The importance of per-, poly-fluoroalkyl substances (PFASs) effects on riverine microbiomes is receiving increased recognition in the environmental sciences. However, few studies have explored how PFASs affect microbiomes across trophic levels, specifically through predator-prey interactions. This study examined the community profiles of planktonic archaea, bacteria, fungi, algae, protozoa, and metazoa in a semi-industrial and agricultural river alongside their interactions with 15 detected PFASs. As abiotic factors, PFASs affected community coalescence more than biogenic substances (p < 0.05). For biotic regulations, sub-communities in rare biospheres (including always rare taxa-ART and critically rare taxa-CRT) contributed to spatial community coalescence more than sub-communities in abundant biospheres (always abundant taxa-AAT and critically abundant taxa-CAT) (p < 0.05). Metazoa-bacteria (Modularity = 1.971) and protozoa-fungi (1.723) were determined to be the most stable predator-prey networks. Based on pathway models, short-chain PFBA (C4) was shown to weaken the trophic transfer efficiencies from heterotrophic bacteria (HB) to heterotrophic flagellates (HF) (p < 0.05). Long-chain PFTeDA (C14) promoted HB to amoeba (p < 0.05), which we postulate is the pathway for PFTeDA to enter the microbial food chain. Our preliminary results elucidated the influence of PFASs on planktonic microbial food webs and highlighted the need to consider protecting and remediating riverine ecosystems containing PFASs.

Under intensive human activity, sewage discharge causes eutrophication-driven cyanobacteria blooms as well as nanomaterial pollution. In biological control of harmful cyanobacteria, top-down effect of protozoan has great potentials for removing cyanobacterial populations, degrading cyanotoxins, and improving phytoplankton community. ZnO nanoparticles as a kind of emerging contaminants have attracted increasing attention because of wide application and their high bio-toxicity effects on reducing the ingestion of aquatic animals including Paramecium, thereby possibly disturbing top-down control of cyanobacteria. Therefore, this study investigated the effects of ZnO nanoparticles at environmental-relevant concentrations on the protozoan Paramecium removing toxic Microcystis. Results showed Paramecium effectively eliminated all the Microcystis, despite exposure to ZnO nanoparticles. However, their ingestion rate was significantly reduced at more than 0.1 mg L⁻¹ ZnO nanoparticles, thereby delaying Microcystis removal. Nevertheless, at 0.1 mg L⁻¹ ZnO nanoparticles, the time to Microcystis extinction decreased compared to the group without ZnO nanoparticles, because Microcystis populations were reduced under this circumstance, while ingestion rate of Paramecium was unaffected. Furthermore, ZnO nanoparticles obviously accumulated in food vacuoles of Paramecium, and the size of nanoparticles aggregates and zinc concentrations in Paramecium were increased with ZnO nanoparticles concentrations. At the end of experiment, these food vacuoles were not dissipated. Overall, these findings suggest that ZnO nanoparticles impair protozoan top-down effects through reducing Microcystis and ingestion rate as well as disturbing functions of their digestive organelles, and highlight the need to consider the interfering effects of environmental pollutants on cyanobacterial removal efficiency by protozoans in natural waters.

Silver nanoparticles (AgNPs) are highly toxic to aquatic organisms, however, there is no consensus whether the toxicity is caused solely by released Ag-ions or also by reactive oxygen species (ROS). Here, the effects of protein-coated AgNPs (14.6 nm, Collargol) were studied on viability, oxidative stress and gene expression levels in wild type strains (CU427 and CU428) of unicellular ciliate Tetrahymena thermophila. Viability-based 24 h EC50 values of AgNPs were relatively high and significantly different for the two strains: ∼100 mg/L and ∼75 mg/L for CU427 and CU428, respectively. Similarly, the expression profiles of oxidative stress (OS) related genes in the two strains were different. However, even though some OS related genes were overexpressed in AgNP-exposed ciliates, intracellular ROS level was not elevated, possibly due to efficient cellular antioxidant defence mechanisms. Compared to OS related genes, metallothionein genes were upregulated at a considerably higher level (14 versus 5000-fold) suggesting that Ag-ion mediated toxicity mechanism of AgNPs prevailed over OS related pathway. Also, comparison between Ag-ions released from AgNPs at EC50 concentration and the respective EC50 values of AgNO3 indicated that Ag-ions played a major role in the toxicity of AgNPs in T. thermophila. The study highlights the importance of combining physiological assays with gene expression analysis in elucidating the mechanisms of action of NPs to reveal subtle cellular responses that may not be detectable in bioassays. In addition, our data filled the gaps on the toxicity of AgNPs for environmentally relevant and abundant organisms. The parallel study of two wild type strains allowed us to draw conclusions on strain to strain variability in susceptibility to AgNPs.

