Combined effects of azoxystrobin and oxytetracycline on rhizosphere microbiota of Arabidopsis thaliana

The rhizosphere is one of the key determinants of plant health and productivity. Mixtures of pesticides are commonly used in intensified agriculture. However, the combined mechanisms underlying their impacts on soil microbiota remain unknown. The present study revealed that the rhizosphere microbiota was more sensitive to azoxystrobin and oxytetracycline, two commonly used pesticides, than was the microbiota present in bulk soil. Moreover, the rhizosphere microbiota enhanced network complexity and stability and increased carbohydrate metabolism and xenobiotic biodegradation as well as the expression of metabolic genes involved in defence against pesticide stress. Co-exposure to azoxystrobin and oxytetracycline had antagonistic effects on Arabidopsis thaliana growth and soil microbial variation by recruiting organic-degrading bacteria and regulating ABC transporters to reduce pesticide uptake. Our study explored the composition and function of soil microorganisms through amplicon sequencing and metagenomic approaches, providing comprehensive insights into the synergistic effect of plants and rhizosphere microbiota on pesticides and contributing to our understanding of the ecological risks associated with pesticide use.

A prospective ecological risk assessment of high-efficiency III-V/silicon tandem solar cells

III-V/Silicon tandem solar cells offer one of the most promising avenues for high-efficiency, high-stability photovoltaics. However, a key concern is the potential environmental release of group III-V elements, especially arsenic. To inform long-term policies on the energy transition and energy security, we develop and implement a framework that fully integrates future PV demand scenarios with dynamic stock, emission, and fate models in a probabilistic ecological risk assessment. We examine three geographical scales: local (including a floating utility-scale PV and waste treatment), regional (city-wide), and continental (Europe). Our probabilistic assessment considers a wide range of possible values for over one hundred uncertain technical, environmental, and regulatory parameters. We find that III-V/silicon PV integration in energy grids at all scales presents low-to-negligible risks to soil and freshwater organisms. Risks are further abated if recycling of III-V materials is considered at the panels' end-of-life.

Glyphosate Disorders Soil Enchytraeid Gut Microbiota and Increases Its Antibiotic Resistance Risk

Pesticides promote the stable development of intensive global agriculture. Nevertheless, their residues in the soil can cause ecological and human health risks. Glyphosate is a popular herbicide and is generally thought to be ecologically safe and nontoxic, but this conclusion has been questioned. Herein, we investigated the interaction among soil fauna (Enchytraeus crypticus) exposed to glyphosate and found that glyphosate induced oxidative stress and detoxification responses in E. crypticus and disturbed their lipid metabolism and digestive systems. We further demonstrated that glyphosate disordered the gut microbiota of E. crypticus and increased the abundance of resistance determinants with significant human health risks. Empirical tests and structural equation models were then used to confirm that glyphosate could cause E. crypticus to generate reactive oxygen species, indirectly interfering with their gut microbiota. Our study provides important implications for deciphering the mechanisms of the ecotoxicity of pesticides under the challenge of worldwide pesticide contamination.

Effect of chlorpyrifos on freshwater microbial community and metabolic capacity of zebrafish

Chlorpyrifos is a widely used organophosphorus insecticide because of its high efficiency and overall effectiveness, and it is commonly detected in aquatic ecosystems. However, at present, the impact of chlorpyrifos on the aquatic micro-ecological environment is still poorly understood. Here, we established aquatic microcosm systems treated with 0.2 and 2.0 µg/L chlorpyrifos, and employed omics biotechnology, including metagenomics and 16S rRNA gene sequencing, to investigate the effect of chlorpyrifos on the composition and functional potential of the aquatic and zebrafish intestinal microbiomes after 7 d and 14 d chlorpyrifos treatment. After 14 d chlorpyrifos treatment, the aquatic microbial community was adversely affected in terms of its composition, structure, and stability, while its diversity showed only a slight impact. Most functions, especially capacities for environmental information processing and metabolism, were destroyed by chlorpyrifos treatment for 14 d. We observed that chlorpyrifos increased the number of risky antibiotic resistance genes and aggravated the growth of human pathogens. Although no clear effects on the structure of the zebrafish intestinal microbial community were observed, chlorpyrifos treatment did alter the metabolic capacity of the zebrafish. Our study highlights the ecological risk of chlorpyrifos to the aquatic environment and provides a theoretical basis for the rational use of pesticides in agricultural production.

