Rhizoremediation half-lives of PCBs: Role of congener composition, organic carbon forms, bioavailability, microbial activity, plant species and soil conditions, on the prediction of fate and persistence in soil

The q-RASPR approach for predicting the property and fate of persistent organic pollutants

This study presents a quantitative read-across structure-property relationship (q-RASPR) approach that integrates the chemical similarity information used in read-across with traditional quantitative structure-property relationship (QSPR) models. This novel framework is applied to predict the physicochemical properties and environmental behaviors of persistent organic pollutants, specifically polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). By utilizing a curated dataset and incorporating similarity-based descriptors, the q-RASPR approach improves the accuracy of predictions, particularly for compounds with limited experimental data. The models' performances were assessed using internal cross-validation and external testing, demonstrating significant enhancements in predictive reliability compared to conventional QSPR models. The findings highlight the potential of q-RASPR for use in regulatory risk assessments and optimizing remediation strategies by providing more precise insights into the environmental fate of these contaminants.

Machine Learning Models for Predicting Bioavailability of Traditional and Emerging Aromatic Contaminants in Plant Roots

To predict the behavior of aromatic contaminants (ACs) in complex soil-plant systems, this study developed machine learning (ML) models to estimate the root concentration factor (RCF) of both traditional (e.g., polycyclic aromatic hydrocarbons, polychlorinated biphenyls) and emerging ACs (e.g., phthalate acid esters, aryl organophosphate esters). Four ML algorithms were employed, trained on a unified RCF dataset comprising 878 data points, covering 6 features of soil-plant cultivation systems and 98 molecular descriptors of 55 chemicals, including 29 emerging ACs. The gradient-boosted regression tree (GBRT) model demonstrated strong predictive performance, with a coefficient of determination (R2) of 0.75, a mean absolute error (MAE) of 0.11, and a root mean square error (RMSE) of 0.22, as validated by five-fold cross-validation. Multiple explanatory analyses highlighted the significance of soil organic matter (SOM), plant protein and lipid content, exposure time, and molecular descriptors related to electronegativity distribution pattern (GATS8e) and double-ring structure (fr_bicyclic). An increase in SOM was found to decrease the overall RCF, while other variables showed strong correlations within specific ranges. This GBRT model provides an important tool for assessing the environmental behaviors of ACs in soil-plant systems, thereby supporting further investigations into their ecological and human exposure risks.

Unboxing PGPR-mediated management of abiotic stress and environmental cleanup: what lies inside?

Abiotic stresses including heavy metal toxicity, drought, salt and temperature extremes disrupt the plant growth and development and lowers crop output. Presence of environmental pollutants further causes plants suffering and restrict their ability to thrive. Overuse of chemical fertilizers to reduce the negative impact of these stresses is deteriorating the environment and induces various secondary stresses to plants. Therefore, an environmentally friendly strategy like utilizing plant growth-promoting rhizobacteria (PGPR) is a promising way to lessen the negative effects of stressors and to boost plant growth in stressful conditions. These are naturally occurring inhabitants of various environments, an essential component of the natural ecosystem and have remarkable abilities to promote plant growth. Furthermore, multifarious role of PGPR has recently been widely exploited to restore natural soil against a range of contaminants and to mitigate abiotic stress. For instance, PGPR may mitigate metal phytotoxicity by boosting metal translocation inside the plant and changing the metal bioavailability in the soil. PGPR have been also reported to mitigate other abiotic stress and to degrade environmental contaminants remarkably. Nevertheless, despite the substantial quantity of information that has been produced in the meantime, there has not been much advancement in either the knowledge of the processes behind the alleged positive benefits or in effective yield improvements by PGPR inoculation. This review focuses on addressing the progress accomplished in understanding various mechanisms behind the protective benefits of PGPR against a variety of abiotic stressors and in environmental cleanups and identifying the cause of the restricted applicability in real-world.

PCB169 exposure aggravated the development of non-alcoholic fatty liver in high-fat diet-induced male C57BL/6 mice

Polychlorinated biphenyls (PCBs) are lipophilic environmental toxicants. Epidemiological studies have established a link between PCBs and both metabolic syndrome and nonalcoholic fatty liver disease (NAFLD). Multiple studies have reported that exposure to both PCB156 and PCB126 among the 12 dioxin-like PCBs leads to the development of NAFLD. However, studies to elucidate whether PCB169 induces the development of NAFLD by constructing in vivo models have not been reported. Therefore, we evaluated the effects of exposure to PCB169 (5 mg/kg-bw) on hepatic lipid metabolism in C57BL/6 mice from control diet and high-fat diet cohorts. The results showed that PCB169 exposure reduced body weight and intraperitoneal fat mass in mice on the control diet, but the liver lipid levels were significantly increased, exacerbating NAFLD in mice on a high-fat diet. Through transcriptomics studies, it was found that PCB169 exposure induced significant up-regulation of Pparγ, Fasn, and Aacs genes involved in hepatic lipogenesis, as well as remarkable up-regulation of Hmgcr, Lss, and Sqle genes involved in cholesterol synthesis. Additionally, there was notable down-regulation of Pparα and Cpt1 genes involved in lipid β-oxidation, leading to abnormal lipid accumulation in the liver. In addition, we found that PCB169 exposure significantly activated the Arachidonic acid metabolism, PPAR signaling pathway, Metabolism of xenobiotics by cytochrome P450, and Retinol metabolism pathways, and so on. Our study suggests that PCB169 can modify gene expression related to lipid metabolism, augument lipid accumulation in the liver, and further contribute to the development of NAFLD, thereby revealing the detrimental effects associated with PCB exposure on animal growth and metabolism.

Response and adaptation of rhizosphere microbiome to organic pollutants with enriching pollutant-degraders and genes for bioremediation: A critical review

Phytoremediation largely involves microbial degradation of organic pollutants in rhizosphere for removing organic pollutants like polycyclic aromatic hydrocarbons, phthalates and polychlorinated biphenyls. Microbial community in rhizosphere experiences complex processes of response-adaptation-feedback up on exposure to organic pollutants. This review summarizes recent research on the response and adaptation of rhizosphere microbial community to the stress of organic pollutants, and discusses the enrichment of the pollutant-degrading microbial community and genes in the rhizosphere for promoting bioremediation. Soil pollution by organic contaminants often reduces the diversity of rhizosphere microbial community, and changes its functions. Responses vary among rhizosphere microbiomes up on different classes of organic pollutants (including co-contamination with heavy metals), plant species, root-associated niches (e.g., rhizosphere, rhizoplane and endosphere), geographical location and soil properties. Soil pollution can deplete some sensitive microbial taxa and enrich some tolerant microbial taxa in rhizosphere. Furthermore, rhizosphere enriches pollutant-degrading microbial community and functional genes including different gene clusters responsible for biodegradation of organic pollutants and their intermediates, which improve the adaptation of microbiome and enhance the remediation efficiency of the polluted soil. The knowledge gaps and future research challenges are highlighted on rhizosphere microbiome in response-adaptation-feedback processes to organic pollution and rhizoremediation. This review will hopefully update understanding on response-adaptation-feedback processes of rhizosphere microbiomes and rhizoremediation for the soil with organic pollutants.

Transfer and Degradation of PAHs in the Soil-Plant System: A Review

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic, persistent organic pollutants that threaten ecosystems and human health. Consistent monitoring is essential to minimize the entry of PAHs into plants and reduce food chain contamination. PAHs infiltrate plants through multiple pathways, causing detrimental effects and triggering diverse plant responses, ultimately increasing either toxicity or tolerance. Primary plant detoxification processes include enzymatic transformation, conjugation, and accumulation of contaminants in cell walls/vacuoles. Plants also play a crucial role in stimulating microbial PAHs degradation by producing root exudates, enhancing bioavailability, supplying nutrients, and promoting soil microbial diversity and activity. Thus, synergistic plant-microbe interactions efficiently decrease PAHs uptake by plants and, thereby, their accumulation along the food chain. This review highlights PAHs uptake pathways and their overall fate as contaminants of emerging concern (CEC). Understanding plant uptake mechanisms, responses to contaminants, and interactions with rhizosphere microbiota is vital for addressing PAH pollution in soil and ensuring food safety and quality.

