantly reduced As uptake by plants, but promoted plant Cd accumulation. Using an analytical hierarchy process, we quantified the negative impacts of MNP exposure on soil health as a mean value of -10.2% (-17.5% to -2.57%). Overall, this analysis provides new insights for assessing potential risks of MNP pollution to soil ecosystem functions., (© 2024 John Wiley & Sons Ltd.)

Given the increasing concern over Cd contamination of agricultural soils in China, reducing the availability of the toxic metal has become an important remedial strategy. However, the lack of a unified evaluation framework complicates the assessment of remediation efficiency of different practices. Here, we evaluated the general extraction method (GEM) of available Cd in nine typical soil types by comparing extraction agents, including CaCl 2 , EDTA, Mehlich-Ⅲ, HCl and DTPA. The safe grain concentration of different agricultural products from National Food Safety Standards Limits of Contaminants in Food (GB 2762-2022) was then applied to understand soil limited available Cd concentration based on dose-response curves. We also derived environmental risk threshold (HC 5 ) values for Cd remediation in agricultural soils by constructing species sensitivity distribution (SSD) curves. The results showed that Mehlich-Ⅲ best predicted Cd accumulation in crops (with 76.5% of explanation of grain Cd) and was selected as the GEM of soil available Cd for subsequent analyses. The regression coefficient (R 2 ) of dose-response curves fitting between Cd absorption in crop tissues and soil available Cd extracted by GEM based on 30 different crop species varied from 51.0% to 79.5%, and the derived limit concentration of soil available Cd based on standard GB 2762-2022 was 0.18-0.76 mg‧kg -1 . An HC 5 of 0.19 mg‧kg -1 was then calculated, meaning that a concentration of available Cd in agricultural soil below 0.19 mg‧kg -1 ensures that 95% of agricultural products meet the quality and safety requirements of standard GB 2762-2022. The prediction model was well verified in the field test, indicating that can correctly estimate the soil available Cd based on the content of Cd in plant. This study provides a robust scientific framework for deriving the risk threshold for Cd remediation in agricultural soils and could be quite useful for establishing soil remediation standards., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Soil and terrestrial contamination with microplastics and nanoplastics has been discussed extensively, while tire wear particles (TWPs) have been largely overlooked. We investigated the root-surface interactions and growth response of mung bean ( Vigna radiata L.) plants exposed to tire wear particles (TWPs) (0.05, 0.1, and 0.25% w/w) and nickel sulfate (50 and 100 mg kg -1 NiSO 4 ) alone and in co-exposure scenarios for the full life cycle (105 days) under soil conditions. The results show that TWPs adhered to the root surface and reduced the water and nutrient uptake by the plant, particularly at higher concentrations of TWPs (0.25% w/w), without any observed organic contaminant accumulation in the root tissue. TWPs alone at 0.01, 0.1, and 0.25% (w/w) decreased mung bean yield by 11, 28, and 52%, respectively. Co-exposure to TWPs at 0.01, 0.1 and 0.25% w/w with 100 mg kg -1 NiSO 4 decreased yield by 73, 79 and 88%, respectively. However, co-exposure to TWPs at 0.01 and 0.1% w/w with 50 mg kg -1 NiSO 4 enhanced the yield by 32% and 7%, respectively. These changes in yield and nutritional aspects appear to be linked to Ni's regulatory influence on mineral homeostasis. Moreover, exposure to NiSO 4 at 100 mg kg -1 increased Ni uptake in the root, shoot, and grain by 9, 26, and 20-fold, respectively as compared to the unamended control; this corresponded to increased antioxidant enzyme activity (10-127%) as compared to the control. TWPs caused blockages, significantly reducing plant yield and altering nutrient dynamics, highlighting emerging risks to plant health.

The presence of per- and poly-fluoroalkyl substances (PFAS) in soils is a global concern as these emerging contaminants are highly resistant to degradation and cause adverse effects on human and environmental health at very low concentrations. Sequestering PFAS in soils using carbon-based materials is a low-cost and effective strategy to minimize pollutant bioavailability and exposure, and may offer potential long-term remediation of PFAS in the environment. This paper provides a comprehensive evaluation of current insights on sequestration of PFAS in soil using carbon-based sorbents. Hydrophobic effects originating from fluorinated carbon (C-F) backbone "tail" and electrostatic interactions deriving from functional groups on the molecules' "head" are the two driving forces governing PFAS sorption. Consequently, varying C-F chain lengths and polar functional groups significantly alter PFAS availability and leachability. Furthermore, matrix parameters such as soil organic matter, inorganic minerals, and pH significantly impact PFAS sequestration by sorbent amendments. Materials such as activated carbon, biochar, carbon nanotubes, and their composites are the primary C-based materials used for PFAS adsorption. Importantly, modifying the carbon structural and surface chemistry is essential for increasing the active sorption sites and for strengthening interactions with PFAS. This review evaluates current literature, identifies knowledge gaps in current remediation technologies and addresses future strategies on the sequestration of PFAS in contaminated soil using sustainable novel C-based sorbents., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

To investigate the mechanisms by which g-C 3 N 4 alleviates metal(loid)-induced phytotoxicity, rice seedlings were exposed to 100 and 250 mg/kg graphitic carbon nitride (g-C 3 N 4 ) with or without coexposure to 10 mg/kg Cd and 50 mg/kg As for 30 days. Treatment with 250 mg/kg g-C 3 N 4 significantly increased shoot and root fresh weight by 22.4-29.9%, reduced Cd and As accumulations in rice tissues by 20.6-26.6%, and elevated the content of essential nutrients (e.g., K, S, Mg, Cu, and Zn) compared to untreated controls. High-throughput sequencing showed that g-C 3 N 4 treatment increased the proportion of plant-growth-promoting endophytic bacteria, including Streptomyces , Saccharimonadales , and Thermosporothrix , by 0.5-3.30-fold; these groups are known to be important to plant nutrient assimilation, as well as metal(loid) resistance and bioremediation. In addition, the population of Deinococcus was decreased by 72.3%; this genus is known to induce biotransformation As(V) to As(III). Metabolomics analyses highlighted differentially expressed metabolites (DEMs) involved in the metabolism of tyrosine metabolism, pyrimidines, and purines, as well as phenylpropanoid biosynthesis related to Cd/As-induced phytotoxicity. In the phenylpropanoid biosynthesis pathway, the increased expression of 4-coumarate (1.13-fold) and sinapyl alcohol (1.26-fold) triggered by g-C 3 N 4 coexposure with Cd or As played a critical role in promoting plant growth and enhancing rice resistance against metal(loid) stresses. Our findings demonstrate the potential of g-C 3 N 4 to enhance plant growth and minimize the Cd/As-induced toxicity in rice and provide a promising nanoenabled strategy for remediating heavy metal(loid)-contaminated soil.

Molybdenum disulfide (MoS 2 ) nanosheets are increasingly applied in several fields, but effective and accurate strategies to fully characterize potential risks to soil ecosystems are lacking. We introduce a coelomocyte-based in vivo exposure strategy to identify novel adverse outcome pathways (AOPs) and molecular endpoints from nontransformed (NTMoS 2 ) and ultraviolet-transformed (UTMoS 2 ) MoS 2 nanosheets (10 and 100 mg Mo/L) on the earthworm Eisenia fetida using nontargeted lipidomics integrated with transcriptomics. Machine learning-based digital pathology analysis coupled with phenotypic monitoring was further used to establish the correlation between lipid profiling and whole organism effects. As an ionic control, Na 2 MoO 4 exposure significantly reduced (61.2-79.5%) the cellular contents of membrane-associated lipids (glycerophospholipids) in earthworm coelomocytes. Downregulation of the unsaturated fatty acid synthesis pathway and leakage of lactate dehydrogenase (LDH) verified the Na 2 MoO 4 -induced membrane stress. Compared to conventional molybdate, NTMoS 2 inhibited genes related to transmembrane transport and caused the differential upregulation of phospholipid content. Unlike NTMoS 2 , UTMoS 2 specifically upregulated the glyceride metabolism (10.3-179%) and lipid peroxidation degree (50.4-69.4%). Consequently, lipolytic pathways were activated to compensate for the potential energy deprivation. With pathology image quantification, we report that UTMoS 2 caused more severe epithelial damage and intestinal steatosis than NTMoS 2 , which is attributed to the edge effect and higher Mo release upon UV irradiation. Our results reveal differential AOPs involving soil sentinel organisms exposed to different Mo forms, demonstrating the potential of liposome analysis to identify novel AOPs and furthermore accurate soil risk assessment strategies for emerging contaminants.