Understanding the ecological effects of the fungicide difenoconazole on soil and Enchytraeus crypticus gut microbiome

Increasing knowledge of the impacts of pesticides on soil ecological communities is fundamental to a comprehensive understanding of the functional changes in the global agroecosystem industry. In this study, we examined microbial community shifts in the gut of the soil-dwelling organism Enchytraeus crypticus and functional shifts in the soil microbiome (bacteria and viruses) after 21 d of exposure to difenoconazole, one of the main fungicides in intensified agriculture. Our results demonstrated reduced body weight and increased oxidative stress levels of E. crypticus under difenoconazole treatment. Meanwhile, difenoconazole not only altered the composition and structure of the gut microbial community, but also interfered with the soil-soil fauna microecology stability by impairing the abundance of beneficial bacteria. Using soil metagenomics, we revealed that bacterial genes encoding detoxification and viruses encoding carbon cycle genes exhibited a dependent enrichment in the toxicity of pesticides via metabolism. Taken together, these findings advance the understanding of the ecotoxicological impact of residual difenoconazole on the soil-soil fauna micro-ecology, and the ecological importance of virus-encoded auxiliary metabolic genes under pesticide stress.

Negative effects of abamectin on soil microbial communities in the short term

With the widespread use of abamectin in agriculture, there is increasing urgency to assess the effects of abamectin on soil microorganisms. Here, we treated plant-soil microcosms with abamectin at concentrations of 0.1 and 1.0 mg/kg and quantified the impacts of abamectin on bulk and rhizosphere soil microbial communities by shotgun metagenomics after 7 and 21 days of exposure. Although abamectin was reported to be easily degradable, it altered the composition of the soil microbial communities, disrupted microbial interactions, and decreased community complexity and stability after 7 days of exposure. After treatment with abamectin at a concentration of 1.0 mg/kg, some opportunistic human diseases, and soil-borne pathogens like Ralstonia were enriched in the soil. However, most ecological functions in soil, particularly the metabolic capacities of microorganisms, recovered within 21 days after abamectin treatment. The horizontal and vertical gene transfer under abamectin treatments increased the levels of antibiotic resistance genes dissemination. Overall, our findings demonstrated the negative effects of abamectin on soil ecosystems in the short-term and highlight a possible long-term risk to public and soil ecosystem health associated with antibiotic resistance genes dissemination.

Machine learning predicts ecological risks of nanoparticles to soil microbial communities

With the rapid development of nanotechnology in agriculture, there is increasing urgency to assess the impacts of nanoparticles (NPs) on the soil environment. This study merged raw high-throughput sequencing (HTS) data sets generated from 365 soil samples to reveal the potential ecological effects of NPs on soil microbial community by means of metadata analysis and machine learning methods. Metadata analysis showed that treatment with nanoparticles did not have a significant impact on the alpha diversity of the microbial community, but significantly altered the beta diversity. Unfortunately, the abundance of several beneficial bacteria, such as Dyella, Methylophilus, Streptomyces, which promote the growth of plants, and improve pathogenic resistance, was reduced under the addition of synthetic nanoparticles. Furthermore, metadata demonstrated that nanoparticles treatment weakened the biosynthesis ability of cofactors, carriers, and vitamins, and enhanced the degradation ability of aromatic compounds, amino acids, etc. This is unfavorable for the performance of soil functions. Besides the soil heterogeneity, machine learning uncovered that a) the exposure time of nanoparticles was the most important factor to reshape the soil microbial community, and b) long-term exposure decreased the diversity of microbial community and the abundance of beneficial bacteria. This study is the first to use a machine learning model and metadata analysis to investigate the relationship between the properties of nanoparticles and the hazards to the soil microbial community from a macro perspective. This guides the rational use of nanoparticles for which the impacts on soil microbiota are minimized.

