Particle Size Determines the Phytotoxicity of ZnO Nanoparticles in Rice (Oryza sativa L.) Revealed by Spatial Imaging Techniques.

To understand the nanotoxicity effects on plants, it is necessary to systematically study the distribution of NPs in vivo. Herein, elemental and particle-imaging techniques were used to unravel the size effects of ZnO NPs on phytotoxicity. Small-sized ZnO NPs (5, 20, and 50 nm) showed an inhibitory effect on the length and biomass of rice (Oryza sativa L.) used as a model plant. ZnO NP nanotoxicity caused rice root cell membrane damage, increased the malondialdehyde content, and activated antioxidant enzymes. As a control, the same dose of Zn2+ salt did not affect the physiological and biochemical indices of rice, suggesting that the toxicity is caused by the entry of the ZnO NPs and not the dissolved Zn2+. Laser ablation inductively coupled plasma optical emission spectroscopy analysis revealed that ZnO NPs accumulated in the rice root vascular tissues of the rhizodermis and procambium. Furthermore, transmission electron microscopy confirmed that the NPs were internalized to the root tissues. These results suggest that ZnO NPs may exist in the rice root system and that their particle size could be a crucial factor in determining toxicity. This study provides evidence of the size-dependent phytotoxicity of ZnO NPs.

Time-dependent effects of microplastics on soil bacteriome.

Microplastic threats to biodiversity, health and ecological safety are adding to concern worldwide, but the real impacts on the functioning of organisms and ecosystems are obscure owing to their inert characteristics. Here we investigated the long-lasting ecological effects of six prevalent microplastic types: polyethylene (PE), polypropylene (PP), polyamide (PA), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC) on soil bacteria at a 2 % (w/w) level. Due to the inertia and lack of available nitrogen of these microplastics, their effects on bacteriome tended to converge after one year and were strongly different from their short-term effects. The soil volumes around microplastics were very specific, in which the microplastic-adapted bacteria (e.g., some genera in Actinobacteria) were enriched but the phyla Bacteroidetes and Gemmatimonadetes declined, resulting in higher microbial nitrogen requirements and reduced organic carbon mineralization. The reshaped bacteriome was specialized in the genetic potential of xenobiotic and lipid metabolism as well as related oxidation, esterification, and hydrolysis processes, but excessive oxidative damage resulted in severe weakness in community genetic information processing. According to model predictions, microplastic effects are indirectly derived from nutrients and oxidative stress, and the effects on bacterial functions are stronger than on structure, posing a heavy risk to soil ecosystems.

The toxic differentiation of micro- and nanoplastics verified by gene-edited fluorescent Caenorhabditis elegans.

The increased emission and accumulation of micro- or nanoplastics (M-NPs) have posed a severely threaten to organisms in the environment. Though the toxicity of M-NPs has been observed in many species, the fundamental factors determining the biotoxicity are rarely expounded on. In this work, typical polystyrene (PS) M-NPs were set up with a multiparameter variation in size gradient, surface charge contrast and concentration variant, and evaluated by the Caenorhabditis elegans (C. elegans) model. From the endpoints of body length, brood size, survival rate and lifespan, an adverse effect was found on the growth and development of C. elegans caused by PSs. In general, the toxicity of PS was found to be concentrated- and size-dependent, with 100 nm positively charged nano-PS having the highest physio-toxicity. Monitoring by fluorescent imaging, it showed that positively charged nano-PS was mainly ingested and accumulated in the intestinal tract of C. elegans. In addition, the penetrated PS induced severe biological stress reactions with the increase of reactive oxygen species (ROS) and lipofuscin. Furthermore, the following expression of antioxidation-related enzymes was activated in vivo as indicated by the GFP-labelled C. elegans. All the results supplied visually toxic parameters of M-NPs to organisms, which sheds light on the biosecurity and ecological risks of M-NPs in the future.

Combined toxicity of zinc oxide nanoparticles and cadmium inducing root damage in Phytolacca americana L.