This present study investigated pork bone-derived biochar as a promising amendment to reduce Cd accumulation and alleviate Cd-induced oxidative stress in rice. Micro/nanoscale bone char (MNBC) pyrolyzed at 400 °C and 600 °C was synthesized and characterized before use. The application rates for MNBCs were set at 5 and 25 g·kg -1 and the Cd exposure concentration was 15 mg·kg -1 . MNBCs increased rice biomass by 15.3-26.0% as compared to the Cd-alone treatment. Both types of MNBCs decreased the bioavailable Cd content by 27.4-54.8%; additionally, the acid-soluble Cd fraction decreased by 10.0-12.3% relative to the Cd alone treatment. MNBC significantly reduced the cell wall Cd content by 50.4-80.2% relative to the Cd-alone treatment. TEM images confirm the toxicity of Cd to rice cells and that MNBCs alleviated Cd-induced damage to the chloroplast ultrastructure. Importantly, the addition of MNBCs decreased the abundance of heavy metal tolerant bacteria, Acidobacteria and Chloroflexi, by 29.6-41.1% in the rhizosphere but had less impact on the endophytic microbial community. Overall, our findings demonstrate the significant potential of MNBC as both a soil amendment for heavy metal-contaminated soil remediation and for crop nutrition in sustainable agriculture., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Metal(loid)s contamination poses a serious threat to ecosystem biosafety and human health. Phytoremediation is a cost-effective and eco-friendly technology with good public acceptance, although the process does require a significant amount of time for success. To enhance the phytoremediation efficiency, numerous approaches have been explored, including soil amendments application with chelators to facilitate remediation. Sulfur (S), a macronutrient for plant growth, plays vital roles in several metabolic pathways that can actively affect metal(loid)s phytoextraction, as well as attenuate metal(loid) toxicity. In this review, different forms of S-amendments (fertilizers) on uptake and translocation in plants upon exposure to various metal(loid) are evaluated. Possible mechanisms for S application alleviating metal(loid) toxicity are documented at the physiological, biochemical and molecular levels. Furthermore, this review highlights the crosstalk between S-assimilation and other biomolecules, such as phytohormones, polyamines and nitric oxide, which are also important for metal(loid) stress tolerance. Given the effectiveness and potential of S amendments on phytoremediation, future studies should focus on optimizing phytoremediation efficiency in long-term field studies and on investigating the appropriate S dose to maximize the food safety and ecosystem health., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Nano-enabled phytoremediation is an emerging remediation strategy for soils that are moderately contaminated with persistent organic contaminants, and there is a significant need for increased mechanistic understanding and for case studies. Herein, we evaluated the remediation of PCB28-contaminated soil using combined alfalfa and Fe-based materials, including zero-valent iron at 20 nm, 100 nm, and 5 µm, and also iron oxide nanomaterials including α-Fe 2 O 3 , γ-Fe 2 O 3 , and Fe 3 O 4 around 20-30 nm. Compared with alfalfa remediation alone (63.2%), Fe-based nanomaterials increased PCB28 removal values to 72.4-93.5% in planted soil, with α-Fe 2 O 3 treatment promoting the most effective pollutant removal. Mechanistically, the crystalline Fe-based nanoparticles were transformed into amorphous forms in the plant rhizosphere, resulting in greater availability and enhanced iron nutrition. This nutritional shift induced root metabolic reprogramming of amino acid and carbohydrate cycling, and related functional bacterial enrichment of Ramlibacter, Dyella, Bacillus, and Paraburkholderia in rhizosphere. A significant positive correlation between amorphous iron and root metabolites-associated microbes with PCB28 removal was evident, implying that iron supplementation selected for rhizospheric microorganisms favored PCBs degradation. Overall, this rhizoremediation promotion strategy of Fe species-metabolites-microbes highlights the potential for the hybrid application of nano-enabled phytotechnology in the remediation of soils contaminated with persistent organic xenobiotics., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The presence of manufactured nano-objects (MNOs) in various consumer or their (future large-scale) use as nanoagrochemical have increased with the rapid development of nanotechnology and therefore, concerns associated with its possible ecotoxicological effects are also arising. MNOs are releasing along the product life cycle, consequently accumulating in soils and other environmental matrices, and potentially leading to adverse effects on soil biota and their associated processes. Earthworms, of the group of Oligochaetes, are an ecologically significant group of organisms and play an important role in soil remediation, as well as acting as a potential vector for trophic transfer of MNOs through the food chain. This review presents a comprehensive and critical overview of toxic effects of MNOs on earthworms in soil system. We reviewed pathways of MNOs in agriculture soil environment with its expected production, release, and bioaccumulation. Furthermore, we thoroughly examined scientific literature from last ten years and critically evaluated the potential ecotoxicity of 16 different metal oxide or carbon-based MNO types. Various adverse effects on the different earthworm life stages have been reported, including reduction in growth rate, changes in biochemical and molecular markers, reproduction and survival rate. Importantly, this literature review reveals the scarcity of long-term toxicological data needed to actually characterize MNOs risks, as well as an understanding of mechanisms causing toxicity to earthworm species. This review sheds light on this knowledge gap as investigating bio-nano interplay in soil environment improves our major understanding for safer applications of MNOs in the agriculture environment., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Rice is known to accumulate arsenic (As) in its grains, posing serious health concerns for billions of people globally. We studied the effect of nanoscale sulfur (NS) on rice seedlings and mature plants under As stress. NS application caused a 40% increase in seedling biomass and a 26% increase in seed yield of mature plants compared to untreated control plants. AsIII exposure caused severe toxicity to rice; however, coexposure of plants to AsIII and NS alleviated As toxicity, and growth was significantly improved. Rice seedlings treated with AsIII + NS produced 159 and 248% more shoot and root biomass, respectively, compared to plants exposed to AsIII alone. Further, AsIII + NS-treated seedlings accumulated 32 and 11% less As in root and shoot tissues, respectively, than the AsIII-alone treatment. Mature plants treated with AsIII + NS produced 76, 110, and 108% more dry shoot biomass, seed number, and seed yield, respectively, and accumulated 69, 38, 18, and 54% less total As in the root, shoot, flag leaves, and grains, respectively, compared to AsIII-alone-treated plants. A similar trend was observed in seedlings treated with AsV and NS. The ability of sulfur (S) to alleviate As toxicity and accumulation is clearly size dependent as NS could effectively reduce bioavailability and accumulation of As in rice via modulating the gene expression activity of As transport, S assimilatory, and glutathione synthesis pathways to facilitate AsIII detoxification. These results have significant environmental implications as NS application in agriculture has the potential to decrease As in the food chain and simultaneously enable crops to grow and produce higher yields on marginal and contaminated lands.