Machine learning predicts the impact of antibiotic properties on the composition and functioning of bacterial community in aquatic habitats

In the past decades, hundreds of antibiotics have been isolated from microbial metabolites or have been artificially synthesized for protecting humans, animals and crops from microbial infections. Their everlasting usage results in impacts on the microbial community composition and causes well-known collateral damage to the functioning of microbial communities. Nevertheless, the impact of different antibiotic properties on aquatic microbial communities have so far only poorly been disentangled. Here we characterized the environmental risk of 50 main kinds of antibiotics from 9 classes at a concentration of 10 μg/L for aquatic bacterial communities via metadata analysis combined with machine learning. Metadata analysis showed that the alpha diversity of the bacterial community increased only after treatment with aminoglycoside and β-lactam antibiotics, while its structure was changed by almost all tested antibiotics. The antibiotic treatment also disturbed the functions of the bacterial community, especially with regard to metabolic pathways, including amino acids, cofactors, vitamins, xenobiotics and carbohydrate metabolism. The critical characteristics (atom stereocenter count, number of hydrogen atoms in the antibiotic, and the adipose water coefficient) of antibiotics affecting the composition of the bacterial community in aquatic habitats were screened by machine learning. The key characteristics of antibiotics affecting the function bacterial communities were the number of hydrogen atoms, molecular weight and complexity. In summary, by developing machine learning models and by performing metadata analysis, this study provides the relationship between the properties of antibiotics and their adverse impacts on aquatic microbial communities from a macro perspective. The study also provides guidance for the rational design of antibiotics.

Phyllosphere Microorganisms: Sources, Drivers, and Their Interactions with Plant Hosts

The leaves of plants are colonized by various microorganisms. In comparison to the rhizosphere, less is known about the characteristics and ecological functions of phyllosphere microorganisms. Phyllosphere microorganisms mainly originate from soil, air, and seeds. The composition of phyllosphere microorganisms is mainly affected by ecological and abiotic factors. Phyllosphere microorganisms execute multiple ecological functions by influencing leaf functions and longevity, seed mass, fruit development, and homeostasis of host growth. A plant can respond to phyllosphere microorganisms by secondary metabolite secretion and its immune system. Meanwhile, phyllosphere microorganisms play an important role in ecological stability and environmental safety assessment. However, as a result of the instability of the phyllosphere environment and the poor cultivability of phyllosphere microorganisms in the current research, there are still many limitations, such as the lack of insight into the mechanisms of plant-microorganism interactions, the roles of phyllosphere microorganisms in plant growth processes, the responses of phyllosphere microorganisms to plant metabolites, etc. This review summarizes the latest progress made in the research of the phyllosphere in recent years. This is beneficial for deepening our understanding of phyllosphere microorganisms and promoting the research of plant-atmosphere interactions, plant pathogens, and plant biological control.

Does biological rhythm transmit from plants to rhizosphere microbes?

Plant physiological and metabolic processes are modulated by rhythmic gene expression in a large part. Meanwhile, plants are also regulated by rhizosphere microorganisms, which are fed by root exudates and provide beneficial functions to their plant host. Whether the biorhythms in plants would transfer to the rhizosphere microbial community is still uncertain and their intricate connection remains poorly understood. Here, we investigated the role of the Arabidopsis circadian clock in shaping the rhizosphere microbial community using wild-type plants and clock mutants (cca1-1 and toc1-101) with transcriptomic, metabolomic and 16S rRNA gene sequencing analysis throughout a 24-h period. Deficiencies of the central circadian clock led to abnormal diurnal rhythms for thousands of expressed genes and dozens of root exudates. The bacterial community failed to follow obvious patterns in the 24-h period, and there was lack of coordination with plant growth in the clock mutants. Our results suggest that the robust rhythmicity of genes and root exudation due to circadian clock in plants is an important driving force for the positive succession of rhizosphere communities, which will feedback on plant development.

Alteration of dominant cyanobacteria in different bloom periods caused by abiotic factors and species interactions

Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide. Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months. To find out the factors impacting the cyanobacterial blooms, the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom. The most interesting finding is that two major cyanobacteria, Planktothrix and Microcystis, dramatically alternated during a cyanobacterial bloom in 2016, which is less mentioned in previous studies. When the temperature of the water began increasing in July, Planktothrix appeared first and showed as a superior competitor for M. aeruginosa in NO₃^--rich conditions. Microcystis became the dominant genus when the water temperature increased further in August. Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen (TDN) form on the growth of Planktothrix and Microcystis in a co-culture system. Besides, species interactions between cyanobacteria and non-cyanobacterial microorganisms, especially the prokaryotes, also played a key role in the alteration of Planktothrix and Microcystis. The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature, TDN forms as well as the species interactions. These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.