In recent years, nano-contamination in the soil environment has aroused concern. But it is still uncertain whether the interactions of nano- and metal-pollutants would have a combined toxic effect on plants. In this study, we investigated the effects of joint exposure to zinc oxide nanoparticles (ZnO NPs) and Cd on the root tissue of Phytolacca americana L. Spin-polarized density functional theory simulations assumed that the plant may undergo metal toxicity or acidosis upon joint exposure to ZnO NPs/Cd. Subsequently, experimental exposure of P. americana verified the combined toxic effects. The plant grew normally with a single treatment of ZnO NPs (500 mg/kg) or low doses of Cd (10 mg/kg). However, root growth was significantly inhibited with the combined treatments (up to 43% reduction); additionally, Cd ions were transported to the shoot, leading to shoot growth inhibition (translocation factor > 1). The antioxidant enzymes in the root (superoxide dismutase, peroxidase, and catalase) were highly activated to resist stress, accompanied by a greater than two-fold increase in thiobarbituric acid reactive substances. Corresponding to physiological indicators, biological transmission electron microscopy revealed severe damage to the root cells. Moreover, ZnO NPs/Cd accumulation was observed in the root cytoderm, which confirmed the toxicity of the combined effects. Our study provides insight into the potential combined toxicity of ZnO NPs and heavy metals in polluted environments, such as mining areas and electronic waste sites, and agricultural soils.

Systematical review of interactions between microplastics and microorganisms in the soil environment.

Terrestrial ecosystems are widely contaminated by microplastics due to extensive usage and poor handling of plastic materials, but the subsequent fate and remediate strategy of these pollutants are far from fully understood. In soil environments, microplastics pose a potential threat to the survival, growth, and reproduction of soil microbiota that in turn threaten the biodiversity, function, and services of terrestrial ecosystems. Meanwhile, microorganisms are sensitive to microplastics due to the adaptability to changes in substrates and soil properties. Through the metabolic and mineralization processes, microorganisms are also crucial participator to the plastic biodegradation. In this review, we present current knowledges and research results of interactions between microplastics and microorganisms (both fungi and bacteria) in soil environments and mainly discuss the following: (1) effects of microplastics on microbial habitats via changes in soil physical, chemical, and biological properties; (2) effects of microplastics on soil microbial communities and functions; and (3) soil microbial-mediated plastic degradation with the likely mechanisms and potential remediation strategies. We aim to analyze the mechanisms driving these interactions and subsequent ecological effects, propose future directives for the study of microplastic in soils, and provide valuable information on the plastic bioremediation in contaminated soils.

Microorganism structure variation in urban soil microenvironment upon ZnO nanoparticles contamination.

Nanoparticles (NPs) sink into the soil via agricultural spreading, surface water, atmospheric deposition, and industrial emission, which affects plant growth and soil microenvironment. To understand how NPs influence urban soil microenvironment, the effect of typical nano-pollutants zinc oxide nanoparticles (ZnONPs) was investigated in urban solid-waste land. Pokeweed (Phytolacca Americana L.) soil samples from solid-waste land were collected and exposed to 200, 500, and 1000 mg kg-1 ZnONPs. The physiological characteristics of pokeweed, soil bacterial community composition, and soil physiochemical properties and enzymatic activities were determined. Our results show that pokeweed growth was slightly inhibited, and soil acid-base homeostasis was affected in ZnONPs-contaminated samples. Meanwhile, enzymatic activities related to soil C cycle were enhanced, and bacterial community structure at the phylum and genus levels was altered. Specifically, the abundance of hydrocarbon-degrading taxa reduced substantially upon ZnONPs exposure. The phenoloxidase (PPO) activity and the refractory hydrocarbon-degrading bacteria Bacteroidetes was adversely affected by ZnONPs exposure. In addition, Subgroup_10 of Acidobacteria was identified as an indicator of soil ZnONPs contamination. Our study detected changes in plant growth, soil environmental factors, and soil microbe community composition in urban solid-waste land treated by ZnONPs. The results of this research provide evidence for ZnONPs toxicology on urban soil microenvironment.