Increasing rates of commercialization and industrialization have led to the comprehensive evaluation of toxic effects of microplastics on crop plants. However, research on the impact of functionalized polystyrene nanoplastics on the toxicity of heavy metals remains limited. This study investigated the effects of polystyrene, carboxy-modified polystyrene, and amino-modified polystyrene on lead (Pb) toxicity in dandelion seedlings. The results showed that carboxy -modified polystyrene with a negative charge absorbed more Pb²⁺ than polystyrene and amino-modified polystyrene, and their maximum adsorption amounts were 5.328, 0.247, and 0.153 μg g⁻¹, respectively. The hydroponic experiment demonstrated that single amino-modified polystyrene was more toxic to dandelion seedlings than polystyrene and carboxy-modified polystyrene. The presence of Pb²⁺ was found to increase antioxidant enzymes (superoxide dismutase and catalase) and non-antioxidant enzymes (glutathione and ascorbic acid) activities in response to excessive reactive oxygen species in dandelion leaves and roots treated with polystyrene and carboxy-modified polystyrene, while it did not change much when amino-modified polystyrene was added. Interestingly, compared with single Pb²⁺, the addition of amino-modified polystyrene with positive charges induced an obvious decrease in the above parameters; however, they declined slightly in the treatments with polystyrene and carboxy-modified polystyrene despite a stronger adsorption capacity for Pb²⁺. Similarly, the bioactive compounds, including flavonoids, polyphenols, and polysaccharides in dandelion, showed a scavenging effect on O₂⁻ and H₂O₂, thereby inhibiting the accumulation and reducing medicinal properties. This study found that the effects of microplastics on the uptake, distribution, and toxicity of heavy metals depended on the nanoparticle surface charge.

Dissolved organic matter (DOM) and dissolved ions are two integral parameters to affect the environmental fate of As in different ways. Numerous studies chose surrogate of DOM, humic substances (HSs), to investigate the As complexation behavior. However, microbial secretion (protein and polysaccharide) was also considered for a great proportion in surface aquatic system, and its effect was still not fully understood. The present research distinguished the As complexation behavior with different DOM components (HSs, protein, polysaccharide and synthetic organic matter) in natural and simulated water samples. The results indicated that different DOM components exhibited various binding capacities for As. HSs showed the strongest affinity for As, followed by long-chain compounds (polysaccharide and synthetic organic matter) and proteins. In water source, HSs were probably the primary parameter for As complexation. In eutrophic water system, however, polysaccharide maybe the main DOM component to bind As. Cationic bridge function was prone to occur in the presence of HSs, but not observed in the presence of protein. PO₄³⁻ competed for binding sites with As, consequently decreasing the As complexation with all the DOM components. The research implied that a comprehensive and meticulous analyses of DOM fractions and coexist ions are the prerequisite to understanding the behavior of As (or other pollutants) in different natural aquatic systems.

ZnO nanoparticles (NPs) have been detected in various wastewater treatment plants. It is widely assumed that size has a crucial effect on the NPs toxicity. Concerns have been raised over probable size-dependent toxicity of ZnO NPs to activated sludge, which could eventually affect the treatment efficiencies of wastewater treatment facilities. The size-dependent influences of ZnO NPs on performance, microbial activities, and extracellular polymeric substances (EPS) from activated sludge were examined in sequencing batch reactor (SBR) in present study. Three different sizes (15, 50, and 90 nm) and five concentrations (2, 5, 10, 30, and 60 mg L⁻¹) were trialled. The inhibitions on COD and nitrogen removal were determined by the particle size, and smaller ZnO NPs (15 nm) showed higher inhibition effect than those of 50 and 90 nm, whereas the ZnO NPs with size of 50 nm showed maximum inhibition effect on phosphorus removal among three sizes of ZnO NPs. After exposure to different sized ZnO NPs, microbial enzymatic activities and removal rates of activated sludge represented the same trend, consistent with the nitrogen and phosphorus removal efficiency. In addition, apparent size- and concentration-dependent effects on EPS contents and components were also observed. Compared with the absence of ZnO NPs, 60 mg L⁻¹ ZnO NPs with sizes of 15, 50, and 90 nm increased the EPS contents from 92.5, 92.4, and 92.0 mg g⁻¹ VSS to 277.5, 196.8, and 178.2 mg g⁻¹ VSS (p < 0.05), respectively. The protein and polysaccharide contents increased with the decreasing particle sizes and increasing ZnO NPs concentrations, and the content of protein was always higher than that of polysaccharide.