Uptake and translocation of organic pollutants in Camellia sinensis (L.): a review

Camellia sinensis (L.) is a perennial evergreen woody plant with the potential for environmental pollution due to its unique growth environment and extended growth cycle. Pollution sources and pathways for tea plants encompass various factors, including atmospheric deposition, agricultural inputs of chemical fertilizers and pesticide, uptake from soil, and sewage irrigation. During the cultivation phase, Camellia sinensis (L.) can absorb organic pollutants through its roots and leaves. This review provides an overview of the uptake and translocation mechanisms involving the absorption of polycyclic aromatic hydrocarbons (PAHs), pesticides, anthraquinone (AQ), perchlorate, and other organic pollutants by tea plant roots. Additionally, we summarize how fresh tea leaves can be impacted by spraying pesticide and atmospheric sedimentation. In conclusion, this review highlights current research progress in understanding the pollution risks associated with Camellia sinensis (L.) and its products, emphasizing the need for further investigation and providing insights into potential future directions for research in this field.

Exposure to three herbicide mixtures influenced maize root-associated microbial community structure, function and the network complexity

Herbicide mixtures are a new and effective agricultural strategy for managing suppress weed resistance and have been widely used in controlling weeding growth in maize fields. However, the potential ecotoxicological impact of these mixtures on the microbial community structure and function within various root-associated niches, remains inadequately understood. Here, the effects of nicosulfuron, mesotrione and atrazine on soil enzyme activity and microbial community structure and function were investigated when applied alone and in combination. The findings indicated that herbicide mixtures exhibit a prolonged half-life compared to single herbicides. Ecological niches are the major factor influencing the structure and functions of the microbial community, with the rhizosphere exhibiting a more intensive response to herbicide stress. Herbicides significantly inhibited the activities of soil functional enzymes, including dehydrogenase, urease and sucrose in the short-term. Single herbicide did not drastically influence the alpha or beta diversity of the soil bacterial community, but herbicide mixtures significantly increased the richness of the fungal community. Meanwhile, the key functional microbial populations, such as Pseudomonas and Enterobacteriaceae, were significantly altered by herbicide stress. Both individual and combined use of the three herbicides reduced the complexity and stability of the bacterial network but increased the interspecific cooperations of fungal community in the rhizosphere. Moreover, by quantification of residual herbicide concentrations in the soil, we showed that the degradation period of the herbicide mixture was longer than that of single herbicides. Herbicide mixtures increased the contents of NO3--N and NH4+-N in the soil in the short-term. Overall, our study provided a comprehensive insight into the response of maize root-associated microbial communities to herbicide mixtures and facilitated the assessment of the ecological risks posed by herbicide mixtures to the agricultural environment from an agricultural sustainability perspective.

Environmental fate of sulfonated-PCBs: Soil partitioning properties, bioaccumulation, persistence, and mobility

Two new classes of PCB metabolites were recently discovered: sulfonated-polychlorinated biphenyls (sulfonated-PCBs) and hydroxy-sulfonated-polychlorinated biphenyls (OH-sulfonated-PCBs). These metabolites, originating from PCB degradation, seem to possess more polar characteristics than their parent compounds. However, no other information, such as their chemical identity (CAS number) or their ecotoxicity or toxicity, is available so far, although more than about one hundred different chemicals were observed in soil samples. In addition, their physico-chemical properties are still uncertain since only estimations are available. Here we show the first evidence on the fate of these new classes of contaminants in the environment, producing results from several experiments, to evaluate sulfonated-PCBs and OH-sulfonated-PCBs soil partition coefficients, degradation in soil after 18 months of rhizoremediation, uptake into plant roots and earthworms, as well as a preliminary analytical method to extract and concentrate these chemicals from water. The results give an overview of the expected environmental fate of these chemicals and open questions for further studies.

Adaptation of bacterial community in maize rhizosphere for enhancing dissipation of phthalic acid esters in agricultural soil

Rhizospheric degradation is a green and in situ strategy to accelerate dissipation of organic pollutants in soils. However, the mechanism on microbial degradation of phthalic acid esters (PAEs) in rhizosphere is still unclear. Here, the bacterial community and function genes in bulk and rhizospheric soils of maize (Zea mays L.) exposed to gradient concentrations of di-(2-ethylhexyl) phthalate (DEHP) were analyzed with 16 S rRNA, metagenomic sequencing and quantitative PCR (qPCR). Maize rhizosphere significantly increased the dissipation of DEHP by 4.02-11.5% in comparison with bulk soils. Bacterial community in rhizosphere exhibited more intensive response and shaped its beneficial structure and functions to DEHP stress than that in bulk soils. Both rhizospheric and pollution effects enriched more PAE-degrading bacteria (e.g., Bacillus and Rhizobium) and function genes in rhizosphere than in bulk soil, which played important roles in degradation of PAEs in rhizosphere. The PAE-degrading bacteria (including genera Sphingomonas, Sphingopyxis and Lysobacter) identified as keystone species participated in DEHP biodegradation. Identification of PAE intermediates and metagenomic reconstruction of PAE degradation pathways demonstrated that PAE-degrading bacteria degraded PAEs through cooperation with PAE-degrading and non-PAE-degrading bacteria. This study provides a comprehensive knowledge for the microbial mechanism on the superior dissipation of PAEs in rhizosphere.

A Generic Pharmacokinetic Model for Quantifying Mother-to-Offspring Transfer of Lipophilic Persistent Environmental Chemicals

Lipophilic persistent environmental chemicals (LPECs) can accumulate in a woman's body and transfer to her developing child across the placenta and via breast milk. To assess health risks associated with developmental exposures to LPECs, we developed a pharmacokinetic (PK) model that quantifies mother-to-offspring transfer of LPECs during pregnancy and lactation and facilitates internal dosimetry calculations for offspring. We parameterized the model for mice, rats, and humans using time-varying functions for body mass and milk consumption rates. The only required substance-specific parameter is the elimination half-life of the LPEC in the animal species of interest. We used the model to estimate whole-body concentrations in mothers and offspring following maternal exposures to hexachlorobenzene (HCB) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) and compared these with measured concentrations from animal studies. We also compared estimated concentrations for humans to those generated using a previously published human LPEC PK model. Finally, we compared human equivalent doses (HEDs) calculated using our model and an allometric scaling method. Estimated and observed whole-body concentrations of HCB and PCB 153 in offspring followed similar trends and differed by less than 60%. Simulations of human exposure yielded concentration estimates comparable to those generated using the previously published model, with concentrations in offspring differing by less than 12%. HEDs calculated using our PK model were about 2 orders of magnitude lower than those generated using allometric scaling. Our PK model can be used to calculate internal dose metrics for offspring and corresponding HEDs and thus informs assessment of developmental toxicity risks associated with LPECs.

Pollution and edaphic factors shape bacterial community structure and functionality in historically contaminated soils

Studies about biodegradation potential in soils often refer to artificially contaminated and simplified systems, overlooking the complexity associated with contaminated sites in a real context. This work aims to provide a holistic view on microbiome assembly and functional diversity in the model site SIN Brescia-Caffaro (Italy), characterized by historical and uneven contamination by organic and inorganic compounds. Here, physical and chemical analyses and microbiota characterization were applied on one-hundred-twenty-seven soil samples to unravel the environmental factors driving bacterial community assembly and biodegradation potential in three former agricultural fields. Chemical analyses showed a patchy distribution of metals, metalloids and polychlorinated biphenyls (PCB) and allowed soil categorization according to depth and area of collections. Likewise, the bacterial community structure, described by molecular fingerprinting and 16S rRNA gene analyses, was significantly different according to collection site and depth. Pollutant concentrations (i.e., hexachloro-biphenyls, arsenic and mercury), nitrogen content and parameters related to soil texture were identified as main drivers of microbiota assembly, being significantly correlated to bacterial community composition. Moreover, bacteria putatively involved in the aerobic degradation of PCBs were enriched over the total bacterial community in topsoils, where the highest activity was recorded using fluorescein hydrolysis as proxy. Metataxonomic analyses revealed the presence of bacteria having metabolic pathways related to PCB degradation and tolerance to heavy metals and metalloids in the topsoil samples collected in all areas. Overall, the provided dissection of soil microbiota structure and its degradation potential in the SIN Brescia-Caffaro can contribute to target specific areas for rhizoremediation implementation. Metagenomics studies could be implemented in the future to understand if specific degradative pathways are present in historically polluted sites characterized by the co-occurrence of multiple classes of contaminants.