Due to high biomass and an ability to accumulate metals, fast-growing tree species are good candidates for phytoremediation. However, little is known about the long-distance transport of heavy metals in woody plants. The present work focused on the xylem transport and phloem remobilization of copper (Cu) in Salix integra Thunb. Seedlings with 45 d preculture were grown in nutrient solutions added with 0.32 and 10 μM CuSO 4 for 5 d. Micro X-ray fluorescence imaging showed the high Cu intensity in xylem tissues of both stem and root cross sections, confirming that the xylem played a vital role in Cu transport from roots to shoots. Cu was presented in both xylem sap and phloem exudate, which demonstrates the long-distance transport of Cu via both vascular tissues. Additionally, the 65 Cu spiked mature leaf exported approximately 78 % 65 Cu to newly emerged shoots, and approximately 22 % downward to the new roots, confirming the bidirectional transport of Cu via phloem. To our knowledge, this is the first report to characterize Cu vascular transport and remobilization in fast-growing woody plants, and the findings provide valuable mechanistic understanding for the phytoremediation of Cu-contaminated soils., Competing Interests: Declaration of Competing Interest The authors declared that they have no conflicts of interest to this work. We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Climate change has increased flooding frequency, making the heavy metal polluted areas more vulnerable, and led to increased global land degradation. Information about the alteration of soil microbiota under heavy metal pollution and flooding is still rather limited. Fast-growing trees are candidates for phytoremediation of heavy metal polluted soils. Therefore, the impact of Cu pollution on microbiota in soil used for cultivating Salix integra Thunb. was investigated with and without flooding for 60 d. Bacterial and fungal communities were accessed via partial 16S rRNA (V 3 -V 4 ) and internal transcribed spacer (ITS) genes. The activity of invertase, urease and cellulase were markedly decreased by 28.5-59%, 55.0-76.7% and 17.3-34.1%, respectively, with increasing Cu levels. Flooding significantly increased the activity of polyphenol oxidase and peroxidase by 56.3% and 41.4% at the highest Cu level compared to its respective non-flooded condition. High Cu concentration significantly decreased the richness and diversity of the bacterial community, and fungi were more sensitive than bacteria under flooding conditions. Redundancy analysis suggests that Cu, Fe and soil organic matter are the key determinants affecting the composition of microbial communities. Our findings provide new insight into the responses of soil microbes to Cu-contamination and contribute to our understanding of metal toxicity in soil-woody plant systems under flooded conditions., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Copper (Cu) induced phytotoxicity has become a serious environmental problem as a consequence of significant metal release through anthropogenic activity. Understanding the spatial distribution of Cu in plants such as willow is essential to elucidate the mechanisms of metal accumulation and transport in woody plants, particularly as affected by variable environment conditions such as soil flooding. Using synchrotron-based X-ray fluorescence (μ-XRF) techniques, the spatial distribution of Cu and other nutrient elements were investigated in roots and stems of Salix (S.) integra exposed to 450 mg kg -1 Cu under non-flooded (NF)/flooding (F) conditions for 90 d. S. integra grown in the F condition exhibited significant higher tolerance index (TI, determined by the ratio of total biomass in Cu treatments to control) (p < 0.05) than that in the NF condition, indicating soil flooding alleviated Cu toxicity to willow plants. The μ-XRF revealed that Cu was preferentially located in the root cap and meristematic zone of the root tips. Under the NF condition, the Cu intensity in the root epidermis was more highly concentrated than that of the F condition, suggesting the soil flooding significantly inhibited Cu uptake by S. integra. The pattern of the Cu spatial distribution in the S. integra stem indicated that the F condition severely reduced Cu transport via the xylem vessels as a consequence of decreasing the transpiration rate of leaves. To our knowledge, this is the first study to report the in vivo Cu distribution in S. integra in a scenario of co-exposure to the Cu and the soil flooding over a long period. The finding that Cu uptake varies significantly with flooding condition is relevant to the development of strategies for plants to detoxify the metals and to maintain the nutrient homeostasis., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The accumulation and metabolism of 2, 2', 4, 4', 5, 5'-hexabrominated diphenyl ether (BDE-153) in Amaranthus mangostanus L. (amaranth) as affected by different concentrations of biochar (1.3 to 26.6 g/L) under hydroponic conditions exposed to 10 μg/L BDE-153 after 10 days were investigated. Biochar significantly reduced BDE-153 shoot and root content by 27.5-61.6% and 73-95.3%, respectively. In general, BDE-153 migration from solution to amaranth decreased with increasing the doses of biochar. BDE-153 metabolites altered with doses of biochar. The ratio of de-BDEs to BDE-153 in root was polynomial correlated to biochar dose (R 2  = 0.9356**). Root and shoot Fe content was positively correlated with the BDE-153 amounts (R 2  = 0.948** and 0.822*, respectively). Though the higher biochar dose could obviously control BDE-153 uptake by the vegetable, the toxicity was caused more significantly. For instances, the high concentration of biochar at 26.6 g/L reduced pigment content, increased total ROS, and elevated antioxidant enzyme activity. At the same time, the O 2 - intensity was linearly positively correlated with de-BDEs in root (R 2  = 0.7324*) while photosynthetic parameter F v /fm intensity was polynomial correlated to BDEs in shoot (R 2  = 0.9366*). Transmission electron microscopy (TEM) confirmed that exposure to BDE-153 and high concentration biochar at 26.6 g/L severely altered the chloroplasts in terms of the organelle shape and the presence of starch granules in the chloroplast. Taken together, biochar as a soil amendment could significantly control BDE-153 uptake and enhance BDE-153 metabolism in vegetables, but considering the dose of biochar to avoid its toxicity with higher dose., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The interactions of nanoparticles (NPs) with biochar and soil components may substantially influence NP availability and toxicity to biota. In the present study, earthworms ( Eisenia fetida) were exposed for 28 days to a residential or agricultural soil amended with 0-2000 mg of CeO 2 NP/kg and with biochar (produced by the pyrolysis of pecan shells at 350 and 600 °C) at various application rates [0-5% (w/w)]. After 28 days, earthworms were depurated and analyzed for Ce content, moisture content, and lipid peroxidation. The results showed minimal toxicity to the worms; however, biochar (350 or 600 °C) was the dominant factor, accounting for 94 and 84% of the variance for the moisture content and lipid peroxidation, respectively, in the exposed earthworms. For both soils with 1000 mg of CeO 2 /kg at 600 °C, biochar significantly decreased the accumulation of Ce in the worm tissues. Amendment with 350 °C biochar had mixed responses on Ce uptake. Analysis by micro X-ray fluorescence (μ-XRF) and micro X-ray absorption near edge structure (μ-XANES) was used to evaluate Ce localization, speciation, and persistence in CeO 2 - and biochar-exposed earthworms after depuration for 12, 48, and 72 h. Earthworms from the 500 mg of CeO 2 /kg and 0% biochar treatments eliminated most Ce after a 48 h depuration period. However, in the same treatment and with 5% BC-600 (biochar pyrolysis temperature of 600 °C), ingested biochar fragments (∼50 μm) with Ce adsorbed to the surfaces were retained in the gut after 72 h. Additionally, Ce remained in earthworms from the 2000 mg of CeO 2 /kg and 5% biochar treatments after depuration for 48 h. Analysis by μ-XANES showed that, within the earthworm tissues, Ce remained predominantly as Ce 4+ O 2 , with only few regions (2-3 μm 2 ) where it was found in the reduced form (Ce 3+ ). The present findings highlight that soil and biochar properties have a significant influence in the internalization of CeO 2 NPs in earthworms; such interactions need to be considered when estimating NP fate and effects in the environment.

Although the use of engineered nanomaterials continues to increase, how these materials interact with coexisting contaminants in the environment is largely unknown. The effect of silver (Ag) in bulk, ionic, and nanoparticle (NP; bare and polyvinyl pyrrolidone-coated) forms at 3 concentrations (0 mg/kg, 500 mg/kg, 1000 mg/kg, 2000 mg/kg; ion at 69 mg/kg, 138 mg/kg, 276 mg/kg) on the accumulation of field-weathered chlordane and dichlorodiphenyldichloroethylene + metabolites (DDX) by Eisenia fetida (earthworm) was investigated. Earthworm biomass and survival were unaffected by treatment. At the 500 mg/kg and 1000 mg/kg exposure levels, NP-exposed earthworms contained significantly greater Ag (194-245%) than did the bulk exposed organisms; NP size or coating had no impact on element content. Generally, exposure to Ag of any type or at any concentration significantly reduced pesticide accumulation, although reductions for DDX (35.1%; 8.9-47.0%) were more modest than those for chlordane (79.0%; 17.4-92.9%). For DDX, the reduction in pesticide accumulation was not significantly affected by Ag type or concentration. For chlordane, the 3 NP exposures suppressed chlordane accumulation significantly more than did bulk exposure; earthworms exposed to bulk Ag contained 1170 ng/g chlordane, but levels in the NP-exposed earthworms were 279 ng/g. At the 500 mg/kg exposure, the smallest coated NPs exerted the greatest suppression in chlordane accumulation; at the 2 higher concentrations, chlordane uptake was unaffected by NP size or coating. The findings show that in exposed earthworms Ag particle size does significantly impact accumulation of the element itself, as well as that of coexisting weathered pesticides. The implications of these findings with regard to NP exposure and risk are unknown but are the topic of current investigation. Environ Toxicol Chem 2017;36:1864-1871. © 2016 SETAC., (© 2016 SETAC.)

