Accumulation of metals by plants is an important area of investigation in plant ecology and evolution as well as in soil contamination/phytoremediation practices. This paper reports that hormetic-biphasic dose-response relationships were commonly observed for multiple agents (i.e. arsenic, cadmium, chromium, fluoride, lead, and zinc) and 20 species in plant (hyper)accumulator studies. The hormetic stimulation was related to metal accumulation in affected tissues, with the metal stimulation concentration zone unique for each metal, species, tissue, and endpoint studied. However, quantitative features of the hormetic dose response were similar across all (hyper)accumulation studies, with results independent of plant species, endpoints measured, and metal. The dose-dependent stimulatory and inhibitory/toxic plant responses were often associated with the up- and down-regulation of adaptive mechanisms, especially those involving anti-oxidative enzymatic processes. These findings provide a mechanistic framework to account for both the qualitative and quantitative features of the hormetic dose response in plant (hyper)accumulator studies.

Excessive nutrient discharges have resulted in pervasive water pollution and aquatic eutrophication. China has made massive efforts to improve water quality since 2000. However, how long-term policy interventions govern external and internal fluxes as well as nitrogen (N) concentrations is not well known. Here we examined the historical N concentration change and its key drivers in eutrophic Lake Dianchi (southwest China) over the period 2002–2018, based on monthly observations of water quality and external N fluxes, local surveys of mitigation measures, and process-based model simulations of internal N fluxes. Our data indicated that N concentrations peaked at 3.0 mg L⁻¹ in 2007–2010 but afterwards declined down to 1.2 mg L⁻¹ in 2018. Compared with 2010, the decline in lake N concentrations was attributed to reduced riverine N inflow decreasing by 0.20 g N m⁻³ month⁻¹ and the water-sediment exchange flux decreasing by 0.07 g N m⁻³ month⁻¹ from 2010 to 2018. Adoptions of wastewater treatment, pollution interception, and transboundary water transfer dominated the changes in external and internal fluxes of N and thereby the decline of lake N concentrations. These findings underscore the priority of reducing external discharge for historical lake water quality improvement and the need of enhancing internal N removal for future lake ecosystem restoration.

Water pollution by microplastics (MPs) is a contemporary issue which has recently gained lots of attentions. Despite this, very limited studies were conducted on the degradation of MPs. In this paper, we reported the treatment of synthetic mono-dispersed suspension of MPs by using electrooxidation (EO) process. MPs synthetic solution was prepared with distilled water and a commercial polystyrene solution containing a surfactant. In addition to anode material, different operating parameters were investigated such as current intensity, anode surface, electrolyte type, electrolyte concentration, and reaction time. The obtained results revealed that the EO process can degrade 58 ± 21% of MPs in 1 h. Analysis of the operating parameters showed that the current intensity, anode material, electrolyte type, and electrolyte concentration substantially affected the MPs removal efficiency, whereas anode surface area had a negligible effect. In addition, dynamic light scattering analysis was performed to evaluate the size distribution of MPs during the degradation. The combination of dynamic light scattering, scanning electron microscopy, total organic carbon, and Fourier-transform infrared spectroscopy results suggested that the MPs did not break into smaller particles and they degrade directly into gaseous products. This work demonstrated that EO is a promising process for degradation of MPs in water without production of any wastes or by-products.

Microplastics (MPs; <5 mm) released into freshwaters from anthropogenic sources accumulate in sediments, where they may pose an environmental threat to benthic organisms, such as nematodes. Several studies have examined the effects of nano- and microplastics on the nematode Caenorhabditis elegans, whereas reduced food availability was suggested as a possible explanation for the observed inhibitory effects. Therefore, this study should clarify whether micro-beads of different sizes (1.0 and 6.0 μm in diameter) and materials (polystyrene PS, silica) are able to interfere with the feeding of C. elegans on its bacterial diet (Escherichia coli), and, by this, lowering its consumption rate within 7 h of exposure. Moreover, it was examined whether an inhibited bacterial consumption was caused by a reduction of the nematode’s pumping rate, as a primary indicator of food ingestion. Bacterial consumption by C. elegans was significantly decreased in the presence of 1.0- and 6.0-μm PS beads (49–67% lower bacterial consumption compared to control), whereas in the presence of 1.0-μm silica beads feeding was not impeded. Interestingly, the pumping rate was significantly lower in the presence of non-ingestible 6.0-μm PS beads with 161 ± 16 pumps min⁻¹, while it was largely unchanged for nematodes exposed to ingestible 1.0-μm PS beads with 205 ± 12 pumps min⁻¹, compared to control conditions with 210 ± 18 pumps min⁻¹, respectively. As reduced bacterial consumption leads to generally lower energy reserves in C. elegans, these results allow to link observed inhibitory effects of MPs on the nematodes to a lower food availability. Such indirect, food-web related, effects of MPs should raise concern of ecological consequences in natural habitats, where temporal food deficiencies can occur. Consequently, disturbances in food availability and feeding efficiency should be regarded as important parameters in environmental risk assessments focusing on MPs.

