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.

Recently, there has been a growing concern that climate change may rapidly and extensively alter global ecosystems with unknown consequences for terrestrial and aquatic life. While considerable emphasis has been placed on terrestrial ecology consequences, aquatic environments have received relatively little attention. Limited knowledge is available on the biological effects of increments of seawater temperature and pH decrements on key ecological species, i.e., primary producers and/or organisms representative of the basis of the trophic web. In the present study, we addressed the biological effects of global warming and ocean acidification on two model organisms, the microbenthic marine ciliate Euplotes crassus and the green alga Dunaliella tertiocleta using a suite of high level ecological endpoint tests and sub-lethal stress measures. Organisms were exposed to combinations of pH and temperature (TR1: 7.9[pH], 25.5 °C and TR2: 7.8[pH], 27,0 °C) simulating two possible environmental scenarios predicted to occur in the habitats of the selected species before the end of this century. The outcomes of the present study showed that the tested scenarios did not induce a significant increment of mortality on protozoa. Under the most severe exposure conditions, sub-lethal stress indices show that pH homeostatic mechanisms have energetic costs that divert energy from essential cellular processes and functions. The marine protozoan exhibited significant impairment of the lysosomal compartment and early signs of oxidative stress under these conditions. Similarly, significant impairment of photosynthetic efficiency and an increment in lipid peroxidation were observed in the autotroph model organism held under the most extreme exposure condition tested.

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.

This paper is a part of a multi-disciplinary research “Application of Decentralized On-Site Water Treatment System in Egypt for Use in Agriculture and Producing Safe Fish and Animal Proteins”.The project aimed to investigate the environmental impact of implementing sewage water before and after treatment using the effluent of the on-site decentralized Japanese' Johkasou system, in agriculture and producing fish protein. The aim is to establish such system in Egypt to strengthen the sanitary conditions of water resources. In the present study, the impact of the sewage pollution in some fish farms at El-Fayyum, Port Said and El-Dakahlia governorates in Egypt was carried out. Water and fish (Oreochromis niloticus and Mugil cephalus) samples were collected from private fish farms of such localities. Bacteriological and chemical examination of water samples revealed the existence of coliforms and many other bacterial species of significant human health hazards. The chemical parameters of water showed a marked deviation from normal levels while examination of fish flesh specimens indicated contamination with Streptococcus Sp., Staphylococcus Sp., and Salmonella in all examined localities. Other bacterial isolates of human health importance (Morganella morganii, Pseudomonas cepacia and Enterococcos durans) were identified. The parasitological examination revealed the presence of encysted metacercariae (EMC); Diplostomatidae, Prohemistomatidae and Heterphyidae. Moreover, two protozoan parasites (Mxyoboulus tilapiae and Ichthyophthirius multifilis) were also recorded. The histopathological examination revealed mild tissue reaction in case of bacterial infection and severe pathological lesions in different organs in case of EMC infection. Lamellar hyperplasia and mononuclear cell infiltration in branchial tissue was common findings. In skeletal muscles, atrophy of muscle fibres, myolysis and myophagia were detected.

Theory predicts that in freshwater communities under chemical stress secondary production will decrease while the rate of biomass turnover (P/B) will increase. However, this concept has never been tested on organisms of smaller size (bacteria, protozoans, small metazoans), although they form the basis of the heterotrophic food web. The present work describes the results of a 7-month microcosm study, in which the effects of low and high toxic stress on an entire sediment community were examined, with cadmium (Cd) as the model pollutant (50 and 400mg Cd kg⁻¹ dry sediment). While metazoans and protozoans generally followed the expected trend, in bacteria both production and P/B decreased under Cd stress. These observations provide new insights into the functioning of freshwater ecosystems and demonstrate the functional consequences of toxicants on biological systems.

Oil spills offshore can cause long-term ecological effects on coastal marine ecosystems. Despite their important ecological roles in the cycling of energy and nutrients in food webs, effects on bacteria, protists or arthropods are often neglected. Environmental DNA (eDNA) metabarcoding was applied to characterize changes in the structure of micro- and macro-biota communities of surface sediments over a 7-year period since the occurrence of Hebei Spirit oil spill on December 7, 2007. Alterations in diversities and structures of micro- and macro-biota were observed in the contaminated area where concentrations of polycyclic aromatic hydrocarbons were greater. Successions of bacterial, protists and metazoan communities revealed long-term ecological effects of residual oil. Residual oil dominated the largest cluster of the community-environment association network. Presence of bacterial families (Aerococcaceae and Carnobacteriaceae) and the protozoan family (Platyophryidae) might have conferred sensitivity of communities to oil pollution. Hydrocarbon-degrading bacterial families (Anaerolinaceae, Desulfobacteraceae, Helicobacteraceae and Piscirickettsiaceae) and algal family (Araphid pennate) were resistant to adverse effects of spilt oil. The protistan family (Subulatomonas) and arthropod families (Folsomia, Sarcophagidae Opomyzoidea, and Anomura) appeared to be positively associated with residual oil pollution. eDNA metabarcoding can provide a powerful tool for assessing effects of anthropogenic pollution, such as oil spills on sediment communities and its long-term trends in coastal marine environments.

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 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.

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.