This study evaluates the bioaccumulation of unweathered (U) and weathered (W) CuO in NP, bulk and ionic form (0-400 mg/kg) by lettuce exposed for 70 d in soil co-contaminated with field incurred chlordane. To evaluate CuO trophic transfer, leaves were fed to crickets (Acheta domestica) for 15 d, followed by insect feeding to lizards (Anolis carolinensis). Upon weathering, the root Cu content of the NP treatment increased 214% (327 ± 59.1 mg/kg) over unaged treatment. Cu root content decreased in bulk and ionic treatments from 70-130 mg/kg to 13-26 mg/kg upon aging in soil. Micro X-ray fluorescence (μ-XRF) analysis of W-NP-exposed roots showed a homogenous distribution of Cu (and Ca) in the tissues. Additionally, micro X-ray absorption near-edge (μ-XANES) analysis of W-NP-exposed roots showed near complete transformation of CuO to Cu (I)-sulfur and oxide complexes in the tissues, whereas in unweathered treatment, most root Cu remained as CuO. The expression level of nine genes involved in Cu transport shows that the mechanisms of CuO NPs (and bulk) response/accumulation are different than ionic Cu. The chlordane accumulation by lettuce upon co-exposure to CuO NPs significantly increased upon weathering. Conversely, bulk and ionic exposures decreased pesticide accumulation by plant upon weathering. The Cu cricket fecal content from U-NP-exposed insects was significantly greater than the bulk or ion treatments, suggesting a higher initial NP accumulation followed by significantly greater elimination during depuration. In the lizard, Cu content in the intestine, body and head did not differ as a function of weathering. This study demonstrates that CuO NPs may undergo transformation processes in soil upon weathering that subsequently impact NPs availability in terrestrial food chains.

Engineered nanomaterials (ENMs) are released into the environment with unknown implications in the food chain. Recent findings demonstrate that ENMs may accumulate and/or increase concentrations of the component metal or carbon nanomaterials in the fruits/grains of agricultural crops, have detrimental or beneficial effects on the agronomic traits, yield, and productivity of plants, induce modifications in the nutritional value of food crops, and transfer within trophic levels. Given this information, important questions needed to be resolved include a determination of actual or predicted concentrations of ENMs through the development of new and perhaps hybridized analytical tools, assessment of the nutritional content modifications and/or accumulation of ENMs, component metal, and cocontaminants in edible plants and their implications on human diet, nutrition, and health, assessment of the consequences of ENM-induced changes in soil health, physiological process, and yield on agricultural production and food security, and transfer of ENMs in trophic levels. Given the significant implications of ENMs exposure and the rather large knowledge gaps that exist, it will be prudent to observe judicious and targeted use of ENMs so as to minimize environmental release until a comprehensive environmental fate and effects assessment can be undertaken.

The use of engineered nanomaterials has increased dramatically in recent years, but an understanding of nanomaterial fate and effects in the environment is lacking. In particular, the interaction of nanomaterials with coexisting organic contaminants and the subsequent implications for sensitive biota is almost completely unknown. Here, the effect of C60 fullerenes on the accumulation of weathered dichlorodiphenyldichloroethylene (p,p'-DDE; DDT metabolite) by Cucurbita pepo (pumpkin) and Eisenia fetida (earthworm) was determined under single and multispecies conditions. The plants, in the presence or absence of earthworms, were grown in soil containing weathered DDE (200 ng/g) and 0 or 1,670 mg/kg C60 fullerenes. Plants and earthworms were added either simultaneously or sequentially (earthworms after plants). Neither DDE nor C60 had an impact on survival or biomass of plants and earthworms, although fullerenes significantly decreased (29.6-39.0%) the relative root mass. Under single or multispecies conditions, C60 had little impact on DDE bioaccumulation by either species. The DDE concentrations in non-fullerene-exposed shoots, roots, and earthworms were 181, 7,400, and 8,230 ng/g, respectively. On fullerene exposure, the DDE content was nonsignificantly lower at 163, 7280, and 7540 ng/g, respectively. In the presence of the earthworms, C60 significantly decreased the shoot DDE content (28.6%), but no impact on root concentrations was observed. Root DDE content was unaffected by the presence of fullerenes and decreased by 21.6 to 37.5% during coexposure with earthworms. Earthworm DDE content was decreased by plant presence. Earthworms added to soils after plant harvest accumulated more DDE but were unaffected by the C60 exposure. Additional work is necessary, but these findings suggest that fullerenes may have minimal impact on the bioaccumulation of weathered cocontaminants in soil., (Copyright © 2013 SETAC.)

The effect of multiwalled carbon nanotubes (MWCNT) or C60 fullerenes on the uptake of weathered chlordane or DDx (DDT + metabolites) by Cucurbita pepo (zucchini), Zea mays (corn), Solanum lycopersicum (tomato), and Glycine max (soybean) was investigated. The plants were grown in 50 g of soil with weathered chlordane (2150 ng/g) and DDx (118 ng/g) that was amended with 0, 500, 1000, or 5000 mg/kg MWCNT or C60. After 28 d, the root and shoot content of chlordane components and DDx was determined by GC-MS. Zucchini and tomato growth were unaffected by carbon nanomaterial coexposure, although C60 at 500 mg/kg reduced corn and soybean biomass by 36.5-45.0%. Total chlordane content ranged from 1490 (tomato) to 4780 (zucchini) ng; DDx amounts ranged from 77.8 (corn) to 395 ng (zucchini). MWCNT coexposure decreased chlordane and DDx accumulation 21-80% across all crops, depending on species and nanotube concentration. Conversely, C60 had species- and contaminant-specific effects on pesticide uptake, ranging from complete suppression of DDx uptake (corn/tomato) to 34.9% increases in chlordane accumulation (tomato/soybean). The data show that pesticide accumulation varies greatly with crop species and carbon nanomaterial type/concentration. These findings have implications for food safety and for the use of engineered nanomaterials in agriculture.

Cucurbita pepo spp pepo (zucchini) is known as an exceptional weathered dichlorodiphenyldichloroethylene (DDE) accumulator, whereas Cucurbita pepo ssp ovifera (squash) is termed a nonaccumulator. Experiments were conducted with hybridized zucchini and squash to assess the inheritance pattern of DDX (the sum of p,p'-dichlorodiphenyltrichloroethane [p,p'-DDT], p,p'-dichlorodiphenyldichloroethane [p,p'-DDD], and p,p'-dichlorodiphenyldichloroethylene [p,p'-DDE]) accumulation potential in xylem sap and tissues of parental, F1 hybrids, and F1 backcross (BC) generations of plants. Plants were grown in pots containing soil with weathered DDX at 732 to 1,130 ng/g soil or under field conditions in soil with 322 to 2,700 ng/g. The DDX stem bioconcentration factors and xylem sap values showed differences between parental and hybridized plants of squash and zucchini. For squash grown in greenhouse conditions, the DDX flow rate in the xylem sap was 17.3, 121, and 40.8 ng/h in parental, F1 hybrids, and F1 BC plants, respectively. Similarly, the stem DDX content of parental, F1, and F1 BC squash was 11, 253, and 96 ng/g (dry wt), respectively. A similar inheritance pattern for squash was observed when the plants were grown under field conditions. The DDX flow rates in the xylem sap of pot-grown parental, F1, and F1 BC zucchini cultivars were 100, 8.5, and 26 ng/hr, respectively, and the stem DDX content was 191, 102, and 142 ng/g, respectively. Again, similar trends in accumulation potential were observed for hybridized zucchini grown under field conditions. The DDX concentrations in parental plants matched the expected pattern, with hybrids midway between the two species, and the backcross being more like the parent again for both species. This inheritance pattern of contaminant accumulation and translocation ability follows classical Mendelian segregation and suggests single-gene or single-locus control., (Copyright © 2012 SETAC.)