A comprehensive review of recent research concerning the role of low molecular weight organic acids on the fate of organic pollutants in soil

Plants exude through the roots different compounds, including, among others, low-molecular weight organic acids (LMWOAs), with a relevant effect on multiple metabolic activities. Numerous studies have revealed their role in improving soil mineral acquisition and tolerance against inorganic pollutants. However, less information is available on how they may alter the fate of organic pollutants in soil, which may cause environmental problems, compromise soil quality and have a detrimental effect on animal and human health. This review intends to cover recent studies (from 2015 onwards) and provide up-to-date information on how LMWOAs influence environmental key processes of organic pollutants in soil, like adsorption/desorption, degradation and transport, without forgetting plant uptake, with obvious environmental and health repercussions. Critical knowledge gaps and future research needs are also discussed, because understanding these processes will help searching effective strategies for pollutant reduction and control in soil.

Environmental contamination and human exposure of polychlorinated biphenyls (PCBs) in China: A review

Polychlorinated biphenyls (PCBs), together with 11 other organic compounds, were initially listed as persistent organic pollutants (POPs) by the Stockholm Convention because of their potential threat to ecosystems and humans. In China, many monitoring studies have been undertaken to reveal the level of PCBs in environment since 2005 due to the introduced stricter environmental regulations. However, there are still significant gaps in understanding the overall spatial and temporal distributions of PCBs in China. This review systematically discusses the occurrence and distribution of PCBs in environmental matrices, organisms, and humans in China. Results showed that PCB contamination in northern and southern China was not significantly different, but the PCB levels in East China were commonly higher than those in West China, which might have been due to the widespread consumption of PCBs and intensive human activities in East China. Serious PCB contamination was found in e-waste disassembling areas (e.g., Taizhou of Zhejiang Province and Qingyuan and Guiyu of Guangdong Province). Higher PCB concentrations were also chronicled in megalopolises and industrial clusters. The unintentionally produced PCBs (UP-PCBs) formed during industrial thermal processes may play an increasingly significant role in PCB pollution in China. Low PCB levels were recorded in rural and underdeveloped districts, particularly in remote and high-altitude localities such as the Tibetan Plateau and the South China Sea. However, these data are limited. Human exposure to PCBs is closely related to the characteristics of environmental pollution. This review also discusses existing issues and future research prospects on PCBs in China. For instance, the accumulation characteristics and migration regularities of PCBs in food webs should be further studied. More investigations should be undertaken to assess the quantitative relationship between external and internal exposure to PCBs. For example, bioaccessibility and bioavailability studies should be supplemented to evaluate human health risks more accurately.

Life cycle exposure of plants considerably affects root uptake of PCBs: Role of growth strategies and dissolved/particulate organic carbon variability

Plant roots can accumulate organic chemicals, including PCBs, and this could be relevant in spreading chemicals through the food chain. To estimate such uptake, several equations are available in the literature, mostly developed in lab conditions, to obtain the root concentration factor (RCF). Here, a long-term (18 months) greenhouse experiment, using an aged, contaminated soil, was performed to reproduce root uptake in field-like conditions and to account for the ecological variability of exposure during the entire life cycle. Specific growth strategies (i.e., annual vs. perennial), root development (e.g., timing of root production and decaying), and soil parameters (e.g., dissolved organic carbon (DOC), and the particulate organic carbon (POC)) may interfere with the uptake of contaminants into the roots of plants. In this study, we investigate the effects of these factors on the RCF, obtained for 79 PCBs. New predictive equations were calculated for 5 different plants species at four different growth times (from few months to 1.5 years) and stages (growing vs maturity). The relationships highlighted a species-specific and time-dependent accumulation of PCB in plants roots, with higher RCFs in summer than in fall for some species, and the relevant influence of DOC and POC in affecting root uptake.

Phytoremediation of PCB: contaminated Algerian soils using native agronomics plants

Pot cultivation experiments were conducted to assess the phytoremediation potential of two local agronomic plants, namely Avena sativa and Vicia sativa. Several soils with long-standing contamination and different levels of Polychlorinated biphenyl (PCB) contamination were used for this study. The soil samples came from different regions of Algeria and had different physico-chemical parameters. We studied the influence of these parameters on remediation potential of the two tested plants. The removal rate of the seven PCBs (PCB 28, 52, 101, 138, 153, 156 and 180) was examined after 40 and 90 days. The results showed that the presence of the plants reduced significantly the overall PCB content, ranging initially from 1.33-127.9 mg kg¹. After 90 days, the forage plant Vicia sativa allowed us to reach an excess dissipation rate of 56.7% compared to the unplanted control for the most polluted soil. An average dissipation rate of 50% was obtained in the moderately polluted soil. The less contaminated soil had an excess dissipation rate of about 24% for both plants and a predominant dissipation of the low chlorinated PCBs.

Mercury vertical and horizontal concentrations in agricultural soils of a historically contaminated site: Role of soil properties, chemical loading, and cultivated plant species in driving its mobility

The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.

Bioremediation strategies with biochar for polychlorinated biphenyls (PCBs)-contaminated soils: A review

Polychlorinated biphenyls (PCBs) are hazardous organic contaminants threatening human health and environmental safety due to their toxicity and carcinogenicity. Biochar (BC) is an eco-friendly carbonaceous material that can extensively be utilized for the remediation of PCBs-contaminated soils. In the last decade, many studies reported that BC is beneficial for soil quality enhancement and agricultural productivity based on its physicochemical characteristics. In this review, the potential of BC application in PCBs-contaminated soils is elaborated as biological strategies (e.g., bioremediation and phytoremediation) and specific mechanisms are also comprehensively demonstrated. Further, the synergy effects of BC application on PCBs-contaminated soils are discussed, in view of eco-friendly, beneficial, and productive aspects.

New approach for reproductive toxicity assessment: chromatoid bodies as a target for methylmercury and polychlorinated biphenyls in prepubertal male rats

This study investigated the reproductive toxicity of methylmercury (MeHg) and Aroclor (Sigma-Aldrich), alone or in combination, following exposure of prepubertal male rats considering the chromatoid body (CB) as a potential target. The CB is an important molecular regulator of mammalian spermatogenesis, primarily during spermatid cytodifferentiation. Male Wistar rats were exposed to MeHg and/or Aroclor , according the following experimental design: control group, which was administered in corn oil (vehicle) only; MeHg-treated group, which was administered 0.5mg kg-1 day-1 MeHg; Aroclor-treated group, which was administered 1mg kg-1 day-1 Aroclor; Mix-LD, group which was administered a low-dose mixture of MeHg (0.05mg kg-1 day-1) and Aroclor (0.1mg kg-1 day-1); and Mix-HD group, which was administered a high-dose mixture of MeHg (0.5mg kg-1 day-1) and Aroclor (1.0mg kg-1 day-1). MeHg was diluted in distilled water and Aroclor was made up in corn oil (volume 1mL kg-1). Rats were administered the different treatments from PND23 to PND53 by gavage, . The morphophysiology of CBs was analysed, together with aspects of steroid hormones status and regulation, just after the last treatment on PND53. In addition, the long-term effects on sperm parameters were assessed in adult animals. MeHg exposure increased mouse VASA homologue (MVH) protein levels in seminiferous tubules, possibly affecting the epigenetic status of germ cells. Aroclor produced morphological changes to CB assembly, which may explain the observed morphological defects to the sperm flagellum and the consequent decrease in sperm motility. There were no clear additive or synergistic effects between MeHg and Aroclor when administered in combination. In conclusion, this study demonstrates that MeHg and Aroclor have independent deleterious effects on the developing testis, causing molecular and morphological changes in CBs. To the best of our knowledge, this is the first study to show that CBs are targets for toxic agents.

A new dataset of PCB half-lives in soil: Effect of plant species and organic carbon addition on biodegradation rates in a weathered contaminated soil

This paper presents a new dataset of Polychlorinated Biphenyls (PCBs) half-lives in soil. Data were obtained from a greenhouse experiment performed with an aged contaminated soil under semi-field conditions, collected from a National Relevance Site (SIN) located in Northern Italy (SIN Brescia-Caffaro). Ten different treatments (combination of seven plant species and different soil conditions) were considered together with the respective controls (soil without plants). PCB concentration reduction in soil was measured over a period of 18 months to evaluate the ability of plants to stimulate the biodegradation of these compounds. Tall fescue, tall fescue cultivated together with pumpkin and tall fescue amended with compost reduced more than the 50% of the 79 measured PCB congeners, including the most chlorinated ones (octa to deca-PCBs). However, the data obtained showed that no plant species was uniquely responsible for the effective degradation of all isomeric classes and congeners. The obtained half-lives ranged from 1.3 to 5.6 years and were up to a factor of 8 lower compared to generic HL values reported in literature. This highlighted the importance of cultivation and plant-microbe interactions in speeding up the PCB biodegradation. This new dataset could contribute to substantially improve the predictions of soil remediation time, multimedia fate and the long-range transport of PCBs. Additionally, the half-lives obtained here can also be used in the evaluation of the food chain transfer of these chemicals, and finally the exposure and potential for effects on ecosystems.