Nitric oxide (NO) plays a critical role in atmospheric chemistry and also is a precursor of nitrate, which affects particle matter formation and nitrogen deposition. Agricultural soil has been recognized as a main source of atmospheric NO. However, quantifying the NO fluxes emitted from croplands remains a challenge and in situ long-term measurements of NO are still limited. In this study, we used an automated sampling system to measure NO fluxes with a high temporal resolution over two years (April 2017 to March 2019) from a rainfed maize field in the Northeast China. The cumulative annual NO emissions were 8.9 and 2.3 kg N ha⁻¹ in year 1 (April 2017 to March 2018) and year 2 (April 2018 to March 2019), respectively. These interannual differences were largely related to different weather conditions encountered. In year 1, a month-long drought before and after the seeding and fertilizing reduced plant N uptake and dramatically increased soil N concentration. The following moderate rainfalls promoted large amount of NO emissions, which remained high until late September. The NO fluxes in both years showed clearer seasonal patterns, being highest after fertilizer application in summer, and lowest in winter. The seasonal patterns of NO fluxes were mainly controlled by soil available N concentrations and soil temperatures. The contribution of NO fluxes during the spring freeze-thaw in both years was no more than 0.2% of the annual NO budget, indicating that the freeze-thaw effect on agricultural NO emissions was minimal. In addition, with high-resolution monitoring, we found that soil not only act as a NO source but also a sink. Long-term and high-resolution measurements help us better understand the diurnal, seasonal, and annual dynamics of NO emissions, build more accurate models and better estimate global NO budget and develop more effective policy responses to global climate change.

Seafood contamination with, and human consumption of, microplastics (MPs) have recently been highlighted as an emerging concern for global food security. While there is evidence that commercial marine species are contaminated with MPs, it is still unknown if seafood can act as a vector for MP transfer to human consumers. Microplastics have been reported in the digestive tract, gills and in select internal organs of marine animals. However, many of these tissues are not typically eaten by human consumers but discarded. In this critical review, we examined the peer-reviewed literature for evidence of MP contamination in seafood, and the potential transfer to human consumers. Based on known seafood consumption patterns in a typical Australian diet, we assessed the relevance and reliability of the current body of literature to examine the prospect and risk of MP transfer. The relevance of data was considered based on the organism studied, origin of the samples, and the tissues analysed, while reliability was assessed based on procedural methodologies used to derive the data. A review of 132 studies found limited evidence of MP contamination in edible tissues from fresh fish or crustaceans. MP presence was confirmed in packaged fish, as well as in fresh and packaged bivalve molluscs. The limited number of studies satisfying the relevance and reliability criteria (n = 24) precluded a quantitative assessment of the potential risk associated with MP transfer. While consumption of packaged fish and bivalve molluscs may result in the consumption of MPs by humans, it is currently unknown whether this presents a health risk.

Mercury (Hg) is a neurotoxic element with severe effects on humans and wildlife. Widely distributed by atmospheric deposition, it can also be localized near point sources such as mines. Mercury has been shown to reduce the reproduction of bird populations in field observations in North America and Europe, but studies are needed in Asia, where the majority of emissions now occur. We investigated the reproduction of two passerines, Japanese Tit (Parus minor) and Russet Sparrow (Passer rutilans), in a large-scale Hg mining district, and a non-mining district, both in Guizhou, southwest China. Concentrations of Hg were elevated in the mining district (blood levels of 2.54 ± 2.21 [SD] and 0.71 ± 0.40 μg/g, in adult tits and sparrows, respectively). However, we saw no evidence of decreased breeding there: metrics such as egg volume, nestling weight, hatching and fledgling success, were all similar between the different districts across two breeding seasons. Nor were there correlations at the mining district between Hg levels of adults or juveniles, and hatching or fledgling success, or nestling weight. Nest success was high even in the mining district (tit, 64.0%; sparrow: 83.1%). This lack of reproductive decline may be related to lower blood levels in nestlings (means < 0.15 μg/g for both species). Concentrations of selenium (Se), and Se-to-Hg molar ratio, were also not correlated to breeding success. Although blood levels of 3.0 μg/g have been considered as a threshold of adverse effects in birds, even leading to severe effects, we detected no population-level reproductive effects, despite ~25% of the adult tits being above this level. Future work should investigate different locations in the mining district, different life-stages of the birds, and a wider variety of species. The hypothesis that bird populations can evolve resistance to Hg in contaminated areas should also be examined further.