Cucurbita pepo ssp pepo (zucchini) roots phytoextract significant amounts of persistent organic pollutants (POPs) from soil, followed by effective translocation to aboveground tissues. The closely related C. pepo ssp ovifera (squash) does not have this ability. In a DDE-contaminated field soil, zucchini roots and stems contained 3.6 and 6.6-fold greater contaminant than did squash tissues, respectively, and zucchini phytoextracted 12-times more DDE from soil than squash. In batch hydroponics, squash was significantly more sensitive to DDE (2-20 mg/L) exposure; 4 mg/L DDE significantly reduced squash biomass (14%) whereas for zucchini, biomass reductions were observed at 20 mg/L (20%). PCR select Suppression Subtraction Hybridization was used to identify differentially expressed genes in DDE treated zucchini relative to DDE treated squash or non-treated zucchini. After differential screening to eliminate false positives, unique cDNA clones were sequenced. Out of 40 shoot cDNA sequences, 34 cDNAs have homology to parts of phloem filament protein 1 (PP1). Out of 6 cDNAs from the root tissue, two cDNAs are similar to cytochrome P450 like proteins, and one cDNA matches a putative senescence associated protein. From the DDE exposed zucchini seedlings cDNA library, out of 22 differentially expressed genes, 14 cDNAs were found to have homology with genes involved in abiotic stresses, signaling, lipid metabolism, and photosynthesis. A large number of cDNA sequences were found to encode novel unknown proteins that may be involved in uncharacterized pathways of DDE metabolism in plants. A semiquantitative RT-PCR analysis of isolated genes confirmed up-regulation in response to DDE exposure.

Cucurbita pepo ssp pepo (zucchini) has been shown to uniquely phytoextract percent level amounts of dichlorodiphenyldichloroethylene (DDE) and other organic contaminants from soil. Since C. pepo ssp ovifera (squash) does not have this ability, a three-year field trial was conducted to follow the inheritance pattern of DDE accumulation for cross pollinated C. pepo cultivars. Parental zucchini and squash cultivars (3 each) had stem-to-soil bioconcentration factors (BCF, contaminant ratio of stem to soil) of 16 and 1.7, respectively, and phytoextracted 1.8 and 0.18% of the DDE from soil. The 18 possible first filial (F1) hybrids of zucchini and squash accumulated significantly different DDE levels than the respective parents. The zucchini F1 hybrid (zucchini pollinated with squash) stem BCFs and percent phytoextraction values were 10 and 0.96, respectively, or 36% and 47% less than the parental zucchini. The squash F1 hybrid (squash pollinated with zucchini) stem BCFs and percent phytoextraction values were 8.3 and 0.68, respectively, or 490% and 370% greater than the parental squash. When backcrossed (BC) with the original parent, the nine zucchini F1 BC cultivars did not regain the capability to take up DDE; stem BCFs and percent phytoextraction values were equivalent to those of the F1 generation. However, the nine squash F1 BC cultivars lost much of the DDE uptake capability of the F1 generation; stem BCFs and percent phytoextraction values were intermediate but closer to those of the parental squash. The inheritance patterns suggest single locus control for persistent organic pollutant (POP) uptake ability in C. pepo ssp pepo.

Field studies show shoots of zucchini (Cucurbita pepo L.) accumulate various hydrophobic contaminants from soil, although many other plants do not, including cucumber (Cucumis sativus L.). To investigate the mechanism for this uptake, we presented p,p'-dichlorodiphenyldichloroethylene (DDE) to these two species in hydroponics solution. A mixture of DDE bound to Tenax beads stirred with a solution of water passing through a reservoir provided a flowing solution containing DDE at approximately 2 microg/L for many weeks duration. Approximately 90% of the DDE supplied in solution was adsorbed on the roots of both cucumber and zucchini. Less than 10% of the sorbed DDE was released subsequently when clean solution flowed past these contaminated roots for 9 d. The shoots of both species accumulated DDE, but the fraction that moved from the roots to the shoot in zucchini, ranging from 6 to 27% in various trials, was 10-fold greater than that in cucumber, 0.7 to 2%. The gradient in DDE concentration in zucchini tissues was in the order root more more than stem > petiole > leaf blade, indicating the movement was through the xylem in the transpiration stream. Some DDE in leaf blades might have been absorbed from the air, because the concentration in this tissue varied less with time, position in trough, or species, than did DDE in stems and petioles. The remarkable ability of zucchini to translocate DDE could not be attributed to differences in tissue composition, growth rate, distribution of weight among plant parts, or in the leaf area and rate of transpiration of water from leaves. Some other factor enables efficient translocation of hydrophobic organic contaminants in the xylem of zucchini.

Two plant species, Cucurbita pepo and Cucurbita maxima, and two earthworm species, Eisenia fetida and Lumbricus terrestris, were exposed to soil and compost with equivalent p,p'-DDE contamination. Pollutant bioconcentration was equal in plant roots in both media, but translocation was higher in C. pepo. Bioaccumulation by E. fetida was approximately 6- and 3-fold higher than that by L. terrestris in the soil and compost, respectively. For all species, p,p'-DDE uptake was significantly greater from soil than from compost; 7- to 8-fold higher for plant roots and 3- to 7-fold higher for worms. Abiotic desorption from soil was approximately twice that from the compost. When all the data are normalized for organic-carbon content of the media, the contaminant is more tightly bound by soil than compost. Although the risk associated with p,p'-DDE is higher in soil than compost, important mechanistic differences exist in contaminant binding to organic carbon in the two media.

Experiments were conducted to assess the bioavailability of polyclycic aromatic hydrocarbons (PAHs) in soil from a Manufactured Gas Plant site. Three plant species were cultivated for four consecutive growing cycles (28 days each) in soil contaminated with 36.3 microg/g total PAH. During the first growth period, Cucurbita pepo ssp. pepo (zucchini) tissues contained significantly greater quantities of PAHs than did Cucumis sativus (cucumber) and Cucurbita pepo ssp. ovifera (squash). During the first growth cycle, zucchini plants accumulated up to 5.47 times more total PAH than did the other plants, including up to three orders of magnitude greater levels of the six ring PAHs. Over growth cycles 2-4, PAH accumulation by zucchini decreased by 85%, whereas the uptake of the contaminants by cucumber and squash remained relatively constant. Over all four growth cycles, the removal of PAHs by zucchini was still twice that of the other species. Two earthworm species accumulated significantly different amounts of PAH from the soil; Eisenia foetida and Lumbricus terrestris contained 0.204 and 0.084 microg/g total PAH, respectively, but neither species accumulated measurable quantities 5 or 6 ring PAHs. Lastly, in abiotic desorption experiments with an aqueous phase of synthetically prepared organic acid solutions, the release of 3 and 4 ring PAHs from soil was unaffected by the treatments but the desorption of 5-6 ring constituents was increased by up to two orders of magnitude. The data show that not only is the accumulation of weathered PAHs species-specific but also that the bioavailability of individual PAH constituents is highly variable.