Rhizosphere Microbiome Assembly and Its Impact on Plant Growth

Microorganisms colonizing the plant rhizosphere provide a number of beneficial functions for their host. Although an increasing number of investigations clarified the great functional capabilities of rhizosphere microbial communities, the understanding of the precise mechanisms underlying the impact of rhizosphere microbiome assemblies is still limited. Also, not much is known about the various beneficial functions of the rhizosphere microbiome. In this review, we summarize the current knowledge of biotic and abiotic factors that shape the rhizosphere microbiome as well as the rhizosphere microbiome traits that are beneficial to plants growth and disease-resistance. We give particular emphasis on the impact of plant root metabolites on rhizosphere microbiome assemblies and on how the microbiome contributes to plant growth, yield, and disease-resistance. Finally, we introduce a new perspective and a novel method showing how a synthetic microbial community construction provides an effective approach to unravel the plant-microbes and microbes-microbes interplays.

Offspring toxicity of silver nanoparticles to Arabidopsis thaliana flowering and floral development

Many studies have considered silver nanoparticles (AgNPs) cytotoxicity to mammalian and human cell lines and plant growth. However, only few studies considered toxic effects of AgNPs on plant offspring, especially on flowering. Arabidopsis thaliana was treated with 12.5 mg/kg AgNPs employing parental-(P-AgNPs) and offspring-generation (O-AgNPs) exposure to study the effects of AgNPs on flowering and floral development. Exposure to P-AgNPs was found to significantly decrease petal and pollen viability and subsequently reduced pod production. The inhibition of A. thaliana vegetative growth caused by P-AgNPs exposure was transferred to offspring and even became more severe in the O-AgNPs group. Further, the transcription of genes related to flowering and floral organ development in P-AgNPs and O-Con plants was downregulated by approximately 10-40% compared to the transcription in P-Con plants and showed a stronger decrease in the O-AgNPs group to 30-50% of that in the P-AgNPs group. This resulted in a delay in flowering of 4, 3 and 8 days in P-AgNPs, O-Con and O-AgNPs plants, respectively. Our research shows that the negative effects on floral development can be transferred to the offspring in A. thaliana, which may have significant implications with regard to the risks posed by NPs to food safety and security.

Insights into the transcriptional responses of a microbial community to silver nanoparticles in a freshwater microcosm

Silver nanoparticles (AgNPs) are widely used because of their excellent antibacterial properties. They are, however, easily discharged into the water environment, causing potential adverse environmental effects. Meta-transcriptomic analyses are helpful to study the transcriptional response of prokaryotic and eukaryotic aquatic microorganisms to AgNPs. In the present study, microcosms were used to investigate the toxicity of AgNPs to a natural aquatic microbial community. It was found that a 7-day exposure to 10 μg L^-1 silver nanoparticles (AgNPs) dramatically affected the structure of the microbial community. Aquatic micro eukaryota (including eukaryotic algae, fungi, and zooplankton) and bacteria (i.e., heterotrophic bacteria and cyanobacteria) responded differently to the AgNPs stress. Meta-transcriptomic analyses demonstrated that eukaryota could use multiple cellular strategies to cope with AgNPs stress, such as enhancing nitrogen and sulfur metabolism, over-expressing genes related to translation, amino acids biosynthesis, and promoting bacterial-eukaryotic algae interactions. By contrast, bacteria were negatively affected by AgNPs with less signs of detoxification than in case of eukaryota; various pathways related to energy metabolism, DNA replication and genetic repair were seriously inhibited by AgNPs. As a result, eukaryotic algae (mainly Chlorophyta) dominated over cyanobacteria in the AgNPs treated microcosms over the 7-d exposure. The present study helps to understand the effects of AgNPs on aquatic microorganisms and provides insights into the contrasting AgNPs toxicity in eukaryota and bacteria.