PCB vertical and horizontal movement in agricultural soils of a highly contaminated site: Role of soil properties, cultivation history and PCB physico-chemical parameters

The agricultural areas of a historically contaminated National Relevance Site (SIN Brescia Caffaro) in Italy are an ideal case for studying the long term vertical and horizontal movement of polychlorinated biphenyls (PCBs) in soil. Here, a former large producer of PCBs (Caffaro S.p.A.) discharged its wastewaters, contaminated by PCBs and other chemicals, to a ditch used for about 80 years as source of irrigation waters for the adjacent agricultural areas. This caused a spread of contamination along both a vertical and a horizontal soil gradient. PCB concentrations of about 80 congeners, including PCB 209, peculiar of Caffaro production, were measured in three areas, selected for their different soil properties and cultivation history. The contamination levels with depth ranged from about 30 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at the depth of 1 m. The concentrations varied also horizontally, since each field was surface irrigated from the short edge of each field, showing that PCBs could spread with length halving the initial concentrations in the topsoil only after about 30-35 m. The concentration gradients detected were explained considering the historic soil use and its change with time, the pedological properties as well as PCB physico-chemical parameters and halflives, developing equations which could be employed as guidance tools for evaluating PCBs (and similar chemicals) movement and direct further studies.

Unlocking the potential of plant growth-promoting rhizobacteria on soil health and the sustainability of agricultural systems

The concept of soil health refers to specific soil properties and the ability to support and sustain crop growth and productivity, while maintaining long-term environmental quality. The key components of healthy soil are high populations of organisms that promote plant growth, such as the plant growth promoting rhizobacteria (PGPR). PGPR plays multiple beneficial and ecological roles in the rhizosphere soil. Among the roles of PGPR in agroecosystems are the nutrient cycling and uptake, inhibition of potential phytopathogens growth, stimulation of plant innate immunity, and direct enhancement of plant growth by producing phytohormones or other metabolites. Other important roles of PGPR are their environmental cleanup capacities (soil bioremediation). In this work, we review recent literature concerning the diverse mechanisms of PGPR in maintaining healthy conditions of agricultural soils, thus reducing (or eliminating) the toxic agrochemicals dependence. In conclusion, this review provides comprehensive knowledge on the current PGPR basic mechanisms and applications as biocontrol agents, plant growth stimulators and soil rhizoremediators, with the final goal of having more agroecological practices for sustainable agriculture.

Role of photo- and biodegradation of two PAHs on leaves: Modelling the impact on air quality ecosystem services provided by urban trees

Urban trees provide important ecosystem services, including air quality improvement. Polycyclic aromatic hydrocarbons (PAHs) are among the most important pollutants in air, due to their elevated concentrations and toxicity. Plants can act as filters of PAHs and as "chemical reactors" for pollutant removal, therefore reducing air concentrations. Here, the first assessment of photo- vs. biodegradation of PAHs on leaves of urban trees is presented. A dynamic air-vegetation-soil model (SoilPlusVeg) was improved to simulate the fate of two representative PAHs with contrasting physico-chemical properties (phenanthrene and benzo[a]pyrene). Simulations were performed for two different environmental scenarios from Italy (Como and Naples), selected for their dissimilar meteorological parameters, plant species and emission levels. The effect of photo- and biodegradation on leaf concentrations and fluxes towards air and soil was investigated comparing deciduous (maple, cornel and hazelnut) and evergreen (holm oak) broadleaf woods. The results showed that biodegradation in the phyllosphere could not be neglected when evaluating the ecosystem services provided by urban trees, as this process contributed significantly to the reductions (up to 25% on average) in PAH leaf concentrations and fluxes to air and soil; however, the reductions revealed ample variations with time (up to more than two orders of magnitude) showing the dependence on meteorological parameters, air compartment structure, as well as type of woods. These findings permitted to improve the ecological realism of the simulations and obtain more accurate results when predicting organic contaminant uptake and release by plant leaves, including potential for food chain transfer and long-range transport.

Utilization of PCB-contaminated Hudson River sediment by thermal processing and phytoremediation

The need to dispose of dredged sediments and development of appropriate technology for their safe utilization has become a growing problem in recent years. It has been proposed that dredged, fresh sediments can be utilized in agriculture or environment; however there is also growing interest in the use of thermally-treated sediments. Hence, the aim of this study was threefold: 1) to evaluate the effect of two incineration temperatures (300 °C and 600 °C) on the chemical and ecotoxicological properties of sediment; 2) select the appropriate treatment for further phytoremediation experiments with zucchini; and 3) assess the impact of sediment admixture on the physico-chemical parameters of soil, based on the responses of Aliivibrio fischeri and growth of zucchini (Cucurbita pepo L. cv 'Black Beauty'). A range of chemical (inductively-coupled plasma optical emission spectrophotometry for macro- and trace elements; gas chromatography for polychlorinated biphenyls (PCBs)), ecotoxicological (Microtox assay), and plant morphology (biomass measurement) as well as physiological analyses (spectrophotometry for chlorophyll) were applied. River sediments incinerated at 600 °C resulted in better chemical and ecotoxicological properties than incinerated at 300 °C or no incinerated. Incineration at 600 °C removed PCBs from sediment. In culture experiments conducted with zucchini, sediment treated at 300 °C demonstrated a 51-81% reduction in PCB concentrations compared to untreated sediment. After four weeks of growth, the raw sediment showed a significant increase in K, Fe, Cr, Pb, Zn concentrations, whereas the thermally-processed sediment showed a decrease in Ca, Na, P, Cd, Cu, Ni, and Zn concentrations. Both the fresh and thermally-treated sediment types influenced plant growth positively: they demonstrated higher biomass production than plants grown in control soil; however, plants grown on soil with thermally-processed sediment demonstrated lower biomass than those grown in raw sediment. Chlorophyll content was affected negatively by admixtures of soil with treated or untreated sediment, while a lower chlorophyll a/b ratio was observed in plants grown on an admixture of thermally-treated sediment with soil. Our findings suggest that the use of sediments as a growth medium component may be a promising way for their utilization and transformation from waste material to a valuable resource enhancing the benefits to the environment.

New Data Set of Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Half-Lives: Natural Attenuation and Rhizoremediation Using Several Common Plant Species in a Weathered Contaminated Soil

In this paper, a new data set of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) half-lives (HLs) in soil is presented. Data are derived from a greenhouse experiment performed with an aged contaminated soil under semi-field conditions, obtained from a National Relevance Site (SIN) located in Northern Italy (SIN Brescia-Caffaro). Ten different treatments (combination of seven plant species with different soil conditions) were considered together with the respective controls (soil without plants). The ability of the plants to stimulate the biodegradation of these compounds was evaluated by measuring the PCDD/F concentration reduction in soil over a period of 18 months. The formation of new bound residues was excluded by using roots as a passive sampler of bioaccessible concentrations. The best treatment which significantly reduced PCDD/F concentrations in soil was the one with Festuca arundinacea (about 11-24% reduction, depending on the congener). These decreases reflected in HLs ranging from 2.5 to 5.8 years. Simulations performed with a dynamic air-vegetation-soil model (SoilPlusVeg) confirmed that these HLs were substantially due to biodegradation rather than other loss processes. Because no coherent PCDD/F degradation HL data sets are currently available for soil, they could substantially improve the predictions of soil remediation time, long-range transport, and food chain transfer of these chemicals using multimedia fate models.

How synthetic biology can help bioremediation

The World Health Organization reported that "an estimated 12.6 million people died as a result of living or working in an unhealthy environment in 2012, nearly 1 in 4 of total global deaths". Air, water and soil pollution were the significant risk factors, and there is an urgent need for effective remediation strategies. But tackling this problem is not easy; there are many different types of pollutants, often widely dispersed, difficult to locate and identify, and in many cases cost-effective clean-up techniques are lacking. Biology offers enormous potential as a tool to develop microbial and plant-based solutions to remediate and restore our environment. Advances in synthetic biology are unlocking this potential enabling the design of tailor-made organisms for bioremediation. In this article, we showcase examples of xenobiotic clean-up to illustrate current achievements and discuss the limitations to advancing this promising technology to make real-world improvements in the remediation of global pollution.