Field experiments were conducted to optimize the phytoextraction of weathered p,p'-DDE (p,p'-dichlorodiphenyldichloroethylene) by Cucurbita subspecies. The effects of two soil amendments, mycorrhizae or a biosurfactant, on p,p'-DDE accumulation was determined. Also, p,p'-DDE uptake was assessed during plant growth (12, 26, 38, and 62 d), and cultivars that accumulate weathered p,p'-DDE were intercropped with cultivars known not to have that ability. Cucurbita pepo L. ssp. pepo accumulated large amounts of the contaminant, having stem bioconcentration factors, amounts of p,p'-DDE translocated, and contaminant phytoextraction that were 14, 9.9, and 5.0 times greater than C. pepo L. ssp. ovifera (L.) D.S. Decker, respectively. During 62 d, the stem BCF (bioconcentration factor) for p,p'-DDE in subspecies pepo remained constant and the total amount of contaminant accumulated was correlated with plant biomass (r(2) = 0.86). For subspecies ovifera, the stem BCF was highest at 12 d (1.5) but decreased to 0.39 by 62 d, and p,p'-DDE removal was not correlated with plant biomass. Mycorrhizal inoculation increased p,p'-DDE accumulation by both subspecies by an average 4.4 times. For subspecies pepo, mycorrhizae increased the percentage of contaminant extracted from 0.72 to 2.1%. Biosurfactant amendment also enhanced contaminant accumulation by both subspecies, although treatment reduced subspecies ovifera biomass by 60%. The biosurfactant had no effect on the biomass of subspecies pepo, increased the average contaminant concentration by 3.6-fold, and doubled the overall amount of p,p'-DDE removed from the soil. Soil amendments that enhance the mobility of weathered persistent organic pollutants will significantly increase the amount of contaminant phytoextraction by Cucurbita pepo.

Three Cucurbitaceae, Cucurbita pepo L. subsp. pepo (cv. Black Beauty, true zucchini), Cucurbita pepo L. intersubspecific cross (cv. Zephyr, summer squash), and Cucumis sativis (cv. Marketmore, cucumber), were grown in rhizotrons containing soil contaminated with three classes of highly weathered, hydrophobic organic contaminants: (1) technical chlordane, (2) dichlorodiphenylethanes (DDT and DDD) and -ethene (DDE), (3) polyaromatic hydrocarbons (PAHs), and heavy metal residues. Movement of the contaminants through the soil/plant system was studied by comparing contaminant concentration in the bulk soil, the rhizosphere soil pore water, the xylem sap, and aerial tissue. This permitted, for the first time, calculation of bioconcentration factors (BCFs) based on concentration in the xylem sap versus that in the rhizosphere soil pore water. The bioconcentration factors so determined for the sum of five chlordane residues (two enantiomers of trans-chlordane, TC; two enantiomers of cis-chlordane, CC; and achiral trans-nonachlor, TN) were 36, 40, and 23 for Black Beauty, Zephyr, and Marketmore, respectively. In addition, the xylem sap of each cultivar had a consistent enantioselective profile for some of the chiral chlordane components. For the sum of dichlorodiphenylethanes and -ethene, comparable BCF values were 19, 4, and 0.8, respectively. In the case of PAHs, different BCF patterns among the cultivars were noted for three- versus four-ring compounds. Similarly, movement of heavy metals was cultivar-dependent, with cadmium BCF values 9.5, 3.5, and 0.6for Black Beauty, Zephyr, and Marketmore, respectively; the analogous BCFs for zinc were 9, 11, and 2. Thus, passage from ex planta to in planta regions of the soil/plant system is dependent not only on properties of the plant, but also on those of the pollutant. Such data will provide insight into transport mechanisms of highly hydrophobic organic contaminants, as well as heavy metal contaminants, in the soil/plant system.

A series of small and large pot trials were conducted to assess the phytoextraction potential of several plant species for weathered polychlorinated biphenyls (PCBs) in soil (105 microg/g Arochlor 1268). In addition, the effect of citric acid on PCB bioavailability to both plants and earthworms was assessed. Under small pot conditions (one plant, 400 g soil), three cucurbits (Cucurbita pepo ssp pepo [zucchini] and ssp ovifera [nonzucchini summer squash], Cucumis sativus, cucumber) accumulated up to 270 microg PCB/g in the roots and 14 microg/g in the stems, resulting in 0.10% contaminant removal from soil. Periodic 1 mM subsurface amendments of citric acid increased the stem and leaf PCB concentration by 330 and 600%, respectively, and resulted in up to a 65% increase in the total amount of contaminant removed from soil. Although citric acid at 10 mM more than doubled the amount of PCB desorbed in abiotic batch slurries, contaminant accumulation by two earthworm species (Eisenia foetida and Lumbricus terrestris) was unaffected by citric acid at 1 and 10 mM and ranged from 11-15 microg/g. Two large pot trials were conducted in which cucurbits (C. pepo ssp pepo and ssp ovifera, C. sativus) and white lupin (Lupinus albus) were grown in 70 kg of PCB-contaminated soil White lupin was the poorest accumulator of PCBs, with approximately 20 microg/g in the roots and 1 microg/g in the stems. Both C. pepo ssp ovifera (summer squash) and C. sativus (cucumber) accumulated approximately 65-100 microg/g in the roots and 6-10 microg/g in the stems. C. pepo ssp pepo (zucchini) accumulated significantly greater levels of PCB than all other species, with 430 microg/g in the roots and 22 microg/g in the stems. The mechanism by which C. pepo spp pepo extracts and translocates weathered PCBs is unknown, but confirms earlier findings on the phytoextraction of other weathered persistent organic pollutants such as chlordane, p,p'-DDE, and polycyclic aromatic hydrocarbons.

Laboratory experiments were conducted to study the effects of soil moisture content, planting density, plant age, and the growth of multiple generations on the bioconcentration of weathered p,p'-DDE by the plant Cucurbita pepo. As soil moisture content increased from 7.4% to 29.9% (by weight), rates of contaminant accumulation by plant roots were increased by more than a factor of 2. Higher planting density also led to higher uptake, as the root bioconcentration factor (BCF, dry-weight ratio of contaminant concentration in the tissue to that in the soil) increased by 15-fold as the number of plants per pot was raised from 1 to 3. Concentrations of the compound in plant roots were inversely related to plant age, with root BCF declining by approximately a factor of 3 as plants aged from 14 to 28 d. Finally, no change in the bioavailability of the compound was observed in successive generations of plants grown in the same contaminated soil. The results suggest that phytoremediation is influenced by a number of factors and that the cleanup of contaminated soil can be enhanced by an understanding of environmental and other conditions affecting plant growth and bioconcentration.

The impact of interactions between the earthworms Eisenia foetida and Lumbricus terrestris and the plants Cucurbita pepo and Cucurbita maxima on the uptake of weathered p,p'-DDE from soil was determined. Although some combinations of earthworm and plant species caused significant changes in the p,p'-DDE burden in both organisms, the effects were species specific. Contaminant bioconcentration in C. pepo was increased slightly by E. foetida and by 3-fold when the plant was grown with L. terrestris. E. foetida had no effect on the contaminant BCF by C. maxima, but L. terrestris caused a 2-fold reduction in p,p'-DDE uptake by the plant. Contaminant levels in E. foetida and L. terrestris were unaffected by C. pepo. When grown with C. maxima, the concentration of p,p'-DDE decreased by approximately 4-fold and 7-fold in E. foetida and L. terrestris, respectively. The data suggest that the prediction of contaminant bioavailability should consider interactions among species.

Laboratory experiments were conducted to study the effects of species differences, soil concentration, and contaminant-residence time in soil on the bioaccumulation factor (BAF; dry-weight ratio of contaminant concentration in the tissue to that in the soil) of 2,2-bis (p-chlorophenyl)- 1,1-dichloroethylene (p,p'-DDE) for three species of earthworms. In four field-weathered soils, the BAF for Eisenia foetida, an epigeic species (surface habitat), was approximately 10-fold higher than those for Lumbricus terrestris, an anecic species (deep habitat) and Aporrectodea caliginosa, an endogeic species (habitat within the soil profile). Preliminary analysis indicates that BAF may decline with increasing pollutant concentration in soil. With regard to contaminant-residence time, the BAF for E. foetida was lower in weathered soils relative to that in freshly amended soils, but age of p,p'-DDE did not significantly alter the BAF for A. caliginosa. These data suggest total chemical concentration alone is not a reliable indicator of the toxicological significance of a contaminated soil and that species-specific differences and environmental factors significantly impact overall exposure and risk.