Evaluation of the taxonomic and functional variation of freshwater plankton communities induced by trace amounts of the antibiotic ciprofloxacin

Ciprofloxacin (CIP), one of the most frequently detected antibiotics in water systems, has become an aquatic contaminant because of improper disposal and excretion by humans and animals. It is still unknown how trace amounts of CIP affect the aquatic microbial community diversity and function. We therefore investigated the effects of CIP on the structure and function of freshwater microbial communities via 16S/18S rRNA gene sequencing and metatranscriptomic analyses. CIP treatment (7 μg/L) did not significantly alter the physical and chemical condition of the water body as well as the composition of the main species in the community, but slightly increased the relative abundance of cyanobacteria and decreased the relative abundance of eukaryotes. Metatranscriptomic results showed that bacteria enhanced their phosphorus transport and photosynthesis after CIP exposure. The replication, transcription, translation and cell proliferation were all suppressed in eukaryotes, while the bacteria were not affected in any of these aspects. This interesting phenomenon was the exact opposite to both the antibacterial property of CIP and its safety for eukaryotes. We hypothesize that reciprocal and antagonistic interactions in the microcosm both contribute to this result: cyanobacteria may enhance their tolerance to CIP through benefiting from cross-feeding and some secreted substances that withstand bacterial CIP stress would also affect eukaryotic growth. The present study thus indicates that a detailed assessment of the aquatic ecotoxicity of CIP is essential, as the effects of CIP are much more complicated in microbial communities than in monocultures. CIP will continue to be an environmental contaminant due to its wide usage and production and more attention should be given to the negative effects of antibiotics as well as other bioactive pollutants on aquatic environments.

The biodistribution and immuno-responses of differently shaped non-modified gold particles in zebrafish embryos

Important questions raised in (nano)ecotoxicology are whether biodistribution of nanoparticles (NPs) is affected by particle shape and to what extent local adverse responses are subsequently initiated. For nanomedicine, these same questions become important when the labeled NPs lose the labeling. In this study, we investigated the biodistribution patterns of gold nanoparticles (AuNPs) as well as immune-related local and systemic sublethal markers of exposure and behavioral assessment. Hatched zebrafish embryos were exposed to four differently shaped non-coated AuNPs with comparable sizes: nanospheres, nanorods, nano-urchins, and nano-bipyramids. Shape-dependent trafficking of the particles resulted in a different distribution of the particles over the target organs. The differences across the distribution patterns indicate that the particles behave slightly different, although they eventually reach the same target organs - yet in different ratios. Mainly local induction of the immune system was observed, whereas systemic immune responses were not clearly visible. Macrophages were found to take AuNPs from the body fluid, be transferred into the veins and transported to digestive organs for clearance. No significant behavioral toxicological responses in zebrafish embryos were observed after exposure. The trafficking of the particles in the macrophages indicates that the particles are removed via the mononuclear phagocytic system. The different ratios in which the particles are distributed over the target organs indicate that the shape influences their behavior and eventually possibly the toxicity of the particles. The observed shape-dependent biodistribution patterns might be beneficial for shape-specific targeting in nanomedicine and stress the importance of incorporating shape-features in nanosafety assessment.

Phytotoxic effects of silver nanoparticles and silver ions to Arabidopsis thaliana as revealed by analysis of molecular responses and of metabolic pathways

The acute (3 days) and chronic (whole life history) responses of Arabidopsis thaliana following exposure to silver nanoparticles (AgNPs) and Ag⁺ ions (AgNO₃) in respectively a hydroponic medium and in soil were studied. After 3 days of hydroponic exposure, AgNPs (1.0 and 2.5 mg/L) exerted more severe inhibitory effects on plant (shoot and root) growth and photosynthesis than the same concentrations of Ag⁺ ions. In soil cultivation, the photoperiod, the autonomous, and the vernalization pathways were down-regulated to 0.15- to 0.5-fold of the control after 12.5 mg/kg AgNPs treatment. This exposure caused a decrease of approximately 25%-40% as compared to the control of the transcription of flowering key genes including AP1, LFY, FT and SOC1, and finally resulted in a delayed flowering time of 5 days. Only autonomous and vernalization pathways were inhibited by Ag⁺ ion treatment and ultimately the time of flowering in treated plants was delayed by 3 days. The energy production related metabolic pathways in the tricarboxylic acid cycle and in sugar metabolism were stimulated stronger by AgNPs than by Ag⁺ ion treatment, thus releasing more energy and accelerating the physiological metabolic responses against stress in the AgNPs treatment while subsequently reducing the plant growth and yield at the maturation stage. Importantly, shikimate-phenylpropanoid biosynthesis, and tryptophan and galactose metabolisms were regulated only by the AgNPs treatment, which was a specific effect of nanoparticles. This work provides a systematic understanding at the molecular, physiological as well as metabolic level of the effects of AgNPs and Ag⁺ ions in A. thaliana.