Immunotoxicological effects of dioxin-like polychlorinated biphenyls extracted from Zhanjiang Bay sediments in zebrafish

Dioxin-like polychlorinated biphenyls (DLPCBs) are ubiquitous environmental contaminants spread all over the world. They can cause disorders in the reproductive, nervous, gut, and immune systems. We investigated the effects of DL-PCB extracted from Zhanjiang (Guangdong Province, China) offshore area on the immune functions of adult zebrafish. Zebrafish were exposed to different levels of DL-PCBs, i.e., control, positive control (PCB77 at 16.0 μg/L), low (LD; PCB81 + PCB118 at 0.32 μg/L), and high-dose (HD; PCB81 + PCB118 at 16.0 μg/L) groups for 28 days. Compared with the control group, positive control and HD group showed a significant decrease (P < 0.05) in the number of red blood cells (RBC) on day 7 and the same decrease was observed in the LD group (P < 0.05) on day 21. The results of white blood cell (WBC) profiles were opposite to that of RBCs. Moreover, the serum lysozyme activity was significantly lower in positive control and HD group (P < 0.05) on day 21 but no significant effect was observed in the LD group. The mucus lysozyme activity and immunoglobulin concentration in positive control and HD group decreased significantly (P < 0.05) from day 14. A similar effect was observed in the LD group but was significant (P < 0.05) only on day 28. Additionally, histopathological examination showed accumulation of hemosiderin in the spleen of experimental animals, which was significant in positive control and HD group. Further, renal tubular epithelial cells of head kidney were swollen in the positive control and HD group while the expansion of lumen and renal interstitial edema was observed in the LD group on day 21 and with significant presence on 28 days. Therefore, these findings suggest that the exposure of zebrafish to DL-PCBs at > 16.0 μg/L can impair their immune functions.

Combined Effects of Compost and Medicago Sativa in Recovery a PCB Contaminated Soil

The effectiveness of adding compost and the plant Medicago sativa in improving the quality of a soil historically contaminated by polychlorinated biphenyls (PCBs) was tested in greenhouse microcosms. Plant pots, containing soil samples from an area contaminated by PCBs, were treated with the compost and the plant, separately or together. Moreover, un-treated and un-planted microcosms were used as controls. At fixed times (1, 133 and 224 days), PCBs were analysed and the structure (cell abundance, phylogenetic characterization) and functioning (cell viability, dehydrogenase activity) of the natural microbial community were also measured. The results showed the effectiveness of the compost and plant in increasing the microbial activity, cell viability, and bacteria/fungi ratio, and in decreasing the amount of higher-chlorinated PCBs. Moreover, a higher number of α-Proteobacteria, one of the main bacterial groups involved in the degradation of PCBs, was found in the compost and plant co-presence.

Effects of soil amendment with PCB-contaminated sediment on the growth of two cucurbit species

The aim of the study was to evaluate the influence of the application of increasing proportions (0%, 10%, 25%, 50%, 75%, and 100%) of an admixture of PCB-contaminated Hudson River sediment collected from the Upper Hudson River, near Waterford, Saratoga county (New York, USA) on soil properties, phytotoxicity, and biometric and physiological responses of cucumber (Cucumis sativus L. cv 'Wisconsin SMR 58') and zucchini (Cucurbita pepo L. cv 'Black Beauty') grown as potential phyto- and rhizoremediators. The experiment was performed for 4 weeks in a growth chamber under controlled conditions. Amendment of Hudson River sediment to soil led to a gradual increase in PCB content of the substratum from 13.7 μg/kg (with 10% sediment) to 255 μg/kg (with 100% sediment). Sediment amendment showed no phytotoxic effects during the initial stages, even Lepidium sativum root growth was stimulated; however, this positive response diminished following a 4-week growth period, with the greatest inhibition observed in unplanted soil and zucchini-planted soil. The stimulatory effect remained high for cucumber treatments. The sediment admixture also increased cucurbit fresh biomass as compared to control samples, especially at lower doses of sediment admixture, even though PCB content of the soil amended with sediment increased. Cucurbits' leaf surface area, in turn, demonstrated an increase for zucchini, however only for 50% and 75% sediment admixture, while cucumber showed no changes when lower doses were applied and decrease for 75% and 100% sediment admixture. Chlorophyll a + b decreased significantly in sediment-amended soils, with greater inhibition observed for cucumber than zucchini. Our results suggest that admixture of riverine sediment from relatively less-contaminated locations may be used as soil amendments under controlled conditions; however, further detailed investigation on the fate of pollutants is required, especially in terms of the bioaccumulation and biomagnification properties of PCBs, before contaminated sediment can be applied in an open environment.

Concentrations and accumulation rates of polychlorinated biphenyls in soil along an urban-rural gradient in Shanghai

This study proposed an in situ soil experimental system to quantify concentration and accumulation rates of polychlorinated biphenyl (PCB) congeners in the soil in a rural-urban fringe and correlated them with multiple variables in the area. Variables, including road density, normalized difference vegetation index (NDVI), distance to the nearest highway and industrial area from the soil experimental sites, land-use impact index, population density, population change index (PCI), total population, and percentage of water area, were used to explain the concentration of different PCB congeners in soil during the experimental period. A proportion of 40.1%, 22.6%, 56.9%, and 34.3% accumulation rates of PCB8, PCB18, PCB28, and PCB118, respectively was explained by industrial developments, using stepwise linear regression analysis. NDVI was used to explain 33.6%, 61.5%, 49.1%, and 53.2% accumulation rates of PCB44, PCB101, PCB187, and PCB180, respectively. Filtering and transferring of airborne organic pollutants from atmosphere to soil by forests or tree stands and farmlands were all NDVI-related factors that affected the concentrations and accumulation rates of PCB congeners in soil. The traffic-related particle deposition might be the reason why the concentrations and accumulation rates of PCB congeners in soil were affected by road density. The findings can help quantitatively understand urbanization and the associated environmental effects. Graphic abstract.

Adolescent exposure to environmental level of PCBs (Aroclor 1254) induces non-alcoholic fatty liver disease in male mice

Polychlorinated biphenyls (PCBs) are persistent organic pollutants found in various environmental media, and there is growing evidence that PCBs may contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). The purposes of this study were to investigate whether environmental level of Aroclor 1254 (a commercial mixture of PCBs) exposure to adolescent male mice could induce the development of NAFLD and the mechanisms involved. Twenty-one-day-old male C57BL/6 mice were exposed to Aroclor 1254 (0.5-500 μg/kg body weight) by oral gavage once every third day for 60 days. The results showed that exposure to Aroclor 1254 increased body weight and decreased the liver-somatic index in a dose-dependent manner. Aroclor 1254 administration increased lipid accumulation in the liver and induced the mRNA expression of genes associated with lipogenesis, including acetyl-CoA carboxylase 1 (Acc1), acetyl-CoA carboxylase 2 (Acc2) and fatty acid synthase (Fasn). Moreover, Aroclor 1254 decreased peroxisome proliferator-activated receptor alpha (PPARα) signaling and lipid oxidation. In addition, we found that Aroclor 1254 administration induced oxidative stress in mouse liver and elevated the protein level of cyclooxygenase 2 (COX-2), an inflammatory molecule, possibly via the endoplasmic reticulum (ER) stress inositol-requiring enzyme 1α-X-box-binding protein-1 (IRE1α-XBP1) pathway, but not the nuclear factor-κB (NF-κB) pathway. In summary, adolescent exposure to environmental level of PCBs stimulated oxidative stress, ER stress and the inflammatory response and caused NAFLD in male mice. This work provides new insight into the idea that adolescent exposure to environmental level of PCBs might induce the development of NAFLD under the regulation of ER stress in males.