Microalgal aggregation is a key to many ecosystem functions in aquatic environments. Yet mechanistic understanding of microalgae aggregation, especially the interactions with ubiquitous bacteria populations, remains elusive. We reported an experimental study illustrating how the emerging bacterial populations interacted with a model microalga (Chlamydomonas microsphaera) cells and the consequent aggregation patterns. Results showed that the emergence of bacterial populations significantly stimulated C. microsphaera aggregation. Both bacterial and C. microsphaera motilities were remarkably excited upon coculturing, with the mean cell velocity being up to 2.67 and 1.80 times of those of separate bacterial and C. microsphaera cultures, respectively. The stimulated bacterial and C. microsphaera cell velocity upon coculturing would likely provide a mechanism for enhanced probability of cell-cell collisions that led to amplified aggregation of C. microsphaera population. Correlation analysis revealed that bacterial resource foraging (for polysaccharides) was likely a candidate mechanism for stimulated cell motility in an organic carbon source-limited environment, whereby C. microsphaera-derived polysaccharides serve as the sole organic carbon source for heterotrophic bacteria which in turns facilitates bacteria-C. microsphaera aggregation. Additional analysis showed that bacterial populations capable of successive decomposing algal-derived organic matters dominated the cocultures, with the top five abundant genera of Brevundimonas (24.78%), Shinella (17.94%), Sphingopyxis (11.62%), Dongia (5.82%) and Hyphomicrobium (5.45%). These findings provide new insights into full understanding of microalgae-bacteria interactions and consequent microbial aggregation characteristics in aquatic ecosystems.

Soil contamination by toxic heavy metals such as copper is a serious problem. In this study, the extracellular polymeric substance (EPS) extracted from Rahnella sp. LRP3 was found with the potential of immobilizing Cu-polluted in soil. The EPS could bond to Cu (II) through functional groups (polysaccharides, amide, proteins, and carboxyl groups), which further developed into the porous sphere with a diameter of 20 μm. Besides, EPS could induce the formation of Cu₅(PO₄)₂(OH)₄ crystal by the biomineralization process. Finally, the EPS in the culture solution reduced 89.4 mg/kg of DTPA-Cu content by 78.99% in soil for 10 d under the condition of 25 °C via biomineralization. The results demonstrated that EPS produced by Rahnella sp. LRP3 will be a promising factor in the remediation of Cu contaminated soil.

Hydroxymethylfurfural (HMF) is a plant-based chemical building block that could potentially substitute petroleum-based equivalents, yet ecotoxicological data of this compound is currently limited. In this study, the effects of HMF on the reproduction and survival of Daphnia magna were assessed through validated ecotoxicological tests. The mechanism of toxicity was determined by analysis of transcriptomic responses induced by exposure to different concentrations of HMF using RNA sequencing. HMF exerted toxicity to D. magna with an EC₅₀ for effects on reproduction of 17.2 mg/l. HMF exposure affected molecular pathways including sugar and polysaccharide metabolism, lipid metabolism, general stress metabolism and red blood cell metabolism, although most molecular pathways affected by HMF exposure were dose specific. Hemoglobin genes, however, responded in a sensitive and dose-related manner. No induction of genes involved in the xenobiotic metabolism or oxidative stress metabolism pathway could be observed, which contrasted earlier observations on transcriptional responses of the terrestrial model Folsomia candida exposed to the same compound in a similar dose. We found 4189 orthologue genes between D. magna and F. candida, yet only twenty-one genes of those orthologues were co-regulated in both species. The contrasting transcriptional responses to the same compound exposed at a similar dose between D. magna and F. candida indicates limited overlap in stress responses among soil and aquatic invertebrates. The dose-related expression of hemoglobin provides further support for using hemoglobin expression as a biomarker for general stress responses in daphnids.

Undissolved humic acid (HA) is known to substantially effect the migration and transformation of hexavalent chromium [Cr(VI)] in soils. The mechanisms of Cr(VI) retention in soils by undissolved HA have been reported; however, past studies are inconclusive about the types of HA functional groups that are involved in Cr(VI) retention and the retention mechanisms. Utilizing a two-dimensional correlation spectroscopy (2DCOS) analysis for FTIR and 13C CP/MAS NMR, this study investigated the variations of HA function groups and molecular structures after reactions with aqueous Cr(VI) under different pH conditions. Based on the changing sequence of functional groups interpreted from the 2DCOS results, a four-step mechanism for Cr(VI) retention was determined as follows: (1) electrostatic adsorption of Cr(VI) to HA surface, (2) complexation of adsorbed Cr(VI) by carboxyl and ester, (3) reduction of complexed Cr(VI) to Cr(III) by phenol and polysaccharide, and (4) complexation of reduced Cr(III) by carboxylic groups. These functional groups that are involved in Cr(VI) retention were determined to occur in aromatic domains.