Impact of copper nanoparticles and ionic copper exposure on wheat (Triticum aestivum L.) root morphology and antioxidant response

Copper nanoparticles (nCu) are widely used in industry and in daily life, due to their unique physical, chemical, and biological properties. Few studies have focused on nCu phytotoxicity, especially with regard to toxicity mechanisms in crop plants. The present study examined the effect of 15.6 μM nCu exposure on the root morphology, physiology, and gene transcription levels of wheat (Triticum aestivum L.), a major crop cultivated worldwide. The results obtained were compared with the effects of exposing wheat to an equivalent molar concentration of ionic Cu (Cu²⁺ released from CuSO₄) and to control plants. The relative growth rate of roots decreased to approximately 60% and the formation of lateral roots was stimulated under nCu exposure, possibly due to the enhancement of nitrogen uptake and accumulation of auxin in lateral roots. The expression of four of the genes involved in the positive regulation of cell proliferation and negative regulation of programmed cell death decreased to 50% in the Cu²⁺ treatment compared to that of the control, while only one gene was down-regulated to about half of the control in nCu treatment. This explained the decreased root cell proliferation and higher extent of induced cell death in Cu²⁺- than in nCu-exposed plants. The increased methane dicarboxylic aldehyde accumulation (2.17-fold increase compared with the control) and decreased antioxidant enzyme activities (more than 50% decrease compared with the control) observed in the Cu²⁺ treatment in relation to the nCu treatment indicated higher oxidative stress in Cu²⁺- than in nCu-exposed plants. Antioxidant (e.g., proline) synthesis was pronouncedly induced by nCu to scavenge excess reactive oxygen species, alleviating phytotoxicity to wheat exposed to this form of Cu. Overall, oxidative stress and root growth inhibition were the main causes of nCu toxicity.

Investigation of Rhizospheric Microbial Communities in Wheat, Barley, and Two Rice Varieties at the Seedling Stage

The plant rhizosphere microbiota plays multiple roles in plant growth. We investigated the taxonomic and functional variations in the rhizosphere microbial community, examining both prokaryotes and eukaryotes, of four crops at the seedling stage: wheat, barley, and two rice varieties ( indica and japonica) seeded in paddy soil. The diversity of rhizosphere communities in these four species was determined. Results showed that wheat and barley had much stronger selection effects than rice for the rhizosphere microbial community. Functional metagenomic profiling indicated that a series of sequences related to glycan, limonene, and pinene degradation pathways as well as some relatively rare functions related to N or S metabolism were enriched in the rhizosphere soil. We conclude that the four tested crops induced the formation of the microbial community with specific features that may influence the plant growth but stochastic processes also appreciably influenced the functional selection.

Multiwall carbon nanotubes modulate paraquat toxicity in Arabidopsis thaliana

Carbon nanotubes can be either toxic or beneficial to plant growth and can also modulate toxicity of organic contaminants through surface sorption. The complex interacting toxic effects of carbon nanotubes and organic contaminants in plants have received little attention in the literature to date. In this study, the toxicity of multiwall carbon nanotubes (MWCNT, 50 mg/L) and paraquat (MV, 0.82 mg/L), separately or in combination, were evaluated at the physiological and the proteomic level in Arabidopsis thaliana for 7-14 days. The results revealed that the exposure to MWCNT had no inhibitory effect on the growth of shoots and leaves. Rather, MWCNT stimulated the relative electron transport rate and the effective photochemical quantum yield of PSII value as compared to the control by around 12% and lateral root production up to nearly 4-fold as compared to the control. The protective effect of MWCNT on MV toxicity on the root surface area could be quantitatively explained by the extent of MV adsorption on MWCNT and was related to stimulation of photosynthesis, antioxidant protection and number and area of lateral roots which in turn helped nutrient assimilation. The influence of MWCNT and MV on photosynthesis and oxidative stress at the physiological level was consistent with the proteomics analysis, with various over-expressed photosynthesis-related proteins (by more than 2 folds) and various under-expressed oxidative stress related proteins (by about 2-3 folds). This study brings new insights into the interactive effects of two xenobiotics (MWCNT and MV) on the physiology of a model plant.