Modelling peak exposure of pesticides in terrestrial and aquatic ecosystems: importance of dissolved organic carbon and vertical particle movement in soil

In the present work, an existing vegetation/air/litter/soil model (SoilPlusVeg) was modified to improve organic chemical fate description in terrestrial/aquatic ecosystems accounting for horizontal and vertical particulate organic carbon (POC) transport in soil. The model was applied to simulate the fate of three pesticides (terbuthylazine, chlorpyrifos and etofenprox), characterized by increasing hydrophobicity (log K_OW from about 3 to 7), in the soil compartment and more specifically, their movement towards surface and groundwater through infiltration and runoff processes. The aim was to evaluate the role of dissolved organic carbon (DOC) and POC in the soil in influencing the peak exposure of pesticides in terrestrial/aquatic ecosystems. Simulation results showed that while terbuthylazine and chlorpyrifos dominated the free water phase (C_W-FREE) of soil, etofenprox was mainly present in soil porewater as POC associated chemical. This resulted in an increase of this highly hydrophobic chemical movement towards groundwater and surface water, up to a factor of 40. The present work highlighted the importance of DOC and POC as an enhancer of mobility in the water of poor or very little mobile chemicals. Further studies are necessary to evaluate the bioavailability change with time and parameterize this process in multimedia fate models.

Plant growth, root distribution and non-aqueous phase liquid phytoremediation at the pore-scale

The success of phytoremediation is dependent on the exposure of plants to contaminants, which is controlled by root distribution, physicochemical characteristics, and contaminant behavior in the soil environment. Whilst phytoremediation has been successful in remediating hydrocarbons and other organic contaminants, there is little understanding of the impact of non-aqueous phase liquids (NAPLs) on plant behavior, root architecture and the resulting impact of this on phytoremediation. Light NAPLs (LNAPLs) may be present in pore spaces in the capillary zone as a continuous or semi-continuous phase, or as unconnected ganglia which act as individual contaminant sources. Experimental work with ryegrass (Lolium perenne) grown under hydroponic conditions in idealised pore scale models is presented, exploring how plant growth, root distribution and development, and oil removal are affected through direct physical contact with a model LNAPL (mineral oil). In the presence of low levels of LNAPL, a significant decrease in root length was observed, whilst at higher LNAPL levels root lengths increased due to root diversion and spreading, with evidence of root redistribution in the case of LNAPL contamination across multiple adjacent pores. Changes to root morphology were also observed in the presence of LNAPL with plant roots coarse and crooked compared to long, fine and smooth roots in uncontaminated columns. Root and shoot biomass also appear to be impacted by the LNAPL although the effects are complex, affected by both root diversion and thickening. Substantial levels of LNAPL removal were observed, with roots close to LNAPL sources able to remove dissolved-phase contamination, and root growth through LNAPL sources suggest that direct uptake/degradation is possible.

Microcosm Experiment to Assess the Capacity of a Poplar Clone to Grow in a PCB-Contaminated Soil

Polychlorinated byphenyls (PCBs) are a class of Persistent Organic Pollutants extremely hard to remove from soil. The use of plants to promote the degradation of PCBs, thanks to synergic interactions between roots and the natural soil microorganisms in the rhizosphere, has been proved to constitute an effective and environmentally friendly remediation technique. Preliminary microcosm experiments were conducted in a greenhouse for 12 months to evaluate the capacity of the Monviso hybrid poplar clone, a model plant for phytoremediation, to grow in a low quality and PCB-contaminated soil in order to assess if this clone could be subsequently used in a field experiment. For this purpose, three different soil conditions (Microbiologically Active, Pre-sterilized and Hypoxic soils) were set up in order to assess the capacity of this clone to grow in the polluted soil in these different conditions and support the soil microbial community activity. The growth and physiology (chlorophyll content, chlorophyll fluorescence, ascorbate, phenolic compounds and flavonoid contents) of the poplar were determined. Moreover, chemical analyses were performed to assess the concentrations of PCB indicators in soil and plant roots. Finally, the microbial community was evaluated in terms of total abundance and activity under the different experimental conditions. Results showed that the poplar clone was able to grow efficiently in the contaminated soil and to promote microbial transformations of PCBs. Plants grown in the hypoxic condition promoted the formation of a higher number of higher-chlorinated PCBs and accumulated lower PCBs in their roots. However, plants in this condition showed a higher stress level than the other microcosms, producing higher amounts of phenolic, flavonoid and ascorbate contents, as a defence mechanism.

Rhizoremediation of weathered PCBs in a heavily contaminated agricultural soil: Results of a biostimulation trial in semi field conditions

This paper describes the results of a rhizoremediation greenhouse experiment planned to select the best plant species and soil management for the bioremediation of weathered polychlorinated biphenyls (PCBs). We evaluated the ability of different plant species to stimulate activity and diversity of the soil microbial community leading to the reduction of PCB concentrations in a heavily contaminated soil (at mg kg-1 dw level), of the national priority site for remediation (SIN) "Brescia-Caffaro" in Italy. Biostimulation was determined in large size (6kg) pots, to reflect semi-field conditions with a soil/root volume ratio larger than in most rhizoremediation experiments present in the literature. In total, 10 treatments were tested in triplicates comparing 7 plant species (grass and trees) and 5 soil/cultivation conditions (i.e., only one plant species, plant consociation, redox cycle, compost or ammonium thiosulfate addition) with the appropriate unplanted controls. After 18months of biostimulation the overall reduction of total PCBs varied between 14 and 20%. Microbial analysis revealed a shift in the microbial community structure over time and showed that all the planted treatments significantly enhanced microbial hydrolytic activity and the abundance of bacterial populations, including potential PCB degraders, in the soil surrounding plant roots. The plant species most effective in reducing the contaminant concentrations were Festuca arundinacea cultivated adding compost or in consociation with Cucurbita pepo ssp. pepo and Medicago sativa cultivated with Rhizobium spp. and mycorrhizal fungi; they reduced total PCB concentrations of about 20% and showed the significant depletion of a high number of PCB congeners (29, 37 and 23, respectively, out of the 79 measured). Our results suggest that these plant species are particularly efficient in increasing soil PCB bioavailability and in stimulating microbial degradation. They could be used in field rhizoremediation strategies to enhance the natural attenuation process and reduce PCB levels in historically contaminated sites.

Identification of Sulfonated and Hydroxy-Sulfonated Polychlorinated Biphenyl (PCB) Metabolites in Soil: New Classes of Intermediate Products of PCB Degradation?

In this paper we describe the identification of two classes of contaminants: sulfonated-PCBs and hydroxy-sulfonated-PCBs. This is the first published report of the detection of these chemicals in soil. They were found, along with hydroxy-PCBs, in soil samples coming from a site historically contaminated by the industrial production of PCBs and in background soils. Sulfonated-PCB levels were approximately 0.4-0.8% of the native PCB levels in soils and about twice the levels of hydroxy-sulfonated-PCBs and hydroxy-PCBs. The identification of sulfonated-PCBs was confirmed by the chemical synthesis of reference standards, obtained through the sulfonation of an industrial mixture of PCBs. We then reviewed the literature to investigate for the potential agents responsible for the sulfonation. Furthermore, we predicted their physicochemical properties and indicate that, given the low pK_a of sulfonated- and hydroxy-sulfonated-PCBs, they possess negligible volatility, supporting the case for in situ formation from PCBs. This study shows the need of understanding their origin, their role in the degradation path of PCBs, and their fate, as well as their (still unknown) toxicological and ecotoxicological properties.

Novel PCB-degrading Rhodococcus strains able to promote plant growth for assisted rhizoremediation of historically polluted soils

Extended soil contamination by polychlorinated biphenyls (PCBs) represents a global environmental issue that can hardly be addressed with the conventional remediation treatments. Rhizoremediation is a sustainable alternative, exploiting plants to stimulate in situ the degradative bacterial communities naturally occurring in historically polluted areas. This approach can be enhanced by the use of bacterial strains that combine PCB degradation potential with the ability to promote plant and root development. With this aim, we established a collection of aerobic bacteria isolated from the soil of the highly PCB-polluted site “SIN Brescia-Caffaro” (Italy) biostimulated by the plant Phalaris arundinacea. The strains, selected on biphenyl and plant secondary metabolites provided as unique carbon source, were largely dominated by Actinobacteria and a significant number showed traits of interest for remediation, harbouring genes homologous to bphA, involved in the PCB oxidation pathway, and displaying 2,3-catechol dioxygenase activity and emulsification properties. Several strains also showed the potential to alleviate plant stress through 1-aminocyclopropane-1-carboxylate deaminase activity. In particular, we identified three Rhodococcus strains able to degrade in vitro several PCB congeners and to promote lateral root emergence in the model plant Arabidopsis thaliana in vivo. In addition, these strains showed the capacity to colonize the root system and to increase the plant biomass in PCB contaminated soil, making them ideal candidates to sustain microbial-assisted PCB rhizoremediation through a bioaugmentation approach.