It has been observed that plants are susceptible to uptake from soil and in planta transport of technical chlordane, in spite of its hydrophobicity and sequestration within the soil matrix due to weathering. Field and rhizotron studies were conducted with Cucurbitaceae planted in highly weathered, chlordane-contaminated soil to investigate details of soil-to-plant contaminant uptake. In the field-work, Cucurbita pepo L. (zucchini) was grown in soil at four levels of chlordane contamination: Clean (

Bioavailability is an important consideration in risk assessment of soil contaminants and in the selection of appropriate remediation technologies for polluted sites. The present study examined the bioavailability and biodegradation potential of phenanthrene with respect to a pseudomonad in 15 different soils through separate measurements of mineralization, transformation, and desorption to a polymeric infinite sink (Tenax) after 180-d sterile pre-equilibration with phenanthrene. Fractions strongly resistant to desorption and mineralization at long times were evident in all cases. After correcting for bioconversion (moles mineralized per mole transformed) determined in aqueous particle-free soil extracts, a correlation was found between the biotransformation-resistant fraction and the Tenax desorption-resistant fraction. Indices are proposed to assess bioavailability (BAt) and biotransformation potential (BTPt) of a compound in a soil based on parallel desorption and degradation studies over a selected period t. The BAt is the ratio of moles biotransformed to moles desorbed to an infinite sink, and it reflects the biotransformation rate relative to the maximal desorption rate. Values of BA30 (30-d values) ranged from 0.64 (for dark gray silt loam) to 1.12 (Wurtsmith Air Force Base [AFB] 2B, Oscoda, MI, USA). The BTPt is the ratio between moles biotransformed and moles of contaminant remaining sorbed after maximal desorption. The BTPt provides an indication of the maximum extent of biotransformation that may be expected in a system, assuming desorption is a prerequisite for biodegradation. Values of BTP30 ranged between 0.3 (Wurtsmith AFB 1B) and 13 (Mount Pleasant silt loam, NY, USA). The combination of BAt and BTPt provides insights regarding the relationship between physical availability (desorption) and biological processes (biotransformation kinetics, toxicity, other soil factors) that occur during biodegradation and are suggested to represent the remediation potential of the chemical. The BA30 values less than 0.9 and BTP30 values less than five indicate poor potential for site remediation.

Previous studies have shown that zucchini (Cucurbita pepo) and cucumber (Cucumis sativus) under field conditions are good and poor accumulators, respectively, of persistent organic pollutants from soil. Here, each species was grown under three cultivation regimes: dense (five plants in 5 kg soil): nondense (one plant in 80 kg soil): and field conditions (two to three plants in approximately 789 kg soil). p,p'-DDE and inorganic element content in roots, stems, leaves, and fruit were determined. In addition. rhizosphere, near-root, and unvegetated soil fractions were analyzed for concentrations of 11 low-molecular-weight organic acids (LMWOA) and 14 water-extractable inorganic elements. Under field conditions, zucchini phytoextracted 1.3% of the weathered p,p'-DDE with 98% of the contaminant in the aerial tissues. Conversely, cucumber removed 0.09% of the p,p'-DDE under field conditions with 83% in the aerial tissues. Under dense cultivation, cucumber produced a fine and fibrous root system not observed in our previous experiments and phytoextracted 0.78% of the contaminant, whereas zucchini removed only 0.59% under similar conditions. However. cucumber roots translocated only 5.7% of the pollutant to the shoot system, while in zucchini 48% of the p,p'-DDE in the plant was present in the aerial tissue. For each species, the concentrations of LMWOA in soil increased with increasing impact by the root system both within a given cultivation regime (i.e., rhizosphere > near-root > unvegetated) and across cultivation regimes (i.e., dense > nondense > field conditions). Under dense cultivation, the rhizosphere concentrations of LMWOAs were significantly greater for cucumber than for zucchini; no species differences were evident in the other two cultivation regimes. To enable direct comparison across cultivation regimes, total in planta p,p'-DDE and inorganic elements were mass normalized or multiplied by the ratio of plant mass to soil mass. For cucumber, differences in total p,p'-DDE and inorganic element content among the cultivation regimes largely disappear upon mass normalization, indicating that greater uptake of both types of constituents in the dense condition is due to greater plant biomass per unit soil. Conversely, for zucchini the mass normalized content of p,p'-DDE and inorganic elements is up to two orders of magnitude greater under field conditions than under dense cultivation, indicating a unique physiological response of C. pepo in the field. The role of cultivation conditions and nutrient availability in controlling root morphology, organic acid exudation, and contaminant uptake is discussed.

Previous studies indicate that Cucurbita pepo can phytoextract highly weathered persistent organic pollutants (POPs) from soil and translocate large quantities to aerial tissues. To investigate intraspecific variability in uptake potential, a field study was conducted to quantify the phytoextraction of weathered p,p'-DDE by 21 cultivar varieties of summer squash from two distinct subspecies, C. pepo ssp texana and C. pepo ssp pepo. Significant differences exist between the two subspecies, with average root and stem to soil bioconcentration factors (BCF, dry weight ratio of contaminant concentration in the vegetation to that in the soil) of 7.22 and 5.40 for ssp pepo and of 2.37 and 0.454 for spp texana, respectively. The amounts of weathered p,p-DDE extracted from the soil by ssp pepo and ssp texana were 0.301 and 0.065%, respectively, with maximum values within each subspecies of 0.780 and 0.182%, respectively. The quantities of 14 inorganic elements were determined in both the soil and tissues (roots, stems, leaves, and fruit) of all 21 cultivar varieties. Phosphorus concentrations in the tissues of ssp pepo were 14 (fruit)-73% (stems) greater than those of ssp texana. These data support our hypothesis that the unique ability of certain cultivars of C. pepo to phytoextract highly weathered POPs from soil is the result of low molecular weight organic acid exudation as a unique phosphorus acquisition mechanism.

In order to assess fully the impact of persistent organic pollutants (POPs) on human health, pollutant exchange at the interface between terrestrial plants, in particular food crops, and other environmental compartments must be thoroughly understood. In this regard, transfers of multicomponent and chiral pollutants are particularly informative. In the present study, zucchini (Cucurbita pepo L.) was planted in containerized, uncontaminated soil under both greenhouse and field conditions and exposed to air-borne chlordane contamination at 14.0 and 0.20 ng/m(3) (average, greenhouses), and 2.2 ng/m(3) (average, field). Chiral gas chromatography interfaced to an ion trap mass spectrometer was used to determine the chiral (trans-chlordane, TC, and cis-chlordane, CC) and achiral (trans-nonachlor, TN) chlordane components in vegetation, air, and soil compartments. The chlordane components of interest were detected in all vegetation tissues examined--root, stem, leaves, and fruits. When compared with the data from a soil-to-plant uptake study, the compositional profile of the chlordane components, i.e. the component fractions of TC, CC, and TN, in plant tissues, showed significantly different patterns between the air-to-plant and soil-to-plant pathways. Changes in the enantiomer fractions of TC and CC in plant tissues relative to the source, i.e. air or soil, although observed, were not markedly different between the two routes. This report provides the first comprehensive comparison between two distinct plant uptake routes for POPs and their subsequent translocation within plant tissues.

The half-lives of some persistent organic pollutants (POPs) in environmental compartments such as soil and air can be as long as decades. In spite of the hydrophobicity of many POPs, the literature contains reports of their uptake by, and translocation through, a variety of plants. Both these observations prompt the investigation of whether a vegetation-based environmental compartment such as compost contains significant residues of POPs. Previous reports imply that residues of technical chlordane will be found in compost. Due to its physicochemical properties, technical chlordane provides insights into the fate of POPs in the environment, which are not accessible through determinations of other pollutants in this group. Accordingly, we undertook the first comprehensive examination of technical chlordane residues in a variety of composts, specifically, 13 commercial and 39 municipal compost products, to both characterize and quantify the magnitude of this point source of contamination. Using chiral gas chromatography interfaced to ion trap mass spectrometry, the concentration and the compositional and enantiomeric profiles of chlordane components were determined. Of the 13 commercial products, 9 contained detectable chlordane concentrations, ranging from 4.7 to 292 microg/kg (dry wt.), while all 39 municipal products contained chlordane residues ranging from 13.9 to 415 microg/kg (dry wt.). The residue concentrations and profiles suggest possible feedstock sources for the chlordane in the finished compost product. The data also support the conclusion that some composts contribute to anthropogenic cycling of POPs through the biosphere.