The interactive effects of diclofop-methyl and silver nanoparticles on Arabidopsis thaliana: Growth, photosynthesis and antioxidant system

Diclofop-methyl (DM), a common post-emergence herbicide, is frequently used in agricultural production. Silver nanoparticles (AgNPs) are one of the most widely used nanoparticles, and as such, have been detected and monitored in several environmental systems. Here we investigated the interactive effects of DM and AgNPs on the physiological morphology, photosynthesis and antioxidant system of Arabidopsis thaliana. Our results demonstrated that a 1.0 mg/L DM treatment had no significant effect on the fresh weight of plant shoots and the content of total chlorophyll and anthocyanin. However, a 0.5 mg/L AgNPs treatment was found to significantly inhibit plant growth and chlorophyll synthesis, and was found to cause more severe oxidative damage in plants compared to the effects observed in a hydroponic suspension in which DM and AgNPs were jointly present. Meanwhile, the relative transcript levels of photosynthesis related genes (psbA, rbcL, pgrl1A and pgrl1B) in the combined group were found to be slightly increased compared to transcript levels in the AgNPs group, in order to maintain ATP generation at relatively normal levels in order to repair light damage. One explanation for these observed antagonistic effects was that the existence of DM affects the stability of AgNPs and reduced Ag⁺ release from AgNPs in the mixed solution. Thereupon, the Ag⁺-content was found to decrease in shoots and roots in the combined group by 15.2% and 9.4% respectively, compared to the AgNPs group. The coexistence of herbicides and nanomaterials in aquatic environments or soil systems will continue to exist due to their wide usages. Our current study highlights that the antagonistic effects between DM and AgNPs exerted a positive impact on A. thaliana growth.

Exploring uptake and biodistribution of polystyrene (nano)particles in zebrafish embryos at different developmental stages

In ecotoxicology, it is continuously questioned whether (nano)particle exposure results in particle uptake and subsequent biodistribution or if particles adsorb to the epithelial layer only. To contribute to answering this question, we investigated different uptake routes in zebrafish embryos and how they affect particle uptake into organs and within whole organisms. This is addressed by exposing three different life stages of the zebrafish embryo in order to cover the following exposure routes: via chorion and dermal exposure; dermal exposure; oral and dermal exposure. How different nanoparticle sizes affect uptake routes was assessed by using polystyrene particles of 25, 50, 250 and 700nm. In our experimental study, we showed that particle uptake in biota is restricted to oral exposure, whereas the dermal route resulted in adsorption to the epidermis and gills only. Ingestion followed by biodistribution was observed for the tested particles of 25 and 50nm. The particles spread through the body and eventually accumulated in specific organs and tissues such as the eyes. Particles larger than 50nm were predominantly adsorbed onto the intestinal tract and outer epidermis of zebrafish embryos. Embryos exposed to particles via both epidermis and intestine showed highest uptake and eventually accumulated particles in the eye, whereas uptake of particles via the chorion and epidermis resulted in marginal uptake. Organ uptake and internal distribution should be monitored more closely to provide more in depth information of the toxicity of particles.

Trait modality distribution of aquatic macrofauna communities as explained by pesticides and water chemistry

Analyzing functional species' characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2-4 % to pesticides, and for 3-11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.

Population responses of Daphnia magna, Chydorus sphaericus and Asellus aquaticus in pesticide contaminated ditches around bulb fields

The goal of this study was to investigate the effects of ambient concentrations of pesticides combined with abiotic factors on the key aquatic species Daphnia magna, Chydorus sphaericus and Asellus aquaticus by means of 21 days field exposure experiments. In situ bioassays were deployed in ditches around flower bulb fields during spring and autumn 2011-2012. The results showed that phosphate was the most variable parameter followed by pesticides expressed as toxic units, as the main factors explaining differences between sites. Variation in reproduction and growth of cladoceran D. magna was largely explained by nutrients, whereas dissolved oxygen contributed mostly to variations in reproduction of C. sphaericus. Dissolved organic carbon contributed to variations in growth of the detrivore A. aquaticus. It is concluded that abiotic stressors rather than pesticides contributed significantly to the performance of aquatic invertebrates.

A review of the ecological effects of radiofrequency electromagnetic fields (RF-EMF)

OBJECTIVE

This article presents a systematic review of published scientific studies on the potential ecological effects of radiofrequency electromagnetic fields (RF-EMF) in the range of 10 MHz to 3.6 GHz (from amplitude modulation, AM, to lower band microwave, MW, EMF).