Trace metals and broad-spectrum antibiotic drugs are common environmental contaminants, the importance of which is increasing due to global climate change-related effects.In the present study, the biological model organism E. crassus was first acclimated to five temperatures, from 25 °C to 33 °C, followed by exposure to nominal concentrations of copper, the antibiotic model compound oxytetracycline and mixtures of both, at increasing thermal conditions. Variations of temperature-related toxicity were assessed by two high-level endpoint tests, survival and replication rates, and two sublethal parameters: endocytosis rate and lysosomal membrane stability. The selected toxicants presented opposite behaviours as the protozoa's survival rates increased following an increasing thermal gradient in the oxytetracycline-related treatments, and a decline of tolerance in metal-related treatments was observed. Results of tests combining binary mixtures of tested toxicants showed a complex pattern of responses.

Concentrations of metals associated with sediments have traditionally been analysed to assess the extent of heavy metal contamination in freshwater environments. Stream biofilms present an alternative medium for this assessment which may be more relevant to the risk incurred by stream ecosystems as they are intensively grazed by aquatic organisms at a higher trophic level. Therefore, we investigated zinc, copper and lead concentrations in biofilms and sediments of 23 stream sites variously impacted by urbanisation. Simultaneously, biofilm bacterial and ciliate protozoan community structure was analysed by Automated Ribosomal Intergenic Spacer Analysis and Terminal Restriction Fragment Length Polymorphism, respectively. Statistical analysis revealed that biofilm associated metals explained a greater proportion of the variations observed in bacterial and ciliate communities than did sediment associated-metals. This study suggests that the analysis of metal concentrations in biofilms provide a good assessment of detrimental effects of metal contaminants on aquatic biota.

Soil suspensions (slurries) are commonly used to estimate the potential of soil microbial communities to mineralize organic contaminants. The preparation of soil slurries disrupts soil structure, however, potentially affecting both the bacterial populations and their protozoan predators. We studied the importance of this “slurry effect” on mineralization of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA, ¹⁴C-labelled), focussing on the effects of protozoan predation. Mineralization of MCPA was studied in “intact” soil and soil slurries differing in soil:water ratio, both in the presence and absence of the protozoan activity inhibitor cycloheximide. Protozoan predation inhibited mineralization in dense slurry of subsoil (soil:water ratio 1:3), but only in the most dilute slurry of topsoil (soil:water ratio 1:100). Our results demonstrate that protozoan predation in soil slurries may compromise quantification of contaminant mineralization potential, especially when the initial density of degrader bacteria is low and their growth is controlled by predation during the incubation period.

The acute toxicity of CuO and ZnO nanoparticles in artificial freshwater (AFW) and in natural waters to crustaceans Daphnia magna and Thamnocephalus platyurus and protozoan Tetrahymena thermophila was compared. The L(E)C50 values of nanoCuO for both crustaceans in natural water ranged from 90 to 224 mg Cu/l and were about 10-fold lower than L(E)C50 values of bulk CuO. In all test media, the L(E)C50 values for both bulk and nanoZnO (1.1–16 mg Zn/l) were considerably lower than those of nanoCuO. The natural waters remarkably (up to 140-fold) decreased the toxicity of nanoCuO (but not that of nanoZnO) to crustaceans depending mainly on the concentration of dissolved organic carbon (DOC). The toxicity of both nanoCuO and nanoZnO was mostly due to the solubilised ions as determined by specific metal-sensing bacteria. Natural waters remarkably reduced the toxicity of nanoCuO but not nanoZnO.