The changes in the biofilm community due to organic matter enrichment, eutrophication and metal contamination derived from fish farming were studied. The biofilm biomass, polysaccharide content, trophic niche and element accumulation were quantified along an environmental gradient of fish farm wastes in two seasons. Biofilm structure and trophic diversity was influenced by seasonality as well as by the fish farm waste load. Fish farming enhanced the accumulation of organic carbon, nutrients, selenium and metals by the biofilm community. The accumulation pattern of these elements was similar regardless of the structure and trophic niche of the community. This suggests that the biofilm communities can be considered a reliable tool for assessing dissolved aquaculture wastes. Due to the ubiquity of biofilms and its wide range of consumers, its role as a sink of dissolved wastes may have important implications for the transfer of aquaculture wastes to higher trophic levels in coastal systems.

The complexation with extracellular polymeric substances (EPS) greatly reduces the toxicity of heavy metals towards organisms in the environment. However, the molecular mechanism of EPS−metal complexation remains unclear owing to the limitation of precise analysis for key fractions and functionalities in EPS that associate with metals. Herein, we explored the EPS−Cd (II) complexation by fluorescence excitation emission matrix coupled with parallel factor (EEM−PARAFAC), two-dimensional Fourier transform infrared correlation spectroscopy (2D-FTIR−COS) and X-ray photoelectron spectroscopy (XPS), attempting to explain the mechanisms of EPS in alleviating Cd (II) toxicity toward a green alga Chlorella vulgaris (C. vulgaris). When the algal EPS were removed, the cell internalizations of Cd (II), growth inhibition rate and chlorophyll autofluorescence increased, but the surface adsorption and esterase activities decreased, indicating that the sorption of Cd (II) by EPS was crucial in alleviating the algal toxicity. Moreover, the complexation with proteins in EPS controlled the sorption of Cd (II) to algal EPS, resulting in the chemical static quenching of the proteins fluorescence by 47.69 ± 2.37%. Additionally, the complexing capability of the main functionalities, COO⁻ and C–OH in proteins with Cd (II) was stronger than that of C–O(H) and C–O–C in polysaccharides or C–OH in the humus-related substances. Oxygen atom in protein carboxyl C–O might be the key site of EPS−Cd (II) complexation, supported by the modified Ryan−Weber complexation model and the obvious shift of oxygen valence-electron signal. These findings provide deep insights into understanding the interaction of EPS with heavy metals in aquatic environment.

The honeybee has economic importance both for the commercial value of bee products and for its role in the pollination of agricultural crops. Despite the fact that the fungicides are widely used in agriculture, studies comparing the effects of this group of pesticides on bees are still scarce. There are many gaps preventing the understanding of bees’ responses to exposure to fungicides, including the influence of the age of the exposed workers. However, this study aimed to compare the effects of residual concentrations of pyraclostrobin on young and old bees of Africanized Apis mellifera. The parameters analyzed were the survival rates, as well as the histopathological and histochemical changes in midgut of orally exposed workers to different sublethal concentrations of this strobilurin fungicide: 0.125 ng a.i./μL (C1), 0.025 ng a.i./μL (C2) e 0.005 ng a.i./μL (C3). The results showed a significant decrease in the longevity only for old bees exposed to the three concentrations of pyraclostrobin. After the five-day exposure period, the fungicide induced sublethal effects in the midgut only from the old bees. These effects were the increase both in cytoplasmic vacuolization of digestive cells and morphological changes in the nests of regenerative cells, which reflected in the higher lesion index of organ for groups C1 and C2. Additionally, there was a reduction in total protein staining in the intestinal epithelium in C1 and C2. At the same exposure period, the midgut of young bees presented only a reduction in the staining of neutral polysaccharides in the group C1. Concluding, old workers are more sensitive to the fungicide than young workers. This study showed different responses according to worker age, which can affect the maintenance of colony health. Future studies should take into account the age of the workers to better understand the effects of fungicides on bees.