Experiments were conducted to assess the effect of seven organic acids [succinic, tartaric, malic, malonic, oxalic, citric, ethylene-diaminetetraacetic (EDTA)] over a concentration range of two orders of magnitude (0.001-0.10 M) on the abiotic desorption of weathered p,p'-DDE and the extraction of polyvalent inorganic ions from soil. At 0.05 M all organic acids significantly increased contaminant desorption by 19-80%. Organic acids also increased the aqueous concentration of eight inorganic constituents extracted from soil, with at least a six-fold increase in the release of Al, Fe, Mn, and P at 0.001 M. Zucchini seedlings grown for 28 d in soil containing weathered p,p'-DDE (300 ng/g, dry weight) were periodically amended with distilled water, citric or oxalic acids (0.01 M). Plants receiving water removed 1.7% of the p,p'-DDE from the soil. Seedlings amended with citric or oxalic acids removed 2.1 and 1.9% of the contaminant, respectively, and contained up to 66% more contaminant in the shoot system than unamended vegetation. A second crop of untreated (distilled water) zucchini in the same soil removed more contaminant than the first crop (2.5%), although the addition of organic acids did not further enhance contaminant uptake. The data indicate that the addition of low molecular weight organic acids causes the partial dissolution of the soil structure through the chelation of inorganic structural ions, potentially enhancing bioavailability and having implications for the phytoremediation of persistent organic pollutants in soil.

Sorption-desorption kinetics play a major role in transport and bioavailability of pollutants in soils. Contaminant concentration is a potentially important factor controlling kinetics. A previous paper dealt with the effect of solute concentration on fractional uptake rates of phenanthrene and pyrene from a finite aqueous source. In this study we determined the effect of initial phenanthrene sorbed concentration (q(0)) on the fractional mass desorption rates from each of six soils to a zero-concentration solution, approximated by including a polymer adsorbent (Tenax) as a third-phase sink. The soils were preequilibrated with phenanthrene for 180 d. Consistent with theory, the fractional desorption rates determined by empirical curve fitting increased with q(0) provided the isotherm was nonlinear. After 500 to 600 d of desorption at the steepest possible concentration gradient, all soils retained a highly resistant fraction, which ranged from 4 to 31% of q(0), except for one soil at a high q(0). The highly resistant fraction decreased with increasing q(0), for nonlinear isotherm cases, but increased with q(0) for linear or nearly linear isotherm cases. Application of a nonlinear diffusion model, the dual-mode diffusion model (DMDM), to the nonresistant fraction gave reasonably good fits. The DMDM attributes the increase with concentration of the apparent diffusivity to a decrease in the proportion of sorbate occupying immobile sites (holes) in soil organic matter. The concentration-dependent term in the expression for the apparent diffusivity correlated with either of two indices that reflect the linearity of the sorption isotherm. Bunker C oil present in one soil acted as a partition domain. The findings of this study are consistent with heterogeneous models of soil organic matter, and indicate that concentration effects should be taken into account whenever desorption rate is important.

We investigated competitive sorption and desorption of phenanthrene, anthracene, and pyrene added to an estuarine sediment from Guilford (CT, USA) on Long Island Sound. The reduction in the equilibrium uptake of a primary solute in the presence of one or both cosolutes was well predicted over the entire isotherm by the dual-mode model, which postulates dissolution and hole-filling domains in sediment organic matter. Isotherms obtained in binary or ternary solute systems were suppressed, and the shapes were more linear than the corresponding single-solute isotherms. In the limit of infinite dilution of the single solute, sorption in the hole-filling domain is a factor of 1.4 to 1.9 times more favorable than sorption in the dissolution domain. A competitive dual-mode radial diffusion model was applied to the batch uptake and sequential-batch desorption rate data. The model captures the uptake and release curves well. The competitive effect slightly accelerates sorption, as predicted. The competitive effect accelerates desorption, but from the existing data it was not possible to decide how much was due to favorable thermodynamic versus favorable kinetic effects. The concentration-independent diffusion rate parameter corresponding to the dissolution domain was approximately the same for sorption and desorption (0.02/h), and little or no sorption hysteresis was observed.

Field experiments were conducted to assess the bioavailability of weathered p,p'-DDE in soil to plants in the Cucurbita (squash, pumpkin) and Cucumis (cucumber, melon) genera. As expected, significant variability exists in the uptake of p,p'-DDE between plants of different genera. Root:soil concentration factors, defined as the ratio of p,p'-DDE (ng/g, dry weight) in the roots to that in the soil, approach 1.8 for cucumbers/melons and 16 for squash/pumpkin. However, significant differences were also observed among varieties of squash and pumpkin, with greater than an order of magnitude variation in the root:soil concentration factors and up to two orders of magnitude difference in the absolute amount of contaminant present within the plant. Although root systems routinely contain the highest concentration of p,p'-DDE (ng/g), this compartment comprises less than 2% of the total plant biomass. In all varieties but one, more than 86% of the extracted pollutant was in the shoot system. For two of varieties of Cucurbita pepo, concentrations of p,p'-DDE in the stems reached 1.1-2.2 mg/g and estimations of percent contaminant extraction from the soil ranged from 0.40% to 2.4%. These values approach those observed in the phytoremediation of heavy metals by "hyperaccumulating" species and indicate the potential for a plant-based remediation approach to soils contaminated with persistent organic pollutants.

The cycling of chlordane and other persistent organic pollutants through the environment must be comprehensively elucidated to assess adequately the human health risks posed from such contaminants. In this study the compositional and chiral profiles of weathered chlordane residues in the soil and vegetative compartments were investigated in order to provide details of the fate and transport of this persistent pesticide. Zucchini was planted in a greenhouse in three bays containing chlordane-contaminated soil. At harvest the vegetation and soil were extracted and analyzed for chlordane content using chiral gas chromatography/ion trap mass spectrometry. Both achiral and chiral chlordane components were quantified. The chlordane concentration in the rhizosphere (soil attached to roots) was significantly less than that in the bulk soil. However, the enantiomeric ratio of the chiral components and overall component ratios had changed little in the rhizosphere relative to the bulk soil. Significant levels of chlordane were detected in the vegetation, the amount varying in different plant tissues from a maximum in roots to a minimum in fruit. In addition to the chlordane concentration gradient in plant tissues, significant shifts in compositional profile, as indicated by the component ratios, and in chiral profile, as indicated by the enantiomeric ratio, of the contaminant were observed in the plant tissues. The data indicate that abiotic processes dominate the transport of the chlordane components through the soil to the plant. This is the first report of the effect of rapid biotic processes within the plant compartment on chlordane compositional and chiral profiles.

Experiments were conducted to determine the ability of citrate to enhance the plant uptake of weathered 2,2-bis(p-chlorophenyl)1,1-dichloroethylene (p,p'-DDE) from soil. Plots containing three rows of clover, mustard, hairy vetch, or rye grass were constructed in soils containing p,p'-DDE. On 11 occasions, the rows of each crop received water or sodium citrate (0.005 or 0.05 M). For each crop, there were significant reductions in p,p'-DDE concentration in the soil fractions (near root and rhizosphere) closely associated with the plant versus bulk soil. The roots of each crop accumulated 2 to 5 times more of the weathered contaminant (dry wt) than present in the bulk soil. Citrate (0.05 M) increased the concentration of p,p'-DDE in the roots of clover, mustard, and hairy vetch by 39% compared with vegetation that received water. In batch desorption studies, the release of weathered p,p'-DDE was significantly greater in the presence of 0.05 M citrate than in water. Citrate increased the extracted aqueous concentrations of five metal ions (Al, Fe, Ca, K, Mn) from soil by five- to 23-fold over distilled water. We hypothesize that citrate physically disrupts the soil through chelation of structural metal ions and release of bound humic material, facilitating p,p'-DDE availability and uptake by plants.