Periphyton, composed of algae, bacteria, protozoa, epiphytes, and detritus, is widely distributed on the surfaces of paddy soils. Little is known about the interactions between the periphyton and arsenic (As) in the paddy soil. In the present study, model paddy ecosystems with and without periphyton were set up to explore the effects of periphyton on As migration and transformation in soil. According to the results, periphyton played dual roles in the mobility of As in soil. Periphyton on the surface of paddy soil could significantly increase the mobility and bioavailability of As in soils in the rice tillering stage because of the increased pH and the decreased Eh. The As uptake by rice also increased in the presence of periphyton. However, a significant fraction of the released As was further entrapped by the periphyton, significantly decreasing As concentration in pore water. As biotransformation genes, including aioA, arrA, arsC, and arsM, were identified in periphyton, with arsM being the most abundant in periphyton and soil. Periphyton significantly decreased the abundance of aioA, but increased the abundance of arsC in soils. Cupriavidus and Afipia, which are involved in As(V) cytoplasmic reduction, significantly increased in the presence of periphyton. Periphyton exerted minor effects on the highly abundant and predominant bacteria but had major effects on the less abundant bacteria in the paddy soil. The results of the present study could facilitate the regulation of As contamination in paddy soil, and enhance our understanding of the role of periphyton in the As biogeochemical cycle.

Disinfection means the killing of pathogenic organisms (e.g. bacteria and its spores, viruses, protozoa and their cysts, worms, and larvae) present in water to make it potable for other domestic works. The substances used in the disinfection of water are known as disinfectants. At municipal level, chlorine (Cl₂), chloramines (NH₂Cl, NHCl₂), chlorine dioxide (ClO₂), ozone (O₃) and ultraviolet (UV) radiations, are the most commonly used disinfectants. Chlorination, because of its removal efficiency and cost effectiveness, has been widely used as method of disinfection of water. But, disinfection process may add several kinds of disinfection by-products (DBPs) (∼600–700 in numbers) in the treated water such as Trihalomethanes (THM), Haloacetic acids (HAA) etc. which are detrimental to the human beings in terms of cytotoxicity, mutagenicity, teratogenicity and carcinogenicity. In water, THMs and HAAs were observed in the range from 0.138 to 458 μg/L and 0.16–136 μg/L, respectively. Thus, several regulations have been specified by world authorities like WHO, USEPA and Bureau of Indian Standard to protect human health. Some techniques have also been developed to remove the DBPs as well as their precursors from the water. The popular techniques of DBPs removals are adsorption, advance oxidation process, coagulation, membrane based filtration, combined approaches etc. The efficiency of adsorption technique was found up to 90% for DBP removal from the water.

Acid mine drainage (AMD),characterized by strong acidity and high metal concentrations, generates from the oxidative dissolution of metal sulfides, and acidophiles can accelerate the process significantly. Despite extensive research in microbial diversity and community composition, little is known about seasonal variations of microbial community structure (especially micro eukaryotes) in response to environmental conditions in AMD ecosystem. To this end, AMD samples were collected from Nanshan AMD lake, Anhui Province, China, over a full seasonal cycle from 2013 to 2014, and water chemistry and microbial composition were studied. pH of lake water was stable (∼3.0) across the sampling period, while the concentrations of ions varied dramatically. The highest metal concentrations in the lake were found for Mg and Al, not commonly found Fe. Unexpectedly, ultrahigh concentration of chlorophyll a was measured in the extremely acidic lake, reaching 226.43–280.95 μg/L in winter, even higher than those in most eutrophic freshwater lakes. Both prokaryotic and eukaryotic communities showed a strong seasonal variation. Among the prokaryotes, “Ferrovum”, a chemolithotrophic iron-oxidizing bacterium was predominant in most sampling seasons, although it was a minor member prior to September, 2012. Fe2+ was the initial geochemical factor that drove the variation of the prokaryotic community. The eukaryotic community was simple but varied more drastically than the prokaryotic community. Photoautotrophic algae (primary producers) formed a food web with protozoa or flagellate (top consumers) across all four seasons, and temperature appeared to be responsible for the observed seasonal variation. Ochromonas and Chlamydomonas (responsible for high algal bloom in winter) occurred in autumn/summer and winter/spring seasons, respectively, because of their distinct growth temperatures. The closest phylogenetic relationship between Chlamydomonas species in the lake and those in Arctic and Alpine suggested that the native Chlamydomonas species may have been both acidophilic and psychrophilic after a long acclimation time in this extreme environment.