Identification and characterization of a meta-cleavage product hydrolase involved in biphenyl degradation from Arthrobacter sp. YC-RL1

Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants (POPs) widely existing in the environment. Arthrobacter sp. YC-RL1 is a biphenyl-degrading bacterium that shows metabolic versatility towards aromatic compounds. A 2-hydroxy-6-oxo-6-phenylhexa-2, 4-dienoate (HOPDA) hydrolase (BphD) gene involved in the biodegradation of biphenyl was cloned from strain YC-RL1 and heterologously expressed in Escherichia coli BL21 (DE3). The recombinant BphD_YC-RL1 was purified and characterized. BphD_YC-RL1 showed the highest activity at 45 °C and pH 7. It was stable under a wide range of temperature (20-50 °C). The enzyme had a K_m value of 0.14 mM, K_cat of 11.61 s^-1, and V_max of 0.027 U/mg. Temperature dependence catalysis exhibited a biphasic Arrhenius Plot with a transition at 20 °C. BphD_YC-RL1 was inactivated by SDS, Tween 20, Tween 80, Trition X-100, DTT, CHAPS, NBS, PMSF, and DEPC, but insensitive to EDTA. Site-directed mutagenesis of the active-site residues revealed that the catalytic triad residues (Ser115, His275, and Asp247) of BphD_YC-RL1 were necessary for its activity. The investigation of BphD_YC-RL1 not only provides new potential enzyme resource for the biodegradation of biphenyl but also helps deepen our understanding on the catalytic process and mechanism.

Gasification treatment of poplar biomass produced in a contaminated area restored using plant assisted bioremediation

Remediation of polluted soils using phytoremediation techniques is an effective strategy. However, the use of the biomass from these soils for energy purposes may raise efficiency and pollution emission problems and there is currently little research on this issue. In this work, the main results of a fluidized-bed gasification treatment conducted on poplar biomass pruning residues from a multi-contaminated area are presented. The samples were collected from an experimental site in which a plant-assisted bioremediation (PABR) technology has been applied since 2013 to reduce the soil heavy metal (HM) and polychlorinated biphenyl (PCB) contents. The main goal of this study was to identify the specific treatment necessary, in addition to conventional tar reforming, for trapping possible residues of HMs and PCBs in ashes during the gasification process. In our study, we demonstrate that gasification of contaminated biomass coming from PABR (where contaminant residues are concentrated mainly in the roots and are insignificant in the shoots) produces syngas whose characteristics are similar to those obtained using non-contaminated biomass. The results showed that contaminant concentrations in the prunings were negligible; the total amount of PCBs was 1.63 ng/g, while HMs ranged from 0.01 to 0.70 mg/kg, except for Cu and Zn (∼20 mg/kg). Furthermore, the presence in the biomass of Ca and traces of other metals showed a possible catalytic effect with an improvement in the tar conversion in the gasifier leading to a reduction of 5-10% in tar content. The overall results suggest that a specific treatment for pollutant capture is necessary only when the roots, the part of the plants where these contaminants are concentrated, are sampled and used for the gasification process. Although energy from biomass produced on a contaminated site is currently considered waste and involves disposal costs, this paper shows that the poplar biomass grown on a multi-contaminated soil can be used for energy purposes without any impact on the environment.

A review of the predictive models estimating association of neutral and ionizable organic chemicals with dissolved organic carbon

Dissolved organic carbon (DOC) plays a key role in environmental transport, fate and bioavailability of organic chemicals in terrestrial and aquatic ecosystems. Predicting the association of contaminants to DOC is therefore crucial in modelling chemical exposure and risk assessment. The models proposed so far to describe interaction mechanisms between chemicals and DOC and the most influential variables have been reviewed. The single-parameter linear free energy relationships (sp-LFERs) and the poly-parameter linear free energy relationships (pp-LFERs) in the form of linear solvation energy relationships (LSERs) currently available in literature for estimating dissolved organic carbon/water partition (K_DOC) and distribution (D_DOC) coefficients for organic chemicals were discussed, and limits of the existing approaches explored. For neutral chemicals many predictive equations are currently available in literature, but the quality of the input data on which they are based is often questionable, due to the lack of an unequivocal definition of DOC among different references and to the different and often unreliable K_DOC measurement method. For ionizable chemicals instead there is a substantial lack of predictive approaches that need to be fulfilled since just few models are nowadays available to predict D_DOC of ionized species. This paper reviews the current approaches for neutral and ionizable chemicals proposing guidelines to select conditions for obtaining reliable data and predictive equations for an improved estimation of K_DOC and D_DOC.

Sex-specific alterations of lipid metabolism in zebrafish exposed to polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic pollutants (POPs) mixtures exerting environmental health risk. In mammals, PCBs have been shown to disrupt metabolic state, especially lipid metabolism, and energy balance, but their effects on lipid metabolism in fish are largely unknown. The zebrafish were selected as model and both male and female adult zebrafish were exposed to different concentrations of PCBs at gradient concentrations of 0.2, 2.0 and 20.0 μg/L for 6 weeks. PCB exposure did not affect survival, but a significant inhibition of growth was observed in the males after exposure to 20.0 μg/L. The lower concentrations of 0.2 and 2.0 μg/L increased hepatic lipid accumulation to a greater extent in male fish, but the higher concentration of 20.0 μg/L did not cause significant fat accumulation in either male or female fish. In males, the expression of genes related to lipogenesis and lipid catabolism was upregulated in a concentration-dependent manner in the liver and visceral mass without liver and gonad; the effects of exposure on lipid metabolism-related genes in female fish were less pronounced. PCB exposure did not induce significant oxidative stress, but did upregulate the expression of stress- and apoptosis-related genes, mostly in male fish. The low concentrations of PCBs (0.2 μg/L and 2.0 μg/L) exerted sex-specific effects on zebrafish lipid metabolism, and male fish were more sensitive to the exposure. This study provides new mechanistic insights into the complex interactions between PCBs, lipid metabolism, and sex in zebrafish, and may contribute to a future systematic assessment of the effects of PCBs on aquatic ecosystems.

Predicting dissolved organic carbon partition and distribution coefficients of neutral and ionizable organic chemicals

Estimating K_DOC (dissolved organic carbon/water partition coefficient) and D_DOC (dissolved organic carbon/water distribution coefficient) of neutral and ionizable organic chemicals is a crucial task for assessing mobility, modelling transport, environmental fate of a variety of chemicals and for evaluating their bioavailability in terrestrial and aquatic environments. A critical literature search of reliability-selected K_DOC and D_DOC values was performed to setup novel predictive relationships for K_DOC and D_DOC of neutral and ionizable organic chemicals. This goal was pursued by using: 1) LSER (linear solvation energy relationship) models to predict K_DOC for neutral chemicals using Abraham solute parameters calculated for different DOC sources (all DOC sources together, soil porewater, surface water, wastewater and Aldrich humic acid (HA)); 2) linear regressions for predicting D_DOC of organic acids from the octanol/water partition coefficient (Log K_OW or Log P) and the dissociation constant (pKa), accounting separately for the contribution of the neutral and ionic fraction. The proposed models predicted Log K_DOC and D_DOC values within a root mean square deviation (RMSD) generally smaller than 0.3 log units.

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.

Polychlorinated biphenyls in apple snails from an abandoned e-waste recycling site, 2010-2016: A temporal snapshot after the regulatory efforts and the bioaccumulation characteristics

The rudimentary recycling of electronic waste (e-waste) has been banned in China since the late 2000s, leaving many abandoned e-waste sites. However, knowledge is limited on the concentrations and fates of the e-waste derived contaminants such as polychlorinated biphenyls (PCBs) in these abandoned sites. In this work, we assessed the temporal trend of PCB concentrations in the year 2010, 2012, and 2016 at an abandoned e-waste site in South China, using apple snail as a bioindicator. The mean ∑PCBs concentrations in apple snails sampled in 2016 (53.2 ng/g dry weight) was approximately 11-fold higher than that (4.68 ng/g dry weight) in apple snails from a reference site. The result suggested that the abandoned e-waste recycling site was still heavily polluted by PCBs, despite of the fact that crude e-waste recycling processes have been prohibited for nearly 10 years. The concentrations of ∑PCBs were significantly decreased in 2016 compared to those in 2010 (mean: 115 ng/g dry weight) and 2012 (mean: 92.3 ng/g dry weight), but there were no significant differences in the concentrations between 2010 and 2012. Regarding the congener profiles, the contributions of lower chlorinated congeners (tri- and tetra-PCBs) in the snails tended to be higher over the years. The ∑PCBs in snails were significantly correlated with those in soils. Additionally, PCB profiles in snails resembled those in soils. These results suggested that apple snails can be used as an ideal bioindicator for PCBs in the paddy soils. Field determined biota-soil accumulation factors (BSAFs) for PCBs ranged from 0.31 to 1.9, with most of the values being 1-2; indicating that theoretical BSAFs can be used to predict the bioaccumulation of PCBs in the snails with a reasonable degree of certainty.