METHODS

Publications in English were searched in ISI Web of Knowledge and Scholar Google with no restriction on publication date. Five species groups were identified: birds, insects, other vertebrates, other organisms, and plants. Not only clear ecological articles, such as field studies, were taken into consideration, but also biological articles on laboratory studies investigating the effects of RF-EMF with biological endpoints such as fertility, reproduction, behaviour and development, which have a clear ecological significance, were also included.

RESULTS

Information was collected from 113 studies from original peer-reviewed publications or from relevant existing reviews. A limited amount of ecological field studies was identified. The majority of the studies were conducted in a laboratory setting on birds (embryos or eggs), small rodents and plants. In 65% of the studies, ecological effects of RF-EMF (50% of the animal studies and about 75% of the plant studies) were found both at high as well as at low dosages. No clear dose-effect relationship could be discerned. Studies finding an effect applied higher durations of exposure and focused more on the GSM frequency ranges.

CONCLUSIONS

In about two third of the reviewed studies ecological effects of RF-EMF was reported at high as well as at low dosages. The very low dosages are compatible with real field situations, and could be found under environmental conditions. However, a lack of standardisation and a limited number of observations limit the possibility of generalising results from an organism to an ecosystem level. We propose in future studies to conduct more repetitions of observations and explicitly use the available standards for reporting RF-EMF relevant physical parameters in both laboratory and field studies.

External validation of EPIWIN biodegradation models

The BIOWIN biodegradation models were evaluated for their suitability for regulatory purposes. BIOWIN includes the linear and non-linear BIODEG and MITI models for estimating the probability of rapid aerobic biodegradation and an expert survey model for primary and ultimate biodegradation estimation. Experimental biodegradation data for 110 newly notified substances were compared with the estimations of the different models. The models were applied separately and in combinations to determine which model(s) showed the best performance. The results of this study were compared with the results of other validation studies and other biodegradation models. The BIOWIN models predict not-readily biodegradable substances with high accuracy in contrast to ready biodegradability. In view of the high environmental concern of persistent chemicals and in view of the large number of not-readily biodegradable chemicals compared to the readily ones, a model is preferred that gives a minimum of false positives without a corresponding high percentage false negatives. A combination of the BIOWIN models (BIOWIN2 or BIOWIN6) showed the highest predictive value for not-readily biodegradability. However, the highest score for overall predictivity with lowest percentage false predictions was achieved by applying BIOWIN3 (pass level 2.75) and BIOWIN6.

Monitoring approaches to assess bioaccessibility and bioavailability of metals: matrix issues

Bioavailability and bioaccessibility are complex issues that determine whether or not adverse effects are to be expected when organisms or plants are exposed to contaminants. Clearly, the determinants of bioavailability and bioaccessibility must be understood if one is to monitor or, ultimately, predict the effects of metals. On the basis of a dynamic conceptual model, this article offers an analysis of the physicochemical and biological determinants underlying bioavailability and bioaccessibility. This analysis is used as the basis for a general monitoring strategy for assessing potentially and actually available and accessible metal fractions in the environmental matrices of water, soil, and sediment. We conclude that, lack of a universal expression of bioavailable and bioaccessible metal fractions precludes the presentation of a detailed monitoring strategy that is broadly applicable. Instead, we recommend that a critical assessment of the endpoints of determination become the basis for a need-specific monitoring strategy.

Minimum requirements for reporting analytical data for environmental samples (IUPAC Technical Report)

In view of the significance of environmental analytical data, it is essential that the quality of both sampling strategy and analysis be assured and that procedures used, as well as all relevant additional information, are reported. There is a minimum level of information required in order to guarantee the fitness-for-use of the data. Emanating from discussions on the fundamental problems of the analysis of environmental samples for chemical or biological contaminants, a general guidance is given regarding the minimum information that should be provided to adequately describe the sampling strategy, method of sampling, sample properties, handling between sampling and analysis (including storage conditions, pretreatments, homogenization, subsampling), and the analytical methodology (including calculation and validation procedures). Special attention and specific guidance are given for the environmental compartments soil, pore water, groundwater, inland surface water, sediment, seawater, precipitation water, and air.