Pyraclostrobin is a widely used and highly efficient fungicide that also has high toxicity to aquatic organisms, especially fish. Although some research has reported the toxic effects of pyraclostrobin on fish, the main toxic pathways of pyraclostrobin in fish remain unclear. The present study has integrated histopathological, biochemical and hematological techniques to reveal the main toxic pathways and mechanisms of pyraclostrobin under different exposure routes. Our results indicated that pyraclostrobin entered fish mainly through the gills. The highest accumulation of pyraclostrobin was observed in the gills and heart compared with accumulation in other tissues and gill tissue showed the most severe damage. Hypoxia symptoms (water jacking, tummy turning and cartwheel formation) in fish were observed throughout the experiment. Taken together, our results suggested that the gills are important target organs. The high pyraclostrobin toxicity to gills might be associated with oxidative damage to the gills, inducing alterations in ventilation frequency, oxygen-carrying substances in blood and disorders of energy metabolism. Our research facilitates a better understanding of the toxic mechanisms of pyraclostrobin in fish, which can promote the ecotoxicological research of agrochemicals on aquatic organisms.

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have attracted increasing attention in recent years for organic pollutants removal. Herein, we put forward a facile method to form cobalt phosphide/carbon composite for PMS activation. Combining impregnation approach with pyrolysis treatment enabled the formation of Co₂P/biochar composites using baker’s yeast and Co²⁺ as precursors. The as-synthesized products exhibited excellent catalytic activity for sulfamethoxazole (SMX) degradation over the pH range 3.0–9.0 b y activating PMS. For example, 100% of SMX (20 mg L⁻¹) removal was achieved in 20 min with catalyst dosage of 0.4 g L⁻¹ and PMS loading of 0.4 g L⁻¹. Near zero Co²⁺ leaching was observed during catalytic reaction, which remarkably lowered the toxic risk of transition metal ion in water. Meanwhile, the reusability of catalyst could be attained by thermal treatment. SMX degradation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS), which facilitated the proposal of possible SMX degradation pathways. Ecological Structure Activity Relationships (ECOSAR) analysis indicated that SMX degradation intermediates may not pose ecological toxicity to the environment. Further investigation verified that Co₂P/biochar composites could set off PMS activation not only for the degradation of SMX but also for other sulfonamides. In this study, we not only developed a facile method of utilizing environmental-benign biomass for transition metal phosphide/carbon composite formation, but also achieved highly efficient antibiotic elimination by PMS-based AOP.

Nitrogen dioxide (NO₂) is an important air pollutant and highly related to air quality, short- and long-term health effects, and even climate. A national model was developed using the extreme gradient boosting algorithm with high-resolution tropospheric vertical column NO₂ densities from the Sentinel-5 Precursor/Tropospheric Monitoring Instrument and general meteorological variables as input to generate daily mean surface NO₂ concentrations across mainland China. Model-derived daily NO₂ estimates were high accuracy with sample-based cross-validation coefficient of determination of 0.83, a root-mean-square error of 7.58 μg/m³, a mean prediction error of 5.56 μg/m³, and a mean relative prediction error of 18.08%. It has good performance in NO₂ estimations at both regional and individual site scale. The model also performed well in terms of estimating monthly, seasonal, and annual mean NO₂ concentrations across China. The model performance appears to better than or comparable to most previous related studies. The seasonal and annual spatial distributions of surface NO₂ across China and several regional NO₂ hotspots in 2019 were derived from the model and analyzed. Also evaluated were the population exposure levels of NO₂ for cities in and provinces of China. At the national scale, about 12% of the population experienced annual mean NO₂ concentrations exceeding the Chinese national air quality standard. The nationwide model with conventional predictors developed here can derive high-resolution surface NO₂ concentrations across China routinely, benefitting air epidemiological and environmental related studies.