Phytoremediation of soil contaminated with PCBs using different plants and their associated microbial communities

In this work, we evaluate the abilities of the plants Brassica juncea, Avena sativa, Brachiaria decumbens, and Medicago sativa to uptake polychlorinated biphenyls (PCBs) and induce degradation of soil microorganisms from contaminated soil. Removal of PCBs 44, 66, 118, 153, 170, and 180 was evaluated in both rhizospheric and nonrhizospheric soils. Microbial and bphA1 gene quantifications were performed by real-time PCR. The PCB concentrations in plant tissues and soil were determined, and a fluorescein diacetate (FDA) hydrolysis assay was used to measure microbial activity in soil. The removal percentages for all PCB congeners in planted soil versus unplanted control soil were statistically significant and varied between 45% and 63%. PCBs 118, 153, 138, and 170 were detected in Brachiaria decumbens roots at different concentrations. In planted soil, an increase in the concentration of bacteria was observed compared to the initial concentration and the concentration in unplanted control soil; however, no significant differences were identified between plants. The number of copies of the bphA1 gene was higher in rhizospheric versus non- rhizospheric soil for all plants at the end of the experiment. However, alfalfa and oat rhizospheric soil showed significant differences in the copy number of the bphA1 gene. In general, the concentration of fluorescein in the rhizospheric soil was greater than that in the nonrhizospheric soil. Although the plants had a positive effect on PCB removal, this effect varied depending on the type of PCB, the plant, and the soil.

How good are the predictions of mobility of aged polychlorinated biphenyls (PCBs) in soil? Insights from a soil column experiment

A column leaching experiment was performed to evaluate the influence of some relevant environmental factors (soil/water contact time, temperature, saturation) on mobility of aged polychlorinated biphenyls (PCBs) in soil together with transport mediated by dissolved organic carbon (DOC) and mobile organic carbon (OC) coated fine particles/colloids. Consecutive fractions of leachates were collected after a variable pre-equilibration time (2, 5, 7, 48 days), using leaching solutions with different DOC content (tap water vs. Aldrich humic acid), in saturated vs. field capacity conditions and at different temperatures (25 °C vs. 15 °C). The data obtained were compared to the predicted values using a multimedia model (SoilPlusVeg) to evaluate model behaviour. Contact time and temperature determined a relevant effect on DOC and particle/colloid availability, with significant variations in leachate concentrations (up to 1 order of magnitude), typically overlooked by most environmental fate models. Results obtained at different temperatures show a modulation of the DOC/particles production with temperature and therefore the role of temperature changes in the environmental scenarios (e.g. seasonal variations). Transport of PCBs enhanced by Aldrich DOC was not linearly correlated to chemical hydrophobicity but revealed a threshold to ~Log K_OW 6.5, likely because of the slow sorption kinetics of more hydrophobic chemicals. Additionally, variation of the saturation conditions (e.g. drying-wetting cycles) can determine contamination peaks at the beginning of an irrigation/rainfall event because of the soil/water equilibration. Model simulations, even when including DOC in the water phase, but not accounting for the particle/colloidal transport and sorption/desorption kinetics, mismatched the ratio of dissolved vs. DOC-associated and particle-associated PCBs and substantially underpredicted concentrations, especially for the high chlorinated congeners. The results indicated that some of the common assumptions and paradigms in fate modelling of such hydrophobic compounds should be revisited and models updated.

Early-life exposure to endocrine disrupting chemicals associates with childhood obesity

Increasing prevalence of childhood obesity poses threats to the global health burden. Because this rising prevalence cannot be fully explained by traditional risk factors such as unhealthy diet and physical inactivity, early-life exposure to endocrine disrupting chemicals (EDCs) is recognized as emerging novel risk factors for childhood obesity. EDCs can disrupt the hormone-mediated metabolic pathways, affect children's growth and mediate the development of childhood obesity. Many organic pollutants are recently classified to be EDCs. In this review, we summarized the epidemiological and laboratory evidence related to EDCs and childhood obesity, and discussed the possible mechanisms underpinning childhood obesity and early-life exposure to non-persistent organic pollutants (phthalates, bisphenol A, triclosan) and persistent organic pollutants (dichlorodiphenyltrichloroethane, polychlorinated biphenyls, polybrominated diphenyl ethers, per- and polyfluoroalkyl substances). Understanding the relationship between EDCs and childhood obesity helps to raise public awareness and formulate public health policy to protect the youth from exposure to the harmful effects of EDCs.

Comparative evaluation of influence of aging, soil properties and structural characteristics on bioaccessibility of polychlorinated biphenyls in soil

Though bioaccessibility commonly recognized as a guideline for risk assessment is closely related with pollution occurrence and chemical species of compounds, the mechanistic links are barely evaluated particularly for widespread polychlorinated biphenyls (PCBs) in soil. With the biomimetic extraction of hydroxypropyl-β-cyclodextrin (β-HPCD), the temporal and spatial influences of soil properties, aging and structural characteristics, e.g. polarity of PCB congeners on bioaccessibility were investigated for PCBs. Sensitive variation of bioaccessibility with aging, soil organic matter (SOM), particle size and soil moisture were clearly evidenced for different PCB congeners. Due to aging, the bioaccessibility decreased in the long term after stabilization for 36 h. In concert with the first-order kinetics, the decay rates of bioaccessibility were shown with congener-specificity and were well correlated with dipoles of PCBs. The increment of SOM diminished the bioaccessibility for the strengthened adsorption while the increased particle size and soil moisture elevated it possibly due to the less adsorption on soil particles and more accommodation of PCBs in soil pore water. Except the positive correlations with particle size, soil moisture and dipole moment, the greater dependency on aging and SOM was highlighted for bioaccessibility by partial least squares (PLS) analysis. The mutual relationship with influential factors was quantitatively formulated for accelerative prediction of bioaccessibility, and the comparative evaluation and detailed insights into the mechanistic links would thus help enhance the precise determination of bioaccessibility and risk assessment of PCBs in soil.

Contrasting dynamics of polychlorinated biphenyl dissipation and fungal community composition in low and high organic carbon soils with biochar amendment

Biochar amendment has been advocated as an effective method to remediate organic pollutant-contaminated soils through adsorption and stimulating microbial degradation. However, such effects can vary depending on soil properties and biochar physiochemical characteristics. The objective of this study was to compare the dynamic variations of polychlorinated biphenyls (PCBs) in low and high soil organic carbon (SOC) soils both amended with biochar and to investigate its linkage with fungal community composition. Two soils having the same texture and soil type but varying in SOC contents were contaminated with PCBs to a final concentration of 60 mg kg^-1 and amended with 2% bamboo biochar. Temporal changes of PCB remaining in soils and adsorbed on biochar particles were determined during a 2-month incubation. Diversity and composition of fungal communities in both low and high SOC soils were investigated with Illumina MiSeq sequencing. The results showed that the PCB concentrations in low SOC soil were significantly lower than those in high SOC soil during the incubation. In the low SOC soil, the biochar particle adsorbed higher amounts of PCB, tetra-, and penta-chlorobiphenyls (CBs) than those in high SOC soil, and stimulated the dissipation of di- and tri-CBs. The nonmetric multidimensional scaling profile showed significant (p < 0.05) differences in the fungal community composition between the low and high SOC soils. The relative abundances of Eurotiomycetes were gradually increased, whereas those of Sordariomycetes and Dothideomycetes were decreased with increasing incubation time in the low SOC soils. In contrast, the fungal communities in high SOC soils were relatively stable. The relative abundances of Eurotiomycetes and Sordariomycetes were positively correlated with PCB dissipation in low and high SOC content soils, respectively. Our results suggest that SOC content affects PCB dissipation and fungal community composition in biochar-amended soils, and biochars have a high remediation potential of PCB in soils with low SOC contents.